Abstract:
In the framework of the Herbert Hoover Dike Rehabilitation project, BAUER Foundation Corp. has been tasked with the installation of 17.5 miles (28 km) of seepage cutoff wall distributed over three task orders. The cutoff wall is 50 to 65 feet (15 to 20 m) deep and minimum 24 inches (0.61 m) wide. The cement deep soil mixing method of Cutter Soil Mixing (CSM) is being used to install the wall. Challenging ground conditions such as organic soils and limestone and sandstone layers found in large portions of the project require a pretreatment of the foundation soils. This is performed via replacement borings applying cased Kelly drilling techniques or via pre-drilling using continuous flight augers (CFA). Up to nine fixed-mast rigs of the types Bauer BG28, BAUER BG30 and RTG RG 27 are being used concurrently to perform the replacement borings, predrilling and the cutoff wall installation. The project also requires connecting the new wall to existing structures. These connections, partly to near vertical faces, partly to the stepped backsides of gravity walls are executed using jet grouting. Due to high quality requirements soil replacement is also performed for jet grouting to pretreat areas where rock layers are present. The paper introduces the project, the geotechnical site conditions and the requirements specified by USACE. It describes the pursued CSM and jet grouting approaches, the equipment used and focuses on the specific adaption of the method to the site conditions. Strength and permeability results obtained from an extensive testing program are presented. The paper also discusses challenges encountered and related lessons learned.