Construction method of tunnel pre-stressed anchor rod dynamic supporting method based on surrounding rock plastic zone

Abstract

A construction method of a tunnel pre-stressed anchor rod dynamic supporting method based on a surrounding rock plastic zone comprises the following steps that A, in the non-excavation stage, the plastic deformation area of surrounding rock after tunnel excavation is predicted through numerical simulation, B, the size of needed pre-stress is calculated based on the relation between the total plastic deformation energy of the surrounding rock and the elastic strain energy of an anchor rod, and the size of the pre-stress is calculated. C, performing numerical simulation on excavation of a left hole, performing five to nine different pre-stressed anchor rod arrangement working conditions on a left hole arch shoulder position, identifying a most dangerous point position, applying a pre-stressed anchor rod, and completing excavation construction of the left hole; D, performing numerical simulation on excavation of a right hole, and applying a pre-stressed anchor rod to a left shoulder key point position on the basis of applying a pre-stressed anchor rod to the left shoulder key point position; and E, building a left-right asymmetric plastic zone prediction model through numerical simulation, and carrying out construction of a tunnel or an underground space after the left-right asymmetric plastic zone prediction model is built.

Description

Technical Field

[0001] The invention belongs to the technical field of tunnel construction, and in particular relates to a construction method of a tunnel prestressed anchor dynamic support method based on the plastic zone of surrounding rock. Background Art

[0002] The rapid development of tunnels requires more efficient and safer tunnel support technologies to ensure safe construction and operation. While prestressed anchors are a method for enhancing rock mass stability, their unlimited use is not feasible due to cost considerations. Safety and efficiency must be fully considered in design and construction.

[0003] In actual construction, prestressed anchor rods are generally used in tunnels with weak surrounding rock, large cross-sections or high sidewalls, and deep soft rock roadways. Currently, for left-right pilot tunnel excavation, the prestressed anchor rod support technology mostly uses a symmetrical spandrel arrangement. However, this support method fails to account for the left-right asymmetry of the plastic zone as the tunnel is excavated, resulting in a lower actual effectiveness of the prestressed anchor rods. Therefore, in tunneling conditions with left-right excavation, it is necessary to improve the efficiency of prestressed anchor rods to ensure their more rational use.

[0004] Therefore, the construction of prestressed anchors has become a critical issue in tunnel engineering. How to safely and efficiently use prestressed anchors to ensure tunnel safety has become both a key and challenging aspect of engineering construction. This paper proposes a dynamic tunnel support method using prestressed anchors based on the plastic zone of the surrounding rock. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a construction method for a tunnel prestressed anchor dynamic support method based on the plastic zone of the surrounding rock. The purpose is to enable a smooth transition to a larger cross-section when the left and right pilot tunnels are expanded into the main tunnel, thereby reducing the risks and uncertainties during the construction process.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: a construction method of a tunnel prestressed anchor dynamic support method based on the plastic zone of the surrounding rock, comprising the following steps: A. To achieve the supporting effect of prestressed anchor rods on surrounding rock, numerical simulation calculations are performed before excavation to predict the plastic deformation area of ​​surrounding rock after tunnel excavation, thereby determining the potential unstable area. B. Based on the relationship between the total plastic deformation energy of the surrounding rock and the elastic strain energy of the anchor, calculate the required prestressing force. C. Numerical simulation of the excavation of the left tunnel. 5 to 9 different prestressed anchor arrangements were performed at the spandrel of the left tunnel using numerical simulation. The most dangerous points were identified as the key points of the left shoulder, and prestressed anchors with sufficient prestress were applied at the key points of the left shoulder. D. Numerical simulation of the excavation of the right tunnel. Based on the application of prestressed anchors at the key points of the left shoulder, numerical simulation was used to perform 5 to 9 different prestressed anchor arrangement conditions at the spandrel position of the right tunnel. The most dangerous points were identified as the key points of the right shoulder, and prestressed anchors with sufficient prestress were applied at the key points of the right shoulder. E. Through numerical simulation, a left-right asymmetric plastic zone prediction model is built. Once completed, construction in the tunnel or underground space can begin.

[0007] In certain embodiments, in step A, it is necessary to input parameters for the numerical simulation, and the parameters include elastic modulus, density, Poisson's ratio, internal friction angle and cohesion of the surrounding rock and support.

