Length design method for tunnel prestressed anchoring system

Abstract

The invention discloses a length design method for a tunnel prestressed anchoring system. The length design method comprises the steps that supporting resultant force and surrounding rock mechanical parameters are obtained to calculate the range of a plastic zone; according to the range of the plastic zone, the allowable length range of an anchoring system is determined; performing an orthogonal test based on the allowable length range of the anchoring system to obtain a plurality of first anchoring systems; and performing surrounding rock displacement analysis and plastic zone analysis on the multiple first anchoring systems based on the three-dimensional numerical simulation model, and determining an optimal scheme of the first anchoring systems according to a three-dimensional numerical simulation calculation result. According to the method, the plastic zone range is determined by combining the supporting effect of the prestressed anchoring system on the plastic zone of the surrounding rock, and meanwhile, the optimal scheme of the anchoring system is rapidly screened out by utilizing an orthogonal test and three-dimensional numerical simulation.

Description

Technical Field

[0001] The present application relates to the field of tunnel engineering, and specifically to a method for designing the length of a tunnel prestressed anchorage system. Background Art

[0002] The prestressed anchorage system is widely used in tunnel engineering. Especially in high-stress soft rock tunnels, the use of a high-strength prestressed anchorage system has achieved excellent surrounding rock deformation control effects.

[0003] However, the length design method of the anchorage system mainly relies on empirical design methods. At present, the main design parameters of various anchorage system length design methods at home and abroad are the surrounding rock conditions and the tunnel width, among which it mainly depends on the tunnel width value. However, corresponding the length of the anchorage system to structural geometric parameters such as the tunnel width actually deviates from the support core of the anchorage system. It is necessary to provide a cable length design method with the prediction of the plastic zone as the core and comprehensive analysis of the deformation control effect and the excavation plastic zone.

[0004] In the invention patent with the application number CN201510767522.9, in the method for determining the length and radial prestress value of the prestressed reinforcement bolt for tunnel surrounding rock, the method for determining the length and radial prestress value of the prestressed reinforcement bolt for tunnel surrounding rock is disclosed. Based on the elastic-plastic theory of the surrounding rock and the distribution law of the plastic zone, on the basis of comprehensively determining the radius R of the tunnel plastic circle and the surrounding rock pressure, the minimum length of the tunnel surrounding rock reinforcement bolt is determined. However, the above patent only determines the minimum length of the bolt, does not consider the support effect of the prestressed anchorage system on the plastic zone of the surrounding rock and cannot determine the optimal value of the cable length. Summary of the Invention

[0005] The purpose of the present application is to provide a method for designing the length of a tunnel prestressed anchorage system, combining the support effect of the prestressed anchorage system on the plastic zone of the surrounding rock, obtaining the allowable length range of the anchorage system, and determining the optimal value of the anchorage system therefrom.

[0006] In the prior art, the anchorage length of the bolt is often obtained by establishing the radius R of the tunnel plastic circle, but the obtained length is a unique value, and this unique value is not the best value. Insufficient or excessive anchorage length will reduce the stability of the anchorage structure, making it difficult to achieve the purpose of rock mass anchorage.

[0007] The purpose of the present application is mainly achieved through the following technical solutions:

[0008] A method for designing the length of a tunnel prestressed anchorage system, comprising the following steps:

[0009] Obtain the shotcrete support force, steel support force and anchorage system support force, and calculate the resultant support force;

[0010] Based on the surrounding rock mechanical parameters and the resultant support force, calculate the range of the plastic zone;

[0011] Determine the allowable length range of the anchoring system according to the range of the plastic zone;

[0012] Based on the allowable length range of the anchoring system, through orthogonal experiments, obtain a variety of first anchoring systems, where the first anchoring systems include combinations of anchoring systems with equal lengths and combinations of anchoring systems with different lengths;

[0013] Based on the variety of first anchoring systems, establish a three-dimensional numerical simulation model to conduct surrounding rock displacement analysis and plastic zone analysis on different combinations within the variety of first anchoring systems, and determine the optimal solution of the first anchoring system according to the results of the three-dimensional numerical simulation calculation: that is, the adopted values of the two bolts respectively in the optimal solution of the first anchoring system.

