A rockburst discrimination method following a strict mechanical process

Abstract

The present invention discloses a rockburst discrimination method following a rigorous mechanical process, and the method includes: calculating the secondary maximum stress of surrounding rock by using a numerical simulation method or a regression statistical method; calculating the uniaxial compressive strength of surrounding rock by using a rock mass strength criterion; obtaining indexes related to the integrity or quality of surrounding rock and comparing them with corresponding reference values, judging and calculating a correction term considering the change in the integrity or quality of surrounding rock; defining a rockburst criterion according to the secondary maximum stress of surrounding rock, the uniaxial compressive strength of surrounding rock and the correction term; and dividing the rockburst risk level according to the magnitude of the rockburst criterion value. The rockburst criterion of the present invention adopts control factors directly affecting the rockburst risk, namely the secondary maximum stress of surrounding rock and the uniaxial compressive strength of surrounding rock, and has a reliable theoretical basis. Moreover, the present invention considers the influence of the change in the integrity or quality of surrounding rock through the correction term, greatly improving the engineering reliability of the judgment result.

Description

Technical Field

[0001] The present invention belongs to the technical field of underground engineering construction, and specifically provides a rockburst discrimination method that follows a rigorous mechanical process. Background Art

[0002] Rockburst is a common and extremely harmful geological disaster during the excavation of deep underground engineering. The earliest awareness of the rockburst phenomenon by humans can be traced back to 1908. The strongest rockburst energy recorded is equivalent to a magnitude 5.1 earthquake on the Richter scale, causing devastating damage to the entire project. In many cases of large-scale infrastructure construction projects in western China, including the Sichuan-Tibet Railway, rockburst becomes the key to the success or failure of the project.

[0003] Over the past 100-odd years, a variety of rockburst criteria have been proposed internationally, but without exception, they have ignored the necessary mechanical solution process and are all empirical methods: the parameter values are derived from relatively simple tests or empirical estimations. Among all these criteria, the application of the stress intensity ratio, which originated from the mining engineering practice in South Africa in the 1950s, is the most widespread; although the rockburst criteria recommended in industry codes such as water conservancy and hydropower in China are different in form, the strength stress ratio, they are essentially the same. The strength therein refers to the uniaxial compressive strength of the rock, and the indoor test value of the standard specimen or the result of empirical judgment is adopted; the stress refers to the maximum principal stress in the initial in-situ stress field, and the in-situ test or empirical estimation result is adopted.

[0004] The greatest advantage of these empirical criteria is simplicity and speed, and all indicators can be obtained based on empirical estimations. However, the disadvantages are also very prominent: Firstly, the indicators are too simple, resulting in the lack of necessary theoretical basis, and the large dispersion of parameter values makes it difficult to make a choice. Secondly, the mechanical relationship existing in reality is ignored during the application process, and the final result is that the engineering reliability is seriously insufficient.

[0005] Firstly, rockburst is the result of the contradiction between the secondary stress of the surrounding rock and the strength of the surrounding rock mass after the excavation of underground engineering. Although it is still stress and strength literally, there are significant differences between the secondary stress of the surrounding rock and the initial in-situ stress, and between the rock strength and the rock mass strength. The initial in-situ stress of the surrounding rock is only one of the factors affecting the secondary stress of the surrounding rock, and the uniaxial compressive strength of the rock is also only one of the factors affecting the strength of the rock mass. For example, the invention patent with publication number CN102749660A discloses a comprehensive prediction method for rockburst in nearly horizontal rock strata in high in-situ stress areas, which uses the ratio of the magnitude of the maximum principal stress and the uniaxial compressive strength of the rock to judge the possible rockburst intensity. The maximum principal stress is not equivalent to the secondary stress of the surrounding rock. Therefore, simply using the rock strength and the initial in-situ stress is difficult to describe the direct indicators affecting rockburst: the strength of the surrounding rock (rock mass) and the secondary stress of the surrounding rock.

[0006] The invention patent with the publication number CN107748103A discloses a method for predicting tunnel rockburst. The boundary value of the rockburst prediction index is the ratio of the Hoek-Brown rock mass strength to the maximum in-situ stress in the direction perpendicular to the tunnel axis of the in-situ stress field. However, the ratio calculated from the maximum in-situ stress in the direction perpendicular to the tunnel axis of the in-situ stress field can only be used as the rockburst prediction boundary value, and the effect of the rockburst criterion will be discounted.

