Research On Tunneling Parameters And Settlement Control Of Shield Tunnels Crossing The River In A Section Of Qingdao Metro

With the upsurge of subway construction in Qingdao,the lines inevitably pass through rivers,buildings,bridges,etc.However,due to the strict requirements on settlement of above-ground structures,it poses a great challenge to subway construction.Because the settlement requirements of the above-ground structures are generally more stringent,it poses a great challenge to the construction of the subway.Due to the high construction safety and fast tunneling speed of shield tunneling method(including soft soil shield machine and tunnel boring machine),it is widely used in the construction of Qingdao Metro Line 4.Based on the shield tunneling interval between Shazikou Station and Laoshan No.6 Middle Station in the east section of Qingdao Metro Line 4,this paper uses theoretical calculation,numerical simulation,field test,mathematical statistics and multiple linear regression methods to control the surface subsidence and tunneling parameters.The main conclusions of the research are as follows:(1)Using the theoretical calculation and Midas GTS NX numerical simulation software,the necessity of taking reinforcement measures for the tunnel crossing the river is analyzed.The results show that certain reinforcement measures should be taken before the shield tunnel crosses the river in this area.(2)The numerical model before river bed reinforcement was established by Midas GTS NX numerical simulation software,the surface settlement law of the tunnel crossing the river was analyzed,and the reinforcement range of the river bed was studied.The results show that the longitudinal surface subsidence increases with the decrease of the buried depth of the tunnel;the variation law of the lateral surface subsidence conforms to the Peck formula;the variation law of the surface subsidence over time is that it first slightly uplifts and then subsides,and the third stage accounts for the proportion of the total subsidence.The largest;the reinforcement range of the river bed is that the central axis of the right-line tunnel extends 25 m to the left and12.5m to the right.(3)Using the method of combining mathematical statistics and theoretical formulas,the tunneling parameters of the test section are studied.The theoretical control formulas for grouting pressure,grouting volume,tunneling volume,total thrust,cutter head torque and soil tank pressure are obtained for the water-rich sand and clay stratum.And obtained 9 kinds of tunneling parameter control intervals corresponding to the shield tunnel crossing the river basin.(4)Using the method of mathematical statistics,the control effect of 9 kinds of tunneling parameters in the river section was evaluated.The results show that the control effect of the tunneling parameters in the river basin is good,and the control interval is reasonable.And through the multiple linear regression analysis,a more suitable prediction model for the driving speed of the water-rich sand-stick composite strata in the river basin is obtained.(5)Using Midas GTS NX numerical simulation software,the numerical model of the river bed after reinforcement was established,the law of tunnel surface settlement was studied,and the settlement control effect and the effectiveness of reinforcement range were evaluated.The results show that the vertical surface subsidence does not increase with the smaller depth of the tunnel;the change curve of the lateral surface subsidence is approximately normal distribution;the change law of the surface subsidence over time is first slight uplift and then subsidence,and the third stage accounts for the total subsidence.The proportion of the river bed surface subsidence is good,and the scope of the reinforcement area is reasonable.(6)Using the method of mathematical statistics,the measured and simulated values of the surface subsidence of the 150 th ring are analyzed.The results show that the maximum surface subsidence of the measured data and the proportion of the subsidence in the third stage are both smaller than the numerical simulation values,which can verify that the reinforcement effect of the river bed is good;The lateral surface subsidence curve of the measured data and the numerical model is consistent with the change trend of the surface subsidence curve over time,which can verify the correctness of the numerical model.