| Underwater tunnels are widely used in the transportation industry because they are not subject to meteorological conditions,do not affect shipping,and have high strategic significance.Shield tunneling is the most commonly used method for underwater tunnels.It is moving toward large depth,large sections,and long distances.Nowadays,many in the construction of tunnels,shields with large diameters(greater than 14m)were used and gradually became the mainstream technology in the construction of underwater tunnels.The diameter of the tunnel through the Yellow tunnel in Ji'nan is 15.76m.It is the first large diameter shield tunnel in the Yellow River which contains the highway and rail transit.It's one of the largest shield tunnels in the country.Based on the tunnel construction of the super large diameter underwater shield tunnel,the risk analysis is carried out on the basis of the Ji'nan Ji Luo road tunnel.The following main conclusions are obtained.(1)According to the engineering geological conditions and the surrounding environment,it is the three major risk sources for the project to determine the initiation and reception of the shield,the the Yellow River dike under the shield and the high speed Viaduct under the shield under the shield of Ji'nan.(2)Firstly,the longitudinal reinforcement range of end soil under different safety factors was calculated in light of elastic thin plate theory,and the strength and stability of the soil were calculated by means of strength theory and sliding instability theory.Secondly,the transverse reinforcement range of end soil of shallow shield was determined by means of Terzaghi's theory of rock pressure.Then,the influence of different reinforcement ranges on the surrounding environment was analyzed via FLAC3D modeling.Finally,from the perspective of economy and stability,the reinforcement scope of the end soil is determined,and the perfect technical measures are made to ensure the safety of shield launching and reaching.(3)Firstly,the disturbance mechanism of shield construction,the cause of formation loss and the diachronic law of ground settlement are analyzed.According to the superposed Peck formula of the double track tunnel,the maximum value of ground settlement is calculated to be-9.016mm.The three-dimensional finite element model of the construction phase of the double line shield tunnel is established by using the Midas finite element software.The results are in agreement with the Peck formula,and the prediction value of the maximum surface settlement of the project is obtained.Secondly,the two-dimensional finite element model of seepage calculation is established,and the maximum escape ratio is reduced within the allowable range,and the seepage flow is very small within the design condition.It is concluded that the water inrush accident in the section of the suspension river will not appear on the section of the river.Finally,the special construction plan of shield tunnel crossing the the Yellow River embankment under the control of shield tunnelling parameters,two reinforcement grouting and monitoring measurement is put forward.(4)It is determined that the failure of the pile-soil balance system is the cause of the pile foundation deformation.The relationship between the bearing capacity of the pile foundation and the friction resistance of the pile side and the pile end is the main determinant of the settlement of the pile foundation.The numerical model is set up by Midas to analyze the effect of single and double line shield construction on the pile foundation and soil deformation.The results show that the maximum deformation value of the pile is 4.9mm,which meets the requirements of the standard.And put forward strict control of tunneling parameters and timely grouting control measures. |
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