What is the difference between consolidated and unconsolidated soil

This process continues until the entire pressure is transferred to the soil grains. This process is known as consolidation and occurs in cohesive soils only. Pore water dissipation in granular soil is immediate. A clay soil is said to be normally consolidated if the effective overburden pressure that it is currently experiencing is the maximum it has ever experienced in its history. On the other hand, it is said to be overconsolidated if the present overburden pressure is less than the effective overburden pressure it has experienced in the past.

The overconsolidation ratio of a normally consolidated clay is unity, while the overconsolidation ratio of an overconsolidated soil is greater than unity. The nature of consolidation of a clay soil affects its behaviour in the field and when tested in the laboratory.

For instance, the natural moisture content of a normally consolidated clay is usually close to the liquid limit , while the natural moisture content of an overconsolidated clay is usually close to the plastic limit. Clay soils in their natural state have memory of the magnitude of the highest pressure they have experienced in the past. This memory is locked in the soil structure and can only be broken when the clay is remoulded or reconstituted at a moisture content that is equal to or greater than the liquid limit.

The stress-strain curve of an overconsolidated clay is likely to exhibit more elastic behaviour when compared with the stress-strain curve of a normally consolidated clay.

Since a normally consolidated clay is experiencing the maximum pressure of its history, it is more likely to get compressed without recovery plastic recovery when subjected to additional external pressure in their natural state. This is not the same for overconsolidated soils which will exhibit elastic behaviour whenever an external pressure that is less than what they have experienced in the past is placed and removed. Preconsolidation pressure can be determined from the field or in the laboratory from the e-log P curve plot void ratio against log of pressure after carrying out a consolidation test in the laboratory.

The most widely used method was proposed by Casagrande in the year see Figure below. This stress is identified in comparison with the effective stress in its present state. For soil at state Q or F, this would correspond to the effective stress at point P. If the current effective stress, s ' , is equal note that it cannot be greater than to the preconsolidation stress, then the deposit is said to be normally consolidated NC.

If the current effective stress is less than the preconsolidation stress, then the soil is said to be over-consolidated OC. It may be seen that for the same increase in effective stress, the change in void ratio is much less for an overconsolidated soil from e 0 to e f , than it would have been for a normally consolidated soil as in path OP.

In unloading, the soil swells but the increase in volume is much less than the initial decrease in volume for the same stress difference. Home Improvement. Connect with:. Username or Email Address. Remember Me. What is the difference between consolidated and unconsolidated sediments? April 26, consolidated sediments unconsolidated.