Abstract:
Forest Hill Station is an underground station located in Toronto. It is part of the 19 km long Eglinton Crosstown Light Rail Transit (LRT) which features 15 no. above ground stations and 10 no. underground stations. Forest Hill Station is being built using a topdown construction method which enables the simultaneous construction of the permanent structure and the subsurface excavation advancement. Secant pile walls form the shoring system along with king piles to support the new structure. During the installation of a king pile, an additional 25 m3 of concrete was required (approximately 63% of theoretical volume). A significant decrease in the density of the native soil in the vicinity of the king pile and adjacent piles were identified during a supplemental investigation program. As such, a remedial base grouting program was executed. Multiple port sleeve piles (MPSP) were installed from inside the adjacent LRT tunnel and advanced under artesian conditions and challenging subsurface profile. All MPSP’ s extended from the face of the tunnel to approximately 3 metres below the founding elevation of the piles. Remedial grouting was performed by injecting cementitious grout under high pressure to verify and/or stabilize the soil below the underside of the piles without causing excessive movement and fracturing of the soil. A total of 7.9 m3 of grout was injected through 41 no. ports where a clear refusal pattern was observed in 37 no. ports. This paper provides a detailed case history of this project, an overview of the project settings, the challenging subsurface conditions, details of the grouting program analysis, construction methodology, and quality control program that was developed and implemented by the specialty geotechnical contractor.