subsurface exploration and geotechnical … reports (geotechnical report).pdfsubsurface exploration...

Subsurface Exploration and Geotechnical Evaluation

Hotel at 13311 Burnet Road (MoPac) Austin, Texas

Prepared for:

Visvanath, LP 3120 Montopolis Drive

Austin, Texas 78744

Prepared by:

Capital Geotechnical Services PLLC Cedar Park, Texas

Texas Engineering Firm Registration # 9458

Capital Geotechnical Services Project # 15-0179

November 1, 2015

Nicholas F. Kauffman, M.S., P.E.

Principal Geotechnical Engineer

Hotel at 13311 Burnet Road (MoPac), Austin, Texas Capital Geotechnical Services Project #15-0179

TABLE OF CONTENTS Page:

SCOPE .......................................................................................................................................................... 1

SUMMARY .................................................................................................................................................... 1

SITE LOCATION AND CONDITIONS .......................................................................................................... 3

LANDFILL LITERATURE REVIEW ............................................................................................................... 3

PROPOSED DEVELOPMENT AND CONSTRUCTION ............................................................................... 4

GEOLOGY AND SOIL MAPPING INFORMATION ...................................................................................... 4

SUBSURFACE EXPLORATION ................................................................................................................... 5

LABORATORY TESTING ............................................................................................................................. 5

SUBSURFACE CONDITIONS ...................................................................................................................... 6

POTENTIAL MOVEMENT OF THE CLAY SOILS ........................................................................................ 7

SITE PREPARATION AND EARTHWORK .................................................................................................. 8

FOUNDATIONS .......................................................................................................................................... 13

Drilled Pier Option................................................................................................................................. 14

Stiffened Slab Option ............................................................................................................................ 17

Driven Steel Pipe Piles ......................................................................................................................... 22

STRUCTURALLY SUPPORTED SLAB (if used) ........................................................................................ 22

SEISMIC DESIGN ....................................................................................................................................... 23

PAVEMENT THICKNESS DESIGN ............................................................................................................ 23

CONCRETE PAVEMENT COMMENTARY ................................................................................................ 26

PAVEMENT MAINTENANCE ..................................................................................................................... 27

PAVEMENT MATERIAL RECOMMENDATIONS AND TESTING ............................................................. 28

SURFACE DRAINAGE, VEGETATION, AND UTILITY CONNECTIONS .................................................. 33

POST-TENSIONING (IF USED) ................................................................................................................ 34

LIMITATIONS .............................................................................................................................................. 35

INSPECTIONS ............................................................................................................................................ 36

FIGURES: Figure 1: Vicinity Map Figure 2: Local Lot Plan Figure 3: Geology Map Figure 4: Approximate Locations of Exploratory Borings Figure 5 to Figure 8: Boring Logs Figure 9: Standard Reference Notes for Boring Logs Figures 10 and 11: Swell Test Results Figure 12: City of Austin Landfill Check Form

Hotel at 13311 Burnet Road, Austin, Texas Capital Geotechnical Services PLLC Project #15-0179

1

SCOPE

This report presents the results of a geotechnical evaluation for a proposed 3-story hotel

building on the northbound frontage road of the MoPac Expressway in Austin, Texas. This study

was performed to evaluate subsurface conditions and to provide recommendations for the design

and construction of the foundation system and for pavement thickness design. Capital

Geotechnical Services PLLC performed this subsurface exploration and geotechnical evaluation

in accordance with our proposal # P15-0081 authorized (signed) on September 17, 2015.

The scope of services for this study included the determination of subsurface conditions

through field and laboratory testing, an evaluation of the subsurface conditions relative to the

proposed construction, and the preparation of a geotechnical report. This report includes results,

evaluations, and recommendations concerning earthwork, foundations, groundwater, pavement,

quality control testing, and other geotechnical related aspects of the project. A summary of our

conclusions is presented in the following section of this report. More complete descriptions and

findings of our field and laboratory testing are presented in the rest of the report.

The scope of services did not include any environmental site assessments (ESAs) for the

presence or absence of wetland or hazardous or toxic materials in the soil, air, surface water, or

groundwater at this site.

SUMMARY

The subsurface conditions encountered during our exploration and our geotechnical

engineering evaluations and recommendations are summarized in the following paragraphs. This

summary should not be considered apart from the entire text of this report. This report should be

read and evaluated in its entirety prior to using our engineering recommendations for the

preparation of design or construction documents. Details of our findings and recommendations

are provided in subsequent sections of this report and in the attached figures.

1. Four (4) exploratory borings were drilled to evaluate soil conditions. The subsurface

profile varies slightly among the boring locations. At borings B-1 and B-2 (southeast area

of site) the subsurface profile consisted of 5 to 6 feet of dark grayish brown, light gray,

light yellowish brown, medium grayish brown, and medium yellowish olive-brown highly

plastic clay and gravel with some sand content (CH and GC classifications), overlying a

massive stratum of light gray, light yellowish brown, and light olive-brown highly plastic

clay (“Del Rio Cay”) to a depth of at least 30 feet. At boring B-3 the surface stratum (upper

6 feet) of dark brown and medium yellowish brown clay only contained trace gravel content

and was underlain by the massive highly plastic “Del Rio Clay”. At a 4th boring location

the surface stratum (8 feet thick) of dark brownish gray and medium yellowish brown clay

was only moderately plastic (CL) beyond a depth of 2 feet. Groundwater was not


2

encountered during the drilling operation in October 2015. The maximum depth of

exploration was 30 feet.

2. The “Del Rio Clay” can be susceptible to significant swelling and shrinkage potential. The

TxDOT PVR site index was calculated to range between 2 ½ inches to 3 ¾ inches due to

the plasticity and soil profile (gradation). Potential vertical soil movement (design PVR)

however was calculated to be over 7 inches at the surface if no soil improvement is

performed and notable changes in moisture content occur within an active zone 15 feet

deep. The design PVR under a lightly to moderately loaded foundation slab was

calculated to be 5 ½ inches to 7 inches if no soil improvement is performed and notable

changes in moisture content occur post-construction within a 15-ft deep active zone.

3. Based on the available soil information, proposed construction, and assumed structural

loads, the project team can consider two foundation options:

Option A: The approximately 9,100 square-foot building can be constructed on a

structurally supported slab cast on void boxes and constructed on deep concrete belled

drilled piers. Recommendations concerning the design and construction of the drilled

piers are presented in this report. Recommendations concerning a driven steel pipe pile

alternative to concrete drilled piers can be provided upon request.

Option B: Perform significant soil improvement and construct the 3-story building on a

ground-supported stiffened slab foundation system (foundation slab). The building must

be designed to accommodate some differential soil movement. Various options for soil

improvement and foundation slab design are presented in this report.

4. Based on a finished floor elevation assumed to be close to existing grade at the upslope

side of the building, we assume 4 inches to 40 inches of fill will be required to reach

planned slab subgrade elevation across the footprint before consideration of any soil

improvement. Recommendations concerning earthwork and pavement thickness design

are also included in this report.

5. Surface drainage should be designed, constructed, and subsequently not adversely

altered by the Owner, to provide rapid removal of water runoff away from all sides of the

building and away from the edges of pavement or flatwork.


3

SITE LOCATION AND CONDITIONS

The project site is a 1.23-acre lot located on the east side of the MoPac Expressway

northbound frontage road (Burnet Road) and the south side of Grand Blvd., in the north area of

Austin, Travis County, Texas (Figure 1 and Figure 2). The site was wooded across the northern

area and contained wild shrubs across the central and southern areas. An existing concrete

driveway ramp is present in the southwest corner. The underbrush was cleared from parts of the

central and south areas by the Owner to provide access to a drill rig in the non-wooded areas.

The USGS topographic map shows no indication of any potentially

backfilled pre-existing pond, quarry pit, or landfill at the site at the time

the map was made (see graphic). An old creek valley is aligned

northwest to southeast across the north end of the site. The USGS map

presents the original alignment of Burnet Road, which is now under the

MoPac Expressway mainlanes. The pond in the old USGS map is still

present in 2015.

LANDFILL LITERATURE REVIEW

The City of Austin 2004 Supplemental Assessment: Landfills in the Vicinity of Austin, Texas,

and the 2002 CAPCO (Capital Area Planning Council; now the Capital Area Council of

Governments) Closed and Abandoned Landfill Inventory report (and the 2010 update) for Travis

County were reviewed and there were no small unpermitted landfills (dumps) identified at the

subject property. A City of Austin Certification of Compliance form is provided as Figure 12.


4

PROPOSED DEVELOPMENT AND CONSTRUCTION

The proposed development includes a 3-story, approximately 9,100 square-foot, hotel

building with associated parking lot paving. A site plan was provided to Capital Geotechnical

Services and was used for the boring location plan (Figure 4).

Information concerning structural loads was not provided to Capital Geotechnical Services.

We have assumed that the building will consist of wood framing and structural loads will not

exceed 75,000 lbs for any column loads and 3,000 lbs per foot for wall loads.

Information concerning planned finished floor (FF) elevation and existing topographic ground

surface elevation data was not provided to Capital Geotechnical Services by the time of this

report. We have therefore assumed that planned finished floor elevation will be close to, but just

above, existing grade on the upslope side of the building (i.e. FF elevation 8 inches above upslope

grade). Based on a cursory observation of the site, there appears to be approximately 3 feet of

ground surface elevation difference across the planned building footprint area. Therefore we

assume 4 inches to 40 inches of fill will be required to reach planned slab subgrade elevation

before consideration of soil improvement. We assume minor cut and fill grading will be required

to reach planned pavement subgrade elevation and to accomplish final grades for drainage

design purposes.

If the proposed construction varies from what is described in this report, Capital Geotechnical

Services must be contacted to determine if revisions to our recommendations are required.

GEOLOGY AND SOIL MAPPING INFORMATION

According to the USDA Natural Resources Conservation Service shallow soil mapping

information, the shallow soils (upper 5 feet) of the project site may be a member of the “Heiden

Clay” soil series. This soil generally classifies according to the USCS as fat clay (CH). According

to the survey, the soil is commonly dark grayish brown and is commonly mapped above the “Del

Rio Clay” formation.