[0007] Secondly, all existing rockburst criteria do not consider the influence of the integrity of the surrounding rock or the change in the quality of the surrounding rock, and all assume that the rockburst risk has a monotonic relationship with the quality of the surrounding rock, which does not conform to the actual situation: under the given stress conditions of the surrounding rock, the rockburst risk is the highest at a certain critical strength of the surrounding rock. A significantly lower strength makes the surrounding rock lack the ability to accumulate elastic strain energy, reducing the rockburst risk or even eliminating the rockburst risk. A significantly higher strength also results in a relatively lower rockburst risk because it is in a safe state.

[0008] On the other hand, the parameter values and calculation processes do not follow any mechanical relationships. If all indicators are test values or even empirical estimates, the mechanical process is missing, and the mechanical rationality of the results cannot be guaranteed.

[0009] That is to say, the empirical criterion lacks the necessary theoretical support in both the foundation and process links, resulting in the consequence that the reliability is difficult to guarantee. For example, in the Jinping deep-buried tunnel in Liangshan Prefecture, Sichuan Province, China, the single tunnel is 16.7 km long, and the length of the tunnel section with a burial depth exceeding 1500 m is about 10 km. The uniaxial compressive strength of the rock is about 100 MPa. According to these empirical criteria, there is a strong rockburst risk in all 10 km of the deep-buried section. However, the actual length of the rockburst section revealed by the project construction is only about 500 m, and the accuracy rate is only about 5%.

[0010] Therefore, the existing technology lacks a rockburst criterion with a reliable theoretical basis and a rigorous mechanical process support. Summary of the Invention

[0011] In view of this, the present invention proposes a rockburst discrimination method that follows a rigorous mechanical process to solve the problem that the existing rockburst criteria lack a rigorous mechanical process support.

[0012] The present invention discloses a rockburst discrimination method that follows a rigorous mechanical process, and the method includes:

[0013] Calculating the secondary maximum stress σ of the surrounding rock by using a numerical simulation method or a regression statistical method based on the numerical simulation results max ;

[0014] Calculating the uniaxial compressive strength σ of the surrounding rock by using a rock mass strength criterion cm ;

[0015] Obtain the indexes related to the surrounding rock integrity or surrounding rock quality and compare them with the corresponding reference values, judge and calculate the correction term Δ considering the change of surrounding rock integrity or surrounding rock quality;

[0016] According to the secondary maximum stress σ of the surrounding rock max , the uniaxial compressive strength σ of the surrounding rock cm and the correction term Δ, define the rockburst criterion λ;

[0017] Divide the rockburst risk level according to the value of the rockburst criterion λ.

[0018] On the basis of the above technical solutions, preferably, when calculating the secondary maximum stress σ of the surrounding rock max by using the regression statistics method based on the numerical simulation results, assume multiple initial conditions and conduct numerical calculations and simulations for multiple excavation processes, and statistically analyze the buried depth, lateral pressure coefficient and σ max data in the numerical calculation results, and calculate the secondary maximum stress of the surrounding rock under given conditions based on the regression statistical formula of the numerical calculation results.

[0019] On the basis of the above technical solutions, preferably, the indexes related to the surrounding rock integrity or surrounding rock quality include the rock quality designation RQD, integrity coefficient Kv, rock mass rating RMR, geological strength index GSI, national standard BQ, surrounding rock quality Q or the classification T of surrounding rocks in underground water conservancy and hydropower caverns.

[0020] On the basis of the above technical solutions, preferably, the correction term Δ considers the influence of the weakening of brittle characteristics and the reduction of rockburst risk when the indexes related to the surrounding rock integrity or surrounding rock quality are less than the corresponding set reference values. The specific steps of judging and calculating the correction term Δ considering the change of surrounding rock integrity or surrounding rock quality include:

[0021] When the indexes related to the surrounding rock integrity or surrounding rock quality are less than the corresponding reference values, calculate the value of the correction term Δ according to the probability distribution form of the corresponding indexes; otherwise, the correction term Δ = 0.

[0022] On the basis of the above technical solutions, preferably, the expression for defining the rockburst criterion λ according to the secondary maximum stress σ of the surrounding rock max , the uniaxial compressive strength σ of the surrounding rock cm and the correction term Δ is:

[0023]

[0024] where k1, k2, and k3 are constant coefficients.

[0025] On the basis of the above technical solutions, preferably, the expression for defining the rockburst criterion λ according to the secondary maximum stress σ of the surrounding rock max , the uniaxial compressive strength σ of the surrounding rock cm and the correction term Δ is:

[0026]

[0027] Among them, k1, k2, and k3 are constant coefficients.

