Example Final

Example Final 2015 Soil Mechanics
Problem 1
A large fill is put on a compressible 7.5-m layer of clay. The average total stress increase on the clay layer is 30
kPa. The ground water table is at the surface. The consolidation behavior of the clay is: Preconsolidation
pressure, p = 74 kPa, recompression index (Cr) = 0.1, Compression index (Cc) = 0.4). The void ratio and water
content of the clay are 1.3 and 48%. Determine the ultimate settlement due to the fill.
Problem 2
A simple shear test is performed on a sandy soil. The applied vertical stress is 70 kPa. The lateral stress is 35
kPa. At failure, the shear stress is 45 kPa.
1. Determine the principal stresses at failure
2. Determine the strength parameter of the sandy soil
3. Is this a real soil based on the strength parameter of sandy soil
4. Determine the tangential load at fail if a direct shear test is carried out on the same soil with a normal
load of 200 N
Problem 3
At a planned construction site, a 2-m thick buried clay layer lies beneath a surficial stratum of free draining
granular soil. Free-draining soil also underlies the clay layer. Double drainage from the clay layer can
therefore occur when construction load cause consolidation. The coefficient of consolidation for the clay is
0.001 m2/day. Settlement calculations indicate that the clay will eventually compress 4 cm due to the effect of
building loads.
The relationship between degree of consolidation, U, and dimensionless time factor, T, is
U < 60%, T = 0.25**(U/100)2, for U  60%, T = 1.781 – 0.9333log(100 - U)
Require:
1. Estimate the theoretical time period for the 4 cm settlement to be completed?
2. Estimate the settlement after 12 months?
3. If the bottom drainage does not exist, estimate the settlement after 12 months.
Problem 4.
A soil sample taken from a borrow pit has a natural void ratio of 1.15. The soil will be used for a highway
project where a total of 100,000 m3 of soil is needed in tis compacted state; its compacted void ratio is 0.73.
How much volume has to be excavated from the borrow pit to meet the job requirement.
Problem 5.
A 592-cm3 volume of moist sand weights 1090 g. Its dry weight is 920 g and the density of solid is 2680 kg/m3.
Compute the void ratio, water content, degree of saturation, and dry density.
Problem 6
Given the flow net shown below, determine the water pressure at point A. The elevation of A from the Datum is
6 m.
A