Question

Direction : The following items consists of two statements; one labelled as 'Assertion (A)' and the other as 'Reason (R)'. You are to examine these two statements carefully and select the answers to these items using the codes given below:

Codes :

Assertion (A) : Pile driving formulae have very limited use in the case of cohesive soils.

Reason (R) : Pile driving in cohesive soils results in liquefaction of clays.

• A. both A and R are true and R is the correct explanation of A
• B. both A and R are true but R is not a correct explanation of A
• C. A is true but R is false
• D. A is false but R is true

Answer 1

The correct option is C A is true but R is false

In general, the dynamic pile driving formulae appear to be more appropriate to piles driven in cohesionless soils. If the pile is driven into saturated loose silt and sand, liquefaction might reduce the pile capacity. Dynamic pile driving formulae are not considered to be applicable to piles driven into cohesive soils. This is because there may be apparent increase in driving resistance due to developement of pore pressures, while there may be a tendency for it to decrease later due to dissipation of pore pressure. Pile driving in cohesive soil distrubs the soil structure and consequently the resistance tends to decrease due to remoulding in sensitive clays although there might be same regaining of strength with passage of time, due to thixotropy.