Study on deformation mechanism and reinforcement measures of flat-top grotto roof

Abstract

With the intensification of global warming, the frequency and intensity of extreme rainfall events continue to rise, especially unstable precipitation, which poses a significant challenge to the stability of grottoes. The variations in water pressure and humidity induced by rainfall exacerbate the propagation of fissures in the roof plate, further compromising the structural integrity of the grotto's roof. This study takes the Dazu Rock Carvings in China as a case study, utilising Rayleigh wave imaging monitoring, theoretical analysis, numerical simulation, and on-site multi-dimensional monitoring methods to reveal the mechanisms behind the formation of fissures in the grotto roof and the deformation behaviour under both natural and rainfall conditions. Based on these findings, corresponding support strategies are proposed. The results show that the fissures in the grotto roof are primarily caused by the settlement deformation and tensile-shear failure of the surrounding rock. Rainfall increases the tensile stress on the roof plate, further exacerbating the fissure propagation. In addition, the formation of a cavity on the southern side accelerates the instability of the roof. The concentration of tensile and shear stresses causes instability in the grotto sidewalls near the cavity, and rainfall further intensifies this trend. To mitigate the expansion of fissures in the roof plate, the proposed reinforcement strategy utilises the bearing capacity of the overlying rock layers to support the roof while minimising interference with the sculptures inside the grotto. This study not only helps clarify the evolution of the roof damage process but also provides theoretical guidance for formulating appropriate support strategies.