[0014] Since the physical and mechanical parameters of the rock mass will affect the distribution of the elastic-plastic zone of the rock mass, and different stress states of the rock mass result in different distributions of the elastic-plastic zone, this application comprehensively considers the stress condition of the rock mass itself and the external support force of the rock mass, and comprehensively analyzes the stress of the rock mass to make the obtained result of the plastic zone range more accurate;

[0015] Since the prestressed anchoring system is essentially to repair the stress in the plastic zone to fully improve the self-bearing capacity of the anchored rock mass, the allowable length range of the anchoring system is initially determined based on the range of the plastic zone of the surrounding rock after excavation;

[0016] This application utilizes the characteristics of the orthogonal experiment method, which is scientific, simple to operate, efficient and economical, converts the allowable length range of the anchoring system into a variety of first anchoring systems, combines the intuitiveness of the three-dimensional numerical simulation model, conducts surrounding rock displacement analysis and plastic zone analysis on the variety of first anchoring systems, and can quickly lock the optimal first anchoring system with the minimum deformation according to the results of the three-dimensional numerical simulation calculation, saving the screening time and increasing the persuasiveness of the optimal result;

[0017] Insufficient anchoring length will affect the bearing capacity of the concrete, the bolt force is small, resulting in structural instability, causing phenomena such as rock mass deformation, cracking and even bolt detachment; too long anchoring length will lead to excessive bolt tension, wasting materials and increasing the construction difficulty, and at the same time will also cause problems such as low structural stability and easy deformation and cracking of the rock mass; and the existing technology cannot determine the combination scheme of the anchoring system, with poor applicability and low economic benefits; in view of the above problems, this solution proposes a new design method:

[0018] First, comprehensively consider the stress condition of the rock mass after support to obtain the range of the calculated plastic zone;

[0019] Secondly, obtain the allowable length range of the anchoring system according to the range of the plastic zone;

[0020] Obtain the combination scheme of the anchoring system through orthogonal experiments;

[0021] Finally, a preferred first anchoring system is determined by three-dimensional numerical simulation calculation;

[0022] Compared with the prior art, the present application considers the comprehensive stress of the tunnel rock mass after support, making the design result more in line with the actual situation of the construction site, capable of withstanding sufficient loads and reducing the deformation of the tunnel; through orthogonal experiments and numerical simulation, the optimal first anchoring system can be determined simply and efficiently, effectively preventing the problems that an overly long or short anchoring length reduces the bonding force between the steel bar and the surrounding concrete and the stability of the structure, resulting in insufficient bond strength between the steel bar and the concrete and cracks, increasing the later maintenance cost and construction difficulty. At the same time, as a combined scheme, the optimal first anchoring system has better support effect and reduces the selection and simulation process of the bolt combination compared with the length scheme of a single bolt.

[0023] Furthermore, the shotcrete support force and the steel support force are calculated by structural mechanics methods; the equivalent prestressed load value is used to represent the value of the anchoring system support force.

[0024] Furthermore, the surrounding rock mechanical parameters include rock mass strength σcm, rock cohesion c, and internal friction angle φ;

[0025] Because the rock mass strength, rock cohesion, and internal friction angle directly affect the elastic-plastic deformation results of the rock mass;

[0026] If the rock mass strength is high, the rock mass is mostly elastically deformed due to its dense and hard structure, and the area of the plastic zone formed is small, while the structure with low rock mass strength often mainly undergoes plastic deformation, and the area of the plastic zone formed is large;

[0027] Rock cohesion and internal friction angle are two mechanical indexes of the shear strength of the rock mass. The shear strength of the rock mass is the ultimate resistance ability of the rock mass to shear failure. The internal friction angle reflects the frictional resistance property of the rock and soil. The greater the rock cohesion, the stronger the shear strength of the rock mass. On the contrary, the shear strength is smaller, and it is easy to cause adverse effects such as displacement and inclination; and the internal friction angle decreases with the increase of stress within the elastic deformation of the rock mass. After breaking through, when the internal friction angle is zero, the rock mass changes from elastic deformation to plastic deformation.