[0008] In some embodiments, the constitutive model of the numerical simulation adopts the Mohr-Coulomb constitutive model to determine the plastic zone of the surrounding rock, and the excavation model of the numerical simulation adopts the plane model excavation model, and the stress release coefficient is set to 25%-35%.

[0009] In certain embodiments, the prestressed anchor rods are arranged radially.

[0010] In certain embodiments, in step B, the total plastic deformation energy of the surrounding rock is By initial support and the plastic deformation energy of the anchor system Shared responsibility, where the anchor system energy includes the elastic strain energy of ordinary anchors and prestressed anchor compensation , by calculating the total plastic deformation energy of the surrounding rock , minus the energy completely absorbed by the initial support and the elastic strain energy of ordinary anchor , the compensation energy of prestressed anchor rod is obtained , and finally calculate the prestress design value P0 of the prestressed anchor rod.

[0011] In certain embodiments, in step B, the total plastic deformation energy of the surrounding rock is and the elastic strain energy of the anchor The calculation process is as follows: First, the energy density per unit volume in the plastic zone is calculated. , total volume Calculation of total plastic deformation energy of surrounding rock : u p = σ peak , , , in: is the peak strength of surrounding rock, The equivalent plastic strain can be obtained through numerical simulation or experiment. is the plastic zone radius, is the tunnel radius, calculate the plastic deformation energy borne by the anchor : , , The energy absorbed by the ordinary anchor is then evaluated: , in: is the number of common anchor rods, is the working tension of ordinary anchor (passively generated by surrounding rock deformation), 2EA is the anchor system stiffness, L is the effective free length of the prestressed anchor, Then calculate the energy required to compensate for the prestressed anchor : , Calculation of prestressed anchor compensation energy : , Prestressing efficiency coefficient η It is recommended to take 0.6~0.8; Finally, the prestress design value of the prestressed anchor is calculated : but .

[0012] In certain embodiments, the cross-section of the main tunnel is in the form of a straight wall circular arch + side wall corbel, with an excavation width of 22.4m and an excavation height of 19.68m to 20.93m. The surrounding rock of the tunnel body mainly includes sandstone, quartz sandstone, sandstone-shale interlayers, mudstone, and siltstone. The left and right pilot tunnels on the upper steps of the tunnel are reinforced with left and right prestressed anchor rods.

[0013] In certain embodiments, in step C, every 8-12 meters forward, 5 to 9 different prestressed anchor arrangement conditions are performed on the arch shoulder position of the left hole, and the most dangerous point is identified as the key point of the left shoulder, until the excavation of the left hole is completed, and then step D is entered. Similarly, in step D, every 8-12 meters forward, 5 to 9 different prestressed anchor arrangement conditions are performed on the arch shoulder position of the right hole, and the most dangerous point is identified as the key point of the right shoulder, until the excavation of the left hole is completed.

[0014] In certain embodiments, in step E, actual monitoring data is used to further verify the effectiveness and make adjustments as needed. The actual monitoring data includes the extent of the surrounding rock plastic zone, the stress and deformation of the support structure. This real-time on-site monitoring data allows for dynamic adjustment of anchor bolt positions, improving the placement of prestressed anchor bolts and further ensuring tunnel safety.

[0015] In certain embodiments, the angle between the anchor and the y-axis, the proportion of the plastic zone, and the size of the surrounding rock pressure, as well as their respective weights, are set. Based on the given weights: the angle between the anchor and the y-axis is 20%-30%, the proportion of the plastic zone is 30%-50%, and the proportion of the surrounding rock pressure is 30%-40%, the weighted scoring method is used to calculate the risk level of each anchor position on the left side. The formula is as follows: , in, θ : The angle between the anchor rod and the y-axis under the corresponding working condition. The larger the angle, the smaller the axial force component and the higher the risk. is the normalized value of the angle between the anchor rod and the y-axis under the corresponding working condition, θ min: 5 to 9 different prestressed anchor rods, with optimal angles, θ Max: 5 to 9 different prestressed anchor rods, with the worst angle value. is the normalized value of the plastic zone proportion, The plastic zone range refers to the plastic zone range corresponding to the working condition position. Plastic zone range max refers to the maximum plastic zone range in all working conditions. Plastic zone range min refers to the minimum plastic zone range in all working conditions; is the normalized value of surrounding rock pressure, Surrounding rock pressure refers to the surrounding rock pressure at the corresponding working position. Surrounding rock pressure max refers to the maximum surrounding rock pressure in all working positions. Surrounding rock pressure min refers to the minimum surrounding rock pressure in all working positions.

