Kajian Geologi Dan Analisis Faktor Keamanan Pada Geobencana Tanah Longsor Di Jalan Sumbar Di Kilometer 84 – 89 Kecamatan Harau, Kabupaten Lima Puluh Kota, Provinsi Sumatra Barat

The research area is including the Kelok Sembilan area, Harau District, Lima Puluh Kota Regency, West Sumatra Province which is located along the Riau – West Sumatra crossroads of kilometer 84-89, on coordinates 00˚02’40’’ LU - 0˚05’20’’ LU and 100˚41’20’’ BT - 100˚42’00’’ BT. The purpose of this research are identification of geological condition, geomorpologhy, landslide type, geological structure and safety factor on the study area. The analysis method used are geomorpologhy, litology, petrography, direct shear stress, slope safety factor and landslide type. The geomorpologhy unit are steep high hills structural unit (S2) and moderately steep high hills denudational (D3). The litology found are claystone, sandstone and siltstone with drainage pattern are subdendritic. The geological structure is joint with the direction of the main stress is North-South. The cohesion value and friction angle on the ST 2 is 0,029 kg/cm², 25°, ST 6 is 0,020 kg/cm², 47°, ST 8 is 0,301 kg/cm², 20° and ST 10 is 0,018 kg/cm², 24° which could be concluded is medium class by aerodibility, very soft consistency and very loose density. The safety factor is unstable type with the lowest value 0.106 and higest value 0.681. Then, the landslide type are debris avalanche, rock fall and translational landslide