A method for designing the length of a tunnel prestressed anchoring system

Abstract

The application discloses a tunnel prestressed anchoring system length design method, comprising the following steps: obtaining support resultant force and surrounding rock mechanical parameters to calculate the range of plastic zone; determining the length range of the anchoring system according to the range of the plastic zone; based on the length range of the anchoring system, carrying out orthogonal test to obtain a plurality of first anchoring systems; based on the plurality of first anchoring systems of the three-dimensional numerical simulation model, carrying out surrounding rock displacement analysis and plastic zone analysis, and determining the optimal scheme of the first anchoring system according to the three-dimensional numerical simulation calculation result. The application combines the supporting effect of the prestressed anchoring system on the plastic zone of the surrounding rock to determine the range of the plastic zone, and simultaneously utilizes the orthogonal test and the three-dimensional numerical simulation to quickly screen out the optimal scheme of the anchoring system.

Description

Technical Field

[0001] This application relates to the field of tunnel engineering, specifically a method for designing the length of a tunnel prestressed anchorage system. Background Technology

[0002] Prestressed anchoring systems are widely used in tunnel engineering, especially in high-stress soft rock tunnels, where the use of high-strength prestressed anchoring systems has achieved excellent results in controlling the deformation of the surrounding rock.

[0003] However, the length design method of anchoring system mainly relies on empirical design methods. At present, the main design parameters of various anchoring system length design methods at home and abroad are the surrounding rock conditions and tunnel width, with the tunnel width value being the primary factor. However, corresponding the length of the anchoring system to structural geometric parameters such as tunnel width deviates from the core of anchoring system support. It is necessary to provide an anchor cable length design method that takes plastic zone prediction as the core and integrates deformation control effect and excavation plastic zone analysis.

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

[0005] The purpose of this application is to provide a method for designing the length of a tunnel prestressed anchoring system, which combines the support effect of the prestressed anchoring system on the plastic zone of the surrounding rock to obtain the allowable length range of the anchoring system and determine the preferred value of the anchoring system from it.

[0006] In existing technologies, the anchorage length of anchor bolts is often obtained based on the radius R of the plastic zone of the tunnel. However, the obtained length is a unique value, which is not the optimal 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 objective of this application is mainly achieved through the following technical solutions:

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

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

[0010] The extent of the plastic zone is calculated based on the surrounding rock mechanical parameters and the resultant force of the support.

[0011] The allowable length range of the anchoring system is determined based on the range of the plastic zone.

[0012] Based on the allowable length range of the anchoring system, multiple first anchoring systems are obtained through orthogonal experiments. The first anchoring system includes a combination of anchoring systems of equal length and a combination of anchoring systems of different lengths.

[0013] Based on the various 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 various first anchoring systems. Based on the results of the three-dimensional numerical simulation calculation, the optimal scheme of the first anchoring system is determined: that is, the values ​​of the two anchor rods in the optimal scheme of the first anchoring system.

[0014] Because the physical and mechanical parameters of the rock mass affect the distribution of the elasto-plastic zone, the distribution of the elasto-plastic zone will be different depending on the stress state of the rock mass. Therefore, this application comprehensively analyzes the stress of the rock mass by combining the stress of the rock mass itself with the external support force, so as to obtain a more accurate result of the plastic zone range.

[0015] Since the prestressed anchoring system is essentially a stress repair system for the plastic zone in order 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 scientific, simple, efficient and economical characteristics of orthogonal experimental methods to transform the allowable length range of the anchoring system into multiple first anchoring systems. Combined with the intuitiveness of the three-dimensional numerical simulation model, it performs surrounding rock displacement analysis and plastic zone analysis on multiple first anchoring systems. Based on the results of the three-dimensional numerical simulation calculation, the optimal first anchoring system with the minimum deformation can be quickly identified, saving screening time and increasing the persuasiveness of the optimal results.

[0017] Insufficient anchorage length can affect the load-bearing capacity of concrete, resulting in weak anchor force and structural instability, causing rock deformation, cracking, and even anchor detachment. Excessive anchorage length leads to excessive tensile force on the anchor, wasting materials, increasing construction difficulty, and causing structural instability and easy rock deformation and cracking. Furthermore, existing technologies cannot determine the optimal combination of anchorage systems, resulting in poor applicability and low economic efficiency. To address these issues, this paper proposes a new design method:

[0018] First, the range of the plastic zone is calculated by considering the stress conditions after rock mass support.

