Method for determining underground cavern full-face excavation support timing and support force

Abstract

The application provides a method for determining the supporting time and supporting force of full-face excavation of an underground cavern. The application applies a numerical simulation method to the determination of the supporting time and minimum supporting force of the underground cavern, establishes the deformation control standard and safety early warning index of the underground cavern, combines the longitudinal section deformation curve of the surrounding rock obtained by the numerical method, and quantitatively determines the optimal supporting time from the perspective of the safety early warning control of the surrounding rock, so as to effectively solve the problem that the time node of the surrounding rock loosening and instability is difficult to accurately obtain in the existing method. Meanwhile, the application also provides a method for determining the minimum supporting force and supporting scheme for maintaining the stability of the surrounding rock, which can effectively avoid the engineering risks caused by the subjective understanding deviation of engineers compared with the conventional engineering analogy method, and has better safety and economy.

Description

Technical Field

[0001] This invention belongs to the field of underground engineering technology, specifically relating to a method for determining the timing and force of support during full-section excavation of underground caverns. It can be used to determine the optimal timing for applying the support structure during full-section excavation construction, as well as the support force required to maintain the stability of the surrounding rock, ensuring safety during construction. It is widely applicable to the design and construction of underground engineering support in fields such as hydropower, water conservancy, transportation, and mining. Background Technology

[0002] In underground engineering, the support structure mainly bears the load of the surrounding rock released during the excavation of the cavern, thereby controlling the stability of the surrounding rock and ensuring construction safety. The support force that the support structure can provide is not only related to the safety of the support structure itself, but also a key factor affecting the stability of the surrounding rock of the cavern, and is an important parameter in the design of underground cavern support schemes.

[0003] The timing of applying the support structure also plays a crucial role in controlling the support force and the stability of the surrounding rock. During the interaction between the surrounding rock and the support, if the support structure is applied too early, the stress in the surrounding rock cannot be effectively released, and the support structure bears most of the original rock stress, requiring greater support strength. Conversely, if the support is applied too late, harmful loosening and deformation of the surrounding rock will occur, affecting construction safety. Therefore, the design of tunnel support structures should consider both safety and economy. The optimal support timing should allow for a certain degree of plastic deformation in the surrounding rock, but should control it to prevent excessive harmful loosening. Thus, determining the support timing is a critical issue that needs to be addressed.

[0004] The explanation of Clause 7.4.7 of the "Technical Specification for Rock and Soil Anchors and Shotcrete Support Engineering GB50086-2015" suggests using the interaction diagram of rock characteristic curves and support characteristic curves to determine the timing of support by the inflection point of loosening deformation of the surrounding rock. However, the specification does not provide a method for determining the rock characteristic curve and the inflection point of loosening deformation. Currently, it is difficult to accurately establish a rock characteristic curve that conforms to reality using either theoretical or numerical analysis methods, especially regarding how to determine the inflection point of loosening deformation of the surrounding rock.

[0005] Currently, the timing of applying tunnel support structures is largely determined on-site based on the experience and subjective understanding of construction personnel. At the same time, support schemes are mainly designed using engineering analogy methods. There is a lack of a quantitative method for determining the timing and force of support, which poses a huge challenge to the safety of underground engineering. Therefore, there is an urgent need to provide a method for determining the timing and force of underground cavern support. Summary of the Invention

[0006] The purpose of this invention is to address the aforementioned problems by providing a method for determining the timing and support force of full-section excavation support for underground caverns. This method is used for underground cavern support design and construction control, and helps improve the stability control of surrounding rock and construction safety in underground engineering projects.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A method for determining the timing and support force for full-section excavation of underground caverns includes the following steps:

[0009] S1. Establish standards for controlling the permissible deformation of underground caverns;

[0010] S2. Set the safety early warning level of the surrounding rock of the underground cavern and the corresponding deformation index;

[0011] S3. Determine the excavation cycle advance of the underground cavern;

[0012] S4. Establish a numerical analysis model of the underground cavern and the surrounding rock mass, and divide the cavern to be excavated into several excavation sections according to the cycle advance.

