PHYSICAL MODELLING OF TUNNELS UNDER STATIC LOADING

Abstract

The study of stresses around the tunnels is an important step for any type of tunnel construction. The surrounding may be either rock or soil depending on the site and topography of the area. In the Himalayan ranges, the geology of the ground is rocky strata which are initially stressed due to the heavy overburden of more than 1000 meters. The rocks are also stressed due to the excavation process of the tunnel construction which induce secondary stresses in the surrounding rocks. The study of these stresses is done by geologists using various physical and numerical modeling techniques. The hazards in the tunnel construction can be mitigated with better measures of safety such as lining and support system. This requires an expert knowledge of rock mechanics as well as material technology. These stresses are highly affected due to the cover depth of the tunnels below the ground as well as lining material. In this report, we have made an attempt to study the effect of a change in the cover depth and lining of the tunnel by physical modeling technique. In Jammu & Kashmir, Chenani-Nashri tunnel has been recently constructed which is broadly affected by the action of stresses due to the mountains above it causing it critical for deformation. The tunnel has become an important link between the two districts Udhampur and Ramban and the stability of this tunnel has become an important issue for safe transportation. So, this tunnel is selected as a case study for this thesis to check the stability of the tunnel using physical modelling technique. To determine the existing properties of the surrounding V

rocks, tests have been performed in the laboratory to determine the properties which affect the stability of the tunnel. Physical models are prepared by the theory of stresses which include the ratio of diameter of tunnel and distance from the center of the tunnel for the dimensioning of the model and test is performed to examine the failure mechanism of the tunnels and which is based on the study area. The models are also analyzed for the critical region of deformation.