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ENVIRONMENTAL CONSTRUCTION AND REMEDIATION Jet Grouting As part of the overall environmental remediation program required for the former EXPO '86 site in Vancouver, B.C., Geo-Con constructed a groundwater control system consisting of deep soil mixing and jet grouting cutoff-barrier walls. The property comprised 83 hectares of contiguous lots bordering the north shore of False Creek in downtown Vancouver. The site, which had a long history of industrial activity dating back to the 1800s when the city was first developed, was to be sold for residential and commercial land uses. Construction of the walls was through deep, highly contaminated and heterogeneous fill material in the property, called the Pacific Place site, was completed during the summer of 1992 within the construction window to meet project commitments.
An evaluation of remedial alternatives led to the conclusion that in-place management of wastes using control measures was suitable for the project and the most cost effective. The risk assessment/risk management (RA/RM) approach was applied and a baseline risk assessment was conducted to assess control measures required. Since groundwater discharging into False Creek was a major pathway of concern, a surface liner was designed to limit infiltration into part of the site and a groundwater control system using vertical cutoff walls was selected.
The barrier wall design consisted of seven segments, which were evaluated relative to performance requirements, subsurface conditions, site constraints and relative cost.
Site performance requirements called for a barrier wall permeability of 1 x 10-6cm/sec or less and a design life of 50 years. Selected construction methods to successfully meet short and long-term criteria included DSM augering and jet grout mixing.
Geo-Con worked with the engineering representatives of Golder Associates, Ltd., and Sandwell Inc., the owner, Concord Pacific Developments, Ltd. and the British Columbia Ministry of Environment, Lands and Parks throughout the development and construction of this project.
Prior to construction of the barrier wall, approximately 2,000 lineal feet of the trench alignment was pre-excavated to a depth of 37 feet to remove an old reinforced concrete creosote holding basin and various other concrete structures. The water table was located approximately 2 feet below the ground surface.
The barrier wall construction began on March 9, 1992 and was completed on August 26, 1992. Concurrent site activities such as the Dragon Boat Festival, the adjacent construction of Carrall Street and Pacific Boulevard South, and the preparation for the Molson Indy Race had to be accommodated during the construction period.
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