Construction simulation method for shield tunnel undercrossing railway soft soil pile foundation

Abstract

The invention relates to the technical field of tunnel construction, in particular to a construction simulation method for a shield tunnel undercrossing railway soft soil pile foundation, which comprises the following steps: S1, determining model construction parameters according to an investigation report; s2, FLAC3D software is adopted, and a three-dimensional model of the shield tunnel under-crossing railway soft soil pile foundation is built according to the model building parameters; and S3, the construction process of the shield tunnel underneath passing railway soft soil pile foundation is simulated based on the three-dimensional model. The device has the advantages that the reinforcing effect of a pile group foundation is simulated, and the reinforcing effect of a cement mixing pile is effectively simulated. Therefore, more data support is provided for the construction that the shield tunnel passes through the soft soil roadbed of the existing railway, the construction that the shield tunnel passes through the pile foundation of the existing railway is ensured to be carried out smoothly, and meanwhile, the normal operation of the existing railway and the smooth propulsion of the shield tunnel are ensured.

Description

Technical Field

[0001] The invention relates to the technical field of tunnel construction, in particular to a construction simulation method for a shield tunnel passing under a railway soft soil pile foundation. Background Art

[0002] The shield method has become the preferred construction method for urban subway construction due to its safety, economy, efficiency, low impact on the environment and no interference with ground traffic. However, the shield tunneling process will inevitably cause disturbance to the surrounding rock and soil, destroy the original stress balance, and in severe cases may cause ground collapse and casualties.

[0003] With the boom of subway construction, many scholars have conducted three-dimensional dynamic simulation research on the construction process of shield tunnels, and analyzed the deformation characteristics of the ground during shield tunneling by establishing a three-dimensional numerical model. In traditional numerical simulations, for pile foundations with existing structures above, solid units are usually used for simulation, and contact surfaces are set to consider the potential sliding between piles and soil.

[0004] Although the existing numerical simulation can simulate the mechanical response of a small number of pile foundations well, when dealing with a large number of pile foundations such as CFG piles or cement mixing piles, the solid unit modeling needs to consider the coupling between the pile foundation mesh and the overall mesh, and often faces mesh quality problems. Refining the pile foundation mesh will increase the number of overall meshes, which is not conducive to calculation. At the same time, there are also challenges in setting the contact surface of the pile group foundation. Therefore, it is necessary to develop a new construction simulation method specifically for the case of shield tunnels passing under railway soft soil pile foundations, so as to simplify the numerical simulation of pile foundations, provide guidance for the actual construction of shield tunnels passing under existing railway pile foundations, and ensure the normal operation of the railway and the smooth advancement of the tunnel. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a construction simulation method for a shield tunnel passing through a soft soil pile foundation of a railway, so as to provide more experimental data for the construction of a shield tunnel passing through the soft soil roadbed of an existing railway, thereby facilitating the actual construction of a shield tunnel passing through the pile foundation of an existing railway, ensuring the normal use of the existing railway and the smooth advancement of the shield tunnel.

[0006] In order to achieve the above-mentioned purpose, a construction simulation method for a shield tunnel under a railway soft soil pile foundation is designed, comprising the following steps: S1. determining model construction parameters according to a survey report; S2. using FLAC3D software to establish a three-dimensional model of a shield tunnel under a railway soft soil pile foundation according to the model construction parameters; S3. simulating the construction process of the shield tunnel under a railway soft soil pile foundation based on the three-dimensional model; wherein the railway pile foundation in the three-dimensional model is simulated using a pile unit, and the pile unit simulation comprises the following steps: S3.1 inputting the starting position coordinates of the pile structure unit; S3.2 inputting the mechanical parameters of the pile foundation itself; S3.3 inputting the shear coupling spring parameters and the normal coupling spring parameters of the pile unit; S3.4 the shear coupling spring parameters are determined according to the soil mechanical parameters obtained from the on-site survey, and the soil mechanical parameters include cohesion and internal friction angle; S3.5 simulating the friction between the pile foundation and the soil by activating the shear coupling spring characteristics of the pile unit itself; S3.6 simulating the end bearing effect of the pile foundation itself and the friction effect between the pile foundation and the soil by the pile unit.

