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Earthwork Design

The following information supplements PDDM Section 9.5.1.

While roadway excavation is not classified for measurement or payment purposes, it may be categorized for computation of earthwork design and mass purposes as the following types:

  1. Common Material. Common material is largely earth or earth with detached boulders less than 0.5 cuyd [0.5 m3].
  2. Rippable Rock. Rippable rock refers to material ready for excavating after being loosened by a ripper.
  3. Solid Rock. Solid rock includes hard rock in place, ledge rock and boulders requiring drilling and blasting equipment for removal. Any blasting work will be performed according to the rock blasting section specifications.

Determination of Excavation and Embankment Volumes

Use the average end-area method of determining volumes. The total volume of earthwork is the sum of the volumes of the prismoids formed by adjacent cross sections.

When using the average end-area method, the prismoid is treated as a prism whose cross section is the mean of the two end areas of the prismoid. Equation 9.5.1A(1) presents the formula for use in the average end-area method.

 Equation 9.5.1A(1)
V=L(A1+A2)/2

Where:

V = Volume, cubic yard [m3]
A1 and A2 = Cross sectional end areas, square feet [m2]
L = Distance between the cross sections, ft [m]

This formula is approximately correct. Due to its simplicity and substantial accuracy in the majority of cases, it has become the formula in common use. It gives results, in general, larger than the true volume.

When the earthwork center of mass (centroid of the area of cut or fill) is not centered about the roadway, and the alignment is in curvature, the actual volume calculated is not correct since the true distance between the end area centroids will differ from the distance along the centerline. In this case it may be necessary to adjust excavation volumes for curvature in order to properly account for earthwork. In many cases this is not necessary since the eccentricities about centerline of the earthwork mass tend to equalize themselves over the route.

Shrink and Swell Factors

Using data furnished by the Geotechnical Unit, the designer must check the characteristics of the material to be excavated or placed in embankments. The excavation used for embankments will range from rock to earth and have shrink/swell factors assigned for design purposes.

The values shown in Exhibit 5.1 A may be used for estimating purposes prior to obtaining the project specific information from the Geotechnical Unit.

MaterialMeasured
In-Situ
Mass Density1
LooseEmbankment
Mass Density2%
Swell3
Mass Density2%
Swell3
lb/yd3kg/m3lb/yd3kg/m3lb/yd3kg/m3
Andesite4950293029701760673460205043
Basalt4950293530201790643640216036
Bentonite270016002000118535
Breccia4050240030401800333190189027
Calcite-Calcium450026702700160067
Caliche24301440210012451632001900-25
Chalk4060241021701285503050181033
Charcoal1030610
Cinders1280760960570331420840-10
Clay
 – Dry
 – Damp

3220
3350

1910
1985

2150
2010

1275
1180

50
67

3570
3720

2120
2205

-10
-10
Conglomerate372022052800166033
Decomposed rock
 – 75%R. 25%E.
 – 50%R. 50%E.
 – 25%R. 75%E.

4120
3750
3380

2445
2225
2005

3140
2710
2370

1865
1610
1405

31
38
43

3680
4000
3720

2185
2375
2205

12
-6
-9
Diorite5220309531301855673650216543
Diotomaceous earth147087091054062
Dolomite4870289029101725673400201543
Earth, loam
 – Dry
 – Damp
 – Wet, mud

3030
3370
2940

1795
2000
1745

2070
2360
2940

1230
1400
1745

50
43
0

3520
3520
3520

2090
2090
2090

-12
-4
-20
Feldspar4410261526401565673080182543
Gabbro5220309531301855673650216543
Gneiss4550270027201615673180188543
Gravel (Dry)
 – Uniformly Graded
 – Avg. Gradation
 – Well Graded

2980
3280
3680

1770
1945
2180

2700
2730
2770

1600
1620
1645

10
20
33

3150
3570
4130

1870
2120
2450

-5
-8
-11
Gravel (Wet)
 – Uniformly Graded
 – Avg. Gradation
 – Well Graded

3310
3640
4090

1965
2160
2425

3150
3290
3520

1870
1950
2090

5
10
16

3150
3570
4130

1870
2120
2450

-5
-2
-1
Granite4540269526401565723170188043
Gumbo
 – Dry
 – Wet

3230
3350

1915
1985

2150
2020

1275
1200

50
67

3570
3720

2120
2205

-10
-10
Gypsum408024202380141072
Igneous rocks4710279528201675673300196043
Kaolinite
 – Dry
 – Wet

3230
3350

1915
1985

2150
2010

1275
1190

50
67






Limestone4380260026901595633220191036
Loess
 – Dry
 – Wet

3220
3350

1910
1985

2150
2010

1275
1190

50
67

3570
3720

2120
2205

-10
-10
Marble4520268027001600673160187543
Marl3740222022401330672620155543
Masonry, rubble3920232523501395672750163043
Mica486028852910172567
Pavement
 – Asphalt
 – Brick
 – Concrete
 – Macadam

