Subsoil investigation of ice lensing at the Calgary, Canada, frost heave test facility

Abstract

Several frost heave mitigation modes were studied at the Calgary, Canada, chilled pipeline frost heave test facility. These included deeper burial (to increase the pressure on the frost front below the pipe) and replacement of the silty soil around the pipe with gravel for a noninsulated pipe. Frost heave at the deep-burial section and at the gravel section was less than the heave at a control section. Other pipe sections tested the effects of insulation of the pipe on the long-term frost heave, as well as the effects of replacing the silt around an insulated pipe with gravel. Summer thawing of the frost bulb around the insulated pipe results in seasonal thaw settlement of the pipe, thus reducing the long-term pipe heave, at least for the warmer ground temperature environment at the Calgary facility.Thermal simulations of the frost bulb growth and predictions of frost heave using the segregation potential model agree well with the observations.Recent excavation of two frost bulbs in silty soil led to field observations of the interior of the frost bulbs, and subsequent laboratory analysis of frost bulb samples. Ice distribution was logged and photographed following excavation of each frost bulb. Key words: frost heave, pipeline, silt, mitigation, instrumentation, field observations.