A tunnel slope stability research and anchor cable support optimization method

Abstract

The application discloses a tunnel slope stability research and anchor cable supporting optimization method, and the anchor cable supporting optimization method comprises the following steps: A1, according to the slope state of the researched range, the supporting parameters of the prestressed anchor cable are calculated, serving as a preliminary design scheme of the construction process; A2, the influence of the vertical interval of the prestressed anchor cable on the slope stability is quantified; A3, the influence of the inclination angle of the prestressed anchor cable on the slope stability is quantified; A4, the influence of the non-quantitative prestressed anchor cable on the slope stability is quantified; and A5, the influence of the bonding length of the prestressed anchor cable on the slope stability is researched. The application provides a tunnel slope stability research method, lays a foundation for exploring the influence of different supporting modes of the prestressed anchor cable on the rock slope stability, and further provides a method for exploring the optimal prestressed anchor cable supporting mode by changing the supporting parameters, which takes into account the safety and the economy, and can effectively improve the overall stability of the slope.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of tunnel safety, and particularly relates to a tunnel slope stability research and anchor cable support optimization method. BACKGROUND

[0002] Due to the complex regional geological structure, low surrounding rock grade, and high degree of weathering and fragmentation of rock mass in the western region, tunnel slope treatment has become a difficulty in engineering construction.

[0003] At present, many scholars have made fruitful achievements in the research on the stability of rock slope and support methods. Deng Huifang et al. rely on a certain tunnel portal slope, model and analyze the change law of plastic zone and displacement of rock slope through Flac3D software, and consider that the prestressed anchor cable support has good control on the slope displacement and can improve the stability of the slope; Zuo Yahui analyzes the displacement change of rock slope before and after reinforcement, the stability of rock slope after reinforcement under different platform widths, different anchoring forces and seismic load by numerical simulation, and considers that the prestressed anchor cable reinforcement can significantly reduce the plastic strain and X, Y direction displacement of rock slope; Li Tao et al. establish a slope excavation deformation analysis model based on discrete element software UDEC, and consider that the use of prestressed anchor cable reinforcement can effectively improve the stability of the slope, and timely follow-up support after excavation can effectively control the shear deformation of the slope. Lv Qing et al. take the prestressed anchor cable engineering of broken rock slope as the research object, analyze the diffusion mode of anchor cable prestress, and reveal the reinforcement mechanism of prestressed anchor cable of broken rock slope by using mechanical principles. The above researches all show that the prestressed anchor cable has high applicability to the reinforcement engineering of rock slope.

[0004] However, there is still a lack of tunnel slope stability research and anchor cable support optimization method in the prior art. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a tunnel slope stability research method, which has simple and effective method steps and lays a foundation for exploring the influence of different support modes of prestressed anchor cable on the stability of rock slope, in view of the deficiencies in the prior art.

[0006] To solve the above technical problems, the technical scheme adopted by the present application is as follows: a tunnel slope stability research method, which comprises the following steps:

[0007] Step S1, detailed investigation is carried out on the tunnel, and the characteristics of the unstable slope distributed in the tunnel are obtained according to the detailed investigation report;

[0008] Step S2, according to the characteristics of the unstable slope distributed in the tunnel, a numerical simulation software is used to simplify and construct the complex tunnel slope stability problem into an operable numerical analysis model;

[0009] Step S3, calculating the slope safety factor of the numerical analysis model by using the strength reduction method in the numerical simulation software;

[0010] Step S4, judging the stability state of the unstable slope distributed in the tunnel according to the calculated slope safety factor and in accordance with the building slope engineering technical specification.

[0011] The tunnel slope stability research and anchor cable support optimization method, the characteristics of the unstable slope distributed in the tunnel in step S1 and step S2 include slope instability factors.

[0012] The tunnel slope stability research and anchor cable support optimization method, the numerical simulation software in step S2 and step S3 is FLAC 3D finite difference method numerical simulation software.

[0013] The tunnel slope stability research and anchor cable support optimization method, the specific process of calculating the slope safety factor of the numerical analysis model by using the strength reduction method in the numerical simulation software in step S3 is:

[0014] Step S301, defining the slope safety factor F s The ratio of the actual shear strength index to the virtual reduction strength index at the critical state of landslide destruction is expressed by the formula:

[0015] (F1)

[0016] wherein, the safety factor, the cohesion, the normal stress, the internal friction angle, the shear stress, the sliding surface area, an initial value, which is defaulted as , and the coefficient of each reduction is defaulted as .

