Construction and Verification Testing of Cement Deep Soil Mix Panels to Mitigate Seismic Displacements for the Evergreen Line Rapid Transit Project

A 2 km section of the Evergreen Line Rapid Transit Project is supported on improved ground consisting of cement deep soil mix (CDSM) panels because of highly variable and challenging soil conditions, especially the potential for seismic liquefaction-induced lateral spreading. This paper discusses the selection of soil-cement parameters for use in the performance-based design, the preconstruction testing undertaken, and some construction challenges including the proximity to mainline railway tracks, highly variable soil types including sticky clays, the presence of obstructions (buried tree trunks, boulders, and glacial erratics) and artesian pressures. Wet grab samples were collected daily from select columns and field monitoring was conducted to demonstrate that the installation of CDSM panels would not adversely impact the safety of the adjacent tracks or other sensitive infrastructure. Significant challenges were experienced with verification testing because of the variable nature of the soils, difficult workability of sticky clay, core barrel size, and the abundance of gravel which effected the recovery of intact core samples.