A layer of normally consolidated clay has been filled with 2m of gravel at a unit weight of 17kN/m3 for a long period of time and the settlement of the clay layer monitored giving a total final settlement of 330mm.
Drilling, sampling and testing is now undertaken to back figure some properties of the clay. Testing reveals that the clay layer is currently 1960mm thick and has the water table at a depth of 0.4m below the top of the clay layer.
A sample from the mid-depth of the clay layer has a moisture content of 36% and a total unit weight of 17.4kN/m3.
Determine the compression index of the clay. It can be assumed that the water table stays at the same level throughout.