[0016] In some embodiments, based on the determination of the most dangerous point on the left, it is necessary to combine the most dangerous point on the right and highlight the risk on the right side through asymmetric weighting of the left and right sides. The weighted formula for the left and right sides is designed: Comprehensive risk = Dl × Wl + Dr × Wr × β， Among them: Dl , Dr : The most dangerous point on the left / right, Wl + Wr =1: Weight distribution, if there is a higher risk on the right side, increase the weight on the right side Wr ‌, Β : Correction coefficient of the right dangerous point, ranging from 1.2 to 1.5. The higher the risk on the right side, β The bigger.

[0017] The scope of the present invention is not limited to technical solutions formed by a specific combination of the above-mentioned technical features, but also includes other technical solutions formed by any combination of the above-mentioned technical features or their equivalents. For example, technical solutions formed by replacing the above-mentioned features with (but not limited to) technical features with similar functions disclosed in this application.

[0018] Due to the application of the above technical solution, the present invention has the following advantages over existing technologies: It first uses numerical simulations of tunnel excavation to determine the distribution of the plastic zone, which then guides actual construction, making the entire construction process safer and more controllable. Based on the numerically simulated plastic zones of the left and right pilot tunnels, prestressed anchors are sequentially applied at the most dangerous locations in the plastic zone, ensuring optimal support and ensuring tunnel construction safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Flowchart of a method for dynamic support of tunnel prestressed anchor bolts based on the plastic zone of surrounding rock according to an embodiment of the present invention; Figure 2 The cloud diagram of the plastic zone and the working condition diagram of the prestressed anchor rods in the left pilot tunnel after excavation without prestressed anchor rods are shown in the embodiment of the present invention; Figure 3 This is a comparison diagram of the reduction of plastic zones under different working conditions when a prestressed anchor rod is applied during the excavation of the left pilot tunnel in an embodiment of the present invention; Figure 4 The cloud diagram of the plastic zone when no prestressed anchor rods are applied during the excavation of the right pilot tunnel and the working condition diagram of the prestressed anchor rods of the right pilot tunnel in the embodiment of the present invention; Figure 5 This is a comparison diagram of the reduction of the plastic zone under different working conditions when a prestressed anchor rod is applied during the excavation of the right pilot tunnel in an embodiment of the present invention. DETAILED DESCRIPTION

[0020] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0021] The specific implementation process is as follows Figure 1 As shown. In tunnel engineering, when it comes to the excavation of left and right pilot tunnels. Before starting the excavation of the left tunnel, an in-depth numerical simulation calculation is first carried out on the tunnel. This simulation must first predict the plastic zones that may appear during the excavation process, and through in-depth analysis of these plastic zones, find out potential unstable areas, and help identify those locations where collapse or other safety problems may occur during the actual construction process. Then, based on the balance relationship between the plastic deformation energy of the surrounding rock and the elastic strain energy of the anchor, the required prestressing force is calculated to provide a basis for subsequent reinforcement measures. For the numerical simulation excavation of the left tunnel, the plastic zone that will appear after the excavation of the left tunnel is predicted, and the numerical simulation method is used to analyze 5 to 9 different prestressed anchor arrangement schemes at the spandrel position, identify the most dangerous points, and install prestressed anchors. Similarly, for the numerical simulation excavation of the right tunnel, the plastic zone that will appear after the excavation of the right tunnel and its most dangerous points are predicted. Based on the numerical simulation results of the left and right tunnels, the present invention adjusts and optimizes the arrangement and number of prestressed anchors. After completing all the above preparations, the construction phase of the tunnel officially begins. At this stage, because all preventative measures are in place and well-planned, the entire construction process becomes safer and more manageable. By reinforcing these vulnerable areas, the risk of any safety issues arising during actual construction can be greatly reduced. The implementation of these preventative measures not only protects the lives of workers but also ensures construction progress and quality. This includes the following steps: A. To achieve the supporting effect of prestressed anchor rods on the surrounding rock, in the pre-excavation stage, numerical simulation is used to predict the plastic deformation area of ​​the surrounding rock after tunnel excavation, thereby determining the potential unstable area. B. Based on the balance between the plastic deformation energy of the surrounding rock and the elastic strain energy of the anchor, the required prestress is calculated to provide a basis for subsequent reinforcement measures. C. Use numerical simulation to simulate the excavation of the left tunnel and analyze 5 to 9 different prestressed anchor arrangements at the spandrel of the left tunnel. Identify the most dangerous points and identify them as the key points of the left shoulder. Apply prestressed anchors with sufficient prestress to enhance stability. D. Using numerical simulation to simulate the excavation of the right tunnel, based on the application of prestressed anchors at the key points of the left shoulder, 5 to 9 different prestressed anchor arrangement conditions were performed at the spandrel positions of the right tunnel. The most dangerous points were identified as the key points of the right shoulder, and prestressed anchors with sufficient prestress were applied at the key points of the right shoulder to enhance stability. E. Through numerical simulation, a left-right asymmetric plastic zone prediction model is constructed. Once completed, it can be used for on-site construction in tunnels or underground spaces. Its effectiveness can be further verified through actual monitoring data, and adjustments can be made as needed.