According to available geology mapping information by the U.T. Bureau of Economic Geology,

the site is located in the “Balcones Escarpment” (fault zone) geologic physiographic province and

consists of a clay sedimentary deposit categorized as the “Del Rio Clay” geologic formation. The

local area is faulted and a limestone rock sedimentary deposit categorized as the “Georgetown

Limestone” formation might be present along the west area of the site. A geology map is provided

in Figure 3.


5

SUBSURFACE EXPLORATION Partial site mowing was performed in the non-wooded areas to

remove tall underbrush. Four (4) exploratory borings were drilled to

evaluate soil conditions. The borings drilled in this exploration were

located in the field by Capital Geotechnical Services by measurements

from existing structures and site features such as the southeast property

corner, the eastern property line, and the fire hydrant at the northwest

corner. The boring locations were selected to be along the east edge of

the building area due to the potential presence of a fault line and

limestone rock formation in the west area of the site. The presence of

clay had to be determined to avoid potential significant design errors if

only limestone rock was exposed in borings on the west side of the

building. The borings were drilled on October 9, 2015, to a depth of 30

feet in the building area at the approximate locations indicated in Figure 4. Drilling was performed

using a truck-mounted drill rig equipped with 4-inch diameter continuous flight solid stem augers,

a Shelby tube sampler, and a split-spoon sampler. A hammer weighing 140 pounds falling 30

inches was used to drive the split-spoon sampler. Boreholes were backfilled with available auger

cuttings. The soil samples were delivered to our laboratory where they were visually classified

by a Geotechnical Engineer and selected samples were subjected to laboratory testing. Detailed

boring logs are provided as Figures 5 to 8.

LABORATORY TESTING

Representative soil samples were selected and tested to assist the visual classifications and

to determine pertinent engineering and physical characteristics. Tests were performed in general

accordance with applicable ASTM standards. Results of the laboratory tests are included on the

boring logs. Specialized testing to determine the presence of chemicals in soil samples (e.g.,

sulfates, chlorides) was not requested. A Geotechnical Engineer classified each soil sample on

the basis of texture and plasticity in accordance with the Unified Soil Classification System

(USCS). The USCS group symbols for each soil type are indicated in parentheses following the

soil descriptions on the boring logs.

Expansive properties of 4 samples of clay soil were evaluated by performing swell tests. The

test consists of placing a remolded specimen in a rigid ring at the as-sampled moisture content,

applying a light seating load, allowing the sample to absorb water, and measuring the vertical

heave of the sample while not allowing horizontal (lateral) strain. The results of such testing are

used by the Geotechnical Engineer to help properly evaluate the clay mineralogy and the shrink-

swell behavior of the clay soil.


6

Soil samples that remain after testing will be kept for 3 weeks after the date of this report.

Samples will then be discarded unless we receive instructions regarding their disposition.

SUBSURFACE CONDITIONS

Information from the exploratory borings indicates that the soil stratigraphy may generally

consist of 4 distinguishable strata above a depth of 30 feet. The characteristics of these strata

are summarized in the following paragraphs.

Stratum A: Dark to Medium Clays with Variable Gravel Content

The upper 5 to 6 feet of soil in the building area appears to consist of dark grayish brown, dark

brown, medium yellowish brown, light gray, light yellowish brown, medium yellowish olive-brown,

and medium grayish brown, highly plastic clay with trace gravel and trace sand (CH) and clayey

gravel with sand (GC). The darker colored soil was generally within the upper 2 feet. The gravelly

soils were encountered at B-1 and B-2. SPT N-values ranged between 13 blows per foot (bpf)

and 37 bpf for the 8 tests performed exclusively in this stratum. Two samples of the finer fraction

of the soils were tested to determine plasticity (Atterberg limits) and yielded a liquid limit (LL) of

59% and 61%, and a plasticity index (PI) of 40 and 41. One remolded specimen was subjected

to swell testing and exhibited 26.2% vertical swell (Figure 11) from an initially hard and moderate

moisture condition, indicating the soil has relatively high shrinkage and swelling potential.

Stratum A2: Yellowish Brown Lean Clay

At boring B-4 exclusively, a stratum of light to medium yellowish brown lean clay (CL) (moderately

plastic clay) was evident from a depth of approximately 2 feet to a depth of at least 8 feet. This

soil is slightly different from the shallow soils encountered in the building area but might simply be

of the “Del Rio Clay” geologic formation that frequently includes clay minerology and gradation

that produce a lean clay classification. One sample was tested to determine plasticity and yielded

a LL of 44% and a PI of 29.

Stratum B: “Del Rio” Clay

Beyond a depth of 5 to 6 feet in the building area the soils consisted of light gray, light yellowish

brown, and light olive-brown highly plastic clay (CH) to a depth of at least 30 feet. The soil

included trace white gypsum, trace black mottling, some varved structure with medium gray

lenses, and trace orange-brown color. The clay was very stiff to hard, exhibiting SPT N-values

ranging between 23 bpf to 79 bpf for the 16 tests performed in this stratum. Five samples were

tested to determine plasticity and yielded a LL of 57%, 58%, 64%, 65%, and 66%, and a PI of 37,

39, 40, 43, and 45. Three remolded specimens were subjected to swell testing and exhibited

28.5%, 28.6%, and 32.9% vertical swell from an initially hard condition and moderate moisture

condition, indicating the soil is susceptible to significant shrinkage and swelling movement.


7

Stratum D: Hard Pale Silty Clay

At boring B-1 exclusively, a stratum of dry to moist, very hard, pale grayish brown lean clay (CL)

was encountered starting at a depth of approximately 22 feet and extended to a depth of at least

30 feet. Some fine sand content was present in the deeper sample. SPT results were 50/5” and

50/4”, indicating the soil was very hard. One sample was tested to determine plasticity and yielded

a LL of 34% and a PI of 19.

The above descriptions are of a generalized nature to highlight the major soil stratification

features and soil characteristics. The boring logs provided in the Appendix should be reviewed

for specific information at each location. The stratification of the soil represents our interpretation

of the subsurface conditions at the boring locations based on observations of the soil samples by

a Geotechnical Engineer. Variations from the conditions shown on the boring logs could occur in

areas in between borings or in areas around the borings. The stratification lines shown in the

boring logs represent approximate boundaries between soil types and condition, and the

transitions may be gradual rather than distinct. It is sometimes difficult to identify changes in

stratification within narrow limits. It may also be difficult to distinguish between fill and discolored

natural soil deposits if foreign substances are not present.

Groundwater was not encountered in our exploratory borings at the time of drilling. Moisture

contents were relatively low, indicating that groundwater was not present. Groundwater, however,

can be temporary instead of perennial. Although groundwater was not encountered during the

drilling and sampling operation, our experience requires us to emphasize that groundwater can

still appear later (e.g. during construction of drilled shafts). The Owner, General Contractor, and

drilling subcontractor should not be surprised if groundwater appears and requires temporary

mitigation measures. Groundwater may develop after periods of rain and can develop after

construction in response to landscaping irrigation or changes to nearby drainage conditions.

Perched groundwater will most likely appear within fissures in the clayey soils.

POTENTIAL MOVEMENT OF THE CLAY SOILS

The clay soils within the zone of seasonal moisture change (or within a potential active zone)

will experience changes in condition due to changes in environmental conditions (rainfall

quantities and frequency; temperature; evaporation; tree roots) and man-made conditions

(leaking water lines; irrigation; poor drainage) that affect the moisture content of the clay soils.

The clay soil may harden, shrink, and crack when subjected to drying, swell when subjected to

wetting, and soften when subjected to saturation.

The TxDOT Potential Vertical Rise (PVR) index (Tex-124-E) considering existing conditions

and existing overburden pressure was calculated to be between 2 ½ inches and 3 ¾ inches based

on the plasticity of the soil and the soil profile (gradation). It was assumed that the clay would be


8

in an initially “dry” condition as defined by the method at the time of construction and that the

thickness of the active zone is 15 feet. Note that the TxDOT PVR method assumes limited wetting

occurs and should only be used as an index tool for comparing sites. The TxDOT PVR value

should not be considered an estimate of maximum potential vertical heave.

Using reasonable estimates of relatively dry and relatively moist suction profiles or moisture

content profiles and physical properties of the clay soil, the swelling potential of the clay soils

within the active zone (assumed to be 15 feet deep) may be 7 inches or more at the surface under

new flatwork if the moisture content changes between a relatively dry condition and a relatively

moist condition near the surface, tapering to negligible change at a depth of 15 feet. The design

PVR does not consider extreme moisture change conditions (i.e. 200-year to 500-year drought,

rainfall, or groundwater event, etc.) but does consider significant potential changes due to man-

made and environmental conditions. Under a light to moderate foundation slab load, a design

PVR of 5 ¾ inches to 7 inches was calculated considering the same potential changes in moisture

content within the active zone.

The potential amount of total and differential heave or shrinkage is difficult to accurately

predict because it will depend on the extent of impervious cover, seasonal changes in climate

conditions, drainage conditions, presence of leaking water pipes, groundwater conditions,

landscape watering, vegetation planting, thickness of clay soil affected, and varying physical

characteristics and mineralogy of the clay soils. The PVR is not a static value because it depends

on how the soil behavior and the boundary conditions are modeled such as what changes in

moisture content to consider and what initial moisture condition to consider at the time of

construction. Deep-seated swell movements can also occur if swelling of the deeper clay soils is

caused by water sources other than those that affect moisture content variations near the surface

(notable groundwater development; leaking nearby water main; leaking deep sewer pipe; etc).

SITE PREPARATION AND EARTHWORK

The primary geotechnical concern that will influence foundation or slab performance at this

site is the presence of expansive clay soils. We believe that the impact of swelling and shrinking

soils can be mitigated with proper planning, engineering design, and construction quality control

as discussed in this report.

Soil Improvement in the Building Area The potential soil movement due to shrinkage and swelling can be reduced by using soil

improvement techniques to change the characteristics and properties of the subgrade soils.

Options for soil improvement include:


9

Option 1: Removal of a certain thickness of existing clay soil and replacement with properly

compacted select fill (structural fill).

Option 2: Pre-swelling and modification of clay soil by water and chemical pressure injection

(i.e. “electro chemical injection”, “acid treatment injection”, or “ionic stabilizer injection”; or

potassium chloride injection). A deep perimeter moisture-evaporation barrier might be

required depending on the results of the quality control testing of the injection operation. A

cap of properly compacted select fill will also be required to provide durably stiff subgrade

support immediately under the foundation slab.

