A sensitivity analysis method for design parameters of shallow buried sections of ultra-long span tunnels

Abstract

The present invention relates to the technical field of tunnel reinforcement, and more specifically, to a method for analyzing the sensitivity of design parameters of shallow buried sections of ultra-large-span tunnels. The present invention simulates a complete excavation cycle construction length as a benchmark for modeling, analyzes and statistically analyzes the changes in various parameters of advance small conduits, and finds the relationship between the spacing of the advance small conduits and settlement, deformation, and tension, thereby realizing a sensitivity analysis method for spacing settings and providing assistance for the design and construction of the spacing of the advance small conduits.

Description

Technical Field

[0001] The present invention relates to the technical field of tunnel reinforcement, and in particular to a sensitivity analysis method for design parameters of a shallow buried section of an ultra-large span tunnel. Background Art

[0002] In recent years, with the demand for underground space development, large or ultra-large span caverns exceeding 30 meters have become increasingly common, and even giant spans have been developed. In the tunnel entrance section, due to its shallow burial depth, the surrounding rock cannot form a natural arch after excavation, resulting in poor self-stability or a short self-stabilization time, which can easily lead to collapse.

[0003] In order to enter the tunnel safely, small guide tubes and mortar guide tubes are set on the side slope to reinforce the side slope and ensure the safety of entering the tunnel. The advance small guide tube is a very effective auxiliary construction method to stabilize the excavation working face. In the construction of weak and broken rock strata, the advance small guide tube plays a reinforcing role on the loose rock strata. After grouting, the stability of the loose and weak surrounding rock is enhanced, which is conducive to the stability of the surrounding rock after the completion of excavation and the completion of the initial support time, so as to prevent the surrounding rock from becoming unstable and damaged until it collapses. It is suitable for weak surrounding rock in the tunnel arch, loose, unbonded soil layers, sand layers with poor self-stabilization ability, and gravel (pebble) stone-level broken rock layers.

[0004] Advance small-pipe grouting can change the condition and stability of the surrounding rock. After the grout is injected into the weak, loose strata or cracks of the water-containing and broken surrounding rock, it can closely contact with them and solidify. The grout replaces the water and air between soil particles and rock cracks by filling and splitting, and then takes up the position. After a certain period of solidification, it cements the original loose soil particles or cracks into a whole, forming a new structure with high strength and good waterproof performance. The loose and broken condition of the surrounding rock is greatly improved.

[0005] However, there is currently no sensitivity analysis of the spacing design of advance small guide tubes in the ultra-shallow buried section of ultra-large span tunnels, making it impossible to provide a scientific and effective spacing design basis and optimization measures.

[0006] Based on the above reasons, the present invention designs a sensitivity analysis method for the design parameters of the shallow buried section of an ultra-large span tunnel. By simulating the complete excavation cycle construction length as the benchmark model, the changes in various parameters of the advance small ducts are analyzed and statistically analyzed to find the relationship between the spacing of the advance small ducts and settlement, deformation, and tension, thereby realizing a sensitivity analysis method for the spacing setting, which provides assistance for the design and construction of the spacing of the advance small ducts. Summary of the Invention

[0007] The purpose of the present invention is to overcome the shortcomings of the existing technology and provide a sensitivity analysis method for the design parameters of the shallow buried section of an ultra-large span tunnel. By simulating the complete excavation cycle construction length as a benchmark model, the changes in various parameters of the advance small ducts are analyzed and statistically analyzed to find the relationship between the spacing of the advance small ducts and settlement, deformation and tension, thereby realizing a sensitivity analysis method for the spacing setting, and providing assistance for the design and construction of the spacing of the advance small ducts.