[0013] S5. Select the rock mass constitutive model, assign mechanical parameters to the rock mass, and apply displacement and stress boundaries;

[0014] S6. Simulate the step-by-step excavation process of the underground cavern. During the simulation, record the curve of the relationship between the deformation of the cavern roof arch and the distance to the working face at the monitoring section, i.e., the longitudinal section deformation curve of the surrounding rock (LDP curve).

[0015] S7. Determine the support timing. When the arch deformation U0 on the LDP curve reaches the warning level set in step S2, the distance between the corresponding monitoring section and the working face is the latest time to apply the support.

[0016] S8. Determine the minimum support force P;

[0017] S9. The selection of support type and the design of support scheme require that the support structure can provide a support force greater than the minimum support force P determined in step S8.

[0018] As a preferred technical solution of the present invention: In step S1, the allowable deformation control standard U of the underground cavern... n The value should be determined comprehensively based on relevant standards and specifications, taking into account factors such as the excavation dimensions, depth, and rock mass quality. For tunnel projects with an excavation span D within 10m and a height-to-span ratio of 0.8 to 1.2, the allowable relative convergence deformation value ε around the tunnel perimeter can also be selected according to the following table:

[0019]

[0020] Among them: 1. The relative convergence deformation value refers to the ratio of the crown displacement to the tunnel span; 2. The smaller value is taken for brittle rock mass and the larger value is taken for plastic rock mass.

[0021] Underground cavern allowable deformation control standard U n U is the product of the cavern span D and the allowable relative convergent deformation value ε. n =D*ε.

[0022] As a preferred embodiment of the present invention: In step S2, the safety warning level can be set to three levels: safety level, warning level, and danger level. The deformation index for each warning level should be based on the allowable deformation control standard U determined in step S1. n The settings are based on geological conditions, hydrological conditions, and monitoring results. When data is lacking, coefficients can be set for different safety levels. The coefficients can be taken from the following table:

[0023]

[0024] As a preferred technical solution of the present invention: In step S3, the excavation cycle advance should be determined comprehensively based on the construction method, geological conditions, support scheme, etc. For tunnel projects using full-section excavation, it can generally be adopted according to the following table:

[0025]

[0026] As a preferred embodiment of the present invention: In step S5, the rock mass can be modeled using the Mohr-Coulomb constitutive model or the Hoek-Brown constitutive model, and the rock mass mechanical parameters can be obtained through laboratory and in-situ tests or empirical formulas. When data is unavailable, the values ​​can be referenced in the table below:

[0027]

[0028] As a preferred embodiment of the present invention, step S8, determining the minimum support force P, specifically includes the following steps:

[0029] S81. Select the initial support force. The initial support force can be determined based on geological conditions, cavern size, etc., through expert experience or engineering analogy.

[0030] S82. Based on the support timing determined in step S7, the support force is simplified into a uniformly distributed load and applied to the excavation surface of the tunnel.

[0031] S83. Simulate the cyclic excavation process after support to obtain the maximum deformation U of the tunnel arch after support. max ;

[0032] S84, the maximum deformation U obtained in step S83 maxCompare with the hazard level set in step S2, if U max If the hazard level is too low, the requirements are not met, and the support force P needs to be increased. Steps S81-S83 should be repeated until the maximum deformation U is reached. max < Danger level, at this point the support force P is the minimum support force to maintain the stability of the surrounding rock.

[0033] As a preferred technical solution of the present invention: the incremental value of the support force in step S84 is between 0.05 and 0.1 MPa. When the geological conditions are poor, a higher value is taken, and when the geological conditions are good, a lower value is taken.

[0034] As a preferred technical solution of the present invention: In step S9, when anchor spraying support is used, the support force P that the support structure can provide can be calculated by the following formula:

[0035]

[0036] In the formula: S c The spacing between anchor bolts along the circumference of the cavern;

[0037] S l The anchor spacing is along the axis of the tunnel.

