Civil Engineering PE Shallow and Deep Foundations 5

Question 1

A drilled shaft is constructed in a deep clay layer. The alpha (α) method is used to estimate skin friction. If Su = 1,200 psf and α = 0.55, the unit skin friction is:

Accepted Answer

660 psf

Answer

720 psf

Answer

540 psf

Answer

840 psf

Question 2

The primary advantage of a belled (underreamed) drilled shaft over a straight-shaft drilled pier is:

Accepted Answer

Significantly increased tip bearing area, which increases end-bearing capacity without increasing shaft diameter

Answer

Reduced installation cost due to shorter length

Answer

Better performance in liquefiable soils

Answer

Elimination of casing requirements in cohesionless soils

Question 3

A 20-ft × 20-ft raft foundation on soft clay settles 2 inches at the center. To reduce this settlement by 50%, an engineer could:

Accepted Answer

Replace 6 ft of soil with compacted structural fill to reduce stress on the compressible layer

Answer

Increase the raft thickness by 50%

Answer

Add waterproofing membrane beneath the raft

Answer

Increase column spacing to redistribute load

Question 4

In the LRFD design of deep foundations per AASHTO, the resistance factor φ for compression in a driven pile with dynamic testing (signal matching) is approximately:

Accepted Answer

0.65

Answer

0.45

Answer

0.75

Answer

0.90

Question 5

The lateral capacity of a single pile in soft clay (short rigid pile) under horizontal load is governed by:

Accepted Answer

Passive resistance of the surrounding soil and the pile's structural moment capacity

Answer

Skin friction along the pile shaft only

Answer

The end bearing at the pile tip

Answer

Downdrag forces from consolidating clay

Question 6

For a pile group in clay, the block failure mode should be checked when:

Accepted Answer

Pile spacing is less than 3 pile diameters and the group acts as a single block

Answer

The pile cap is designed as a rigid plate

Answer

Individual piles are longer than 40 ft

Answer

The clay has an Su greater than 2,000 psf

Question 7

The tolerable differential settlement for a typical steel frame building with brick cladding, per standard practice, is approximately:

Accepted Answer

1/300 to 1/500 of the span

Answer

1/100 of the span

Answer

1/1000 of the span

Answer

Absolute settlement of 1 inch maximum