Slug Test in Soil-Bentonite Cutoff Walls Using a Push-In Piezometer Tip

Two advantages of slug tests for measuring the hydraulic conductivity of soil-bentonite in a cutoff wall are that the soil-bentonite is tested in-place in the cutoff wall and that a larger amount of soil-bentonite is tested than in typical laboratory tests. This paper describes equipment and procedures for performing slug tests using a push-in piezometer tip. Chart solutions are provided for reducing the data considering proximity of the trench walls and the influence of bentonite filter cakes. The procedures described here for performing slug tests using a push-in piezometer tip produce measurements of soil-bentonite hydraulic conductivity that are in very good agreement with the results of other reliable test methods. By performing falling head tests and evaluating the data over a limited range of head drops, it is not necessary to complicate data reduction by taking backfill compressibility into account; however, the excess heads applied in falling head tests must be small to avoid hydraulic fracture because the effective stresses in the backfill are small.