A numerical analysis method for revealing the action characteristics of various support forms

Abstract

The application discloses a numerical analysis method for revealing action characteristics of various supporting forms, comprising the following steps: 1) obtaining construction information and geological information of a construction site; 2) performing mechanical equivalent on different supporting structure forms; 3) combining a reinforcing mode to establish a finite element model, and generating a finite element model for static force analysis of a tunnel; 4) establishing numerical simulation working conditions under different supporting structure forms, and performing mechanical equivalent setting on the different supporting structure forms in the step 2) mode; 5) running the model and extracting results, and using the results to analyze surrounding rock pressure and supporting bearing characteristics, and evaluate tunnel surrounding rock stability. The method provided by the application conforms to engineering practice, can accurately reflect supporting action characteristics, can scientifically and reasonably reveal matching of supporting rigidity and coordination of surrounding rock pressure distribution through comprehensive analysis of information such as tunnel surrounding rock deformation, surface subsidence and stress of a supporting structure, and provides theoretical guidance for reasonable design of supporting combination and efficient and safe construction of a tunnel.

Description

Technical Field

[0001] This invention relates to the field of tunnel engineering technology, and in particular to a numerical analysis method for revealing the performance characteristics of various support methods. Background Technology

[0002] Large-section tunnels in weak and fractured surrounding rock have poor self-stability. Inadequate support measures during excavation can easily lead to roof falls and collapses, causing severe economic losses and loss of life and property. For complex tunnel projects such as long-span tunnels in weak surrounding rock, advanced support methods such as pipe roofs, grouting pipes, and pre-anchor bolts are mainly used to improve the self-stabilizing bearing capacity of the surrounding rock, creating favorable conditions for tunnel excavation. How to select the most suitable combination of one or more advanced support methods from among the many available options to fully utilize the matching of support stiffness and the coordination of surrounding rock distribution, thereby improving tunnel stability and construction safety, is a pressing issue that needs to be addressed.

[0003] In response to this situation, the present invention proposes a numerical analysis method to reveal the characteristics of various support forms. This method can fully understand the deformation and mechanical properties of the tunnel surrounding rock under different support combinations, and can be used to analyze the surrounding rock pressure and support bearing characteristics, and evaluate the stability of the tunnel surrounding rock. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a numerical analysis method for revealing the functional characteristics of various support forms.

[0005] To achieve the above-mentioned technical objectives, the technical solution adopted by this invention is as follows:

[0006] This invention provides a numerical analysis method for revealing the functional characteristics of various support forms, including:

[0007] 1) Obtain construction and geological information of the construction site;

[0008] 2) Perform mechanical equivalence on different support structure forms;

[0009] 3) Establish a finite element model by combining reinforcement methods, and generate a finite element model for static analysis of the tunnel;

[0010] 4) Establish numerical simulation working conditions under different support structure forms. The mechanical equivalence settings for different support structure forms are performed using the method in step 2).

[0011] 5) Run the model and extract the results to analyze the surrounding rock pressure and support bearing characteristics, and evaluate the stability of the tunnel surrounding rock.

[0012] Furthermore, the construction information and geological information mentioned in step 1) include the topographic and geological conditions of the construction site, the physical and mechanical properties of the soil, the geometric characteristics of the tunnel structure, the form of the support structure, and the tunnel excavation method.

[0013] Furthermore, the tunnel excavation methods include the bench method, the central partition wall method, the cross central partition wall method, and the double-side wall pilot tunnel method.

[0014] Furthermore, the construction information and geological information specifically include the depth of the tunnel, topographical bias, lithology and integrity, the spacing and positional relationship of multiple tunnels, and the cross-sectional area of ​​the tunnel.

[0015] Furthermore, step 2) specifically involves: calculating the equivalent parameters for the pipe roof, small guide pipes, grouting reinforcement zone, initial support, and secondary lining; the equivalent method is as follows:

[0016] The pre-support grouting reinforcement is calculated according to the principle of equivalent reinforcement, extending into the corresponding soil layer. The thickness of the reinforcement ring is D, and the elastic modulus of the reinforcement zone is E. m As shown in the following formula:

[0017]

[0018]

[0019] In the formula: R is the grout diffusion radius, S is the distance between two adjacent grouting holes, and E m E0 is the equivalent elastic modulus of the formation, and S is the original elastic modulus of the formation. g For the equivalent interface of pipe roof support, E g S0 is the elastic modulus of the pipe roof, and S0 is the cross-sectional area of ​​the support section.

