SLURRY WALLS FOR GROUNDWATER CONTROL: A COMPARISON OF UK AND US PRACTICEa

Abstract: In both the UK and the US, low permeability, vertical barriers (slurry walls) are widely used in systems designed and constructed for the control of groundwater such as in to temporary excavations. These vertical barriers may result in more economical dewatering for larger and/or more complex underground excavation projects than dewatering wells, the conventionally used alternative. In the US, soil-bentonite slurry wall technology is the predominant method for the construction of these low permeability barriers. In contrast, slag-cement-bentonite slurry wall technology is the most widely employed me thod in the UK. These barriers are made with water, cement, and granulated ground blast furnace slag. This paper presents an examination, comparison, and assessment of each of these practices. It is concluded that slag-cement-bentonite techniques could readily be adopted by US designers and contractors. Permeability data developed in the US using US sourced ingredients are presented which show that a mixture of about 20 % cementitious material to 80 % slurry (where the cementitious material is about 25 % Portland cement and 75 % slag) results in a barrier having a hydraulic conductivity less than 1x10-7 cm/s. Evidence points to a current trend towards the increased use of slag-cement-bentonite cutoffs in the US