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Principles of Geotechnical Enginee...

9th Edition
Braja M. Das + 1 other
ISBN: 9781305970939

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BuyFindarrow_forward

Principles of Geotechnical Enginee...

9th Edition
Braja M. Das + 1 other
ISBN: 9781305970939
Textbook Problem

Refer to the 15-ft high embankment shown in Figure 3.8. Embankments are generally constructed in several lifts or layers that are compacted according to geotechnical specifications. Each lift thickness is 3 ft and must have a dry unit weight of 118 lb/ft3. It is known that the soil at the borrow pit has a moist unit weight of 111 lb/ft3, moisture content of 23%, and Gs = 2.67. Perform the following tasks.

a. Determine the moist weight of borrow soil needed to construct the first lift (bottom layer) per ft of the embankment.

b. On the day of the construction, there was a heavy rain that caused the borrow pit to reach a near saturated condition. Recalculate the moist weight of the borrow soil needed to construct the first lift.

images

Figure 3.8

(a)

To determine

Calculate the moist weight of borrow soil needed to construct the first lift per ft of the embankment.

Explanation

Given information:

The height of the embankment (H) is 15 ft.

The width of the embankment (b) is 25 ft.

The thickness of each lift (t) is 3 ft.

The dry unit weight (γd) is 118lb/ft3.

The moist unit weight (γborrow) of borrow pit soil is 111lb/ft3.

The specific gravity of soil solids (Gs) is 2.67.

The moisture content of borrow pit soil (w) is 23%.

The relation between the plane is 1V:2H.

Calculation:

Calculate the dry unit weight of the borrow pit (γdborrow) soil using the relation.

γdborrow=γborrow1+w

Substitute 23% for w and 111lb/ft3 for γborrow.

γdborrow=1111+23100=1111.23=90.24lb/ft3

Calculate the volume of the first lift as shown below.

V1=bt+2×12t×2t=bt+2t2

Substitute 25 ft for b and 3 ft for t.

Volume=25×3+2×32=93ft3/ft

Calculate the volume of borrow soils using the relation

(b)

To determine

Calculate the moist weight of borrow soil needed to construct the first lift after heavy rain.

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