Calculation method of shield starting reinforcement range in water-rich sandy gravel strata

Abstract

The present application relates to the field of tunnel engineering technology, and discloses a method for calculating the starting reinforcement range of a shield in a water-rich sand and gravel formation, aiming to solve the problem of poor accuracy in the existing method for determining the starting reinforcement range of a shield. The scheme mainly includes: establishing a three-dimensional model of the starting reinforcement of a shield; obtaining the physical parameters of the soil of each formation in the construction section; assigning corresponding physical parameters to the soil units of each formation in the three-dimensional model and establishing a fluid-solid coupling model; setting the end soil reinforcement range, performing static analysis on the three-dimensional model before the shield starts, and balancing the initial stress; simulating the start of the shield to obtain the surface settlement value and the vertical displacement value of the tunnel; after changing the end soil reinforcement range, obtaining the surface settlement value and the vertical displacement value of the tunnel for different end soil reinforcement ranges; combining the shield tunnel control standard to obtain the optimal end soil reinforcement range. The present application improves the accuracy of the calculation of the starting reinforcement range of a shield, and is suitable for water-rich sand and gravel formations.

Description

Technical Field

[0001] The present application relates to the technical field of tunnel engineering, and in particular to a method for calculating the initial reinforcement range of a shield tunnel in a water-rich sand and gravel stratum. Background Art

[0002] ‌With the acceleration of urbanization, the increase in population density, and the continuous increase in the development of urban underground space, the shield method has been widely used in the construction of urban tunnels due to its high efficiency, safety, and fully mechanized construction characteristics. Shield start refers to the construction process from the assembly and commissioning of the shield machine until the shield machine completely enters the interval tunnel and completes the trial excavation, that is, the process of the shield machine entering the soil and excavating along the designed route. Shield start is a key process in shield tunnel construction and is directly related to whether the shield tunnel can be smoothly constructed. ‌With the increase in the diameter of the shield and the increase in the complexity of the stratum environment, it is easy for the stratum and tunnel deformation values ​​to exceed the limit, or even serious accidents such as landslides, to occur during the shield start process. Reinforcement of the end soil before the shield starts is an effective means to solve the above problems.

[0003] The initial reinforcement range of the shield refers to the area where the end soil around the tunnel entrance is reinforced before the shield construction is carried out. In the existing research on the reinforcement of the initial end soil of the shield, although the construction method of the initial end soil reinforcement of the shield has been proposed, the reinforcement of the initial end soil of the shield under the conditions of water-rich sand and gravel strata has not been analyzed based on the characteristics of the stratum, and the reinforcement range of the end soil is mostly determined based on engineering experience. There is no calculation method for the initial reinforcement range of the shield in water-rich sand and gravel strata, and the accuracy is poor. With the increase of the diameter of the shield and the complexity of the stratum environment, the above construction method is difficult to effectively ensure the safety of the initial construction of the shield. Summary of the invention

[0004] The present application aims to solve the problem of poor accuracy in the existing method for determining the initial reinforcement range of a shield machine, and proposes a method for calculating the initial reinforcement range of a shield machine in a water-rich sand and gravel stratum.

[0005] The technical solution adopted by this application to solve the above technical problems is:

[0006] A method for calculating the initial reinforcement range of a shield tunnel in a water-rich sandy gravel stratum, the method comprising the following steps:

[0007] S1. Establish a three-dimensional model of shield starting reinforcement in water-rich sand and gravel strata, and perform structured grid division on the three-dimensional model, wherein the three-dimensional model includes a physically simulated stratum, a starting shield shaft, a shield casing unit, a segment unit, and a grouting layer unit;

[0008] S2, obtaining stratum distribution information of the shield tunneling starting construction section, and obtaining physical parameters of soil in each stratum according to the stratum distribution information, wherein the physical parameters at least include permeability coefficient;

[0009] S3, assigning corresponding physical parameters to the soil units of each layer in the three-dimensional model, and establishing a fluid-solid coupling model according to the groundwater level height and the permeability coefficient of the soil unit;

[0010] S4. Set the end soil reinforcement range, conduct static analysis on the three-dimensional model before the shield starts, and balance the initial stress;

[0011] S5. Simulating the start of the shield tunneling based on the three-dimensional model and the fluid-solid coupling model to obtain corresponding surface settlement values ​​and tunnel vertical displacement values;

[0012] S6. After changing the end soil reinforcement range, repeat S4 to S5 to obtain the ground settlement values ​​and tunnel vertical displacement values ​​corresponding to different end soil reinforcement ranges;

[0013] S7. According to the surface settlement values ​​and tunnel vertical displacement values ​​corresponding to different end soil reinforcement ranges and combined with the shield tunnel control standards, the optimal end soil reinforcement range for shield tunneling is obtained.

[0014] Furthermore, a three-dimensional model of shield tunneling reinforcement in water-rich sand and gravel strata was established, including:

[0015] According to the geological environment of the shield construction starting section, the FLAC3D finite element software was used to establish a three-dimensional model of the shield starting reinforcement in the water-rich sand and gravel stratum. The X direction of the three-dimensional model is the cross-sectional direction of the shield tunnel, the Y direction is the shield excavation direction, and the Z direction is the vertical direction.

