Relationship between rain and/or meltwater, pore-water pressure and displacement of a reactivated landslide

In order to clarify the relationship between rain and/or meltwater (MR), pore-water pressure and landslide displacement, continuous monitorings were conducted at a reactivated landslide comprised mainly of weathered mudstone of Tertiary in age. An exponential relationship was found between the total amount of MR at each event and the amount of pore-water pressure increment integrated by time (impulse of pore-water pressure). In addition, as the total MR increased, the difference between the minimum and maximum values of pore-water pressure for each event (fluctuation range of pore-water pressure) also increased, but the intensity of MR had little effect on the fluctuation range of pore-water pressure. The correlation coefficient for the fluctuation range of pore-water pressure and cumulative landslide displacement, and that for the impulse of pore-water pressure and cumulative displacement were similar, but were only 0.57 to 0.66. On the other hand, the correlation coefficient for the total MR and cumulative landslide displacement was large (0.65–0.69). Cumulative landslide displacement was very highly correlated with effective MR (which shows the estimated water content in the ground) for a half-life period of 4 days, and correlation coefficients were 0.89–0.92. Thus, the displacement characteristics of this reactivated landslide which has a long history of landsliding can be explained using the hydrological factor of water content rather than the hydraulic characteristics of pore-water pressure.