[0028] Based on the above technical solutions, preferably, assuming that the current Geological Strength Index (GSI) is less than the corresponding reference value, if the Geological Strength Index (GSI) follows a normal distribution, the calculation formula for the correction term Δ is:

[0029]

[0030]

[0031] Among them, K0 is the coefficient of lateral pressure, GSI0 is the representative Geological Strength Index measured on-site, and d is the standard deviation of the normal distribution.

[0032] The present invention has the following beneficial effects compared with the prior art:

[0033] 1) The present invention defines the rockburst criterion based on the secondary maximum stress of the surrounding rock, the uniaxial compressive strength of the surrounding rock, and the correction term. Compared with all previous rockburst criteria, the rockburst criterion of the present invention adopts the control factors directly affecting the rockburst risk, namely the secondary maximum stress of the surrounding rock and the uniaxial compressive strength of the surrounding rock (rock mass). Therefore, the theoretical basis is reliable, and the present invention considers the influence of the integrity of the surrounding rock or the change in the quality of the surrounding rock (deviating from a certain reference value) through the correction term, which is more in line with the actual engineering requirements;

[0034] 2) The present invention determines the secondary maximum stress of the surrounding rock through numerical simulation or regression statistics method. No matter which method is used, the acquisition of this parameter value follows a strict mechanical calculation process, which can consider the influence of multiple factors on the secondary maximum stress value of the surrounding rock at the same time, and the accuracy is higher; the uniaxial compressive strength of the rock mass also follows the strength criterion calculation, and both follow a strict mechanical calculation process;

[0035] 3) When defining the rockburst criterion, the present invention calculates the value of the correction term according to the probability distribution form of the corresponding index when the index related to the integrity of the surrounding rock or the quality of the surrounding rock is less than the corresponding reference value, which greatly improves the engineering reliability of the judgment result. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0037] Figure 1Flow chart of the rockburst discrimination method that follows a rigorous mechanical process for the present invention;

[0038] Figure 2 Taking a circular cross-section tunnel as an example, it is a schematic diagram for simulating the excavation process of underground chambers with the help of finite element or discrete element numerical calculation software;

[0039] Figure 3 It is the principal stress nephogram obtained by using the numerical simulation method;

[0040] Figure 4 It is the regression fitting result of the secondary maximum stress of the surrounding rock with the buried depth and the lateral pressure coefficient after a large number of numerical calculations. Specific implementation mode

[0041] Next, in combination with the implementation modes of the present invention, the technical solutions in the implementation modes of the present invention will be clearly and completely described. Obviously, the described implementation modes are only a part of the implementation modes of the present invention, rather than all the implementation modes. Based on the implementation modes in the present invention, all other implementation modes obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0042] The implementation of the present invention has the same requirements for basic data as conventional rock mechanics numerical analysis, and it is necessary to obtain the cross-section profile data of the underground project and corresponding exploration data (such as the buried depth, lateral pressure coefficient, and relevant indexes of rocks and rock masses).

[0043] Please refer to Figure 1 , the present invention proposes a rockburst discrimination method that follows a rigorous mechanical process, and the method includes:

[0044] S1. Calculate the secondary maximum stress σ of the surrounding rock by using the numerical simulation method or the regression statistical method based on the numerical simulation results max .

[0045] Specifically, as Figure 2 shown, taking a circular cross-section tunnel as an example, the numerical simulation of the underground chamber excavation process can be carried out with the help of finite element or discrete element numerical calculation software to obtain the distribution of the maximum principal stress of the surrounding rock. As Figure 3 shown is the principal stress nephogram obtained by using the numerical simulation method, and the secondary maximum stress σ of the surrounding rock can be read from it max .

[0046] It is also possible to refer to other results and calculate the secondary maximum stress σ of the surrounding rock under given conditions based on the regression statistical formula of a large number of numerical calculation results max . For example, when calculating σ by using the regression statistical method of a large number of numerical calculation results maxWhen conducting numerical calculation simulations of multiple excavation processes under various hypothetical conditions, statistical data such as burial depth and lateral pressure coefficient are obtained based on the results of multiple numerical calculations. Regression statistics are performed based on data such as burial depth and lateral pressure coefficient to calculate the secondary maximum stress σ of the surrounding rock max , and the calculation formula is as follows:

[0047] σ max = aH + bK + c

[0048] Where a, b, and c are regression coefficients; H is the burial depth; K is the lateral pressure coefficient, which refers to the ratio of the maximum and minimum initial principal stresses on the cross-section. When the unit of σ max is MPa and the unit of H is m, the value ranges of the three parameters a, b, and c are [80, 90], [80, 90], and [-110, -130] respectively, which are related to the surrounding rock conditions of specific projects

