Excerpts from actual PMI Evaluations

•“Works well when under constant supervision and cornered like a rat in a trap.”•“His men would follow him anywhere, but only out of morbid curiosity.”•“When she opens her mouth, it is only to change feet.”•“He doesn’t have ulcers, but he is a carrier.”•“If you see two people talking and one looks bored, he’s the other one.”

Pipe Trench Preparation and Backfill History

Workers excavate a culvert at the circa-2725 B.C. site of the Harappa settlement in Pakistan (file photo). PHOTOGRAPH BY RANDY OLSON, NATIONAL GEOGRAPHIC

1997 STUDY•Justin F. Lundvall and John P. Turner, Ph.D, P.E.•65 page report

Objective

•To identify the likely causes of settlement and roadway damage at culverts sites on Wyoming highways

Field Investigation

• WYO 487 - Medicine Bow to Casper (47-55)– Settlement within the first year of construction in 1992. Prior to 1992 no extensive maintenance had been required since 1956 – maintenance foreman

• WYO 70 - Baggs– Encampment (2-4) • WYO 113 - Pine Haven Road(0-4)• Various locations in District 5

1. Determine if roadway settlement appears to be related to culvert or pipe characteristics, geological environment, construction practices, or other factors.

2. Establish the mechanism(s) of settlement, for example, compression settlement of fill around and above culverts and pipes under traffic loads, settlement of soil beneath culverts and pipes, deformation of the culverts and pipes, or some combination of causes.

3. Evaluate design and/or construction procedures to prevent or minimize roadway settlement.

What did they want to accomplish with this study?

Probable Causes of Settlement

• Inadequate compaction of backfill around and above culverts due to lack of inspection.

• Low cover from the top of the pipe to the surfacing

• The use of poor material for backfill (plastic, compressible soils)

1997 study recommendations to reduce settlement

1. Use high quality granular materials compacted to a high density for backfilling culverts

2. Avoid the use of highly plastic, compressible fine-grained soils

3. Use a controlled low strength materials (CLSM), commonly referred to as flowable fill, for backfilling culverts

What did we do with the recommendations from the 1997 final report?

2006 FHWA Directive - from the federal HWY Bill From 2006 and 2007 Memos

“State DOT’s should develop culvert selection policies that consider all available pipe products judged to be of satisfactory quality and equally acceptable on the basis of engineering and economic analyses.”

“Division Offices should now be working with their respective State DOT’s to ensure that the State’s culvert material selection procedures provide for competition with respect to the specification of alternative types of culvert pipes. Division Offices should ensure that the State’s procedures are based on sound engineering and economic reasons and not based on arbitrary factors.”

“With the potential for significant savings, the implementation schedule should not be based on protracted (drawn-out) evaluation periods for experimental or pilot project installations.”

The policy is intended to ensure plastic pipes are being considered for use.

2012 StudyObjectiveTo provide the WYDOT Culvert Committee with all of the tools and information they need to draft a policy on culvert selection that satisfies the FHWA directive while also meeting the needs of WYDOT. The policy must be based on rational consideration of costs, performance, engineering design practice for culverts, constructability, and quality.

163 page report

2012 Study Benefits•will allow the Wyoming DOT to satisfy the FHWA directive• develop culvert selection policies that consider all available pipe products, in a manner that provides fair competition and which is consistent with acceptable engineering practice.• will provide WYDOT with higher quality and more cost-effective culvert installations.

The final report included recommendations for:

• Maximum Fill Height • Minimum Fill Height • Bedding and Backfill • Compaction• CLSM (controlled low-strength material)• Trench Width • Embankment Construction • Pipe Foundation / Bedding Thickness • Haunch • Backfill Lift Thickness• Corrosion • Abrasion • Joints • End treatments • Allowable Pipe Diameter • Deflection Testing and Inspection

What needs Revised?• Section 206 – Excavation and Backfill for

Culverts – spec book• Section 603 – Culverts and Storm Drains –

spec book• Section 800 – Materials – spec book• Section 603 of the Standard Plans

Culvert Selection and Backfill Committee Members

Bill Wilson, P.E. – Standards Engineer – chair of the committeeAndy Long, P.E. – State Construction EngineerCharlie Bauer, P.E. – Construction Staff EngineerMark Falk, P.G. – Assistant State GeologistMike Menghini, P.E. – Assistant State Bridge EngineerChris Romo, P.E. – Materials EngineerMark Boushelle – FHWA, Pavement and Structures EngineerJanis Kotlark – Administrative AssistantDon Fuller, P.E. – Retired Resident Engineer – replaced by Ralph Tarango

OTHER CONTRIBUTERSWCACONTECH ENGINEERING SOLUTIONSPRINSCOTrueNorth SteelPlastic Pipe Industry

Please note that these proposed changes are a draft. There are

still changes to be made.