[0008] To achieve the above object, the present invention provides a method for analyzing the sensitivity of design parameters of a shallow buried section of an ultra-long span tunnel, comprising the following steps:

[0009] S1, establish a three-dimensional engineering geological model:

[0010] S1-1: Determine the modeling scope based on the front-to-back distance between the left and right pilot pits, the step length of the side pilot pits, the lead distance of the side pilot pits relative to the main tunnel, and the step length of the main tunnel, taking the simulation of a complete excavation cycle as the construction length;

[0011] S1-2: Simplify the geological model appropriately based on the geological longitudinal profile of the shallow buried section of the outlet and the drilling histogram survey data;

[0012] S1-3: Based on the excavation construction process and initial support design of the shallow buried section of the surrounding rock, a three-dimensional finite element model of the tunnel excavation and support using the double-sidewall pilot method was established;

[0013] S1-4, simplified model, specifically including:

[0014] S1-4-1, ignoring the influence of the open hole section, which is outside the boundary model;

[0015] S1-4-2, using continuous plate elements to simulate the actual thickness of the C25 primary support, the plate internal forces can be used to verify the internal forces of the steel arch;

[0016] S1-4-3, boundary conditions at the terminal position of the excavation model, strengthen the primary support of the last ring of the end head, and increase the stiffness to 2 times to provide a good end head support effect;

[0017] S1-5, the 3D model was meshed using 10-node high-order tetrahedral elements, and the mesh was refined near the structure, resulting in a total of 60,064 solid elements and 110,507 nodes;

[0018] S2, set model parameters:

[0019] S2-1, the rock mass is assumed to be an elastic-plastic material, and the fragmented strongly weathered granite adopts the small strain soil hardening model;

[0020] S2-2, initial support C25 shotcrete, the initial support shotcrete is tightly integrated with the surrounding rock without setting a contact surface. The small conduit is simulated using the Embedded Pile unit. The Embedded Pile unit is a simulation function in the PLAXIS general geotechnical finite element calculation software. The Embedded Pile is a linear solid unit that takes into account the interaction between piles and soil. It can be used to simulate the embedded layer, grouting body and pile foundation of foundation pit anchor cables. In this invention, the Embedded Pile unit simulates the role of the advanced small conduit in the tunnel rock layer. The built-in interface is used to simulate the interaction between the conduit body and the surrounding rock; the interface strength is automatically generated according to the strength and stiffness of the adjacent strata.

[0021] S3, tunnel excavation process simulation: The construction process of the double-side wall pilot tunnel method in the shallow surrounding rock section under advanced support is simulated. An excavation cycle is simulated, and the upper left pilot tunnel, upper right pilot tunnel, and upper, middle, and lower steps of the main tunnel are excavated separately;

[0022] S4, changes in design parameters of advanced small catheters:

[0023] According to the construction process in S3, the design parameter variables of the small conduit are analyzed respectively:

[0024] S4-1, based on the slurry diffusion radius, assume the horizontal spacing and perform the vertical spacing change analysis;

[0025] S4-2: Select the appropriate longitudinal spacing based on the S4-1 analysis and conduct a transverse spacing variation analysis;

[0026] S4-3, design corresponding models according to the horizontal and vertical spacings of S4-1 and S4-2;

[0027] S5, analysis of changes in parameters of the advanced small catheter:

[0028] Based on the model of the advance small pipe set in S4-3, the surface settlement, initial support settlement and advance support tension are modeled and output. The numerical changes and effects of the horizontal and vertical spacing of the small pipes on the surface settlement, initial support settlement and advance support tension are analyzed through the visual charts of the output model.

[0029] In S1-3, the model size is X×Y×Z=40m×80m×45m. The horizontal distance from the left and right sides of the tunnel to the side boundary of the model is greater than 30m. The depth direction along the Z axis includes the surface blocky strongly weathered and moderately weathered granite.

[0030] In S2-2, the small tube itself is made of linear elastic material with a stiffness of E = 1E7 kN / m 2 , with a diameter of 0.5m. Here 1E71*10^7=10000000.

[0031] In S4, in order to eliminate the influence of the thickness variation of the overlying soil and thus conduct efficient analysis and design, the overlying soil is simplified to 8m thick uniformly distributed overlying soil.

[0032] The design parameter variables in S4 are the longitudinal spacing and horizontal spacing of the small ducts.

[0033] The horizontal spacing in S4-1 is 0.4m to 1.2m.

