Water Inflow Prediction And Water-reducing Effect Of Grouting For A Deep Buried Diversion Tunnel Crossing Faults

With the rapid development of underground engineering construction in China,tunnel and other underground engineerings is faced with severe tests of complex structure,variable geological environment and frequently occurred disasters.Nearly eighty percent of major safety accidents in underground engineering construction is caused by water inflow and the improper disposal of geological disasters,which brings a high person casualties and economic losses.Water inflow has become one of the main geological disasters in tunnel construction.Safety accidents of water inflow caused by each kinds of bad geological structure and engineering disturbution effects gradually become the bottleneck which restrict the development of underground space construction in China.The total length of Longjinxi diversion tunnel in Fujian province is 13.842km.Water inflow,geothermy and rock burst are main technical difficulties in the construction process because of complex and changeable geological conditions.And the greatest difficulty and danger is the massive frequently water inflow during the construction.According to the survey report and the field investigation situation,the water inflow disaster factor of the tunnel is the faults,which doesn't belong to the routine karst tunnel water inrush.Therefor on the premise of sufficient tunnel site investigation of the engineering geological and hydrogeological conditions,the water inflow prediction of a deep buried diversion tunnel crossing fault is carried out in this paper to provide guidance and reference basis for the design and construction of tunnel under fault condition.The research results are mainly including:?1?Fault structure is divided into five regions with three zones,that when the tunnel passes through the fault structure,it will pass through the normal surrounding rock zone,the fault fracture zone,the fault zone,the fault fracture zone and the normal surrounding rock zone in turn.Based on the division,the tunnel rock mass structure characteristics and the hydrogeological characteristics are respectively analyzed,which lays the foundation of the analysis of water inflow law and forecast in tunnel passes through the fault.?2?A series of water pressure tests are carried out atthe 12+500 section near the F61 faults in Longjinxidiversion tunnel.The zone permeability coefficient variation law of fault zone and fault fracture zone are studied,and different regions seepage features of the three fault zones based on Gaussian function are obtain.On the basis of division theory,a method is put forward that the Darcy equations is adopted to describe water seepage in the ordinary surrounding rock zone,and the modified Brinkman equations is adopted to describe the water seepage in fault zone and fault fracture zone.A Darcy-Brinkman seepage model in fault is established based on the theory of fault zone with different regions,which provides a new method to forecast tunnel water inflow passes through the fault.?3?The improved Brinkman equation is adopted to study the flow law of groundwater in fault.Thecoupling calculation model of the typical Darcy seepage and the Brinkman rapid flow is established.Four fault influence factors of the fault dip angle,the fault zone width,the fracture zonewidth,the fault zone permeability and construction factors of different excavation location are selected to set up 23 conditions to carry out the water inflow numerical calculation,with five different fault dip angles are respectively 30°,60°,90°,120°,five kinds of fault zone width are respectively 1m,2m,3m,4m and 5m,five kinds of fracture zone width are respectively 5m,12.5m,20m,27.5m and 35m,three kinds of fault zone permeability are10^-11m²,10^-13m² and10^-16m²,and five kinds of excavation position arerespectively-31.5m and-11.5m,0m,11.5m and 31.5m away from the fault center.The influence law of the single fault to the tunnel groundwaterstress field,seepage field and the water inflow are obtained.The influence law of the single fault to the tunnel groundwater stress field,seepage field and the water inflow are obtained.?4?The influence law of the composite fault to water inflow in the process of tunnel excavation is further studied.By using the seepage coupling calculation model,water pressure,fluid velocity,and tunnel water inflow under five different fault cross positions is analyzed comprehensively.And the influence law of the faults different cross positions to tunnel surrounding water pressure field,seepage field,and tunnel water inflow is obtained.At the same time,the influence of construction step to water inflow when the tunnel passes throughparallel composite fault are studied.By studying characteristic of the overlap zone of the parallel composite fault,the water inflow condition are studied when the tunnel face in different position during the process of tunnel pass through parallel composite fault.According to the different surrounding rock conditions when tunnel pass through parallel composite fault,seven calculation conditions are carried out.And the change law of the tunnel groundwater stress field,seepage field and the water inflow are obtained under the tunnel pass through the parallel composite fault condition are obtained.?5?In order to quantitatively study the water reducing effect of grouting treatment in tunnel passes through fault,three factors which can influence the grouting effect are selecteded analyzed.The permeability values of grouting cycle are respectively 10^-12m²,10^-13m² and 10^-14m².The thicknesses of grouting circle are respectively 0.5m,1m,2m,3m and 4m.The advanced lengths of grouting circle are respectively 1m,2m,3m,4m and 5m.And thirteen kinds of grouting simulation conditions of composite cross faults are designed.And the change laws of underground seepage and water inflow of tunnel under different condition are studied.?6?Based on four kinds of water inflow forecasting theory,the atmospheric precipitation infiltration,groundwater runoff modulus method,groundwater dynamic research method and analytical method,the corresponding calculation formulas were adopted for water inflow prediction in tunnel.Hierarchical structure model for water inflow prediction is established,index weight value and membership degree value of water inflow forecasting factors were determined,tunnel water inflow was forecasted based on the fuzzy mathematics theory.The water inflow prediction results of the theoretical formula method,COMSOL Mutiphysics numerical simulation method based on Darcy-Brinkman flow calculation model and COMSOL Mutiphysics software,were compared with the field monitoring data.By analyzing the applicability and limitation of each water inflow prediction method,comprehensive prediction method in site was determined.Finally,according to the numerical analysis results,the grouting parameters are optimized,and the water-reducing effect of grouting is analyzed according to water pressure test and geological radar detection before and after grouting.