Question

a) Describe briefly how the coefficient of consolidation (Cv) value can also be estimated based on a fullscale loading trial. Explain why it is more reliable to use the Cv value obtained from a field trial than from a lab test.

b) Based on a quick search on the internet, briefly describe the principles of a piezometer and suggest how it can be used in the field to measure and monitor groundwater pressure.

c) Suggest briefly two practical uses of the continuous monitoring of pore water pressure using piezometers following the completion of filling.

Answer 1

a) It is more reliable to use the Cv value obtained from a field trial than from a lab test because:

1. due to sampling disturbances Cv values get affected

2. it depends on the specimen size and method of test adopted

3. it also depends on the load- increment ratio taken and duration for which loading is applied

Due to these reasons the settlements obtained in field using Cv values calculated from laboratory observations differs much than actual.

b) piezometer works on the principle of height of liquid column raised against gravity in a tube and the height of raised liquid column corresponds to the pressure exerted by the fluid at the point where the piezometer is installed.

Piezometer can be installed in the ground to measure the ground water pressure at a particular depth by measuring the height of water column raised above that point. That height of water column gives the ground water pressure at that point and that height can be monitored continuously depending on the purpose.

c) 1. It gives an estimation about the extent of consolidation reached.

2. It gives an estimation about how the pore water pressure is getting dissipated.