Question.
A 6 m thick layer of clay is located between 4 m and 10 m depth. Coarse sand lies over and under the clay. The water table is I m below the ground surface. A pore water pressure transducer is buried at the centre of the clay layer.
A laboratory consolidation test was conducted on a 25 mm thick sample from the centre of this clay layer, which is believed to be representative of the whole layer. In this test, the vertical effective stress was increased from the in situ value by Δσ'v = 120 kPa. In this loading increment, the permeability k was found to be 5 x 10-10 m/s, and the void ratio e reduced from 0.9 to 0.75.
(a) What is the value of E'oed for this increment, and what is the value of the coefficient of consolidation cv?
At time t = to, a surface load is placed over a very wide area at the site, which produces a total stress increase Δσv = 120 kPa.
(b) What is the reading in the pore pressure transducer immediately before to and immediately after to?
(c) How long before 60% of the final settlement will have occurred?
(d) What is the pore pressure transducer reading (at the centre of the clay layer) at this stage?