[0020] The elastic modulus E of the pipe roof g As shown in the following formula:

[0021] E g =(E1I1+E2I2) / (I1+I2) (3)

[0022] In the formula: E g E1 is the equivalent modulus of the grouting long pipe roof; E2 is the elastic modulus of the steel pipe; I1 is the moment of inertia of the steel pipe; I2 is the moment of inertia of the grout section.

[0023] The equivalent severity γ is shown in the following formula:

[0024] γ=(A1γ1+A2γ2) / (A1+A2) (4)

[0025] In the formula: γ1 is the unit weight of the steel pipe; γ2 is the unit weight of the mortar filling the pipe; A1 is the cross-sectional area of ​​the steel pipe; A2 is the cross-sectional area of ​​the mortar filling.

[0026] The initial support calculation parameters are as follows:

[0027] The steel arch frame and steel grating in the initial support are considered using the equivalent method. Based on the principle of equal compressive stiffness, the elastic modulus of the steel frame is converted into that of the shotcrete, and the calculation formula is as follows:

[0028]

[0029] In the formula: E n E represents the converted elastic modulus of concrete. c S represents the elastic modulus of shotcrete. r E is the cross-sectional area of ​​the I-beam. r S represents the elastic modulus of the steel arch or steel grating. c This represents the cross-sectional area of ​​the sprayed concrete.

[0030] Preferably, in step 3), MAIDAS-GTS is used to establish the finite element model.

[0031] Furthermore, the model establishment methods in step 3) include: ① directly generating a finite element model; ② first modeling the solid structure, and then generating a finite element model; ③ combining the actual characteristics of the engineering structure to initially establish a geometric model and mesh it in the CAD system, and then importing it into the simulation software platform for adjustment to generate a finite element model.

[0032] Furthermore, step 4) specifically involves: establishing corresponding numerical simulation conditions based on the actual support conditions of the excavated section. The simulated support conditions include advanced small guide pipes, advanced pipe roofs, advanced anchor bolts, shotcrete initial support, or combinations thereof. Different support structure forms are mechanically equivalently set using the method in step 2).

[0033] By adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art:

[0034] The numerical analysis method provided by this invention reveals the characteristics of various support forms, enabling a comprehensive understanding of the deformation and mechanical properties of tunnel surrounding rock under different support combinations. It can be used to analyze surrounding rock pressure and support bearing capacity, and to evaluate tunnel surrounding rock stability. This method can highly replicate actual construction processes on-site, allowing for a thorough understanding of tunnel safety at critical junctures. It provides significant guidance for the construction safety of complex tunnel projects and the rational selection of support forms. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 This is a schematic diagram of the tunnel cross-section dimensions.

[0037] Figure 2 This is a sample diagram of tunnel cross-section support.

[0038] Figure 3 This is a schematic diagram of the cross-section of the double-side-wall pilot tunnel method.

[0039] Figure 4 This is a finite element model of a tunnel.

[0040] Figure 5 Different support mechanical models.

[0041] Figure 6 This is a diagram showing the principal stress distribution of the initial support. (Unit: MPa)

[0042] Figure 7 This is a comparison chart of the calculated and measured deformation values. Detailed Implementation

[0043] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be particularly noted that the following embodiments are for illustrative purposes only and do not limit the scope of the invention. Similarly, the following embodiments are only some, not all, embodiments of the present invention, and all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] This invention provides a numerical analysis method for revealing the functional characteristics of various support forms, including:

[0045] 1) Obtain construction and geological information of the construction site. This includes information on the site's topographic and geological conditions, soil physical and mechanical properties, tunnel structure geometry, support structure type, and tunnel excavation methods. Specifically, this includes information on tunnel depth, topographic pressure, lithology and integrity, spacing and location relationships between multiple tunnels, and tunnel cross-sectional area. Excavation methods for complex tunnel projects typically include bench excavation, central partition wall excavation, cross-central partition wall excavation, and double-sided wall pilot tunnel excavation, which can be selected based on the specific project requirements.