[0038] A s This represents the cross-sectional area of ​​a single anchor bolt.

[0039] f y This refers to the design value of the tensile strength of the anchor bolt;

[0040] t c The thickness of the shotcrete;

[0041] f c The uniaxial compressive strength of shotcrete;

[0042] r is the excavation radius of the cavern.

[0043] When steel arch supports are used, the support force P that the support structure can provide can be calculated using the following formula:

[0044]

[0045] In the formula: σ is the yield strength of the steel;

[0046] A is the cross-sectional area of ​​the steel arch frame;

[0047] W represents the height of the steel arch frame section;

[0048] d represents the spacing of the steel arch frame.

[0049] The beneficial effects of this invention are as follows:

[0050] This invention applies numerical simulation methods to determine the timing and minimum support force for underground cavern support. By establishing allowable deformation control standards and safety early warning indicators for underground caverns, and combining the longitudinal profile deformation curve of the surrounding rock obtained by numerical methods, the optimal support timing is quantitatively determined from the perspective of surrounding rock safety early warning control. This effectively solves the problem of accurately obtaining the time node of surrounding rock loosening and instability in existing methods. At the same time, it also proposes a method for determining the minimum support force and support scheme to maintain surrounding rock stability. Compared with the conventional engineering analogy method, it can effectively avoid engineering risks caused by the subjective perception bias of engineers, and has better safety and economy. Attached Figure Description

[0051] Figure 1 This is a flowchart of the method for determining the support timing and support force according to the present invention.

[0052] Figure 2 This is a schematic diagram of the numerical model of the tunnel established in the embodiment.

[0053] Figure 3 This is a schematic diagram of the displacement boundary settings for the model.

[0054] Figure 4 This is a schematic diagram illustrating the determination of support timing in the embodiment.

[0055] Figure 5 This is a schematic diagram simulating the support force in the embodiment.

[0056] Figure 6 This is a schematic diagram illustrating the determination of the minimum support force in the embodiment. Detailed Implementation

[0057] To enable those skilled in the art to better understand the technical solutions of the present invention, the implementation schemes of the present invention are described below in conjunction with specific embodiments:

[0058] like Figure 1 As shown, a method for determining the timing and support force for underground cavern support specifically includes the following steps:

[0059] S1. Establish standards for controlling the allowable deformation of underground caverns.

[0060] Underground cavern allowable deformation control standard U n The allowable relative convergence deformation value around the tunnel should be determined comprehensively based on relevant standards and specifications, taking into account factors such as tunnel excavation dimensions, depth, and rock mass quality. For tunnel projects with an excavation span D within 10m and a height-to-span ratio of 0.8 to 1.2, the allowable relative convergence deformation value around the tunnel can also be selected according to the following table:

[0061]

[0062] Among them: 1. The relative convergence deformation value refers to the ratio of the crown displacement to the tunnel span; 2. The smaller value is taken for brittle rock mass and the larger value is taken for plastic rock mass.

[0063] Underground cavern allowable deformation control standard U n U is the product of the cavern span D and the allowable relative convergent deformation value ε. n =D*ε.

[0064] S2. Set the safety warning level of the surrounding rock of the underground cavern and the corresponding deformation index.

[0065] The safety warning level can be set to three levels: safety level, warning level, and danger level. The deformation index for each warning level should be based on the allowable deformation control standard U determined in step S1. n The settings are based on geological conditions, hydrological conditions, and monitoring results. When data is lacking, values ​​can be taken from the table below:

[0066]

[0067] S3. Determine the excavation cycle advance of the underground cavern.

[0068] The excavation cycle advance should be determined by comprehensively considering the construction method, geological conditions, and support scheme. For tunnel projects using full-face excavation, the following table can generally be used:

[0069]

[0070] S4. Establish a numerical analysis model of the underground cavern and the surrounding rock mass, and divide the cavern to be excavated into several excavation sections according to the cyclic advance.

