Investigasi Geobencana Tanah Longsor dan Identivikasi Nilai Kohesi Tanah Menggunakan Metode Direct Shear Stress di Jalan Lintas Riau Sumbar KM 83-88, Kecamatan Pangkalan Kabupaten Lima Puluh Kota Provinsi Sumatera Barat.

The study area is located along Riau-West Sumatera cross road. Administratively, located on the western road of km 83-88, Pangkalan Sub-district, Lima Puluh Kota District, West Sumatera Province, located between 00o 25 '28.71' 'LU and 00o 22'14,52' 'LS. The objective of the study was to analyze the internal shear angle and soil cohesion using direct shear test analysis. Using the geomorphology analysis, lithology analysis, Direct Shear Test analysis, slope stability analysis, and landslide type analysis. While the resulf of analysis concluded that the geomorphology is classified imto two geomorphological units such as Structural Steep Hilly Geomorphological Unit (S2) and Denudasional Steep Geomorphological Unit (D3). And concain of lithology that Claystone, and Sandstone. River flow patterns are classified into Parallel patterns. The values of cohesion and internal shear angle obtained from Direct Shear Test, ST 3 (0.301 kg / cm², 18 °), ST 5 (0.261 kg / cm², 27 °), ST 6 (0.171 kg / cm², 22 °), ST 13 (0.296 kg / cm², 19 °), ST 16 (0.286 kg / cm², 19 °). soil erodobility class analysis was moderate, with density is very loose. Safety factors are classified as labile type with FK: ST 3 (FK: 0.095) and ST 5 (FK: 0,127), ST 6 (FK: 0,126) and ST 13 (FK: 0,098) ST 16 (FK: 0.104). Types of land failure that was dominant are avalanche debris, and Earth Flow. The appropriate avalanche mitigation recommendations in the study area were cutting 45 ° hills and installation of nails and cement (Rock Anchor), Southwest-Northeast