[0049] Figure 4 Shown is the regression fitting result of the secondary maximum stress of the surrounding rock with the burial depth and lateral pressure coefficient after a large number of numerical calculations

[0050] The secondary maximum stress σ of the surrounding rock of the present invention max is obtained by using a numerical simulation method or through regression statistics of the results of a large number of numerical calculations under various hypothetical conditions. Regardless of which method, the acquisition of the value of the secondary maximum stress of the surrounding rock follows a strict mechanical calculation process and can consider the influence of multiple factors on the value of the secondary maximum stress of the surrounding rock

[0051] S2. Calculate the uniaxial compressive strength σ of the surrounding rock using the rock mass strength criterion cm .

[0052] The uniaxial compressive strength of the surrounding rock (rock mass) is calculated using common rock mass strength criteria and strictly obeys mechanical theories such as the rock mass strength criterion

[0053] Specifically, if the uniaxial compressive strength of the surrounding rock (rock mass) is based on the Mohr-Coulomb strength criterion, the calculation formula is:

[0054]

[0055] Where c and are both Mohr-Coulomb strength parameters of the rock mass

[0056] If the uniaxial compressive strength of the surrounding rock (rock mass) is based on the Hoek-Brown strength criterion, the calculation formula is:

[0057] σ cm = σ ci * s r

[0058] Where:

[0059] s = e (GSI-11.11)

[0060] r = 0.5 + (e (-GSI / 5) - e -6.667 ) / 6

[0061] Among them, GSI is the geological strength index, which is obtained through on-site cataloging. σ ci is the uniaxial compressive strength of the rock specimen, which is the indoor test value of the standard rock specimen with φ5·10mm.

[0062] S3. Obtain the indexes related to the surrounding rock integrity or the surrounding rock quality and compare them with the corresponding reference values, and judge and calculate the correction term Δ considering the change of the surrounding rock integrity or the surrounding rock quality.

[0063] The addition of the correction term Δ is to consider the influence of the weakening of the brittle characteristics and the reduction of the accuracy of the rockburst risk judgment when the surrounding rock integrity or the surrounding rock quality is less than a certain reference value.

[0064] First, obtain the indexes related to the surrounding rock integrity or the surrounding rock quality. The indexes related to the surrounding rock integrity or the surrounding rock quality include but are not limited to the values of the rock quality designation RQD, the integrity coefficient Kv, the rock mass rating RMR, the geological strength index GSI, the national standard BQ, the surrounding rock quality Q, the surrounding rock classification T for underground water conservancy and hydropower caverns, etc.

[0065] Then, compare the indexes related to the surrounding rock integrity or the surrounding rock quality with the corresponding reference values. When the indexes related to the surrounding rock integrity or the surrounding rock quality are less than the corresponding reference values, calculate the value of the correction term Δ according to the probability distribution form of the corresponding indexes. Otherwise, the correction term Δ = 0.

[0066] Taking the geological strength index GSI as an example, assuming that the current geological strength index GSI is less than the corresponding reference value, if the geological strength index GSI follows a normal distribution, the calculation formula for the correction term Δ is:

[0067]

[0068]

[0069] Among them, K0 is the lateral pressure coefficient, GSI0 is the representative geological strength index measured on site, and d is the standard deviation of the normal distribution. The specific values of these three parameters are determined according to the actual engineering construction situation, but the overall value ranges of these three parameters are [0.8, 1.2], [55, 65], and [14, 20] respectively.

[0070] If the geological strength index GSI follows an exponential distribution, in the above calculation formula for the correction term Δ, the expression of d(GSI) can be replaced by d(GSI) = te -tGSI, where t > 0 is the distribution parameter.

[0071] The calculation of the correction term Δ is not limited to the normal distribution or negative exponential form of these indicators, and may also include other probability distribution forms that conform to statistical laws, which can be obtained through statistical verification by combining on-site data and historical data.

[0072] When defining the rockburst criterion in the present invention, when the indicators related to the surrounding rock integrity or the surrounding rock quality are less than the corresponding reference values, the value of the correction term Δ is calculated according to the probability distribution form of the corresponding indicator, such as the normal distribution form or the negative exponential form, which can accurately reflect the influence of the change in the surrounding rock integrity or the surrounding rock quality and improve the accuracy of the rockburst criterion.

[0073] S4. Define the rockburst criterion λ according to the secondary maximum stress σ of the surrounding rock max , the uniaxial compressive strength σ of the surrounding rock cm and the correction term Δ.