[0034] The longitudinal spacing in S4-2 is 0.7m to 2.1m.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] The present invention establishes a three-dimensional finite element model of excavation and support during a complete excavation cycle construction length, sets the geotechnical materials in the model, and forms multiple models with changes in the lateral and longitudinal spacing of the small guide tubes. Then, parameters such as the ground surface, initial support settlement, and support tension are output and statistical comparisons are made, thereby realizing the analysis of the influence of the spacing of the small guide tubes on the stability and safety during the surrounding rock excavation process. This provides an intuitive and scientific reference for the sensitivity analysis of the spacing of the advance small guide tubes in the ultra-shallow buried section of the ultra-large span tunnel, improves the safety factor of the ultra-large tunnel construction, and also reduces the construction cost to a certain extent and improves the construction efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a three-dimensional engineering geological model diagram of an embodiment of the present invention.

[0038] Figure 2 This is a three-dimensional geometric model diagram of an embodiment of the present invention.

[0039] Figure 3 This is a schematic diagram of the relative position relationship between the tunnel and the rock layer after the surface rock and soil are hidden in an embodiment of the present invention.

[0040] Figure 4 This is a diagram of the tunnel structure model of an embodiment of the present invention.

[0041] Figure 5 This is a three-dimensional grid model diagram of the advanced small-conductor support tunnel according to an embodiment of the present invention.

[0042] Figure 6 This is a model diagram of the construction process of the double-side wall pilot tunnel method under the advance anchor rod embodiment of the present invention.

[0043] Figure 7 Surface subsidence cloud maps at different longitudinal intervals according to an embodiment of the present invention.

[0044] Figure 8 This is a cloud diagram of the settlement of the primary support structure with different longitudinal spacings according to an embodiment of the present invention.

[0045] Figure 9This is a cloud diagram of the advance support tension at different longitudinal spacings according to an embodiment of the present invention.

[0046] Figure 10 Surface subsidence cloud maps at different lateral spacings according to an embodiment of the present invention.

[0047] Figure 11 This is a cloud diagram of the settlement of the primary support structure with different lateral spacings according to an embodiment of the present invention.

[0048] Figure 12 This is a cloud diagram of the advance support tension at different lateral spacings according to an embodiment of the present invention.

[0049] Figure 13 This is a curve diagram of surface and primary support settlement changing with spacing according to an embodiment of the present invention. DETAILED DESCRIPTION

[0050] The present invention will now be further described with reference to the accompanying drawings.

[0051] See also Figures 1 to 13 The present invention provides a method for analyzing the sensitivity of design parameters of shallow buried sections of ultra-large span tunnels:

[0052] 1. Numerical model design:

[0053] The shallow buried section of the V-grade surrounding rock at the left exit of the tunnel was selected. Based on the simulation analysis requirements, the modeling range was determined by taking into account factors such as the front-to-back distance between the left and right pilot pits, the step length of the side pilot pit steps, the lead distance of the side pilot pit relative to the main tunnel, and the step length of the main tunnel steps. The modeling range was determined based on the construction length of a complete excavation cycle. Based on the geological longitudinal profile of the shallow buried section of the left exit, the drill hole histogram and other survey data, a 3D engineering geological model was established by appropriate simplification, such as Figure 1 shown.

[0054] Considering the excavation construction process and initial support design of the shallow buried section of the tunnel surrounding rock, a three-dimensional finite element model of the tunnel double-side wall pilot method excavation support is established. The three-dimensional geometric model is as follows: Figure 2 As shown in Figure 1, the model size is X×Y×Z = 40m×80m×45m. The horizontal distance from the left and right sides of the tunnel to the side boundary of the model is greater than 30m. Along the depth direction (Z axis), it includes the surface layer of broken blocky strongly weathered granite and moderately weathered granite, such as Figure 3 shown.

[0055] This paper mainly analyzes the surrounding rock deformation and primary support stress before and after the adjustment of the double-side wall pilot tunnel construction scheme. On the premise of solving the main problem, the influence of minor and small factors is simplified as much as possible to highlight the main research object and improve the calculation efficiency. The numerical model is simplified as follows:

[0056] (1) Ignore the influence of the open hole section, which is outside the boundary model.

[0057] (2) Considering the steel arch and shotcrete comprehensively, continuous plate elements are used to simulate the C25 primary support of actual thickness. The internal force of the plate result can be used to verify the internal force of the steel arch. The structural model is shown in Figure 4 shown.

[0058] (3) The boundary conditions at the terminal (28m) of the excavation model are determined. The primary support of the last ring of the terminal is strengthened and the stiffness is increased to 2 times to provide a good terminal support effect.

