Horizontal drains have been used since the 1930s to increase the stability of slopes by lowering the groundwater table. Horizontal wick drains represent a new technique that has proven to be effective at stabilizing slopes of fine-grained soils while being less costly and time-consuming to install than traditional polyvinyl chloride (PVC) or steel pipe drains. Their adoption has been slow in part due to uncertainty about clogging and the life span before drain replacement is required. To address these concerns, the degree of clogging and the reduction in flow rate were measured for exhumed wick drains that had been in the ground between less than 1 year and 11 years. The flow rate through the drain samples was measured under constant head conditions, and clogging was measured visually and by increase in drain mass. The results of this study suggest that drain failure does not occur during the first 11 years of use and is not anticipated during continued use in the expected field conditions. A reduction in flow rate of 85 percent was the maximum measured for the drain samples. Despite this reduction in flow rate, horizontal wick drains are able to transport at least two times more water than the surrounding soil will introduce. Though horizontal wick drains are not expected to fail due to clogging, a chart is provided to select the proper drain spacing based on soil hydraulic conductivity and required drain length, in order to prevent the flow capacity of the drains from being exceeded.

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