effects of cutoff wall and drain on uplift pressure and exit gradient under hydraulic structure by numerical solution of general equation of fluid flow in soil using finite volume method

abstract among activities that can be used to prevent piping phenomena and reduce seepage and exit gradient are installation of cutoff wall and drain under hydraulic structures. hence in this study, to investigating the influence of each mentioned parameter on uplift force and exit gradient a computer model has developed in which general equation of fluid flow into the isotropic and anisotropic soil was solved numerically by gauss-seidel method. verify model, experimental result and result of winmseep model that is an acceptable model was used. one of the relative advantages of this model is consideration of permeability value for cutoff curtain. the result of this study showed, bye construction of one cutoff curtain in any location values of exit gradient relative to basic exit gradient (without cutoff) reduces. also, maximum uplift force and minimum exit gradient is observed when cutoff curtain is located in toe. for situation with two cutoff walls in toe and heel of dam and one drain in between it is observed that when drain is located at far distance whit respect to heel influence of it on uplift force and exit gradient increases. additionally with increasing upstream cutoff depth in comparison to downstream cutoff, values of exit gradient decreases and intensity of this decrease for shallow downstream cutoff is more sensible. distribution of uplift pressure and calculated exit gradient for isotropic and anisotropic condition are very consistences to those are computed by winmseep model.