Dynamic design method for TBM tunnel supporting structure

Abstract

The invention discloses a dynamic design method for a TBM tunnel supporting structure, which belongs to the technical field of tunnel construction and comprises the following steps: S1, calculating supporting stiffness generated by different supporting operations according to actual tunnel surrounding rock parameters, supporting parameters and construction procedures, and calculating virtual supporting force; s2, constructing a two-dimensional plane strain model, substituting the support rigidity obtained in the step S1 into the model to calculate final settlement of the tunnel, and obtaining reasonable surrounding rock parameters required by numerical simulation under the surrounding rock condition of the tunnel; and S3, three-dimensional rough hole excavation model calculation is carried out, a surrounding rock pressure release rule is obtained, supporting resistance is adjusted by adjusting supporting parameters, and optimal selection of the supporting parameters is carried out while the surrounding rock pressure release rule is met. According to the dynamic design method for the TBM tunnel supporting structure, the supporting scheme can be adjusted according to different surrounding rock parameters, so that the supporting design is more efficient, the construction cost is effectively reduced, and the construction efficiency and the supporting quality are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of tunnel construction, and in particular to a dynamic design method for a TBM tunnel support structure. Background Art

[0002] With the accelerated pace of urbanization in my country, the development and utilization of underground space has become a crucial component of urban construction. Tunnels, as crucial underground space projects, have a direct impact on people's lives and socioeconomic development through their safety, stability, and construction efficiency. However, in tunnel surrounding rock support, selecting appropriate support methods to ensure surrounding rock stability and improve construction efficiency has become a pressing issue. Therefore, this study explores this issue and proposes a new method for surrounding rock support in TBM tunnels. Summary of the Invention

[0003] The purpose of the present invention is to provide a dynamic design method for a TBM tunnel support structure to solve the problems existing in the above-mentioned background technology.

[0004] To achieve the above object, the present invention provides a dynamic design method for a TBM tunnel support structure, comprising the following steps:

[0005] S1. Calculate the support stiffness generated by different support operations and the virtual support force based on the actual tunnel surrounding rock parameters, support parameters, and construction procedures.

[0006] S2. Construct a two-dimensional plane strain model and substitute the support stiffness obtained in S1 into the model to calculate the final settlement of the tunnel. This settlement must correspond to the settlement data measured on site within the allowable error range. By adjusting the surrounding rock parameters, the reasonable surrounding rock parameters required for numerical simulation under the surrounding rock conditions of this tunnel can be fine-tuned. These parameters are the optimal parameters required for the simulation.

[0007] S3. Perform three-dimensional rough tunnel excavation model calculation to obtain the surrounding rock pressure release law for this tunnel. This law can determine the minimum required support resistance at different construction stages. The support resistance is adjusted by adjusting the support parameters. While satisfying the surrounding rock stress release law, the support parameters are optimized. Therefore, the optimized support parameters for this tunnel can be obtained, which can provide a basis for support selection.

[0008] Preferably, the support stiffness provided by the steel arch and anchor in S1 is:

[0009]

[0010] Among them, R0 is the excavation diameter; A set is the cross-sectional area of ​​the steel arch; E stis the elastic modulus of steel; d is the longitudinal spacing of the steel arch; h set is the vertical height of the steel arch cross section; Q bolt is the load-deformation constant of the anchor end and the anchor head; E bolt is the elastic modulus of the anchor rod; D bolt is the anchor diameter; L bolt is the anchor rod length; S t 、S l are the circumferential spacing and longitudinal spacing of the anchor rods, respectively;

[0011] When selecting the support type, different working conditions can be fully set, and the above formula can be used to calculate the support stiffness. Finally, it can be integrated into the support resistance calculation to determine whether it meets the requirement of not exceeding the reasonable value range.

[0012] For shotcrete, when its thickness is greater than 1 / 25 of the tunnel radius, its maximum support stiffness can be calculated based on the elastic thick-walled tube principle:

[0013]

[0014] Among them, E con is the elastic modulus of shotcrete; v con is the Poisson's ratio of shotcrete; t shot is the elastic thickness of shotcrete.

