Test: Soil Mechanics - Civil Engineering (CE) MCQ

Assumptions made in Boussinesq’s Theory are:

1. Soil is homogeneous, semi-infinite, elastic and isotropic.

2. Hooke’s law is valid.

3. Any change in the volume of soil due to application of load is neglected.

4. Distribution of stresses along the vertical axis is symmetrical.

5. Self-weight of soil is neglected.

Terzaghi in 1922 demonstrated a model (Spring-piston model) to study the mechanism of consolidation in clay. The model consists of a cylindrical vessel with the series of pistons separated by springs. The space between the springs is filled with water and the pistons are perforated so as to allow through communication to water. Piezometers are inserted at the centres of each of the compartments to measure the pressure heads due to excess pore water pressures. The springs surrounded by water represent the saturated soil. The springs represents the soil skeleton and the water in the vessel represents the water filling the voids in the soil.

The value of Allowable Bearing Pressure on soil depends on the nature of ground and the type of building. The maximum safe bearing capacity of soil is generally more than the allowable bearing pressure on soil.

C_u = 16

C_c = 1

16=Cu

D₆₀ = 16 D₁₀

In first stage (application of cell pressure stage) soil will consolidate because drainage valve is open and pore water is drain out of soil leads to consolidation, In second stage (Shearing stage) drainage valves are closed leads to development of excess pore water pressure, this implies first stage is consolidated(C) and second stage is undrained(U). So the test is CU test.

Where S_s = specific surface area = 

Where d = grain size

So, permeability is directly proportional to the square of grain size.

e = 0.68

Volume of soil = 1m³

0.67 V_S = 1 – V_S

1.67 V_S = 1

V_V = V – V_S = 1 – 0.598 = 0.402 m³

Initially we assume that soil is completely dry

V_V = V_water required to fully saturate the soil mass

V_water = 0.402 × 1000 = 402 litres

Fineness modulus of sand:

1. Fine sand: 2.2 to 2.6

2. Medium sand: 2.6 to 2.9

3. Coarse sand: 2.9 to 3.2

So, Fineness modulus 3 corresponds to coarse sand.

corresponding change in the water content of the soil above shrinkage limit.

are percentage change of volume from liquid limit to dry state and plastic limit to dry state respectively

W1 and W2 are corresponding water content

In Vane shear test, the vane is pushed in to the soil and torque is applied manually which is measured by a calibrated torsional spring. The rate of rotation of vane is nearly 6^o per minute or 0.1^o per second.

Specific Surface area is inversely proportional to grain size. Out of sand, silt, clay and colloids, Sand has highest grain size while colloids have least grain size.

Assumptions given by Rankine are:

1. The soil is homogeneous and isotropic, which means c, φ and γ have the same values everywhere, and they have the same values in all directions at every point.

2. The most critical shear surface is a plane.

3. The ground surface is a plane.

4. The wall is infinitely long so that the problem may be analysed in only two dimensions.

5. The wall moves sufficiently to develop the active or passive condition.

6. The wall surface at the back is vertical and smooth.

Se = ωG

1 = ωG

Discharge through the open well is in the range of (3-6) litres/sec while discharge through the tube well is in the range of (200 - 220) l/sec. So the approximate ratio is 50.

The pile provided with one or more bulbs in the vertical shaft is known as under reamed pile. This kind of pile is provided in case of expansive soil like black cotton soil.

The angle of inclination of the plane at which the body begins to move down the plane, is called angle of repose.

Depth at which the earth pressure become zero in case of cohesive soil is given by expression,

So the depth of unsupported vertical cut is,

Shearstrength,τ=C+σtanϕ

Where C = Cohesion

σ = Nomal stress

ϕ = Angle of internal friction.

So all the above options are correct. Shear strength will increase with increase in cohesion, angle of internal friction and normal stress on soil.