Slope Stability Analysis Based on Rock Mass Shear Strength on Changes in Water Content in Coal Mining in the Menyango Block Area

Abstract

Mining activities is commonly to work with the problem of stability of rock mass, then befor
desaining mine’s slope should know rock shear strength parameters, such as cohesion (c) and
internal friction angle value ( . Beside those parameters, also needed to know the impact of
water content to the rocks. The water content will effect rock’s shear strength, proof by the rock
condition which is ductile when it is dry and soft when it is wet. Based on test results was done
using sandstone with laboratory scale of direct shear test were analyzed using mohr – coulomb
and patton criteria (1966). It is known that the cohesion (c) of sandstone decreased from 510,35
kPa at natural condition down to 133,75 kPa at wet condition. The internal friction angle ( ) also
decreased from 54,56° at natural condition down to 48,45° at wet condition. The reduction of the
shear 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 reduce the active normal
stress so that working the shear stress required to cause the shear failure become
weaker. From the results, it is also known that the shear surface roughness had a lot of
influence on the shear strength the normal stresses applied on the direct shear tests were
very low under 20% of UCS.