Analysis of an anthropogenically-induced landslide with emphasis on geological precursors

Abstract

A landslide occurred at Nhachüko on 2nd June 2017. Indiscriminate dumping of hill-cut debris along a narrow stream channel blocked the flow of water, which raised the water levels on the uphill side. The area is made up of very weak geological material, which is a consequence of intense tectonic activity in the region. The landslide was triggered when the pore pressure exceeded the shearing strength of the underlying geological mass, thereby affecting the channel floor and the banks. This event suddenly washed away the road and other infrastructure due to the accumulation of excess water in the area during heavy rains. This landslide is analysed to determine the role of human activity and the influence of local geology. Geological and geophysical studies were carried out in the area and supported by geotechnical analysis. Data indicates that the soils are highly unstable with low values of soil cohesion and friction angle. Slope mass rating also points to an unstable slope condition. Geophysical surveys show underlying layers of weathered shales. Paleostress analysis depicts the impact of tectonic forces on the structural setup of the study area, which is in agreement with the regional trend. The sudden increase in rainfall over a short period, prior to the landslide event, led to increased pore pressure. The sudden collapse of the debris barrier caused mudflows to erode the floor and banks of the stream channel to cause extensive damage to the surroundings, including the total destruction of the road.