Limestone Mining and Slope Management at Mt. Buko

Abstract

The limestone deposit of Mt. Buko, located in the Chichibu region of the Saitama Prefecture, is being mined by Chichibu Taiheiyo Cement, Ryoko Lime Industry, and Buko Mining companies limited. In 1974, the three mining companies made agreement on the cooperative mining operations by bench-cut from the top of Mt. Buko and organized “The Task Group for Research on Rock Slope in Chichibu Area” or shortly “Chichibu Zanken” in Japanese. Since the scale of the final rock slope at the end of operations will be 800 m high and 5,000 m wide, the most important and critical issue of Mt. Buko operations is the stability management of the huge rock slope. The cooperative production started in April of 1981 and at the end of March 2017, the 36 years long cooperative operations mined out about 248 million tonnes of limestone. The mechanical behavior of the Mt. Buko's rock slope has been monitored by several kinds of devices and methods since November 1994. In September 2007, a heavy rainfall of a typhoon caused unprecedentedly distinct but short-term movements in some part of the rock slope, which made the three mining companies intensify monitoring and prompt groundwater drainage from the rock slope. In order to reduce permeation of rain into limestone, paving works of roads on the rock slope are being carried out. Moreover, twenty three steel pipes (80 m long × 600 mm in diameter) were piled into the rock slope and retaining rock piles of total weight of some 2.4 million tonnes are being constructed to reinforce the sher resistance of invisible planes of weakness.