Reference no: EM13859826

OBJECTIVE

The objective of this experiment is to determine appropriate values of E'o and cv to calculate the magnitude and timescale of soil settlement and heave below the office block and the car park described in example problem Q1 (note that Q1 in this booklet differs slightly but significantly from Q1 in SMCA). An oedometer test must be carried out which replicates as far as possible the typical stress changes expected to occur in the field. (Hint: the initial and final values of vertical effective stress calculated in Q1 define the appropriate stress ranges which must be included in the oedometer test). It is up to you to determine the stress increments for the oedometer test. You must do this, and have your proposals ready to be checked by the demonstrator when you come to the laboratory for the practical session.
The following notes describe the general experimental procedure and the determination of E'o and cv from the data you will obtain.

Q1. An office block with an adjacent underground car park is to be built at a site where a 6m-thick layer of saturated clay (γ = 20 kN/m3) is overlain by 4m of sands and gravels (γ = 18 kN/m3) and underlain by permeable fractured bedrock. The water table is at the top of the clay layer, and pore water pressures are hydrostatic below this depth. The foundation for the office block will exert a uniform surcharge of 75 kPa at the surface of the sands and gravels. The foundation for the car park will exert a surcharge of 30 kPa at the surface of the clay, following removal by excavation of the sands and gravels. Calculate the initial and final vertical total stress, pore water pressure and vertical effective stress, at the mid-depth of the clay layer, (a) beneath the office block; and (b) beneath the car park. Take the unit weight of water as 9.81kN/m3.

Initially σv = 132 kPa; u = 29.4 kPa; σ'v = 102.6 kPa. Finally beneath the office block σv = 212 kPa; u = 29.4 kPa; σ'v = 177.6 kPa. Finally beneath the car park σv = 90 kPa; u = 29.4 kPa; σ'v = 60.6 kPa