Soil Mechanics and Geotechnical Engineering Review

A collection of questions and answers based on lecture notes for Soil Mechanics and Geotechnical Engineering.

What is the degree of consolidation directly proportional to?

Time

What happens to the ultimate strength of a loose sand sample and dense sand sample consolidated to the same effective stress?

Ultimate strength is the same but peak strength of dense is greater than that of loose sand.

What occurs within the consolidation process of a saturated clay?

A gradual increase in neutral pressure and a gradual decrease in effective pressure takes place, and the sum of the two is constant.

What is the valid range for S, the degree of saturation of soil in percentage?

0 ≤ S ≤ 100

What state is a soil mass in when its natural water content lies between its liquid limit and plastic limit?

Plastic state.

What is the average coefficient of permeability of natural deposits parallel to stratification?

Always greater than that perpendicular to stratification.

By how much does the rise of the water table in cohesionless soils reduce the net ultimate bearing capacity?

Approximately by 50%.

Which method is more suitable for determining the permeability of clayey soil?

Falling head method.

In Terzaghi's bearing capacity equation, what factors are functions of Nc, Nq, and D?

Cohesion and effective angle of shearing resistance.

If the water content of a fully saturated soil mass is 100%, what can be said about the voids ratio?

It is equal to the specific gravity of soil.

If the volume of voids equals the volume of solids in a soil mass, what are the respective values of porosity and voids ratio?

Porosity is 0.5, and voids ratio is 1.0.

Which unconfined compressive strength test is considered an undrained test?

Consolidated undrained test.

In which way does the effective stress act on normally consolidated clay?

Effective stress increases with depth but water content and undrained strength decrease with depth.

What happens at the liquid limit of soils?

Soils possess the same shear strength of small magnitude.

Which method is most accurate for determining the water content of soil?

Oven drying method.

In the tri-axial shear test, what is one advantage of it over direct shear?

It can be performed under all three drainage conditions with complete control.

What does Rankine's theory of earth pressure assume about the back of the wall?

It is vertical and smooth.

What is the effect of increasing compaction on optimum water content and maximum dry density?

Optimum water content increases but maximum dry density decreases.

What is defined as the angle that Coulomb's failure makes with the horizontal?

The angle of internal friction.

What is the compressibility of sandy soils compared to clayey soils?

Much less than that of clayey soils.

If the degree of saturation of a partially saturated soil is 60%, what is its air content?

40%.

What does effective stress depend on?

The stress at particle contact.

What is true when the plasticity index (PI) of a soil mass is zero?

The soil is considered non-plastic.

What happens when the water table rises above the ground surface?

Pore water pressure increases, which influences total stress.

What is a consequence of effective stress in soil mechanics?

It is a function of engineering properties of soil.

What is the relationship of shear strength of a soil to the angle of internal friction?

It is directly proportional to the angle of internal friction.

What happens to effective stress with the rise of the water table to ground surface?

It reduces due to the increase in pore water pressure.

What does the water content of soil represent at the boundary between plastic state and liquid state?

Liquid limit.

How is a fully saturated soil characterized?

As a two-phase system with soil and water.

What is the shape of the particle size distribution curve represented by?

Uniformity coefficient.

What characterizes a soil that has a volume of voids equal to the volume of solids?

It has a porosity of 0.5 and a voids ratio of 1.0.

What is a common trait of uniform soils compared to non-uniform soils?

Uniform soils have more strength and stability.