[0016] Furthermore, the physical parameters of each layer are obtained, including:

[0017] The stratum lithology and stratum thickness are divided according to the geological survey results of the shield construction starting section, and the stratum distribution information of the shield construction starting section is obtained. Based on the stratum distribution information, the physical parameters of the soil after grouting reinforcement of each stratum are obtained through indoor tests.

[0018] Furthermore, the physical parameters also include density, cohesion, friction angle, elastic modulus and Poisson's ratio.

[0019] Furthermore, a static analysis is performed on the 3D model before the start of the shield tunneling and the initial stress is balanced, including:

[0020] Set boundary conditions for the 3D model and add Earth gravity;

[0021] The Mohr-Coulomb elastoplastic model is selected as the constitutive model for the shield starting simulation;

[0022] The initial stress balance is performed on the three-dimensional model when the excavation of the initial shield shaft is completed but not yet started, so that the initial displacement of each grid unit in the three-dimensional model is zero.

[0023] Furthermore, based on the three-dimensional model and the fluid-solid coupling model, the shield start-up is simulated, specifically including:

[0024] S51, setting the excavation steps of the shield machine, applying a thrust force in the excavation direction in front of the shield machine, and using the stiffness transfer method to simulate the excavation process of the leading line and the trailing line of the shield machine respectively;

[0025] S52. After the tunneling process simulation of the leading line and the trailing line of the shield machine is completed, the corresponding surface settlement value and the vertical displacement value of the tunnel are obtained.

[0026] Furthermore, the stiffness transfer method is used to simulate the tunneling process of the leading line and the trailing line of the shield machine, including:

[0027] A. When the shield machine excavates to the nth step, the soil unit at the nth step tunnel position is killed, and the shield machine shell unit at the nth step tunnel position is activated;

[0028] B. When the tunneling step number n of the shield machine is greater than a, the segment unit at the position of the n-a+1th tunnel step is activated, the grouting layer unit at the position of the nath tunnel step is activated, and the grouting pressure is applied vertically to the wall surface corresponding to the activated grouting layer unit, where a represents the preset tunneling step number;

[0029] C. Set the grouting layer unit at the na-th tunnel position to liquid state, the grouting layer unit at the na-1-th tunnel position to solidified state, and the grouting layer unit at the na-2-th tunnel position to solid state.

[0030] Furthermore, the thrust force in the tunneling direction applied in front of the shield machine is greater than the active earth pressure and less than the passive earth pressure;

[0031] The calculation formula of the active earth pressure is as follows:

[0032] ;

[0033] The calculation formula of the passive earth pressure is as follows:

[0034] ;

[0035] in, represents the active earth pressure, represents the passive earth pressure, represents the number of strata at the tunnel location, Indicates The active earth pressure coefficient of the stratum is Indicates The passive earth pressure coefficient of the stratum is Indicates The soil weight of each stratum, Indicates The soil thickness of each layer, Indicates The soil cohesion of a stratum.

[0036] Furthermore, the end soil reinforcement range includes a transverse reinforcement length and a vertical reinforcement length, and the optimal end soil reinforcement range includes an optimal transverse reinforcement length and an optimal vertical reinforcement length.

[0037] Furthermore, the S7 specifically includes:

[0038] The maximum surface settlement value and the maximum tunnel vertical displacement value corresponding to the soil reinforcement range at different ends are determined, the surface settlement threshold and the tunnel vertical displacement threshold are determined according to the shield tunnel control standard, and the optimal transverse reinforcement length and the optimal vertical reinforcement length are determined according to the maximum surface settlement value and the surface settlement threshold value as well as the maximum tunnel vertical displacement and the tunnel vertical displacement threshold value.

[0039] The beneficial effects of the present application are as follows: the method for calculating the starting reinforcement range of a shield machine in a water-rich sand and gravel formation provided by the present application constructs a three-dimensional model of the starting reinforcement of a shield machine in a water-rich sand and gravel formation, and constructs a fluid-solid coupling model. In the process of simulating the starting of a shield machine under the conditions of a water-rich sand and gravel formation, a fluid-solid coupling analysis is performed, which fully considers the fluid-solid coupling phenomenon of water-rich sand and gravel formations in actual engineering projects, and improves the accuracy of the simulation of the starting of a shield machine in a water-rich sand and gravel formation and the calculation of the reinforcement range. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 A schematic flow chart of a method for calculating the initial reinforcement range of a shield tunnel in a water-rich sandy gravel stratum provided in an embodiment of the present application;

[0041] Figure 2 A schematic flow chart of another method for calculating the initial reinforcement range of a shield tunnel in a water-rich sand and gravel stratum provided in an embodiment of the present application;

[0042] Figure 3 A schematic diagram of the structure of a three-dimensional model provided in an embodiment of the present application;

[0043] Figure 4 A schematic diagram of the structure of the starting part of a shield machine in a three-dimensional model provided in an embodiment of the present application;

