Volume 24, Issue 1 (March 2001)
Determining Hydraulic Conductivity of Soil-Bentonite Using the API Filter Press
The American Petroleum Institute (API) filter press is commonly used to measure the hydraulic conductivity of soil-bentonite, both during mix design and as a part of construction quality assurance and quality control. However, interpretation of the test results is complicated by the fact that, during the test, the soil-bentonite specimen is consolidated by seepage forces, which produce a variation in effective consolidation stress from the top of the specimen to the bottom. This paper presents the results of a laboratory investigation undertaken to illustrate that seepage consolidation theory provides a logical way to interpret filter press test results. A description of seepage consolidation theory, which relates stress, compressibility, and hydraulic conductivity in soil consolidated by seepage forces, is presented. Following this is a description of the laboratory testing program that involved comparing the hydraulic conductivity of two soil-bentonite mixes, as measured in rigid wall consolidometer permeameter cells, a flexible wall permeameter, and an API filter press. Using seepage consolidation theory to interpret the filter press tests produces hydraulic conductivities consistent with those obtained from the other tests. The filter press test results are used to illustrate a method for estimating the hydraulic conductivity of soil-bentonite in a cutoff wall by taking backfill consolidation pressures into account.