In case of highly compressible saturated soft clay, imposition of load generates excess pore water pressure in soft layer. This excess pore water pressure is initially borne by water molecules existing within the soft layer. Initial excess pore pressure in the water is equal to the applied external pressure on the soil. Slowly and slowly, as water oozes out of pore space depending upon permeability of soil, excess pore water pressure dissipates and the load gets transferred to soil grains. With the passage of time, excess pore water pressure decreases and correspondingly, the effective stresses in the layer increases. After a very long time the excess hydrostatic pressure becomes zero and the entire consolidation pressure becomes an effective stress transmitted from grain to grain of the soil.
As a result, soft soil gets compressed and the consolidation process continues over a long period of time unless measures are taken for quick dissipation of excess pore water pressure. Throughout this process, the foundation of structure would settle until the complete consolidation takes place. By this time, irreparable damage to structure occurs.
Because of low permeability and poor drainage characteristics of soft soil, it becomes essential to drain out pore water before construction begins, otherwise the added weight of new structure will cause water to squeeze out for a long period of time. Moreover, due to high compressibility of these soils, the consolidation settlements are of a very high order and from structural safety point of view, it would be better if major portion of this consolidation settlement takes place before/during construction phase itself.
CONSOLIDATION METHODOLOGY
For constructing any structure, it is necessary to accelerate the process of consolidation. To achieve this, the following methods are generally adopted-
i) Preloading
ii) Stage Construction
iii) Vertical Sand Drains
iv) Prefabricated Vertical Drains
v) Vacuum Assisted Consolidation
The choice of method depends upon the importance of structure, applied loading, site conditions and time period available for construction etc. Therefore, it is important to select the appropriate method for a given situation.
As a result, soft soil gets compressed and the consolidation process continues over a long period of time unless measures are taken for quick dissipation of excess pore water pressure. Throughout this process, the foundation of structure would settle until the complete consolidation takes place. By this time, irreparable damage to structure occurs.
Because of low permeability and poor drainage characteristics of soft soil, it becomes essential to drain out pore water before construction begins, otherwise the added weight of new structure will cause water to squeeze out for a long period of time. Moreover, due to high compressibility of these soils, the consolidation settlements are of a very high order and from structural safety point of view, it would be better if major portion of this consolidation settlement takes place before/during construction phase itself.
CONSOLIDATION METHODOLOGY
For constructing any structure, it is necessary to accelerate the process of consolidation. To achieve this, the following methods are generally adopted-
i) Preloading
ii) Stage Construction
iii) Vertical Sand Drains
iv) Prefabricated Vertical Drains
v) Vacuum Assisted Consolidation
The choice of method depends upon the importance of structure, applied loading, site conditions and time period available for construction etc. Therefore, it is important to select the appropriate method for a given situation.
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