Test: Soil Mechanics- 3 - Civil Engineering (CE) MCQ

Permeability (k) =
· More will be the representative grain size, more will be the permeability of the soil.

· Higher is the degree of saturation Higher is the permeability of the medium as lesser is the resistance available to the flow of fluid in the form of air blocks

· More will be the unit weight of fluid, more will be permeability of the medium

· Higher is the presence of entrapped gases, lower is the permeability of the medium as higher is the resistance available to the flow of the fluid.

The rise in water level in the pond causes equal increase in total stress and pore pressure so effective stress does not change. The pore pressure will increase by 20 kN/m².

Above the water table pore pressure will be negative

Pore pressure at 1.5 m above the WT

= - γ_wz = - 10 × 1.5 = -15 kN/m².

Darcy established that the flow occurring per unit time is directly proportional to the head causing flow and the area of cross – section of the soil sample but is inversely proportional to the length of the soil sample

Dividing both sides by A

i.e., hydraulic gradient

Total stress at C = γ_wh + γ_satZ

Pore pressure at C = γ_w(h + z)

Effective stress = (γ_sat - γ_w)Z = γ_subZ

Concept:

Critical hydraulic Gradient, i_cr 
Factor of safety (F.O.S) = Calculation:

Height of Capillary rise = 

Height of Capillary rise given by Hazen:

C = 0.435 cm²

Correct Answer :- b

Explanation : Pore water pressure, µ = γw. h.

µP = γw × 1.5 m

µR = γw × (2.5 + 0.1) = γw × 2.6

Effective stress, σ = σ – U

at Q = γsat. h – UQ.

= 18 × 2 – 2.05 × 9.81 = 15. 89 kPa

γ’ = γ_sat - γ_w

γ_sat = γ’ + γ_w = 9.5 + 10 = 19.5 kN/m³

σ’ = σ - u

At at depth of 15 m below lake

σ = γ_w × 10 + γ_sat × 15

σ = 10 × 10 + 19.5 × 15

σ = 392.5 kw/m²

u = 25 × γ_w = 25 × 10 = 250 kN/m²

= σ - 4

= 392.5 - 250

= 142.5 kN/m²

Since the river bed level does not change and the depth of water is changing only above the river bed, the effective stress below the river bed will not change.

Total stress at a depth of 10 m below river bed.

σ = 20 × 10 = 200 kN/m²

Pore water pressure,

u = 10 × 10 = 100 kN/m²

∴ Effective stress,

= 100 kN/m²

Thus effective stress will be 100 kN/m² each on the month of February, July and December.