Analysis and evaluation of stability for the reactivated road landslide using electrical resistivity and induced polarization in Muara Badak district, East Kalimantan, Indonesia

Muara Badak is one of the districts that prone to the road landslide in Kutai Kertanegara Regency of East Kalimantan province in Indonesia. Reactivated landslides have been identified in several locations in the road access to Muara Badak district, for instance the Simpang-3 Sambera. Geophysical study has been carried out using Wenner Alpha of Electrical Resistivity Tomography (ERT) and Time Domain of Induced Polarization (IP) methods. Assessment and measurement conducted in three lines parallel to the road using MAE Unit-48 electrodes with three meters interval. Resistivity inversion shows the area predominantly composed of clay, sandy clay and coal, with resistivity value within 1-80 ohm.m, 81-200 ohm.m and >200 ohm.m respectively. Slip surface has been interpreted about 6 meter depth, occurring between the contacts of less-consolidated sandy clay and consolidated clay with translation pattern and thicker to the toe of the landslide. The IP data using to interpret the groundwater table at the depth of 3-4 meter based on the pattern of chargeability that closed to the surface. Furthermore and correlated to the Standard Penetration Test (SPT) data, the contact between the weak zone and the hard zone is interpreted to be at the depth of 6 meters. It is concluded that the trigger of the reactivated landslide in Simpang-3 Muara Badak were triggered by several factor including, rainfall and run of water, groundwater and steeply slope.