Option 1: Removal and Replacement

The thickness of removal and replacement will be selected by the Owner, Architect, and the

Structural Engineer since multiple factors affect how much vertical movement can be tolerated by

the structure (type of cosmetics used, flexibility of framing detailing and cosmetics, aversion to

risk, tolerance to cosmetic cracking and functional distress, stiffness of framing to resist wind

loads, rigidity of slab, design deflection tolerance, etc). Design parameters for various thickness

of soil improvement are provided in this report.

Select fill should extend at least 5 feet beyond the perimeter of the building. Select fill

extending beyond the building footprint should be capped in landscaped areas with an 18-inch

thick clay soil to limit infiltration of surface water into the pad fill.

Option 2: Water and Chemical Pressure Injection

Water and chemical pressure injection is performed by a specialty subcontractor. The

purpose of the water and chemical pressure injection is to pre-swell the existing clay soil and

modify the soil characteristics. The depth of treatment should be 12 feet and the treatment should

extend horizontally at least 5 feet beyond the perimeter of the slab footprint area. The equipment

is typically similar to a tracked dozer equipped with a custom injection rod frame and system.

Injection treatment will require a follow-up investigation to

determine if the method produced the desired pre-swelling and

modifications to the physical properties of the clay soil. The

quality or extent of the modification will partially depend on the

extent of cracking and fissures within the clay strata. The low

permeability of the clay soil and the potential lack of sufficient

cracks will cause the method to not produce a homogeneous

modification of the clay soil. Quality control (QC) testing is

necessary to achieve good quality results.


10

Completion of the pre-swelling aspect of the injection improvement operation is achieved

when the desired moisture condition is reached. We do not propose any method-based

specifications, only end-result based specifications. After performance of the injection procedure,

drilling and sampling will be required to obtain soil samples. The target moisture condition can

be associated with stiffness and swell potential. Moisture content, pocket penetrometer, and swell

tests will have to be performed to measure the success of the pre-swelling injection operation.

Pocket penetrometer test results should be between 1.0 tsf and 3.5 tsf after a successful injection

operation. The vertical swell of a post-injection sample should not exceed 2% if a remolded

specimen or 1% if an undisturbed sample. Atterberg limits tests and shrink-swell tests will have

to be performed to determine if the chemical compounds changed the physical properties of the

clay soil. Capital Geotechnical Services should be retained to inspect the injection operation to

document means and methods, and the follow-up QC testing should be performed by Capital

Geotechnical Services. The recommended design PVR after a successful injection operation is

1 ½ inches unless the chemical modification aspect is suspected of yielded poor results. If the

quality of the chemical modification is suspect, deep vertical moisture-evaporation barriers must

be installed.

Note that water and chemical pressure injection will produce a soft subgrade. The

construction schedule must allow for at least 2 weeks of “curing” time in the cool season (when

no rainfall is forecast) or 1 week during the summer season after completion of the injection

operation to permit the shallow treated clay soils to dry out and stiffen to support construction

traffic and to permit the proper installation of the first lift of new fill.

Stripping and Clearing

All of the grass topsoil (soil with high organic content), tree roots and root bulbs, vegetation,

and deleterious forest materials (downwood, litter, duff) must be removed from the proposed

building and pavement areas at the start of construction. The stripped organic materials and

organic-rich soils must be stockpiled separate from excavated soil that will be re-used as minor

grading fill. Stripping should be observed and documented to record that unsuitable materials

were removed prior to placement of fill, slab, or pavement materials.

Backfilling of Buried Utilities

Water and sewer lines are typically constructed beneath paved parking lots. Compaction of

trench backfill or lack thereof can have a significant effect on the performance of the pavement.

Trench backfill should be placed in lifts not exceeding six (6) inches in loose lift thickness if using

lightweight compaction equipment (walk-behind or remote controlled rollers, mechanical tampers,

vibratory plate compactors, boom-mounted trench rollers), and eight (8) inches if using heavy


11

trench rollers. Onsite clay soil backfill should be moisture conditioned to between +2% and +5%

above optimum. All other backfill soils should be moisture conditioned to between -1 and +3

percentage points of optimum, and compacted to achieve a relative compaction of 95% or higher

based on the Standard Proctor method (ASTM D 698). The placement and compaction of the

backfill should be observed, tested, and documented by a Capital Geotechnical Materials

Technician.

Utility trenches within clay soils, backfilled with “clean” sand or gravel can function as post-

construction conduits for water below the building or pavement. This can result in swelling of clay

soils affected by the water along the trench and result in development of cracking and heaving in

the pavement or building and slab along the trench alignment. Capital Geotechnical Services

recommends using fine-grained backfill such as on-site trench cuttings or imported low to medium

plasticity clay (CL) or clayey sand (SC) to backfill utility trenches. The backfill must not be densely

compacted under the building slab (i.e. allow some soil compressibility within the trench). An

alternative is to surround the trench with a geosynthetic geomembrane between the backfill and

the surrounding clay soil and design the trench system to drain water to an acceptable outfall area

or stormwater sewer system. Alternatively, concrete cut-off collars or clay plugs should be

included in the trench design to prevent water from entering sections of trench beneath slab and

pavement areas.

Utility trenches within clay soils under a structurally supported slab and backfilled with “clean”

sand or gravel can result in development of heaving of pipes and fixtures near the trench as the

clay under the trench swells. Although sleeves through the slab can permit movement, the fixtures

connected to the pipes cannot tolerate notable movement. Recommendations for plumbing

installation when using a slab cast on void boxes are provided later in this report.

Fill Placement

Select fill that is imported to the site for use under a foundation slab or pavement should be

classified according to the Unified Soil Classification System (USCS) as SM-SC, SC, GM-GC, or

GC, and should meet the following criteria:

Percent passing the #4 sieve: 50% to 80% (20% to 50% gravel)

Percent passing the #200 sieve: 20% to 45%

PI of soil passing the #40 sieve: 6 to 19

Maximum size of gravel or rock fragments: 3 inches in any dimension


12

If a soil improvement excavation is performed, the project team should consider extending the

excavation and subsequent fill pad horizontally more than 5 feet from the edge of the building

where deemed necessary to include flatwork. Note that joint faulting or crack faulting can impact

ADA compliance associated with tripping hazards.

Select fill should be placed in horizontal loose lifts of not more than 6 to 8 inches in thickness

depending on the size and weight of the compaction equipment. Select fill should be moisture

treated and compacted to achieve a minimum relative compaction of 98% based on the maximum

dry unit weight as determined by the Standard Proctor method (ASTM D 698). Moisture content

of select fill material should be within -1 and +3 percentage points of the optimum moisture content

at the time of compaction (-1% to +3%). Some wetting or drying might be required to produce the

necessary moisture content at the time of compaction.

The performance of slabs and pavement placed on new fill material is influenced by the quality

of the compaction and materials selection of the fill material. Capital Geotechnical Services

should be retained to perform quality control testing and inspection during selection, placement,

and compaction of the fill material. Appropriate laboratory tests such as Proctor moisture-density

tests should be performed on samples of fill material and pavement base course material. Field

moisture-density tests and visual observation of lift thickness and material types should be

performed during compaction operations to verify that the construction satisfies material and

compaction requirements. In-place moisture-density tests and lift thickness checks must be

performed on every lift of fill.

Fill materials should not be placed on soils that have been recently subjected to precipitation

or saturation. All wet soils should be removed, or reworked, or stabilized, or allowed to dry prior

to continuation of fill placement operations.

Fill soils must be free of wood debris (organics) such as large branches, thick roots, and wood

chips since over time these organic materials will decay, causing localized settlement or creating

voids. Water entering voids can eventually lead to collapse of the void and settlement under

pavement or under a slab.

Boulders and cobbles must be removed from the fill mass during placement. Soil around the

edges of such stones cannot be properly compacted, and unfilled voids might be created due to

bridging of soil over adjacent boulders or cobbles. Loose soil can compress when wetted, and

soil above voids can migrate into the void space, causing settlement.

If any problems are encountered during the earthwork operations, or if newly exposed soil and

site conditions are different from those encountered during our subsurface exploration, the


13

Geotechnical Engineer must be notified immediately to determine the effect on recommendations

expressed in this report.

If construction is performed during winter or spring seasons when the occurrence of rainfall is

more frequent, to limit effects of wet weather, the building pad or pavement area can be initially

graded high or left “crowned” to protect the slab or pavement subgrade. The additional soil can

be removed when slab or pavement construction can begin.

Certain construction practices can reduce the magnitude of problems associated with

moisture content increases of subgrade soil for pavement, slabs, and areas to receive compacted

fill. If rainfall appears imminent, the contractor should seal exposed subgrade areas at the end of

the work day with a smooth drum roller to reduce the potential for infiltration of water into the

subgrade. Pavement base course should preferably consist of well graded aggregate and not

open graded aggregate, but should conform to any locally developed guidelines. Site grading

should be continuously evaluated to assure that surface runoff will drain away from pavement,

slab, and fill areas.

In pavement areas, final grading of the subgrade must be carefully controlled so that low spots

in the subgrade that could trap water in the base course (asphalt pavement) or under a concrete

joint are eliminated.

FOUNDATIONS

Based on the subsurface conditions encountered and our experience with similar

construction, the project team can consider two foundation options:

Option A: The approximately 9,100 square-foot building can be constructed on a

structurally supported slab cast on void boxes and constructed on deep concrete belled

drilled piers. An alternative to concrete belled piers is to use driven steel pipe piles.

Option B: Perform significant soil improvement and construct the 3-story building on a

ground-supported stiffened slab foundation system (foundation slab). The building must

be designed to accommodate some differential soil movement. Various options for soil

improvement and foundation slab design are presented in this report.

Recommendations concerning the design and construction of the foundations are presented

in the following paragraphs. The Owner, in consultation with the design team, should decide on

the level of performance desired and the relative economics of constructing either a shallow or

deep foundation system.


14

Drilled Pier Option:

1. Based on the assumed maximum structural loads and on the soil conditions encountered,

the 3-story wood-framed building can be supported by belled concrete drilled piers. Piers

should have a shaft diameter of 12 inches or larger and must be adequately belled and

penetrate deep enough to provide significant uplift force resistance against swelling clay

soil in contact with the pier.