[0007] Preferably, the method provided by the present invention also includes other technical features, wherein the model construction parameters include: the overall external dimensions of the three-dimensional model; the tunnel, railway pile foundation and shield machine parameters within the three-dimensional model; and the geotechnical structure parameters of each layer within the three-dimensional model.

[0008] Preferably, the method provided by the present invention also includes other technical features, wherein the strata of the three-dimensional model are simulated using ideal elastic-plastic materials; the pipe segments of the three-dimensional model are simulated using linear elastic constitutive models; and the contact surface between the railway pile foundation and the soil of the three-dimensional model is simulated using the pile-clay contact surface.

[0009] Preferably, the method provided by the present invention also includes other technical features, which also include the following steps: S4. Obtaining railway pile foundation parameters, tunnel stratum structure parameters, shield machine parameters and isochronous layer parameters; S5. Obtaining construction load parameters based on the railway pile foundation parameters, tunnel stratum structure parameters, shield machine parameters and isochronous layer parameters; S6. The construction load parameters include soil bin pressure and synchronous grouting pressure.

[0010] Preferably, the method provided by the present invention also includes other technical features, wherein the construction process simulation includes the following steps: S3.7 determining the simulated working conditions, the simulated working conditions including soil bin pressure and grouting pressure; S3.8 obtaining the shield stratum deformation and the change law of the existing pile foundation according to the working conditions.

[0011] Preferably, the method provided by the present invention also includes other technical features, wherein the construction process simulation includes the following stages: excavation advancement stage: activating the shield shell and applying soil bin pressure on the excavation surface; segment assembly stage: after the shield machine advances two ring lengths forward, segments and equivalent layers are applied at the last two ring lengths of the shield machine, and the corresponding parameters before consolidation are assigned to the segments and equivalent layers respectively; shield tail grouting stage: applying normal grouting pressure to the segments and the soil at the corresponding positions; grouting body hardening stage: when excavating to the 6th ring segment position, the equivalent layer parameters of the first two ring segment positions excavated are changed to the corresponding parameters after the equivalent layer consolidation, and at the same time, the grouting pressure applied to the segments and the soil at the corresponding positions is removed.

[0012] Preferably, the method provided by the present invention also includes other technical features, wherein the bearing capacity improvement effect of the composite foundation composed of cement mixing piles and strata is evaluated by analyzing the settlement changes in the cement mixing pile reinforcement area and the pile foundation force cloud map in the simulation results.

[0013] Compared with the prior art, the present invention has the following advantages: The present invention uses pile units to simulate the reinforcement effect of pile group foundations, aiming to solve the problems of poor mesh quality and overly complex contact surface settings in traditional numerical simulations. By assigning appropriate parameters to the pile units, the reinforcement effect of cement mixing piles can be effectively simulated. This provides more data support for the construction of shield tunnels crossing the soft soil roadbed of existing railways, ensures the smooth construction of shield tunnels crossing the pile foundations of existing railways, and at the same time ensures the normal operation of existing railways and the smooth advancement of shield tunnels. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 , is a schematic diagram of the construction method of the embodiment; Figure 2 , is a schematic diagram of a three-dimensional model of soft soil pile foundation; Figure 3 , is a schematic diagram of the positional relationship between railway pile foundation and railway roadbed; Figure 4 , ground deformation diagram after excavation; Figure 5 , pile foundation force cloud diagram. DETAILED DESCRIPTION

[0015] In order to make the purpose, principle and structure of the present invention more clear, it is further described below in conjunction with the drawings and specific embodiments.

[0016] Combination Figure 1As shown, this example provides a construction simulation method for a shield tunnel passing under a railway soft soil pile foundation, comprising: step 1, determining model construction parameters according to the survey report; step 2, establishing a three-dimensional model of the shield tunnel passing under the railway soft soil pile foundation according to the model construction parameters; step 3, simulating the construction process of the shield tunnel passing under the railway soft soil pile foundation based on the three-dimensional model. Embodiment 1: The specific operations are as follows: The shield tunnel construction area is surveyed using refined engineering geophysical exploration and other methods to obtain a survey report, which includes engineering geological information of the construction area and railway pile foundation structure information.

