The response of pore water pressure to snow accumulation on a low-permeability clay landslide

A snowpack is known to affect landslide stability as the snow loading changes. Furthermore, the snowpack can have effects on the hydrological behavior in the landslide mass. To clarify the response of pore water pressure to snow loading, continuous field-based monitoring of hydraulic and meteorological factors in landslides was conducted for a deposit of extremely low-permeability “quick clay” in Mid-Norway. The pore water pressure increased during every snow-covered period. The pressure exhibited little response to meltwater and/or rain, but corresponded closely to changes in snow accumulation. The increase in pore water pressure during the snow-covered period was considered to be excess pore water pressure generated by undrained snow loading on the extremely low-permeability quick clay. The pore water pressure displayed a positive linear relation with the snow load, and the ratio of the increase in the pore water pressure to the snow load (rusnow) was 0.49-0.53. These values show that approximately half of the snow load contributed to the excess pore water pressure. Continuous field-based monitoring was also conducted for another landslide in relatively high-permeability deposits in Japan, where the pore water pressure showed a relatively low rusnow of about 0.15 and a different timing of the pressure peak. This comparative result indicates that the response characteristics of pore water pressure to the snow loading are strongly affected by the permeability of the landslide mass. Although the excess pore water pressure generated by the snow load theoretically had a negative effect on the slope stability, the value of excess pore water pressure at the monitored landslide was relatively too small to affect its stability.