[0017] Step S302, with the reduction of the coefficient , the different are calculated by the formula:

[0018] (F2)

[0019] ; the different are calculated by the formula:

[0020] (F3)

[0021] ; the different are calculated by the formula:

[0022] Step S303, the parameters and are put into the numerical simulation software for repeated iterative calculation, and when the landslide is in a critical state, the safety factor Fs at this time is the slope safety factor to be solved.

[0023] The application also provides an anchor cable support optimization method using the tunnel slope stability research method, which takes into account safety and economy, and can effectively improve the overall stability of the slope, and the method comprises the following steps:

[0024] Step A1, according to the slope state of the research range, the support parameters of the prestressed anchor cable are calculated as a preliminary design scheme of the construction process; the support parameters include the number of anchor cables and the anchoring length of the anchor cables;

[0025] Step A2, quantitatively calculate the influence of the vertical spacing of the prestressed anchor cable on the slope stability: control the number and inclination angle of the prestressed anchor cable, adjust the vertical spacing of the anchor cable, calculate the slope stability coefficient, and compare and select the optimal model;

[0026] Step A3, quantitatively calculate the influence of the inclination angle of the prestressed anchor cable on the slope stability: control the number of the prestressed anchor cable to be a fixed number, and regard the included angle with the horizontal plane as a variable, and explore the influence of the inclination angle change of the anchor cable on the slope stability coefficient;

[0027] Step A4, non-quantitative influence of the prestressed anchor cable on the slope stability: establish an optimization model with the optimal prestressed anchor cable inclination angle explored in step A3, increase or decrease the number of anchor cables, and simulate and analyze the change of the slope stability coefficient and the displacement control of the anchor cable on the monitoring point in the case of non-quantitative anchor cables;

[0028] Step A5, study the influence of the prestressed anchor cable bonding length on the slope stability: select the support mode with the best slope support effect according to steps A1-A4, increase or decrease the anchoring length, and explore the slope stability coefficient and the displacement control of the anchor cable on the monitoring point corresponding to different anchoring lengths under the condition of the same prestress.

[0029] The anchor cable support optimization method, the formula for the number of anchor cables in step A1 is:

[0030] (F4)

[0031] Calculation;

[0032] Wherein, is the number of anchor cables, is the uplift resistance of the prestressed anchor cable; represents the component force in the normal direction of the slope sliding surface; This represents the component of force along the tangent to the slope sliding surface; α This represents the angle between the anchor cable and the slope sliding surface, and the internal friction angle of a rock slope. This indicates a safety factor exceeding 2; It represents the total resultant force of sliding force as the slope slides downwards.

[0033] In the above-mentioned anchor cable support optimization method, the formula used for the anchorage length of the anchor cable in step A1 is: (F5)

[0034] in, This refers to the anchorage length of the anchor cable. d Indicates the diameter of the anchor cable; P Indicates the anchor cable bearing capacity; τ Indicates the shear strength between the anchoring agent and the anchor cable; n This indicates the number of steel strands in the anchor cable.

[0035] Compared with the prior art, the present invention has the following advantages:

[0036] 1. This invention proposes a method for studying the stability of tunnel slopes based on numerical simulation software, laying the foundation for exploring the influence of different prestressed anchor cable support methods on the stability of rock slopes.

[0037] 2. This invention proposes a research method for studying the influence of different support parameters of prestressed anchor cables on the support effect of rock slopes. It provides a method to explore the optimal prestressed anchor cable support method by changing the support parameters, which takes into account both safety and economy and can effectively improve the overall stability of the slope.

[0038] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0039] Figure 1 This is a flowchart of the method for studying tunnel slope stability according to the present invention;

[0040] Figure 2 This is a current model diagram of the slope cross-section in a specific embodiment of the present invention;

[0041] Figure 3 This is a slope modeling diagram in a specific embodiment of the present invention;

[0042] Figure 4 This is a slope displacement cloud diagram in a specific embodiment of the present invention;

[0043] Figure 5 This is a schematic diagram of the exploration unit in a specific embodiment of the present invention;

[0044] Figure 6A schematic diagram of a critical state of a slope in an embodiment of the present application;

[0045] Figure 7 A method flowchart of the anchor cable support optimization method of the present application;

