Investigation of Hillslope Failure and Mitigation: A Case Study of Sillewani Ghat, Chhindwara, India.

Hillslope failure along the highway is one of the most hazardous natural phenomena that leads to economic loss. One such slope failure occurred during the 2019 and 2020 monsoon, along National Highway (NH-547) at Sillewani Ghat, Chhindwara, state of Madhya Pradesh, India. After the first failure (2019), the slope was reinstated by the construction of a gabion wall with a mattress. Again, in 2020, the downhill slope failed which resulted in the washing away of one outer lane of pavement while the uphill slope was stable. Detailed field and laboratory investigations were carried out to explore the possible causes of slope failure and recommendations for appropriate remedial measures. Field investigation includes reconnaissance survey, geophysical test (electrical resistivity tomography and seismic refraction tomography), and standard penetration test. Soil and rock samples were collected and different geotechnical characteristics were determined in the laboratory. Seepage coupled slope stability analysis was carried out simulating field conditions. The result of the geotechnical investigation indicates that rock formation is moderately weathered and stable while the downhill slope has four-layers of loose clayey sand, gravel soil, highly and moderately weathered basalt rock. Due to heavy rainfall in 2020, downhill overburden soil (sand and gravel) got saturated and water channel formed at the interface of soil and rock resulted in the slip failure of the slope due to a reduction in effective shear strength. Seepage analysis revealed that phreatic line was existing at shallow depth during heavy rainfall which also supported the failure. Different remedial measures were recommended to reinstate the pavement namely stabilization of slope using soil nailing with and without gabion wall and provision of proper surface/subsurface drainage systems. [ABSTRACT FROM AUTHOR]