Design of a two-screen probe to measure in-situ horizontal and vertical hydraulic conductivities under saturated and unsaturated conditions.

摘要

The horizontal and vertical conductivities (K) of soil layers are factors of great importance for many engineering developments, including pond and dam design, drainage, soil compaction and remediation of contaminated soils. Previous attempts to measure K, such as pump or slug tests, have encountered many problems, such as soil disturbance and clogging, which affect the accuracy of the results. Furthermore, only the effective K can be obtained from these tests, rather than separate horizontal and vertical hydraulic conductivities.;In 2004, the Florida Department of Transportation (FDOT) sponsored a research project at the University of Florida to design a device, the "Vertical and Horizontal In-situ Permeameter" (VAHIP), for easy and cost-effective measurements of horizontal and vertical conductivity at various depths of soil formation. However, problems were encountered during testing, indicating that further studies were needed to improve the design of VAHIP and to prototype another device to measure the anisotropic conductivity under saturated conditions and the isotropic conductivity under unsaturated conditions.;In this project, the axisymmetric potential flow theory was used to model the saturated horizontal and vertical conductivities and volume of influence (VOI) for various probe designs. The model considers soils with different conductivities and applications to various types of boundary conditions and several boundary locations with respect to the probe. The hydraulic conductivity predictions were tested in the laboratory with four total probe designs. Under saturated conditions, two-screen probes were used for injection and recirculation tests; additionally, an injection test with injection from one screen and head measurement at the other screen was used. Under unsaturated conditions, another method was used to measure the saturated hydraulic conductivity. Also, the equivalent spherical radius for cylindrical injection cavities was improved by using the principle of equivalent shape factors F. The results of anisotropic conductivities under saturated conditions and isotropic conductivity under unsaturated conditions compared well to independent testing via the constant head test and other existing methods. Using the theoretical and laboratory results, improvements to subsurface testing probes were suggested and possible probe designs were described to perform all the tests in a single device.