Fantasy Gardens is a mixed-use development which includes a common parkade supporting several mid-rise buildings. One building is designed with a second basement level and requires dewatering during construction. Due to the groundwater’s high iron content, the Owner has requested to significantly reduce the amount of dewatering required and the associated water treatment costs. To address this issue, the Engineer recommended the construction of a 28m deep cut-off wall surrounding the excavation.
Menard Canada successfully proposed the use of Cutter Soil Mixing (CSM) technology to construct the cut-off wall. The CSM process utilizes specialized equipment to mix self-hardening grouts with in-situ soils. The CSM equipment is capable of installing 2.8×0.5m panels by cutting and mixing the in-situ soil with bentonite slurry and cement grout. A continuous wall is constructed by installing a series of overlapping panels. The resulting cut-off wall is designed to have very low permeability and increased strength compared to the surrounding native soil. The CSM cut-off wall borders the rectangular shaped excavation and measures 320m in length, 0.5m in width and 28m in depth. A cut slope was used for three of the four sides of the excavation where the CSM wall was designed as a buried gravity wall. For the fourth side along Steveston Highway, site boundary conditions did not allow the use of a sloped excavation and the CSM wall was also designed to act as a 2.6m high retaining wall. Earth pressures were resisted by reinforcing the CSM wall with steel H-beams.