Shear strength parameters of peat soil of district of Asahan by direct shear test

Abstract

Peat is a wetland ecosystem characterized by the accumulation of organic matter happens for a long time. This accumulation occurs because of the slow decomposition rate compared to the rate of accumulation of organic found in the wetland forest. The purposes of this study were to determine the index properties, to classify the peat soil classification, to obtain the optimum water content and maximum dry unit weight, γd by Standard Proctor test, and to examine the shear strength of peat soil by direct shear test. The peat soil had water content, w of 726.34 % and a specific gravity, Gs of 1.302. Based on ASTM D4427-92, the classification of peat soil was high ash peat and highly acidic. Based on the Standard Proctor test, the optimum water content obtained was 34% and the maximum dry unit weight was 0.518 gr/cm3. The Standard Proctor test increased the value of the dry unit weight of the undisturbed soil samples from 0.154 gr/cm3 to 0.556 gr/cm3. The original internal friction angle, φ and cohesion, c were 0.595° and 0.019 MPa while the Standard Proctor test resulted in 3.539° of internal friction angle, φ and 0.020 MPa of cohesion, c.