Anchor rod and anchor cable support design method for weakly cemented surrounding rock roadway eroded by alkaline water

Abstract

The invention provides a method for designing an anchor rod and anchor cable support of a weakly cemented surrounding rock roadway eroded by alkaline water. The method comprises the following steps: S1, collecting an alkaline water sample of a roadway roof water spraying area on site, analyzing basic physicochemical properties of alkaline water, constructing an alkaline corrosion index, and establishing a dynamic relation model of erosion strength and time; s2, constructing an index regression nonlinear surrounding rock deterioration degree model according to multivariate data of the alkali corrosion index, the deformation amount, the permeability and the strength during the service period of the target region roadway; s3, according to the resistivity and the polarization potential of the anchor rod and the anchor cable in the service period of the roadway, an anchor rod and anchor cable resistivity increasing rate and erosion rate model is constructed; and S4, according to the deterioration degree, the anchor rod and anchor cable resistivity increasing rate and the erosion rate, the anchor rod and anchor cable supporting design scheme is dynamically adjusted. According to the method, different alkaline water environments, erosion strengths, weakly cemented surrounding rock deterioration degrees and anchor rod and anchor cable erosion states are comprehensively considered, and a supporting design scheme of the anchor rod and anchor cable is dynamically adjusted based on the method.

Description

Technical Field

[0001] The invention relates to the technical field of coal mine tunnel support, in particular to a design method for anchor rod and cable support of a weakly cemented surrounding rock tunnel corroded by alkaline water. Background Art

[0002] Under special geological conditions, the long-term stability of the surrounding rock support is a necessary condition to ensure the safety and efficient production of the mine. In the process of supporting components and surrounding rocks working together to support the tunnel, groundwater often has an impact on it. Groundwater contains a large amount of OH- ions and other mineral ion components, which will chemically react with different minerals and materials in the rock mass and supporting components, resulting in a decrease in the mechanical properties of the bearing structure, which in turn causes the weakening or even failure of the anchoring efficiency.

[0003] In the Jurassic and Cretaceous strata, the surrounding rock has a low degree of cementation, and the groundwater is highly mineralized and mostly alkaline, and these characteristics are common in western mining areas. At present, anchor rods and anchor cables are the main support methods for most of the tunnels in my country's coal mines. However, under the long-term erosion of alkaline groundwater and its physical and chemical effects, the deterioration of weakly cemented surrounding rock and the corrosion of support components (such as anchor rods and anchor cables) have intensified. In addition, the weakly cemented surrounding rock within the anchoring range is softened, making the anchoring system more likely to fail than normal, and the anchor rods and anchor cables are rusted and broken, resulting in a significant reduction in the anchoring efficiency of the surrounding rock and severe and difficult-to-control deformation of the tunnel.

[0004] At present, in view of the problem of weakly cemented surrounding rock tunnel support in alkaline water environment, the support design of anchor rods and cables usually fails to fully consider multiple influencing factors, and there are unreasonable aspects, resulting in insufficient support strength and failure of the anchoring system. Therefore, it is an urgent problem to comprehensively consider the design of anchor rod and cable support parameters under different alkaline water environments, erosion intensity, degradation degree of weakly cemented surrounding rocks and erosion state of anchor rods and cables. Summary of the invention

[0005] In order to solve the problem in the prior art that the weakly cemented surrounding rock in the anchoring range is softened under alkaline environment, making the anchoring system more likely to fail than normal, resulting in corrosion and fracture of anchor rods and cables, which greatly reduces the anchoring efficiency of the surrounding rock and causes serious deformation and difficulty in controlling the tunnel. The present invention proposes a design method for anchor rod and cable support in weakly cemented surrounding rock tunnels corroded by alkaline water. The method comprehensively considers different alkaline water environments, corrosion intensity, degradation degree of weakly cemented surrounding rocks and corrosion state of anchor rods and cables, and dynamically adjusts the support design scheme of anchor rods and cables based on this to solve the problems of serious corrosion of surrounding rocks and supporting components, failure of anchoring system and difficulty in controlling the tunnel roof.

[0006] The present invention is achieved through the following technical solution: comprising the following steps:

[0007] S1. Collect alkaline water samples from the tunnel roof watering area on site, analyze the basic physical and chemical properties of alkaline water, and construct an alkaline corrosion index A. x , a dynamic relationship model between erosion intensity and time is established as a quantitative indicator for evaluating the erosion intensity of alkaline water on the anchoring system, and then the erosion intensity level of alkaline water is determined;

[0008] S2. Based on the multivariate data of alkali corrosion index, deformation, permeability and strength of the target tunnel during service, an exponential regression nonlinear surrounding rock degradation model was constructed to evaluate the impact of weakly cemented surrounding rock degradation on the bolt and cable support system;

[0009] S3. According to the resistivity and polarization potential of the anchor cables during their service in the tunnel, a model of the resistivity increase rate and erosion rate of the anchor cables is constructed to evaluate the erosion state of the anchor cables.