[0044] Figure 5 A schematic diagram of the lateral reinforcement range of an end soil mass provided in an embodiment of the present application;

[0045] Figure 6 A schematic diagram of the longitudinal reinforcement range of an end soil mass provided in an embodiment of the present application;

[0046] Figure 7 A schematic diagram of a shield tunneling simulation process provided in an embodiment of the present application;

[0047] Figure 8 A surface settlement curve diagram under different transverse reinforcement lengths provided in an embodiment of the present application;

[0048] Fig. 9 A curve diagram of tunnel vertical displacement under different transverse reinforcement lengths provided in an embodiment of the present application;

[0049] Fig.10 A surface settlement curve diagram under different longitudinal reinforcement lengths provided in an embodiment of the present application;

[0050] Fig.11 A curve diagram of tunnel vertical displacement under different longitudinal reinforcement lengths provided in an embodiment of the present application;

[0051] Description of reference numerals:

[0052] 1-stratum; 2-starting shield shaft; 3-shield tunnel; 4-shield casing unit; 5-segment unit; 6-grouting layer unit; 7-soil to be excavated; B-side reinforcement length of shield outer diameter; h1-reinforcement length of top of shield outer diameter; h2-reinforcement length of bottom of shield outer diameter, n-10, n-9, ..., n+1-excavation step. DETAILED DESCRIPTION

[0053] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application.

[0054] The technical solution of the embodiment of the present application is applicable to the application scenario of the initial construction of the shield in water-rich sand and gravel formations. Since the current method for determining the soil reinforcement range of the initial end of the shield is basically determined by technical personnel based on engineering experience, the accuracy of this method is relatively low. And for water-rich sand and gravel formations, the existing method does not take into account the impact of the fluid-solid coupling phenomenon on the reinforcement range. When the tunnel shield construction is carried out in a soil layer or a water-rich sand layer with rich groundwater storage, the pore water pressure and permeability coefficient of the soil within the shield influence range will change with the excavation of the tunnel shield. At the same time, the stratum will also undergo consolidation settlement as the permeability coefficient decreases and the pore water pressure dissipates, eventually causing deformation of the tunnel and stratum.

[0055] Based on this, the technical solution of the present application is proposed. In the embodiment of the present application, a three-dimensional model of shield starting reinforcement in water-rich sand and gravel strata is established, and the three-dimensional model is structured and meshed. The three-dimensional model includes a physically simulated stratum, a starting shield shaft, a shield casing unit, a segment unit, and a grouting layer unit. The stratum distribution information of the shield starting construction section is obtained, and the physical parameters of the soil of each stratum are obtained according to the stratum distribution information, and the physical parameters include at least the permeability coefficient. The soil units of each stratum in the three-dimensional model are assigned corresponding soil physical parameters, and the soil units are assigned the corresponding soil physical parameters according to the groundwater level height and the permeability coefficient. The fluid-solid coupling model is established based on the permeability coefficient; the end soil reinforcement range is set, and the three-dimensional model before the shield starts is statically analyzed, and the initial stress is balanced; based on the three-dimensional model and the fluid-solid coupling model, the shield starts are simulated to obtain the corresponding surface settlement value and tunnel vertical displacement value; after changing the end soil reinforcement range, the above steps are repeated to obtain the surface settlement value and tunnel vertical displacement value corresponding to different end soil reinforcement ranges; according to the surface settlement value and tunnel vertical displacement value corresponding to different end soil reinforcement ranges, and in combination with the shield tunnel control standard, the optimal end soil reinforcement range for shield starting is obtained.

[0056] Specifically, the embodiment of the present application first establishes a three-dimensional model of shield starting reinforcement in water-rich sand and gravel formations, assigns corresponding physical parameters to the soil in the three-dimensional model according to the actual geological conditions of the project, and establishes a fluid-solid coupling model according to the groundwater level and the permeability coefficient of the soil unit, and then sets a variety of different end soil reinforcement ranges, and simulates the shield starting excavation process after each setting, and performs fluid-solid coupling simulation analysis during the simulation process. After the simulation is completed, the surface settlement values ​​and tunnel vertical displacement values ​​corresponding to different end soil reinforcement ranges are calculated, and finally, combined with the shield tunnel control standard, the optimal end soil reinforcement range for shield starting can be obtained. The embodiment of the present application fully considers the fluid-solid coupling phenomenon of water-rich sand and gravel formations in actual engineering, and improves the accuracy of shield starting simulation and reinforcement range calculation for water-rich sand and gravel formations.

[0057] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments.

[0058] See also Figure 1 and Figure 2 The method for calculating the initial reinforcement range of a shield in a water-rich sand and gravel stratum provided in an embodiment of the present application includes the following steps:

[0059] S1. Establish a three-dimensional model of shield starting reinforcement in water-rich sand and gravel strata, and perform structured grid division on the three-dimensional model. The three-dimensional model includes a physically simulated stratum 1, a starting shield shaft 2, a shield casing unit 4, a segment unit 5, and a grouting layer unit 6.