[0046] Figure 8a A schematic diagram of a vertical spacing of 1 m in an embodiment of the present application;

[0047] Figure 8b A schematic diagram of a vertical spacing of 2 m in an embodiment of the present application;

[0048] Figure 8c A schematic diagram of a vertical spacing of 3 m in an embodiment of the present application;

[0049] Figure 8d A schematic diagram of a vertical spacing of 4 m in an embodiment of the present application;

[0050] Figure 8e A schematic diagram of a vertical spacing of 5 m in an embodiment of the present application;

[0051] Figure 9a A schematic diagram of a horizontal inclination angle of 10° of an anchor cable in an embodiment of the present application;

[0052] Figure 9b A schematic diagram of a horizontal inclination angle of 15° of an anchor cable in an embodiment of the present application;

[0053] Figure 9c A schematic diagram of a horizontal inclination angle of 20° of an anchor cable in an embodiment of the present application;

[0054] Figure 9d A schematic diagram of a horizontal inclination angle of 25° of an anchor cable in an embodiment of the present application;

[0055] Figure 9e A schematic diagram of a horizontal inclination angle of 30° of an anchor cable in an embodiment of the present application;

[0056] Figure 10a A schematic diagram of a displacement control of a slope top by a non-quantitative prestressed anchor cable monitoring point in an embodiment of the present application;

[0057] Figure 10b A schematic diagram of a displacement control of a slope foot by a non-quantitative prestressed anchor cable monitoring point in an embodiment of the present application;

[0058] Figure 11a A schematic diagram of a displacement control of a slope top by a different bonding length monitoring point in an embodiment of the present application;

[0059] Figure 11b A schematic diagram of a displacement control of a slope foot by a different bonding length monitoring point in an embodiment of the present application. DETAILED DESCRIPTION EMBODIMENT

[0060] As Figure 1 shown, the tunnel slope stability research method of the embodiment includes the following steps:

[0061] Step S1, detailed investigation is performed on the tunnel, and the characteristics of the unstable slope distributed in the tunnel are obtained according to the detailed investigation report;

[0062] In the embodiment, the Yuejin No. 3 tunnel is taken as an example. The Yuejin No. 3 tunnel is located in the Saladaban Township of Urumqi County, and the entrance and exit of the tunnel are located on the right bank of the Urumqi River, opposite the G216 national road.

[0063] The tunnel area belongs to the tectonic-erosion medium mountain landform area, with an elevation of about 2515-2745 meters and a relative height difference of about 390 meters. The tunnel site area is generally distributed along the northeast-southwest direction, and the entrance and exit of the tunnel are located on the upper part of the slope on the right bank of the Urumqi River. The mountain slope direction of the tunnel entrance is 45°, and the slope is about 30-40°. The mountain slope direction of the exit is 138°, and the overall slope of the mountain is large, with a gentle slope at the top of the slope, about 10-25°. The middle and lower parts of the slope are relatively steep, with a natural slope of about 45-85°. The slope of the middle part of the tunnel is large, about 50-75°, and the local rock mass is steep and bare, with little vegetation.

[0064] The tunnel exit is located in the middle of the mountain slope, with a mountain slope direction of 138°. The overall slope of the mountain is large, with a gentle slope at the top of the slope, about 10-25°. The middle and lower parts of the slope are relatively steep, with a natural slope of 45-85°. The original slope surface of the slope is a forward slope, and excavation is prone to cause rock collapse in the upper part. The original slope surface of the tunnel exit section is about 135m long, and the rock wall is forward. The tunnel exit is located in the middle and lower part of the rock wall, and the exit section is shallowly buried. Therefore, the slope of the exit section cannot be excavated on a large scale, and the original slope surface needs to be strongly supported before tunnel excavation.

[0065] In the embodiment, according to the detailed investigation report, there is an unstable slope distributed in the tunnel exit section, ZK67+454-ZK67+534.5, with a length of 80.5m, which is a V-class surrounding rock section and a shallowly buried section. It belongs to the tectonic-erosion medium mountain landform, and the middle and lower parts of the slope are covered with Quaternary colluvial debris, with the bedrock being Upper Devonian (D3t b ) tuffaceous sandstone. This section is a shallowly buried section of the tunnel, the original slope surface is a forward slope, the rock layer has a steep inclination, the natural slope is steep, the surrounding rock is broken and developed, and the engineering geological conditions are poor.

