Rockfall Analysis of State Highway along the Southern Vicinity of Aizawl, Mizoram

Slope failure in the form of rockfall is a common phenomenon that occur in the hilly ranges of Himalayas. Mizoram, being a part of it experiences a high rate of rockfall throughout the year especially during the monsoon season. This paper focus on frequent rock fall along the State highway between Aizawl to Lunglei via Thenzawl at Midumkham, Sumsuih village. Damage of passenger vehicles, public goods carrier trucks, private vehicles and road blocks are the common phenomenon due to various forms of landslide within the study area. The death of a couple on 14th October 2016 due to rockfall within the study area captivate attention of government as well as the local about the condition of the area. Thus, detailed study of the area becomes mandatory so as to reduce rockfall and to educate the government and locals about the actual condition of the area. Field reconnaissance has been carried out to collect joint data for kinematic analysis. The behaviour of rockfall was determined by kinematic analysis using Rocscience software Dips 6.0, the stereograph shows that toppling, planar and wedge type are the potential modes of failures. The rock beddings are classified based on RMR (Rock Mass Rating) and SMR (Slope Mass Rating). About 90% of the selected site shows that low RMR as well as SMR value. The RMR values of the rock exposed in the study area indicated a very poor quality of rock mass. The average stand up time obtained 30 min for 1m span suggest high rate of erosion of rocks in the area. The rock slopes represent Class V of Romana classification, considered as very bad rock mass and completely unstable. The low value of rebound number and strength of the rock along with presence of numerous joints determined the high vulnerability of the study area