[0017] The project address information includes soil layer conditions. The soil layer conditions from top to bottom are miscellaneous fill, clay, silty clay, silty silty clay, silt sand, silty silty clay and silty clay. The model construction parameters are determined according to the survey report, including: determining the overall external dimensions of the three-dimensional model according to the survey report, and determining the tunnels, railway pile foundations and shield machines within the three-dimensional model as well as the geotechnical structures of each layer within the three-dimensional model.

[0018] According to the actual situation of the construction site, considering the influence of boundary effect and size effect, the external overall model size of the 3D model is set to 82m×72m×62m, where the length direction is the tunnel excavation direction, the width direction is perpendicular to the tunnel excavation direction, and the height direction is the tunnel burial depth direction. The overall 3D model is as follows Figure 2 In the 3D model, the positional relationship between the railway pile foundation, shield tunnel, and railway subgrade is shown in Figure 3 shown.

[0019] The pile foundation in the three-dimensional model is a cement-mixed pile with a pile length of 14m, a pile weight of 2500 kN / m3, an elastic modulus of 100MPa, and a Poisson's ratio of 0.25.

[0020] The three-dimensional model plans to use two earth pressure balance shield machines with a cutter head diameter of about 6.8m and a body length of 9m; the segments are made of C50 concrete with a width of 1.5m.

[0021] Among them, the soil structure in the three-dimensional model is divided into 7 layers, and the soil conditions from top to bottom are miscellaneous fill, clay, silty clay, silty silty clay, silt, silty silty clay and silty clay.

[0022] Among them, a three-dimensional model of the shield tunnel passing through the soft soil pile foundation of the railway is established according to the model construction parameters, including using FLAC 3D software to establish a three-dimensional model of the shield tunnel passing through the soft soil pile foundation of the railway according to the model construction parameters, and setting the model boundary conditions.

[0023] The model boundary of the three-dimensional model is as follows: fixed constraints are added to the ground, corresponding normal displacement constraints are added to the four sides, and the upper surface is the free surface of the ground.

[0024] Among them, the strata of the three-dimensional model are simulated using ideal elastic-plastic materials; the pipe segments of the three-dimensional model are simulated using linear elastic constitutive models; the railway pile foundation of the three-dimensional model is simulated using pile units; and the contact surface between the railway pile foundation and the soil in the three-dimensional model is simulated using the pile-clay contact surface.

[0025] The construction process of the shield tunnel passing under the railway soft soil pile foundation is simulated based on the three-dimensional model, which also includes the existing pile foundation simulation, roadbed backfill simulation and tunnel excavation simulation.

[0026] The existing pile foundation simulation was carried out through the built-in pile unit in FLAC3D to simulate the cement soil mixing pile. In the model, the piles were laid out in a square pattern with an interval of 1.3m, and a total of 1,173 pile units were laid.

[0027] Among them, the connection of the bottom node of the pile unit in FLAC3D only provides general interaction between the pile and the grid, and does not reflect the bearing effect of the deep foundation of the pile foundation. In order to simulate the bearing effect of the deep foundation, it is necessary to delete the bottom node connection of the pile unit, adopt a new connection that contains an axial normal yield spring, and adopt a new connection stiffness.

[0028] Among them, the roadbed backfill simulation calculates the cement mixing piles to balance, assigns the roadbed grid Mohr-Coulomb model, and continues to calculate until balance before simulation.

[0029] Among them, the tunnel excavation simulation is divided into four stages: excavation advancement, segment assembly, shield tail grouting and grouting body hardening. The construction of each stage is simulated in the three-dimensional model, and each stage is cycled in sequence until the construction is completed.

