Research On The Characteristics Of Frost Heaving And The Reinforcement Of Shield Lauching In The High Water-Rich Sandy Soil

At present,traffic congestion has appeared in major cities in China,which seriously affects the national economic development and people's happiness index.Thus,there is a lot of development of underground space in China,in which the construction of shield method is widely used in metro construction with the advantages of minimal impact on environment,pipeline and adjacent buildings.However,over the years,a number of major accidents have occurred between the shield lauching and the receiver,and the construction accidents occurred most frequently.In view of the reasons mentioned above,take the reinforcement method of shield lauching and excavating control engineering of Shuangta west street of Taiyuan Subway Line 2 as example,Safety construction innovation is carried out by referring to shield launching reinforcement methods.By combining theoretical analysis,laboratory tests,numerical calculation and field measurement,The reinforcement method and scope of shield lauching are studied.This paper mainly focused and drew the conclusions as follows:(1)The experiment of frost heave and thawing collapse of soil mass was carry out under the condition of limited deformation at the around and bottom of the specimen by the multifunctional experiment system.The variation rules of frost heave,thawing collapse and water migration are analyzed.Experimental research shows that: The frost heave quantity of the four kinds of soil samples is different,but the change trend is consistent with freezing temperature.With the decrease of freezing temperature,the frost heave amount of soil sample increases gradually and finally tends to be stable.The curve shows obvious phasing.It is divided into slow frost heave stage,fast frost heave stage and stable frost heave stage.Load has obvious inhibition effect on frost heave.The larger the load applied on the top of the sample,the smaller the frost heave and the greater the inhibition.With the increase of frost heave,the melting weight increases.(2)The method of sorting and comparing the reinforcement effect of the soil mass at the shield lauching is proposed for the first time.Finally,two schemes of vertical freezing method or vertical freezing + steel sleeve reinforcement are put forward to reinforce at the shield lauching.In addition,the reinforcement range of the west street of the Twintowers is checked and simulated by the vertical freezing closed-loop reinforcement method.Through in-depth analysis of the deformation of the soil body after the excavation of the tunnel door,the deformation law of the soil body after the shield tunneling,the deformation law of the pipe segment and the deformation law of the house,the reinforcement scope using the vertical freezing method is finally determined.The numerical simulation results show that the displacement of the soil mass(along the X,Y and Z directions)decreases gradually with the increase of the longitudinal reinforcement length after the excavation of the portal.After the reinforcement of 6m,the displacement of the soil mass is basically unchanged and close to zero with the increase of the reinforcement length.With the increase of the longitudinal reinforcement range,the width coefficient I(the distance from the center line of the tunnel to the inflection point)of the surface subsidence tank decreases gradually.After the tunneling of single and double tunnels is completed,the displacement of the soil mass along the Z direction gradually decreases with the increase of the longitudinal reinforcement range.After the reinforcement of 6m,the deformation of the soil mass is basically unchanged with the increase of the reinforcement length,and eventually tends to be stable.With the increase of the longitudinal reinforcement range,the vertical deformation of the pipe segment gradually decreases after the reinforcement of 6m.With the increase of the reinforcement length,both the floating amount of the lower part of the pipe segment and the compression amount of the upper part of the pipe segment are basically not changing.The reinforcement at the beginning of shield construction plays a certain role in the deformation of the house.With the increase of the longitudinal reinforcement range,the tilt rate of the house starts to decline and eventually becomes stable.When the longitudinal reinforcement scope remains 12 m,the above deformation decreases gradually with the increase of the transverse reinforcement scope.When the transverse reinforcement is given a certain condition,the deformation basically does not change.(3)It is proposed for the first time that non-closed-loop reinforcement is adopted to reinforce the shield lauching,which is mainly suitable for the upper soft and lower hard strata.In addition,numerical simulation is carried out on the reinforcement range of the west street of the twin towers under the condition of vertical freezing and non-closed loop reinforcement,and the non-closed loop vertical freezing reinforcement range is determined.(4)The comparative analysis and research on the reinforcement situation of shuangta west street with closed loop reinforcement or with non-closed loop reinforcement are carried out.It is concluded that the influences caused by the two reinforcement methods are not significantly different,and 95% of them can be judged that there is no difference between them.(5)The measured values of freezing temperature at the shield lauching of the west street of twin towers were studied.The freezing stage was divided into two stages: the first stage was active freezing stage,and the second stage was maintenance freezing stage.