DRAINED SHEAR STRENGTH PARAMETERS OF COMPACTED KHON KAEN LOESS BY DIRECT SHEAR TEST

This study aims to determine the relationship between drained shear strength and matric suction of compacted Khon Kaen loess soil from a consolidated drained method by a direct shear test. All soil samples were compacted by a modified method at the wet side. The initial dry density of samples was 1.95 t/m3, which was 90% of the maximum dry density and the initial moisture content was 11.85%. The shear rates of 0.005 mm/min, which was determined by a consolidation test. Moreover, soil samples of this study were tested under soaked and unsaturated conditions. Soaked samples were infiltrated with water for seven days in the direct shear box prior to the test. Unsaturated soil samples had been divided into three series. The first series was airdried for 30 minutes. The second and the third series was air-dried for 60 minutes and 90 minutes, respectively. Then all unsaturated samples were wrapped up for one day to stabilize the moisture content. The results presented that the drained shear strength was increasing with the matric suction, but the slope of graph or the φb value was not constant with matric suction. The slope of graph or the φb value was increasing with net stress. Moreover, the friction angle (φ) was slightly increasing (2 degrees) with matric suction from the saturation regime to the first translation regime. Then the friction angle at the first translation regime was constant of 26 degrees.