[0046] 2) Mechanical equivalence is applied to different support structures, specifically: the calculation parameters for equivalent pipe roofs, small guide pipes, grouting reinforcement zones, initial support, and secondary lining are calculated; the physical and mechanical parameters of the tunnel surrounding rock can be obtained from geological survey reports or laboratory tests. The specific equivalence methods are as follows:

[0047] The pre-support grouting reinforcement is calculated according to the principle of equivalent reinforcement, extending into the corresponding soil layer. The thickness of the reinforcement ring is D, and the elastic modulus of the reinforcement zone is E. m As shown in the following formula:

[0048]

[0049]

[0050] In the formula: R is the grout diffusion radius, S is the distance between two adjacent grouting holes, and E m E0 is the equivalent elastic modulus of the formation, and S is the original elastic modulus of the formation. g For the equivalent interface of pipe roof support, E g S0 is the elastic modulus of the pipe roof, and S0 is the cross-sectional area of ​​the support section.

[0051] The elastic modulus E of the pipe roof g As shown in the following formula:

[0052] E g =(E1I1+E2I2) / (I1+I2) (3)

[0053] In the formula: E g E1 is the equivalent modulus of the grouting long pipe roof; E2 is the elastic modulus of the steel pipe; I1 is the moment of inertia of the steel pipe; I2 is the moment of inertia of the grout section.

[0054] The equivalent severity γ is shown in the following formula:

[0055] γ=(A1γ1+A2γ2) / (A1+A2) (4)

[0056] In the formula: γ1 is the unit weight of the steel pipe; γ2 is the unit weight of the mortar filling the pipe; A1 is the cross-sectional area of ​​the steel pipe; A2 is the cross-sectional area of ​​the mortar filling.

[0057] The initial support calculation parameters are as follows:

[0058] The steel arch frame and steel grating in the initial support are considered using the equivalent method. Based on the principle of equal compressive stiffness, the elastic modulus of the steel frame is converted into that of the shotcrete, and the calculation formula is as follows:

[0059]

[0060] In the formula: E nE represents the converted elastic modulus of concrete. c S represents the elastic modulus of shotcrete. r E is the cross-sectional area of ​​the I-beam. r S represents the elastic modulus of the steel arch or steel grating. c This represents the cross-sectional area of ​​the sprayed concrete.

[0061] 3) A finite element model is established by combining the reinforcement method, and a finite element model for tunnel static analysis is generated. This invention uses MAIDAS-GTS finite element technology for simulation. This numerical simulation method has a variety of constitutive models to choose from, mainly including: Mohr-Coulomb constitutive model (MC model), modified Mohr-Coulomb constitutive model (hard soil model HS model), modified Cambridge model (MCC model), etc. The HS model is suitable for soft and hard soils, and the calculation parameters of the HS model and MCC model are numerous and complex, making it difficult to obtain complete parameters. The relevant calculation parameters of the MC model can be directly obtained through conventional geotechnical tests and in-situ tests, and it is more widely used.

[0062] The model establishment methods include: ① directly generating a finite element model; ② first modeling the solid structure, and then generating a finite element model; ③ combining the actual characteristics of the engineering structure to initially establish a geometric model and mesh it in the CAD system, and then importing it into the simulation software platform for appropriate adjustments to generate a finite element model, so that the model has better adaptability to the geometric properties of the tunnel.

[0063] 4) Establish numerical simulation conditions under different support structure forms. The mechanical equivalence settings for different support structure forms are performed using the method described in step 2). Specifically:

[0064] Based on the actual support conditions of the excavated section, corresponding numerical simulation conditions are established. The simulated support conditions include advanced small guide pipes, advanced pipe roofs, advanced anchor bolts, shotcrete initial support, and other support forms or combinations thereof. Different support structure forms are mechanically equivalently set using the method in step 2).