[0015] When the three support structures jointly bear the surrounding rock pressure, the combined structure can be regarded as a parallel system composed of various support structure units, and the total support stiffness of the support system is approximately equal to the sum of the support stiffness of each support unit.

[0016] Preferably, the calculation formula of the virtual support force in S1 is:

[0017]

[0018] Where p0 is the original rock stress; x is the distance from the excavation surface; is the virtual support force; is the final displacement around the tunnel without support.

[0019] It can be considered that the support force p = p0-p2, so the load borne by the combined structure is calculated by the following formula:

[0020]

[0021] Among them, x B K is the distance between the excavation face and the tunnel face during anchor bolting; com is the comprehensive stiffness of the surrounding rock; G is the shear modulus.

[0022] Preferably, in the two-dimensional plane strain model in S2, each support method is equivalent to a support equivalent reinforcement ring, and the parameters of the equivalent reinforcement ring are the parameters obtained by calculation in S1. The final settlement of the tunnel is calculated through this two-dimensional plane strain model, and the surrounding rock parameters are continuously adjusted under the condition of not exceeding the allowable error, so that the final model deformation is consistent with the actual measured variable diameter conditions on site, and the reasonable surrounding rock parameters of the tunnel are obtained.

[0023] Preferably, in S3, based on the reasonable surrounding rock parameters selected in S2, the deformation of the unsupported excavation of the three-dimensional model is calculated, and then the surrounding rock pressure release rate is calculated based on the deformation data of the three-dimensional model surrounding rock simulation. The formula is:

[0024]

[0025] Where λ is the stress release rate of the surrounding rock.

[0026] Preferably, the surrounding rock pressure release law in S3 is the change law of the surrounding rock pressure release rate at a certain section as the tunnel face moves away from the tunnel face under the tunnel conditions, thereby obtaining the theoretically acceptable minimum support resistance of the tunnel. The specific calculation method is:

[0027] The original rock stress of this tunnel is multiplied by the surrounding rock pressure release rate at different stages. This is the magnitude of stress release at different stages. After eliminating the effect of the virtual support force, the minimum support resistance is obtained.

[0028] Preferably, in S3, support parameters are continuously adjusted through numerical simulation to meet the requirement of not less than the minimum support resistance, and support parameters that are better than the current support situation are selected. After verification with measured data, it can provide a design basis for actual projects.

[0029] Therefore, the present invention adopts the above-mentioned dynamic design method of TBM tunnel support structure, which can adjust the support scheme according to different surrounding rock parameters, making the support design more efficient, effectively reducing construction costs, and improving construction efficiency and support quality.

[0030] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a flow chart of a dynamic design method for a TBM tunnel support structure according to the present invention;

[0032] Figure 2 Schematic diagram of virtual support force in an embodiment of the present invention;

[0033] Figure 3 This is a schematic diagram of reasonable surrounding rock selection parameters according to an embodiment of the present invention;

[0034] Figure 4A schematic diagram of surrounding rock pressure release law according to an embodiment of the present invention;

[0035] Figure 5 Schematic diagram of anchor rod and shotcrete support force according to an embodiment of the present invention; (a) is anchor rod support force; (b) is shotcrete support force;

[0036] Figure 6 Schematic diagram of the maximum support resistance of a steel frame according to an embodiment of the present invention;

[0037] Figure 7 Schematic diagram of surrounding rock stress release rate according to an embodiment of the present invention;

[0038] Figure 8 This is the arch stress monitoring curve of the embodiment of the present invention;

[0039] Figure 9 This is the spray mixing stress monitoring curve of an embodiment of the present invention;

[0040] Figure 10 This is the axial force monitoring curve of the left arch waist anchor rod in the embodiment of the present invention;

[0041] Figure 11 This is the arch stress monitoring curve of the embodiment of the present invention;

[0042] Figure 12 This is a concrete stress monitoring curve according to an embodiment of the present invention;

[0043] Figure 13 This is the axial force monitoring curve of the arch anchor rod in the embodiment of the present invention. DETAILED DESCRIPTION

[0044] The following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort shall fall within the scope of protection of the present invention.

