part 79 pe exam

8/9/2019 Part 79 PE Exam

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Professional Publications, Inc. • Belmont, CA

CivilEngineeringReference

Manualfor the PE Exam

Eleventh Edition

Michael R. Lindeburg, PE

http://ppi2pass.com/ppi/PPIShop?pr=CERM11&ct=CIVIL&idx=0











79 Construction Earthwork. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1. Definition . . . . . . . . . . . . . . . . . . . . 79-12. Unit of Measure . . . . . . . . . . . . . . . . 79-13. Swell and Shrinkage . . . . . . . . . . . . . . 79-14. Classification of Materials . . . . . . . . . . . 79-25. C ut and Fill . . . . . . . . . . . . . . . . . . 79-26. Field Measurement . . . . . . . . . . . . . . 79-27. Cross Sections . . . . . . . . . . . . . . . . . 79-28. Original and Final Cross Sections . . . . . . 79-29. Typical Sections . . . . . . . . . . . . . . . . 79-2

10. Distance Between Cross Sections . . . . . . . 79-211. Grade Point . . . . . . . . . . . . . . . . . . 79-312. Volumes of Piles . . . . . . . . . . . . . . . . 79-313. Earthwork Volumes . . . . . . . . . . . . . . 79-414. Average End Area Method . . . . . . . . . . 79-415. Prismoidal Formula Method . . . . . . . . . 79-416. Borrow Pit . . . . . . . . . . . . . . . . . . . 79-417. Mass Diagrams . . . . . . . . . . . . . . . . . 79-6

Nomenclature

a dimension ft mA area ft2 m2

b dimension ft md distance ft mh height ft mHI height of the instrument ft m

L length ft mL load factor – –r radius ft ms side-slope – –V volume ft3 m3

w width ft m

Symbols

φ angle deg deg

Subscripts

b bank measurec compactedl loose measurem mean

1. DEFINITION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Earthwork is the excavation, hauling, and placing of soil, rock, gravel, or other material found below thesurface of the earth. This definition also includes themeasurement of such material in the field, the compu-tation in the office of the volume of such material, andthe determination of the most economical method of

performing such work. Specific information about ex-cavation analysis, bracing, bulkheads, and cofferdamsis in Ch. 39.

2. UNIT OF MEASURE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

In the United States, the cubic yard (i.e., the “yard”) isthe unit of measure for earthwork. However, the volumeand density of earth changes under natural conditionsand during the operations of excavation, hauling, andplacing.

3. SWELL AND SHRINKAGE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

A cubic yard of earth measured in its natural positionwill be more than a cubic yard after it is excavated. If the earth is compacted after it is placed, the volumemay be less than a cubic yard.

The volume of the earth in its natural state is known asbank-measure . The volume during transport is known asloose-measure . The volume after compaction is knownas compacted-measure .

When earth is excavated, it increases in volume becauseof an increase in voids. The change in volume of earthfrom its natural to loose state is known as swell . Swell isexpressed as a percentage of the natural volume. A soilsload factor , L, in a particular excavation environmentis the inverse of the swell factor , the sum of 1 and thedecimal swell.

V l =

100% + % swell

100%

V b =

V b

L 79.1

The decrease in volume of earth from its natural stateto its compacted state is known as shrinkage . Shrinkagealso is expressed as a percent decrease from the naturalstate.

V c =

100%−% shrinkage

100%

V b 79.2

As an example, 1 yd3 in the ground may become 1.2yd3 loose-measure and 0.85 yd3 after compaction. Theswell would be 20%, and the shrinkage would be 15%.Swell and shrinkage vary with soil types.

Refer to Table 79.1 for load factors and swell percent-ages for many different soil types.

P R O F E S S I O N A L P U B L I C A T I O N S , I N C .
































































































































































79-2 C I V I L E N G I N E E R I N G R E F E R E N C E M A N U A L

Table 79.1 Typical Swell and Load Factors of Materials

loadmaterial swell, % factor

claydry 40 0.72wet 40 0.72

clay and graveldry 40 0.72wet 40 0.72

coal, anthracite 35 0.74coal, bituminous 35 0.74earth, loam

dry 25 0.80wet 25 0.80

graveldry 12 0.89wet 12 0.89

gypsum 74 0.57hardpan 50 0.67limestone 67 0.60

rock, well blasted 65 0.60sanddry 12 0.89wet 12 0.89

sandstone 54 0.65shale and soft rock 65 0.60slate 65 0.60traprock 65 0.61

Adapted from Standard Handbook for Civil Engineers.

4. CLASSIFICATION OF MATERIALS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Excavated material is usually classified as common ex-

cavation or rock excavation . Common excavation is soil.In highway construction, common road excavation issoil found in the roadway. Common borrow is soil foundoutside the roadway and brought in to the roadway.Borrow is necessary where there is not enough materialin the roadway excavation to provide for the embank-ment.

5. CUT AND FILL. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Earthwork that is to be excavated is known as cut . Ex-cavation that is placed in embankment is known as fil l .

Payment for earthwork is normally either for cut and

not for fill, or for fill and not for cut. In highway work,payment is usually for cut; in dam work, payment isusually for fill. To pay for both would require measuringtwo different volumes and paying for moving the sameearth twice.

6. FIELD MEASUREMENT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Cut and fill volumes can be computed from slope-stakenotes, from plan cross sections, or by photogrammetricmethods.

7. CROSS SECTIONS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Cross sections are profiles of the earth taken at rightangles to the centerline of an engineering project (suchas a highway, canal, dam, or railroad). A cross sectionfor a highway is shown in Fig. 79.1.

