| Research Abstract |
It is well recognized that in-situ measurements of saturated and unsaturated moisture properties of soil are essential for accurate prediction of contaminant transport as well as water movement in soil such as agricultural field, compacted soil, natural slope and landfill. In the Research Project field and laboratory investigations are conducted to develop an in-situ permeability test that has a superior feature that an equipment to measure data as well as a procedure to determine the soil permeability is quite simple. The in-situ permeability test investigated consists of a Guelph pressure infiltrometer (GPI) method combined with a Guelph well permeameter (GWP) method, both of which have been proposed by the researchers of Guelph University, Canada. The GPI and GWP methods determine a field-saturated hydraulic conductivity of soil Kfs based on a measurement of constant-head steady infiltration into a soil from a single ring inserted a small depth into the soil and from a well bored a
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small depth into the soil, respectively. Kfs can describe well water movement in soil because many natural and man-made infiltration processes result in significant air entrapment within the soil.
In the first and second years of the Research Project, a practical accuracy and an applicability of the GPI and the GWP methods were examined by a field investigation, a laboratory soil bin test and a numerical analysis. If is found out that the GPI and the GWP methods determine accurately and effectively Kfs in plane and along depth of soil, respectively. Also is found that a statistical property of the soil permeability can be determined,effectively by the GPI method because it does not require a tedious time to determine Kfs at a site. The in-situ permeability test investigated was applied to sand sediment soil formed by a debris flow of soil. From the test results and a permeability test of the sand sediment soil additionally conducted in the laboratory, an integrated procedure is effectively proposed to determine the hydraulic permeability of the sand sediment which is characterized by a inclusion of large gravel and cobbles into the sand soil. In the last year of the Research Project, the in-situ permeability test was extended so that it was able to determine unsat urated moisture properties of soil as well as the hydraulic conductivity of soil. Both an infiltration rate from the GPI ring or the GWP well and a moisture content of soil were measured during the constant-head infiltration with time, and were numerically back-calculated to estimate soil parameters which defined optimally unique relationships between moisture content, negative pressure head and unsaturated hydraulic conductivity of soil. Less
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