Himalayan Geology, Vol. 43 (1A), 2022, pp. 61-72, Printed in India
Geotechnical and structural analyses of Senam and Kotlen landslides on National Highway-37(53), Manipur, Northeast India
JOYRAJ SINGH THOUNAOJAM*, MAISNAM PRADIPCHANDRA SINGH, SOIBAM IBOTOMBI
Department of Earth Sciences, Manipur University, Imphal-795003, India
*Email (Corresponding Author): luwangchajoy@gmail.com
Abstract: Geotechnical and structural analyses are carried out to evaluate possible causes of the two landslides: Kotlen and Senam that not only blocked the transportation through the NH-37, connecting Imphal and Silchar via Jiribam but also caused damages to settlement and some houses especially of Kotlen slide area. Mechanical strength determination by using Schmidt Hammer (R) shows that Kotlen sandstone is more competent than that of the silty-sandstone of Senam slide. Kinematics analyses on rock masses indicate planar failures; and fractures associated with regional extension and shear are the factors for producing small blocks of slope or rock masses. Evaluation of Slope Mass Rating (SMR) points out that Kotlen as well as Senam is stable and good. Kotlen landslide is mainly controlled by bedding, however some joint sets trending along i) 266°, 78°/356° and ii) 162°, 41°/252° caused block falling of the area while Senam landslide is controlled by E-W trending joints.
Soil erodibility studies reveal that the slide areas lie in the category of moderate erodibility while rainfall intensity values are less than their threshold values. Natural moisture contents (w) of the slide areas are found to be greater than their plastic limits. Plastic index values figure out moderate plasticity implying that they can remain in the plastic state for a longer duration, which makes the soils vulnerable to deformation and slides. Slides appear to be controlled by slope angles as amount of slope angles are greater than that of internal friction angles. Seepages along the bedding and joint surfaces are the main reason for reducing shear strength parameters (effective stresses) leading to slides during the rainy season.
Keywords: Plane failure, Kinematic analyses, Rainfall intensity, Index properties, Moisture content
