Foundation & Soil Analysis Flashcards

A soil sample has a liquid limit of 45 and a plastic limit of 20. What is the plasticity index?

Answer: 25

Plasticity index (PI) = Liquid Limit − Plastic Limit = 45 − 20 = 25.

Which field test is commonly used to estimate the in-situ undrained shear strength of cohesive soils?

Answer: Vane shear test

The field vane shear test directly measures undrained shear strength in soft to medium cohesive soils.

A mat (raft) foundation is most appropriate when:

Answer: Individual footings would cover more than half the building area

When individual footings would overlap or cover more than 50% of the plan area, a mat foundation is more economical and effective.

Which soil classification group under USCS is described as 'poorly graded gravel with little or no fines'?

Answer: GP

GP (Poorly Graded Gravel) has a wide range of particle sizes missing, resulting in a poor gradation curve.

During pile driving, a 'set' refers to:

Answer: Penetration per blow at final driving

Set is the permanent penetration of a pile per blow measured at final driving, used in pile driving formulas to estimate capacity.

What does a negative skin friction on a pile indicate?

Answer: Surrounding soil is settling and dragging the pile downward

Negative skin friction (downdrag) occurs when consolidating soil surrounding a pile settles, imposing additional downward load on the pile.

The allowable bearing capacity of a soil differs from ultimate bearing capacity in that it:

Answer: Includes a factor of safety and accounts for acceptable settlement

Allowable bearing capacity = ultimate bearing capacity divided by a factor of safety (typically 2–3), also considering tolerable settlement limits.