[0028] Furthermore, the size of the plastic zone is calculated by a variety of empirical theoretical methods;

[0029] The present application calculates the range of the plastic zone by a variety of methods. Since the calculated values of the plastic zone range are different due to different calculation methods, compared with calculating only by one method, calculating by a variety of methods can avoid the influence of the omission of extreme values and calculation errors, which is economical and safe.

[0030] Further, based on the calculation result of the size of the plastic zone, the lower limit value of the allowable length range of the anchoring system is the smallest integer greater than the minimum plastic zone value, and the upper limit value of the allowable length range of the anchoring system is the smallest integer greater than the maximum plastic zone value;

[0031] The allowable length range of the anchoring system in this application is limited by the plastic zone range, ensuring that the allowable length range of the anchoring system covers the entire plastic zone, so that the obtained data is complete and accurate;

[0032] The length of the anchoring system is an integer, which is convenient for later production, manufacturing and inspection.

[0033] Further, based on the allowable length range of the anchoring system, through orthogonal experiments, a variety of first anchoring systems are obtained, including:

[0034] Obtain a second anchoring system with a first length and a third anchoring system with a second length;

[0035] Take the second anchoring system and the third anchoring system as the factors of the orthogonal experiment, and take the value ranges of the first length and the second length as the factor levels of the orthogonal experiment to conduct an orthogonal experiment, and generate combinations of the second anchoring system and the third anchoring system at various different lengths as a variety of first anchoring systems;

[0036] The first anchoring system includes a second anchoring system with a first length and a third anchoring system with a second length. Select several representative first anchoring systems from a variety of first anchoring systems to conduct an orthogonal experiment, take the first length and the second length as the experimental factors of the orthogonal experiment, and the value ranges of the first length and the second length as the factor levels of the orthogonal experiment, and thus screen out the optimal combination of the first length value and the second length value.

[0037] Further, determining the preferred scheme of the first anchoring system includes the following steps:

[0038] For the combinations of the second anchoring system and the third anchoring system at various different lengths, establish a three-dimensional numerical model, and conduct a simulation analysis on the prestressed anchoring system and the surrounding rock deformation state of the combinations of the second anchoring system and the third anchoring system at various different lengths;

[0039] Excavate the unlined bare tunnel. Based on the simulation of the prestressed anchoring system and the surrounding rock deformation state, and conduct an elastoplastic analysis on the excavated bare tunnel, and select the anchoring system with the smallest surrounding rock deformation as the optimal scheme according to the analysis results;

[0040] Based on the combination of the first length value and the second length value established by the orthogonal test, the excavation of the bare tunnel is simulated through a three-dimensional numerical model, which intuitively reflects the displacement and deformation of the rock mass under different combinations of the first length value and the second length value. Based on the deformation of the rock mass, the scheme with the smallest plastic deformation is selected as the optimal combination of the first length value and the second length value.

[0041] Furthermore, based on the optimal scheme of the above anchoring system, analyze the displacement and the size of the plastic zone of the rock mass when the optimal scheme is adopted, and obtain that the length of the first anchoring system should exceed the size of the plastic zone.

[0042] In summary, compared with the prior art, the present application has the following beneficial effects:

[0043] (1). This method not only considers the physical and mechanical parameters of the rock mass, but also takes into account the supporting effect of the prestressed anchoring system on the plastic zone of the surrounding rock, and the obtained results are more accurate and reliable;

[0044] (2). After determining the length range of the anchoring system, this method can quickly determine the optimal value of the combination scheme of the anchoring system by using orthogonal tests and three-dimensional numerical simulations;

[0045] (3). This method is not only applicable to the length design of a single anchoring system, but also can be used for the length design of a combined anchoring system. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, form a part of this application, and do not limit the embodiments of the present invention. In the drawings:

[0047] Figure 1 is a flow chart of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0048] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with the embodiments and the drawings. The illustrative embodiments and descriptions thereof of the present invention are only used to explain the present invention and do not limit the present invention.

