EXPERIMENTAL STUDY ON THE EFFECT OF NANO SILICA PARTICLES ON CREEP BEHAVIOR OF SOFT CLAY SOIL

The compressibility behavior of clay soil has been a major concern in geotechnical engineering. When clay is subjected to a load, effective stress increases with time as a result of dissipation of induced excess pore water pressure, which is known as primary consolidation. After the complete dissipation of the excess pore water pressure, if the load is continuously maintained on the clay, further deformation can be observed over a long period of time, which is known as the secondary compression or creep. When buildings, embankments, and other structures are built on clay soils, large settlements can often be found. Especially, time-dependent deformation in structures built on soft soil may cause damage. Therefore, the study of creep behavior of clay soil for geotechnical application is necessary. Before construction of a structure, to provide a suitable bed, different ways, such as preloading, consolidation and appropriate additives, are applied. In recent years, improvement of soil characteristics using different additives is widely employed. In this study experimental programs are conducted to investigate the effects of low percent Nano silica on creep behavior. One-dimensional single stage and stepwise compression creep tests are conducted using standard oedometer apparatus under different stress levels on soft clay samples. Creep mechanisms are explained based on contacts and deformation of particle and relationship between coefficients of secondary compression and void ratio. Test results clearly indicate that the behavior of soft clay affects percentage of Nano silica and stress levels. With increasing the Nano silica to a specified level, the creep rate of samples decreases, and thus, the soil sample becomes denser. However by a more increase in ratio of Nano silica, porosity and coefficient of secondary compression decreases. On the other hand, it was observed that there is a nonlinear relation between the vertical stress level and coefficient of secondary compression. Also in stabilized samples with Nano silica, the values of compressibility index are smaller than the samples without Nano silica. Of course with increasing the Nano silica to 0.5 weight percentage, due to soil resistance increment against settlement the compressibility index decreases, and with more increase in the weight percentage of Nano silica the compressibility index increases.