[0060] In the embodiment of the present application, according to the geological environment of the shield starting construction section, the FLAC3D finite element software is used to establish a three-dimensional model of the shield starting reinforcement in the water-rich sand and gravel stratum. The X direction of the three-dimensional model is the cross-sectional direction of the shield tunnel 3, the Y direction is the shield excavation direction, and the Z direction is the vertical direction.

[0061] Figure 3 A schematic diagram of a three-dimensional model is shown. Figure 4 The schematic diagram of the structure of the starting part of the shield in a three-dimensional model is shown. In the three-dimensional model, the size of the starting shield shaft 2 is 60m (length) × 40m (width) × 47m (height), the shield excavation diameter is 15.4m, the outer diameter of the segment unit 5 is 14.5m, the buried depth of the shield tunnel 3 is 30m, the groundwater level is 1m underground, the length of the shield casing unit 4 is 14m, and the ring width of the segment unit 5 is 2m; after considering the construction impact range, the size of the established three-dimensional model is 300m (length) × 300m (width) × 130m (height), and the three-dimensional The model is used to simulate the tunneling process of the shield machine on the soil body 7 to be excavated, wherein the segment unit 5 is used to resist soil pressure, groundwater pressure and other special loads in the shield simulation, and is the permanent lining structure of the shield tunnel 3. The grouting layer unit 6 is used to fill the gap between the segment unit 5 and the surrounding rock with grouting materials in the shield simulation to prevent the formation deformation and collapse caused by these gaps. After the grouting material is solidified, it can provide additional support force to enhance the stability of the shield tunnel 3. After solidification, the grouting layer forms a waterproof barrier to effectively prevent groundwater from penetrating into the tunnel through the gaps. By setting the segment unit 5 and the grouting layer unit 6, accurate simulation of the start of the shield can be achieved.

[0062] S2. Acquire the stratum distribution information of the shield tunneling starting construction section, and acquire the physical parameters of the soil of each stratum according to the stratum distribution information, wherein the physical parameters at least include the permeability coefficient.

[0063] In the embodiment of the present application, the soil physical parameters of each stratum are obtained, specifically including:

[0064] According to the geological survey results of the shield construction starting section, the stratum lithology and stratum thickness are divided to obtain the stratum distribution information of the shield construction starting section. According to the stratum distribution information, the physical parameters of the soil after grouting reinforcement of each stratum are obtained through indoor tests. The physical parameters also include density, cohesion, friction angle, elastic modulus and Poisson's ratio.

[0065] The distribution information of water-rich sand and gravel strata and the physical parameters of each stratum in a certain shield starting construction section are shown in Table 1.

[0066] Table 1 Stratigraphic distribution information and physical parameter data

[0067]

[0068] S3. Assigning corresponding physical parameters to the soil units of each layer in the three-dimensional model, and establishing a fluid-solid coupling model according to the groundwater level height and the permeability coefficient of the soil unit.

[0069] For the soil unit of the stratum in the three-dimensional model, the physical parameters of the soil corresponding to the stratum in the shield starting construction section are assigned to it, that is, the physical parameters of the soil in the actual project. At the same time, considering the groundwater infiltration effect, the groundwater level is set to 1m underground, and the fluid-structure interaction model (FSI) is established according to the permeability coefficient of each soil layer. The fluid-solid coupling model is used to describe the interaction and mutual influence between fluid and solid in water-rich sand and gravel strata. Through the fluid-solid coupling model, the influence of solid deformation on fluid load and the influence of fluid reaction force on solid in water-rich sand and gravel strata can be determined, so that the shield starting simulation is closer to the actual working condition, thereby improving the accuracy of the shield starting simulation.

[0070] ‌S4. Set the end soil reinforcement range, conduct static analysis on the three-dimensional model before the shield starts, and balance the initial stress.

[0071] In the embodiment of the present application, the end soil reinforcement range includes the transverse reinforcement length and the vertical reinforcement length. Figure 5 A schematic diagram of the transverse reinforcement range is shown, in which the shaded part represents the transverse reinforcement area, and the transverse reinforcement length includes equal shield outer diameter side reinforcement length B, shield outer diameter top reinforcement length h1 and shield outer diameter bottom reinforcement length h2. Figure 6 A schematic diagram of the longitudinal reinforcement range is shown, wherein the shaded portion represents the longitudinal reinforcement area, and the longitudinal reinforcement length is L.

[0072] In practical applications, various working conditions of the end soil reinforcement range can be set first. Specifically, in order to determine a reasonable transverse reinforcement length, the longitudinal reinforcement length L can be kept constant at 7m, and the transverse reinforcement length of the end soil can be taken as 1m, 3m, and 6m respectively, and a control condition of no reinforcement of the end soil can be set; then, the transverse reinforcement length of the end soil can be kept constant, and the longitudinal reinforcement length of the end soil can be taken as 7m, 20m, and 30m respectively. The specific working conditions are shown in Table 2.

