CAUSE ANALYSIS OF SNOWMELT-INDUCED EXPRESSWAY SLOPE FAILURE THROUGH LABORATORY TESTING

Snowmelt in early spring is one cause of slope failure and landslides in snowy regions. The infiltration of meltwater into a cut slope along an expressway plays a critical role in reducing resistance to sliding. Despite its significant impact on snowmelt-induced slope failure, snowmelt runoff process has not been addressed in most specifications. This paper examines the case of a recent cut slope failure in the Hokkaido Expressway in the snowmelt season, and describes how snow melts and how meltwater infiltrates the ground to destabilize the cut slope. Snowmelt runoff tests were conducted both inside and outside of the laboratory and these tests focused on the fact that when a small snow block melts, meltwater drips only from the lowest part of the block. As part of the tests, snow blocks were placed on two slopes made of sandy soil. While one slope was completely covered with snow blocks, the other slope was covered on the upper part. As the result of the tests in the former case, meltwater moved downslope and flowed out from the snow layer, leaving the soil slope in a sound condition. In the latter case, meltwater flowing out of the lowest part of the snow layer infiltrated into sandy soil, resulting in a failure. The paper discusses how snowmelt processes similar to those observed in the laboratory tests can be seen on natural slopes. Since the site of the expressway cut-slope failure is located at the lower end of a snow-covered area of an expressway cut slope, it can be inferred that phenomena similar to those observed in the laboratory occurred at the slope failure site.