Date of Award
Doctor of Philosophy
Civil, Construction, and Environmental Engineering
Richard L. Handy
The problem of permeability and preferential direction of groundwater flow in fractured glacial till has increasingly attracted the attention of researchers, particularly with regard to the possible contribution of fractures to contamination of groundwater;This research consists of a field and a laboratory phase. In the field tests, stepped blade tests (SBT) were conducted at several depths and boring locations in a glacial till deposit containing vertical and sub-vertical fractures to determine if there was any directional anisotropic nature of lateral stresses attributable to glacial flow and the formation of the fractures;The laboratory tests included soil classification and triaxial confining permeability test. Soil classification was to verify the character of till deposit at the test site. The triaxial confining test, in which a modified triaxial cell was used, was to study the effect of lateral stresses on vertical permeability of the intact and split soil samples;Soil classification indicates that the soils at the test site through the boring depth can be classified as a basal till deposit which matches the properties of the Alden Member of the Dows Formation of Des Moines Lobe;The results of SBTs indicate that the lateral stress distribution at the test site is isotropic and independent of the direction of the glacial till flow or topographic location. The isotropic lateral stress distribution implies that the vertical and sub-vertical fractures are caused by desiccation and other weathering processes rather than shear stresses induced by glacial action;The permeability tests on intact samples show that the in-situ lateral stress has a significant influence on the measurement of hydraulic conductivity. The results of the test on split samples indicate that the artificial fractures may be closed under a "certain" confining stress. The results of the permeability tests suggest that controlling the confining stresses in the test is important.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Wang, Hung-yu, "In situ lateral earth pressure and its effect on vertical hydraulic conductivity in a glacial till deposit " (1990). Retrospective Theses and Dissertations. 9906.