The Une Mine is located in the Chichibu region of Saitama Prefecture, Japan, and excavates limestone from the top of the Mt. Buko using the bench cut method. The scale of the final rock slope when mining operations ends will be 800 m high and 5 km wide; therefore monitoring devices such as the Automated Polar System and Global Positioning System have been used to monitor the movement of the slope surface. In addition to these slope surface monitoring, detailed monitoring devices were installed inside the rock slope to clarify the cause of displacements of the Une Mine's rock slope that have occurred since September 2007. Long-term monitoring data such as groundwater level and crack gages inside an observation drift have shown that groundwater fluctuation due to rainfalls could adversely effect on the displacements of the rock slope. Therefore, the drainage of groundwater from the rock mass and the prevention of infiltration of rainfall into the rock mass were considered to be effective countermeasures. Since 2012, the Une Mine has implemented various countermeasures, including drilling drainage holes from the slope surface and observation drifts, well pumping, and paving work on the mine road to reduce risks resulting from groundwater rise. Moreover, deep steel pipes and retaining rock piles were constructed to reinforce the shear resistance of possible planes of weakness in the lower part of the final slope. As a result of the series of countermeasures for the displacements caused by rainfall and groundwater fluctuations, the rock slope of the Une Mine is now in a stable condition. In addition, a simulation study on the prediction of groundwater behavior by multiple regression analysis suggests that the groundwater level will be well-controlled, even at heavier rainfalls than those recorded in the past.