[0049] Embodiment:

[0050] As Figure 1 shown, a method for designing the length of a tunnel prestressed anchoring system includes the following steps:

[0051] A method for designing the length of a tunnel prestressed anchoring system includes the following steps:

[0052] Obtain the shotcrete support force, the steel support force and the anchoring system support force, and calculate the resultant support force;

[0053] Calculate the range of the plastic zone based on the mechanical parameters of the surrounding rock and the resultant support force;

[0054] Determine the allowable length range of the anchoring system according to the range of the plastic zone;

[0055] Based on the allowable length range of the anchoring system, obtain multiple first anchoring systems through orthogonal experiments. The first anchoring systems include combinations of anchoring systems with equal lengths and combinations of anchoring systems with different lengths;

[0056] Based on the multiple first anchoring systems, establish a three-dimensional numerical simulation model to analyze the surrounding rock displacement and plastic zone of different combinations within the multiple first anchoring systems, and determine the optimal scheme of the first anchoring system according to the results of the three-dimensional numerical simulation calculation: that is, the values taken by the two bolts respectively in the optimal scheme of the first anchoring system.

[0057] Since the physical and mechanical parameters of the rock mass will affect the distribution of the elastic-plastic zone of the rock mass, and the stress state of the rock mass is different, the distribution of the elastic-plastic zone is also different. Therefore, this application comprehensively considers the stress condition of the rock mass itself and the external support force of the rock mass, and comprehensively analyzes the stress of the rock mass to make the obtained result of the plastic zone range more accurate;

[0058] Since the prestressed anchoring system is essentially to repair the stress in the plastic zone to fully improve the self-bearing capacity of the anchored rock mass, the allowable length range of the anchoring system is initially determined based on the range of the plastic zone of the surrounding rock after excavation;

[0059] This application uses the characteristics of scientific, simple, efficient and economical orthogonal experiment method to convert the allowable length range of the anchoring system into multiple first anchoring systems. Combining the intuitiveness of the three-dimensional numerical simulation model, analyze the surrounding rock displacement and plastic zone of the multiple first anchoring systems. According to the results of the three-dimensional numerical simulation calculation, the optimal first anchoring system with the minimum deformation can be quickly locked, saving the screening time and increasing the persuasiveness of the optimal result.

[0060] Insufficient anchoring length will affect the bearing capacity of the concrete, the bolt force is small, resulting in unstable structure, causing phenomena such as rock mass deformation, cracking and even bolt shedding; too long anchoring length will lead to excessive bolt tension, wasting materials and increasing the construction difficulty, and at the same time will also cause problems such as low structural stability and easy deformation and cracking of the rock mass; the construction of a tunnel may involve the combined use of multiple bolts, there will be many combination methods, and the support results of different combination methods may vary greatly, and it is difficult to select the bolt combination scheme;

[0061] In view of the above problems, the embodiment of this application provides a brand-new bolt system selection scheme, which requires

[0062] First, comprehensively consider the stress conditions of the rock mass after support to obtain the range of the plastic zone; select the anchoring system at different lengths from the range of the plastic zone;

[0063] Through orthogonal experiments, combine the anchoring systems of different lengths to form a large number of possible anchoring system combination schemes for actual use; screen a large number of anchoring system combination schemes through a numerical model to select the optimal anchoring system combination scheme;

[0064] Compared with the prior art, this application considers the comprehensive stress of the tunnel rock mass after support, making the design result more in line with the actual situation of the construction site, being able to withstand sufficient loads and reduce the deformation of the tunnel; through orthogonal experiments and numerical simulations, the optimal first anchoring system can be simply and efficiently determined, effectively preventing the problems that the excessive or too short anchoring length reduces the bond force between the steel bar and the surrounding concrete and the stability of the structure, resulting in insufficient bond force between the steel bar and the concrete and cracks, increasing the later maintenance cost and construction difficulty, etc. At the same time, as a combination scheme, the optimal first anchoring system, compared with the length scheme of a single bolt, has a better support effect while reducing the selection and simulation process of bolt combinations, and meets the requirements of bearing capacity and construction difficulty at the same time.

[0065] Furthermore, the shotcrete support force and the steel support force are calculated and obtained by using structural mechanics methods; the equivalent prestress load value is used to represent the value of the anchoring system support force.