[0065] 5) Run the model and extract the results to analyze the deformation of the surrounding rock (arch settlement, horizontal convergence, and surface settlement) and the stress characteristics of the support structure. Analyze the matching of support stiffness and the coordination of surrounding rock pressure distribution under different support conditions, reveal the stability of the tunnel surrounding rock system under different support structure forms, provide a basis for the rational design of tunnel support systems in different sections and under different working conditions, and ensure the efficiency, economy, and safety of tunnel support structure design.

[0066] The invention will be further illustrated below with an application example.

[0067] Application example:

[0068] (1) Project Overview

[0069] A municipal highway tunnel in Fujian Province is a four-bore, ultra-large cross-section tunnel project with a small clearance, consisting of two central eight-lane dual carriageways for motor vehicles and two pedestrian tunnels on either side (see...). Figure 1 The tunnel site has complex terrain with numerous isolated boulders, and exhibits shallow burial and topographical bias. The exposed lithology is primarily moderately to strongly weathered granite, with tectonic fracture zones passing through it, making it prone to landslides upon disturbance. Therefore, this four-bore tunnel with a small clearance is characterized by shallow burial bias, large span, and poor stability of the fractured surrounding rock, making it a key and critical engineering project. To ensure construction safety, it is proposed to use advanced pipe roof and advanced small-diameter pipe supports to reinforce the surrounding rock ahead, and to adopt a double-layer initial support scheme (see...). Figure 2 For large-span tunnels, the double-side-wall pilot tunnel method is used for excavation.

[0070] (2) Information acquisition and parameter setting

[0071] Based on the principle of mechanical equivalence, the physical and mechanical parameters of materials such as surrounding rock, grouting reinforcement zone, and advanced pipe roof are shown in Table 1 below. This complex, small-clearance, large-span tunnel project adopts the double-side-wall pilot tunnel method for construction. The excavation sequence is as follows: First, advanced support and grouting pre-support are carried out using pipe roof or small-diameter pipes. The left pilot tunnel is then excavated using a drilling rig on the upper bench. Immediately after excavation, wet spraying is carried out, with an initial shotcrete layer of 3-5cm. After completion, anchor bolts are drilled and grouting is performed on the working face. Then, a double-layer steel mesh is installed, steel supports are erected, and a second shotcrete operation is carried out. The second layer of initial support is then constructed. The left pilot tunnel is then excavated and supported on the lower bench, and promptly closed into a ring with a 2m stagger between the upper and lower benches. The right and middle pilot tunnels are then excavated and supported in sequence, with the overall procedure being the same as that of the left pilot tunnel. Each excavation step is completed by erecting one steel arch frame at a time, constituting one excavation cycle. The longitudinal spacing between the left and right pilot tunnels is 10m, and the longitudinal spacing between the central pilot tunnel and the left and right pilot tunnels is also 10m, to minimize mutual interference and adverse effects during construction. Once the entire cross-section is formed, the invert arch should be constructed promptly to seal the entire cross-section into a ring (see...). Figure 3 ).

[0072] Table 1 Calculation parameters

[0073]

[0074]

[0075] (3) Model building

[0076] This invention employs a third model-building method in the actual engineering modeling process. First, a geometric model is created in CAD, then imported into Midas software to build a solid model. After the solid model is built, meshing is performed. A tetrahedral hybrid meshing method is used, with the mesh size of the upper tunnel layer slightly larger than that of the main tunnel body. During the main tunnel meshing, the mesh size is reduced at special locations such as the arch foot and arch waist to improve calculation accuracy. After the tunnel meshing is completed, appropriate constraints are applied to the finite element model, and finally, construction phase management is implemented according to the actual on-site construction conditions.

[0077] The Mohr-Coulomb model was selected as the constitutive model. Based on the actual site conditions, a 3D model with dimensions x×y×z of 140m×120m×60m was chosen. Boundary constraints were applied to the front, back, left, right, and bottom boundaries of the model, while the top boundary was a free surface. Rotational constraints were applied within the pipe roof. Only the self-weight stress field was considered, with a gravitational acceleration of 9.8 m / s². 2 The overall model and mesh generation are as follows: Figure 4 As shown in the figure. The excavation method of the model is consistent with the on-site construction, adopting the double-sidewall excavation method. During the tunnel excavation, each excavation advance is 2m, and a total of 30 excavation advances are made. Each excavation step is supported according to the actual construction. The left pilot tunnel is excavated first. The upper and lower steps of the left pilot tunnel are 2m apart. The left and right pilot tunnels are 10m apart. The middle pilot tunnel is 10m away from the right pilot tunnel. After the excavation of each pilot tunnel is completed, the internal support is removed 4m away. Finally, the secondary lining is poured. In the model, anchor bolts and small guide pipes are simulated using embedded trusses, pipe roofs are simulated using beam elements, and initial supports are simulated using plate elements. Grouting reinforcement and secondary lining are simulated using solid elements, and the properties are changed through construction stages.