[0010] S4. Dynamically adjust the anchor bolt and cable support design scheme according to the exponential regression nonlinear surrounding rock degradation degree obtained in step S2 and the anchor bolt and cable resistivity increase rate and erosion rate obtained in step S3.

[0011] Furthermore, the step S1 constructs an alkaline corrosion index A x The specific steps to establish the dynamic relationship model between erosion intensity and time are as follows:

[0012] S11. Constructing Alkali Corrosion Index A x , the formula is as follows:

[0013]

[0014] Where: OH - The molar mass of the ion, Respectively represent the removal of OH - ions, and T is the molar mass of all corrosive ions other than ions, and T is the erosion time of alkaline water on the anchoring system;

[0015] S12. Calculate the alkaline corrosion index A in mol / L. x , determine the corrosion intensity level of alkaline water as:

[0016] Weak alkaline corrosion: A x ≤50, the erosion of alkaline water on surrounding rocks and anchoring systems is weak;

[0017] Medium alkali corrosion: 50 x ≤100, alkaline water has significant corrosive effect on surrounding rock and anchoring system;

[0018] Strong alkaline corrosion: A x >100, alkaline water is highly destructive to the surrounding rock, and the anchoring system is also prone to failure due to erosion. ​

[0019] Furthermore, the specific steps of step S2 are as follows:

[0020] S21. Through on-site and experimental monitoring, define the deterioration degree threshold interval of weakly cemented surrounding rock as (0, 1), and record the surrounding rock deformation ε(t), surrounding rock permeability k(t), surrounding rock compressive strength σ c (t) and the corresponding deterioration rate D(t) at different time points t under different alkali corrosion environments;

[0021] S22. Construct an exponential regression non-linear surrounding rock deterioration degree model, the formula is as follows:

[0022]

[0023] In the formula: α is the proportionality coefficient, A x (t) is the alkali corrosion index, ε(t) is the surrounding rock deformation, k(t) is the surrounding rock permeability, σ c (t) is the surrounding rock compressive strength, and β1, β2, β3, and β4 are the regression coefficients of the alkali corrosion index, surrounding rock deformation, surrounding rock permeability, and surrounding rock compressive strength respectively;

[0024] Step S23. Take the natural logarithm of the exponential regression non-linear surrounding rock deterioration degree D(t) to obtain a linearized model, the formula is as follows:

[0025] ln(D(t)) = α' + β1A x (t) + β2ε(t) + β3k(t) + β4σ c (t)

[0026] Step S24. Take the value of ln(D(t)) as the dependent variable, and set the independent variables as A x (t), ε(t), k(t), σ c (t), use the least squares method for fitting, continuously iterate and optimize to solve the optimal values of the regression coefficients α', β1, β2, β3, and β4, restore the logarithm, and substitute each regression coefficient into the surrounding rock deterioration degree model D(t);

[0027] Step S25. Evaluate the influence on the bolt and cable support system according to the exponential regression non-linear surrounding rock deterioration degree D(t):

[0028] When 0 < D(t) ≤ 0.3, the surrounding rock deterioration degree is low, and the influence on the bolt and cable support system is small;

[0029] When 0.3 < D(t) ≤ 0.7, the surrounding rock deterioration degree is significant, and the influence on the bolt and cable support system is large;

[0030] When 0.7 < D(t) < 1, the surrounding rock deterioration degree is high, seriously affecting the bolt and cable support system.

[0031] Furthermore, the specific steps of step S3 are as follows:

[0032] S31. Arrange several test sections in different erosion intensity areas of the tunnel, arrange several measuring points in each test section, select several measuring point anchor rods and measuring point anchor cables for each measuring point, arrange resistivity monitoring sensors and polarization potential monitoring sensors in the measuring point anchor rods and measuring point anchor cables respectively, and apply prestress to the anchor rod cables;

[0033] S32, according to the resistivity ρ at time t t and initial resistivity ρ0, according to the formula The resistivity increase rate Δρ is obtained;

[0034] S33, based on the measured polarization potential E, corrosion potential E corr , Tafel slope b, molar mass M of the material, number of electron transfer n of the electrochemical reaction, Faraday constant F, and density ρ of the material m , construct the anchor cable erosion rate model, the formula is as follows:

[0035]

[0036] Where: K is the unit conversion constant;

[0037] S34. Evaluate the erosion state of anchor bolts and cables by stress-alkaline water according to the resistivity increase rate and erosion rate of anchor bolts and cables:

[0038] If Δρ<10%, 0.01mm / a≤V f <0.1mm / a, it is slight corrosion;

[0039] If 10%≤Δρ<30%, 0.1mm / a≤V f <1.0mm / a, it is moderate corrosion;

[0040] If Δρ≥30%, V f ≥1.0mm / a, it is severe corrosion.