[0073] Table 2 Data table of working conditions of end soil reinforcement range

[0074]

[0075] After setting the working conditions, set the end soil reinforcement range in sequence according to the working condition sequence number, and then perform static analysis on the three-dimensional model before the shield starts, which specifically includes the following steps:

[0076] S41. Set the boundary conditions of the 3D model and add the earth's gravity.

[0077] Specifically, the boundary conditions for the shield tunneling numerical simulation were set, the sides and bottom of the three-dimensional model were set as fixed boundaries, and the earth's gravity of 9.8 N / kg was added to the entire three-dimensional model.

[0078] S42. The Mohr-Coulomb elastoplastic model is selected as the constitutive model for the shield starting simulation. The Mohr-Coulomb model is also called the shear failure criterion, which means that when the soil reaches the limit equilibrium state and fails, its cohesion and internal friction angle also reach the limit value of the soil shear strength.

[0079] S43, performing initial stress balance on the three-dimensional model in the state where the excavation of the starting shield shaft is completed but not yet started, so that the initial displacement of each grid unit in the three-dimensional model is zero, that is, clearing the initial displacement of each grid unit in the three-dimensional model before the shield starts.

[0080] S5. Based on the three-dimensional model and the fluid-solid coupling model, the shield start-up is simulated to obtain the corresponding surface settlement value and tunnel vertical displacement value.

[0081] In the embodiment of the present application, the shield machine shell unit 4, the segment unit 5 and the grouting layer unit 6 are located at the location of the newly built tunnel. After the shield machine advance line breaks the tunnel door and kills the grid unit corresponding to the shield starting shaft, the shield starting is simulated, which specifically includes the following steps:

[0082] S51. Set the excavation steps of the shield machine, apply a thrust force in the excavation direction in front of the shield machine, and use the stiffness transfer method to simulate the excavation process of the leading line and the trailing line of the shield machine respectively.

[0083] Specifically, the tunneling simulation of the leading line and the trailing line of the shield machine includes the following steps respectively:

[0084] A. When the shield machine excavates to the nth step, the soil unit at the nth step tunnel position is killed, and the shield machine shell unit 4 at the nth step tunnel position is activated;

[0085] B. When the number of tunneling steps of the shield machine n is greater than a, the segment unit 5 at the position of the n-a+1-th tunnel step is activated, the grouting layer unit 6 at the position of the na-th tunnel step is activated, and the grouting pressure is applied vertically to the wall surface corresponding to the activated grouting layer unit 6;

[0086] C. Set the grouting layer unit 6 at the na-th tunnel position to a liquid state (elastic modulus 0.5 MPa), the grouting layer unit 6 at the na-1-th tunnel position to a solidified state (elastic modulus 280 MPa), and the grouting layer unit 6 at the na-2-th tunnel position to a solid state (elastic modulus 400 MPa).

[0087] Wherein, a represents the preset excavation step number, and a can be set according to the set excavation step number and shield machine size. In the embodiment of the present application, a total of 20 excavation steps are set in the entire simulation process. Figure 7 After the leading line of the shield machine enters the soil as a whole, that is, after 7 excavation steps, the rear line of the shield machine starts to start, and the value of a is 6.

[0088] When the number of excavation steps n of the shield machine is 7, the soil unit at the 7th step tunnel position is first killed, and the shield machine shell unit 4 at the 7th step tunnel position is activated, and then the segment unit 5 at the 2nd step tunnel position is activated, and then the grouting layer unit 6 at the 1st step tunnel position is activated, and the grouting pressure is applied vertically to the wall surface corresponding to the activated grouting layer unit 6, and then the grouting layer unit 6 at the 1st step tunnel position is set to liquid state.

[0089] When the number of excavation steps n of the shield machine is 8, the soil unit at the 8th step tunnel position is first killed, and the shield machine shell unit 4 at the 8th step tunnel position is activated, and then the segment unit 5 at the 3rd step tunnel position is activated, and then the grouting layer unit 6 at the 2nd step tunnel position is activated, and the grouting pressure is applied vertically to the wall surface corresponding to the activated grouting layer unit 6, and then the grouting layer unit 6 at the 2nd step tunnel position is set to liquid state, and the grouting layer unit 6 at the 1st step tunnel position is set to solidified state.

[0090] When the number of excavation steps n of the shield machine is 9, first kill the soil unit at the 9th step tunnel position, activate the shield machine shell unit 4 at the 9th step tunnel position, then activate the segment unit 5 at the 4th step tunnel position, and then activate the grouting layer unit 6 at the 3rd step tunnel position, and apply grouting pressure vertically to the wall surface corresponding to the activated grouting layer unit 6, then set the grouting layer unit 6 at the 3rd step tunnel position to liquid state, set the grouting layer unit 6 at the 2nd step tunnel position to solidified state, and set the grouting layer unit 6 at the 1st step tunnel position to solid state.

[0091] This is done by analogy until the tunneling process simulation of the leading and trailing lines of the shield machine is completed. By simulating details such as the end soil reinforcement range and the time-curing of the grouting layer unit 6, the accuracy of the shield machine start simulation and reinforcement range calculation can be further improved.