[0066] Step S2, according to the characteristics of the unstable slope distributed in the tunnel, a numerical simulation software is used to simplify and construct an operable numerical analysis model for the complex tunnel slope stability problem;

[0067] The model is established on the basis of detailed understanding of the survey report and design drawings, focusing on the problems to be solved, simplifying the complex actual engineering problems into operable numerical analysis models, including geometric simplification, soil layer simplification, and working condition simplification.

[0068] In this embodiment, the characteristics of the unstable slope distributed in the tunnel in steps S1 and S2 include slope instability factors.

[0069] In this embodiment, the numerical simulation software in step S2 is FLAC 3D finite difference method numerical simulation software.

[0070] In this embodiment, according to the site investigation and drilling exposure, the slope instability factors are mainly gravel (Q col+dl ), limestone (C1y), and tuffaceous sandstone (D3t b ). Combined with the characteristics of the project construction, the gravel (Q col+dl ) will be removed before construction, and the above strata can be divided into two geological units according to the engineering characteristics.

[0071] In this embodiment, the ZK67+533 rock slope section is calculated, Figure 2 the present situation of the section is intercepted, the overlying limestone is the lower mountain body, the tunnel body is partially in the mountain, and according to the design, the tunnel body is supported by anti-slide piles. The upper mountain of the tunnel body is loose limestone, which may have landslide disease. The research object of this embodiment is the slope stability of the upper mountain of the tunnel body and the optimization of the prestressed anchor support, and it is considered that the anti-slide pile support fully meets the specification and safety requirements. The upper mountain of the tunnel body is intercepted as the research object, the simulation rock mass adopts the Mohr-Coulomb yield criterion, the model section size is 50 m long, 40 m high, and 3 m wide. The bottom of the model is completely constrained, the two sides and the front and back of the model are constrained in horizontal displacement and velocity by the fix command, the top and the slope surface are not constrained, and the initial stress generation is generated under the action of gravity. This model includes 12192 units and 14283 nodes, and the specific mesh division is as shown in Figure 3 .

[0072] Step S3, the strength reduction method is used in the numerical simulation software to calculate the slope safety factor of the numerical analysis model.

[0073] In this embodiment, the numerical simulation software in step S3 is FLAC 3D finite difference method numerical simulation software.

[0074] In this embodiment, the rock mass physical and mechanical parameters are determined according to the specification and combined with the indoor soil test, as shown in Table 1.

[0075]

[0076] In this embodiment, the specific process of calculating the slope safety factor in the numerical analysis model by using the strength reduction method in the numerical simulation software in step S3 is as follows:

[0077] Step S301, defining the slope safety factor F s The ratio of the actual shear strength index to the virtual reduction strength index when the landslide is in the critical state of destruction is expressed by the formula:

[0078] (F1)

[0079] wherein, Fs is the safety factor, C is the cohesion, σ is the normal stress, φ is the internal friction angle, τ is the shear stress, A is the area of the sliding surface, is an initial value, which is by default, the coefficient of each default reduction;

[0080] In this embodiment, the value of is 2, and the value of

[0081] is 0.1. Step S302, with the reduction of the coefficient

[0082] , the different are calculated by the formula:

[0083] (F2)

[0084] (F3)

[0085] ;

[0086] Step S303, the parameters and are put into the numerical simulation software for repeated iteration calculation, and when the landslide is in the critical state, the safety factor Fs at this time is the slope safety factor to be solved.

[0087] In specific implementation, the slope stability state is divided into four cases as shown in Table 2. According to the Technical Code for Building Slope Engineering GB 50330-2013, the slope stability state can be divided into the four cases in the table.

[0088]

[0089] In this embodiment, the numerical simulation results show that the ZK67+533 section rock slope is in an unstable state. The slope displacement nephogram is shown in Figure 4

[0090] Step S4, according to the calculated slope safety factor and in accordance with the building slope engineering technical specification, the stability state of the unstable slope distributed in the tunnel is judged.

[0091] Embodiment 2

[0092] As shown in the figure, the anchor cable support optimization method of the embodiment comprises the following steps:

[0093] Step A1, according to the slope state of the studied range, the support parameters of the prestressed anchor cable are calculated as a preliminary design scheme of the construction process; the support parameters include the number of anchor cables and the anchoring length of the anchor cables;

[0094] According to the preliminary design scheme, the prestressed anchor cable has reached the specification safety requirement, and the stability of the ZK67+533 slope section is significantly improved. With the same number of anchor cables, whether the support effect can be further improved is considered, and under the same budget investment, the slope support effect is further improved.