[0041] Furthermore, the dynamic adjustment scheme of step S4 is as follows:

[0042] When the deterioration degree of weakly cemented surrounding rock is low, the original support scheme is adopted;

[0043] When the weakly cemented surrounding rock deteriorates significantly, the support density of anchor bolts and cables should be increased;

[0044] When the weakly cemented surrounding rock is highly deteriorated, the anchoring length is lengthened on the basis of increasing the support density of anchor rods and cables;

[0045] When the anchor rod and cable are slightly corroded, it is not necessary to apply an anti-alkali corrosion layer;

[0046] When the anchor bolts and cables are moderately corroded, hot-dip galvanizing and organic polymer coatings are used to protect the anchor bolts and cables from alkali corrosion.

[0047] When the anchor rods and cables are severely corroded, the thickness of the anti-alkali corrosion layer needs to be further increased.

[0048] Furthermore, in step S31, the length of the test section is 100 m, 5 measuring points are arranged in each test section, and 3 measuring point anchor rods and 2 measuring point anchor cables are selected for each measuring point.

[0049] Furthermore, in step S33, the value of the Tafel slope b is 0.12V.

[0050] Furthermore, the value of K in step S33 is 3.27×10 -3 .

[0051] Furthermore, the electron transfer number n of the electrochemical reaction in step S33 is 2.

[0052] Furthermore, the value of the Faraday constant F in step S33 is 96485 C / mol.

[0053] Compared with the prior art, the present invention has the following beneficial effects:

[0054] (1) The present invention establishes an alkali corrosion index model, a surrounding rock degradation rate model and an anchor erosion state assessment model, and comprehensively considers factors such as alkaline water environment, surrounding rock degradation, and anchor cable corrosion. It can monitor and dynamically evaluate changes in the support system in real time, ensure that the support design adapts to changes in actual working conditions, and improve the safety and reliability of the support scheme.

[0055] (2) The present invention optimizes the support design by dynamically adjusting the support parameters to avoid over-design or support failure, thereby improving the safety of the support system and reducing the engineering cost, thus having significant economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 It is a flow chart of the design method of the present invention.

[0057] Figure 2 It is a schematic diagram of the arrangement of on-site electrochemical monitoring equipment for anchor rods and cables in the design method of the present invention.

[0058] Figure 3 It is a schematic diagram of the layout of the on-site electrochemical monitoring test section of anchor rods and cables in the design method of the present invention.

[0059] Indicated in the figure:

[0060] 1. Anchor rod; 2. Anchor cable; 3. Resistivity monitoring sensor; 4. Polarization potential monitoring sensor; 5. Measuring point anchor rod; 6. Measuring point anchor cable; 7. Test section. DETAILED DESCRIPTION

[0061] Advantages and features of the present invention will be illustrated and explained by the following non-limiting description of preferred embodiments thereof, which are given by way of example only with reference to the accompanying drawings.

[0062] like Figure 1 As shown, the present invention provides a design method for anchor rod and cable support in weakly cemented surrounding rock tunnels corroded by alkaline water, comprising the following steps:

[0063] Step S1: Collect alkaline water samples from the tunnel roof watering area on site, analyze the basic physical and chemical properties of the alkaline water, and construct an alkaline corrosion index A. x , a dynamic relationship model between erosion intensity and time is established as a quantitative indicator to evaluate the erosion intensity of alkaline water on the anchoring system, and then the erosion intensity grade of alkaline water is determined.

[0064] Step S11: constructing an alkaline corrosion index A x , the formula is as follows:

[0065]

[0066] Where: OH - The molar mass of the ion, Respectively represent the removal of OH - ions, and T is the molar mass of all corrosive ions other than ions, and T is the erosion time of alkaline water on the anchoring system;

[0067] Step S12: Calculate the alkaline corrosion index A in mol / L. x , determine the corrosion intensity level of alkaline water as:

[0068] Weak alkaline corrosion: A x ≤50, the erosion of alkaline water on surrounding rocks and anchoring systems is weak;

[0069] Medium alkali corrosion: 50 x ≤100, alkaline water has significant corrosive effect on surrounding rock and anchoring system;

[0070] Strong alkaline corrosion: A x >100, alkaline water is highly destructive to the surrounding rock, and the anchoring system is also prone to failure due to erosion.