[0071] S5. Select the rock mass constitutive model, assign mechanical parameters to the rock mass, and apply displacement and stress boundaries.

[0072] The rock mass can be modeled using the Mohr-Coulomb or Hoek-Brown constitutive models. Rock mass mechanical parameters can be obtained through laboratory and in-situ tests or empirical formulas. When data is unavailable, the values ​​in the table below can be used as a reference:

[0073]

[0074] S6. Simulate the step-by-step excavation process of the underground cavern. During the simulation, record the curve of the relationship between the deformation of the cavern roof arch and the distance to the working face at the monitoring section, i.e., the longitudinal section deformation curve of the surrounding rock (LDP curve).

[0075] S7. Determine the support timing. When the arch deformation U0 on the LDP curve reaches the warning level set in step S2, the distance between the corresponding monitoring section and the working face is the latest time to apply the support.

[0076] S8. Determine the minimum support force P. The specific steps are as follows:

[0077] S81. Select the initial support force. The initial support force can be determined based on geological conditions, cavern size, etc., through expert experience or engineering analogy.

[0078] S82. Based on the support timing determined in step S7, the support force is simplified into a uniformly distributed load and applied to the excavation surface of the tunnel.

[0079] S83. Simulate the cyclic excavation process after support to obtain the maximum deformation U of the tunnel arch after support. max .

[0080] S84, the maximum deformation U obtained in step S83 max Compare with the hazard level set in step S2, if U max If the hazard level is too low, the requirements are not met, and the support force P needs to be increased. Steps S81-S83 should be repeated until the maximum deformation U is reached. max < Danger level, at this point the support force P is the minimum support force to maintain the stability of the surrounding rock.

[0081] Preferably, the range of the support force increment in step S84 is suggested to be between 0.05 and 0.1 MPa. When the geological conditions are poor, a higher value should be used, and when the geological conditions are good, a lower value should be used.

[0082] S9. The selection of support type and the design of support scheme require that the support structure can provide a support force greater than the minimum support force P determined in step S8.

[0083] When anchor-sprayed support is used, the support force P that the support structure can provide can be calculated using the following formula:

[0084]

[0085] In the formula: S c The spacing between anchor bolts along the circumference of the cavern;

[0086] S l The anchor spacing is along the axis of the tunnel.

[0087] A s This represents the cross-sectional area of ​​a single anchor bolt.

[0088] f y This refers to the design value of the tensile strength of the anchor bolt;

[0089] t c The thickness of the shotcrete;

[0090] f c The uniaxial compressive strength of shotcrete;

[0091] r is the excavation radius of the cavern.

[0092] When steel arch supports are used, the support force P that the support structure can provide can be calculated using the following formula:

[0093]

[0094] In the formula: σ is the yield strength of the steel;

[0095] A is the cross-sectional area of ​​the steel arch frame;

[0096] W represents the height of the steel arch frame section;

[0097] d represents the spacing of the steel arch frame.

[0098] The present invention will be further described in detail below through examples:

[0099] Taking a water diversion tunnel of a hydropower station as a specific example, the timing and force of support were designed. The tunnel is a gate-shaped tunnel with a span of 8m, a height of 8m, and a vertical burial depth of 500m. The surrounding rock is Class III deviation rock mass. The initial support scheme is to adopt anchor spraying support.

[0100] The methods for determining the timing and force of tunnel support are as follows:

[0101] The first step is to establish allowable deformation control standards for underground caverns, which are determined comprehensively based on factors such as the tunnel's burial depth, excavation dimensions, and surrounding rock conditions.

[0102] In this embodiment, the tunnel has a burial depth of 500m, a span of 8m, a height of 8m, a height-to-span ratio of 1.0, and a surrounding rock category of Class III. The allowable relative convergence deformation value is ε=0.7%, and the allowable deformation control standard U... n =56mm.

