The rock slope failures occur along preexisting natural rock discontinuities or plane of weakness. In rock slope stability problems, the actual failure or sliding surface depends upon spatial orientation, frequency and distribution of the discontinuities and the inherent shear strength of filling material in the discontinuities. Rock Mass Quality and Rock Defect study by determining the complicated features of rock helps to characterize the rock slope and indicate the causes of slope failure in specific location. The new and modified techniques help to establish the cost and complexity of both design and re-construction of rock slope for a restoration of damaged road or a new road alignment by-passing the existing one as an alternative solution. These remedial measures generally comprise of improving surface and sub-surface drainage, restraining structures, reinforcement techniques, Rock bolts, Shotcrete, Steel fiber reinforced shotcrete(SIRS), etc. A new technique of Rock Engineering investigation and remediation for unstable rock slope is attempted to identify the elements of a high quality investigation in different stretches of National highways and state highways of India.
The slope stability is one of the most common problems in natural hill slopes in India. There are several failure criteria available to describe the deformation of the rock mass. These failure criteria are based on the rock mass properties. Mainly two types of failure are noticed in the rock mass viz. shear failure and tensile failure. The joint controlled rock slopes prone to failure need an immediate attention to find out cost optimum solution in the form of remediation programmes for execution in hilly terrain of India. Unstable blocks of rocks adjacent to roadways can have a significant effect on the safety and economic feasibility of highways. Rock slope failure causes extensive damages to roads, buildings, forest, plantations and agricultural fields and habitats. Cloudbursts, flash floods and short duration high intensity rainfall often triggers natural disasters in Himalayas. There are a few examples of earthquake induced landslides triggered by seismic waves. However, they do cause lot of damage to infrastructure as well as habitat. The stabilization of hill rock slope is attempted in a process as shown in Benn diagram in Fig.1. The physical evidences of rock slope failures investigated so far indicate that almost all rock slope failures occur along preexisting natural rock discontinuities or plane of weakness. In rock slope stability problems, the actual failure or sliding surface depends upon spatial orientation, frequency and distribution of the discontinuities and the inherent shear strength of material present in the discontinuities.
Rock Quality Designation (RED) and core recovery determination has to be carried out during logging of bore holes. Variation in thickness of strata and presence of discontinuities such as joints, faults, shear zones etc. beneath the slope may be interpreted from the data collected from the field using geophysical techniques. Presence of water body located underneath the hill slope may also be demarcated by these techniques. The use of ground penetrating radar is an effective substitution for bore hole investigations.