[0059] The 3D solid model mesh is divided into 10-node high-order tetrahedron elements, and the mesh is encrypted near the structure, with a total of 60,064 solid elements and 110,507 nodes. Figure 5 shown.

[0060] 2. Model parameter design:

[0061] The rock and soil are assumed to be elastic-plastic materials, and the fragmented strongly weathered granite is simulated using the small strain soil hardening model (HSS). The physical and mechanical parameters of the rock and soil are shown in the following table:

[0062] Table 1 Physical and mechanical parameters of rock and soil

[0063]

[0064] The primary support C25 shotcrete is used. In addition, considering the contact characteristics between the primary support shotcrete and the surrounding rock, it is assumed that the two are closely integrated and no contact surface is set. The small pipe is simulated using the Embedded pile element, and the built-in interface is used to simulate the interaction between the pipe body and the surrounding rock. The interface strength is automatically generated based on the strength and stiffness of the adjacent strata. The small pipe itself is a linear elastic material with a stiffness of E = 1E7kN / m 2 , diameter 0.5m.

[0065] 3. Tunnel excavation process simulation:

[0066] According to the construction process of the double-side wall pilot tunnel method in the shallow buried section of the tunnel surrounding rock under advanced support, an excavation cycle construction process is simulated, such as Figure 6 shown.

[0067] 4. Advanced small catheter design parameter change plan:

[0068] According to the construction process of the double-side wall pilot tunnel method for the shallow buried section of the tunnel surrounding rock under advanced support, Small The design parameters of the catheter were analyzed for variations.

[0069] The main variables are the longitudinal and horizontal spacing of the small pipes. In order to eliminate the influence of the thickness change of the overlying soil and thus conduct efficient analysis and design, the overlying soil is simplified to 8m thick uniformly distributed overlying soil.

[0070] Parameter design of longitudinal spacing and horizontal spacing:

[0071] First, based on the slurry diffusion radius, assuming the horizontal spacing is 0.4m, the vertical spacing change analysis is performed;

[0072] Then, through the analysis in the previous step, the reasonable longitudinal spacing is selected as 1.4m, and the horizontal spacing change analysis is carried out.

[0073] The specific creation model and parameters are shown in Table 2 below:

[0074] Table 2 Changes in small catheter design parameters

[0075]

[0076] 5. Analysis of the design of advanced small catheter parameter changes:

[0077] 5.1. Vertical spacing analysis:

[0078] The length of the small duct is 4 m, and the setting values ​​of the longitudinal spacing of the small ducts in Model 1, Model 2 and Model 3 are 0.7 m, 1.4 m and 2.1 m respectively (1, 2 and 3 times of the cycle step respectively).

[0079] A. Surface subsidence:

[0080] Output surface settlement displacement cloud maps of Model 1, Model 2 and Model 3, such as Figure 7 shown.

[0081] Figure 7 As can be seen from the figure, the maximum surface settlement values ​​are 2.85mm, 3.04mm, and 3.58mm respectively. As the longitudinal spacing increases, the surface settlement also increases accordingly.

[0082] B. Primary support settlement:

[0083] Output the initial support structure settlement displacement cloud diagram of Model 1, Model 2 and Model 3, such as Figure 8 shown.

[0084] Figure 8 It can be seen that the settlement values ​​at the arch top of each model are the largest, which are 4.10mm, 4.39mm and 5.01mm respectively.

[0085] C. Advance support tension:

[0086] Output the tensile axial force of the small conduits of Model 1, Model 2 and Model 3, such as Figure 9 shown.

[0087] Figure 9 As can be seen from the figure, the maximum tensile forces on the small conduits near the tunnel face are 44.6 kN, 65.3 kN, and 79.3 kN, respectively. As the longitudinal spacing increases, the ultimate tensile forces on the small conduits increase significantly.

[0088] 5.2. Horizontal spacing analysis:

[0089] According to 5.1, a longitudinal spacing of 1.4 m was selected to establish Model 4 and Model 5. The transverse spacing of the small conduits in Model 2, Model 4, and Model 5 was set to 0.4 m, 0.8 m, and 1.2 m, respectively.

[0090] A. Surface subsidence:

[0091] Output surface settlement displacement cloud maps of Model 2, Model 4 and Model 5, such as Figure 10 shown.