[0103] The second step is to set the safety warning level of the surrounding rock of the underground cavern and the corresponding deformation index. The specific deformation warning index in this embodiment is shown in the table below:

[0104]

[0105] The third step is to determine the excavation cycle advance of the underground cavern. In this embodiment, drilling and blasting construction is adopted, and the excavation cycle advance is determined to be 3m based on the geological conditions.

[0106] The fourth step involves using the finite difference numerical analysis software "FLAC3D" to establish a numerical model of the tunnel and the surrounding rock mass, such as... Figure 2 As shown, the tunnel is divided into several sections of 3m each to be excavated based on the cyclic advance.

[0107] Step 5: Assign parameter values ​​to the model according to the rock mass quality classification. In this embodiment, the rock mass is a Class III deviation surrounding rock. The Mohr-Coulomb constitutive model is used, and the mechanical parameters are: elastic modulus E=6GPa, Poisson's ratio υ=0.32, cohesion c=0.70MPa, and internal friction angle φ=35°.

[0108] Displacement constraints are applied to the model boundaries, with each boundary using normal displacement constraints, such as... Figure 3 As shown.

[0109] Stress boundaries are applied to the model. In this embodiment, the burial depth is 500m, the average unit weight of the rock mass is γ=25kN / m, and the lateral pressure coefficient is K=1.0. The vertical and horizontal stresses applied to the model are as follows:

[0110]

[0111] Step 6: Simulate the phased excavation process of the underground cavern. During the simulation, record the curve showing the relationship between the cavern arch deformation and the distance to the working face at the monitoring section, i.e., the longitudinal section deformation curve of the surrounding rock (LDP curve). Figure 4 As shown.

[0112] Step 7: Determine the timing of support application. When the arch deformation U0 on the LDP curve reaches the warning level set in Step 2, the distance between the corresponding monitoring section and the working face is the latest time to apply support.

[0113] In this embodiment, the warning level U0 = 39.2 mm, and the determined support timing is 2 m after the working face. Figure 4 As shown;

[0114] Step 8: Determine the minimum support force P.

[0115] 1) Select the initial support force. In this embodiment, the initial support force is set to 0.5 MPa;

[0116] 2) Based on the support timing determined in step seven, the support force is simplified into a uniformly distributed load and applied to the excavation face of the tunnel, such as... Figure 5 As shown;

[0117] 3) Simulate the cyclic excavation process after support to obtain the maximum deformation U of the tunnel arch after support. max =53.5mm, such as Figure 6 As shown;

[0118] 4) Determine U max =53.5mm>50.4mm (hazard level), does not meet the requirements, and gradually increase the support force P in increments of 0.05MPa;

[0119] 5) When P = 0.65 MPa, Umax =50.0mm < 50.4mm (hazard level), such as Figure 6 As shown, the minimum support force in this embodiment is P=0.65MPa.

[0120] Step 9: Selection of support type and design of support scheme;

[0121] In this embodiment, anchor-sprayed support is adopted. Based on the minimum support force P = 0.65 MPa determined in step eight, the designed support scheme is as follows: anchor bolt diameter 28 mm, spacing 1.2 m × 1.2 m, and the tensile strength design value of the anchor bolt material is 360 MPa; the sprayed concrete thickness is 12 cm, the strength grade is C35, and the corresponding uniaxial compressive strength is 16.7 MPa. The support force that the support structure can provide is:

[0122]

[0123] The support strength meets the requirements.

[0124] The above description of the embodiments is provided to enable those skilled in the art to understand and apply the present invention. It will be apparent to those skilled in the art that various modifications can be made to the above embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made to the present invention by those skilled in the art based on the disclosure thereof should be within the scope of protection of the present invention.

