| With the rapid development of China's economy and transportation,the urbanization process is accelerating,and the demand for underground rail transit is increasing.The shield method has become the preferred method for urban tunnel construction because of its convenience in construction and low disturbance to surrounding areas.During the construction process,the shield tunnel inevitably passes through shallow land areas such as rivers and lakes,which may easily cause the tunnel to float.Aiming at the problem of tunnel floating,on the basis of summarizing the current status of related research,theoretical analysis and numerical simulation are used to study and analyze the shallow overburden tunnel under the river.The main research contents of this article are as follows:(1)Based on the Mindlin solution,the planar two-dimensional solution of the displacement of the stratum with the effect of buoyancy taking into account the loss of the soil is derived and compared with the numerical simulation results.Summarize the calculation method of the minimum overburden thickness of the tunnel under the requirement of anti-floating,and compare with the actual engineering design overburden thickness to verify whether the designed thickness meets the requirements of anti-floatability.(2)Establish a two-dimensional finite element model through Midas,analyze the influence of overlying soil thickness and soil elastic modulus on tunnel floating problem,and focus on the changes of segments and surface and deep soil under various factors.(3)Establish a three-dimensional finite element model in combination with the actual project to discuss the effects of grouting pressure,grouting layer thickness and driving pressure on the rise of segment and formation deformation,and study the changes of grouting pressure and driving pressure of segment and surrounding soil Sensitivity.By comparing the deformation of the tunnel stratum and the floating amount of the segment,reasonable construction parameters are determined.The results show that:(1)The calculation formula of surface displacement under the combined action of formation loss and buoyancy is close to the numerical simulation results,which indicates that the theoretical formula derived by this paper has certain reference significance.(2)Through the analysis of the thickness of the overburden,it is obtained that the rise of the pipe segment,the vertical and horizontal displacement of the ground surface are negatively correlated with the thickness of the overburden,and the anti-floating effect of the equal thickness of the overburden on the pipe segment gradually decreases with the increase of the thickness.(3)The floating amount of the segment and the vertical displacement of the soil layer are negatively correlated with the elastic modulus of the soil.With the increase of the elastic modulus,the influence of the elastic modulus per unit on the displacement of the segment and the soil gradually decreases.(4)The increase of grouting pressure and digging force will increase the floating amount of the segment,and the vertical displacement of the ground surface will increase accordingly;while the increase of the thickness of the grouting layer will reduce the floating amount of the segment and increase the surface settlement.For grouting pressure,the vertical displacement of the soil vault is the most sensitive to the grouting pressure change,followed by the segment floating,the minimum sensitivity is the soil arch bottom;for the driving pressure,the segment floating amount is vertical to the soil vault vertical Displacement is the most sensitive to changes in heading pressure.The sensitivity of the two is relatively close.The least sensitive is the vertical displacement of the soil arch.Therefore,in the process of shield excavation,it is necessary to strictly control the grouting pressure and the digging pressure,and plan an appropriate building gap to ensure the rationality of the thickness of the grouting layer. |
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