[0019] Secondly, the allowable length range of the anchoring system is obtained based on the extent of the plastic zone;

[0020] A combination scheme for the anchoring system was obtained through orthogonal experiments;

[0021] Finally, the preferred first anchoring system was determined using three-dimensional numerical simulation calculations.

[0022] Compared to existing technologies, this application considers the comprehensive stress of the tunnel rock mass after support, making the design results more consistent with the actual conditions of the construction site, capable of withstanding sufficient loads and reducing tunnel deformation. Through orthogonal experiments and numerical simulations, the optimal first anchoring system can be determined simply and efficiently, effectively preventing excessively long or short anchoring lengths from reducing the bond strength between the steel bars and the surrounding concrete and the stability of the structure, leading to insufficient bond strength between the steel bars and concrete, cracks, and increased maintenance costs and construction difficulties in the later stages. At the same time, this optimal first anchoring system, as a combination scheme, provides better support effects than single anchor length schemes while reducing the selection and simulation process of anchor combinations.

[0023] Furthermore, the shotcrete 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 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 elastoplastic deformation results of the rock mass;

[0026] If the rock mass has high strength, it will undergo elastic deformation due to its dense and hard structure, resulting in a smaller area of ​​plastic zone. In contrast, the rock mass with low strength tends to undergo plastic deformation, resulting in a larger area of ​​plastic zone.

[0027] Rock cohesion and internal friction angle are two mechanical indicators of rock mass shear strength. Rock mass shear strength is the ultimate resistance of rock mass to shear failure, while internal friction angle reflects the frictional properties of rock and soil. The greater the rock mass cohesion, the stronger the rock mass shear strength, and vice versa, the weaker the shear strength, which is prone to adverse effects such as displacement and tilting. The internal friction angle decreases with increasing stress within the elastic deformation range of the rock mass. After exceeding this range, 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 using a variety of empirical theoretical methods;

[0029] This application uses multiple methods to calculate the range of the plastic region. The range of the plastic region is different because the calculation methods are different. Compared with using only one method, multiple methods can avoid the omission of extreme values ​​and the impact of calculation errors, which is economical and safe.

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

[0032] The length of the anchoring system is an integer to facilitate subsequent production, manufacturing, and inspection.

[0033] Furthermore, based on the allowable length range of the anchoring system, various first anchoring systems were obtained through orthogonal experiments, including:

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

[0035] The second anchoring system and the third anchoring system are used as factors in the orthogonal experiment, and the range of values ​​of the first length and the second length are used as factor levels in the orthogonal experiment to generate a variety of combinations of the second anchoring system and the third anchoring system with 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. Several representative first anchoring systems are selected from a variety of first anchoring systems to conduct orthogonal experiments. The first length and the second length are the experimental factors of the orthogonal experiments, and the value range of the first length and the second length are the factor levels of the orthogonal experiments. The optimal combination of the first length value and the second length value is selected from the results.

[0037] Furthermore, determining the preferred solution for the first anchoring system includes the following steps:

[0038] For combinations of second and third anchoring systems with various lengths, a three-dimensional numerical model is established to simulate and analyze the prestressed anchoring system and surrounding rock deformation state of combinations of second and third anchoring systems with various lengths.

[0039] For the excavation of the unsupported bare tunnel, based on the simulation of the prestressed anchoring system and the deformation state of the surrounding rock, and the elastoplastic analysis of the excavated bare tunnel, the anchoring system with the smallest deformation of the surrounding rock is selected as the optimal solution according to the analysis results.

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

[0041] Furthermore, 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.

[0042] In summary, this application has the following advantages compared with the prior art:

[0043] (1) Based on the physical and mechanical parameters of the rock mass, this method also takes into account the support effect of the prestressed anchoring system on the plastic zone of the surrounding rock, and the results obtained 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 anchoring system combination scheme by using orthogonal experiments and three-dimensional numerical simulation.

[0045] (3) This method is not only applicable to the length design of a single anchoring system, but also to the length design of a combined anchoring system. Attached Figure Description

[0046] The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and form part of this application, do not constitute a limitation thereof. In the drawings:

[0047] Figure 1 This is a flowchart of the present invention. Detailed Implementation

[0048] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0049] Example:

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

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

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

[0053] The extent of the plastic zone is calculated based on the surrounding rock mechanical parameters and the resultant force of the support.

[0054] The allowable length range of the anchoring system is determined based on the range of the plastic zone.

[0055] Based on the allowable length range of the anchoring system, multiple first anchoring systems are obtained through orthogonal experiments. The first anchoring system includes a combination of anchoring systems of equal length and a combination of anchoring systems of different lengths.

