Case history of pile supported highway embankments on very soft and compressible soils

ABSTRACT: This paper describes the design and construction of pile supported highway embankments on very soft and compressible soils. This case history is from the South Fraser Perimeter Road project, located in Delta and Surrey, British Columbia. The subsurface conditions along the road alignment included highly compressible soils, consisting of peat, very soft silts and clays, thickness varying from less than 10 m to more than 100 m. Groundwater table was located at or within a few metres of the ground surface. Soft soil treatment methods included preloading, use of light-weight fill and use of driven piles to support the embankments. Design of the pile supported embankments included selection of pile type, method of installation, axial capacity, load transfer mechanism from the embankments to the piles to the deep soil strata and seismic response. The design work included simple limit-equilibrium analyses to the more advanced soil-structure interaction analyses. Instrumentations to monitor the performance of the embankments included settlement gauges, piezometers and slope inclinometers. The instrumentation data was used to confirm or modify the final design recommendations, preload treatment duration and the predicted post-construction settlement. Details of the design, construction, instrumentation, monitoring and analysis of the monitoring data are presented.