SHEAR STRENGTH. OF COMPACTED SOILS

Abstract

Whenever we excavate soil and use soil for construction as construction material it will be loose and has to be compacted. The compaction to increase strength and reduce compressibility. When soil is compacted in earth dams or embankments it becomes pertinient to study the short term stability i.e. immediately after construction. Generally we will have to analyse these problems by taking ...undrained strength into consideration as there will be hardly any time for drainage e.g. 'end of construction. Skempton and Sowa (1963) have done experiments on saturated soils concluded that for identical specimens of saturated clay if are subjected to different changes in total stress, the undrained strength will be practically the same and closely equal to the strength in the ground. The present study deals with the determination of undrained strength in a triaxial machine. In the field where there is failure of slope the rupture surface is taken as part of a circle for finding the factor of safety. The slope of the rupture surface changes from point to point Generally we take vertical samples to find the undrained strength for analysis. The failure plane for vertical sample will make an angle of 450+ p/2 with tree horizontal forming the part of the rupture surface. If this strength is taken the slope of the rupture surface should be 45 + 9/2 with the horizontal at every point which is contrary to the fact. In this study the undrained strengths have been fouid for diff-erent orientations of samples. Four soils were studied, Kaoli,n,Bentonite, Black-Cotton Soil and Dhanauri Clay. These are chosen on the basis of clay minerals viz., Kaolinite, i],lite, llonite. The equations for variations of undrained strength with respect to orientation have been derived and the polar diagrams are shown. The study has also been made for orien-tation effect on percentage strain at failure energy used by the sample, m50 etc. :1 simple problem of stability taking only one rupture surface has been studied. The rupture surface has been considered circular and the values of factor of safety have been found out by taking only vertical strength i.e. no orientation effect by taking oriented strengths. The orienta- tion is found to cause reduction in the f~etor of safety and if not considered it will lead to failure.