[0071] The alkaline water samples collected on site from the tunnel roof sprinkling area were placed in a laboratory environment for laboratory analysis of the basic physical and chemical properties of the alkaline water, including the pH value of the alkaline water, the concentration of the main corrosive ions, and the temperature value. The main corrosive ions were OH - , Cl​- 、SO4 2- 、Na + , Ca 2+ et al., established a dynamic relationship model between erosion intensity and time by constructing an alkali corrosion index as a quantitative indicator for evaluating the erosion intensity of alkaline water on the anchoring system, and then determined the erosion intensity level of alkaline water. Get the alkaline corrosion index A x , where: OH - The molar mass of the ion, Respectively represent the removal of OH - ions, and T is the molar mass of all corrosive ions except for the anchoring system.

[0072] The laboratory tested ion concentration is mg / L. Since the chemical properties of ions are more scientifically evaluated based on the amount of substance (mol), the main corrosive ion concentration is converted from mg / L to mol / L to calculate the alkaline corrosion index A. x , determine the corrosion intensity level of alkaline water as:

[0073] Weak alkaline corrosion: A x ≤50, the erosion of alkaline water on surrounding rocks and anchoring systems is weak;

[0074] Medium alkali corrosion: 50 x ≤100, alkaline water has significant corrosive effect on surrounding rock and anchoring system;

[0075] Strong alkaline corrosion: A x >100, alkaline water is highly destructive to the surrounding rock, and the anchoring system is also prone to failure due to erosion.

[0076] Step S2: Based on the multivariate data of alkali corrosion index, deformation, permeability and strength of the target tunnel during service, an exponential regression nonlinear surrounding rock degradation model is constructed to evaluate the impact of the weakly cemented surrounding rock degradation on the anchor bolt and cable support system.

[0077] Step S21: through on-site and experimental monitoring, define the threshold interval of weakly cemented surrounding rock degradation as (0,1), and record the surrounding rock deformation ε(t), surrounding rock permeability k(t), and surrounding rock compressive strength σ at different time points t under different alkaline corrosion environments. c (t) and the corresponding degradation rate D(t);

[0078] Step S22: construct an exponential regression nonlinear surrounding rock degradation model, the formula is as follows:

[0079]

[0080] Where: α is the proportionality coefficient, A x ​(t) is the alkali corrosion index, ε(t) is the surrounding rock deformation, k(t) is the surrounding rock permeability, and σ c (t) is the compressive strength of the surrounding rock, and β1, β2, β3, and β4 are the regression coefficients of the alkali corrosion index, surrounding rock deformation, surrounding rock permeability, and surrounding rock compressive strength, respectively.

[0081] Step S23: Take the natural logarithm of the exponential regression non-linear surrounding rock deterioration degree D(t) to obtain a linearized model, and the formula is as follows:

[0082] ln(D(t)) = α' + β1A x (t) + β2ε(t) + β3k(t) + β4σ c (t)

[0083] Step S24: Take the value of ln(D(t)) as the dependent variable, and set the independent variables as A x (t), ε(t), k(t), σ c (t), and use the least squares method to fit, continuously iterate and optimize to solve the optimal values of the regression coefficients α', β1, β2, β3, and β4, restore the logarithm, and substitute each regression coefficient into the surrounding rock deterioration degree model D(t).

[0084] Step S25: Evaluate the influence on the bolt and cable support system according to the exponential regression non-linear surrounding rock deterioration degree D(t):

[0085] When 0 < D(t) ≤ 0.3, the surrounding rock deterioration degree is low, and the influence on the bolt and cable support system is small;

[0086] When 0.3 < D(t) ≤ 0.7, the surrounding rock deterioration degree is significant, and the influence on the bolt and cable support system is large;

[0087] When 0.7 < D(t) < 1, the surrounding rock deterioration degree is high, seriously affecting the bolt and cable support system.

