STRESS ANALYSIS AROUND TUNNELS IN JOINTED ROCK MASSES

Abstract

The stresses, which exist in undisturbed rock mass, are related to the weight of overlying strata and geological history of rock mass. This stress field is disturbed by the creation of a tunnel opening and the disturbance induces the stresses. Some times these induced stresses are high enough to exceed the strength of Rock mass, in which case failure of rock mass adjacent to the tunnel boundary leads to gradual closure of opening. Since underground openings are associated with high overburden, high stress and different discontinuities, the strength of rock mass will be less at these regions which in;tuspi results into broken or plastic zones. In the present work, analysis proposed by Ladanyi (1974) which considers the elasto-plastic behaviour of rock mass and which represents the actual field situation has been used. This analysis has been used for simulation of an underground drift (YaMatomi et.al.) for which the data for it's deformations measured in the field, is available. The various rock mass properties being considered in analysis are same as those presented by (Yamatomi et.al.). These properties are utilized in predicting ground response characteristics. The Ground Response Curves (GRC) for three different values of uniaxial compressive strength and Support Reaction Curves (SRC) for various support systems have been worked out. The suitability of an appropriate support has been examined. The stress distribution around tunnel has also been studied.