A rockburst proneness evaluation method based on loose circle test results

Abstract

The application provides a rock burst tendency evaluation method based on a loose circle test result, and relates to the technical field of rock burst disaster prediction of underground engineering. The thickness of the surrounding rock loose circle and the chamber equivalent radius are obtained through field test, and the normalized loose circle coefficient is constructed to represent the residual energy storage capacity of the surrounding rock. When the normalized loose circle coefficient is smaller, it indicates that the surrounding rock is more complete, the elastic energy accumulation capacity is stronger, and the rock burst tendency is higher. According to the comparison between the normalized loose circle coefficient and the preset threshold value, the rock burst tendency is divided into four grades of strong, medium, weak and none. The application is completely based on field nondestructive test, does not need indoor mechanical test and experience parameters, has the advantages of simple operation, low cost, clear physical meaning, intuitive grading result and the like, can effectively explain the engineering phenomenon that there is no rock burst in the high ground stress area and rock burst occurs in the low stress area, and provides a scientific basis for rapid evaluation and prevention and control of rock burst risk of deep underground engineering.

Description

Technical Field

[0001] This invention relates to the field of underground engineering rockburst disaster prediction technology, specifically to a rockburst tendency evaluation method based on loosening zone test results. Background Technology

[0002] Rockburst is a dynamic instability failure phenomenon that occurs in deep rock masses under high ground stress conditions during excavation and unloading. It is characterized by its suddenness, severe damage, and unpredictability, seriously threatening personnel safety and project progress in deep metal mines, hydroelectric tunnels, and transportation tunnels. As underground space development continues to extend deeper, ground stress levels increase significantly, leading to an upward trend in the frequency and intensity of rockbursts. Therefore, accurately and quickly assessing the rockburst tendency of the surrounding rock is of significant engineering importance for guiding support design and construction safety.

[0003] Currently, there are three main types of methods for evaluating rockburst tendency: the first is based on rock mechanical properties, using laboratory test parameters such as uniaxial compressive strength, elastic modulus, and brittleness coefficient; the second is based on the relationship between in-situ rock stress and rock strength, using indicators such as stress-intensity ratio and stress concentration factor; and the third is based on energy theory or statistical engineering experience. While these methods have been applied in engineering, they exhibit significant limitations when faced with complex conditions. Numerous field observations have revealed that even with similar lithology and in-situ rock stress conditions, rockburst behavior can vary significantly across different sections, sometimes even contradicting each other: some high-stress sections do not experience rockbursts, while some lower-stress sections experience strong rockbursts. In-depth analysis reveals that the root cause of this contradiction lies in three core deficiencies of existing evaluation techniques: First, laboratory test parameters are insufficient to reflect the true state of the in-situ rock mass. The occurrence of rockburst depends not only on the basic mechanical properties of the rock but also on the actual damage after excavation, the degree of fracture development, and the elastic energy storage conditions. Indoor rock tests cannot reflect the structural characteristics and energy release history of the rock mass after excavation and unloading, leading to significant discrepancies between evaluation results and actual field conditions. Second, existing stress ratio criteria lack characterization of the energy unloading state of the surrounding rock. Traditional methods rely on the ratio of in-situ rock stress to rock strength, implicitly assuming that the surrounding rock is intact and possesses good energy storage conditions. However, excavation disturbance causes the propagation of surrounding rock fissures and stress release. At this time, even if the in-situ rock stress level is high, the actual probability of rockburst is significantly reduced. Existing criteria cannot consider this key factor, easily misclassifying high-stress areas as high-rockburst risk areas. Third, empirical thresholds lack universality and effective quantitative methods. Existing classification thresholds are mostly based on specific projects or regional statistics, and are affected by factors such as lithology, stress environment, and cross-sectional scale, resulting in poor applicability when applied to different geological and engineering conditions. More importantly, there is currently a lack of quantitative methods to establish the relationship between the integrity of the surrounding rock and rockburst, making it impossible to incorporate the actual integrity of the surrounding rock after excavation into the evaluation, thus making it difficult to accurately predict the probability and intensity of rockburst.

