Study on SCB Cut-off Walls to Control the Seepage in Earthen Dams

Slurry trench cutoff walls have been used since the 1970s and have come into widespread usage since the 1980s as a component in overall remedial systems to control groundwater flow, particularly for seepage mitigation in earthen dams. Different types of slurry trench cutoff walls, such as Soil-Bentonite (SB), Cement-Bentonite (CB) and Soil-Cement-Bentonite (SCB) are used to control seepage. Although numerous methods have been adopted, there is still a question about the most effective method to control seepage. As such, this research study reviews the possibility of using Soil-Cement-Bentonite (SCB) cutoff walls for seepage control in earthen dams. This paper discusses the available construction procedures and required engineering characteristics of SCB backfill such as gradation, unconfined compressive strength, permeability and durability. SCB backfill is composed of soil, cement, and bentonite. Most literature indicates that cement and bentonite contents directly affect the strength and permeability characteristics of SCB cutoff walls. SCB cutoff walls become more economical as trench excavated soil is used as the backfill material. It was noted that in order to get the maximum benefit of SCB, fines content of backfill material should be 10%-30%. The addition of cement and bentonite to the SCB mix delivers moderate strength and lower permeability in the cutoff wall. Cement enhances strength, while bentonite reduces permeability. The basic design strength of SCB cutoff walls is 100 kPa, which can be increased up to 1000 kPa by varying the cement and bentonite content. In terms of permeability, values of less than 1 × 10⁻⁶ cm/s can be achieved in SCB cutoff walls. However, there are many incompatibilities between the cement and bentonite ratio suggested after conducting laboratory experiments and those applied in the field. Therefore, it is necessary to investigate the optimum cement and bentonite contents to deliver the most economical and best-performing SCB cutoff wall. Additionally, it is essential to study the influence of alternative wetting-drying condition on the performance of SCB cutoff walls.