[0045] See also Figures 1-13 A dynamic design method for a TBM tunnel support structure includes the following steps:

[0046] S1. Calculate the support stiffness generated by different support operations and the virtual support force based on the actual tunnel surrounding rock parameters, support parameters, and construction procedures.

[0047] S2. Construct a two-dimensional plane strain model and substitute the support stiffness obtained in S1 into the model to calculate the final settlement of the tunnel. This settlement must correspond to the settlement data measured on site within the allowable error range. By adjusting the surrounding rock parameters, the reasonable surrounding rock parameters required for numerical simulation under the surrounding rock conditions of this tunnel can be fine-tuned. These parameters are the optimal parameters required for the simulation.

[0048] S3. Perform three-dimensional rough tunnel excavation model calculation to obtain the surrounding rock pressure release law for this tunnel. This law can determine the minimum required support resistance at different construction stages. The support resistance is adjusted by adjusting the support parameters. While satisfying the surrounding rock stress release law, the support parameters are optimized. Therefore, the optimized support parameters for this tunnel can be obtained, which can provide a basis for support selection.

[0049] In this embodiment, a tunnel is taken as an example. The tunnel depth is 1200 m, the rock type is mainly Himalayan granite, and the TBM method is used for excavation.

[0050] 1. Calculation of virtual support force and support stiffness

[0051] Since the support resistance calculation requires the integration of the virtual support force, Matlab is used to perform relevant calculations of the virtual support force before this.

[0052]

[0053] in, x is the distance between the excavation face and the tunnel face; x>0 means behind the excavation face; R max is the maximum plastic zone radius of the tunnel without support, which can be obtained from field measurements (loosening zone test); is the equivalent stress release rate; p f (x) is the virtual support force; the support stiffness parameters are shown in Table 1-2.

[0054] Table 1 Calculation table of maximum support stiffness of arch anchor

[0055]

[0056] Table 2 Maximum support stiffness of spray-mixed concrete

[0057]

[0058] 2. Reasonable selection of surrounding rock parameters:

[0059] The support stiffness calculated based on the above-mentioned support parameters of this tunnel can be used as the basis for the value of the two-dimensional plane strain equivalent support stiffness parameter. After calculation using the two-dimensional plane strain model, the surrounding rock parameter values ​​for this tunnel can be obtained for subsequent research.

[0060] In conjunction with the "Code for Design of Railway Tunnels" (TB-10003-2016), after multiple calculations and verifications, we ultimately determined reasonable values ​​for surrounding rock parameters for Grades II to V, as shown in Table 3 below. Comparative analysis shows that the model-calculated settlements are consistent with actual settlements, and this research finding can provide support for subsequent work. The settlement calculation results for these surrounding rock parameters are consistent with the actual final settlement of the surrounding rock in the project and can be incorporated into 3D numerical model calculations.

[0061] Table 3 Surrounding rock parameter values

[0062]

[0063] 3. Law of stress release of surrounding rock:

[0064] Based on the above-mentioned surrounding rock parameters at all levels, the deformation of the unsupported excavation of the three-dimensional model is calculated, and then the equivalent stress release rate of the surrounding rock is calculated using the empirical formula based on the surrounding rock simulation data at all levels.

[0065] Calculations show that under unsupported excavation conditions for tunnels with rock masses of grades II to IV, when the analysis section is located beyond a certain range in front of the excavation face, the surrounding rock is unaffected by the excavation, and the equivalent stress release rate is 0. As the excavation face gradually advances, the virtual support force is gradually released, reaching 50% after the shield is dragged out. When the analysis section is located beyond a certain range (approximately five times the tunnel diameter) in front of the excavation face, the spatial constraint effect of the excavation face on it completely disappears, the virtual support force is 0, and the corresponding equivalent stress release rate is 100%.

[0066] 4. Optimization selection of support resistance:

[0067] To further analyze the effects of the support systems working together, it is necessary to calculate different supports separately, consider their support characteristics, and reveal the stress release law after the support is applied. This can determine the value of the support's share of the surrounding rock stress, which can provide a basis for the design of the minimum support resistance.

