Civil Engineering PE Geotechnical Engineering and Slope Stability 1

Question 1

The factor of safety for slope stability is defined as the ratio of:

Accepted Answer

Resisting forces to driving forces

Answer

Driving forces to resisting forces

Answer

Cohesion to friction angle

Answer

Normal stress to shear stress

Question 2

For a soil with friction angle φ = 30°, Rankine's active earth pressure coefficient Ka equals:

Accepted Answer

0.33

Answer

0.50

Answer

0.25

Answer

3.00

Question 3

Bishop's simplified method of slices assumes that:

Accepted Answer

Interslice shear forces are zero

Answer

All interslice forces are zero

Answer

The failure surface is planar

Answer

Pore water pressure is negligible

Question 4

Jaky's formula for the coefficient of earth pressure at rest (K₀) for a normally consolidated soil is:

Accepted Answer

K₀ = 1 − sin φ

Answer

K₀ = 1 + sin φ

Answer

K₀ = tan²(45° − φ/2)

Answer

K₀ = tan²(45° + φ/2)

Question 5

For a cohesionless infinite slope under drained conditions, the factor of safety simplifies to:

Accepted Answer

FS = tan φ′/tan β

Answer

FS = c′/(γz sin β cos β)

Answer

FS = γz cos²β tan φ′/c′

Answer

FS = sin β/(cos β tan φ′)

Question 6

Tension cracks at the crest of a cohesive slope reduce stability primarily because they:

Accepted Answer

Can fill with water, adding a hydrostatic driving force

Answer

Increase cohesion along the failure surface

Answer

Reduce the weight of the sliding mass

Answer

Increase the effective normal stress on the failure plane