Application to Civil Engineering practice: The profile $($cross section$)$ on the following page is

part of a slurry wall excavation made during the construction of the $2$nd Avenue Subway line in New York City. The stratigraphy $($soil layering$)$ and some laboratory data for each layer are given. All soils are inorganic.Soil profile with proposed slurry wall excavation shown. The excavation is $1,000ft$ long into the plane of the paper. $200$darr

Given information for Layer $1$:

A sample of natural soil was taken from the field, which had a total volume in the field of

$1\mathrm{.}24f{t}^3$ and a total weight of $143\mathrm{.}90lb.$ The sample was placed in the oven and the dry

weight was found to be $119\mathrm{.}90lb.G_s=2\mathrm{.}70.$

a$.$ For Layer $1,$ determine e$,{}_t,{}_d,$ and $w.(20$ pts$)$

b$.$ The contractor needs to haul the excavated soil

to a disposal facility several miles away. Trucks

with two rear axles $($called a "tandem" for short $-$

see picture at right$)$ will be used. These can hold

$12$ cubic yards of soil that is placed in the bed

using the clamshell bucket used for slurry trench

excavation.

A big question faced by the contractor at the

time of estimating the project's price is: How

many truckloads will it take to remove the excavated soll trom the s$$te$?$ vvnile we coula

complete this calculation using weight$-$volume relationships directly, it is common in

CIVE $2340-$ Geotechnical Engineering

construction practice to use a Swell Factor. The swell factor is greater than $1\mathrm{.}0$ and is

calculated as follows:

Swell Factor $=\frac{\text{L}\text{o}\text{o}\text{s}\text{e}\text{V}\text{o}\text{l}\text{u}\text{m}\text{e}}{\text{B}\text{a}\text{n}\text{k}\text{V}\text{o}\text{l}\text{u}\text{m}\text{e}}$

A soil's swell factor reflects the reality that the same amount of soil occupies more

volume in the truck $($loose volume$)$ than it does in the ground when undisturbed, before

excavating $("$bank$"$ volume$).$ "Swell" in this case, is a layman's term for the increase in

volume caused by the excavation of soil. Physically, the act of excavation breaks up the

soil into assemblages of various sizes $($clods$).$ This creates more air pockets and results

in an effective increase in the soil's void volume. An increase in volume results in a

corresponding decrease in unit weight. The amount of change varies for soils with

different classifications.

Assume that your company's laboratory conducted some field tests to determine the

swell factor by excavating the in$-$place soil of known unit weight $($from part $($a$))$ with the

slurry trench clamshell and then placing the loose soil in containers of known volume

that are subsequently weighed on a large scale. The average total unit weight of

excavated moist soil over all trials for Layer $1$ is $94$ pcf$.$

What is the swell factor $($expressed as a decimal$)?(6$ pts$)$

How many truckloads will it take to remove all of the excavated soil? $(6$ pts$)$

What does a full truckload of Layer $1$ soil weigh? $(5pts)$