Question

Given below are two statements, one labelled as Assertion (A) and the other labelled as Reason (R).
Assertion (A): In case of soils, compressive normal stresses are taken as positive.
Reason (R): Most of the normal stresses acting on soils are compressive in nature.
In light of the above statements, choose the correct answer from the options given below.

• 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 the correct explanation of (A).
• C. (A) is true but (R) is false.
• D. (A) is false but (R) is true.

Hint:

Think about whether soil grains, unlike solid materials, can carry any tensile stress at all.

Answer 1

The Correct Option is A

Step 1: Evaluate Assertion (A): in soil mechanics, compressive normal stresses are indeed taken as positive, the opposite of the convention often used in general structural mechanics where tension is positive. So (A) is true.
Step 2: Evaluate Reason (R): soil is a particulate assembly of grains that cannot sustain meaningful tensile stress between particles, since the grains simply separate under tension rather than pulling against each other. Almost every stress state in soil, from self-weight, foundation loads or overburden, is compressive. So (R) is also true.
Step 3: Check whether (R) explains (A). Soil mechanics adopts the compressive-is-positive convention precisely because compressive stress is the dominant, practically relevant type of stress in soil, making it mathematically convenient to treat that common case as positive. So (R) correctly and directly explains (A).
Step 4: Since both are true and (R) is the correct explanation of (A), the answer is option 1.