OPTIMIZATION OF DEWATERING AND EXCAVATION COST FOR CONSTRUCTION OF POWER PLANT

Abstract

Selection and design of a dewatering system for excavation work depend on many factors. The important factors are size and depth of the excavation, the height of the ground water above the base of excavation, the permeability of the soil surrounding the excavation and the recharge of ground water from adjacent stream. Duration of dewatering depends upon schedule of excavation that depends upon the capacity of the machine, the manpower and time available for excavation work, which proceeds at certain rate. The design of dewatering system starts with estimation of the flow quantities. In addition to knowing the permeability of the formation, the distance and dimension of adjacent stream from excavation site, the depth and plan of the excavation must be known. Duration of dewatering as it relates to power consumption, operating and maintenance cost, installation cost, discharge facility usage cost are important for determining the most economical set up. Then selection of the system that will perform economically for the parameters and constraints set forth can be accomplished. Size and spacing of the wells and pump sizes are key in design analysis. Continuous pumping and maintaining water table much below the excavation bed means more consumption of energy. Also the water level can be maintained by operating less number of high capacity wells or large number of wells with low capacity. There are effective locations, of well which lead to more drawdown. All these aspects lead to the fact that there is a pumping schedule and arrangement of well locations that will lead to a minimum cost of pumping. The objective of present study is to carry out an analysis to decide about the number of wells to be installed for dewatering during excavation in the construction of Sheetla Hydel project. Duration of dewatering depends upon schedule of excavation that depends upon the capacity of the excavator. To identify the number and location of wells for dewatering in the area with given soil characteristics, cost of dewatering depends on the power of pump with minimum energy consumption, installation cost, and operation cost. To achieve the optimum number of well, the different cost parameters like the cost of pumps, energy cost, and cost of installation have been considered.