EFFECT OF WEAK ROCK IN DAM FOUNDATION INTERACTION OF KISHAU DAM

Abstract

Dams are structures of national importance, due to their application in Irrigation,, Power Generation and Flood Control projects.. The design of such important structures is dependent upon their foundation characteristics. A 236 m high straight concrete gravity dam has been proposed at Kishau (Sambherkhera), 45 km upstream of Dakpathar across river Tons in district Dehradun of Uttar Pradesh. The dam is founded on complex geological formations comprising pink and white quartzite with weak grey quartzitic slates. Besides, a 1.2 to 2.0 in thick shear zone has also been anticipated about 150 m below dam base dipping towards downstream at an inclination of about 102° from vertical. A conventional stability analysis revealed that the safe stresses are within permissible limits in almost all loading conditions. To account for the effect of complex geological formations and shear zone, a 2-D linear finite element analysis has been carried out in this study which is only preliminary in nature. The analysis shows development of large horizontal deflections at top of the dam and vertical settlements at toe of dam. It also shows development of tensile stresses near heel. Further, dam blocks resting on different rock foundations, show differential settlements which may cause operational problems. Therefore, the foundation needs thorough investigation and precise design analysis.