2. Piers can be designed to apply a maximum allowable bearing pressure of 12,000 psf if ¾

to 1 inch of settlement is deemed acceptable, subject to approval of bearing conditions at

the time of construction. We assume a lower bearing pressure will be required for the 3-

story wood framed structure, therefore the anticipated settlement will be less than ¾ inch.

Skin friction should not be considered when using moderate depth belled piers. The

structural design of the piers, including the amount and type of reinforcing steel and the

strength and mix design of the concrete will be determined by the project Structural

Engineer. The project team can refer to ACI 336.1-01 for recommendations concerning

writing specifications for drilled pier construction.

3. Since belling in hard clay is difficult, if there is any uncertainty about the capability of the

belling tool and drilling equipment to open the belling tool fully, or if there is any uncertainty

about the drilling subcontractor performing an adequate number of belling tool runs to form

a complete bell (i.e. time consuming), then the design capacity should consider a reduced

bell diameter for design purposes (i.e. use a 30-inch diameter bell if a 36-inch diameter is

specified, or a 45-inch diameter if a 54-inch belling tool is specified). If piers can be

constructed with a heavy truck-mounted drill, then a full bell diameter can be achieved in

the field with notable effort (multiple belling tool runs; may add water).

4. The center-to-center spacing should be 3 bell diameters or

larger. Closer spacing will require reductions in uplift capacity

and end bearing capacity due to the combined influence on a

zone of bearing material by more than one pier. If piers are

closer than 3 diameters center-to-center, then the capacity

should be reduced to a fraction of the recommended values for

a stand-alone pier. The reduction factor will vary from 0.50 (piers edge-to- edge) to 1.0

(piers at two diameter edge-to-edge spacing). Interpolation can be used for pier spacing

between zero and two diameters edge-to-edge.

5. The potential uplift force anticipated from swelling of the clay soils in the zone of seasonal

moisture change or a reasonable potential active zone can be approximated as 105 D kips

if the clay soils are in a relatively dry condition at the time of construction, where D is the


15

diameter of the pier in feet. The depth of the active zone is assumed to be 15 feet. Note

that no factor has been applied to potential uplift force (i.e. no load factor or LFRD design).

Piers should be sufficiently reinforced to resist tensile stresses associated with swelling of

the surrounding clay.

6. The diameter of the bell should be three times the diameter of the straight shaft to resist

uplift forces associated with the swelling of the upper soils and to reduce the risk of caving

during construction of the bells. Uplift resistance is calculated from empirical models and

the contribution to uplift resistance is likely influenced by the weight of the soil above the

bell, the shear strength of the soil above the bell, the dead weight of the pier, and

downward structural axial load (dead load “DL”). Belled piers will provide uplift resistance

against swelling clay and against wind shear loads and the uplift capacity can be estimated

to be:

12” shaft / 36” bell, embedded 21 feet below grade: 78 kips + DL applied at top of pier

12” shaft / 30” as-built bell, embedded 21 feet: 65 kips+ DL applied at top of pier



12” shaft / 36” bell, embedded 23 feet: 105 kips+ DL applied at top of pier







Note that no factor of safety has been applied to uplift resistance values (i.e. ASD design),

therefore a deeper penetration can be considered.

7. A minimum void of 10 inches should exist beneath the grade level beams between piers

to accommodate future swelling of the clay subgrade soil and prevent the application of

uplift forces on the grade beams and on the piers. The void concentrates the dead loads

onto the piers. The voids can be created using cardboard forms (void boxes). The soils

below the grade beams should be graded to drain away from the piers (grade beam trench

and void space down to middle of trench between piers).

8. A dry method of construction may be adequate to construct open shafts. In the event of

rain or water seepage into the shaft, no more than 5 inches of water should be present at


16

the bottom of the shaft when concrete placement begins because of the risk of washing

out cement in the bottom portion of the pier. Loose soil or debris should not be present at

the bottom of the shaft when concrete placement begins. Poor cleaning of compressible

cuttings at the bottom can lead to significant settlement.

9. Concrete should be placed the same day the shaft drilling is completed to limit changes in

the shaft bottom and shaft sidewalls that can reduce mobilized capacity and to reduce the

risk of bell cave-in.

10. To reduce the potential for arching within the shaft or casing, Capital Geotechnical

recommends using a concrete mix with a slump of 5 inches to 7 inches. If the concrete

has a slump that is less than or equal to 7 inches, the upper 5 feet of concrete should be

vibrated to assure proper consolidation in that region. If the slump is greater than 7 inches,

the concrete should not be vibrated because of the potential to segregate cement and

aggregates.

11. “Mushroom” tops must not be produced or left in place after the concrete placement.

Heaving of clay soil against protruding concrete (enlarged pier top) can produce notable

uplift force that is not considered in the design of the piers.

12. A tremie pipe can be used to place concrete to prevent segregation of concrete ingredients

and to prevent moving the reinforcing steel cage. A free-fall method might allow the

concrete to strike reinforcing steel, casing, or shaft sidewalls, causing segregation and

undesirable concrete strength properties. A free-fall method is acceptable if the concrete

is directed through a hopper and falls down the center of the shaft without striking the

sides of the shaft or the reinforcing steel cage.

13. The contractor can refer to ACI 336.1-01 for ACI recommendations concerning concrete

pier construction.

14. The performance of the foundation system is highly dependent on the quality of the

installation. Therefore, Capital Geotechnical Services should be retained to document the

drilling conditions encountered, the cleaning of the bottom of the shaft, the type of bearing

material, the depth and diameter of pier, and the size, number, configuration, and grade

of steel reinforcement.

15. Concrete material should be sampled and tested for compressive strength, and placement

operations should be monitored to record concrete slump, temperature, and age at time

of placement. Detailed concrete batch tickets should be provided by the supplier to permit

review and documentation of water-cement ratios and cement content.


17

16. Horizontal forces (lateral loads) can be resisted by a combination of the soils around the

piers and the stiffness of the piers. Capital Geotechnical Services can assist the Structural

Engineer with lateral load analysis by providing the soil-related design parameter values

if the method of analysis is indicated to us.

17. A sulfate resistant concrete mix should be used due to historically high sulfate

concentrations in the “Del Rio” clay and clay-shale. We recognize that Type 5 cement

may not be readily available. Concrete made with cement that meets ASTM C 150 Type

2 requirements, 25 percent Class F fly ash, and a maximum water-cementitious material

ratio of 0.40 can be used to provide notable resistance. The fly-ash should meet ASTM

C 618 Class F requirements.

18. Belled piers may be difficult to install if infiltrating groundwater is encountered that can

collapse the bell. The installation of the first belled piers must be carefully observed and

if notable groundwater seepage is encountered, each shaft must be continuously

dewatered (pumped) while waiting for the concrete to be placed (i.e. do not allow

groundwater to build up inside shaft notably above lip at base of bell). This may cause a

slowdown in production as concrete delivery may need to be scattered throughout the day.

19. In expansive clay soils, variations in wetting and drying with depth on opposite sides of a

pier will induce changes in bending moments and shear forces in the pier. This condition

should be considered when analyzing the design of a slender pier.

Stiffened Slab Option:

1. The building structure can be supported on a rigid, monolithically-cast, grid-type grade

beam and slab foundation system (foundation slab) if significant soil improvement is

performed. When placed on expansive soils, subgrade improvement must be performed

to reduce potential soil and foundation movement to levels acceptable to the Owner,

Architect, Structural Engineer, and General Contractor.

2. The rigidity of a stiffened slab will limit the effects of differential soil movement caused by

swelling and shrinkage of clay soils and compression of soils due to structural loads.

However, discernible cracking in brittle construction materials may still occur. This type

of slab should be designed with perimeter grade beams and interior stiffening grade

beams adequate to provide sufficient rigidity to the slab element. The foundation slab can

be designed considering an allowable bearing pressure of 2,500 psf across the grade

beam contact area if all grade beams are placed on properly compacted select fill.


18

3. Perimeter grade beams should extend at least 18 inches below final adjacent exterior

grade and have a minimum width of 10 inches. The grade beam width and depth will be

determined and detailed by the project Structural Engineer. The grade beam details must

specify minimum beam height and minimum beam penetration below exterior grade

(ground surface).

4. Floor coverings (carpet, tile, wood, laminate, vinyl) can be damaged or subject to mold

growth by moisture penetrating the slab, therefore a moisture vapor barrier (i.e. 10 mil

thick geosynthetic geomembrane) should be placed on top of the select fill and properly

sealed to limit the migration of moisture to and through the slab, and to serve as a

separator between the fill (potentially high friction) and concrete slab. The moisture barrier

can be placed after the grade beams are formed. We recommend lapping the sheets of

vapor barrier 12 inches and taping the joints/laps. Since many field crews do not force

membranes down to make continuous contact with the trench walls and bottom to maintain

proper rectangular beam cross section, if a single sheet of geomembrane is placed across

a trench, we recommend cutting the membrane at the bottom of the grade beam trench to

prevent the poured cross section area from being reduced (prevent bridging at bottom

corners), and installing a separate strip of vapor barrier along the bottom to overlap the

cut membrane on either side of the trench.

5. The foundation slab can be post-tensioned or conventionally reinforced. The foundation

slab should be designed using the PTI, WRI, or BRAB soil-related design parameter

values provided in the subsequent paragraphs.

6. Guidelines for the design of a conventionally reinforced foundation slab are provided by

resources such as the Wire Reinforcement Institute (WRI), the International Building Code

(IBC), the International Residential Code (IRC), the 1968 FHA BRAB report, and ACI

360R.

7. We recommend the parameter values in Table 1 when designing a conventionally

reinforced stiffened slab using traditional BRAB or WRI guidelines. We do not recommend

designing and constructing a foundation slab on soil conditions with a design PVR greater

than 1 ½ inches. Parameter values for a design PVR greater than 1 ½ inches are provided

for illustration purposes only or at the exclusive risk of the Owner. The building structure

must be designed to accommodate the potential vertical soil and slab movement (i.e. a

stiff slab does not prevent heave; increased slab stiffness attempts to limit the effects on

deflection to tolerable levels). The acceptable design deflection value will be determined

by the Structural Engineer.