[0022] A detailed, specific embodiment: Taking an underground project in Shenyang as an example, the main tunnel has a straight-walled, circular arch cross-section with sidewall corbels. The excavation width is 22.4m, and the excavation height ranges from 19.68m to 20.93m. The surrounding rock mass of the tunnel primarily consists of sandstone, quartz sandstone, interbedded sandstone and shale, mudstone, and siltstone, ranging from relatively fragmented to relatively intact. To ensure construction safety, the left and right pilot tunnels on the upper steps of the tunnel require reinforcement with left and right prestressed anchor bolts. Therefore, the present invention was used in the prestressed anchor bolt construction design.

[0023] Step A: Perform numerical simulation of excavation calculation without prestressed anchor rods. Based on the calculated values, obtain the plastic zone cloud map using Origin scientific drawing and data analysis software to obtain the total volume of the plastic zone. , energy density per unit volume in the plastic zone : u p = σ peak , , in: is the peak strength of surrounding rock, Equivalent plastic strain (can be obtained through numerical simulation or experiment), is the plastic zone radius, is the tunnel radius.

[0024] Step B: The design value of the prestressed anchor can be obtained through the balance relationship between the plastic deformation energy of the surrounding rock under support and the elastic strain energy of the anchor.

[0025] The radial arrangement of anchor bolts in anchor tunnels (i.e., installation perpendicular to the tunnel contour) is the result of comprehensive optimization based on mechanical mechanisms, construction convenience, and economic efficiency in engineering practice. For example, after tunnel excavation, surrounding rock stress redistributes. Radial anchor bolts directly counteract radial displacement of the surrounding rock, providing support reaction through axial tension and inhibiting the expansion of the plastic zone. When arranged radially, the anchor bolts are evenly tensile along their entire length, fully utilizing their high tensile strength. This radial arrangement forms a uniformly thick reinforcement ring in the surrounding rock, concentric with the tunnel, evenly distributing in-situ stress. Radial anchor bolts can penetrate the plastic zone into the elastic zone, creating a "suspension effect" or "combined arch effect," transferring loads to the deeper, stable rock formations. Radial drilling simplifies construction, as the drill rig only operates along the normal line of the tunnel section, eliminating the need for complex angle adjustments. This results in high efficiency and low cost. The uniform length and angle of all anchor bolts facilitates mass production and rapid installation, making them suitable for mechanized construction (such as drilling rigs).

[0026] The calculation is as follows: the total plastic deformation energy of the surrounding rock By initial support and the plastic deformation energy of the anchor system Shared responsibility, in which the plastic deformation of the anchor system can Contains elastic strain energy of ordinary anchor and prestressed anchor compensation , by calculating the total plastic deformation energy of the surrounding rock , minus the energy completely absorbed by the initial support and the elastic strain energy of ordinary anchor , the compensation energy of prestressed anchor rod is obtained .

[0027] Total plastic deformation energy of surrounding rock and the elastic strain energy of the anchor The calculation process is as follows: First, the energy density per unit volume in the plastic zone is calculated. , total volume Calculation of total plastic deformation energy of surrounding rock : , Calculate the plastic deformation energy borne by the anchor : , , The energy absorbed by the ordinary anchor is then evaluated: , in: is the number of common anchor rods, is the working tension of the ordinary anchor (passively generated by the surrounding rock deformation), 2EA is the anchor system stiffness, and L represents the effective free length of the prestressed anchor. Then, the energy required to be compensated by the prestressed anchor is calculated. : , That is, calculate the compensation energy of prestressed anchor : , unit Pa, The prestressing efficiency coefficient η is recommended to be 0.6~0.8, for example, it is 0.7 in this embodiment; Finally, the prestress design value of the prestressed anchor is calculated : but ,unit , Through the above algorithm, the prestress design value of the prestressed anchor rod is taken in this case , the anchor rod length is 9m.