[0088] By monitoring the changes in the deformation, permeability, and strength of the surrounding rock during the service period of the roadway in the target area, and based on the multi-source data of the alkali corrosion index, deformation, permeability, and strength, an exponential regression non-linear surrounding rock deterioration degree model is constructed to evaluate the influence of the deterioration degree of the weakly cemented surrounding rock on the bolt and cable support system. The exponential regression non-linear surrounding rock deterioration degree model is defined as:

[0089]

[0090] Where: α is the proportionality coefficient, β1, β2, β3, β4 are the regression coefficients of each influencing factor, A x (t) is the alkali corrosion index, ε(t) is the surrounding rock deformation, k(t) is the surrounding rock permeability, and σ c (t) is the compressive strength of the surrounding rock;

[0091] Data preparation: Through on-site and experimental monitoring, the deterioration degree threshold interval of weakly cemented surrounding rock is defined as (0, 1). Record the surrounding rock deformation ε(t), surrounding rock permeability k(t), surrounding rock compressive strength σ c (t) and the corresponding deterioration rate D(t) at different time points t under different alkali erosion environments, and plot them into the monitoring data table shown in Table 1:

[0092] Table 1 Deterioration monitoring data of weakly cemented surrounding rock under different alkali erosion environments and times

[0093]

[0094] Data logarithmic transformation: To simplify the calculation, the natural logarithm can be taken for the deterioration degree D(t) to obtain a linearized model ln(D(t)) = α' + β1A x (t) + β2ε(t) + β3k(t) + β4σ c (t).

[0095] Regression solution: Take the value of ln(D(t)) as the dependent variable, and set the independent variables as A x (t), ε(t), k(t), σ c (t). Use the least squares method for fitting, and continuously iterate and optimize to solve the optimal values of the regression coefficients α', β1, β2, β3, β4. Restore the logarithm and substitute each regression coefficient into the surrounding rock deterioration degree model D(t).

[0096] According to the calculation results of the surrounding rock deterioration degree, evaluate the impact on the bolt and cable support system: When 0 < D(t) ≤ 0.3, the surrounding rock deterioration degree is low, and the impact on the bolt and cable support system is small; when 0.3 < D(t) ≤ 0.7, the surrounding rock deterioration degree is significant, and the impact on the bolt and cable support system is large; when 0.7 < D(t) < 1, the surrounding rock deterioration degree is high, seriously affecting the bolt and cable support system.

[0097] Step S3: Construct a resistivity increase rate and erosion rate model of bolts and cables based on the resistivity and polarization potential of bolts and cables during the service period of the roadway, and evaluate the erosion state of bolts and cables.

[0098] Step S31: Arrange several 100m test sections 7 in different erosion intensity areas of the roadway. Arrange 5 measuring points in each test section, select three measuring point bolts 5 and two measuring point cables 6 at each measuring point. Install resistivity monitoring sensors 3 and polarization potential monitoring sensors 4 in the measuring point bolts 5 and measuring point cables 6 respectively, and apply prestress to the measuring point bolts 5 and measuring point cables 6.

[0099] As Figure 2 and Figure 3As shown, there are several anchor rods 1 and anchor cables 2 arranged at intervals in different erosion intensity areas of the tunnel, and several 100m test sections 7 are arranged in different erosion intensity areas of the tunnel. Five measuring points are arranged in each test section, and three measuring point anchor rods 5 and two measuring point anchor cables 6 are selected for each measuring point. Resistivity monitoring sensors 3 and polarization potential monitoring sensors 4 are arranged in the measuring point anchor rods 5 and the measuring point anchor cables 6, respectively. Prestress is applied to the measuring point anchor rods 5 and the measuring point anchor cables 6, and the resistivity and polarization potential of the anchor rods and cables during their service in the tunnel are monitored. A resistivity increase rate and erosion rate model of the anchor rods and cables is constructed to evaluate the erosion state of the anchor rods and cables.

[0100] Step S32: According to the resistivity p at time t t and initial resistivity ρ0, according to the formula The resistivity increase rate Δρ is obtained.

[0101] The resistivity increase rate is used to reflect the resistivity change of the anchor cable under the influence of stress-alkaline water at different times, and is calculated by the following formula:

[0102]

[0103] Where Δρ represents the resistivity increase rate, ρ t represents the resistivity at time t; ρ0 represents the initial resistivity value (i.e. the resistivity before corrosion begins or before alkaline water erosion).

[0104] Step S33: According to the measured polarization potential E and corrosion potential E corr , Tafel slope b, molar mass M of the material, number of electron transfer n of the electrochemical reaction, Faraday constant F, and density ρ of the material m , construct the anchor cable erosion rate model, the formula is as follows:

[0105]

[0106] Based on the relationship between polarization potential and corrosion current density in the Tafel equation, the anchor cable erosion rate model is constructed:

[0107]

[0108] Where: E is the measured polarization potential; E corr is the corrosion potential; b is the Tafel slope, which is 0.12 V at room temperature; K is the unit conversion constant, which is usually 3.27×10 -3 ; M is the molar mass of the material, which depends on the material of the anchor rod and anchor cable; n is the number of electron transfers in the electrochemical reaction, which is taken as 2; F is the Faraday constant, which is usually taken as 96485C / mol; ρ m The density of the material.

