Flat-plate roof collapse of shallow caverns and protective measures: a case study of Longyou ancient siltstone caverns

Longyou rock caverns were found and were out of water in June 1992, which located in a small hill near to the north bank of Qujiang River, Zhejiang province, China. A series of flat-plate collapses occurred in the roof of cavern No. 24 from 30 September to 4 October in 2010; and finally, a daylight collapse appeared in the roof with a volume of 250 m<Superscript>3</Superscript>. Site investigation and laboratory tests on the surrounding siltstone indicate that the roof collapse can be attributed to the following adverse factors: (1) large span and shallow depth, (2) rock strength reduction due to water saturation, (3) rock weathering, and (4) dynamic loading caused by the walking of a large number of visitors. In order to protect the complete caverns Nos. 1–5 which are currently open to visitors, it is suggested to adopt integrated protection system, including (1) selecting the best tour routes and monitor system, (2) surface water drainage system, (3) beam–pillar supporting system, and (4) effective measures to slow weathering. Copyright Springer Science+Business Media Dordrecht 2015