[0092] In an embodiment of the present application, the jacking force applied in the excavation direction in front of the shield machine is greater than the active earth pressure and less than the passive earth pressure, so as to ensure that the jacking force is sufficient to excavate the soil smoothly, while avoiding the influence of excessive jacking force on the starting simulation.

[0093] The calculation formula of the active earth pressure is as follows:

[0094] ;

[0095] The calculation formula of the passive earth pressure is as follows:

[0096] ;

[0097] in, represents the active earth pressure, represents the passive earth pressure, represents the number of strata at the tunnel location, Indicates The active earth pressure coefficient of the stratum is Indicates The passive earth pressure coefficient of the stratum is Indicates Soil weight of each layer (kN / m3), Indicates Soil thickness of each stratum (m), Indicates The soil cohesion of each layer (kPa).

[0098] S52. After the tunneling process simulation of the leading line and the trailing line of the shield machine is completed, the corresponding surface settlement value and the vertical displacement value of the tunnel are obtained.

[0099] After the simulation is completed, the simulation software automatically calculates the corresponding surface settlement value and tunnel vertical displacement value of the corresponding end soil reinforcement range. At the same time, the fluid-solid coupling model is used for fluid-solid coupling analysis during the calculation, so that the influence of solid deformation on fluid load and fluid reaction force on solid in water-rich sand and gravel formations can be considered when calculating surface settlement value and tunnel vertical displacement value, so that the shield starting simulation is closer to the actual working condition, thereby improving the accuracy of shield starting simulation and calculation of surface settlement value and tunnel vertical displacement value.

[0100] S6. After changing the end soil reinforcement range, repeat S4 to S5 to obtain the surface settlement values ​​and tunnel vertical displacement values ​​corresponding to different end soil reinforcement ranges.

[0101] After completing the current working condition simulation of the end soil reinforcement range, the end soil reinforcement range is set to the next working condition, and steps S4 to S5 are repeated to obtain the surface settlement values ​​and tunnel vertical displacement values ​​under all working conditions of the end soil reinforcement range.

[0102] S7. According to the surface settlement values ​​and tunnel vertical displacement values ​​corresponding to different end soil reinforcement ranges and combined with the shield tunnel control standards, the optimal end soil reinforcement range for shield tunneling is obtained.

[0103] In the embodiment of the present application, the optimal end soil reinforcement range includes the optimal transverse reinforcement length and the optimal vertical reinforcement length. The method for determining the optimal transverse reinforcement length and the optimal vertical reinforcement length specifically includes:

[0104] The maximum surface settlement value and the maximum tunnel vertical displacement value corresponding to the soil reinforcement range at different ends are determined, the surface settlement threshold and the tunnel vertical displacement threshold are determined according to the shield tunnel control standard, and the optimal transverse reinforcement length and the optimal vertical reinforcement length are determined according to the maximum surface settlement value and the surface settlement threshold value as well as the maximum tunnel vertical displacement and the tunnel vertical displacement threshold value.

[0105] In practical applications, a deformation curve can be drawn based on the surface settlement values ​​and tunnel vertical displacement values ​​under all working conditions within the end soil reinforcement range. The deformation curve includes a surface settlement curve diagram under different transverse reinforcement lengths, a tunnel vertical displacement curve diagram under different transverse reinforcement lengths, a surface settlement curve diagram under different longitudinal reinforcement lengths, and a tunnel vertical displacement curve diagram under different longitudinal reinforcement lengths. Then, the maximum surface settlement and the maximum tunnel vertical displacement under the transverse reinforcement length, as well as the maximum surface settlement and the maximum tunnel vertical displacement under the longitudinal reinforcement length, are determined based on the deformation curve.

[0106] In the embodiments of the present application, Figure 8 A surface settlement curve under different transverse reinforcement lengths is shown, which is used to indicate the surface settlement values ​​at different distances from the tunnel portal under different transverse reinforcement lengths while the longitudinal reinforcement length remains unchanged. Figure 8It can be seen that when the longitudinal reinforcement length remains unchanged, when the soil is not reinforced, the maximum surface settlement occurs at a distance of 8m from the tunnel door, reaching 62.18m; when the transverse reinforcement length is 1m, the maximum surface settlement occurs at a distance of 9m from the tunnel door, reaching 43.14mm, which is 30.6% lower than the unreinforced condition; when the transverse reinforcement length is 3m, the maximum surface settlement occurs at a distance of 11m from the tunnel door, reaching 35.52mm, which is 42.9% lower than the unreinforced condition; when the transverse reinforcement length is 6m, the maximum surface settlement occurs at a distance of 10m from the tunnel door, reaching 37.58mm, which is 39.6% lower than the unreinforced condition. The surface settlement value decreases first and then increases with the increase of the transverse reinforcement length. When the transverse reinforcement length is 3m, the surface settlement control is relatively good.

