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Mining Induced Collapse in 1997 and Seismic Records at Changyu, SE China
Quarry induced collapse, an issue of particular concern in the mining industry, is a typical form of manmade disaster. Identification of the morphological characteristics of such collapses is commonly based on seismic records but comprehensive studies regarding the mechanism and energy conversion mode utilizing the seismic record is seldom undertaken. A huge collapse event at the Biyutan mining cavern at Changyu Dongtian in Wenling city, China, lasting for about 20 seconds, was observed on August 11, 1997. After the collapse, nearly 11 million m3 of rock blocks were left on the floor. By conducting a field survey on engineering geology, retrospectively analyzing the collapsing process through interviewing local residents, referring to related documents, and identifying the seismic records obtained from 3 surrounding seismic stations, it was established the roof collapse at the Biyutan cavern, excavated in massive tuff, was due to over excavation of several pillars, which substantially affected the stress field in cavern roof giving rise to a local failure of the roof that gradually developing into a widespread failure in an area EW 800m long, SN 460m wide. During the collapse, outbursts of water and air shock waves result in loss of life and property within a distance of 150m from the mine opening. This reminds us that reasonable allocation of sufficiently strong safety pillars and installation of monitoring system are absolutely essential in quarrying operations to avoid overall failure and ensure the safety of the people nearby.