[0056] Based on the various 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 various first anchoring systems. Based on the results of the three-dimensional numerical simulation calculation, the optimal scheme of the first anchoring system is determined: that is, the values ​​of the two anchor rods in the optimal scheme of the first anchoring system.

[0057] Because the physical and mechanical parameters of the rock mass affect the distribution of the elasto-plastic zone, the distribution of the elasto-plastic zone will be different depending on the stress state of the rock mass. Therefore, this application comprehensively analyzes the stress of the rock mass by combining the stress of the rock mass itself with the external support force, so as to obtain a more accurate result of the plastic zone range.

[0058] Since the prestressed anchoring system is essentially a stress repair system for the plastic zone in order 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 utilizes the scientific, simple, efficient, and economical characteristics of orthogonal experimental methods to transform the allowable length range of the anchoring system into multiple first anchoring systems. Combined with the intuitiveness of three-dimensional numerical simulation models, it performs surrounding rock displacement analysis and plastic zone analysis on multiple first anchoring systems. Based on the results of three-dimensional numerical simulation calculations, the optimal first anchoring system with the minimum deformation can be quickly identified, saving screening time and increasing the persuasiveness of the optimal results.

[0060] Insufficient anchorage length can affect the load-bearing capacity of concrete, resulting in weak anchor force, structural instability, and causing rock deformation, cracking, or even anchor detachment. Excessive anchorage length can lead to excessive tension in the anchor, wasting materials and increasing construction difficulty, while also causing low structural stability and easy deformation and cracking of the rock mass. The construction of a tunnel may involve the combined use of multiple anchors, with many combination methods. The support results of different combinations may vary greatly, making the selection of anchor combination schemes quite difficult.

[0061] To address the aforementioned problems, this application provides a novel anchor bolt system selection scheme, wherein it is necessary to...

[0062] First, the stress condition after rock mass support is considered to obtain the range of the calculated plastic zone; then, anchoring systems of different lengths are selected from the range of the plastic zone.

[0063] Orthogonal experiments were conducted to combine anchoring systems of different lengths, resulting in a large number of possible anchoring system combination schemes for practical use. Numerical models were then used to screen these anchoring system combination schemes and select the optimal one.

[0064] Compared to existing technologies, this application considers the comprehensive stress of the tunnel rock mass after support, making the design results more consistent with the actual conditions of the construction site, capable of withstanding sufficient loads and reducing tunnel deformation. Through orthogonal experiments and numerical simulations, the optimal first anchoring system can be determined simply and efficiently, effectively preventing excessively long or short anchoring lengths from reducing the bond strength between the steel bars and the surrounding concrete and the stability of the structure, leading to insufficient bond strength between the steel bars and concrete, cracking, and increased maintenance costs and construction difficulties in the later stages. At the same time, this optimal first anchoring system, as a combination scheme, provides better support than the single anchor length scheme while reducing the selection and simulation process of anchor combinations, and simultaneously meeting the requirements of load-bearing capacity and construction difficulty.

[0065] Furthermore, the shotcrete 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 anchoring system support force.

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

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

[0068] If the rock mass has high strength, it will undergo elastic deformation due to its dense and hard structure, resulting in a smaller area of ​​plastic zone. In contrast, the rock mass with low strength tends to undergo plastic deformation, resulting in a larger area of ​​plastic zone.

[0069] Rock cohesion and internal friction angle are two mechanical indicators of rock mass shear strength. Rock mass shear strength is the ultimate resistance of rock mass to shear failure, while internal friction angle reflects the frictional properties of rock and soil. The greater the rock mass cohesion, the stronger the rock mass shear strength, and vice versa, the weaker the shear strength, which is prone to adverse effects such as displacement and tilting. The internal friction angle decreases with increasing stress within the elastic deformation range of the rock mass. After exceeding this range, when the internal friction angle is zero, the rock mass changes from elastic deformation to plastic deformation.

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

[0071] This application uses multiple methods to calculate the range of the plastic region. The range of the plastic region is different because the calculation methods are different. Compared with using only one method, multiple methods can avoid the omission of extreme values ​​and the impact of calculation errors, which is economical and safe.

[0072] As a preferred method of the above-mentioned empirical theoretical methods, various empirical theoretical methods may include the Hoek empirical method to calculate the size of the plastic zone. Under the premise of measuring the physical stress of the rock mass and the stress of the support, a mathematical model is established based on factors such as the elastic-plastic properties 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 intensity of the rock mass, thereby determining the size of the plastic zone.

