Perpustakaan Digital ITB

The existence of water in rocks may influence its mechanical properties such as unconfined compressive strength (UCS), tensile strength, shear strength and its characteristics. In mining operations, both open pit and underground mines, it is important to observe the water content because little change of the mechanical properties of rocks may reduce the safety factor of rock slopes or underground openings. The reduction of safety factor can cause either landslides or collapses resulting in environmental damages, threat of death, and financial losses. This research is done on sandstone samples that were taken from a location of sand-mine operation at Cipatat area, Bandung District, West Java. The results of laboratory scale of direct shear test were analyzed using Mohr-Coulomb, Patton (1966) and Barton criteria (1973, 1976, 1977, and 1990). From the test results, it is known that the cohesion of sandstone decreased from 1027.20 kPa (at dry condition), to 728.68 kPa (at natural condition), and down to 105.92 kPa (at wet condition). The internal friction angle also decreased from 28,15o (at dry condition), to 24,58o (at natural condition), and down to 20,55o (at wet condition). The reduction of the hear strength is caused by fragments and clay minerals characteristics which are so reactive and very easy to absorb water so that the cohesion of the sandstone becomes weaker when it is wet. Besides that, pore water pressure at the voids of sandstone reduces the active normal stress so that the shear stress required to cause the shear failure becomes weaker. From the test results, it is also known that the shear surface roughness had a lot of influence on the shear strength because the normal stresses applied on the direct shear tests were very low (under 20 % of UCS).