Study On Dynamic Prediction To The Water Inflow Of Sandu Tunnel During Construction

In recent years, with Chinese rapid economic development, traffic facilitiesbecome an important factor of economic growth, the perfection of road network needto build lots of tunnels through mountains. However, the tunnel construction may leadto water inrush disaster, it may cause the delay of construction period and evencasualties, such engineering accidents is too numerous to mention one by one. Toreduce or even eliminate losses brought by the water gushing, predicting in advanceis necessary and some prevention measures must be done. Therefore，it has veryimportant significance to predicte gushing water timely and accurately.Sandu Tunnel is the control engineering of Guiyang-Guangzhou railway. Thetunnel is located in Guizhou Province, Qiannan Duyun City. Total length is14665m.The tunnel goes through6folds and13faults. The tunnel area geological condition iscomplex, formation lithology is various,which includs a variety of karst and karst.Based on the research of hydrogeological condition, we got the groundwatertypes, water-bearing rock group characteristics and the degree of karst development.Combined water chemistry experiment, master the recharge, runoff and dischargerules of groundwater.According to the information obtained by field investigation,statistic and analysis of the inflow of water monitoring data was done. Masterdynamic situation of the tunnel construction. Dynamic tunnel water inflow and thechange process of tunnel area groundwater flow dynamic was simulated and analysedfor construction process by using Visual Modflow groundwater numerical simulationsoftware. And the following conclusions are obtained.(1) The study area belongs to dissolution grave peak depression and mountainlandscape with erosion structure shape. recharge, runoff, drainage of groundwater ismainly affected by the landform.Groundwater is mainly recharged by atmospheric precipitation,and run off through the surface gully or underpass.The recharge areasmainly are with high altitude, unobstructed runoff path,short cycle,and which waterrock interaction is weak. Groundwater system in the study area is divided intotwo,which respectively attached to Dongting Lake–Qingshui River Basin and PearlRiver--Duliu River Valley. These two systems can be divided into2and3secondaryunit in natural conditions.(2) Groundwater in the tunnel area mainly occurs in the karst strata and fracture,fissure zones of ol O1t O1h and O1d. The main types of groundwater include karstwater and bedrock fissure water. Fold and fault groundwater-rich zones distributed inKarst Stratum，in which water bearing condition is good，is the dominant channelseepage for groundwater.When these kind of segments are being excavated, waterbursting comes easily.And the prevention measures should be done.(3) From the view of research area, there are and only two groundwater systemssempre. Tunnel construction changed the seepage field nearby,but it did not overturnthe macro seepage law of the study area. The regional underground watershed extendalong the ridge (Dalupo、Zhaozi Mountain、Niupipo、Paijiangpo、Longquan Mountain)from southwest to northeast. While Qingshui River and the tributary of Duliu Riverare still the drainage datum plane of the groundwater systems in the west and eastsides.Without considering the tunnel water-resisting support and auxiliary tunnelexcavation interference, level line nearby both ends of the tunnel goes from outwardto inward gradually. As the tunnel constructed,the boundaries of groundwater systemgoes away to the west gradually.At the same time,the boundaries between sub unitspassage to the north and south sides constantly.(4)Use Visual Modflow numerical simulation software to simulate the process oftunnel excavation. The dynamic water inflow and seepage flow field dynamic processin construction process was predicted，and some conclusions are reached in thefollowing:To the seepage field, with the advance of construction, equivalent head appearednear tunnel elevation intensively. Seepage field was disturbed,and the influence scopewas approaching to the tunneling direction. Water level gradually droped near thetunnel line. However, as water-resisting support follow-up, seepage field is graduallyrestored in a few months.While with time goes,the form of seepage field has nosignificant change to the excavated section. And ground water level basicallymaintains stable. To the water inflow,in the main section of tunnel goes roughly with upwardtrend in the process of construction. However,two segments in import section showedobvious rise phenomenon. Analysis shows that,the part of faults and karst developedso well,that is the root cause of water inflow spurt.The water inflow in flat guide andtransverse hole is relative stability to that in main hole,and it fluctuates basicly withthe changes in rainfall.It shows that the water inflow of flat guide and adit is mainlyinfluenced by precipitation. The groundwater seepage field surrounding is relativelystable.Total water inflow goes roughly by upward trend，and it began to fall after theimport section was completed.It could be estimated that in a period of time after thecompletion of the tunnel,variation of the total water inflow in tunnel will be similarwith auxiliary tunnel.Groundwater level is going into a relatively stable state, and willbe mainly affected by precipitation and evaporation.