A layer of sand 9 m thick overlies a layer of clay 6 m thick. The water table is at a depth of m below NSL. Over a short period of time the water rises by 3 m. The effective vertical stress at A immediately after the rise of water table is:

Geotechnical engineering, also known as geotechnics, is the branch of civil engineering concerned with the engineering behavior of earth materials. It uses the principles of soil mechanics and rock mechanics for the solution of its respective engineering problems. (Source: Wikipedia)