An overview of bimrocks and related engineering geological problems in the Nepal Himalaya

Abstract

Rocks falling under the category of bimrocks are common in Nepal and are covering large areas of the country. However, knowledge on their exact distribution is limited, and data on classification and quantification of engineering properties are practically nonexistent. So far, the bimrock terminology is not commonly used for engineering classification of rocks in Nepal. However, three types of bimrocks can be identified in Nepal, they are: cataclastic or shear zone bimrocks, conglomeratic bimrocks and the bimrocks produced by weathering. The thickness of the bimrock strata varies according to the geological and tectonic settings and can reach several kilometres. Due to the relative weakness of bimrocks and the high erodability, they can pose serious problems such as excessive overbreak, water inflow and large rock mass deformations in tunnelling, and slope instabilities in road cuts and other excavations for surface structures. Efforts on the study of bimrocks in Nepal are initiated recently and is considered to help identifying, addressing and solving the associated problems.