[0095] In this embodiment, the formula used for the number of anchor cables in step A1 is:

[0096] (F4)

[0097] Calculation;

[0098] Wherein, is the number of anchor cables, is the pullout resistance of the prestressed anchor cable, which is determined by experiment, and the unit is kN; represents the component force in the normal direction of the slope sliding surface, and the unit is kN; represents the component force in the tangent direction of the slope sliding surface, and the unit is kN; α represents the included angle between the anchor cable and the slope sliding surface and the internal friction angle of the rock slope, and the unit is °; represents the safety factor greater than 2; represents the total sliding force of the slope sliding downward, and the unit is kN.

[0099] In this embodiment, the formula used for the anchoring length of the anchor cable in step A1 is:

[0100] (F5)

[0101] Wherein, is the anchoring length of the anchor cable, d represents the diameter of the anchor cable, and the unit is m;​P represents the anchorage cable bearing capacity, unit: kN; τ represents the shear strength between the anchoring agent and the anchor cable, unit: MPa; n represents the number of steel strands in the anchor cable.

[0102] In this embodiment, the prestressed anchor cable used in the section slope support has a single length of 20 m, wherein the free section length is 12 m, the anchoring section length is 8 m, the anchor cable arrangement interval is 3 m x 3 m, and the inclination angle with the horizontal plane is 15°. Referring to the Technical Code for Building Slope Engineering GB 50330-2013, the anchor cable rod body uses high-strength low-relaxation steel strands, the number of which is 6, the diameter is 15.24 mm, and the standard strength is not less than 1860 Mpa. The anchor cable design tension is 600 KN, and the anchor cable is tensioned and locked with 1.05~1.1 times of the design prestress value during construction. The drilling hole diameter is 130 mm, the anchor cable grouting uses self-hole bottom upward back grouting construction, the grouting material is cement mortar, the grout strength is M30, and the grouting pressure is not less than 0.6 Mpa. The steel strands in the free section are isolated and protected by buttering high-strength plastic hose or PVC pipe. The anchor cable drilling uses a pneumatic dry drilling construction method, and the hole and the anchor cable surface need to be kept clean to ensure the construction quality.

[0103] According to the above requirements, as shown in the Flac 3D prestressed anchor cable uses a cable unit, the anchor cable length is 20 m, 2 m per section, a total of 10 sections. Among them, the first section of each anchor cable is simulated as a tray, which is fixed with the rock mass unit by using the maximum grouting bonding force and stiffness, the 2~6 sections are free sections with prestress, and the 7~10 sections are cement mortar grouting anchoring sections. Figure 5 According to the preliminary slope support design, the anchor cable support is carried out for the ZK67+533 section. As shown in the slope state

[0104] , it is in a stable state, the stability coefficient reaches 1.34, and the safety requirement is met, that is, the preliminary design scheme has met the engineering requirements. Figure 6 Step A2, influence of vertical spacing of quantitative prestressed anchor cable on slope stability: control the number and inclination angle of the prestressed anchor cable, adjust the vertical spacing of the anchor cable, calculate the slope stability coefficient, and compare and select the optimal model;

[0105] In this embodiment, on the basis of the preliminary support scheme, an optimization model is established, the inclination angle of the prestressed anchor cable is controlled to be 15°, the vertical spacing is adjusted to be 1 m, 2 m, 3 m, 4 m, and 5 m respectively, the slope safety coefficient is calculated by using the slope strength reduction method, and the stability coefficient change and the control of the prestressed anchor cable on the displacement of the monitoring point are analyzed.

[0106]

[0107] ​​As shown in Table 3, with the increase of the vertical spacing of the anchor cable, the slope stability coefficient first increases and then decreases, and the two present a quadratic parabolic relationship. When the vertical spacing of the anchor cable is adjusted to 2m, the slope stability coefficient reaches a peak value of 1.52.

