Question

a) Why is consolidation settlement inherently a nonlinear process? b) Name two ways we can increase the rate of consolidation, and explain why they work. c) You are running a consolidation test and your lab group member accidentally clogged the drainage on one side of the sample you are testing. How will this affect the measured settlement? d) Why do some soils expand when sheared, while others contract when sheared?

Answer 1

A.) consolidation settlement is a non linear process as it is not dependent on one parameter of soil. it depends on stress history, soil properties, drainage condition etc. thus its a non linear process.

B.) we can increase the rate of consolidation by the two ways given below

1.) by decreasing the length of drainage parth such as by providing permeable apron at top and bottom. this would decrease length of drainage path, as time factor is inversely proportional to length of drainage path rate of consolidation is enhanced.

2.) providing vertical sand drains- this enhances the permeability in horizontal direction thus rate of consolidation increases.

C.) due to clogging of drainage on one side length of drainage path would get doubled and time factor becomes 1/4th so the corresponding measured settlement has to be corrected accordingly with the help of corrected degree of consolidation. actual settlement would be less than the measured one.

D.) Some soils such as dense sand, overconsolidated clay expands when sheared because in dense sand the particles are in stage of interlocking and they do not have freedom to move around, when sheared due to lever motion bulk expansion of the material takes place similarly in overconsolidated clay cohesion is there which hinders the movement for compaction. while other soils such as loose sand, normally consolidated clay expands on shearing as normally consolidated clay does not have significant cohesion and in loose sand interlocking of particles is not there.