HIGHWAY EMBANKMENT CONSTRUCTION OVER SOFT SOILS IN THE LOWER MAINLAND OF BRITISH COLUMBIA

This paper describes the successful construction of new highway embankments over soft soils alongside existing high-traffic volume highways in the Greater Vancouver area of British Columbia. Highway 10 and Highway 15 intersect at Cloverdale in the City of Surrey. Reconstruction and upgrading of 23 km of these two highways have recently been completed as part of the FederalProvincial Border Infrastructure Program. About 17 km of this upgrading is located in the lowland area of the Nicomekl and Serpentine River floodplains which are underlain by soft and compressible fine-grained and organic soils. In the past, dyke and other embankment failures have been common in the area due to the soft soil conditions. The two projects consisted of highway widening from two lanes to four, construction of over 12 km of new embankment ranging in thickness from 1.5 m to 7.0 m, construction of nine new bridges, relocation of 2 km of railway and 1.2 km of water main, placement of embankment fills over existing sewer, water and gas utilities, and agricultural drainage improvements. Design and construction of the embankments involved: staged preload construction with surcharging to reduce post construction settlements, installation of wick drains and use of lightweight fill materials to reduce the construction time period, and geogrid-reinforced concrete block walls to retain the preload fills. The projects were divided into work areas for the purposes of preload design and construction management. During construction, fill placement was monitored in each work area using a combination of surface and deep settlement gauges, standpipe and pneumatic piezometers, and inclinometers. Instrumentation was monitored on a frequent basis to provide data that allowed project geotechnical engineers to provide approval to allow each stage of preload fill placement to proceed in each work area. This careful approach to embankment construction on the soft soils was very successful as there were no soil failures on the project resulting from the embankment construction. The project was completed on schedule. The paper describes the soil conditions in the area, and the geotechnical challenges to embankment construction posed by these conditions. The embankment design features, staged preload construction methodology, and examples of preload monitoring results are presented.