Soil Permeability – Constant Head Test
Permeability is measured in term of water flow through the soil in a given time. The soil permeability is a very important factor to study the behavior of soil in its natural condition with respect to water flow.
The size of pore space and interconnectivity of the spaces help determine permeability, so shape and arrangement of grains play a role. Often the term hydraulic conductivity is used when discussing groundwater properties. Hydraulic conductivity simply assumes that water is the fluid moving through a soil or rock type. (http://www.co.portage.wi.us/groundwater/undrstnd/soil.htm)
Water can permeate between granular void or pore spaces, and fractures between rocks. The larger the pore space, the more permeable the material. However, the more poorly sorted a sample, the lower the permeability because the smaller grains fill the openings created by the larger grain.
The most rapid water and air movement is in sands and strongly aggregated soils, whose aggregates act like sand grains and pack to form many large pores.
On the other hand, clay has low permeability due to small grain sizes with large surface areas, which results in increased friction. Also these pore spaces are not well connected. Clay often creates confining layers in the subsurface. (http://www.co.portage.wi.us/groundwater/undrstnd/soil.htm)
Therefore, for this experiment to test for the permeability of soil is using the constant head test. The constant head permeability test is a common laboratory testing method used to determine the permeability of granular soils like sands and gravel containing little or no slit.
This testing method is made for testing reconstituted or disturbed granular soil samples. The constant head permeability test involves flow of water through a column of cylindrical soil sample under the constant pressure difference. The test is carried out in the permeability cell, which can vary in size depending on the grain size of the tested material. (http://www.geotechdata.info/geotest/constant-head-permeability-test.html)
The coefficient of permeability varies with the type of soil and condition. It is influenced by: •Size and shape of the soil particles
•Degree of saturation
The objective of this experiment is to introduce the idea of permeability of a soil through tests designed to find the coefficient of permeability, which dictates how quickly water at certain temperature will flow through a soil. The experiment is implements the constant head and falling head methods of calculating the permeability constant.