[0004] In view of this, a series of technical problems urgently need to be solved in the field of rockburst evaluation: how to directly obtain parameters that reflect the actual energy unloading degree of the surrounding rock through field measurement methods, and establish a quantitative correspondence between these parameters and rockburst tendency; how to quantitatively characterize the actual energy unloading degree of the surrounding rock after excavation, and establish a quantitative correlation between the loosened zone thickness and rockburst tendency; and how to propose a rockburst evaluation index that can be directly obtained through field testing, so as to realize the graded output of rockburst tendency and thus provide scientific guidance for the formulation of engineering prevention and control measures. Summary of the Invention

[0005] In view of the technical problems existing in the background art, the present invention provides a rockburst tendency evaluation method based on the results of loosened zone test. The thickness of the loosened zone formed by the surrounding rock after excavation is regarded as the spatial manifestation of the released elastic energy. The smaller the loosened zone, the more intact the surrounding rock and the stronger the elastic energy accumulation capacity, and the higher the rockburst tendency. By constructing a normalized coefficient (the ratio of the loosened zone thickness to the equivalent radius of the cavern), the geometric parameters measured in the field are transformed into indicators that can directly characterize the remaining energy storage capacity of the surrounding rock, and based on this, four levels of rockburst tendency are divided: strong, medium, weak, and none.

[0006] This invention provides a method for evaluating rockburst tendency based on loosened zone test results, which includes the following steps: S1, based on field tests in the area to be evaluated, the thickness of the loosened zone of the surrounding rock after excavation is obtained; S2, determine the equivalent radius of the cavern in the area to be evaluated; S3, construct a normalized loosening ring coefficient, wherein the normalized loosening ring coefficient is the ratio of the loosening ring thickness to the equivalent radius; S4. Determine the rockburst tendency level of the surrounding rock based on the normalized loosening zone coefficient.

[0007] As a further improvement of the present invention, the process of obtaining the thickness of the loosening ring in step S1 includes: Test holes are arranged in the surrounding rock, and at least one of the following methods, namely acoustic logging, cross-hole acoustic testing, and seismic testing, is used to obtain the data sequence of test signals as the hole depth changes. The wave velocity change curve is analyzed based on the data sequence, and the thickness of the loosening ring is determined according to a preset rule.

[0008] As a further improvement of the present invention, the preset rules include: When the wave velocity value is significantly lower than the average wave velocity in the deep stable zone, and the wave velocity change rate is greater than the preset threshold and exists continuously within a certain depth range, the corresponding section is identified as a loosened surrounding rock zone. The depth from the orifice to the wave velocity recovery to the stable zone is defined as the loosening zone thickness.

[0009] As a further improvement of the present invention, the data sequence includes at least one of the following: longitudinal wave velocity, transverse wave velocity, and wave velocity attenuation coefficient.

[0010] As a further improvement of the present invention, in step S2, determining the equivalent radius of the cavity includes: When the cross-section of the cavern is circular, the equivalent radius is half the diameter of the cavern, and the equivalent radius R = D / 2, where D is the diameter of the cavern; When the cross-section of the cavern is not circular, the equivalent radius is determined according to the principle of equivalent area, which is R=A / π, where A is the cross-sectional area.

[0011] As a further improvement of the present invention, the method further includes: S5, output the rockburst tendency evaluation result, which includes the numerical result of the normalized loosening zone coefficient and / or the classification result of the rockburst tendency level, to guide the adjustment of support design, pressure relief measures or construction methods.

