The Effect of Soil Cracks on Cohesion and Internal Friction Angle at Landslide

Abstract

In most cases of landslide in Indonesia and elsewhere in the world there is the fact that landslide occurred during heavy rains, landslide may occur anytime in the rainy season, landslide occurs on rocky slopes or on the stiff silty or clayey soilwith a hard layer, landslide occurs on relatively gentle slopes, landslide does not occur on all part of the slopes even though the condition of rocks and soil along the side of the road is relatively same and the intensity of rainfall are practically the same. In areas with frequent landslide, the data surveyed from some field drill results on the ground outside the landslide area showed that the layers of soil on the slopes of the mountains was not saturated, and the ground water level is quite deep. A preliminary investigation showed that the soil cracks has occurred on the slope. The cracks occur due to soil movement or weathering by plant. Cracks in the soil can be short or long and even form a potential areas of landslides on the slopes. The cracks area is then filled by rainwater. This rainwater that fills the cracksarea causes the independent pore water pressure on the slopes. The purpose of this research is to analyze the influence of cracks on the shear strength parameters of cohesion (c ') and the internal friction angle (). A series of laboratory activities carried out by varying the cracks in the test specimen ranging from 0% to 75% then testing using the direct shear test tool that has been modified. The results showed that the cracks in the soil greatly affects the decrease in cohesion but did not significantly affect to the internal friction angle.