Efficient Construction of Groundwater Level Observation Holes for Monitoring of Slope Disasters

Slope disasters caused by heavy rain are triggered by an increase in pore water pressure due to a rise in groundwater level. Therefore, by understanding the relationship between rainfall on the slope and rise in the groundwater level, the signs of a disaster are monitored in order to detect the possibility of slope disasters. For general groundwater level monitoring, a observation hole with a water level meter installed in the drilling hole is used. However, the installation of the observation hole by drilling requires procedures such as bringing in the machine and drilling by the boring machine, and due to budgetary concerns, it is often limited to implementation at several representative points. Therefore general method, even when the area where there is a risk of landslides blocks or surface collapse is wide, it is difficult to grasp the whole picture because the observation results are predicted from limited information. Instead of drilling, we will introduce a method of making a observation hole by inserting a φ10 mm water level meter into the screw weight sounding test hole. The screw weight sounding test is a test that can evaluate the hardness, tightness, and soil layer composition of the ground by measuring the number of rotations at the time of penetration, and can penetrate up to about 10 m. The work efficiency is good and it is possible to install at multiple locations in a day. The observation hole was installed on the slope using this method and the groundwater level rise was observed, it was confirmed that the groundwater level was formed near the surface layer in conjunction with the rainfall.