[0109] Step S34: Evaluate the stress-alkaline water corrosion state of the anchor rod and anchor cable according to the resistivity increase rate and corrosion rate of the anchor rod and anchor cable:

[0110] If Δρ<10%, 0.01mm / a≤V f <0.1mm / a, it is slight corrosion;

[0111] If 10%≤Δρ<30%, 0.1mm / a≤V f <1.0mm / a, it is moderate corrosion;

[0112] If Δρ≥30%, V f ≥1.0mm / a, it is severe corrosion.

[0113] Step S4, dynamically adjusting the anchor bolt and cable support design scheme according to the exponential regression nonlinear surrounding rock degradation degree obtained in step S2 and the anchor bolt and cable resistivity increase rate and erosion rate obtained in step S3:

[0114] When the degree of deterioration of weakly cemented surrounding rock is low, the tunnel does not need to be reinforced and the original support scheme can be adopted;

[0115] When the weakly cemented surrounding rock deteriorates significantly, it is necessary to increase the support density of anchor bolts and cables to improve the support strength.

[0116] When the degree of deterioration of weakly cemented surrounding rock is high, the anchoring length is lengthened on the basis of increasing the support density of anchor rods and cables to improve the support stability;

[0117] When the anchor rod and cable are slightly corroded, it is not necessary to apply an anti-alkali corrosion layer;

[0118] When the anchor bolts and cables are moderately corroded, hot-dip galvanizing and organic polymer coatings are used to protect the anchor bolts and cables from alkali corrosion.

[0119] When the anchor rods and cables are severely corroded, the thickness of the anti-alkali corrosion layer needs to be further increased.

[0120] Example 1

[0121] This example takes a mine in the west as an example to further illustrate the design method of the present invention, as follows:

[0122] A mining tunnel in a mining area of ​​the mine was selected as the target tunnel, which had been in service for 2 years. Due to the presence of an aquifer above the tunnel roof, the roof was watered to varying degrees during tunnel excavation and support. Since the roof rock layer was weakly cemented mudstone and sandstone, the tunnel surrounding rock was severely deformed and damaged, and the anchor rods and cables were corroded, rusted, and fractured and failed, which had a serious impact on coal mining. To address this problem, the anchor rod and cable support design method of the present invention was adopted:

[0123] S1. By collecting alkaline water samples from the tunnel roof watering area on site and analyzing the basic physical and chemical properties of the alkaline water, the laboratory tested the basic physical and chemical properties of the alkaline water. The test results are shown in Table 2:

[0124] Table 2 Test results of physical and chemical properties of alkaline water from a mine in the west

[0125]

[0126] S11. Based on the test results of the physical and chemical properties of alkaline water in the target tunnel, select Cl - 、Na + 、SO4 2- As the main corrosive ion, construct the alkaline corrosion index A x Calculation formula:

[0127] Calculate OH by using alkaline water pH = 11.5 - Molar mass of ions Cl - 、Na + 、SO4 2- The ion concentration is converted into molar mass. The service life of the tunnel is 2 years. The erosion time of the tunnel by alkaline water is 730 days. Substituting it into the calculation formula of alkali corrosion index, the solution is: A x =(3.16×10 -3 +80.2×10 -3 +46.4×10 -3 +17.34×10 -3 )×730=107.38.

[0128] S12, according to the alkali water erosion intensity classification standard A x >100, the target area tunnel is a strong alkaline corrosion environment.

[0129] S21. On-site monitoring of the target area roadway roof surrounding rock subsidence and permeability, laboratory testing of surrounding rock compressive strength, and recording of surrounding rock deformation ε(t), surrounding rock permeability k(t), and surrounding rock compressive strength σ at different times under the alkaline corrosion environment. c (t) and the corresponding degradation rate D(t), as shown in Table 3:

[0130] Table 3 Monitoring data of weakly cemented surrounding rock degradation at different times

[0131]

[0132] S22, S23, and S24 solve the regression coefficients through the collected 90-day data, and then substitute them into the nonlinear surrounding rock degradation degree model to obtain:

[0133]

[0134] S25. Based on the surrounding rock degradation model, the alkali corrosion index, deformation, permeability and strength multivariate data of the target tunnel after 2 years of use were monitored, and D(t)=0.76 was calculated, which is a high degree of degradation and seriously affects the anchor rod and cable support system.