[0107] Fig. 9 A curve of tunnel vertical displacement under different transverse reinforcement lengths is shown, which is used to indicate the tunnel vertical displacement values ​​at different distances from the tunnel portal under different transverse reinforcement lengths while the longitudinal reinforcement length remains unchanged. The tunnel vertical displacement value is the floating value of the segment unit 5. Fig. 9 It can be seen that when the longitudinal reinforcement length remains unchanged, when the soil is not reinforced, the maximum vertical displacement of the tunnel occurs at a distance of 10m from the tunnel portal, reaching 12.25mm; when the transverse reinforcement length is 1m, the maximum vertical displacement of the tunnel occurs at a distance of 10m from the tunnel portal, reaching 11.11mm; when the transverse reinforcement length is 3m, the maximum vertical displacement of the tunnel occurs at a distance of 6m from the tunnel portal, reaching 11.42mm; when the transverse reinforcement length is 6m, the maximum vertical displacement of the tunnel occurs at a distance of 6m from the tunnel portal, reaching 10.88mm.

[0108] Fig.10 A surface settlement curve under different longitudinal reinforcement lengths is shown, which is used to indicate the surface settlement values ​​at different distances from the tunnel portal under different longitudinal reinforcement lengths while the transverse reinforcement length remains unchanged. Fig.10 It can be seen that when the transverse reinforcement length remains unchanged, when the soil is not reinforced, the maximum surface settlement occurs at a distance of 8m from the tunnel gate, reaching 62.18mm; when the longitudinal reinforcement length is 7m, the maximum surface settlement occurs at a distance of 11m from the tunnel gate, reaching 35.52mm, which is 42.9% lower than the unreinforced condition; when the longitudinal reinforcement length is 20m, the maximum surface settlement occurs at a distance of 8m from the tunnel gate, reaching 24.07mm, which is 61.3% lower than the unreinforced condition; when the longitudinal reinforcement length is 30m, the maximum surface settlement occurs at a distance of 8m from the tunnel gate, reaching 23.05mm, which is 62.9% lower than the unreinforced condition.

[0109] Fig.11 A curve diagram of tunnel vertical displacement under different longitudinal reinforcement lengths is shown, which is used to represent the tunnel vertical displacement values ​​at different distances from the tunnel portal under different longitudinal reinforcement lengths while the transverse reinforcement length remains unchanged. Fig.11 It can be seen that when the transverse reinforcement length remains unchanged, when the soil is not reinforced, the maximum vertical displacement of the tunnel occurs at a distance of 10m from the tunnel portal, reaching 12.25mm; when the longitudinal reinforcement length is 7m, the maximum vertical displacement of the tunnel occurs at a distance of 6m from the tunnel portal, reaching 11.42mm; when the longitudinal reinforcement length is 20m, the maximum vertical displacement of the tunnel occurs at a distance of 6m from the tunnel portal, reaching 11.48mm; when the longitudinal reinforcement length is 30m, the maximum vertical displacement of the tunnel occurs at a distance of 6m from the tunnel portal, reaching 11.47mm.

[0110] According to (GB 50911-2013) "Technical Specifications for Monitoring of Urban Rail Transit Projects" and (GB / T 51438-2021) "Design Standards for Shield Tunnel Projects", in the embodiment of this application, the ground settlement threshold is 25 mm, and the tunnel vertical displacement threshold is 20 mm. Figures 8 to 11 According to the deformation curve analysis, the optimal transverse reinforcement length is 3m and the optimal longitudinal reinforcement length is 20m.

[0111] To summarize, the method for calculating the starting reinforcement range of a shield machine in a water-rich sand and gravel formation provided in the embodiment of the present application constructs a three-dimensional model of the starting reinforcement of a shield machine in a water-rich sand and gravel formation, and constructs a fluid-solid coupling model. In the process of simulating the starting of a shield machine under the conditions of a water-rich sand and gravel formation, a fluid-solid coupling analysis is performed. The fluid-solid coupling phenomenon of water-rich sand and gravel formations in actual engineering projects is fully considered, and the accuracy of the shield machine starting simulation and reinforcement range calculation in water-rich sand and gravel formations is improved.

