The Himalayan ranges have complex geological formation induced with locked up tectonic stresses and squeezing ground conditions. High overburden cover, steep slopes, perennial snow, and forest cover restricts accurate prediction of geological features, resulting in uncertainty during excavation. The tunnel planning under high altitude, extreme climatic difficult approachability conditions requires elaborate detailing. The construction technique and working faces for excavation are influenced by site accessibility/high overburden conditions, restricting the provision of any exploration during investigation stage. Beside induced stress, ground water seepage is one of the most common hindrances faced during tunnel excavation. Many projects in Himalayan ranges have faced time and cost overrun during construction due to this problem. The paper discusses the methodology to predict the maximum possible ground water ingress into the tunnel using deterministic and probabilistic method of calculations. Water leakage into tunnels and rock caverns becomes a major problem during construction of underground structures. During estimation stage or during bid stage an approximate quantity of seepage water inflows is kept for pumping out by various means. It has been observed that most of the time this item becomes a very huge deviation item or if the contract is awarded by keeping the quantity of the dewatering as fixed one then the contractors bears a huge loss on this item alone. The authors have tried to find a rationale method to predict the inflow of seepage water during excavation of tunnels/caverns so that information on the dewatering to be done is shared and entire risk is not passed on to the contractor. Also based on the rationale the quantities kept are not challenged during dispute.
