Measurement of In Situ Hydraulic Conductivity and Coefficient of Consolidation with Prefabricated Vertical Drains

Abstract

Prefabricated vertical drains (PVDs) are often used to improve soils by speeding up the rate of consolidation, and they are increasingly used for remediation of contaminated soils. When PVDs are installed in the ground, there is always a zone of disturbed soil surrounding them. The extent and the impact of this "smear" zone are difficult to quantify, and this uncertainty complicates the use of laboratory values in design. Consequently, obtaining in situ values for the hydraulic conductivity and horizontal coefficient of consolidation that include the effects of smear would be of great use to engineers who use PVDs in design. A method that utilizes PVDs to obtain in situ measurements of these parameters is described. The primary advantages of this method are its cost-effectiveness and the inclusion of smear in the results. A trial test was conducted on San Francisco Bay, California, mud. Some problems encountered during the initial phase of testing are described, and possible solutions are discussed. This promising method yields values that are logical and that compare well with published values for San Francisco Bay mud.