3240
4050
3960
2840

1920
2400
2350
1685

1940
2430
2370
1700

1150
1440
1405
1010

50
67
67
67

3240
2840
2770
2840

1920
1685
1645
1685

0
43
43
0
Peat118070089053033
Pumice108064065038567
Quartz4360258526101550673000178043
Quartzite4520268027101610673160187543
Rhyolite4050240024201435672870170043
Riprap rock4500267026101550723150187043
Sand
 – Dry
 – Wet

2880
3090

1710
1915

2590
3230

1535
1835

11
5

3240
3460

1920
2050

-11
-11
Sandstone4070241525201495613030179534
Schist4530268527101610673170188043
Shale4450264024801470792990177549
Silt32401920238014103638902310-17
Siltstone40702415252014956145602705-11
Slate4500267026001540773150187043
Talc4640275027801650673250193043
Topsoil2430144016209605632801945-26
Tuff4050240027001600503050181033
Footnotes:
  1. Subject to average ±5% variation.
  2. Mass densities are subject to adjustments in accordance with modified swell and shrinkage factors.
  3. Based on average in-situ densities. A negative number represents a shrinkage. Factors subject to ±33% variation.

Roadway excavation is typically measured in the original, undisturbed position. The specifications must clearly state the place and method of measurement because almost all materials change volume in their movement from cut to fill.

Excavated common material will expand beyond its original volume in the transporting vehicle but will typically shrink below the excavated volume when compacted into the fill. To illustrate, 1 cuyd [1 m3] of earth in the cut may use 1.25 cuyd [1.25 m3] of space in the transporting vehicle, and finally occupy only 0.65 to 0.85 cuyd [0.65 to 0.85 m3] in the embankment. This, of course, depends on its original density and the compactive effort applied. This difference between the original volume in a cut and the final volume in a fill is the shrink.

Excavated solid rock placed in a fill typically occupies a larger volume. This change in volume is the swell. When the voids in the rock embankment become filled with earth or other fine material, the volume in the fill will just about equal the combined volumes in the two source locations.

For light soil excavation and for fills constructed on swampy ground subject to settlement, the shrink may range from 20 to 40 percent or even greater. For moderate soil excavation, the shrink ranges from ten to 25 percent. For heavy soil excavation with deep cuts and fills, expect a range of approximately 15 percent shrink to five percent swell. Shrink generally includes the slight waste in transporting material from cut to fill and the loss for material that escapes beyond the toe of slopes. Embankments that are slightly overbuilt also contribute to an apparent shrink.

The underlying soil below embankments may also settle and compact, or be displaced, due to placement and compaction of the embankment, contributing to an apparent shrink. Settlement results in apparent shrinkage, but one is not directly proportional to the other. Do not confuse shrink with subsidence. Subsidence is settlement of the entire embankment due to weak foundation conditions (e.g., placing heavy fill on swampy soil).

A swell of 5 to 25 percent is often anticipated in rock excavation depending upon the proportion of solid rock and upon the size of the rock placed in the fill. Rock blasting, especially cushion blasting, is inexact and may result in slightly over-excavated slopes, contributing to an apparent swell.

When available, the design should consider actual field shrink and swell factors for like material used on adjoining projects.

Balancing Earthwork

It frequently happens that the material from the adjacent cuts is not sufficient to make the intervening fill. In this case, material is borrowed from outside the construction limits.

When there is an excess of excavated material, it may be necessary to dispose of the material. Instead of long hauls, it may be more economical to dispose of the material by widening shoulders or placing the material in disposal areas than to pay hauling costs.

If the earthwork is not in balance, the designer should try to adjust grade line or centerline so it is in balance. When a balanced project is not practical or desirable, the designer either disposes of excess material or borrows material to obtain a balance. Designated disposal or borrow areas require clearance for proper ownership, rights-of-use, environmental concerns and applicable permits.

Waste areas for the disposal of excess material and/or borrow areas should be shown on the plans.

Haul

Haul consists of transporting material from its original position to its final location. The cost to haul material is required to estimate the unit price of various items of work.

Haul costs are based on hauling one cubic yard [cubic meter] of material a distance of 1 mile [1 km] or 1 ton [1 metric ton] of material a distance of 1 mile [1 km] using the shortest practical route. Haul costs are generally based on a rate per unit of time for the hauling equipment multiplied by the actual time needed to move the material. This is quite simple when calculating costs to haul from crusher sites to the middle of a project. It is more complicated to estimate the costs to haul material between balance points on a grading project. The use of a mass diagram as described below will provide the quantity of haul within balance points as well as other helpful information. The haul cost will be much greater for haul in the uphill direction than in the downhill direction.

Updated: Monday, March 28, 2022