Question

A clay layer in field is 3-m thick and is sandwiched between two sand layers (drained from top and bottom). The saturated stratum of clay is under a surcharge loading and underwent 90% primary consolidation in 75 days. The time required in minutes for a 30 mm thick undisturbed clay sample obtained from the field to undergo 90% consolidation in laboratory is most nearly equal to

Select one:

a. 28

b. 67.5

c. 100

d. 10

Answer 1

Question is related to Consolidation:

In this, Time Factor is the parameter which relates to the degree of consolidation and time required for that consolidation and is given as:

where,

is the time factor which solely depends upon the % consolidation which is 90% in the above question.

is the coefficient of consolidation which is the property of the soil, in the given question soil sample properties remains the same as undisturbed sampling is done.

d is the length of the drainage path,

for two-way drainage, d is half of the thickness of the soil.

for one-way drainage, d is equal to the thickness of the soil.

As the given soil is in two-way drainage, so

t is the time taken to achieve a certain % of consolidation (90% in the given question)

As in the given question % Consolidation is 90% for both the condition, equating ;

As the coefficient of consolidation is equal;

So the time required for 90% consolidation in minutes is most nearly equal to Option d. 10 minutes.