[0012] As a further improvement of the present invention, in step S4, the determination of the rockburst tendency level is as follows: When the normalized loosening zone coefficient is less than or equal to the first threshold, it is determined to be a strong rockburst tendency; When the normalized loosening zone coefficient is greater than the first threshold and less than or equal to the second threshold, it is determined to be a moderate rockburst tendency. When the normalized loosening zone coefficient is greater than the second threshold and less than or equal to the third threshold, it is determined to be a weak rockburst tendency; When the normalized loosening zone coefficient is greater than the third threshold, it is determined that there is no tendency for rockburst.

[0013] As a further improvement of the present invention, the first threshold is 0.30, the second threshold is 0.60, and the third threshold is 1.00.

[0014] As a further improvement of the present invention, the normalized loosening zone coefficient is negatively correlated with the rockburst tendency. The smaller the normalized loosening zone coefficient, the higher the integrity of the surrounding rock, the stronger the elastic energy accumulation capacity, and the higher the rockburst tendency.

[0015] As a further improvement of the present invention, the normalized loosening zone coefficient is used to eliminate the influence of different engineering scales on the rockburst tendency evaluation and to characterize the relative relationship between the integrity of the surrounding rock and the elastic energy accumulation capacity.

[0016] Beneficial effects: 1. The method provided by this invention is simple to test and low in cost. It only requires conventional field non-destructive testing such as sonic logging to obtain core parameters, completely eliminating the dependence on indoor rock mechanics tests and empirical formulas.

[0017] 2. The method provided by this invention has a clear physical meaning, is directly related to the actual damage state of the surrounding rock and the remaining energy storage capacity, and the loosening zone index has clear physical and engineering significance.

[0018] 3. The method provided by this invention provides intuitive grading results, outputting four levels of results: strong / medium / weak / no, which is convenient for engineers to use directly for support design, pressure relief measures, or construction method adjustments.

[0019] 4. The method provided by this invention has high spatial resolution and can continuously test along the borehole to achieve precise positioning of rockburst hazard zones.

[0020] 5. The method provided by this invention complements existing criteria and provides a new rapid screening tool for projects such as high-stress hard rock tunnels and deep mines.

[0021] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and in order to make the above and other objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described below. Attached Figure Description

[0022] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the present invention will be briefly described below. Obviously, the drawings described below are merely some embodiments of the present invention, and those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0023] Figure 1 This is a flowchart illustrating the rockburst tendency evaluation method based on loosened zone test results provided in this embodiment of the invention.

[0024] Figure 2 This is a schematic diagram of the calculation of the normalized loosened zone rockburst tendency index provided in an embodiment of the present invention.

[0025] Figure 3 This is a schematic diagram of the wave velocity-hole depth curve and loosening zone division provided in an embodiment of the present invention.

[0026] Figure 4 This is a rockburst tendency zoning map based on loosened zone test results provided in an embodiment of the present invention.

[0027] Figure 5 This is a longitudinal profile of the topography and geology of the Micangshan Tunnel provided in Embodiment 1 of the present invention.

[0028] Figure 6 This is a diagram of the on-site damage provided in Embodiment 1 of the present invention.

[0029] Figure 7 The main unit of the RSM-SY6 borehole acoustic wave tester provided in Embodiment 2 of the present invention is as follows.

[0030] Figure 8 This is a schematic diagram of on-site acoustic wave testing provided in Embodiment 2 of the present invention.

[0031] Figure 9 This is the uniaxial compressive stress-strain curve provided in Embodiment 2 of the present invention.

[0032] Figure 10 This is the uniaxial compression test curve of 1600m granite provided in Embodiment 2 of the present invention.

[0033] Figure 11 This is the uniaxial compression loading and unloading stress-strain curve provided in Embodiment 2 of the present invention.

[0034] Figure 12 This is the cyclic loading and unloading test curve of 1600m granite provided in Embodiment 2 of the present invention. Detailed Implementation

[0035] The embodiments of the technical solution of the present invention will now be described in detail with reference to the accompanying drawings. These embodiments are merely illustrative of the technical solution of the present invention and are therefore intended to limit the scope of protection of the present invention.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the invention, are intended to cover non-exclusive inclusion.