19

Table 1:

Soil Improvement Condition Design PVR

Design PI BRAB Support Index

C

1-C

WRI Cantilever

Length

lc

Undercut 4 feet and replace with compacted select fill *

4 inches 43 0.70 0.30 8 ¼ feet


3 inches 36 0.77 0.23 7 feet


2 ¼ inches 32 0.82 0.18 5 ¾ feet


1 ¾ inches 28 0.86 0.14 4 ¾ feet


1 ¼ inches 24 0.90 0.10 3 ½ feet


1 inch 22 0.92 0.08 3 feet

Water and chemical inject to 12 feet and install a minimum 3-ft thick cap of compacted select fill **

1 ½ inches 26 0.88 0.12 4 feet

*: Under-cut is from existing grade. Clay must be replaced with properly compacted select fill. **: If quality control test results are deemed inadequate, an 8-ft deep vertical moisture-evaporation barrier must be installed around the building to protect the pre-swelled and treated clay soils.

For foundation slabs designed using the BRAB or WRI type methods, long term deflection

of flexural beams resulting from creep and shrinkage of concrete under sustained loading

can be determined using ACI 318-9.5.2.5, as recommended in the Texas Section ASCE

2007 Recommended Practice for the Design of Residential Foundations.

8. Guidelines for the design of post-tensioned slab-on-grade can be found in the PTI manual

Design of Post-tensioned Slabs-on-ground (2nd Edition 1996 or 3rd Edition 2004) and the

PTI manual Standard Requirements for Design and Analysis of Shallow Post-Tensioned

Concrete Foundations on Expansive Soils (2012). We recommend the soil-related

parameter values in Table 2 if using a PTI method of design. We do not recommend

designing and constructing a foundation slab on soil conditions with a design PVR greater

than 1 ½ inches. Parameter values for a design PVR greater than 1 ½ inches are provided

for illustration purposes only. The building structure must be designed to accommodate

the potential vertical soil and slab movement (i.e. a stiff slab does not prevent heave;

increased slab stiffness attempts to limit the effects on deflection to tolerable levels). The

acceptable design deflection value will be determined by the Structural Engineer.


20

Table 2

Soil Improvement Condition Design PVR

PTI Differential Movement (ym)

Edge Moisture Variation Distance (em)

Center Lift Edge Lift Center Lift Edge Lift


4 inches 2 ¾ inches 4 inches 5 feet 3 feet


3 inches 2 inches 3 inches 5 feet 3 feet


2 ¼ inches 1 ½ inches 2 ¼ inches 5 feet 3 feet


1 ¾ inches 1 ¼ inches 1 ¾ inches 5 feet 3 feet


1 ¼ inches 1 inch 1 ¼ inches 5 feet 3 feet


1 inch 1 inch 1 inch 5 feet 3 feet

Water and chemical inject to 12 feet and install a minimum 3-ft thick cap of compacted select fill **

1 ½ inches 1 ½ inches 1 inch 5 feet 3 feet

*: Under-cut is from existing grade. Undercut clay must be replaced with properly compacted select fill.

**: If quality control test results are deemed inadequate, an 8-ft deep vertical moisture-evaporation barrier must be installed around the building to protect the pre-swelled and treated clay soils.

The vertical modulus of elasticity (Es) of immediate subgrade under slab for use in

determination of the PTI beta parameter value can be selected to be 125 tsf (1,736 psi).

The PTI partition load slab stress coefficient (Cp) (3rd Edition PTI manual) can be selected

to be 1.10 for ks = 180 pci (compacted select fill).

9. Although the ground-supported foundation slab can be designed for vertical soil

movement greater than 1 inch, the cosmetic elements of the building might not be able to

tolerate the associated slab deflection. The building occupants might perceive excessive

movement when they see cracking in brittle elements such as drywall, hard tile, and

exterior brittle veneer (brick, stucco, stone masonry). The acceptable design slab

deflection must therefore be carefully selected. The foundation slab can be designed for

a PVR greater than 1 inch if an acceptable slab deflection can be achieved by the design.

Potential tilting and angular distortion, however, cannot be avoided, and the effects are

uncertain. The Owner must compare the risks of tilting and associated consequences,

with the costs of more robust soil improvement associated with a lower risk of tilt and

angular distortion.


21

10. Joints (for contraction and expansion crack control) should be designed and placed in

various portions of the structure (i.e. drywall control joints for long wall spans, above

doorways, in stairway walls, along long ceiling spans, etc). Properly planned placement

of these joints will assist in controlling the degree and location of material cracking that

normally occurs due to soil movements, initial wood shrinkage, expansion and shrinkage

of residential construction materials from changes in humidity and temperature, and strain

in framing from slab tilting, storm wind loads, and storm or man-made vibrations.

11. If the slab will be post-tensioned, the project team may consider requiring that the general

contractor use a subcontractor installer who is PTI certified to help ensure the quality of

the construction.

12. Exposure to the environment may weaken the soils at the grade beam bearing level if the

foundation excavations remain open for an extended duration. Foundation slab concrete

should be placed within 2 weeks of the completion of trench excavations and the moisture

barrier should be installed before any notable rainfall event. If the bearing soils are

softened by surface water intrusion or disturbance, the softened soils must be removed

from the foundation excavation bottom prior to concrete placement.

13. Grade beam dimensions and reinforcing steel should be observed and documented as-

built (“pre-pour” inspection by the Structural Engineer; or by the Geotechnical Engineer if

needed).

14. Prior to installation of reinforcing steel (or tendons) and the moisture-vapor barrier, Capital

Geotechnical Services should be retained to observe and test the grade beam subgrade

to determine if the foundations are being placed on suitable materials and to document

that loose material has been removed. Dynamic Cone Penetrometer (DCP) tests can be

performed to help evaluate subgrade condition. In areas where the subgrade is soft or

loose, the soil should be removed and foundations lowered to bear on firm soil or

foundation subgrade elevations can be restored using flowable fill approved by the

Structural Engineer.

15. Concrete material should be sampled and tested for compressive strength, and placement

operations should be monitored to record concrete slump, temperature, and age at time

of placement. Concrete batch tickets should be provided by the supplier and collected by

the General Contractor to permit inspection and documentation of water-cement ratio,

cement content, and other mix design ingredients.


22

16. We recommend that a floor flatness survey be performed within 2 weeks after the concrete

is poured to document the initial elevation profile condition of the slab. Such information

will be useful if future soil and slab movement is suspected and must be compared with

the initial elevation differences.

Driven Steel Pipe Piles:

Driven steel pipe piles can be considered in lieu of belled concrete piers to support a

structurally supported concrete slab cast on void boxes. Pipe piles are typically 8-inch outside

diameter elements installed to a depth great enough to provide adequate uplift resistance against

swelling clay soil in contact with the pile. Capital Geotechnical Services can provide an addendum

to this report upon request addressing the design of steel pipe piles if piles will be seriously

considered.

STRUCTURALLY SUPPORTED SLAB (IF USED)

A minimum 10-inch void should be included beneath the uniform thickness portions of the slab

to prevent swelling clay from inducing uplift pressures on the slab and associated piers. A void

space should also be included beneath the grade beams, but a low permeability backfill (clay soil)

must be used along the perimeter of the building in unpaved areas to limit water infiltration and

accumulation in these voids.

If carton forms are used, installation must be performed with care to assure that the void boxes

are not allowed to become wet or crushed before and during concrete placement and finishing

operations. Cardboard forms that have been damaged by rain must be replaced or allowed to

dry and have their capacity verified before placement of concrete. Masonite boards can be

applied on top of the carton forms to reduce the risk of crushing.

Regional carton form suppliers include:

Surevoid: http://www.surevoid.com/company/homepage_tech.php

Savway: http://www.savway.com/products.html

VoidForm Products, Inc.: http://www.voidform.com/CaraCor/

Soil retainer strips (i.e. Motzblock “Sureretainer”) can be used to prevent subsequent soil

backfill from displacing the void box.

http://www.surevoid.com/company/homepage_tech.php

http://www.savway.com/products.html

http://www.voidform.com/CaraCor/


23

To prevent potential tripping hazards, access and entry slabs by doors should be designed

with care since the exterior flatwork might heave with the clay soils. The access and entry slabs

can be structurally supported on drilled piers if the project team does not want any risk of joint

faulting between the doorways and the exterior slabs. Doweling can alternatively be considered

to prevent joint faulting but are prone to cracking the flatwork if differential movement occurs. A

hinged toe-beam detail (over void space) can be used as a transition slab between a pier-

supported structural slab and any adjacent concrete flatwork. Capital Geotechnical Services

should be retained to review construction plans and specifications to review details if a toe-beam

transition element is used.

Based on previous experience, we recommend that roof gutter drain downspouts not be

allowed to discharge near void boxes or within nearby perimeter backfill. As part of the final

punch-list inspection for the project, we recommend including an inspection to verify that roof

drains were properly constructed.

Due to the eventual degradation of the void boxes, a bonding moisture barrier composite with

notable peel adhesion properties should be used (i.e. Barrier-Bac VBC-350 31 mil) as the

moisture barrier in lieu of typical smooth thin geomembrane products.

SEISMIC DESIGN

The subject site is located in a region of low seismicity. The region has relatively low spectral

response acceleration and can be assigned to “Seismic Design Category A” according to ASCE

7-05 and Section 1613 of the 2012 IBC guidelines. The subject site can be categorized as a

“Class D” site for determination of design soil shear wave velocities.

PAVEMENT THICKNESS DESIGN

Estimates of traffic loads and volumes were not provided to Capital Geotechnical. Capital

Geotechnical has therefore assumed a daily traffic volume of 319 vehicle trips per day. This value

was estimated using the ITE (Institute of Transportation Engineers) average trip generation rate

of 4.90 vehicle trips per day per room for an “all suites hotel” land use. We understand there will

be approximately 65 units in the hotel.

Information on planned pavement surface grades was not provided to Capital Geotechnical

Services at the time of this report. We assume minor fill or excavation may be required to reach

planned pavement subgrade elevation across the site. Excavated clay can be re-used as fill


24

material for the pavement areas since subsequent soil improvement is expected. Options for

pavement thickness design are presented below.

