Experimental Study on the Controlling Method of Extruded Ice on Subgrade Slope in Sichuan-Tibet Cold Region

The groundwater and negative temperature conditions along the alpine areas of the Sichuan-Tibet traffic corridors are conducive to the development of extruded ice, which is a threat to construction and operation safety. The controlling method of extruded ice mainly aims at building waterproof or drainage system to prevent the exposure or the over-high level of groundwater. Through backfilling the seepage layer with permeable materials to dredge the groundwater, or laying waterproof layer to cut off the groundwater, the formation of extruded ice can be slowed down or eliminated, thus to prevent the damage to the road subgrade. Indoor analogue models were conducted to analyze the effectiveness of three different controlling methods. The results showed that extruded ice would gradually develop when the frozen depth is greater than the depth of groundwater level. Using gravelly coarse sand as the backfill seepage layer to accelerate the drainage of groundwater was an effective way to reduce the pore water pressure. Compared with the untreated natural slope, the volume of extruded ice is reduced by 85.4%, and the pore water pressure is reduced by 46.2%. If using pebble soil as the backfill seepage layer, the size of extruded ice reduced by 93.9% and the pore water pressure reduced by 58.1%. If using waterproof geotextiles to cut off the groundwater, the volume of extruded ice reduced by 97.5%, but the pore water pressure increased. Considering the sufficient pebble (gravel) materials along the Sichuan-Tibet road, it is recommended to use permeable pebble (or gravel) as the backfill layer to accelerate groundwater drainage, plus waterproof geotextile laid between the backfill layer and the ground to prevent groundwater infiltration, so as to control the subgrade extruded ice disaster.