Long-term stability of large span caverns at the 1400-year Heidong quarry

Long-term stability of large span caverns is earnest but poorly understood in preservation of cultural relics. The life span of huge caverns is difficult to extrapolate from short period of monitoring or laboratory testing. A huge ancient quarry with 21 caverns whose original status is well kept over 1400 years was found in Tiantai County of South China. One of the caverns has an 81 m span which is far beyond the 50 m expectation on current knowledge. The tension at the core of long stability is the excavation speed versus deliberation. Here we show a unique technique of Digging Holes for Quarrying Vertical Flagstone (DQF) invented by ancestors to ensure the safety, which is much smarter compared to blasting and casting technique that commonly used after the Industrial Revolution. Furthermore, in addition to selecting competent massive rocks via cutting normally to and through faults, they adopted systematically trial adits, dome-shaped cavern, and disposal of waste rocks inside caverns for support. These ancient achievements mark a high level of quarrying in complex natural conditions with manpower. The results are positive to extend our knowledge in category design of cavern scale and stability assessment, and to some extent, they give solutions to the conflict between fast excavation with blasting and induced excavation damaged zone (EDZ) in surrounding rocks.