Analysis of Behaviour of Caverns with Varying Pillar Widths Between the Caverns

In this study, two caverns viz. Powerhouse Cavern (PHC) and Transformer Cavern (TC) forming major part of hydro-electric project in eastern Himalayas are considered for analysing convergence of cavern components and efficiency of support system with different pillar widths. Detailed comparative analysis of stability of caverns was carried out for unsupported, supported caverns with pillar widths of 30 m and 40 m between PHC and TC. Trend of cavern convergence, maximum principal stress together with deformations, axial, shear forces, bending moment in cavern support components like rock bolts, cable anchors, liner are examined. Pattern of distribution and location of points of concern enable identifying critical locations to resist collapse of cavern system. Evaluation of adequacy of support components were carried out to check the adequacy. Analysis revealed a strength factor greater than 1 for locations along periphery of both caverns and supports provided to the cavern system were adequate. Results establish site applicability of the support systems as well as adequacy of pillar width of 40 m to ensure stability of the entire system. The study concludes that a pillar width of 40 m ensured more stable conditions with minimal shear strain and no overlap of plastic zone between caverns.