Option A: Concrete Pavement w/ Lime Stabilization

6.0 inches jointed reinforced concrete pavement (JRCP)

4.0 inches crushed limestone base material

6.0 inches lime stabilized clay subgrade

Water and chemically treated clay to a depth of 6 feet below planned pavement surface

Concrete pavement should be at least 7.0 inches thick at the ramp to Grand Avenue. Concrete

pavement thickness can be reduced to 5.0 inches along strips of parking lot spaces where there

is no potential for heavy vehicles (i.e. delivery trucks; charter busses) to park temporarily.

Option B: Asphaltic Pavement w/ Lime Stabilization

2.0 inches hot-mix asphalt (HMA) Type D

8.0 inches crushed stone flexible base Grade 1 Type A

6.0 inches lime stabilized clay subgrade


Option C: Asphaltic Pavement w/ Geogrid

2.0 inches hot-mix asphalt (HMA) Type D

10.0 inches crushed stone flexible base Grade 1 Type A

Geosynthetic Geogrid Tensar TX5


The designs are based on the following parameters or assumptions:

- Average daily traffic (ADT): 319, with 50% lane distribution, with 0% annual growth, and 2.82%

trucks of all sizes (9 trucks per day) (small, medium, and large trucks).

- 18-kip ESALs (based on an average equivalency factor of 0.65 for trucks and busses, and

0.0002 for cars, SUVs, and pickup trucks) 43,179 over a 20 year period. - HMA Structural Coefficient: 0.44 - Flexible base Structural Coefficient: 0.14 - Lime stabilized clay Structural Coefficient: 0.07 - AASHTO Terminal Serviceability Index value: 2.0 - Analysis Period: 20 years (20 years to first significant rehabilitation). - Design resilient modulus of subgrade soil: 4,500 psi (untreated CH soil)


25

If the assumptions concerning traffic volume and loads are not reasonably correct, Capital

Geotechnical should be notified so that we can revise our recommendations if necessary.

Geometric pavement design should conform to any locally developed guidelines.

Pavement thickness sections are developed using methods that consider the structural

capacity of the pavement section. Although they account for some loss of serviceability due to

swelling of expansive clays, they do not consider or model the cracking that develops that is

damaging to the aesthetics of the pavement and they do not adequately model the loss of

serviceability (bumps) that develops from cracks and differential vertical movements under the

pavement. Lime stabilizing the upper layer of the clay or placing geogrid alone will not stop

cracking and in fact will still allow significant amounts of cracks to form if the clay soils have

sufficient swelling potential at the time of construction (hard and dry clay). We have therefore

included a soil improvement option to reduce the potential soil heave under pavement by

performing water and chemical pressure injection to a depth of at least 6 feet in the pavement

areas. Another option for deep soil improvement includes removal of several feet of clay and

replacement with properly compacted select fill with adequate fines content.

It is difficult to quantify the benefits of any of the soil improvement (injection; removal and

replacement) and immediate subgrade improvement (lime stabilization; geogrid) alternatives.

Even with these efforts, some cracking should be expected because of the high potential for

vertical movements of the underlying untreated clay soils. Pavement design is a subjective

analysis that involves a tradeoff between performance and cost. The more robust and expensive

the subgrade treatment and pavement section, the better the long term performance. The thinner

and cheaper the pavement section and lack of attention to subgrade treatment, the more the

pavement performance will be poor. Our recommended alternatives offer a balance between the

two. The Owner and project team can choose options based on costs and tolerance to cracking,

joint faulting, crack faulting, changes to surface runoff profile, potential tripping hazards, and other

effects of constructing pavement on expansive clay soils.

If curb and gutter is used, the detail must include reinforcing steel. Expansive clay soils that

heave curb elements can cause severe separation cracking in curb and gutter. Reinforcing steel

will limit crack widths and the associated aesthetic damage.


26

CONCRETE PAVEMENT COMMENTARY

Concrete paving should be used in front of any dumpster pads such that the truck is supported

on concrete pavement while loading and unloading the dumpster, and must be used for the ramp

to Burnet Road at the north area of the site.

Jointed reinforced concrete pavement (JRCP) can be considered to provide a more durable

pavement system. Relative to HMA, the disadvantages of concrete paving may be its initial higher

cost, susceptibility to joint faulting (affects ride quality), the larger amount of effort required to

install future utility trenches (open cut), and the cost of maintenance efforts such as joint cleaning,

joint sealing, and grinding. The advantages of concrete paving may include less frequent

maintenance efforts, more durable ride quality, no deterioration caused by oil leaks, good light

reflectivity that enhances pedestrian and vehicle safety at night and in rainstorms, and relatively

good skid resistance.

Concrete pavement design should conform to recognized design methods such as the ACI

Manual of Concrete Practice, ACI 330R-01: Guide for Design and Construction of Concrete

Parking Lots.

Stabilization of fine-grained soil under concrete is recommended to provide long term stiff

subgrade under concrete. Otherwise, as moisture content increases in soil under concrete occur

over time, the untreated fine-grained soil will lose stiffness and lead to forced displacement of soil

along edges and through cracks or joints with cycles of heavy vehicle loads (garbage trucks,

beverage trucks, delivery trucks, etc..), and lead to slab deflection and cracking in those areas

and possible joint faulting between panels.

Joint patterns should be carefully designed to avoid irregular shapes and to provide a sufficient

number of joints to control cracking associated with concrete expansion and contraction. Capital

Geotechnical recommends that joint spacing not exceed 12 feet for any panel if the tolerance to

shrinkage cracking will be low. Larger joint spacing can be considered by the Owner at the

Owner’s risk. As reported by the FHWA and SHRP, in relatively warm and dry climates like central

Texas, short joint spacing is generally desired to reduce the effects of climate. The greater the

joint spacing, the greater the occurrence of transverse cracking. Joint layout and detailing should

be included on the site civil plans by the project Civil Engineer, or a joint plan can be submitted

by the General Contractor during the submittal process.

Concrete pavement must include steel reinforcement to limit shrinkage cracking, limit the

width of transverse cracks, and limit long term deterioration common in cracked unreinforced

concrete pavement. In the Austin area, concrete parking lot pavement is commonly designed to


27

have #3 steel reinforcement bars at 18-inch spacing in both directions. Alternatively, the project

team can use the drag formula described in ACI 330R.

Steel reinforcement must ideally be interrupted at the contraction joints (not passed into

adjacent panel) except between perimeter panels and the next row of interior panels where

alternating bars can cross the joint to serve as tie-bars. At other joint locations, if steel is placed

through (under) contraction joints, then the pavement becomes a CRCP (continuously reinforced

concrete pavement) and becomes more susceptible to shrinkage cracking, punchouts, and

spalling. Note that steel reinforcement should have at least 2 inches of cover. Ideally, the

reinforcement should be placed 2 inches below top of pavement (ACI 330R-2.8.1; ACI

325.12R.4.6). If irregular shaped panels (neither square nor rectangular) are planned in some

areas of the parking lot, these panels should be reinforced regardless of the joint spacing.

Construction joints may have to be formed if necessary during construction and should line up

with a planned contraction joint.

Dowels can be used to transfer load between concrete panels, to reduce the chance of joint

faulting, and to limit deflections and damage to panel edges when supporting high volume truck

loads. Minimum 24-inch long, 3/4-inch diameter smooth steel dowels, spaced 18 inches apart

should be placed between panels. Dowels are typically placed in the middle of the vertical

pavement section and must be properly horizontally aligned.

Reinforcement, dowel, and joint details should be in accordance with the American Concrete

Institute (ACI) or Portland Cement Association (PCA) guidelines.

Curb-and-gutter concrete elements must be tied to the concrete pavement using tie-bars

wherever there is a downward slope behind the curbline (i.e. slope to a detention pond). Clay

slopes will creep downhill over time, causing severe separation cracking between the curb and

the concrete pavement unless the two elements are tied together.

PAVEMENT MAINTENANCE

Flexible pavements are generally designed by geotechnical engineers to provide a 20-year

service life before requiring an extensive rehabilitation, and only if proper maintenance is

performed. The actual service life of a pavement until full reconstruction is actually performed by

the Owner, however, is commonly 40 to 60 years. Regular maintenance can help extend the

design 20-year service life.


28

Depending on the moisture content fluctuations within the subgrade, the flexible pavement

may develop cracks or separations prematurely. Periodic crack sealing, fog seals, and slurry

seals are to be expected and must be performed to maintain the service life and maintain the

quality of the pavement by preventing water from infiltrating into the subgrade and by maintaining

the quality of the surface.

The 20-year service life assumes that the Owner will perform at a minimum an evaluation

every two (2) years and perform crack sealing as necessary. It is also assumed that a thick

asphalt seal coat or “slurry coat” will be placed as needed but at least three times during the 20

year service life.

A primary cause for deterioration of hot mix asphalt pavement is oxidative aging that results

in brittle HMA. Preventative maintenance (crack sealing, fog seals, slurry seals, and chip seals)

will provide a protective seal or rejuvenate the asphalt binder to extend the life of the HMA.

If concrete pavement is used, the Owner should anticipate performing a crack and joint

cleaning and sealing operation at least twice during the first 20 years of service (e.g. every 7

years). Diamond grinding can be considered at 8 to 10 year intervals if pavement smoothness

needs to be restored (re-leveling areas that exhibit joint faulting or other irregularities) and there

are no issues with drainage, inadequate doweling (load transfer), structural integrity, weak

subgrade with an inadequate pavement section design, D-cracking, and reactive aggregates,

since such issues would have to be addressed (repaired) before spending time, money, and effort

on grinding to restore levelness.

PAVEMENT MATERIAL RECOMMENDATIONS AND TESTING

Selection, transportation, placement, and compaction of pavement materials should be

performed in accordance with locally developed guidelines (e.g. City of Austin Standard

Specifications, Series 200 and 300).

Subgrade Preparation

1. Pavement subgrade must be clear of organic matter. Soil improvement should be

performed as recommended in this report.

2. Pavement subgrades that have local depressions resulting from uneven cut grading or

filling or from equipment traffic (ruts) can lead to ponding of water within the flexible base

layer in that area and subsequent premature loss of subgrade support. Forming and

maintaining a subgrade that is level, smooth, and constructed to required grade is


29

important to produce proper drainage of the base course layer above the less permeable

soil subgrade. The General Contractor and the earthwork or paving subcontractors must

inspect the subgrade for any depressions before placing the first lift of flexible base course.

