Case Study: Construction and In Situ Hydraulic Conductivity Evaluation of a Deep Soil-Cement-Bentonite Cutoff Wall: Fid-Bau Portal

Case Study: Construction and In Situ Hydraulic Conductivity Evaluation of a Deep Soil-Cement-Bentonite Cutoff Wall

Ruffing, D. G. / Evans, J. C.

This paper presents a case study of a deep soil-cement-bentonite (SCB) slurry trench cutoff wall constructed outside of Smithland, KY, in 2010. Installed to a maximum depth of 56 m, this cutoff wall is the deepest known seepage barrier installed using continuous trenching. The wall was installed around the perimeter of a deep excavation to reduce long-term dewatering costs associated with construction of a hydroelectric power plant adjacent to the Ohio River. After wall construction, a dewatering system was installed inside the area enclosed by the wall to facilitate the deep excavation. Preconstruction design and construction details are presented along with the results of a post-construction assessment of the hydraulic conductivity (k) of the wall. Steady-state groundwater flow measurements from the dewatering system coupled with information on the wall thickness and water levels inside and outside of the wall were used to obtain a large-scale estimate of the in situ k of the wall. The in situ k was compared with laboratory k values measured for specimens prepared from grab samples of the as-mixed SCB backfill. Comparisons also were made to the target (design)k and the expected field mixed backfill k established during a preconstruction bench-scale study. The comparisons revealed that the in situ k is approximately one order of magnitude less than the design k and approximately equal to the average laboratory k measured from grab samples and the expected k from the results of the bench-scale study.