Figure 79.1 Typical Highway Cross Section

CL

8. ORIGINAL AND FINAL CROSS SECTIONS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

To obtain volume measurement, cross sections are taken

before construction begins and after it is completed. Byplotting the cross section at a particular station bothbefore and after construction, a sectional view of thechange in the profile of the earth along a certain lineis obtained. The change along this line appears on theplan as an area. By using these areas at various intervalsalong the centerline, and by using distance between theareas, volume can be computed.

9. TYPICAL SECTIONS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Typical sections show the cross section view of the proj-ect as it will look on completion, including all dimen-sions (Fig. 79.2). Highway projects usually show sev-eral typical sections including cut sections, fill sections,and sections showing both cut and fill. Interstate high-way plans also show access-road sections and sectionsat ramps.

10. DISTANCE BETWEEN CROSS SECTIONS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Cross sections are usually taken at each full station andat breaks in the ground along the centerline. In taking

cross sections, it must be assumed that the change inthe earth’s surface from one cross section to the next isuniform, and that a section halfway between the crosssections is an average of the two. If the ground breaksappreciably between any two full-stations, one or morecross sections between full-stations must be taken. Thisis referred to as taking sections at pluses . Figure 79.3shows eleven stations at which cross sections should betaken.

In rock excavation, or any other expensive operation,cross sections should be taken at intervals of 50 ft (15 m)




























































































































C O N S T R U C T I O N E A R T H W O R K 79-3

Figure 79.2 Typical Completed Section

12 ft min6 ft min

6 ft min

12 ft 12 ft

6 ftshoulder

6 ftshoulder

or less. Cross sections should always be taken at the PCand PT of a curve. Plans should also show a section oneach end of a project (where no construction is to takeplace) so that changes caused by construction will notbe abrupt.

Figure 79.3 Cross-Section Locations

1

0 0

2

0 0

3

0 0

4

0 0

5

0 0

2 0

3 6

5 6

8 1

6

0 0

7

0 0

Where a cut section of a highway is to change to afill section, several additional cross sections are needed.Such sections are shown in Fig. 79.4.

Figure 79.4 Cut Changing to Fill

1568152

1563

11. GRADE POINT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

The point where a fill section meets the natural ground(where a cut section begins) is known as the grade point .

12. VOLUMES OF PILES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

The volumes of piles of soil, recycled pavement, andpaving materials can be calculated if the pile shapesare assumed. The angle of repose , φ, depends on thematerial, but is approximately 30◦ for smooth gravel,40◦ for sharp gravel, 25 to 35◦ for dry sand, 30 to 45◦

for moist sand, 20 to 40◦ for wet sand, and 37◦ forcement.

V =

h

3

πr2 [cone] 79.3

V =

h

6

b(2a + a1) = 1

6hb

3a−

2h

tanφ

[wedge] 79.4

V =

h

6

ab + (a + a1)(b + b1) + a1b1

=

h

6

ab + 4

a−

h

tanφ1

b−

h

tanφ2

+

a−

2h

tanφ1

b−

2h

tanφ2

frustrum of a

rectangular pyramid

79.5

a1 = a − 2h

tanφ179.6

b1 = b − 2h

tanφ279.7





























































































































































































































































79-4 C I V I L E N G I N E E R I N G R E F E R E N C E M A N U A L

Figure 79.5 Pile Shapes

r

b

a h

h

a

a 1

a 1

(a) cone

(b) wedge

(c) frustrum of a rectangular pyramid

1

b

a hh

a

a 1b 1

b

b 1

a 1

2

13. EARTHWORK VOLUMES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

A three-dimensional soil volume between two pointsis known as a soil prismoid or prism . The prismoid(prismatic) volume must be calculated in order to es-timate hauling requirements. Such volume is generallyexpressed in units of cubic yards (“yards”) or cubic me-ters. There are two methods of calculating the pris-moid volume: the average end area method and theprismoidal formula method.

Figure 79.6 Soil Prismoid

A1

Am

A2

L

2

L

2

14. AVERAGE END AREA METHOD. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

With the average end area method , the volume is calcu-lated by averaging the two end areas and multiplying bythe prism length. This disregards the slopes and orien-tations of the ends and sides, but is sufficiently accuratefor most earthwork calculations. When the end area iscomplex, it may be necessary to use a planimeter or to

plot the area on fine grid paper and simply count thesquares. The average end area method usually over-estimates the actual soils volume, favoring the contrac-tor in earthwork cost estimates.

V = L(A1 + A2)

2 79.8

The precision obtained from the average end area meth-od is generally sufficient unless one of the end areas isvery small or zero. In that case, the volume should becomputed as a pyramid or truncated pyramid.

V pyramid =

LAbase

3 79.9

15. PRISMOIDAL FORMULA METHOD. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

The prismoidal formula is preferred when the two endareas differ greatly or when the ground surface is irreg-ular. It generally produces a smaller volume than theaverage end area method and thus favors the owner-developer in earthwork cost estimating.

The prismoidal formula uses the mean area, Am, mid-way between the two end sections. In the absence of

actual observed measurements, the dimensions of themiddle area can be found by averaging the similar di-mensions of the two end areas. The middle area is notfound by averaging the two end areas.

V =

L

6

(A1 + 4Am + A2) 79.10

When using the prismoidal formula, the volume is notfound as LAm, although that quantity is usually suffi-ciently accurate for estimating purposes.

16. BORROW PIT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

It is often necessary to borrow earth from an adjacentarea to construct embankments. Normally, the borrow pit area is laid out in a rectangular grid with 10 ft (3 m),50 ft (15 m), or even 100 ft (30 m) squares. Elevationsare determined at the corners of each square by level-ing before and after excavation so that the cut at eachcorner can be computed.

Points outside the cut area are established on the gridlines so that the lines can be reestablished after exca-vation is completed.






























































































































































part 79 pe exam

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