[0092] Figure 10 It can be seen that the maximum surface subsidence was 3.05mm, 3.81mm and 4.98mm respectively; the increase was 24.9% and 63.3% respectively, which shows that the increase was very large.

[0093] B. Primary support settlement:

[0094] Output surface settlement displacement cloud maps of Model 2, Model 4 and Model 5, such as Figure 11 shown.

[0095] Figure 11 It can be seen that the maximum primary branch settlements are 4.39 mm, 5.37 mm and 6.68 mm respectively.

[0096] C. Advance support tension:

[0097] Output surface settlement displacement cloud maps of Model 2, Model 4 and Model 5, such as Figure 12 shown.

[0098] Figure 12 It can be seen that the extreme values ​​of tension are 65.3kN, 83.2kN and 115.2kN respectively.

[0099] In summary, the small pipes are designed with different longitudinal spacings. The surface settlement, primary branch settlement and small pipe tension are obtained through numerical analysis, and the statistics are shown in Table 3 below.

[0100] Table 3 Summary results of longitudinal spacing design

[0101] Numerical model Model 1 Model 2 Model 3 Longitudinal spacing (m) 0.7 1.4 2.1 Surface settlement (mm) 2.85 3.04 3.58 Initial support settlement (mm) 4.10 4.39 5.01 Small catheter tension (kN) 44.6 65.3 79.3

[0102] In order to study the effect of lateral spacing, the spacing was set to 0.8 m (model 4) and 1.2 m (model 4), and the surface settlement, primary branch settlement and small pipe tension were output. The statistics are shown in Table 4 below.

[0103] Table 4 Summary results of horizontal spacing design

[0104] Numerical model Model 2 Model 4 Model 5 Longitudinal spacing (m) 0.4 0.8 1.2 Surface settlement (mm) 3.04 3.81 4.98 Initial support settlement (mm) 4.39 5.37 6.68 Small catheter tension (kN) 65.3 83.2 115.2

[0105] As shown in Table 4, ground settlement, primary support vault settlement, and small conduit tension all increase significantly with increasing lateral spacing. When the lateral spacing reaches 1.2 m, the ground settlement reaches 4.98 mm and the tension reaches 115.2, exceeding the design characteristic value of 100 kN.

[0106] The settlement of the ground surface and primary support vault at different longitudinal and transverse intervals is plotted as a curve, e.g. Figure 13 shown.

[0107] from Figure 13 It can be seen that with the increase of longitudinal and transverse spacing, the settlement of the surface and the primary support vault both increase nonlinearly, and the deformation amplitude increases with the increase of spacing.

[0108] The above are merely preferred embodiments of the present invention, intended only to facilitate understanding of the method and core concepts of this application. The scope of protection of the present invention is not limited to the aforementioned embodiments; all technical solutions within the scope of the present invention are also within the scope of protection of the present invention. It should be noted that improvements and modifications that do not depart from the principles of the present invention, as readily apparent to those skilled in the art, should also be considered within the scope of protection of the present invention.

[0109] The present invention comprehensively solves the lack and deficiency of the existing technology in the design of spacing of advance small guide tubes in ultra-shallow buried sections of extra-large span tunnels, and the lack of sensitivity analysis of their spacing. By establishing a three-dimensional finite element model of excavation support during a complete excavation cycle construction length, and setting the rock and soil materials in the model, the lateral and longitudinal spacing changes of the small guide tubes form multiple models, and then output parameters such as surface, initial support settlement, and support tension and make statistical comparisons, thereby realizing the analysis of the impact of the spacing of the small guide tubes on the stability and safety during the excavation of the surrounding rock, providing an intuitive and scientific reference for the sensitivity analysis of the spacing of advance small guide tubes in ultra-shallow buried sections of extra-large span tunnels, improving the safety factor of ultra-large tunnel construction, and also reducing the construction cost to a certain extent and improving the construction efficiency.

