QUARRYING-INDUCED COLLAPSE IN 1997 AND SEISMIC RECORDS AT CHANGYU CAVERN RELICS SITE

Quarrying-induced collapse, an issue of particular concern in mining industry, is a typical form of man-made 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 are seldom undertaken. A huge collapse event occurred at the Biyutan mining cavern at Changyu Dongtian in Wenling city, China. It lasted for about 20 seconds and was observed and recorded on August 11, 1997. After the collapse, nearly 1.35×10⁶ m³ of rock blocks were left on the floor and occupied an area of about 31 380 m². the authors conducted a field survey on engineering geology, retrospectively analyzed the collapsing process through interviewing local residents and referring related documents, and identified the seismic records from surrounding seismic stations. The roof collapse is established at the Biyutan cavern that was excavated in massive tuff. The over excavation of several pillars substantially affected the stress field in cavern roof, which gave a rise to a local failure of the roof and then gradually developed into a widespread failure. During the collapse, outbursts of water and air shock waves resulted in loss of life and property within a distance of 150 m from the mine opening. The seismic records of Wenzhou Station 93 km south from the site revealed the collapse event, which is agreement with the energy transformation in site retrospective analysis on building failures and subject movement. This event reminds us that reasonable allocation of sufficiently strong safety pillars and installation of monitoring system are absolutely essential in underground quarrying operations to avoid overall failure and ensure the safety of the people nearby.