Stochastic Analysis of Seepage through Natural Alluvial Deposits Considering Mechanical Anisotropy

The soil is a heterogeneous and anisotropic medium. Hydraulic conductivity, an intrinsic property of natural alluvial deposits varies both deterministically and randomly in space and has different values in various directions. In the present study, the permeability of natural deposits and its influence on the seepage flow through a natural alluvial deposit is studied. The 2D Finite Difference code, FLAC 5.0, is used for modeling permeability as a random variable with lognormal distribution and correlated structure. Effect of spatially varying permeability on the seepage flow through deposit is investigated for both isotropic and anisotropic conditions. Results show that in isotropic condition, the mean discharge flow rate calculated from stochastic analyses is less than the equivalent deterministic value and this reduction depends on the coefficient of variation, COV of permeability and the correlation length. The directionality of permeability introduced as mechanical anisotropy was also studied along with the heterogeneity. It was found that increasing the anisotropy ratio of permeability leads to the formation of horizontal flow canals and increasing the seepage flow consequently at a constant vertical permeability. Variation of permeability coefficient was found to have almost no impact on mean discharge flow rate for anisotropic fields in comparison to the isotropic condition.