Claims

1. A sensitivity analysis method for design parameters of shallow buried sections of ultra-long span tunnels, characterized by: The following steps are involved: S1, establish a three-dimensional engineering geological model: S1-1: Determine the modeling scope based on the front-to-back distance between the left and right pilot pits, the step length of the side pilot pits, the lead distance of the side pilot pits relative to the main tunnel, and the step length of the main tunnel, taking the simulation of a complete excavation cycle as the construction length; S1-2: Simplify the geological model appropriately based on the geological longitudinal profile of the shallow buried section of the outlet and the drilling histogram survey data; S1-3: Based on the excavation construction process and initial support design of the shallow buried section of the surrounding rock, a three-dimensional finite element model of the tunnel excavation and support using the double-sidewall pilot method was established; S1-4, simplified model, specifically including: S1-4-1, ignoring the influence of the open hole section, which is outside the boundary model; S1-4-2, using continuous plate elements to simulate the actual thickness of the C25 primary support, the plate internal forces can be used to verify the internal forces of the steel arch; S1-4-3, boundary conditions at the terminal position of the excavation model, strengthen the primary support of the last ring of the end head, and increase the stiffness to 2 times to provide a good end head support effect; S1-5, the 3D model was meshed using 10-node high-order tetrahedral elements, and the mesh was refined near the structure, resulting in a total of 60,064 solid elements and 110,507 nodes; S2, set model parameters: S2-1, the rock mass is assumed to be an elastic-plastic material, and the fragmented strongly weathered granite adopts the small strain soil hardening model; S2-2, primary C25 shotcrete mix. The primary shotcrete mix is ​​tightly integrated with the surrounding rock without setting a contact surface. The small pipe is simulated using Embedded pile elements, and the built-in interface is used to simulate the interaction between the pipe body and the surrounding rock. The interface strength is automatically generated according to the strength and stiffness of the adjacent strata. S3, tunnel excavation process simulation: The construction process of the double-side wall pilot tunnel method in the shallow surrounding rock section under advanced support is simulated. An excavation cycle is simulated, and the upper left pilot tunnel, upper right pilot tunnel, and upper, middle, and lower steps of the main tunnel are excavated separately; S4, changes in design parameters of advanced small catheters: According to the construction process in S3, the design parameter variables of the small conduit are analyzed respectively: S4-1, based on the slurry diffusion radius, assume the horizontal spacing and perform the vertical spacing change analysis; S4-2, selecting a reasonable longitudinal spacing through the analysis in S4-1, and performing a transverse spacing variation analysis; S4-3, designing corresponding models according to the horizontal and vertical spacings corresponding to S4-1 and S4-2; S5, analysis of changes in parameters of the advanced small catheter: Based on the model set up in S4-3 for the advance small pipe, the surface settlement, initial support settlement and advance support tension are modeled and output. The numerical changes and effects of the lateral and longitudinal spacing of the small pipes on the surface settlement, initial support settlement and advance support tension are analyzed through the visual charts of the output model.

2. The method for sensitivity analysis of design parameters of shallow buried section of ultra-long span tunnel according to claim 1 is characterized in that: In S1-3, the model size is X×Y×Z=40m×80m×45m, the horizontal distance from the left and right sides of the tunnel to the side boundary of the model is greater than 30m, and the surface layer includes blocky strongly weathered and moderately weathered granite along the Z-axis depth direction.

3. The method for sensitivity analysis of design parameters of shallow buried section of ultra-long span tunnel according to claim 1 is characterized in that: In S2-2, the small tube itself is made of linear elastic material with a stiffness of E=1E7 kN / m 2 , diameter 0.5m.

4. The method for sensitivity analysis of design parameters of shallow buried section of ultra-long span tunnel according to claim 1 is characterized in that: In S4, in order to eliminate the influence of the thickness variation of the overlying soil and thus perform analysis and design efficiently, the overlying soil is simplified to a uniform overlying soil with a thickness of 8 m.

5. The method for sensitivity analysis of design parameters of shallow buried section of ultra-long span tunnel according to claim 1 is characterized in that: The design parameter variables in S4 are the longitudinal spacing and horizontal spacing of the small tubes.

6. The method for sensitivity analysis of design parameters of shallow buried section of ultra-long span tunnel according to claim 1 is characterized in that: The horizontal spacing in S4-1 is 0.4m to 1.2m.

7. The method for sensitivity analysis of design parameters of shallow buried section of ultra-long span tunnel according to claim 1 is characterized in that: The longitudinal spacing in S4-2 is 0.7m to 2.1m.

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