| This paper aims to study the behaviors around the excavation zone with possibility of water inrush hazards by using the principle of stress and seepage coupling.Theoretical and numerical methods of COMSOL Multiphysics are used in 27 models to analyze stress distributions,deformations and seepage conditions of surrounding rocks of the tunnel with different length and depth of excavation in consideration of continuous excavation in underground rock mass with high in-situ stress and complicated geological conditions of pore water pressure.Wide variation of hydromechanical situation is found in Excavation disturbed zone(Edz)and Excavation Damage zone(EDz).And a burning issue of high chance of water in-rush hazards,which may lead to heavy economic loss and collapse of the tunnel,is put forward when excavation is carried out near the water body.The main contents and results of this paper are shortly described as below:(1)In order to deal with the evolution phenomena in continuous and deep circular excavation,the hydromechanical phenomena was investigated by using Solid mechanics and Darcy's seepage law.Stress distribution,elastic stress-strain relationship,and effective Poro-elastic stress-strain relationship along with seepage law were taken into consideration in the theoretical analysis.Simultaneously,the failure criteria of rock mass using D-P and Mohr-Coulomb criteria and its effect by pore fluids using Biot's effective stress were applied in analysis.The suitable model with assumptions of reasonable coupling mechanism and failure criteria was established to make a research on the surrounding rock mass of the tunnel.(2)To obtain detailed influencing factors,numerical simulation was accomplished on assumption of the principle of hydromechanical coupling of the surrounding rock mass.And the stress,displacement and pore-water pressure evolution with different length of excavation were acquired under conditions of different depth,water pressure,size of excavation,location of water body,and strength of surrounding rock mass.And then the critical zone of stress evolution is observed around 20 m before and after monitoring point.Inverse proportion between stress and water pressure and direct proportion between displacement and water pressure are obtain in analysis.Moreover,the evolution of plastic region related to size of excavation indicates nonlinear function(y=x2-2x),andwith the reduction of the property of elastic modulus and internal friction angle the higher possibilities of evolution of plastic region is observed.(3)Safety assessment of water inrush hazard in weak rock mass(E=5.13GPa& ?= 27.55)is conducted to conclude that the critical safety distance of the excavation from water body was 30 meters by analyzing various finite element models with different location of water body.And pore pressure distribution,yield stress and displacement of the plastic zone are obtained from calculation models of surrounding rock grouting to prove that grouting in advance can effectively control the displacement of roof and floor.The results indicate that the horizontal displacement can be reduced by 23%,and displacements at roof and floor can reduce more than 50%.Therefore,grouting distance of 30 m in advance is effective to protect the stability of surrounding rock pre-reinforcement and prevent water inrush.In conclusion,it is a dynamic phenomenon that whenever there is continuous excavation in underground rock mass and sudden change in the stress,displacement and pore pressure have clearly showed that the pore water pressure played a great role in stability of surrounding rock mass.Therefore,to avoid the possible threat of water inrush hazard,maintaining the critical distance and grouting of the rock mass can be possible measures.Furthermore,details study of development of fracture and its flow are left for future works. |
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