3. The contractor should have a mix design performed using the actual site soils and the

stabilizing agent (lime, fly ash, cement). Scheduling should allow two weeks for the mix

design (e.g. lime series) to be completed prior to construction.

4. Stabilizing agents (lime, fly ash, cement) must come from the same source as used in the

mix design. If a new source is selected, particularly for lime, a new mix design is required.

5. High calcium quicklime shall conform to the requirements of ASTM C977 and C110.

6. Lime stabilization design and construction should conform to local, state or federal

government guidelines. Examples include:

City of Austin Standard Specifications Series 200 Item 203S;

TxDOT Specification Item 260;

U.S. DOT FHWA Lime in Soil Stabilization, Publication FHWA-HI-93-031.

The basic procedure for lime stabilization is listed below:

1. Spread lime (either hydrated lime slurry or dry quicklime)

2. Slake (add water) if quicklime is used

3. Mix

4. Compact

5. Mellow

6. Remix

7. Final compaction

8. Cure

Water must be applied periodically to keep the moisture content of the treated soil above

optimum. Water is a key ingredient for the chemical reactions and the mixture must not

be allowed to have insufficient water. Stabilization should extend horizontally 1 foot or

more beyond the edge of the curb and gutter.

9. Item 203S of the City of Austin Standard Specifications addresses the construction of lime

stabilized soil. Moisture content of the soil-lime mixture should be between the optimum


30

moisture content and 4 percentage points above optimum moisture content at the time of

compaction. The moisture content must be maintained until pavement is placed.

10. Inspection of lime stabilized clay (if applicable) should include documentation of

observations of the method of mixing, the uniformity of mixing, time period between lime

application, mixing, and placement, and measurements of relative compaction and

moisture content at the time of compaction. Atterberg limits tests should be performed to

assure that the PI of the lime stabilized mixture is below 20 during the mellowing period.

Phenolphthalein alcohol indicators can be used to determine the depth of subgrade that

was actually treated.

11. Stabilized clay should be left undisturbed to mellow for at least two days after completion

of the scarifying, lime placement, mixing, and sealing operation, or until the PI is reduced

to below 20. Occasional water sprinkling may be required to keep the surface of the lime

stabilized soil damp. Once mellowing is complete a final mixing should be performed

followed by compaction. In-place moisture-density tests should be performed to confirm

proper construction. The compacted stabilized clay should be left undisturbed and allowed

to cure for a minimum of two days or until trucks can be supported without deflecting the

subgrade. The surface should be kept moist during final curing and be kept moist until

placement of the overlying pavement material. Alternatively a bituminous seal coat can

be applied to protect the stabilized material from drying due to evaporation of moisture.

12. Clay stabilized with dry quicklime should be left undisturbed and allowed to cure for a

minimum of four days after the final scarifying and compaction operation has been

completed.

13. Of locally available geogrid we recommend the Tensar TX5 because it is ideally suited to

the desired function of limiting cracking under swelling and shrinkage conditions and

limiting cracking under soft subgrade conditions. A biaxial geogrid or an approximate

equivalent from another manufacturer approved by Capital Geotechnical may also be

considered but must be submitted for approval. Biaxial geogrid should meet the

requirements of TxDOT DMS-6270: Biaxial Geogrid for Environmental Cracking. Geogrid

must be installed per manufacturer requirements. Sheets of geogrid must overlap at least

18 inches because of the lack of restraint associated with the edge of a sheet. Overlaps

of geogrid should be installed with attention being given to which direction the earth

moving equipment will be pushing the overlying soil; i.e. use a shingle type overlap pattern

in one direction to avoid displacing or lifting a geogrid at the overlaps during fill placement.

If construction is performed when the subgrade soils are relatively moist (soft), a geotextile

can be installed to serve as a filter fabric to maintain separation of the finer-grained


31

subgrade soil and the base material during installation of the geogrid and base course.

Installation of geogrid and base on moist soft subgrade can be difficult if not properly

performed, and the use of a geotextile separator can facilitate the process.

14. The subgrade should be scarified to the required depth and mixed with the stabilizing

agent at the specified concentration until a uniform blend of soil, stabilizing agent, and

water is achieved.

Flexible Base Course

1. Flexible base material should be selected, placed, and compacted in accordance with

Series 200, Section 210S, of the City of Austin Standard Specifications. Placement should

not start until the subgrade is properly prepared and inspected.

2. Flexible base course should extend horizontally to at least the outside edge of the curb-

and-gutter.

3. Flexible base should be placed in maximum 6-inch lifts and should be compacted to

achieve a relative compaction of 100% or higher if using the maximum dry density

determined by the Tex-113-E method, or 95% or higher if using the ASTM D 1557 Proctor

method. Moisture content of the flexible base course material should be within two

percentage points of the optimum moisture content at the time of compaction. Section

210S.5 of Series 200 of the City of Austin Standard Specifications addresses compaction

of flexible base course.

4. Flexible base course should be tested during placement to document thickness, moisture

content, and density at the time of compaction.

5. Crushed recycled concrete can only be considered if the recycled concrete was not

contaminated by calcium sulfate industrial by-products.

Hot Mix Asphalt

1. Hot mix asphalt should be selected, placed, and compacted in accordance with Item 340

of the City of Austin Standard Specifications. Hot mix asphalt surface course can be a

TxDOT Type D gradation (“fine surface” mix) for parking lots. Item 340 addresses specific

material ingredient properties and gradations, as well as production and placement of

HMA.


32

2. A prime coat should be applied on the underlying flexible base.

3. HMA paving should only be performed when the air temperature is above 40 degrees

Fahrenheit.

4. Hot mix asphalt should be compacted to achieve a relative compaction between 92% to

96% of maximum theoretical density.

5. Inspection of hot mix asphalt should include placement temperature and thickness during

installation.

6. The surface must be sealed with a finish roller before the mix cools to 1850 F.

Concrete Pavement

The critical factors affecting the performance of concrete pavement are the strength and

quality of the concrete, proper placement of reinforcing steel for crack control, proper jointing for

crack control, and the uniformity of the subgrade.

A. For rigid pavement, concrete mixing, batching, forming, placing, finishing, and curing

should generally conform to the guidelines described in the City of Austin Standard

Specifications Series 300 Item 360: Concrete Pavement. Placement should not start until

the subgrade is properly prepared and inspected.

B. Concrete should consist of a minimum 500 psi flexural strength concrete at 28 day age.

To achieve this flexural strength, a mix with a 28-day compressive strength of 3,500 psi

or 4,000 psi may be required (i.e. do not order 3,000 psi concrete).

C. Curing and protection procedures should be implemented to protect the pavement from

moisture loss, rapid temperature change, and physical disturbance.

D. Concrete should be sampled and field tested by a representative of Capital Geotechnical.

E. Curing protection and procedures must be implemented to protect the concrete from

moisture loss, rapid temperature change, freezing, and physical disturbance.

F. All joints should be properly sealed with a backer rod and approved joint sealant.


33

SURFACE DRAINAGE, VEGETATION, AND UTILITY CONNECTIONS

Performance of foundation slabs, pavement, and flatwork is influenced by changes in

subgrade moisture conditions. We recommend the following precautions be implemented during

construction:

A. Utility structures that connect to the building should be designed to be flexible enough to

tolerate some differential soil movement. Water supply pipes and sanitary sewer pipes

beneath the slab should be placed in long sections with as few joints (leak-prone) as

possible and should be of durable size and material. Utilities that penetrate the foundation

slab should be designed with either some degree of flexibility or with sleeves in order to

prevent damage or leaking should vertical movement occur (i.e. shower or bathtub drain).

Water supply and sanitary sewer systems should be leak tested after installation.

Telescoping joint or swivel joint pipe fittings can be considered.

If a structurally supported slab is used, water lines should preferably be run above the slab

within the framework. Sanitary sewer lines should preferably be hung in a trench along

the pipe alignment using pipe hangers and wire tied to the horizontal rebar of the slab.

The trench depth must be adequate to maintain the required void space (i.e. 8 inches)

beneath the pipe.

B. The ground surface, pavement, and flatwork around the building should be sloped away

from the building to provide positive drainage away from the building perimeter. A

minimum drop of 6 inches over the first 10 feet from the edge of the foundation is

recommended (IBC 2012: 1804.3).

C. Roof drains should be designed and placed to discharge stormwater at least five feet away

from the building unless pavement abuts the edge of the building at the discharge location.

Roof drain downspouts should also be concentrated on the downslope side of the building.

D. If concrete root barriers are not installed, trees or deep-rooted bushes should not be

planted or allowed to exist adjacent to the building within a distance equal to half of their

mature height because of the root penetration and moisture demand that will dry the

underlying clay soils. Cracks in surrounding pavement or sidewalks should be routinely

sealed to prevent surface water from infiltrating into the subsurface clay soil. Trees should

also not be planted near pavement or flatwork unless a root barrier is installed.

E. Plants placed close to the foundation should be limited to those with low moisture

requirements (do not encourage high rates of irrigation).


34

F. Air conditioner condensation outlet pipes should preferably on the downslope side of the

building or into a controlled drainage system.

G. If shrubs must be placed adjacent to the building, the landscape beds or planters should

not be recessed (place at grade or elevate above grade and drain properly to prevent

ponding adjacent to the foundation slab).

H. If an exterior sprinkler system is installed to water landscaping, the sprinkler lines should

not be placed within 5 feet of the edge of the foundation. Instead the lines should be

placed so that sprinkler heads with sufficient capacity are used and direct water toward

the structure from 5 feet away.

I. Leak tests should be periodically performed on water supply, sprinkler, and sewer systems

to determine if a leak exists. Any leaking pipes should be repaired as soon as possible to

stop the increase in moisture content in the underlying clay soils. The water supply system

can be easily checked by monitoring the water meter when no water is being used.

J. Landscape islands in parking lot pavement are sources of water infiltration into adjacent

pavement subgrade and base material. Islands should consist of self-contained planters

(geomembrane liner or concrete cutoff elements), or drains should be installed to collect

excess rainwater and discharge to the storm sewer system. Weep holes can be drilled

through the curb to help prevent ponding of water behind the curbline and limit water

infiltration into the subgrade under the pavement.