Claims

1. The calculation method of the initial reinforcement range of shield tunneling in water-rich sand and gravel strata is characterized by: The method comprises the following steps: S1. Establish a three-dimensional model of shield starting reinforcement in water-rich sand and gravel strata, and perform structured grid division on the three-dimensional model, wherein the three-dimensional model includes a physically simulated stratum, a starting shield shaft, a shield casing unit, a segment unit, and a grouting layer unit; S2, obtaining stratum distribution information of the shield tunneling starting construction section, and obtaining physical parameters of soil in each stratum according to the stratum distribution information, wherein the physical parameters at least include permeability coefficient; S3, assigning corresponding physical parameters to the soil units of each layer in the three-dimensional model, and establishing a fluid-solid coupling model according to the groundwater level height and the permeability coefficient of the soil unit; S4. Set the end soil reinforcement range, conduct static analysis on the three-dimensional model before the shield starts, and balance the initial stress; S5. Simulating the start of the shield tunneling based on the three-dimensional model and the fluid-solid coupling model to obtain corresponding surface settlement values ​​and tunnel vertical displacement values; S6. After changing the end soil reinforcement range, repeat S4 to S5 to obtain the ground settlement values ​​and tunnel vertical displacement values ​​corresponding to different end soil reinforcement ranges; S7. According to the surface settlement values ​​and tunnel vertical displacement values ​​corresponding to different end soil reinforcement ranges and combined with the shield tunnel control standard, the optimal end soil reinforcement range for shield tunneling is obtained; The shield start-up is simulated based on the three-dimensional model and the fluid-solid coupling model, specifically including: S51, setting the excavation steps of the shield machine, applying a thrust force in the excavation direction in front of the shield machine, and using the stiffness transfer method to simulate the excavation process of the leading line and the trailing line of the shield machine respectively; S52, when the tunneling process simulation of the leading line and the trailing line of the shield machine is completed, the corresponding surface settlement value and the vertical displacement value of the tunnel are obtained; The stiffness transfer method is used to simulate the tunneling process of the leading line and the trailing line of the shield machine, including: A. When the shield machine excavates to the nth step, the soil unit at the nth step tunnel position is killed, and the shield machine shell unit at the nth step tunnel position is activated; B. When the tunneling step number n of the shield machine is greater than a, the segment unit at the position of the n-a+1th tunnel step is activated, the grouting layer unit at the position of the nath tunnel step is activated, and the grouting pressure is applied vertically to the wall surface corresponding to the activated grouting layer unit, where a represents the preset tunneling step number; C. Set the grouting layer unit at the na-th tunnel position to liquid state, the grouting layer unit at the na-1-th tunnel position to solidified state, and the grouting layer unit at the na-2-th tunnel position to solid state.

2. The method for calculating the initial reinforcement range of a shield tunnel in a water-rich sandy gravel stratum according to claim 1 is characterized in that: Establish a three-dimensional model for shield tunneling reinforcement in water-rich sand and gravel strata, including: According to the geological environment of the shield construction starting section, the FLAC3D finite element software was used to establish a three-dimensional model of the shield starting reinforcement in the water-rich sand and gravel stratum. The X direction of the three-dimensional model is the cross-sectional direction of the shield tunnel, the Y direction is the shield excavation direction, and the Z direction is the vertical direction.

3. The method for calculating the initial reinforcement range of a shield tunnel in a water-rich sandy gravel stratum according to claim 1 is characterized in that: Obtain the physical parameters of each layer, including: The stratum lithology and stratum thickness are divided according to the geological survey results of the shield construction starting section, and the stratum distribution information of the shield construction starting section is obtained. Based on the stratum distribution information, the physical parameters of the soil after grouting reinforcement of each stratum are obtained through indoor tests.

4. The method for calculating the initial reinforcement range of a shield tunnel in a water-rich sandy gravel stratum according to claim 3 is characterized in that: The physical parameters also include density, cohesion, friction angle, elastic modulus and Poisson's ratio.

5. The method for calculating the initial reinforcement range of a shield tunnel in a water-rich sandy gravel stratum according to claim 1 is characterized in that: Perform static analysis on the 3D model before the shield starts and balance the initial stress, including: Set boundary conditions for the 3D model and add Earth gravity; The Mohr-Coulomb elastoplastic model is selected as the constitutive model for the shield starting simulation; The initial stress balance is performed on the three-dimensional model when the excavation of the initial shield shaft is completed but not yet started, so that the initial displacement of each grid unit in the three-dimensional model is zero.

6. The method for calculating the initial reinforcement range of a shield tunnel in a water-rich sandy gravel stratum according to claim 1 is characterized in that: The thrust force in the tunneling direction applied in front of the shield machine is greater than the active earth pressure and less than the passive earth pressure; The calculation formula of the active earth pressure is as follows: The calculation formula of the passive earth pressure is as follows: Among them, σ a represents the active earth pressure, σ p represents the passive earth pressure, m represents the number of strata at the tunnel location, k ai represents the active earth pressure coefficient of the ith stratum, k pi represents the passive earth pressure coefficient of the ith stratum, γ i represents the soil weight of the i-th layer, z i represents the soil thickness of the i-th layer, c i represents the soil cohesion of the i-th layer.

7. The method for calculating the initial reinforcement range of a shield tunnel in a water-rich sandy gravel stratum according to claim 1 is characterized in that: The end soil reinforcement range includes a transverse reinforcement length and a vertical reinforcement length, and the optimal end soil reinforcement range includes an optimal transverse reinforcement length and an optimal vertical reinforcement length.

8. The method for calculating the initial reinforcement range of a shield tunnel in a water-rich sandy gravel stratum according to claim 7 is characterized in that: The S7 specifically includes: The maximum surface settlement value and the maximum tunnel vertical displacement value corresponding to the soil reinforcement range at different ends are determined, the surface settlement threshold and the tunnel vertical displacement threshold are determined according to the shield tunnel control standard, and the optimal transverse reinforcement length and the optimal vertical reinforcement length are determined according to the maximum surface settlement value and the surface settlement threshold value as well as the maximum tunnel vertical displacement and the tunnel vertical displacement threshold value.

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