Effect of drains on shear strength and consolidation behaviour of clay

Abstract

The present investigation is concerned with an experimental study of the inward radial and vertical flow consolidation characteristics, and the shear strength behaviour of the consolidated soil due to installation of vertical central model drains and imposed load on a soft fine grained soil of Bangladesh. A laboratory experimental programme has been setup and implemented using three different sizes of circular consolidation moulds. Five open circular model drains were used for a particular sample and loads were applied in three increment s. Two types of locally available dra:inagematerials •. sand and rice husk,were used independently in the vertical drains. The effect of drain diameter, for different drainage materials, on the gain of shear strength measured by different methods (triaxial and vane. shear) were studied. The consolidation characteristics e.g. co-efficient of consolidation, degree of consolidation for radial'and vertical drainage were investigated. Also an attempt was made to study the effect of water content on shear strength of the consolidated soil. The experimental results suggest that the shear strength reaches a maximum at an optimum value of loading diameter - drain diameter ratio, n. The optimum value of n is found to be a function of loading diameter. It is also found that rice husk filled drain gives a higher strength than that for a sand filled drain of same dimension for a particular imposed load. The statistical analyses of the experimental data show strong correlations between shear strength and n, shear strength and water content, triaxial shear strength and vane shear strength. The relations are proposed in the form of equations. The investigation suggests that the co-efficient of consolidation increases upto an optimum value of n and then decreases with n. The co-efficient of consolidation has a higher value in case of a rice husk drains than that for a sand filled drains.