[0066] Furthermore, the surrounding rock mechanical parameters include the rock mass strength σcm, the rock cohesion c, and the internal friction angle φ;

[0067] Because the rock mass strength, the rock cohesion, and the internal friction angle directly affect the elastic-plastic deformation results of the rock mass;

[0068] If the rock mass strength is high, the rock mass is mostly elastically deformed due to its dense and hard structure, and the area of the formed plastic zone is small, while the structure with low rock mass strength often mainly undergoes plastic deformation, and the area of the formed plastic zone is large;

[0069] The rock cohesion and the internal friction angle are two mechanical indexes of the shear strength of the rock mass. The shear strength of the rock mass is the ultimate resistance ability of the rock mass to shear failure. The internal friction angle reflects the frictional resistance property of the rock and soil. The greater the rock cohesion, the stronger the shear strength of the rock mass. On the contrary, the shear strength is smaller, and it is easy to produce displacement and inclination and other adverse effects; and the internal friction angle decreases with the increase of stress within the elastic deformation of the rock mass. After breaking through, when the internal friction angle is zero, the elastic deformation of the rock mass changes to plastic deformation.

[0070] Furthermore, the size of the plastic zone is calculated by using a variety of empirical theoretical methods;

[0071] This application uses multiple methods to calculate the range of the plastic zone. Since different calculation methods result in different values for the range of the plastic zone, compared with using only one method for calculation, using multiple methods can avoid the omission of extreme values and the influence caused by calculation errors, which is economical and safe.

[0072] As a preferred method of the above empirical theory method, multiple empirical theory methods may include calculating the size of the plastic zone by Hoek's empirical method. On the premise of measuring the physical stress of the rock mass and the support stress, a mathematical model is established based on factors such as the elastoplasticity of the rock mass, stress state, dip angle of the rock fracture surface, and lithology of the rock to predict the failure mode and failure strength of the rock mass, thereby determining the size of the plastic zone.

[0073] Furthermore, based on the calculation result of the size of the plastic zone, the lower limit value of the allowable length range of the anchoring system is the smallest integer greater than the minimum plastic zone value, and the upper limit value of the allowable length range of the anchoring system is the smallest integer greater than the maximum plastic zone value.

[0074] The allowable length range of the anchoring system in this application is limited by the range of the plastic zone, ensuring that the allowable length range of the anchoring system covers the entire plastic zone, so that the obtained data is complete and accurate.

[0075] The length of the anchoring system is an integer, which is convenient for later production and inspection.

[0076] Furthermore, based on the allowable length range of the anchoring system, through orthogonal experiments, a variety of first anchoring systems are obtained, including:

[0077] Obtain a second anchoring system with a first length and a third anchoring system with a second length.

[0078] Take the second anchoring system and the third anchoring system as the factors of the orthogonal experiment, and take the value ranges of the first length and the second length as the factor levels of the orthogonal experiment to conduct an orthogonal experiment, generating combinations of the second anchoring system and the third anchoring system at various different lengths as a variety of first anchoring systems.

[0079] The first anchoring system includes a second anchoring system with a first length and a third anchoring system with a second length. Select several representative first anchoring systems from a variety of first anchoring systems to conduct an orthogonal experiment, taking the first length and the second length as the experimental factors of the orthogonal experiment, and the value ranges of the first length and the second length as the factor levels of the orthogonal experiment, and thus screening out the optimal combination of the first length value and the second length value.

[0080] In this embodiment, to make the length reference richer and the design result more accurate, the combination of the first anchoring systems should be richer.

[0081] In this embodiment, to make the orthogonal results more concise and intuitive, a spreadsheet can be used to record the combination schemes of the first anchoring system.

[0082] Furthermore, determining the preferred scheme of the first anchoring system includes the following steps:

[0083] For combinations of the second and third anchoring systems under various different lengths, establish a three-dimensional numerical model, and conduct a simulation analysis on the prestressed anchoring system and the surrounding rock deformation state of the combinations of the second and third anchoring systems under various different lengths;

[0084] Excavate the unlined bare tunnel, based on the simulation of the prestressed anchoring system and the surrounding rock deformation state, and conduct an elastoplastic analysis on the excavated bare tunnel. Select the anchoring system with the smallest surrounding rock deformation as the optimal scheme according to the analysis results;

[0085] Based on the combinations of the first length value and the second length value established by the orthogonal test, simulate the excavation of the bare tunnel through a three-dimensional numerical model, and visually reflect the displacement and deformation conditions of the rock mass under different combinations of the first length value and the second length value. Select the scheme with the smallest plastic deformation as the optimal combination of the first length value and the second length value based on the deformation conditions of the rock mass.

