consolidation

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Primary and Secondary Consolidation
Settlement of saturated soils under increased loading consists of two successive phases, commonly referred to as the primary and secondary consolidation phases. The primary consolidation phase is dominated by pore pressure dissipation and effective stress increase; whereas, the secondary consolidation phase is dominated by creep (viscous deformation) at almost constant effective stress. The consolidation settlement consists of two parts. In conventional soil mechanics, Terzaghi’s theory of one dimensional consolidation is widely used despite some limitations.
In order to know the compressibility behavior of soil, we can make a plot of voids ratio versus log time using one dimensional consolidation tests as shown in figure 1.
Types of consolidation tests:
Conventional incremental loading test (Oedometer test)
Constant rate of strain test (CRS)
Calculation of settlement can be made as follows:
Total settlement (S)=C_c/((1+e_0)) log⁡〖(P_v0^'+∆P)/(P_v0^' )〗+C_α/((1+e_0)) log⁡〖t/t_p 〗
This equation assumes that the secondary consolidation settlement occurs after the dissipation of excess pore water pressure.
One of the most practical questions concerning consolidation is to know how to define the relevant consolidation curves for in situ conditions. The existence of creep during primary consolidation is evident, but there exist opposing opinions on the role of creep in the primary consolidation phase. Many researchers pointed out that, there are two extreme possibilities. Hypothesis A assumes that creep occurs only after the end of primary consolidation and consequently that the stress strain curve followed in situ is the same as the one obtained in the laboratory at the end of primary ...

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... the land reclamation. Finally, the consolidation process is not the only one controlling the rate of settlements in clay. Even when the excess pore water pressure has completely dissipated, the settlement continues, which is called creep or secondary compression. Towards the end of primary consolidation, a contribution of the secondary compression becomes more pronounced and may produce significant increases in settlements long after the primary consolidation is over.
It is important to remember that the consolidation process is not the only one controlling the rate of the settlements in clay. Even when the excess pore water pressure has completely dissipated, different physical phenomena cause continued settlement. While this secondary compression is present from the beginning of the consolidation process, towards the end of primary consolidation its contribution

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