Cutoff Wall Connections to Existing Large Diameter Pipes

In the framework of the Herbert Hoover Dike Rehabilitation project, BAUER Foundation Corp. had 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. Beside numerous connections to existing concrete structures and existing cutoff wall segments, the work included the connection of the cutoff wall to three utility pipes at pump station S-131: one 96-in (2.44 m) diameter corrugated metal pipe (CMP) and two 48-in (1.22 m) steel pipes. The cement deep soil mixing method of Cutter Soil Mixing (CSM) has been used to install the wall.  The contract documents stipulated the use of jet grouting for all pipe connections.  The large diameter and the deteriorated state of the CMP caused the contractor question whether it would be feasible to meet strict contract requirements for the interface utilizing jet grouting methods. The contractor prepared a value engineering cost proposal (VECP) to avoid jetting around the CMP. The proposal included an excavation shored using sheet piling and soldier piling, partial removal of the CMP, jet grouting below the CMP, reconnection of the CMP, backfilling with controlled low strength material (CLSM), jet grouting around the steel pipes and finally CSM tie-ins into the CSLM block and jet grout cutoff wall. The paper introduces the project, the existing conditions, the geotechnical site conditions and the requirements specified by USACE.  It describes the pursued approach, the equipment used, and auxiliary measures needed to facilitate the approach.  Strength and permeability results are presented. The paper also discusses challenges encountered and related lessons learned.