POST-TENSIONING (IF USED)

Post-tensioning cables (tendons) and accessories need to be accurately placed, protected,

and correctly installed. Utility penetrations through the slab must be planned in conjunction with

the placement of post-tensioning cables. The Structural Engineer, or the Geotechnical Engineer

if needed, should be retained to perform a “pre-pour” inspection to observe and document grade

beam dimensions and proper cable installation.

Pulling (tensioning) of cables should be performed by experienced personnel because of the

danger involved during the pulling and lock-off operation. Cable ends must be properly covered

or coated to prevent corrosion that can allow long term relaxation and reduction of design strength,

and potential excessive movement in isolated areas of the slab. Tendon tails should not be cut

until the tensioning (stressing) test data is approved by the project Structural Engineer. The post-

tensioning stressing operation should be observed by the Structural Engineer (or by the


35

Geotechnical Engineer if needed) to document proper construction. Observations should include

obtaining a copy of the calibration sheet correlating force and hydraulic pressure of the jack being

used. Each tendon elongation should be measured and compared to specification requirements.

Results can then be provided to the project Structural Engineer for approval.

LIMITATIONS

This report is subject to the limitations and assumptions presented in the report. Should

conditions change or if assumptions are not accurate, we must be contacted to review our

recommendations.

Borings were spaced to obtain a reasonable indication of subsurface conditions. The data

from the borings is only accurate at the exact boring locations. Variations in the subsurface

conditions not indicated by our borings are possible. The recommendations in this report were

developed considering conditions exposed in the exploratory borings and our understanding of

the type of structure planned.

We believe that the geotechnical services for this project were performed with a level of skill

and care ordinarily used by geotechnical engineers practicing in this area at this time. No

warranty, express or implied, is made.

Capital Geotechnical Services should be retained to review plans and specifications related

to geotechnical elements of the construction to check that our recommendations have been

properly interpreted. Capital Geotechnical Services cannot be responsible for incorrect

interpretations of our recommendations, particularly if we are not retained to review plans and

specifications.

This report is valid until site conditions change due to disturbance (cut and fill grading) or

changes to nearby drainage conditions, or for 3 years from the date of this report, whichever

occurs first. Beyond this expiration date, Capital Geotechnical Services shall not accept any

liability associated with the engineering recommendations in the report, particularly if the site

conditions have changed. If this report is desired for use for design purposes beyond this

expiration date, we recommend drilling additional borings so that we can verify the subsurface

condtions and validate the recommendations in this report.


36

INSPECTIONS

Capital Geotechnical should be retained to perform the field observations, field testing, and

laboratory testing recommended in this report (i.e. City of Austin “Special Inspections”) because

of our familiarity with the project and site conditions. The performance of foundations and

pavement is primarily controlled by the quality of the construction. To prevent misinterpretation

of our recommendations, and to document proper construction, Capital Geotechnical should be

retained to perform quality control (QC) testing, inspection, and documentation during earthwork

and during construction of the foundations and pavement. Quality control (QC) inspections by

Capital Geotechnical Services can include (as applicable depending on design):

Sampling and lab testing of proposed fill material to check and document

classification.

Inspection of soil improvement excavation or soil improvement injection operation.

Testing of compacted fill, pavement base material, or lime stabilized clay subgrade

in-place to check and document proper compaction and moisture-conditioning.

Inspection and documentation of drilled shaft construction.

Pre-pour inspection to check and document grade beam dimensions, void box

installation (if applicable), reinforcing steel installation, and moisture vapor barrier

installation (if not performed by Structural Engineer).

Pre-pour inspection of post-tension cable installation (if not performed by Structural

Engineer).

Concrete sampling and testing to document as-built condition of wet concrete and to

document that the supplier provided an adquate mixture to the site.

Post-tension cable stressing inspection (if not performed by Structural Engineer).

Pre-pour inspection of concrete pavement contruction (reinforcing steel, joint layout,

joint doweling, thickness).

Vicinity Map

Hotel at 13311 Burnet Rd (MoPac)

Austin Travis County, Texas

Prepared By: NFK

Scale: -

Project #: 15-0179

Base Map By: City of Austin

Date: October 2015

Figure #: 1

Capital Geotechnical Services PLLC Austin, Texas

Site Area

Local Lot Plan



Prepared By: NFK

Scale: -

Project #: 15-0179

Base Plan By: Travis County

Date: October 2015

Figure #: 2


Subject Lot

Geology Map



Prepared By: NFK

Scale: -

Project #: 15-0179

Base Map By: U.T. Bureau of Econ. G.

Date: October 2015

Figure #: 3


Site Area

“Kdr”: Clay sedimentary deposit categorized as the “Del Rio Clay” geologic formation. “Kgt”: Limestone rock and marly limestone sedimentary deposit categorized as the “Georgetown Limestone” geologic formation.

Old Burnet Rd (now under MoPac mainlaines)

Approximate Locations of Exploratory Borings


Austin

Travis County, Texas

Prepared By: NFK

Scale: -

Project #: 15-0179

Base Plan By: ADR Designs LLC

Date: October 2015

Figure #: 4


Wooded

Wooded

Wooded

B-1

B-4

B-2

B-3

STANDARD REFERENCE NOTES FOR BORING LOGS I. Sampling & Testing Symbols:

II. Correlations of Penetration Resistance to Soil Properties:

Relative Density of Sand and Sandy Silt Consistency of Clay and Clayey Silt

Relative Density SPT N-value Consistency SPT N-value

(qualitative measure)

Unconfined Compressive Strength

(tsf)

Very loose 0 to 4 Very soft 0 to 3 Under 0.25

Loose 5 to 10 Soft 4 or 5 0.25 – 0.5

Medium dense 11 to 30 Medium stiff 6 to 10 0.5 – 1.0

Dense 31 to 50 Stiff 11 to 15 1.0 – 2.0

Very Dense > 50 Very stiff 16 to 30 2.0 – 4.0

Hard > 30 4.0 – 8.0

III. Unified Soil Classification Symbols:

GP - Poorly Graded Gravel SP - Poorly Graded Sand ML - Low Plasticity Silt GW - Well Graded Gravel SW - Well Graded Sand MH - High Plasticity Silt GM - Silty Gravel SM - Silty Sand CL - Low to Medium Plasticity Clay GC - Clayey Gravel SC - Clayey Sand CH - High Plasticity Clay OH - High Plasticity Organics OL - Low Plasticity Organics

IV. Rock Quality Designation index (RQD): V. Natural moisture content: “Dry” No apparent moisture, crumbles easily

RQD: Description of Rock Quality: “Moist” Damp but no visible water (if all natural fractures) “Wet” Visible water 0-25 % Very poor 25-50 % Poor 50-75 % Fair 75-90 % Good 90-100% Excellent

VI. Grain size terminology: VII. Descriptive terms or symbols:

Cobble: 3-inches to 12-inches “Mottled”: occasional/spotted presence of that color

Gravel: #4 sieve size (4.75 mm) to 3-inches “- […]”: identifies change in soil characteristics

Coarse sand: #10 to #4 sieve size LL: Liquid Limit (moisture content as % of dry weight)

Medium sand: #40 to #10 sieve size PL: Plastic Limit (moisture content as % of dry weight)

Fine sand: #200 to #40 sieve size WOH: Weight of hammer

Silt or clay: smaller than #200 sieve size “with […]”: item identified within that sample only

VIII. Descriptive terms for soil composition: IX. Plasticity of cohesive soil:

(function of PI and clay mineral types)

“Trace” . . . . . . . . . . . . . . . . 1 to 9% Plasticity Index (PI): Plasticity:

“Some” . . . . . . . . . . . . . . . . 10 to 29% 0 to 20 Low

(with suffix –y, e.g. sandy, clayey …) . . . . 30 to 49% 20 to 30 Medium

30 + High

Capital G

eote

chn

ical S

erv

ices P

LLC

- 1

32

00 P

ond S

prings R

d.,

Suite G

-53,

Austin,

Texas 7

872

9

Fig. 9

Shelby Tube Split-Spoon Sampler

Rock core or rock coring barrel

Geoprobe tube

Auger

ST

SS

RC

A

GT

Light gray and light yellowish brown Dry unit weight = 115 pcf

Remolded specimen Initial moisture content = 17 %

B-1 at 6 to 7.5 feet (PP= 4.5+ tsf) Final moisture content = 37 %

Initial liquidity index (LI): Days soaking: 14

Light yellowish brown clay Dry unit weight = 113 pcf


B-2 at 8.5 to 10 feet (PP=4.5+ tsf) Final moisture content = 40 %


Final PP: 0.00 tsf

-0.116

-0.150

-1

1

3

5

7

9

11

13

15

17

19

21

23

25

27

29

-1

1

3

5

7

9

11

13

15

17

19

21

23

25

27

29

Vertical Pressure (ksf)


0.01 1.0 10 100

0.01 1.0 10 100

Vert

ical

Sw

ell (

%)

Swell Test Results

Vert

ical

Sw

ell (

%) Net vertical swell due to wetting

under constant load: 28.6%(125 psf surcharge pressure)

Net vertical swell due to wetting under constant load: 28.5%(60 psf surcharge pressure)

0.1

0.1

Hotel at 13311 Burnet Road (MoPac), Austin, Texas

Capital Geotechnical Services Project #15-0179 Figure 10

Medium to light yellowish brown Dry unit weight = 124 pcf


B-3 at 4 to 5.5 feet (PP= 4.5+ tsf) Final moisture content = 39 %


Lt yellowish brown and lt olive Dry unit weight = 113 pcf


B-3 at 13.5 to 15 feet (PP=4.5+ tsf) Final moisture content = 41 %


Final PP: 0.00 tsf

-0.125

-0.067

-1

1

3

5

7

9

11

13

15

17

19

21

23

25

27

29

-1

1

3

5

7

9

11

13

15

17

19

21

23

25

27

29

31

33



0.01 1.0 10 100

0.01 1.0 10 100

Vert

ical

Sw

ell (

%)

Swell Test Results

Vert

ical

Sw

ell (

%) Net vertical swell due to wetting

under constant load: 32.9%(60 psf surcharge pressure)

Net vertical swell due to wetting under constant load: 26.2%(60 psf surcharge pressure)

0.1

0.1

Hotel at 13311 Burnet Road (MoPac), Austin, Texas

Capital Geotechnical Services Project #15-0179 Figure 11

subsurface exploration and geotechnical … reports (geotechnical report).pdfsubsurface exploration...

Documents