[0068] The support forces of both anchors and shotcrete exhibit time effects, primarily due to the hardening of the concrete. The interaction between anchors, shotcrete, and surrounding rock can be expressed using the stress release rate. For example, to calculate the anchor support force, combining the previously calculated parameters, we need to use MATLAB to plot the integral of y = -35.2K(x)*exp(-3x / 8) / (K(x)+420) with respect to x at (5, 100), where K(x) = 0.0765 - 0.0765*exp(-5x+25).

[0069] Anchor rod:

[0070]

[0071] Spray mixing:

[0072]

[0073] Where p2(x) = p1(x) = virtual support force, x C 、x B They represent the distance between the excavation face and the tunnel face during the construction of shotcrete and anchor respectively, and K is the stiffness required above.

[0074] Arch support is different from anchor rods and shotcrete in that its stiffness does not increase with time. Therefore, when analyzing the steel arch, it is assumed that the arch can reach the maximum support stiffness when the shield is exposed. For a certain analysis section, the steel arch bears the support load, which can be calculated using Matlab according to the following formula.

[0075]

[0076] Among them, K set is the equivalent stiffness of the steel frame; The displacement of the surrounding rock that has occurred when support begins. is the displacement at x from the tunnel face; K i is the support stiffness per unit length; it is calculated by the following formula:

[0077]

[0078] Where v is Poisson's ratio; p f (x B ) is in x B The virtual support force at ; R0 is the tunnel radius;

[0079] The maximum support resistance of the steel frame can be calculated by the following formula:

[0080]

[0081] Where h is the equivalent height of the cross section; b is the equivalent width of the cross section; σ ic is the equivalent compressive strength of the steel frame; A i is the cross-sectional area of ​​the steel frame; σ i The compressive strength of the steel frame.

[0082] From the calculation, we can know that for a certain analysis section:

[0083] Phase I is from the completion of excavation to the exposure of the surrounding rock shield. At this time, support cannot be applied and the surrounding rock free surface is not subjected to support reaction force. Due to the advanced deformation before the exposure of the shield and the weakening of the support effect of the tunnel face, the surrounding rock stress is released in advance, and the stress release reaches 11%.

[0084] Phase II is from the exposed shield of the surrounding rock to the spray bridge. At this time, anchor rods and arch frames have been installed, and the surrounding rock pressure is jointly borne by the anchor rods and arch frames. As the anchor mortar hardens over time, the surrounding rock stress is also released as the anchor mortar gradually hardens. When the anchor support force reaches 40.34 MPa, the surrounding rock stress release reaches 85%.

[0085] Phase III is after the spray bridge, at which time the spray mix has been applied, and the support structure composed of anchor rods + arch frame + spray mix bears the surrounding rock pressure. After the spray mix is ​​applied, it also faces the hardening of the spray mix material. When the spray mix strength is reached, the surrounding rock stress is completely released.

[0086] Based on the above calculation process, the minimum resistance of different support structures in this tunnel is calculated, as shown in Table 4. For example, when the shield is exposed and stress release reaches 50%, the instantaneous support resistance provided by the anchor rods and arches must be greater than 25 MPa. This stiffness is provided instantaneously by the arches, while the anchor rods increase over time. Therefore, the minimum support resistance of each support structure can be calculated separately.

[0087] Table 4 Minimum support resistance of different supports

[0088] Initial contact pressure of surrounding rock Steel arch stress Anchor rod axial force Spray mixing stress Minimum support resistance 0.105MPa 20.123MPa 30.23MPa 1.87MPa

[0089] At a tunnel site, support stress testing equipment was deployed for Class III and IV surrounding rock to monitor support stress. The maximum values ​​of the monitoring results are shown in the table below. After investigation, none of them exceeded the minimum support resistance.

[0090] Under Class III surrounding rock conditions:

[0091] The arch frame stress is in the range of (-40~10MPa); the spray mix stress is in the range of (-20~6MPa); and the anchor rod axial force is in the range of (0~200MPa).