[0028] Step C: Based on the plastic zone distribution cloud map, eight different prestressed anchor arrangement conditions are designed for the spandrel position of the left tunnel. The anchors are arranged radially and the tunnel vault is a circular arc.

[0029] like Figure 2 As shown, working condition 1: 1 grid shear-p 5 grid shear-n shear-p 1 grid shear-p 1 grid shear-nshear-p, Condition 2: 1 grid shear-p, 7 grid shear-n shear-p, 1 grid shear-p, Condition 3: 1 grid shear-p 8 grid shear-n shear-p, Condition 4: 3 grid shear-n shear-p, 2 grid shear-p, 5 grid shear-n shear-p, Condition 5: 6 grid shear-p 4 grid shear-n shear-p, Condition 6: 5 grid shear-p, 1 grid shear-n shear-p, 1 grid shear-p, 3 grid shear-n shear-p, Condition 7: 5 grid shear-p 5 grid shear-n shear-p, Condition 8: 1 grid shear-p tension-p 7 grid shear-n shear-p, Among them, shear-p refers to the shear plastic zone, shear-n refers to the shear non-plastic zone, shear-n shear-p refers to the alternating structural zone of non-plastic zone and plastic zone, and shear-p tension-p refers to the composite structural zone of shear plastic zone and tensile plastic zone. Working conditions 1 2 3 4 5 6 7 8 Angle between anchor rod and y-axis 54.5 51 47.5 44 40.5 37 33.5 30 In the eight different prestressed anchor arrangement working conditions, calculations were performed for each working condition separately. The angle between the anchor and the y-axis, the proportion of the plastic zone, and the size of the surrounding rock pressure were set, and their respective weights were given: the angle between the anchor and the y-axis is 25%, the proportion of the plastic zone is 40%, and the proportion of the surrounding rock pressure is 35%. The weighted scoring method was used to calculate the risk level of each anchor position on the left side. The formula is as follows: , , is the normalized value of the angle between the anchor rod and the y-axis, where the angle between the anchor rod and the y-axis is 25% ‌, θ: Angle between the anchor and the y-axis (the larger the angle, the smaller the axial force component and the higher the risk), θ min=30° (working condition 8, optimal value), θ max=54.5° (working condition 1, worst value), Normalization: , the larger the value, the more dangerous it is. , is the normalized value of the plastic zone ratio, the plastic zone range is max, and the No. 4-7 working conditions are all 10 grids, the maximum is 10, the plastic zone range is min, and the No. 1 and No. 8 working conditions are 8 grids, the minimum is 8, that is, the normalized value of the plastic zone ratio of No. 1 working condition is 0, is the normalized value of surrounding rock pressure. The surrounding rock pressure of the tunnel is obtained through numerical simulation. For each anchor arrangement working condition, it is calculated. Anchor point Angle (θ) Angle score (25%) Plastic zone number Plastic zone proportion (40%) Surrounding rock pressure (35%) Comprehensive risk level Sorting 1 54.5° 0.25×1.00=0.25 8 0.40×0.00=0.00 0.35×0.20=0.01 0.11 7 2 51° 0.25×0.86=0.21 9 0.40×0.50=0.20 0.35×0.30=0.11 0.17 5 3 47.5° 0.25×0.71=0.18 9 0.40×0.50=0.20 0.35×1.00=0.35 0.24 2 4 44° 0.25×0.57=0.14 10 0.40×1.00=0.40 0.35×0.80=0.28 0.27 1 5 40.5° 0.25×0.43=0.11 10 0.40×1.00=0.40 0.35×0.40=0.14 0.22 3 6 37° 0.25×0.29=0.07 10 0.40×1.00=0.40 0.35×0.20=0.07 0.18 4 7 33.5° 0.25×0.14=0.04 10 0.40×1.00=0.40 0.35×0.10=0.04 0.16 6 8 30° 0.25×0.00=0.00 8 0.40×0.00=0.00 0.35×0.00=0.00 0.00 8 , Then, through the numerical simulation of excavation calculation, the values ​​​​are obtained through Origin scientific drawing and data analysis software. Figure 3 As shown in the figure, different prestressed anchor arrangement schemes were used for the left spandrel position to generate a comparison chart of the reduction of plastic zone under different working conditions. The reduction of plastic zone in working condition No. 4 on the left side reached 15.45, which verified each other. It was concluded that working condition No. 4 on the left side (danger level 0.27) was the most dangerous point. As the key point of the left shoulder, prestressed anchors were applied to it.

