Research On Prediction Model Of Water And Sand Inrush In Water-rich Sandy Dolomite Tunne

Sandification of dolomite is a special geological phenomenon.The dolomite after sandification has the characteristics of loose and broken rock mass structure and deterioration of strength.In the process of tunnel excavation,it often faces problems such as difficulty in forming holes,poor forming quality,and landslides.Water and sand inrush hazard are also prone to occur in the water-rich tunnel section,which seriously hinders the normal construction of the project and threatens the safety of tunnel construction and operation.The geological conditions of the sandy dolomite cave section are complex,and there are many strata combinations that may cause water and sand inrush hazard.This paper takes the water and sand inrush event in the Xiaopu Tunnel in the Yuxi section of the Central Yunnan Water Diversion Project as an example.Analysis,based on the Mohr-Coulomb criterion,the prediction formula for the critical thickness of water and sand inrush in the water-rich sandy dolomite cave section is derived;the FLAC3D numerical analysis software is used to simulate the construction process of the sandy dolomite cave section,and the factors affecting the critical thickness of the outburst prevention structure are analyzed.,tunnel face displacement and tunnel water inflow,a catastrophe prediction model based on the evolution law of catastrophic critical thickness of outburst prevention structures is constructed,and the hazard indicators are determined based on the face displacement and the growth rate of water inflow.The adaptability and feasibility of the prediction model and hazard indicators are tested through actual engineering,which provides a basis for reasonably predicting the occurrence and prevention of hazard.The main results of the paper are as follows:(1)The rock mass structure and material structure after sandification of dolomite provide conditions for the infiltration of surface water and the storage of groundwater.Strong water-rich,high head and loose and broken severe sandy dolomite are the main reasons for the occurrence of water and sand inrush in tunnels.(2)The failure modes of sudden surge failure in sandy dolomite caves can be divided into two types:sliding type and shearing type.Insufficient anti-sliding ability of violently sanded dolomite as a filling medium or insufficient strength of strongly sanded dolomite as an antioutburst structure are the main internal causes of inrush hazard in the cave;The change of seepage field and the insufficient thickness of anti-outburst structure are the main external causes of the inrush disaster in the water-rich sandy dolomite tunnel.(3)The slope failure of the outburst-prevention rock mass in the sandy dolomite cave section is the overall shear failure.A geological model was constructed with strongly sandy dolomite as the outburst prevention rock mass and water-rich severe sandy dolomite as the hazard source body.Based on the Mohr-Coulomb criterion,the prediction formula for the critical thickness of the outburst prevention structure in the water-rich sandy dolomite cave section was derived.(4)Numerical simulation studies show that the critical thickness of the outburst prevention structure,the maximum extruded displacement of the tunnel face and the water inflow are positively correlated with the water head of the tunnel,and the dip angle of the interface with the rock layer first decreases and then increases;The internal friction angle and cohesion of the rock are negatively correlated with the critical thickness of the anti-outburst structure,the maximum extrusion displacement of the face and the water inflow.,cohesion and elastic modulus parameters have little effect on the simulation results.A method based on the parametric curve curvature value method to determine the sudden change point is proposed,and a prediction model for water inrush and sand inrush in a water-rich sandy dolomite tunnel under the comprehensive influence of multiple factors is fitted.The maximum extrusion water inflow growth rate of the face is 0.12,respectively.(5)The predicted value of the theoretically derived prediction formula for the critical thickness of the YX06+595.2 working face is 1.97m,and the predicted value of the numerical simulation fitting formula is 3.23m.According to the analysis of the water inflow of the YX06+745.8 working face,the water inflow growth rate before the disaster was 0.21.The results show that the calculated value of the prediction formula derived based on the overall shear failure mode is relatively small;the calculated value of the numerical analysis fitting prediction formula is more consistent with the actual engineering;the water inrush growth rate catastrophe index is closer to the actual.The proposed prediction model and catastrophe index have certain reference value.Suggestions and measures for preventing water and sand inrush hazard in the cave during construction are given.