ABSTRACT
Many rock pillars were adopted to support all large-span underground caverns in the Longyou Grottoes. Therefore, the stability of rock pillars is directly related to the overall security of caverns (Yang et al. 2010), which has attracted much attention of many researchers recently. Yang et al. (2010) deeply studied the distributing form, crosssection shape, crack fracture occurrence, and failure mechanism of rock pillars in the caverns of the Longyou Grottoes from qualitative to quantitative research by the field investigation, theoretical analysis and numerical simulation. They suggested that the irregular section rock pillars of non-uniform distribution not only could improve the stress distribution of the surrounding upper rock pillars and reduce the subsidence value of the roof, but also was beneficial to the overall stability of the caverns. At the same time, they also presented the back analysis of the long-term shear
the expanding and increasing of the roof cracks. Yang et al. (2005) considered the shear stress of each part for the No. 4-2 rock pillar in the No. 4 cavern in the Longyou Grottoes, and presented the back analysis method of the long-term shear strength on the ancient underground engineering, and they achieved good inversion results. Guo et al. (2006) selected the open vertical crack in the No. 1 rock pillar in the No. 1 cavern in the Longyou Niuchang to back analyze the long-term tensile strength of the rock pillars based on the maximum tensile stress theory. In addition, there are a lot of research results, such as the failure mode of the surrounding rock and rock pillars of the underground cavern group in Longyou, the roof fracture development on the rock pillars having an impact on the overall stability of the caverns (Li et al. 2005a), the destruction and weathering law of the surrounding rock and rock pillars under different water filling conditions (Li et al. 2010), as well as the engineering geological conditions and hydrogeological conditions related to the tensile or shear failure of the surrounding rock and rock pillars for ancient underground caverns in Longyou (Li et al. 2005b), in order to study and discuss the stability of the rock pillars and their influence on the stability of caverns from different aspects. According to the short-term unloading and loading condition of hydrostatic pressure because of pumping, dredging and water filling again from the No. 7 cavern in the Longyou Grottoes, the influence of hydrostatic pressure on the strength characteristics and stress states of the rock pillars is studied in this paper using the theoretical analysis method, including the stress, deformation, laws of tensile and plastic damage of the rock pillars under different loading conditions, to explore the effect of hydrostatic pressure on the strength and stability of the rock pillars.