[0037] In the description of the embodiments of this invention, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this invention, "multiple" means two or more, unless otherwise explicitly defined.

[0038] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0039] In the description of the embodiments of this invention, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0040] In the description of the embodiments of the present invention, the term "multiple" refers to two or more (including two), similarly, "multiple groups" refers to two or more (including two groups), and "multiple pieces" refers to two or more (including two pieces).

[0041] In the description of the embodiments of the present invention, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of the present invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of the present invention.

[0042] In the description of the embodiments of the present invention, unless otherwise explicitly specified and limited, the technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of the present invention according to the specific circumstances.

[0043] The loosened zone of the surrounding rock is a direct spatial manifestation of the crack propagation, strength degradation, and stress release that occur in the surrounding rock after excavation. The smaller the thickness of the loosened zone, the more intact the surrounding rock, the stronger its elastic energy accumulation capacity, and the higher its tendency for rockburst. Therefore, the results of loosened zone tests can directly reflect whether the energy release conditions required for rockburst occurrence have been disrupted.

[0044] To address the technical problems of existing technologies neglecting the actual damage and energy release state of surrounding rock after excavation due to disturbance and stress relief, the inability of laboratory test parameters to reflect the true structural state of the surrounding rock after excavation, and the failure of stress indices to consider whether the surrounding rock has released elastic energy in advance through fracture development, thus failing to quantify the relationship between the integrity of the surrounding rock and rockburst, this invention provides a rockburst tendency evaluation method based on loosened zone test results. Through a technical path of measuring damage results (loosened zone thickness), inverting remaining energy storage capacity, and quantifying rockburst tendency, it achieves efficient and direct characterization of the energy conditions for rockburst generation. The loosened zone thickness reflects the actual degree of stress release and fracture development in the surrounding rock after excavation and unloading, providing a quantitative expression of the damage results. The equivalent radius of the cavern eliminates differences in engineering scales, making the normalized loosened zone coefficient comparable across engineering projects. The two work synergistically through their ratio, linking the energy release that has occurred with the remaining energy storage potential. The smaller the normalized loosened zone coefficient, the less energy has been released, the more remaining energy is stored, and the more abundant the rockburst power source.

[0045] Please refer to Figures 1 to 4As shown, this embodiment of the invention provides a method for evaluating rockburst tendency based on loosened zone test results, including the following steps: Step S1, loosened zone test of surrounding rock S11, Testing methods: Test holes are arranged in the surrounding rock of the roadway or tunnel, and one or more of the following testing methods are adopted: sonic logging; cross-hole sonic testing; seismic wave testing; other equivalent surrounding rock damage detection methods.

[0046] S12, Data Acquisition: Acquire the data sequence of the test signal as the hole depth changes, including but not limited to: longitudinal wave velocity; transverse wave velocity; wave velocity attenuation characteristics.

[0047] S13, Rules for determining the thickness of the loosened zone: Analyze the wave velocity variation curve along the hole depth direction, and determine the thickness of the loosened zone according to the following rules. t L : ① When the wave velocity value is significantly lower than the average wave velocity in the deep stable region; ②And the rate of change of wave velocity is greater than a preset threshold; ③ And it exists continuously within a certain depth range; This section is then classified as a loosened rock zone. The depth from the borehole opening to the point where the wave velocity recovers to the stable zone is defined as the loosened zone thickness. t L This judgment rule ensures that the acquisition of the loosening zone thickness is objective and repeatable.

[0048] Step S2, Determine the equivalent radius of the cavern. S21, Circular cross-section: When the cross-section of a roadway or tunnel is circular: R=D / 2 where D is the tunnel diameter.

[0049] S22, Non-circular cross-section: When the cross-section is non-circular, it is determined according to the principle of equivalent area: R=A / π, where A is the cross-sectional area.

