SHEAR STRENGTH OF SAND UNDER LOW TO HIGH PRESSURE CONDITIONS

Abstract

In normal practice soil is subjected to a widely varying range of pressures. Cases of constructions of high earth-rock dams, deep excava-tions and tunnels, or deep oil drilling are not uncommon in whcih soil is subjected to pressure considerably higher than those commonly encountered in soil mechanics practice. On the other hand one can also easily examine the heap of the soil resting at an angle what is known an angle of repose. This is the case in which soil is subjected to negligible confining pressure but it has still got some shear strength. Behaviour of soil in high or low pressure conditions is not the same as in normal pressure conditions. A number of other factors come in the picture which govern the behaviour of soil in such conditions. In the present study the triaxial tests were performed on coarse, medium and .fine grained soil from 1 kg/cm2 to 19 kg/cm2 and various parameters of soils for all the three types of sands has been compared. . Curvature in Mohr's envelope, increase in axial strain at failure, suppression in dila-tahcy rate and crushing of the particles are few common features which were observed for all the three types of sands. Effect of crushing was found maximum for coarse grained soil and minimum for fine grained soil resulting in the reverse trend of angle of internal friction in high pressure conditions. Low pressure testing was performed in a specially fabricated appa- ratus by sliding one block of sand over other. Normal pressure varied from 2.4 gm/cm2 to 4.4 gm/cm2. Contrary to the common practice value of 0 was found to be maximum for fine grained soil. The decrease in value of 0 was also observed with the increase in normal pressure. These obser-vations clearly indicate the marked effect of confining pressure on soil