[0030] Step D: According to the plastic zone distribution cloud map, the plastic zone of the left tunnel spandrel is different from that of the right tunnel spandrel. Based on the application of prestressed anchor rods in the left tunnel, eight different prestressed anchor rod arrangement conditions are designed for the right tunnel spandrel position. The anchor rods are arranged radially, and the tunnel vault is a circular arc.

[0031] like Figure 4 As shown in the figure, among the 8 different prestressed anchor arrangement schemes: Working condition 1, 3 grid shear-p, 2 grid shear-n, shear-p, 1 grid shear-p, 2 grid shear-n, shear-p, Working condition 2, 3 grid shear-p 6 grid shear-n shear-p, Working condition 3, 1 grid shear-p, 8 grid shear-n, shear-p, 1 grid shear-p, Working condition 4, 7 grid shear-n shear-p 3 grid shear-p, Working condition 5, 2 grid shear-p, 4 grid shear-n, shear-p, 5 grid shear-p, Working condition 6, 1 grid shear-p, 8 grid shear-n, shear-p, 1 grid shear-p, Working condition 7, 1 grid shear-n shear-p tension-p 3 grid shear-n shear-p 5 grid shear-p, Working condition 8, 1 grid shear-n shear-p tension-p 2 grid shear-n shear-p 1 grid shear-p, Among them, shear-p refers to the shear plastic zone, shear-n refers to the shear non-plastic zone, shear-n shear-p refers to the alternating structural zone of non-plastic zone and plastic zone, and shear-n shear-p tension-p refers to the composite structural zone of non-plastic zone, shear plastic zone and tensile plastic zone. Working conditions 1 2 3 4 5 6 7 8 Angle between anchor rod and y-axis 54.5 51 47.5 44 40.5 37 33.5 30 The angle between the anchor and the y-axis, the proportion of the plastic zone, the size of the surrounding rock pressure, and their respective weights are set. Based on the given weights: the angle between the anchor and the y-axis is 25%, the proportion of the plastic zone is 40%, and the proportion of the surrounding rock pressure is 35%, the weighted scoring method is used to calculate the risk of each anchor position on the right side. The calculation results are as follows: Anchor point Angle (θ) Angle score (25%) Plastic zone number Plastic zone proportion (40%) Surrounding rock pressure (35%) Comprehensive risk level Sorting 1 54.5° 0.25×1.00=0.25 8 0.40×0.57=0.23 0.35×0.20=0.01 0.18 4 2 51° 0.25×0.86=0.21 9 0.40×0.71=0.29 0.35×0.30=0.11 0.20 3 3 47.5° 0.25×0.71=0.18 10 0.40×0.86=0.34 0.35×1.00=0.35 0.29 ‌1‌ 4 44° 0.25×0.57=0.14 10 0.40×0.86=0.34 0.35×0.80=0.28 0.26 2 5 40.5° 0.25×0.43=0.11 11 0.40×1.00=0.40 0.35×0.40=0.14 0.18 4 6 37° 0.25×0.29=0.07 10 0.40×0.86=0.34 0.35×0.20=0.07 0.18 4 7 33.5° 0.25×0.14=0.04 9 0.40×0.71=0.29 0.35×0.10=0.04 0.13 5 8 30° 0.25×0.00=0.00 4 0.40×0.00=0.00 0.35×0.00=0.00 0.00 6 , After determining that the left side No. 4 working condition is the most dangerous point (comprehensive risk Dl =0.27), combined with the hazard level Dr of working condition No. 3 on the right side, and highlighting the risk value on the right side through asymmetric weighting.

