Experimental study on prevention measures of extruded ice on highway subgrade slope in Sichuan-Tibet cold region

Extruded ice is a common disease in road engineering in Sichuan-Tibet cold region, which seriously threatens the safety of road construction and operation. Preventing groundwater from being exposed to the surface or the groundwater level being too high can slow down or eliminate the formation of extruded ice. Field investigation and satellite map identification show that extruded ice in Sichuan-Tibet cold region is mainly overflow type. The prevention effects on extruded ice of backfilling with gravelly coarse sand or pebbles to dredge groundwater and laying waterproof geotextiles are analyzed by indoor physical simulation experiments. The results show that extruded ice will gradually form when the frozen depth is lower than the depth of groundwater level. Backfilling seepage layer with gravelly coarse sand or pebbles can accelerate the discharge of groundwater and reduce the pore water pressure effectively. Compared with the untreated slope, the volume of extruded ice is reduced by 85.4% and 93.9% respectively, and the pore water pressure is reduced by 46.2% and 58.1% respectively. By blocking groundwater with waterproof geotextile, the volume of extruded ice is reduced by 97.5%, but the pore pressure will increase. Considering the sufficient pebble (or gravel) materials in Sichuan-Tibet alpine region, it is recommended to use permeable pebble (or gravel) as backfill layer to accelerate groundwater drainage and control extruded ice disease in subgrade slope. And waterproof geotextile is recommended to be laid on backfill layer. The research results can provide reference for the prevention of extruded ice in Sichuan-Tibet traffic roads.