Effect of Block-in-Matrix Cover on Stability of a Vulnerable Highway Cut Slope

Block-in-Matrix (BIM) is characterized by heterogeneous materials and exhibits complex failure behavior when present on a hill cut slope. A similar slope stability problem is currently being faced between chainage 4 + 100 km and 4 + 400 km during the 4-laning of the Barhi-Koderma section, along the national highway (NH-31) in Jharkhand, India. The present height of the unstable cut slope is about 16 m inclined at 70–75°. The highway slope is characterized by a layer of about 4 m thick heterogeneous BIM material underlain by 12 m thick highly weathered phyllite mica-schist exhibiting a GSI value of about 10. The most common method adopted for BIM slope stability analysis is by considering a uniform medium, which tends to be conservative. However, many researchers have analyzed such slopes considering the block characteristics such as their distribution, shape, size, position, and volumetric block proportion on the slope. In the present work, the stability analysis of the highway cut slope has been carried out using the finite element method (FEM) based Phase2 v8.0 numerical code, considering a nonuniform distribution of BIM layer to understand its failure mechanism. The generalized Hoek and Brown failure criterion was used in stability simulation. The study results signify the effect of blocks present in the matrix materials on the factor of safety and failure behavior of the highway cut slope. It was observed that the integration of block distribution within the soil layer has a significant influence on the deformation pattern as compared to the uniform soil layer. In the present study, the design of the cut slope with a desired factor of safety has been discussed in detail.