Sudden Rock Fall Prevention Methods and Improved Machine Operations for Excavation Above the Precipice at the Surface Quarry Operation

Abstract

Minowa Mine has been working in west area of Mt. Buko (1,304m above sea level) that is located in southeastern edge of the Chichibu Basin, the western part of Saitama Prefecture. Limestone is produced over 800,000ton a year for cement materials, aggregate materials and lime materials, etc here. Minowa Mine has three benches. One of them, Takeyama bench is situated in west corner of Mt. Buko. At the top bench of Mt. Buko, Minowa Mine, Ryoko Lime Industry Co., Ltd Une Mine and Buko Mining Co., Ltd Buko Mine have been operating in cooperation. It is very difficult to excavate Makuiwa, the huge precipice of north slope below Takeyama bench at the top bench. The excavation was started cautiously around the end of 2000 with setting up benches to prevent sudden falling rocks below the surface quarry. However, massive rock of about 3,000 meters cube, a part of Makuiwa came off and collapsed in April 2002. Moreover, fissure with fear of secondary collapse breaking out was found. Therefore we took preventive measures immediately against collapsing. Since then Makuiwa have been entirely excavated with the improved machine above the precipice with taking preventive measures against collapsing.