Behaviour of underground large caverns using 3DEC numerical modeling: a case study

Creation of underground large caverns is increasing in the country, in order to create large underground spaces for storage of crude oil, accommodating hydroelectric power projects etc. Stability of caverns for a period of at least 100 years is essential while planning such projects. Numerical modeling is an effective tool for the design of underground openings and it provides reliable analysis of stresses and displacements around openings. A case study was taken up involving excavation of two large underground caverns of 20 m x 30 m x 1000 m dimensions in granitic formation at a depth of around 140 m, spaced 30 m apart. Deformational behaviour of rock mass around caverns meant for crude oil storage was analyzed using 3DEC software. Models were formulated to evaluate the effect of structural discontinuities including a mafic dyke encountered during the excavation process on the stability of caverns. The dyke portion was found to have considerable influence on the stress regime and displacement pattern around the caverns. The barrier between two caverns was found to experience high stress concentration ratio.