[0135] S3. Several 100m test sections 7 were set up in the target area tunnels. Five measuring points were set up in the test sections. Three measuring point anchor rods and two measuring point anchor cables were selected for each measuring point. Resistivity monitoring sensors and polarization potential monitoring sensors were arranged in the measuring point anchor rods and measuring point anchor cables. Prestress was applied to the anchor rod cables. The resistivity and polarization potential of the anchor rods and anchor cables during the service of the tunnel were collected. The resistivity increase rate Δρ of the anchor rods and the anchor cables was calculated by the resistivity increase rate and erosion rate model to be 16.7%, 12.4%, and the anchor erosion rate V f is 0.35mm / a, and the anchor erosion rate V f It is 0.27mm / a, which is moderate corrosion.

[0136] S4. Based on the evaluation results of the weakly cemented surrounding rock degradation degree in step S2 and the bolt and cable erosion state in step S3, the bolt and cable support design scheme for the target area roadway is dynamically adjusted as follows:

[0137] During the service of the target area tunnel, alkaline water has a strong deterioration effect on the weakly cemented surrounding rock, and it is necessary to increase the support density and anchoring length of the anchor rods and cables on the basis of the original support; the erosion state of the anchor rods and cables is moderate, and it is necessary to apply hot-dip galvanizing and organic polymer coating on the surface of the anchor rods and cables to prevent alkali corrosion.

[0138] In addition to the above embodiments, the present invention may also have other implementation modes. Any technical solutions formed by equivalent replacement or equivalent transformation shall fall within the protection scope required by the present invention.

Claims

1. A design method for anchor rod and cable support in weakly cemented surrounding rock tunnels corroded by alkaline water, characterized by: It includes the following steps: S1. Collect alkaline water samples from the tunnel roof watering area on site, analyze the basic physical and chemical properties of alkaline water, and construct an alkaline corrosion index A. x , a dynamic relationship model between erosion intensity and time is established as a quantitative indicator for evaluating the erosion intensity of alkaline water on the anchoring system, and then the erosion intensity level of alkaline water is determined; S2. Construct an exponential regression non-linear surrounding rock deterioration degree model based on the multi-element data of alkali corrosion index, deformation amount, permeability and strength during the service period of the target roadway, and evaluate the influence of the deterioration degree of the weakly cemented surrounding rock on the bolt and cable support system; S3. Construct a resistivity increase rate and erosion rate model of bolts and cables based on the resistivity and polarization potential of bolts and cables during the service period of the roadway, and evaluate the erosion state of bolts and cables; S4. Dynamically adjust the bolt and cable support design scheme according to the exponential regression non-linear surrounding rock deterioration degree obtained in step S2 and the resistivity increase rate and erosion rate of bolts and cables obtained in step S3.

2. The anchor rod and cable support design method for weakly cemented surrounding rock tunnels corroded by alkaline water according to claim 1 is characterized by: The step S1 constructs an alkaline corrosion index A x The specific steps to establish the dynamic relationship model between erosion intensity and time are as follows: S11. Constructing Alkali Corrosion Index A x , the formula is as follows: Where: OH - The molar mass of the ion, Respectively represent the removal of OH - ions, and T is the molar mass of all corrosive ions other than ions, and T is the erosion time of alkaline water on the anchoring system; S12. Calculate the alkaline corrosion index A in mol / L. x , determine the corrosion intensity level of alkaline water as: Weak alkaline corrosion: A x ≤50, the erosion of alkaline water on surrounding rocks and anchoring systems is weak; Medium alkali corrosion: 50 x ≤100, alkaline water has significant corrosive effect on surrounding rock and anchoring system;​ Strong alkaline corrosion: A x >100, alkaline water is highly destructive to the surrounding rock, and the anchoring system is also prone to failure due to erosion.