[0108]

[0109] The specific simulation diagram is shown in Figure 8a-8e ;

[0110] The influence of the vertical spacing of the anchor cable on the slope stability has a critical state. By analyzing and comparing the calculation results, under the condition that the number of prestressed anchor cables is controlled to be 6 and the angle with the horizontal plane is 15°, the five anchor cable arrangement conditions all have good slope stability and good constraint on the monitoring points, and the displacement is limited to be below the millimeter level. When the spacing of the anchor cables is controlled to be 2m, the slope stability coefficient reaches a maximum value of 1.52.

[0111] Step A3, influence of the quantitative prestressed anchor cable angle on the slope stability: under the condition that the number of prestressed anchor cables is fixed, the angle with the horizontal plane is regarded as a variable, and the influence of the change of the anchor cable angle on the slope stability coefficient is explored;

[0112] In this embodiment, the number of prestressed anchor cables is controlled to be 6, the prestressed anchor cables are arranged with a vertical spacing of 2m with the highest stability coefficient, and the horizontal angle of the anchor cables is adjusted to be 10°, 15°, 20°, 25° and 30° respectively to establish an optimization model. As shown in Table 4, with the increase of the horizontal angle, the slope stability coefficient slowly increases, and the two present a linear relationship.

[0113]

[0114] The specific simulation diagram is shown in Figure 9a-9e ;

[0115] It is found through calculation that the displacement control of the monitoring points by the five anchor cable arrangement modes is below the millimeter level, with the increase of the horizontal angle of the prestressed anchor cable, the anchor cable gradually tends to be orthogonal to the slope surface, the slope stability coefficient also increases, but the increasing speed slows down, and when the angle is adjusted to be 25° and 30°, the safety coefficient reaches a peak value of 1.59.

[0116] Step A4, influence of the non-quantitative prestressed anchor cable on the slope stability: the influence of different numbers of anchor cables on the slope stability coefficient is explored. The supporting role of each anchor cable is different under different angles of the prestressed anchor cable, and it is observed that the anchor cable in the middle can play a relatively small supporting role. In view of this, an optimization model is established based on the optimal prestressed anchor cable angle explored in step A3, the number of anchor cables is increased or decreased, and the change of the slope stability coefficient and the displacement control of the anchor cable on the monitoring points are simulated and analyzed under the condition of the non-quantitative anchor cable;

[0117] In this embodiment, the prestressed anchor cable inclination is 25° to establish an optimization model; the specific simulation diagram is shown in Figure 10a-10b The results show that different numbers of anchor cables have good control on the displacement of the monitoring points, while the stability coefficients differ greatly. As shown in Table 5, when the number of anchor cables is even, such as 2, 4, and 6, the slope stability coefficient is at a high level and does not differ greatly; when the number of anchor cables is odd, such as 3, 5, and 7, the slope stability coefficient decreases significantly, and the two present a broken line type relationship. Therefore, considering the use of 4 prestressed anchor cables with an inclination of 25° to support the ZK67+533 section slope, both safety and economy are guaranteed, which is the optimal support scheme.

[0118]

[0119] Step A5, research the influence of prestressed anchor cable bonding length on slope stability: according to steps A1-A4, select the support mode with the best slope support effect, increase or decrease the anchoring segment length, and explore the slope stability coefficient and the displacement control of the anchor cable on the monitoring point under the condition of the same prestress.

[0120] The prestressed anchor cable reinforcement effect is related to the anchoring segment, which mainly bears the influence of the slope thrust. On the basis of steps A1-A4, select the arrangement mode with the best slope support effect, 4 prestressed anchor cables with a 3m*3m spacing and a horizontal inclination of 25° to establish an optimization model, the total length of the anchor cable is 20m, the initial free segment is 12m, the anchoring segment is 8m, and the free segment is applied with a prestress of 600Kn; increase or decrease the anchoring segment length, and explore the slope stability coefficient and the displacement control of the anchor cable on the monitoring point under the condition of the same prestress; the results are shown in Table 6.

[0121]

[0122] The specific simulation diagram is shown in Figure 11a-11b

[0123] The results show that the same prestress is applied to the free segment, the anchoring segment is regarded as a variable, five different bonding lengths are applied, the displacement control of the anchor cable on the monitoring point is similar, the slope stability coefficient almost does not fluctuate, and the two do not present a significant correlation. The calculation results show that the support effect of the anchor cable on the slope is mainly borne by the front 1-5m of the anchoring segment. Therefore, the investment can be appropriately controlled during the prestressed anchor cable grouting construction, the cost can be saved, and the overall safety of the slope will not be affected.