[0078] To fully understand the mechanical and deformation characteristics of tunnel surrounding rock under different support conditions, evaluate the stability of tunnel surrounding rock, and provide a theoretical basis for optimizing support schemes, four support combination conditions were designed based on actual engineering conditions (see...). Figure 5 (and Table 2).

[0079] Table 2 Support Summary

[0080]

[0081]

[0082] (4) Results Analysis

[0083] This complex tunnel project was used as an example for calculations. The maximum principal stress data for typical locations of the initial support under various working conditions were extracted. The analysis results show that without advance support, significant compressive stress is widely distributed at the tunnel arch crown, arch waist, and arch foot, with the maximum principal stress at the arch foot reaching 19 MPa, approaching the flexural compressive strength limit of concrete. After implementing advance support, the overall support stress is significantly improved, with reduced stress magnitude and more uniform distribution (see Principal Stress Distribution for details). Figure 6 When using single-layer pre-support (pipe roof or small-diameter pipe), the stress distribution is generally similar. Single pre-support has little impact on the arch foot stress, but it significantly improves the stress in other areas, reducing the stress at the arch waist and arch bottom by about 40%. After implementing double-layer pre-support, the arch foot stress is significantly reduced, by about 47%, the arch bottom stress by about 40%, and the arch waist and arch top stress by about 70%-80%, far less than the ultimate compressive strength of concrete. This is because the shell formed by the pre-support creates an arch effect, bearing the pressure transmitted from the upper surrounding rock. This conclusion is consistent with the above analysis results of anchor bolt internal forces and surrounding rock deformation. It is evident that different pre-support methods have different effects on improving the initial support stress state. Only when a certain support strength is achieved and the support stiffness is well-matched will the initial support stress value decrease, and the distribution of surrounding rock pressure will be more coordinated, resulting in a more reasonable initial support stress. In summary, even with double-layer initial support, the lack of advanced support in this long-span tunnel project will increase the stress on the support, which is not conducive to the safety and long-term stability of tunnel construction.

[0084] The numerical simulation results were compared with the measured deformation results of the trial excavation section. Analysis showed that the overall deformation control effect of single pipe roof or small-diameter pipe pre-support was comparable. In sections under conditions one and two, tunnel deformation tended to stabilize approximately 60-70 days after construction began, with crown settlement of approximately 9.5 mm and horizontal convergence of approximately 10.8 mm, far less than the specified values. The overall deformation control effect of pipe roof + small-diameter pipe or double-layer small-diameter pipe composite pre-support was comparable. In sections under conditions three and four, tunnel deformation tended to stabilize approximately 50-65 days after construction began, with crown settlement of approximately 22.7 mm and horizontal convergence of approximately 23.1 mm, less than the specified values. Comparing the aforementioned calculation results, the measured values ​​are comparable to the calculated values ​​and meet the requirements. Slight differences exist due to the calculation not fully considering the effects of rock mass anisotropy and fracture zones, but the overall deformation is close to the calculated results (see...). Figure 7 The calculation results can effectively reflect the deformation characteristics of the surrounding rock. The deformation value is much smaller than the specified value, indicating that the tunnel surrounding rock system is stable. This demonstrates the rationality of the calculation method and support scheme, and the calculation results provide guidance for the scientific design of the support scheme.