3. The anchor rod and cable support design method for weakly cemented surrounding rock tunnels corroded by alkaline water according to claim 2 is characterized by: The specific steps of step S2 are as follows: S21. Through field and experimental monitoring, the threshold interval of weakly cemented surrounding rock degradation is defined as (0,1), and the surrounding rock deformation ε(t), surrounding rock permeability k(t), and surrounding rock compressive strength σ at different time points t under different alkaline corrosion environments are recorded. c (t) and the corresponding degradation rate D(t); S22. Construct an exponential regression non-linear surrounding rock deterioration degree model, and the formula is as follows: Where: α is the proportionality coefficient, A x (t) is the alkali corrosion index, ε(t) is the surrounding rock deformation, k(t) is the surrounding rock permeability, σ c (t) is the compressive strength of surrounding rock, β1, β2, β3, and β4 are the regression coefficients of alkali corrosion index, surrounding rock deformation, surrounding rock permeability, and surrounding rock compressive strength, respectively; Step S23. Take the natural logarithm of the exponential regression non-linear surrounding rock deterioration degree D(t) to obtain a linearized model, and the formula is as follows: ln(D(t))=α'+β1A x (t)+β2ε(t)+β3k(t)+β4σ c (t) Step S24: Take the value of ln(D(t)) as the dependent variable and set the independent variable to A. x (t),ε(t),k(t),σ c (t), using the least squares method to fit, continuously iterate and optimize to solve the best values ​​of each regression coefficient α', β1, β2, β3 and β4, restore the logarithm, and substitute each regression coefficient into the surrounding rock degradation degree model D(t); Step S25. Evaluate the influence on the bolt and cable support system according to the exponential regression non-linear surrounding rock deterioration degree D(t): When 0 < D(t) ≤ 0.3, the surrounding rock deterioration degree is low and the influence on the bolt and cable support system is small; When 0.3 < D(t) ≤ 0.7, the surrounding rock deterioration degree is significant and the influence on the bolt and cable support system is large; When 0.7 < D(t) < 1, the surrounding rock deterioration degree is high and seriously affects the bolt and cable support system.

4. The design method for anchor rod and cable support in weakly cemented surrounding rock tunnels corroded by alkaline water according to claim 3 is characterized by: The specific steps of step S3 are as follows: S31. Arrange several test sections in different erosion intensity areas of the roadway. Several measuring points are arranged in each test section. Several measuring point bolts and measuring point cables are selected at each measuring point. Resistivity monitoring sensors and polarization potential monitoring sensors are respectively arranged in the measuring point bolts and measuring point cables, and prestress is applied to the bolts and cables; S32, according to the resistivity ρ at time t t and initial resistivity ρ0, according to the formula The resistivity increase rate Δρ is obtained; S33, based on the measured polarization potential E, corrosion potential E corr , Tafel slope b, molar mass M of the material, number of electron transfer n of the electrochemical reaction, Faraday constant F, and density ρ of the material m , construct the anchor cable erosion rate model, the formula is as follows: In the formula: K is a unit conversion constant; S34. Evaluate the erosion state of stress-alkali water on bolts and cables according to the resistivity increase rate and erosion rate of bolts and cables; If Δρ<10%, 0.01mm / a≤V f <0.1mm / a, it is slight corrosion; If 10%≤Δρ<30%, 0.1mm / a≤V f <1.0mm / a, it is moderate corrosion; If Δρ≥30%, V f ≥1.0mm / a, it is severe corrosion.

5. The design method for anchor rod and cable support in weakly cemented surrounding rock tunnels corroded by alkaline water according to claim 4 is characterized in that: The dynamic adjustment scheme of step S4 is as follows: When the deterioration degree of the weakly cemented surrounding rock is low, the original support scheme is adopted; When the deterioration degree of the weakly cemented surrounding rock is significant, increase the support density of bolts and cables; When the deterioration degree of the weakly cemented surrounding rock is high, increase the anchoring length on the basis of increasing the support density of bolts and cables; When the bolts and cables are slightly corroded, there is no need to apply an anti-alkali corrosion layer; When the bolts and cables are moderately corroded, choose hot-dip galvanizing or organic polymer coating to prevent alkali corrosion of the bolts and cables; When the bolts and cables are severely corroded, it is necessary to further increase the thickness of the anti-alkali corrosion layer.

6. The design method for anchor rod and cable support in weakly cemented surrounding rock tunnels corroded by alkaline water according to claim 4 is characterized by: The length of the test section in step S31 is 100m. 5 measuring points are arranged in each test section. 3 measuring point bolts and 2 measuring point cables are selected at each measuring point.

7. The design method for anchor rod and cable support in weakly cemented surrounding rock tunnels corroded by alkaline water according to claim 4 is characterized by: The Tafel slope b in step S33 takes a value of 0.12V.

8. The design method for anchor rod and cable support in weakly cemented surrounding rock tunnels corroded by alkaline water according to claim 4 is characterized by: The value of K in step S33 is 3.27×10 -3 .

9. The design method for anchor rod and cable support in weakly cemented surrounding rock tunnels corroded by alkaline water according to claim 4, characterized in that: The number of electron transfers n of the electrochemical reaction in step S33 takes a value of 2.

10. The design method for anchor rod and cable support in weakly cemented surrounding rock tunnels corroded by alkaline water according to any one of claims 4 to 9, characterized in that: The value of the Faraday constant F in step S33 is 96485 C / mol.

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