[0124] In summary, in the specific embodiments of the present application, the ZK67+533 section rock slope of the Yuejin No. 3 tunnel is taken as an example, Flac 3D ​Numerical simulation method is used to analyze the stability of the slope, and the influence of different supporting parameters of prestressed anchor cable on the supporting effect of rock slope is discussed. By changing the supporting parameters, the optimal prestressed anchor cable supporting method for the high and steep dangerous rock slope at the exit section of the Yuejin No. 3 Tunnel in Weili is explored. The results show that the slope is in an unstable state before the support is applied. After the preliminary prestressed anchor cable support scheme is applied, the slope stability coefficient reaches 1.34, which meets the requirements of the specification and safety. On the basis of the preliminary scheme, the influence of the vertical spacing, horizontal inclination, and anchoring length of the quantitative prestressed anchor cable and the number of non-quantitative prestressed anchor cable on the slope stability and the displacement control of the monitoring points are analyzed. The results show that there is a critical state in the influence of the vertical spacing of the anchor cable on the slope stability. With the increase of the spacing, the safety factor first increases and then decreases. The optimal spacing is 2 m, and the slope stability coefficient reaches a maximum value of 1.52. With the increase of the horizontal inclination of the anchor cable, the slope stability coefficient slowly increases when the inclination gradually approaches the orthogonal direction. When the inclination is adjusted to 25°, the safety factor reaches a peak value of 1.59. When the number of anchor cables is adjusted to an even number, the slope stability coefficient is at a high level and has little difference. When the number of anchor cables is odd, the slope stability coefficient decreases significantly. The influence of different anchoring lengths on the slope stability coefficient and the displacement control of the monitoring points is not significant. The supporting effect of the anchor cable is mainly borne by the front 6 m of the anchoring section. Therefore, the anchoring length can be appropriately shortened during construction, considering the safety and economy, which will not affect the overall stability of the slope.

[0125] For the exit section of the Yuejin No. 3 Tunnel in Weili, the Flac 3D The slope model under actual working conditions is simplified using the finite difference method numerical simulation software. Under the premise of considering the safety and economy of the project, four optimization schemes are proposed for gradual implementation. By comparing the slope stability coefficient and the displacement control of the monitoring points by the prestressed anchor cable of each scheme, the optimal scheme is selected for further optimization. The following conclusions are drawn:

[0126] (1) After simplifying the natural actual working conditions, the slope stability coefficient is 1.01, which is in an unstable state. The stability coefficient reaches 1.34 after the preliminary support scheme is implemented, which meets the safety requirements of the project;

[0127] (2) The influence of the vertical spacing of the quantitative prestressed anchor cable on the slope stability is proposed. By controlling the number, horizontal inclination, prestressed value, and anchoring length of the anchor cable, the optimal vertical spacing of 2 m is obtained by adjusting the vertical spacing of the anchor cable and comparing the displacement control of the monitoring points and the slope stability coefficient under different spacings.

[0128] (3) The influence of the horizontal angle of the quantitative prestressed anchor cable on the slope stability is proposed. Under the condition of the optimal vertical spacing of the prestressed anchor cable, the displacement control of the monitoring point and the slope stability coefficient are compared under different angles. With the increase of the angle between the anchor cable and the horizontal plane, the anchor cable gradually tends to be orthogonal to the slope surface, the safety factor of the slope increases at a slower rate, and it is concluded that the angle of 25° is appropriate;

[0129] (4) The influence of the non-quantitative prestressed anchor cable on the slope stability is proposed. Under the condition of the optimal spacing and angle, the displacement control of the monitoring point and the slope stability coefficient are compared under different numbers of anchor cables. When the number of anchor cables is even, the slope stability coefficient is at a high level; when the number of anchor cables is odd, the slope stability coefficient decreases significantly. Considering the safety and economy of the project, 4 anchor cables are set;

[0130] (5) The influence of the anchoring length of the prestressed anchor cable on the slope stability is proposed. Taking 4 prestressed anchor cables with a spacing of 3m×3m and an angle of 25° as the optimal model, the displacement control of the monitoring point and the slope stability coefficient are compared under different anchoring lengths. It is concluded that the slope support is mainly borne by the front 6m of the anchoring segment, and the long anchoring segment increases the construction cost but has little significance for the safety performance of the project.

