STUDY OF 3- DIMENSIONAL SEEPAGE PRESSURES BELOW HYDRAULIC STRUCTURES WITH CUTOFFS

Abstract

This study has been devoted to the determination of seepage pressures below depressed floors of hydraulic etructures, pressure distribution along the downstream face of downstream cutoff and the exit gradients, in cases 'all/re 3-dimensional seepage is predominant. The variation of the pressures and exit gradient parameters with different ratios of depression and with different sheet pile depths has been studied for two models with different degrees of depression and also for two models of field structures where 8-dimensional effect is expected to be significant. The results of investigation on one of the field models viz. Pili Spillway, have been compared with the field data available for the prototype . The method employed for the study is the electrical analogy of 3-dimensional flow. The free surface has been represented by a number of equipoten-tial wires laid in accordance with an equation developed on the basis of Dupuit's theory. Only one water table elevationon i e. equal to the tail, water level has been considered in the study and it has been found that the uplift pressures below the floor in the 3-dimensional case are lower than the fir-dimensional. The dimensionless exit gradient parameters pc, and pf. 9 on the other hand, tend to get adversely effected by the 3-dtmensio 01 aspects of seepage and therefore, deserve attention. The n+ces$tty of further work, with other water table elevations and with leaky shoet pile.% has been emphasised, as both these factors are likely to have noteworthy effects on the uplift pressures and exit gradients in 3—dimessioeal seepage.