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Introduction, with the increasing economic and population growth in China, more and more urban traffic problems are urgently needed to be solved
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In the eastern and coastal areas of China, the stratum where the urban area is located is mainly soft soil
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The environmental impact and underground space utilization must be considered in the construction of underground engineering
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Therefore, the trenchless technology such as pipe jacking or shield with small clear distance is more and more popular
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At present, there are many difficulties in the design and construction of large section rectangular pipe jacking tunnel
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The most important thing is how to select the clear distance of the tunnel, improve the utilization rate of underground space and ensure the safety of the existing structure environment in the construction process
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Therefore, it is very important to control the settlement of surrounding buildings and surface pavement
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Due to the similarities between pipe jacking construction and shield construction, both belong to trenchless technology
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Therefore, some theoretical and environmental control research results of shield construction can be used as reference for pipe jacking tunnel
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There are many research results on the surface settlement caused by shield tunnel construction
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The research on pipe jacking tunnel construction includes: literature [7] ~ [10] studies the influence of pipe jacking construction on the deformation of surrounding soil; literature [1L], [12] introduces the monitoring and control of curve pipe jacking settlement; literature [13], [14] introduces the settlement control of embankment and underground pipeline in pipe jacking construction; literature [15] introduces pipe jacking settlement The analysis and control measures of this problem
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Have you learned a lot about tunnel construction? To sum up, the numerical simulation analysis of horizontal and vertical ground settlement in the construction process of small clear distance pipe jacking tunnel group in the prosperous urban area of soft soil layer is rare, so this paper will rely on a soft soil pipe jacking tunnel project, using three-dimensional finite element numerical simulation method, through setting different working conditions to study: ① the influence of different clear distance of pipe jacking tunnel on horizontal ground settlement Secondly, the influence of different follow-up distance on the surface settlement above the longitudinal axis of the first tunnel is analyzed, and the calculated results are compared with the measured data
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The conclusion has great engineering application value
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1
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Project introduction and model overview 1.1 project introduction relying on a city double hole small clear distance pipe jacking tunnel project, the total length of the project line is about 25.83km, double hole tunnel, pipe jacking method construction
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The net distance between tunnels is 6m, the tunnel section is circular, the diameter is 5.5m, the reinforced concrete pipe joint is used, and the thickness of pipe joint is 0.3m
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The buried depth of the tunnel is about 9.8m
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Engineering geological conditions: the stratum is muddy soft soil layer with high groundwater level
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The strata from top to bottom are: silt, muddy clay, muddy silty clay and clay layer, in which the stratum of tunnel body is mainly silt layer
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See Figure 1 for details
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1.2 the finite element method is used for numerical simulation
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The model is shown in Figure 2
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The calculation range is 54m in the horizontal direction and 40m in the vertical direction
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The buried depth of the tunnel is 9.8m and the shape of the tunnel is circular
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(1) Boundary conditions
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The displacement of the bottom of the model is limited in the vertical direction, the displacement of both sides of the model is limited in the horizontal direction, and the top bears the self weight stress of the overlying soil layer
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(2) Initial geostress field
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Only the self weight stress field is considered
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(3) The choice of constitutive relation
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The Mohr Coulomb elastic-plastic model is used for stratum and the elastic model is used for segment structure
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(4) The selection of calculation parameters
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According to the geological exploration data, the stratum parameters are shown in Table 1
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C30 concrete is used for segment structure
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The specific parameters are selected according to the specifications, as shown in Table 1
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1.3 calculation condition in order to study the influence of the change of the clear distance of the small clear distance pipe jacking tunnel on the horizontal surface settlement, and the influence of different follow-up distance of the backward tunnel on the surface settlement above the longitudinal axis of the first tunnel, the clear distance between the two tunnels is set as 1D, 0.7d, 0.5d (D is the tunnel diameter), and the follow-up distance of the backward tunnel is set as 1D, 2D, 4D, 8D, etc What’s the matter
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Through calculation, the corresponding conclusions are obtained
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2
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Analysis of the influence of clear distance on horizontal surface settlement Fig
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3 shows the curve of horizontal surface settlement of double hole pipe jacking tunnel under different clear distance conditions
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In order to be more practical in construction, a tunnel (left tunnel) is currently driven during calculation
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When a certain horizontal surface settlement deformation is stable, the tunneling construction of the back tunnel (right tunnel) is simulated until the horizontal surface settlement deformation is stable
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The case of single tunnel excavation (only left tunnel excavation, but no right tunnel excavation) is used to compare the influence of other different clear distance conditions on the horizontal surface settlement
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As can be seen from Fig
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3, since the left tunnel is being driven and the right tunnel is being driven later, the horizontal surface settlement curve shows an asymmetric skew curve, and the surface settlement at the axis of the left tunnel is greater
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This is mainly due to the reduction of the net distance between the two tunnels and the reduction of the ability of the soil to restrain deformation
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In addition, it can be seen from the figure that with the decrease of the clear distance of the tunnel (the clear distance between the right tunnel and the left tunnel can be regarded as infinity for single tunnel excavation), the surface settlement gradually increases, and the skewness of the surface settlement curve gradually disappears
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When the net distance reaches 0.5d, the normal settlement curve can be seen, which indicates that the surface settlement caused by excavation is small It is no longer constrained by the soil between the two tunnels
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Discussion on subcontracting disputes and control measures in tunnel construction! 3
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Analysis of the influence of clear distance on longitudinal surface settlement Figure 4 shows the influence law of tunnel clear distance on longitudinal surface settlement under different follow-up distances (1D, 2D, 4D, 8D)
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In the figure, the ordinate is the percentage of the increase of surface settlement above the current tunnel axis due to the follow-up excavation of the later tunnel, and the abscissa is the distance from the tunnel face in advance, with the face as the zero point, negative to the front of the excavation face (not excavated), and positive to the back of the excavation face (excavated)
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It can be seen from the figure that in front of the heading face of the backward tunnel, the increment of the longitudinal surface settlement of the first tunnel is very small, and with the increase of the follow-up distance, this effect is also smaller and smaller
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When the follow-up distance is 8D, the increment of the longitudinal surface settlement of the first tunnel is almost zero, because the stratum to be excavated in front of the heading face of the backward tunnel has constraints on the settlement deformation
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In the area behind the heading face of the back tunnel, due to the unloading effect of the excavation soil of the back tunnel, the ground settlement increment of the adjacent first tunnel becomes larger, which confirms the result in Figure 3 that the settlement value of the single tunnel excavation is obviously smaller than that of the double tunnel excavation, that is, due to the excavation of the back tunnel, the constraint deformation ability of the stratum soil between the two tunnels is weakened, and at the same time, it can be seen that With the decrease of the net distance, the increment percentage of the longitudinal ground settlement increases, from 0.7d to 0.5d, and the increment percentage of the longitudinal settlement increases from 40% to 120%
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Finally, it can be seen that no matter how long the follow-up distance of the back tunnel is, after 9D behind the heading face of the first tunnel, the percentage of longitudinal ground settlement increment of the first tunnel begins to decrease
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This is because the settlement deformation of this part is stable before the excavation of the back tunnel, and the settlement increment is only caused by the excavation of the back tunnel.
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