[0074] The expression for defining the rockburst criterion λ is:

[0075]

[0076] In the above expression of the rockburst criterion λ, the numerator and the denominator can be interchanged, that is, the expression of the rockburst criterion λ can also be:

[0077]

[0078] Among them, k1, k2, and k3 are constant coefficients, and their values can also all be 1. These changes do not affect the accuracy of the rockburst criterion, but only affect the magnitude of the calculation of the λ value and the specific grade standard in the rockburst grade division.

[0079] In the rockburst criterion of the present invention, the control factors directly affecting the rockburst risk are adopted, that is, the secondary maximum stress σ of the surrounding rock max and the uniaxial compressive strength σ of the surrounding rock (rock mass) cm . Compared with the existing indirect calculation methods through initial stresses such as the maximum principal stress, the theoretical basis of the present invention is more reliable, and the present invention considers the influence of the change in the surrounding rock integrity or the surrounding rock quality (deviating from a certain reference value) through the correction term, which better meets the actual engineering requirements and greatly improves the engineering reliability of the judgment result.

[0080] S5. Divide the rockburst risk level according to the magnitude of the rockburst criterion λ value.

[0081] When dividing the rockburst risk level according to the magnitude of the rockburst criterion λ value, the rockburst risk level is divided into four levels: extremely strong, strong, medium, and weak or none.

[0082] For example, when k1 = k2 = k3 = 1, then according to The value of the rockburst criterion can be calculated, and it can be set that when λ≥4.5, it is extremely strong rockburst; when 3.0≥λ>4.5, it is strong rockburst; when 3.0>λ≥1.8, it is medium rockburst, and when λ<1.8, it is weak or no rockburst.

[0083] The above is only the preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A rockburst discrimination method following a strict mechanical process, characterized in that, The method includes: The secondary maximum stress σ of the surrounding rock is calculated by using numerical simulation methods or regression statistical methods based on numerical simulation results max ; Calculate the uniaxial compressive strength σ of the surrounding rock using the rock mass strength criterion cm ; Obtaining indexes related to the integrity or quality of surrounding rock and comparing them with corresponding reference values, judging and calculating a correction term Δ considering the change in the integrity or quality of surrounding rock; According to the secondary maximum stress σ of the surrounding rock max 、 the uniaxial compressive strength σ of the surrounding rock cm and the correction term Δ to define the rockburst criterion λ; Dividing the rockburst risk level according to the magnitude of the rockburst criterion λ value; The indexes related to the integrity or quality of surrounding rock include the rock quality designation RQD, the integrity coefficient Kv, the rock mass rating RMR, the geological strength index GSI, the national standard BQ, the surrounding rock quality Q, or the classification T of surrounding rock in underground caverns for water conservancy and hydropower projects; The correction term Δ considers the influence of the weakening of brittle characteristics and the reduction of rockburst risk when the indexes related to the integrity or quality of surrounding rock are less than the corresponding set reference values. The judging and calculating the correction term Δ considering the change in the integrity or quality of surrounding rock specifically includes: When the indexes related to the integrity or quality of surrounding rock are less than the corresponding reference values, calculating the value of the correction term Δ according to the probability distribution form of the corresponding indexes; otherwise, the correction term Δ = 0; Assuming that the current geological strength index GSI is less than the corresponding reference value, if the geological strength index GSI follows a normal distribution, the calculation formula for the correction term Δ is: where K0 is the lateral pressure coefficient, GSI0 is the representative geological strength index measured in situ, and d is the standard deviation of the normal distribution.

2. The rockburst discrimination method following a rigorous mechanical process according to claim 1, characterized in that, The regression statistical method based on the numerical simulation results is used to calculate the secondary maximum stress σ of the surrounding rock max When calculating, assume multiple initial conditions and conduct numerical simulations of the excavation process multiple times, and statistically analyze the burial depth, lateral pressure coefficient, and σ max data in the numerical calculation results, and calculate the secondary maximum stress of the surrounding rock under given conditions based on the regression statistical formula of the numerical calculation results.

3. The rockburst discrimination method following a strict mechanical process according to claim 1, characterized in that, The expression for defining the rockburst criterion λ based on the secondary maximum stress σ of the surrounding rock max , the uniaxial compressive strength σ cm of the surrounding rock and the correction term Δ is as follows: where k1, k2, and k3 are constant coefficients.

4. The rockburst discrimination method following a strict mechanical process according to claim 1, characterized in that, The expression for defining the rockburst criterion λ based on the secondary maximum stress σ of the surrounding rock max , the uniaxial compressive strength σ of the surrounding rock cm and the correction term Δ is as follows: where k1, k2, and k3 are constant coefficients.

Images