| With the rapid development of the national strategy and economy,the demand for transportation is getting higher and higher.Our country is a mountainous country,especially in the southwest of the mountains,plateaus,mountains,in order to ensure the best alignment of the road,will build more roads and railway tunnels.When the tunnel is deeper,bigger and longer,accidents occur frequently in the process of tunnel construction,especially the water inrush.Tunnel gushing water,easy to cause the tunnel construction interruption,stop to delay the construction period,improve the project cost,even in the tunnel support or operation after the tunnel damage,reesulting is greater loss of life and property.Based on the construction of second meters' long tunnel-Micangshan tunnel in China.Based on expounding the Micangshan tunnel site engineering geological conditions and hydrogeological characteristics,fracture characteristics,analysis of surrounding rock of tunnel area characteristics,fissure water seepage coefficient of spatial distribution characteristics of tunnel area,stress field distribution and stress field characteristics of the tunnel axis.Using the SEEP/W module in Geo-studio simulation analysis of the tunnel area and groundwater seepage characteristics of underground water,were analyzed using FLAC3 D fluid solid coupling in dolomite and diorite,based on the analysis of Micangshan tunnel with different lithologic fluid solid coupling characteristics.Based on the typical water inrush phenomenon in Micangshan tunnel,the characteristics of water inrush are summarized,and the generalized geological model is established.The main research results are as follows:(1)According to the seepage effect,the surrounding rock of the Cangshan tunnel area is divided into the water conducting fracture,the non water flowing fracture and the water storing fissure.According to the seepage characteristics of fractured rock mass,the surrounding rock structure of the Cangshan tunnel area is divided into loose structure,cataclastic structure,layered fracture structure and massive rock mass.The permeability coefficient of rock mass decreases with the increase of buried depth,and the permeability coefficient is very different in the tunnel.(2)Using the SEEP/W module in Geo-studio to simulate the groundwater head and groundwater seepage in the tunnel area,it can be found that the underground water head of the tunnel site varies with topography,and the overall groundwater head is higher(800m).In the Karst Section,the groundwater hydraulic gradient is larger,the groundwater seepage speed,in non Karst Section,the groundwater hydraulic gradient,seepage velocity is slow.But in Karst and non karst contact zone by the geological structure,groundwater seepage velocity increases.(3)The stress field of the Micangshan tunnel is formed by the superposition of the tectonic stress and the stress field in the horizontal direction.The magnitude of the three principal stresses follows the SH>SV>Sh,and the maximum principal stress and the burial depth show a positive correlation.The axis position of Micangshan tunnel is in the high stress level,the maximum principal stress is about 15~32MPa,under the influence of the buried depth control and the geological structure such as fault folds,the in-situ stress field increases in the axial region of the syncline,and decreases in the fault fracture zone.(4)Numerical calculation of fluid solid coupling in 6 cases of dolomite and diorite using FLAC3 D,it can be found that:the pore water pressure has little effect on the permeability coefficient of surrounding rock,and is proportional to the height of the head and buried depth of the surrounding rock;Due to the change of seepage field caused by the excavation,the water pressure difference is generated around the tunnel,a shape similar to the horseshoe shaped water funnel is formed in finally;After the excavation of the tunnel,the stress field is redistributed,and the stress concentration of the SZZ direction stress occurs at the side wall,and the stress concentration of the SXX direction stress occurs at the vault and the arch bottom;Effective stress with head increased,the effect of the seepage field of surrounding rock can significantly reduce the effective stress,in considering the seepage effect,due to the variation of pore water pressure in the surrounding rock,the surrounding rock changes the effective stress in the rock will reduce the porosity,which leads to greater than that without considering the seepage effect when the settlement of vault.(5)Through the analysis of water inrush site engineering geological conditions and hydrogeological characteristics,combined with water gushing phenomenon,analysis view that K43+190 and XZK0+220 on water inrush mode for hydraulic fracturing,K41+720 water inrush model for tunnel face instability.The water gushing in the process of hydraulic fracturing type water inrush has obvious precursor and process.The instability of tunnel face type water inrush has no obvious precursor,sudden with the water inrush.(6)The hydraulic fracturing water inrush is divided into tension shear composite failure mode and compression shear composite failure mode,the crack stress intensity factor considering the open crack and the pore water pressure,set fracture criterion,the formula of critical water pressure for fracture under tension shear and compression shear failure modes is derived,based on the Bernoulli energy equation,the instantaneous maximum flow velocity of hydraulic fracturing is deduced,finally,in view of the two failure modes,it is considered that under the action of natural forces,the shear failure mode is generally occurred.The face of outburst prevention layer thickness is divided into excavation area and safety area of two parts,considering the water weakening effect caused by the long term effect of fluid solid coupling on the thickness of the safety zone,the water weakening function is introduced,according to the system function,combined with catastrophe theory,derived from the working face safety zone thickness formula,and then get the face of outburst prevention layer thickness formula. |
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