Due to an extremely heavy rainfall during the closure of a flood control and water supply storage dam at Oklahoma near Fort Smith, in May 1949, considerable internal erosion of the dam fill material took place in the closure area.
Countermeasures to repair the damage, such as cement and mud grouting and sheet piling, to form a cut-off wall, were immediately undertaken at the closure section of the dam.
Although the erosion in the damaged area had been continually observed - and the dam had been satisfactorily operated in connection with the Arkansas river dams - the Wister dam had required almost permanent maintenance. Following a recent thorough stability investigation to assess the structural integrity and ability of the dam to safely withstand the seepage potential, the dam owners, the Corps of Engineers of the US Army, decided to carry out the necessary major restoration of the embankment.
The contract to construct an upstream slurry cut-off wall with an impervious cap built up of a cohesive fill material, was awarded to Bauer of America Inc., a subsidiary of BAUER Spezialtiefbau GmbH in Germany.
A substantial requirement of the Corps of Engineers was the need to form a 1,5 m (5 ft.) deep socket in the shale, siltstone and hard sandstone bedrock, to accept the base of the cut-off wall. Installation of the cut-off wall utilized a plastic and impervious cut-off material composed of cement, bentonite, sand and stone powder.
Soon after carrying out some preparatory earth works in July 1990, a Bauer BC 30 cutter commenced excavation of the 64 cm (25 in) wide cut-off trench. By April 1991 Bauer completed the 1'260 m (4'133 ft.) long and maximum 21 m (69 ft.) deep cut-off wall with an area of 19'050 m2 (205'050 ft.2) and the impervious cap.
Environmental restrictions, related to working in a nature reserve, placed unconventional constraints on Bauer of America Inc.. Nevertheless the company complied with all these conditions, completing the contract within the agreed nine month to the total satisfaction of the client and all parties concerned.
Scope of work:
Construction of 19'000 m2 (204'500 ft.2) cut-off wall - 64 cm (25 in) thick to a maximum depth of 21 m (64 ft.) including an impermeable wall cap to seal a damaged section of the dam against underflow and percolation.