[0050] Step S3: Construct the normalized loosening zone index Define the normalized loosening zone coefficient K L : K L = t L / R ; in, t L For the thickness of the loose ring, R This is the equivalent radius of the cavern. This indicator reflects the proportional relationship between the loosened zone thickness and the cavern size, and is used to eliminate the influence of different engineering scales.

[0051] Step S4, Rockburst Tendency Classification Determination according to K L The range of values ​​is used to classify the rockburst tendency of the surrounding rock: when K L ≤0.30, judged as having a strong tendency for rockburst; When 0.30 < K L ≤0.60, judged as moderate rockburst tendency; When 0.60 < K L ≤1.00 indicates a weak tendency for rockburst; when K L >1.00, indicating no tendency for rockburst.

[0052] Step S5: Evaluation Result Output and Application The rockburst tendency assessment results are output as follows: ①Numerical results ( K L ); ② Grading results (none / weak / medium / strong); ③ It can be used to guide support design, pressure relief measures, or adjustments to construction methods.

[0053] In this invention, the normalized loosening zone coefficient K L The threshold is determined based on the following criteria: (1) Threshold for strong rockburst tendency: K L ≤0.30 Studies have shown that stress concentration / stress abrupt changes related to strain bursting often occur at the outer edge of the inner shell of the tunnel perimeter, and their scale can involve 25%-35% of the tunnel radius. For example, in a comparative study of the Jinping II Hydropower Station, acoustic testing revealed that the average depth of the EDZ (Earthquake Zone) in the TBM section was smaller, but the scale and frequency of TBM-induced rockbursts were larger, consistent with the empirical trend of "thin damage zone → stronger energy storage → more prone to strong rockbursts." In the case study, the tunnel excavation diameter was approximately 12.4m (R≈6.2m) and the average depth of the EDZ was approximately 1.82m. Based on the normalized loosened zone rockburst tendency test coefficient, the calculated value is approximately 0.29R, which should be the critical threshold for strong rockburst tendency. Therefore, using... K L A value of ≤0.30 effectively characterizes the strong rockburst tendency of the surrounding rock. TBM is a tunneling method, specifically a section where a tunnel boring machine is used for excavation and lining. EDZ stands for Excavation Damaged Zone, used to characterize the degree of damage to the surrounding rock caused by excavation.

[0054] (2) Threshold for moderate rockburst tendency: 0.30 <K L ≤0.60 The strain bursting depth is the crack propagation depth or plastic deformation depth at which bursting fracture occurs under specific stress conditions. This depth falls between the mean failure depth and the ultimate failure depth, and according to an example in the prior art (from actual observations obtained in 1992 from the URL (Underground Research Laboratory of Canadian Atomic Energy Corporation) underground simulation laboratory), the radius R = 3m. S L When ≤1 ( S L The stress intensity ratio, i.e. S L = σ max / UCS ,in, σ max For the maximum tangential elastic stress, UCS (uniaxial compressive strength), strain burst depth d SB Between 0 and 1.65m, normalized to the radius, it becomes 0 to 0.55R. This provides direct support for the statement that "the upper limit of moderate inclination is close to 0.55R, and 0.60R is used as the boundary in engineering." In existing technology, field records from URL's Mine-by tests (stopeside tests or tunneling tests) also mention that the occurrence scale of sidewall spalling / brittle failure is approximately 0.5-1m (varying with location and stage). In typical small-radius test roadways (1-2m radius), the depth of this type of "spalling / gap" often falls within the range of 0.3-0.6R after normalization (consistent order of magnitude). Therefore, using 0.30 < K L A value of ≤0.60 can effectively characterize the tendency of the surrounding rock to exhibit moderate rockburst.