[0086] Furthermore, based on the optimal scheme of the above anchoring system, analyze the displacement and the size of the plastic zone of the rock mass when the optimal scheme is adopted, and obtain that the length of the first anchoring system should exceed the size of the plastic zone.

[0087] The specific embodiments described above further elaborate on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above description is only the specific embodiments of the present invention and is not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for designing the length of a tunnel prestressed anchor system, characterized in that: The steps include: Obtain the sprayed concrete support force, steel support support force and anchor system support force, and calculate the support resultant force; Calculating the range of the plastic zone based on the mechanical parameters of the surrounding rock and the support force; Determining the allowable length range of the anchoring system according to the range of the plastic zone; Based on the allowable length range of the anchoring system, an orthogonal test is performed to obtain a plurality of first anchoring systems, wherein the first anchoring system includes a combination of anchoring systems of equal length and a combination of anchoring systems of different lengths; Based on the multiple first anchoring systems, a three-dimensional numerical simulation model is established to perform surrounding rock displacement analysis and plastic zone analysis on different combinations within the multiple first anchoring systems, and the optimal solution of the first anchoring system is determined according to the results of the three-dimensional numerical simulation calculation: that is, the respective values ​​of the two anchor rods in the optimal solution of the first anchoring system.

2. A method for designing the length of a tunnel prestressed anchor system according to claim 1, characterized in that: The sprayed concrete support force and the steel support force are calculated using structural mechanics methods; the equivalent prestressed load value is used to represent the value of the anchor system support force.

3. A method for designing the length of a tunnel prestressed anchor system according to claim 1, characterized in that: The surrounding rock mechanical parameters include rock mass strength σ cm , rock cohesion c, internal friction angle φ.

4. A method for designing the length of a tunnel prestressed anchor system according to claim 1, characterized in that: The size of the plastic zone is calculated using a variety of empirical theoretical methods.

5. A method for designing the length of a tunnel prestressed anchor system according to claim 1, characterized in that: Based on the calculation result of the plastic zone size, the lower limit value of the allowable length range of the anchoring system is the smallest integer greater than the minimum plastic zone value, and the upper limit value of the allowable length range of the anchoring system is the smallest integer greater than the maximum plastic zone value.

6. A method for designing the length of a tunnel prestressed anchor system according to claim 1, characterized in that: Based on the allowable length range of the anchoring system, various first anchoring systems are obtained through orthogonal tests, including: obtaining a second anchor system having a first length and a third anchor system having a second length; An orthogonal experiment is performed by taking the second anchoring system and the third anchoring system as factors of the orthogonal experiment, and taking the value range of the first length and the second length as the factor levels of the orthogonal experiment to generate combinations of the second anchoring system and the third anchoring system at multiple different lengths as multiple first anchoring systems.

7. A method for designing the length of a tunnel prestressed anchor system according to claim 1, characterized in that: Determining the preferred solution of the first anchoring system comprises the following steps: A three-dimensional numerical model is established for the combination of the second anchor system and the third anchor system at various lengths, and the deformation state of the prestressed anchor system and the surrounding rock of the combination of the second anchor system and the third anchor system at various lengths is simulated and analyzed; An unsupported bare hole is excavated, and based on the simulation of the deformation state of the prestressed anchoring system and the surrounding rock, an elastic-plastic analysis is performed on the excavated bare hole, and according to the analysis results, the anchoring system with the smallest surrounding rock deformation is selected as the optimal solution.

8. A method for designing the length of a tunnel prestressed anchor system according to claim 1, characterized in that: Based on the optimal solution of the above anchoring system, the displacement of the rock mass and the size of the plastic zone when the optimal solution is adopted are analyzed, and it is found that the length of the first anchoring system should exceed the size of the plastic zone.

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