[0030] During the excavation phase: the shield is activated and soil pressure is applied to the excavation face; In the segment assembly stage: after the shield machine advances two ring lengths, the segments and equivalent layers are constructed at the last two ring lengths of the shield machine, and the corresponding parameters before consolidation are assigned to the segments and equivalent layers respectively; During the shield tail grouting stage: normal grouting pressure is applied to the segments and the soil at the corresponding positions; During the hardening stage of the grouting body: when excavating to the position of the 6th ring of segments, the equivalent layer parameters of the first two rings of segments are changed to the corresponding parameters after the equivalent layer is consolidated, and the grouting pressure applied to the segments and the soil at the corresponding position is removed at the same time.

[0031] Before simulating the construction process of the shield tunnel under the railway soft soil pile foundation based on the three-dimensional model, it also includes: obtaining railway pile foundation parameters, tunnel stratum structure parameters, shield machine parameters and isochronous layer parameters; obtaining construction load parameters according to the railway pile foundation parameters, tunnel stratum structure parameters, shield machine parameters and isochronous layer parameters; the construction load parameters include soil bin pressure and synchronous grouting pressure.

[0032] Among them, the parameters of the isochronous layer before consolidation are elastic modulus 40MPa, natural density 24kN / m3, Poisson's ratio 0.3, and the parameters of the isochronous layer after consolidation are elastic modulus 400MPa, natural density 24kN / m3, Poisson's ratio 0.2.

[0033] Among them, based on the three-dimensional model, the construction process of the shield tunnel passing through the soft soil pile foundation of the railway is simulated, which also includes: determining the simulated working conditions, the simulated working conditions include soil bin pressure and grouting pressure; obtaining the deformation of the shield stratum and the change law of the existing pile foundation according to the working conditions.

[0034] It is worth mentioning that: In FLAC3D, the solid continuous medium is represented by a series of polyhedral units, each of which is connected to a corresponding set of grid points. The structural unit is connected by a set of structural components and structural nodes. The interaction between the structure and the entity is realized by connecting the nodes or units or other nodes. For the installation unit, if the solid unit is selected for modeling, due to the large size difference between the pile foundation in the axial and radial directions, and the formation unit is used as an example to speed up the calculation, the larger size is usually considered to reduce the number of units. When considering the mesh coupling, it will cause the mesh quality to be poor or increase the number of meshes to achieve the purpose of improving the mesh quality, which is not conducive to the calculation. When using the pile unit to simulate the pile foundation in reality, the mesh coupling can be considered. When establishing the pile unit, the software will automatically establish the coupling between the structural unit and the solid unit, thus avoiding the difficulty of mesh unit division (two defects of poor mesh quality and large number of meshes). When modeling, it is necessary to input the starting position coordinates of the pile structure unit, the mechanical parameters of the pile foundation itself, and the shear coupling spring parameters and normal coupling spring parameters of the pile unit.

[0035] For the cement mixing pile mentioned in the present invention, as an end-bearing friction pile, in addition to considering the end-bearing effect of the pile foundation itself, it is also necessary to consider the effect of friction between the pile foundation and the soil. The soil mechanical parameters (such as cohesion and internal friction angle) obtained from the on-site survey will be used to assign the shear coupling spring parameters of the pile unit.

[0036] In the existing numerical simulation of the interaction between pile foundation and soil, the solid unit is usually used to simulate the bearing of the pile foundation itself, and the friction between the pile foundation and the soil is realized by setting the pile-soil contact surface. The pile unit used in the present invention simulates the friction between the pile foundation and the soil by activating its own shear coupling spring characteristics.

[0037] From the deformation diagram of the stratum after excavation, it can be seen that the settlement of the cement mixing pile reinforcement area has been significantly reduced. This is due to the increase in the bearing capacity of the composite foundation composed of cement mixing piles and strata. The higher bearing capacity can reduce the impact of excavation on the existing railway subgrade. It can also be seen from the pile foundation force cloud map that the pile foundation has achieved the effect of strengthening the stratum through its own force.

[0038] For shield tunneling under existing railway lines, reinforcement treatment is usually required. If the reinforcement effect of the existing railway foundation is not considered, it is not economical to select reinforcement measures. Through the numerical simulation method proposed by the present invention, by considering the bearing effect of the existing railway subgrade, it is judged whether the existing railway line needs to be reinforced and what reinforcement measures to choose, so as to achieve the purpose of economic safety.