Reference the proposed Typical Pipe Installation Embankment Details as I go through the specification changes.

SECTION 206Excavation and Backfill for

culverts•New reference section•Add Vertical limits to account for pipe bedding material.

SECTION 206Excavation and Backfill for

culvertsThis is a new subsection

Horizontal Limits – 2012 StudyAASHTO (2010a) only makes recommended embankment widths for concrete pipe that is equal to three times the outside pipe diameter. Although this limit appears to be within reason for concrete pipe, it may not be suitable for flexible pipe. It is recommended WYDOT implements a tentative minimum embankment width equal to five times the pipe diameter for all pipe materials. Vertical LimitsUp to spring line

This section is also for box culverts which does not always required select backfill material

Select bedding and backfill material – Typical Pipe Installation DetailThe type of backfill and the manner in which it is installed is one of the most important considerations when installing pipe

The soil envelope must be able to develop high shear strengths in order to resist lateral pressure induced by vertical loads.

granular, coarse-grained soils with little to no fines typically develop greater shear strength

Max PI of 6

May have to re-evaluate the gradation requirements

Gradation recommended by final report

Report Recommendations• Include a min. air content equal to 6% • Include a max slump of 10 inches •Add a statement requiring CLSM to set for a minimum of 24 hours prior to allowing vehicle loads to travel over the fill •Add a statement requiring the contractor to submit mix designs a minimum of 30 days prior to installation for review •Add a statement requiring the contractor to provide a “delivery” ticket along with each batch of CLSM. The ticket should provide information such as the project designation, date, time, compressive strength, yield and unit weight, and flowability.

Why not fly ash? fly ash can result in higher than anticipated compressive strengths, greater susceptibility to frost heave, and increased corrosion rates when used for metal pipes.

SECTION 603Culverts and Storm Drains

From 2012 Study“results from DOT surveys show there is a learning curve for contractors. Therefore, it is recommended that implementation occurs first through use of pilot projects. Interim specifications should be implemented which do not allow the use of plastic pipe in the following locations:”

We are taking the conservative approach.

What does lab do with the Alkali Samples?

How does WYDOT determine the CR number?

Alkali samples are tested for the following:

• Minimum Resistivity• Ph level• Sulfates

Minimum Resistivity A current is sent through

a uniform soil sample to test the resistance.

less resistance means

the soil has a lot of free ions so corrosion will be more severe. “Hot Soil”

Ph Level (acid level)

Measures the concentration of hydrogen ions

SULFATES

Greater the sulfate level the greater possibility of corrosion. Bacteria feeds on sulfates, free ions can bond and oxidation can occur.

See the Typical Pipe Installation Trench DetailAASHTO (2002) states the central bedding, which is equal to one third of the outside diameter of pipe (refer to figure 4 above) should be “loosely placed” while the remaining portion should be compacted to unit densities discussed in previous sections.

The central bedding zone provides uniform support

Pipe which was installed with highly compacted soil were 70% less than installations with loosely compacted soil.

Annular = ring-shaped

From 2012 Study“Since deflections are in fact controlled more by construction practice than by design, it is increasingly becoming practice to place responsibility for control of deflections on the contractor, rather than the designer.”

DIVISION 800Materials

Cell Classification - An indicator of long term durability based on the coating they put on the pipe to protect from UV light and environmental stress cracking.

Fill HeightBased on the minimum sectional properties. This is a conservative approach.

Eventually the Bridge program is going to develop fill chart tables based on load and resistance factor design (LRFD).

InspectionRead and understand specification and use the Construction Administration Manual as a guide.

Bottom line is to make sure the contractor is installing the pipe in accordance with the plans and specifications

18’X8’1”, 76’ structural plate arch