Northwest Langley Wastewater Treatment Plant

13,400m² of Vibro Replacement stone column densification to a maximum treatment depth of 30m

Metro Vancouver is upgrading their NW Langley WWTP facility with the construction of four new secondary clarifier tanks and ancillary structures.

The subsurface soil conditions generally consist of 5 to 12m of native silt and silt mixtures overlying river sand deposits consisting of interbedded silty sand and fine clean sands extending to depths ranging from 24 to 30m. The initial density of the river sand deposits ranged from loose to compact. Groundwater was encountered approximately 1.5m below working surface elevations.

Ground Improvement by Vibro Replacement stone columns was required beneath and surrounding the proposed tank foundations to mitigate the potential of soil liquefaction and mitigate the extent of lateral spreading towards the adjacent Fraser River during the design seismic event. Stone columns were installed using wet top-feed methods to a maximum treatment depth of 30m. The site’s interbedded and very fine sandy soils proved to be some of the most challenging soil conditions Menard Canada has ever worked with. Several systematic trial areas were carried out to determine the optimum combination of stone column spacing and installation methodology in order to meet the Engineer’s stringent CPT based performance criteria. Two Vibro rigs worked simultaneously on a double shift basis for a period of 4 months to meet the client’s schedule.