[0039] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent substitutions or changes according to the technical solutions and novel concepts of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A construction simulation method for a shield tunnel passing through a railway soft soil pile foundation, characterized in that: The following steps are involved: S1. Determine the model building parameters according to the survey report; S2. Using FLAC3D software, a three-dimensional model of a shield tunnel under a railway soft soil pile foundation is established according to the model construction parameters; S3. Simulate the construction process of the shield tunnel under the railway soft soil pile foundation based on the three-dimensional model; The railway pile foundation in the three-dimensional model is simulated using pile units, and the pile unit simulation includes the following steps: S3.1 Input the starting position coordinates of the pile structure unit; S3.2 Input the mechanical parameters of the pile foundation itself; S3.3 Input the shear coupling spring parameters and normal coupling spring parameters of the pile element; S3.4 The shear coupling spring parameters are determined based on the soil mechanical parameters obtained from the on-site survey, wherein the soil mechanical parameters include cohesion and internal friction angle; S3.5 simulates the friction between pile foundation and soil by activating the shear coupling spring characteristics of the pile unit itself; S3.6 uses pile units to simulate the end bearing effect of the pile foundation itself and the friction between the pile foundation and the soil.

2. The construction simulation method of a shield tunnel under a railway soft soil pile foundation according to claim 1 is characterized in that: The model building parameters include: The overall external dimensions of the 3D model; Tunnel, railway pile foundation and shield machine parameters within the 3D model; Geotechnical structural parameters of each layer in the 3D model.

3. The construction simulation method of a shield tunnel under a railway soft soil pile foundation according to claim 1 is characterized in that: The strata of the three-dimensional model are simulated by ideal elastic-plastic materials; the segments of the three-dimensional model are simulated by linear elastic constitutive models; and the contact surface between the railway pile foundation and the soil of the three-dimensional model is simulated by the pile-clay contact surface.

4. The construction simulation method of a shield tunnel under a railway soft soil pile foundation according to claim 1 is characterized in that: The following steps are also included: S4. Obtaining railway pile foundation parameters, tunnel stratum structure parameters, shield machine parameters and equivalent layer parameters; S5. Obtain construction load parameters according to the railway pile foundation parameters, tunnel stratum structure parameters, shield machine parameters and other generation layer parameters; The construction load parameters described in S6 include soil bin pressure and synchronous grouting pressure.

5. The construction simulation method of a shield tunnel under a railway soft soil pile foundation according to claim 1 is characterized in that: The construction process simulation includes the following steps: S3.7 determining a simulated working condition, wherein the simulated working condition includes soil bin pressure and grouting pressure; S3.8 Obtain the deformation of the shield stratum and the changing rules of the existing pile foundation according to the working conditions.

6. The construction simulation method of a shield tunnel under a railway soft soil pile foundation according to claim 1 is characterized in that: The construction process simulation includes the following stages: Excavation stage: Activate the shield and apply soil pressure to the excavation face; Segment assembly stage: After the shield machine advances two ring lengths, the segments and equivalent layers are constructed at the last two ring lengths of the shield machine, and the corresponding parameters before consolidation are assigned to the segments and equivalent layers respectively; Shield tail grouting stage: normal grouting pressure is applied to the segments and the soil at the corresponding positions; Grouting body hardening stage: When excavation reaches the position of the 6th ring of segments, the equivalent layer parameters of the first two rings of segments are changed to the corresponding parameters after the equivalent layer is consolidated, and the grouting pressure applied to the segments and the soil at the corresponding positions is removed at the same time.

7. The construction simulation method of a shield tunnel under a railway soft soil pile foundation according to claim 1 is characterized in that: By analyzing the settlement changes in the cement-mixed pile-reinforced area and the pile foundation stress contour in the simulation results, the bearing capacity improvement effect of the composite foundation composed of cement-mixed piles and strata is evaluated.

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