Geotechnical & Foundation Engineering

1. A Soil sample has the following properties:

Dry density of soil ( γd) = 18kN/m3

Porosity (n) = 25%

Find the value of water content when the sample is 65% saturated

(A) 0.90

(B) 0.09

(C) 0.78

(D) 0.078

Answer: (A)

Sol. Given, γd = 18 kN/m3

n = 0.25, S = 0.65

To find water content- Put the value of e and Gs

in equation (1)

2. 225g of oven-dried soil sample is placed in a pycnometer. Now the pycnometer is completely filled with water. If the total mass of pycnometer with sample and water is 1800g and the mass of pycnometer filled with water alone is 1660g. determine the specific gravity of soil sample. 

(A) 2.65g 

(B) 2.67g 

(C) 2.70g 

(D) 2.45g 

Answer: (A) 

Sol. Given:- 

Mass of dry sample (M_d) = 225g

Total mass of pycnometer with Soil and water (M₃) = 1800g

Mass of pycnometer with water alone (M₄) = 1660g

Now, 3. A clay sample has 35% particles finer than 0.002mm the soil sample has Wl= 92% 

wp = 30% 

ws = 21.2% 

Indicate the probable type of clay mineral presents in the sample (take G s = 2.7)

(A) Kaolinite 

(B) Illite 

(C) Montmorillonite 

(D) Data is insufficient 

Answer: (C) 

Sol. Activity (Ac)

Given: wl = 92%; wp = 30%; % finer than 2µ = 35% Hence,

We know that, for montmorillonite activity varies between 1-7. hence option (C) is correct

4. Find the ratio of permeability of soil strata (shown in the diagram in the vertical direction to the horizontal direction

Answer: (0.9) [0.9-0.9]

Sol. Equivalent permeability in the horizontal direction (KH)

equivalent permeability in the vertical direction (Kv)

5. A soil specimen of thickness 10m has water table at the ground surface. If the watertable is lowered by drainage to a depth of 2m. What will be the change in effective stress will occur at a point (x) below the depth of 3m. Assume that the soil above water table remains saturated due to capillary action, (take G = 2.7, e = 0.65) Answer: (C)

Sol. Given; G = 2.7, e = 0.65 Effective stress at point x before water table get lowered = (19.92-9.81) × 3 = 30.33 kN/m2
effective stress at point x after water table get lowered = (19.92 × 3 – 9.81 × 1) = 49.95
Change in effective stress= 49.95 – 30.33
= 19.62 kN/m2
Hence the correct option is ‘C’