[0092] Under the IV grade surrounding rock conditions:

[0093] The arch frame stress is in the range of (-40~10MPa); the spray mix stress is in the range of (-12~4MPa); and the anchor rod axial force is in the range of (0~200MPa).

[0094] After all the above calculations, you can adjust the support settings and change the support parameters to ensure that the obtained support resistance is greater than the minimum support resistance given above.

[0095] Therefore, the present invention adopts the above-mentioned dynamic design method of TBM tunnel support structure, which can adjust the support scheme according to different surrounding rock parameters, making the support design more efficient, effectively reducing construction costs, and improving construction efficiency and support quality.

[0096] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A dynamic design method for TBM tunnel support structure, characterized in that: The following steps are involved: S1. Calculate the support stiffness generated by different support operations and the virtual support force based on the actual tunnel surrounding rock parameters, support parameters, and construction procedures. S2. Construct a two-dimensional plane strain model and substitute the support stiffness obtained in S1 into the model to calculate the final settlement of the tunnel, thereby obtaining the reasonable surrounding rock parameters required for numerical simulation under the surrounding rock conditions of this tunnel; S3. Perform three-dimensional rough hole excavation model calculation to obtain the surrounding rock pressure release law, adjust the support resistance by adjusting the support parameters, and optimize the support parameters while satisfying the surrounding rock stress release law.

2. A dynamic design method for TBM tunnel support structure according to claim 1, characterized in that: The support stiffness provided by the steel arch and anchor in S1 are: Among them, R0 is the excavation diameter; A set is the cross-sectional area of ​​the steel arch; E st is the elastic modulus of steel; d is the longitudinal spacing of the steel arch; h set is the vertical height of the steel arch cross section; Q bolt is the load-deformation constant of the anchor end and the anchor head; E bolt is the elastic modulus of the anchor rod; D bolt is the diameter of the anchor rod; L bolt is the anchor rod length; S t 、S l are the circumferential spacing and longitudinal spacing of the anchor rods, respectively; For shotcrete, when its thickness is greater than 1 / 25 of the tunnel radius, its support stiffness is: Among them, E con is the elastic modulus of shotcrete; v con is the Poisson's ratio of shotcrete; t shot is the elastic thickness of shotcrete.

3. A dynamic design method for TBM tunnel support structure according to claim 2, characterized in that: The calculation formula of the virtual support force in S1 is: Where p0 is the original rock stress; x is the distance from the excavation surface; is the virtual support force; is the final displacement around the tunnel without support.

4. The dynamic design method for a TBM tunnel support structure according to claim 1, characterized in that: In the two-dimensional plane strain model in S2, each support method is equivalent to an equivalent reinforcement ring. The parameters of the equivalent reinforcement ring are the parameters obtained by calculation in S1. The final settlement of this tunnel is calculated through this two-dimensional plane strain model. By continuously adjusting the surrounding rock parameters under the condition of not exceeding the allowable error, the final model deformation is consistent with the actual measured variable diameter conditions, and the reasonable surrounding rock parameters of this tunnel are obtained.

5. A dynamic design method for TBM tunnel support structure according to claim 3, characterized in that: In S3, based on the reasonable surrounding rock parameters selected in S2, the deformation of the unsupported excavation of the 3D model is calculated. Then, the surrounding rock pressure release rate is calculated based on the deformation data of the 3D model surrounding rock simulation. The formula is: Where λ is the stress release rate of the surrounding rock.

6. A dynamic design method for TBM tunnel support structure according to claim 5, characterized in that: The surrounding rock pressure release law in S3 is the law of change of the surrounding rock pressure release rate at a certain section as the tunnel face moves away from it under this tunnel condition. The minimum support resistance is obtained from this. The specific calculation method is: The original rock stress of this tunnel is multiplied by the surrounding rock pressure release rate at different stages. This is the magnitude of stress release at different stages. After eliminating the effect of the virtual support force, the minimum support resistance is obtained.

7. A dynamic design method for a TBM tunnel support structure according to claim 6, characterized in that: In S3, the support parameters are continuously adjusted through numerical simulation, and the requirement of not less than the minimum support resistance is met, and the support parameters that are better than the current support situation are selected.

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