[0085] The above description is only a part of the embodiments of the present invention and does not limit the scope of protection of the present invention. Any equivalent device or equivalent process transformation made based on the content of the present invention specification and drawings, or direct or indirect application in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A numerical analysis method for revealing the functional characteristics of various support forms, characterized in that, include: 1) Obtain construction and geological information of the construction site; 2) Mechanical equivalence is applied to different support structure forms, specifically: equivalent calculation parameters are calculated for pipe roof, small guide pipe, grouting reinforcement zone, initial support, and secondary lining; the specific equivalence methods are as follows: The pre-support grouting reinforcement is calculated according to the principle of equivalent reinforcement, extending into the corresponding soil layer. The thickness of the reinforcement ring is D, and the elastic modulus of the reinforcement zone is E. m As shown in the following formula: （1） （2） In the formula: R Where is the slurry diffusion radius, S The distance between two adjacent grouting holes. E m This is the equivalent elastic modulus of the formation. E 0 represents the original elastic modulus of the formation. S g For the equivalent interface of pipe roof support, E g The elastic modulus of the pipe roof. S 0 represents the cross-sectional area of ​​the support section; The elastic modulus E of the pipe roof g As shown in the following formula: （3） In the formula: E g Equivalent modulus for grouting long pipe shed; The elastic modulus of the steel pipe; The elastic modulus of the mortar filling the pipe; Let be the moment of inertia of the steel pipe; The moment of inertia of the mortar filling section; Equivalent Severe γ As shown in the following formula: （4） In the formula: For the weight of steel pipes; The density of the mortar filling the pipe; The cross-sectional area of ​​the steel pipe; The cross-sectional area of ​​the filling mortar; The initial support calculation parameters are as follows: The steel arch frame and steel grating in the initial support are considered using the equivalent method. Based on the principle of equal compressive stiffness, the elastic modulus of the steel frame is converted into that of the shotcrete, and the calculation formula is as follows: （5） In the formula: E n E represents the converted elastic modulus of concrete. c S represents the elastic modulus of shotcrete. r E is the cross-sectional area of ​​the I-beam. r S represents the elastic modulus of the steel arch or steel grating. c This refers to the cross-sectional area of ​​the sprayed concrete. 3) Establish a finite element model by combining reinforcement methods, and generate a finite element model for static analysis of the tunnel; 4) Establish numerical simulation conditions under different support structure forms. The mechanical equivalence settings for different support structure forms are performed using the method in step 2). 5) Run the model and extract the results to analyze the surrounding rock pressure and support bearing characteristics, and evaluate the stability of the tunnel surrounding rock.

2. The numerical analysis method for revealing the functional characteristics of multiple support forms as described in claim 1, characterized in that, The construction information and geological information mentioned in step 1) include the topographic and geological conditions of the construction site, the physical and mechanical properties of the soil, the geometric characteristics of the tunnel structure, the form of the support structure, and the tunnel excavation method.

3. The numerical analysis method for revealing the functional characteristics of multiple support forms as described in claim 1, characterized in that, The tunnel excavation methods include the bench method, the central partition wall method, the cross central partition wall method, and the double-side wall pilot tunnel method.

4. The numerical analysis method for revealing the functional characteristics of multiple support forms as described in claim 2, characterized in that, The construction and geological information specifically includes the depth of the tunnel, topographical bias, lithology and integrity, the spacing and positional relationship of multiple tunnels, and the cross-sectional area of ​​the tunnel.

5. The numerical analysis method for revealing the functional characteristics of multiple support forms as described in claim 1, characterized in that, Step 3) Use MAIDAS-GTS to build the finite element model.

6. The numerical analysis method for revealing the functional characteristics of multiple support forms as described in claim 1, characterized in that, The methods for establishing the model in step 3) include: ① directly generating the finite element model; ② first modeling the solid structure, and then generating the finite element model; ③ initially establishing the geometric model and meshing it in the CAD system based on the actual characteristics of the engineering structure, and then importing it into the simulation software platform for adjustment to generate the finite element model.

7. The numerical analysis method for revealing the functional characteristics of multiple support forms as described in claim 1, characterized in that, Step 4) Specifically, establish corresponding numerical simulation working conditions based on the actual support conditions of the excavated section. The simulated support working conditions include advanced small guide pipes, advanced pipe roofs, advanced anchor bolts, shotcrete initial support or combinations thereof. Different support structure forms are mechanically equivalently set using the method in Step 2).

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