Influence of cement addition on barrier performance of soil-bentonite cut-off wall

Abstract

Soil-bentonite (SB) cut-off wall is widely used for controlling seepage and contamination migration due to its extremely low hydraulic conductivity. Low strength and stiffness of SB can lead to high flexibility and deformability during and after construction, which is one of the merits as cutoff walls, but it limits the application of SB walls when higher strength is required. In such a case, cement addition is a possible way to improve the strength and stiffness properties of SB, but this approach can affect its barrier performance. Soluble elements in cement may decrease the swelling of montmorillonite which may increase hydraulic conductivity of SB. Also, cement addition provides alkaline benefits for SB barrier performance. In this study, the influence of adding cement on hydraulic conductivity and sorption performance of SB cut-off wall was evaluated. Hydraulic conductivity of amended SB was studied by using flexible-wall permeameters with the falling head system with distilled water. The batch test is used to discuss the sorption performance against trivalent arsenic. The results show that adding cement will increase the initial hydraulic conductivity for around 10 times, while hydraulic conductivity of groups with 100kg/m3 cement will decrease to 20% after 60 days curing. The sorption performance of SB with cement will increase with amount of cement increase.