[0032] Left and right side weighted formula design: comprehensive risk = Dl×Wl+Dr×Wr×β, Where: Dl, Dr: is the danger level of the anchor bolts with working conditions No. 4 on the left and No. 3 on the right. It is known that Dl=0.27, Wl+Wr=1: Weight distribution. If there is a higher risk on the right side (such as an abnormal proportion of plastic zone), increase the weight Wr‌ on the right side. β: Correction coefficient for the right-side danger point (recommended range: 1.2~1.5, the higher the risk on the right side, the larger β), Comprehensive risk calculation on the right: The hazard level of anchor bolt No. 4 on the left side is Dl=0.27, the weight distribution is Wl=0.3, Wr=0.7, and the correction coefficient β=1.3: Comprehensive risk = 0.27×0.3+0.29×0.7×1.3=0.35.

[0033] Then, through numerical simulation of excavation calculation values, the Origin scientific drawing and data analysis software was used to obtain the following Figure 5As shown in the figure, different prestressed anchor arrangement schemes were used for the right spandrel position to generate a comparison chart of the reduction of the plastic zone under different working conditions. The reduction of the plastic zone of working condition No. 3 on the left side reached 45.82, which verified each other and led to the conclusion that the most dangerous point on the right side is working condition No. 3 on the right side. As the key point of the right shoulder, its danger level is 0.35, and it is necessary to urgently apply prestressed anchors to it.

[0034] It can be seen that the optimal position of the prestressed anchor rod on the right side is not symmetrical with the optimal position of the prestressed anchor rod on the left side. The asymmetric prestressed anchor rod arrangement is more reasonable, which can minimize the safety risks that may occur during construction. On-site construction ensures that the prestressed anchor rod can be used more reasonably and ensures the safety and controllability of the entire underground space construction process.

[0035] Step E: Conduct on-site construction based on the numerical simulation results. During actual on-site operations and unexpected situations, according to the relevant provisions of the "Technical Specification for Geotechnical Anchor Bolting and Shotcrete Support Engineering" (GB50086-2015), the change in prestress after anchor bolt locking should generally not exceed 10% of the anchor bolt tension design value. If this range is exceeded, control measures should be taken to further improve the prestressed anchor bolt position based on actual investigation and calculation to ensure tunnel safety.

[0036] In summary, the present invention provides a technical solution for a method of dynamic support of tunnel prestressed anchor rods based on the plastic zone of the surrounding rock: the present invention numerically simulates tunnel excavation before construction, so that the entire construction process will be safer and more controllable. Based on the plastic zone numerically simulated during the excavation of the left and right pilot tunnels, multiple working condition calculations are set during the excavation of the left and right pilot tunnels, and the sizes of the plastic zones are compared to select the most dangerous positions for applying prestressed anchor rods so that the prestressed anchor rods can play the best role. Through actual on-site operations and encountering emergencies, the position of the prestressed anchor rods should be further improved according to actual investigations to ensure tunnel safety. By applying prestress, the stability of the surrounding rock is enhanced, deformation is controlled, high bearing capacity and safety, adaptability, flexible construction, shortened construction period and convenient management.

[0037] The above embodiments are intended only to illustrate the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made in accordance with the spirit of the present invention are intended to be covered by the scope of protection of the present invention.

Claims

1. A construction method for a tunnel prestressed anchor dynamic support method based on the plastic zone of the surrounding rock, characterized by: The following steps are involved: A. To achieve the supporting effect of prestressed anchor rods on surrounding rock, numerical simulation calculations are performed before excavation to predict the plastic deformation area of ​​surrounding rock after tunnel excavation, thereby determining the potential unstable area. B. Based on the relationship between the total plastic deformation energy of the surrounding rock and the elastic strain energy of the anchor, calculate the required prestressing force. C. Numerical simulation of the excavation of the left tunnel. 5 to 9 different prestressed anchor arrangements were performed at the spandrel of the left tunnel using numerical simulation. The most dangerous points were identified as the key points of the left shoulder, and prestressed anchors with sufficient prestress were applied at the key points of the left shoulder. D. Numerical simulation of the excavation of the right tunnel. Based on the application of prestressed anchors at the key points of the left shoulder, numerical simulation was used to perform 5 to 9 different prestressed anchor arrangement conditions at the spandrel position of the right tunnel. The most dangerous points were identified as the key points of the right shoulder, and prestressed anchors with sufficient prestress were applied at the key points of the right shoulder. E. Through numerical simulation, a left-right asymmetric plastic zone prediction model is built. Once completed, construction in the tunnel or underground space can begin.

2. The construction method of a tunnel prestressed anchor dynamic support method based on the surrounding rock plastic zone according to claim 1, characterized in that: In step A, it is necessary to input parameters for the numerical simulation, including elastic modulus, density, Poisson's ratio, internal friction angle and cohesion of the surrounding rock and support.