[0073] Furthermore, based on the calculation results of the plastic zone size, the lower limit of the allowable length range of the anchoring system is the smallest integer greater than the minimum plastic zone value, and the upper limit 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 to facilitate subsequent production, manufacturing, and inspection.

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

[0077] Obtain a second anchoring system having a first length and a third anchoring system having a second length;

[0078] The second anchoring system and the third anchoring system are used as factors in the orthogonal experiment, and the range of values ​​of the first length and the second length are used as factor levels in the orthogonal experiment to generate a variety of combinations of the second anchoring system and the third anchoring system with 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. Several representative first anchoring systems are selected from a variety of first anchoring systems to conduct orthogonal experiments. The first length and the second length are the experimental factors of the orthogonal experiments, and the value range of the first length and the second length are the factor levels of the orthogonal experiments. The optimal combination of the first length value and the second length value is selected from the results.

[0080] In this embodiment, to provide more length references and more accurate design results, the combination of the first anchoring system should be more diverse;

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

[0082] Furthermore, determining the preferred solution for the first anchoring system includes the following steps:

[0083] For combinations of second and third anchoring systems with various lengths, a three-dimensional numerical model is established to simulate and analyze the prestressed anchoring system and surrounding rock deformation state of combinations of second and third anchoring systems with various lengths.

[0084] For the excavation of the unsupported bare tunnel, based on the simulation of the prestressed anchoring system and the deformation state of the surrounding rock, and the elastoplastic analysis of the excavated bare tunnel, the anchoring system with the smallest deformation of the surrounding rock is selected as the optimal solution according to the analysis results.

[0085] Based on the combination of the first and second length values ​​established by the orthogonal experiment, the excavation of the bare tunnel is simulated by a three-dimensional numerical model. This intuitively reflects the displacement and deformation of the rock mass under different combinations of the first and second length values. Based on the deformation of the rock mass, the scheme with the minimum plastic deformation is selected as the optimal combination of the first and second length values.

[0086] Furthermore, 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.

[0087] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for designing the length of a tunnel prestressed anchorage system, characterized in that, The process includes the following steps: obtaining the shotcrete support force, steel brace support force, and anchorage system support force, and calculating the resultant support force; The extent of the plastic zone is calculated based on the surrounding rock mechanical parameters and the resultant force of the support. The allowable length range of the anchoring system is determined based on the range of the plastic zone. Based on the allowable length range of the anchoring system, orthogonal experiments were conducted to obtain a variety of first anchoring systems. The first anchoring systems include combinations of anchoring systems of equal length and combinations of anchoring systems of different lengths. Based on the various 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 various first anchoring systems. Based on the results of the three-dimensional numerical simulation calculation, the optimal scheme of the first anchoring system is determined: that is, the values ​​of the two anchor rods in the optimal scheme of the first anchoring system. Based on the allowable length range of the anchoring system, through orthogonal experiments, a variety of first anchoring systems are obtained, including: obtaining a second anchoring system with a first length and a third anchoring system with a second length; The second anchoring system and the third anchoring system are used as factors in the orthogonal experiment, and the range of values ​​of the first length and the second length are used as factor levels in the orthogonal experiment to generate a variety of combinations of the second anchoring system and the third anchoring system with different lengths as a variety of first anchoring systems.

2. The method for designing the length of a tunnel prestressed anchorage system as described in claim 1, characterized in that: The shotcrete 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 anchoring system support force.

3. The method for designing the length of a tunnel prestressed anchorage system as described in claim 1, characterized in that: The surrounding rock mechanical parameters include rock mass strength σcm, rock cohesion c, and internal friction angle φ.

4. The method for designing the length of a tunnel prestressed anchorage system as described in claim 1, characterized in that: The size of the plastic zone was calculated using a variety of empirical theoretical methods.

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

6. The method for designing the length of a tunnel prestressed anchorage system as described in claim 1, characterized in that: Determining the optimal solution for the first anchoring system includes the following steps: For combinations of the second and third anchoring systems with various lengths, a three-dimensional numerical model is established, and the prestressed anchoring system and the surrounding rock deformation state of the combinations of the second and third anchoring systems with various lengths are simulated and analyzed. For the excavation of the unsupported bare tunnel, based on the simulation of the prestressed anchoring system and the deformation state of the surrounding rock, and the elastoplastic analysis of the excavated bare tunnel, the anchoring system with the smallest deformation of the surrounding rock is selected as the optimal solution according to the analysis results.

7. The method for designing the length of a tunnel prestressed anchorage system as described in 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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