MODULE 2

Question 1

effective stress (saturated soil)

Answer 1

σ’ = σ - u(w)

- as pore water pressure increases, friction between grains decreases and thus soil strength decreases

Question 2

effective stress (unsaturated soil)

Answer 2

effective stress = net stress + suction
σ’ = (σ - u(a)) + X(u(a) - u(w))
- suction creates a temporary bonding between grains that is lost when soil becomes saturated => X depends on the degree of saturation ( 0 if dry, 1 if saturated)

Question 3

Principle of Effective Stress

Answer 3

” All measurable effects of change in stress, such as compression, distortion and a change in the shearing resistance are due exclusively to changes in effective stress…” Terzaghi
- NOTE: only valid for fully saturated soils

Question 4

Pore Water Pressure

Answer 4

u = U / A(w)
where U = reaction of water
A(w) = pore water area

Question 5

homogenous soil

Answer 5

γ = constant

Question 6

saturated soil

Answer 6

GL = WL

Question 7

partially saturated soil

Answer 7

WL below GL

Question 8

decrease in water table

Answer 8

σ(v) = no change ; u decreases ; σ(v)’ increases

Question 9

effect of a river

Answer 9

σ(v) increases ; u increases ; σ(v)’ no change

Question 10

effect of embankment or load on ground surface

Answer 10

σ(v) increases ; u = no change ; σ(v)’ increases

Question 11

negative pore water pressure

Answer 11

suction stresses