Claims

1. A method for determining the timing and support force for full-section excavation support of underground caverns, characterized in that, Includes the following steps: S1. Establish standards for controlling the permissible deformation of underground caverns; S2. Set the safety early warning level of the surrounding rock of the underground cavern and the corresponding deformation index; S3. Determine the excavation cycle advance of the underground cavern; S4. Establish a numerical analysis model of the underground cavern and the surrounding rock mass, and divide the cavern to be excavated into several excavation sections according to the cycle advance. S5. Select the rock mass constitutive model, assign mechanical parameters to the rock mass, and apply displacement and stress boundaries; S6. Simulate the step-by-step excavation process of underground caverns, and record the curves showing the relationship between the deformation of the cavern roof arch and the distance to the working face at the monitoring section during the simulation. S7. Determine the timing of support. When the arch deformation U0 on the curve of the relationship between the arch deformation and the working face of the cross-section reaches the warning level set in step S2, the distance between the corresponding monitoring section and the working face is the latest time to apply support. S8. Determine the minimum support force P; S9. The selection of support type and the design of support scheme require that the support structure can provide a support force greater than the minimum support force P determined in step S8.

2. The method for determining the timing and support force of full-section excavation support for underground caverns as described in claim 1, characterized in that, In step S1, the allowable deformation control standard U for underground caverns n The dimensions of the tunnel excavation, its depth, and the quality of the rock mass are determined in accordance with relevant standards and specifications.

3. The method for determining the timing and support force of full-section excavation support for underground caverns as described in claim 1, characterized in that, In step S1, for tunnel projects with an excavation span D within 10m and a height-to-span ratio of 0.8 to 1.2, the allowable relative convergence deformation value ε around the tunnel is selected according to the following table: Underground cavern allowable deformation control standard U n U is the product of the cavern span D and the allowable relative convergent deformation value ε. n =D*ε.

4. The method for determining the timing and support force of full-section excavation support for underground caverns as described in claim 1, characterized in that, The safety warning level is set to three levels: safety level, warning level, and danger level. The deformation index for each warning level is based on the allowable deformation control standard U determined in step S1. n The settings are based on geological conditions, hydrological conditions, and monitoring results.

5. The method for determining the timing and support force of full-section excavation support for underground caverns as described in claim 1, characterized in that, In step S3, the excavation cycle advance should be determined comprehensively based on the construction method, geological conditions, and support scheme. For tunnel projects using full-face excavation, the following table should be used: 。 6. The method for determining the timing and support force of full-section excavation support for underground caverns as described in claim 1, characterized in that, In step S5, the rock mass adopts the Mohr-Coulomb constitutive model or the Hoek-Brown constitutive model, and the rock mass mechanical parameters are obtained through laboratory and in-situ tests or empirical formulas.

7. The method for determining the timing and support force of full-section excavation support for underground caverns as described in claim 1, characterized in that, Determining the minimum support force P in step S8 specifically includes the following steps: S81. Select the initial support force; S82. Based on the support timing determined in step S7, the support force is simplified into a uniformly distributed load and applied to the excavation surface of the tunnel. S83. Simulate the cyclic excavation process after support to obtain the maximum deformation U of the tunnel arch after support. max ; S84, the maximum deformation U obtained in step S83 max Compare with the hazard level set in step S2, if U max If the hazard level is too low, the requirements are not met, and the support force P needs to be increased. Steps S81-S83 should be repeated until the maximum deformation U is reached. max < Danger level, at this point the support force P is the minimum support force to maintain the stability of the surrounding rock.

8. The method for determining the timing and support force of full-section excavation support for underground caverns as described in claim 1, characterized in that, In step S9, when anchor-sprayed support is used, the support force P that the support structure can provide is calculated using the following formula: In the formula: S c The spacing between anchor bolts along the circumference of the cavern; S l The anchor spacing is along the axis of the tunnel. A s This represents the cross-sectional area of ​​a single anchor bolt. f y This refers to the design value of the tensile strength of the anchor bolt; t c The thickness of the shotcrete; f c The uniaxial compressive strength of shotcrete; r is the excavation radius of the cavern; When steel arch supports are used, the support force P that the support structure can provide is calculated using the following formula: In the formula: σ is the yield strength of the steel; A is the cross-sectional area of ​​the steel arch frame; W represents the height of the steel arch frame section; d represents the spacing of the steel arch frame.

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