Crack Cause in the High Slope of Chinese Ancient Copper Mine Relics: A Three-Dimensional Non-Linear Finite Difference Analysis

Preservation of world heritage and archaeological sites depends largely on better understanding of the soil and rock conditions and their alterations caused by natural and anthropogenic forces. This study took the Tonglushan Ancient Copper Mine (TACM), a key cultural relic site under the state protection in China, as an example to discuss that detailed field and numerical studies of rock mechanics can help understand the crack genesis of high slopes at the site, thus better protecting the relic site from damage. Several cracks occurred in the high slopes at TACM, thus in-situ investigations have been conducted to figure out the factors inducing the cracks. After that, a three-dimensional non-linear finite difference numerical model was applied to investigate the factors affecting the deformation and rupture of the high slopes at TACM. The numerical study revealed that certain mining activities in the copper mines around the TACM relic site could be responsible for the generation of cracks. Five typical mining and excavation plans have been simulated via numerical models; meanwhile rational deformation and failure criterions were determined, according to which, case-5, including eight horizontal tunnels sequentially excavated at different elevations, was found to be the most reasonable hypothesis to explain the generation of cracks and failure of slopes. Case-5 involved applying the SPSC (Sill Pillars Sublevel Caving) method to excavate the ore bodies located at the foot of the slopes and to subsequently backfill the empty chambers after the closure of mining activity. Finally, recommendations were given based on this study to remedy the generation of cracks and better preserve the TACM.