STABILITY ANALYSIS of UNDERGROUND OPENINGS
Evaluation of deformation and stress distribution around underground openings in inhomogeneous rock mass with weak zones is a problem of practical interest. It is mainly due to the fact that the behavior of the rock mass may vary from elastic to plastic, depending upon the type of the rock mass, size and geometry of openings made in it. To assess the rock mass stability after openings are made in it, linear elastic, non-linear elastic and non-linear plastic models are commonly employed. However, relative efficiency and suitability of these models remains unexplored.
With this in view, finite element analysis of the underground openings excavated for Koyna hydroelectric project, Maharashtra, India, has been conducted. 2-D and 3-D models have been developed and vertical and horizontal deformations, maximum compressive and tensile stresses occurring in the vicinity of these openings have been computed, under static and dynamic conditions. The results are compared vis-a-vis those obtained from in situ deformations and strength of the rock mass. The study reveals that the 2-D analysis underestimates the deformations. On the other hand, the 3-D elasto-plastic analysis yields results, which compare reasonably well with the in situ deformations. It has also been noted that the major and minor principal stresses obtained by 2-D analysis are lower than those obtained by 3-D analysis. Also, the minimum major principal stresses (tensile), which exist only in the vicinity of the underground openings, when the static analysis is conducted are noted to spread over the entire rock mass when the dynamic analysis is performed.
The study presents a methodology, which can be used for checking the stability of the underground openings, under static and dynamic loading conditions, when extensive realistic input data is available.
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