Off-campus UNL users: To download campus access dissertations, please use the following link to log into our proxy server with your NU ID and password. When you are done browsing please remember to return to this page and log out.
Non-UNL users: Please talk to your librarian about requesting this dissertation through interlibrary loan.
Seepage in stochastic and spatially correlated permeability fields with an application to soil liners
Abstract
Research was undertaken to study seepage in stochastic and spatially correlated permeability fields. Permeability is considered as a random variable. Assuming second-order stationarity and ergodicity, spatially correlated permeability fields were generated using geostatistical methods for two hypothetical flow fields. Second-order stationarity implies the intrinsic hypothesis, hence the spatial correlation can be characterized by variogram functions. Turning bands (kriging) method and conditional simulation techniques were used to generate spatially correlated (dependent) random fields. For comparison, spatially uncorrelated (independent) random fields were generated assuming stationarity. A numerical model was developed and used with the Monte Carlo technique to simulate seepage in the generated random fields. Simulations results are presented as a series of probability distributions for effective permeability. These pdf's are used to discuss and analyze the results and to identify the influence of spatial correlation and layering. Results indicate that the spatial variation and correlation of permeability fields are important factors in flow systems. This study shows that the geometric average of permeability of heterogeneous field is a proper estimate of effective permeability only when correlation is neglected. The effective permeability for a correlated random field has larger mean and larger variance as compared to that of an uncorrelated random field. It is shown that the mean and variance of effective permeability are direct functions of the "sill" and "range" of the variogram, respectively. Results indicates that seepage quantity through a flow system, such as soil liner is an inverse function of layering. Finally, the model is used to simulate an experimental soil liner and the simulated results are compared with measured value. Furthermore, the effect of high conductivity zones (defects) on the results are evaluated, and reliability and failure risk are defined in terms of simulated results. It is shown that the presence of defects causes high seepage quantities, hence failure of the system.
Subject Area
Civil engineering
Recommended Citation
Ghohestani-Bojd, Hamid, "Seepage in stochastic and spatially correlated permeability fields with an application to soil liners" (1988). ETD collection for University of Nebraska-Lincoln. AAI8910694.
https://digitalcommons.unl.edu/dissertations/AAI8910694