Abstract:

 In order to analyze the influence of hydraulic fracturing in hidden karst on the safe thickness and fracture evolution of water resisting rock mass, a high-performance software GDEM-DAS based on continuum-discontinuum element method was used to carry out the three-dimensional numerical simulation. The critical thickness of water resisting rock mass is determined based on the displacement evolution law of working face, and the fracture degree, a dimensionless index, is introduced to quantitatively describe the fracture evolution law of water resisting rock mass during the excavation process. Based on numerical simulation, the changing curves of displacement and fracture degree were obtained when the water pressure is 1MPa, 2MPa and 3MPa. The numerical results show that: 1)The safe thickness of water resisting rock mass under different water pressure is almost same, and the value is equal to 7m. 2)There are inflection points in the curves of displacement and fracture degree, and the inflection point of fracture degree is 6m in front of the inflyelvsuection point of displacement, which shows that the displacement mutation will occur when the internal damage of rock mass reaches the catastrophe.3) Under the same simulation condition, the inflection points of displacement and fracture degree under different water pressure of karst cave are consistent, which indicates that water pressure is not the primary factor affecting the stability of water resisting rock mass.

Key words:

karst tunnels, CDEM; numerical simulation；water resisting rock mass;fractures degree, safe thickness