[0131] The above is only the preferred embodiment of the present application, and does not limit the present application. Any simple modification, change and equivalent structure change based on the technical essence of the present application to the above embodiment are still within the protection scope of the technical solution of the present application.

Claims

1. A method for studying the stability of tunnel slopes, characterized in that, The method includes the following steps: Step S1: Conduct a detailed exploration of the tunnel and obtain the characteristics of the unstable slopes distributed within the tunnel based on the detailed exploration report; Step S2: Based on the characteristics of the unstable slopes distributed within the tunnel, numerical simulation software is used to simplify the complex tunnel slope stability problem and construct an operable numerical analysis model. Step S3: Calculate the slope safety factor of the numerical analysis model using the strength reduction method in the numerical simulation software; Step S4: Determine the stability state of the unstable slopes distributed within the tunnel based on the calculated slope safety factor and in accordance with the technical specifications for building slope engineering. The characteristics of the unstable slopes distributed within the tunnel described in steps S1 and S2 include slope instability factors. The numerical simulation software mentioned in steps S2 and S3 is FLAC. 3D Finite difference method numerical simulation software; The specific process of calculating the slope safety factor of the numerical analysis model using the strength reduction method in the numerical simulation software, as described in step S3, is as follows: Step S301: Define the slope safety factor F s The ratio of the actual shear strength index to the virtual reduced strength index at the critical failure state of the landslide is expressed by the formula: in, For safety reasons, For cohesion, It is normal stress. It is the internal friction angle. For shear stress, Let be the area of ​​the sliding surface. It is initialized to a default value, and is reduced by default each time. The coefficient; Step S302, with the coefficient The reduction is achieved through the formula: Different calculations yielded different results. ; Through the formula: Different calculations yielded different results. ; Step S303: Set parameters and The slope safety factor is obtained by repeatedly iterating and calculating in numerical simulation software until the landslide body is in a critical state.

2. An anchor cable support optimization method using the tunnel slope stability study method as described in claim 1, characterized in that, The method includes the following steps: Step A1: Calculate the support parameters of the prestressed anchor cables based on the slope condition of the studied area, as a preliminary design scheme for the construction process; the support parameters include the number of anchor cables and the anchorage length of the anchor cables. Step A2: Quantitative analysis of the influence of vertical spacing of prestressed anchor cables on slope stability: Control the number and inclination angle of prestressed anchor cables, calculate the slope stability coefficient by adjusting the vertical spacing of anchor cables, and compare and select the optimal model; Step A3: Quantitative analysis of the effect of prestressed anchor cable inclination angle on slope stability: With the number of prestressed anchor cables fixed, the angle between the anchor cables and the horizontal plane is considered as a variable to explore the effect of the change in anchor cable inclination angle on the slope stability coefficient. Step A4, Impact of Non-Quantitative Prestressed Anchor Cables on Slope Stability: An optimization model is established based on the optimal prestressed anchor cable inclination angle explored in Step A3. By increasing or decreasing the number of anchor cables, the changes in slope stability coefficient and the control of anchor cables on the displacement of monitoring points are simulated and analyzed under the condition of non-quantitative anchor cables. Step A5: Study the influence of prestressed anchor cable bonding length on slope stability: Based on steps A1 to A4, select the support method with the best slope support effect, increase or decrease the anchorage length, and explore the slope stability coefficient and the control of anchor cable displacement on monitoring point displacement corresponding to different anchorage lengths under the same prestressing conditions.

3. The anchor cable support optimization method according to claim 2, characterized in that: The formula used for the number of anchor cables mentioned in step A1 is: calculate; in, For the number of anchor cables, This refers to the pull-out force of the prestressed anchor cable; This represents the component of force along the normal direction of the slope sliding surface; This represents the component of force along the tangent to the slope sliding surface; α This represents the angle between the anchor cable and the slope sliding surface, and the internal friction angle of a rock slope. This indicates a safety factor exceeding 2; This represents the total resultant force of the sliding force as the slope slides downwards.

4. The anchor cable support optimization method according to claim 2, characterized in that: The formula used for the anchorage length of the anchor cable mentioned in step A1 is: in, This refers to the anchorage length of the anchor cable. d Indicates the diameter of the anchor cable; P Indicates the anchor cable bearing capacity; τ Indicates the shear strength between the anchoring agent and the anchor cable; n This indicates the number of steel strands in the anchor cable.

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