ASCE Geotechnical and Foundation Engineering 2

Question 1

A clay has a natural water content of 35%, liquid limit of 45%, and plastic limit of 25%. What is its liquidity index?

Accepted Answer

0.50

Answer

LI = (w - PL)/PI = (35 - 25)/(45 - 25) = 0.50.

Question 2

The activity of a clay soil is defined as which ratio?

Accepted Answer

Plasticity index divided by percent clay-size fraction finer than 2 µm

Answer

Skempton's activity A = PI / (% finer than 2 µm) indicates clay mineral swelling potential.

Question 3

Under USCS, a soil with 70% passing the No. 200 sieve, LL = 62, and Atterberg limits plotting above the A-line is classified as:

Accepted Answer

CH

Answer

Fine-grained soil with LL ≥ 50 plotting above the A-line is a high-plasticity clay, CH.

Question 4

The overconsolidation ratio (OCR) of a clay is defined as:

Accepted Answer

Preconsolidation pressure divided by current effective vertical stress

Answer

OCR = σ'p / σ'v0, so normally consolidated clay has OCR = 1.

Question 5

Secondary compression of a clay layer is best described as settlement that:

Accepted Answer

Continues after excess pore pressure has essentially dissipated, due to creep of the soil skeleton

Answer

Secondary compression, governed by Cα, is creep that follows primary consolidation.

ASCE - American Society of Civil Engineers Certification Practice Test