3. The construction method of a tunnel prestressed anchor dynamic support method based on the surrounding rock plastic zone according to claim 1, characterized in that: The constitutive model of the numerical simulation adopts the Mohr-Coulomb constitutive model, the excavation model of the numerical simulation adopts the plane model excavation model, and the stress release coefficient is set to 25%-35%.

4. The construction method of a tunnel prestressed anchor dynamic support method based on the plastic zone of surrounding rock according to claim 1, characterized in that: The prestressed anchor rods are arranged radially.

5. The construction method of a tunnel prestressed anchor dynamic support method based on the plastic zone of surrounding rock according to claim 1, characterized in that: In step B, the total plastic deformation energy of the surrounding rock is By initial support and the plastic deformation energy of the anchor system Shared responsibility, where the anchor system energy includes the elastic strain energy of ordinary anchors and prestressed anchor compensation , by calculating the total plastic deformation energy of the surrounding rock , minus the energy completely absorbed by the initial support and the elastic strain energy of ordinary anchor , the compensation energy of prestressed anchor rod is obtained , and finally calculate the prestress design value P0 of the prestressed anchor rod.

6. The construction method of a tunnel prestressed anchor dynamic support method based on the plastic zone of surrounding rock according to claim 1, characterized in that: The cross-section of the main tunnel is in the form of a straight wall, circular arch + side wall corbel, with an excavation width of 22.4m and an excavation height of 19.68m to 20.93m. The surrounding rock of the tunnel body mainly includes sandstone, quartz sandstone, sandstone-shale interlayers, mudstone, and siltstone. The left and right pilot tunnels on the upper steps of the tunnel are reinforced with left and right prestressed anchor rods.

7. The construction method of a tunnel prestressed anchor dynamic support method based on the plastic zone of surrounding rock according to claim 1, characterized in that: In step C, every time the excavator advances 8-12 meters, 5 to 9 different prestressed anchor arrangements are performed on the arch spandrel position of the left hole, and the most dangerous point is identified as the key point of the left shoulder until the excavation of the left hole is completed, and then step D is entered. Similarly, in step D, every time the excavator advances 8-12 meters, 5 to 9 different prestressed anchor arrangements are performed on the arch spandrel position of the right hole, and the most dangerous point is identified as the key point of the right shoulder until the excavation of the left hole is completed.

8. The construction method of a tunnel prestressed anchor dynamic support method based on the plastic zone of surrounding rock according to claim 1, characterized in that: In step E, the effect is further verified through actual monitoring data, and adjustments are made as needed. The actual monitoring data includes the range of the surrounding rock plastic zone, the stress and deformation of the support structure.

9. The construction method of a tunnel prestressed anchor dynamic support method based on the plastic zone of surrounding rock according to claim 1, characterized in that: The angle between the anchor and the y-axis, the proportion of the plastic zone, and the size of the surrounding rock pressure, as well as their respective weights, are set. Based on the given weights: the angle between the anchor and the y-axis is 20%-30%, the proportion of the plastic zone is 30%-50%, and the proportion of the surrounding rock pressure is 30%-40%, the weighted scoring method is used to calculate the risk level of each anchor position on the left side. The formula is as follows: ， in, θ : The angle between the anchor rod and the y-axis under the corresponding working condition. The larger the angle, the smaller the axial force component and the higher the risk. is the normalized value of the angle between the anchor rod and the y-axis under the corresponding working condition, θ min: 5 to 9 different prestressed anchor rods, with optimal angles, θ Max: 5 to 9 different prestressed anchor rods, with the worst angle value. is the normalized value of the plastic zone proportion, is the normalized value of surrounding rock pressure.

10. The construction method of the tunnel prestressed anchor dynamic support method based on the surrounding rock plastic zone according to claim 9, characterized in that: Based on the most dangerous point on the left, the most dangerous point on the right should be combined with the left and right asymmetric weighting to highlight the risk on the right side. Left and right side weighted formula design: Comprehensive risk = Dl × Wl + Dr × Wr × β， Among them: Dl , Dr : The most dangerous point on the left / right, Wl + Wr =1: Weight distribution, if there is a higher risk on the right side, increase the weight on the right side Wr ‌, β : Correction coefficient of the right dangerous point, ranging from 1.2 to 1.

5. The higher the risk on the right side, β The bigger.

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