[0055] (3) Threshold for weak rockburst tendency: 0.60 < K L ≤1.00 When the surrounding rock is more fragmented / blocky, the more typical problems become rockburst issues such as spalling, wedge instability, and plastic deformation (structurally controlled / gradual), rather than the typical "explosive ejection" found in highly intact, hard, and brittle rocks. This provides directional evidence for the mechanism of "thicker loosened zone → weaker rockburst tendency." K L A value >0.60 indicates that the loosened zone thickness exceeds the maximum depth that typical strain-induced bursting can achieve, making it difficult for dynamic failure to form a "fully ejectable elastic energy body," thus naturally reducing the rockburst tendency. Therefore, using 0.60 < K LThe logic behind ≤1.00 representing “weak tendency” is: exceeding the strain burst depth envelope → dynamic disaster is significantly weakened, but local spalling or local dynamics controlled by structure may still occur before approaching 1.0R.

[0056] (4) Threshold for no rockburst tendency: K L >1.00 When rock masses transition from intact, hard, and brittle to significantly fractured (highly fractured, blocky, or worse), the dominant risk shifts from rockburst to short self-stabilization times, spalling, and plastic deformation. K L A value of >1.0 indicates that the damage / loosening has reached the radius level or above, which is equivalent to "the surrounding rock no longer possesses the complete energy storage body required for a typical rockburst" in engineering terms.

[0057] Example 1 Embodiment 1 of this invention provides a method for evaluating rockburst tendency based on loosened zone test results. The specific application environment is as follows: The Micangshan Ultra-Long Tunnel, the longest highway tunnel under construction in Southwest China, has its entrance located in Nanzheng County, Shaanxi Province, and its exit in Nanjiang County, Sichuan Province, spanning the two provinces. It is a twin-track separated tunnel. The left track is 13,833 m long, the right track is 13,792 m long, the distance between the left and right tracks is 40 m, the design speed is 80 km / h, the tunnel adopts a semi-circular arch shape, the tunnel radius is 8.55 m, and the maximum burial depth is approximately 1000 m. The topography and geological longitudinal section of the Micangshan Tunnel are as follows. Figure 5 As shown, the tunnel site is located in a medium-deeply dissected erosion-tectonic denudation landform area. The surrounding rock is mainly quartz diorite, interbedded with lenses of granite, diorite, etc., which is a typical hard rock tunnel.

[0058] The Micangshan Tunnel has a burial depth of 650-850m in its middle section. According to the hydraulic fracturing method for in-situ stress testing, the stress in the section from K45+900 to K46+200 in the middle of the tunnel is dominated by the maximum horizontal principal stress, with the direction consistent with the structural direction. The maximum horizontal principal stress measured in this section is 15.876 MPa, and the uniaxial saturated compressive strength is 65.7 MPa, indicating that the surrounding rock is brittle and hard. During construction in this section, the tunnel face experienced several collapses, resulting in cracking and spalling of the shotcrete, breakage and detachment of the steel arch frame, and other damage. One instance of this damage is described below. Figure 6 As shown. According to on-site records, these collapses all occurred within 10 minutes after the blasting at the working face, accompanied by muffled sounds from inside the surrounding rock. Finally, the stress released inside the surrounding rock exceeded the bearing capacity of the initial support, causing structural failure and the collapse of the surrounding rock fragments.

[0059] After the area was treated, tunneling continued. During the construction process, the RSM-RCT(B) loosening ring tester was used to conduct single-hole loosening ring tests with one launch and two receivers. A total of 3 locations were selected for detection, with a detection depth of 20m and a measuring point displacement of 0.2m. 40 sets of data were collected for each borehole. The loosening ring depth of borehole #1 was 1.6m, that of borehole #2 was 1.2m, and that of borehole #3 was 1.4m, with an average loosening ring depth of 1.4m.

[0060] Based on the normalized loosening zone coefficient K L Calculation formula K L = t L / R ; in, t L For the thickness of the loose ring, R This is the equivalent radius of the cavern. This indicator reflects the proportional relationship between the loosened zone thickness and the cavern size, and is used to eliminate the influence of different engineering scales.

[0061] Therefore, substituting the loosened zone depth of 1.4m and the tunnel radius of 8.55m into the formula, we can obtain the normalized loosened zone coefficient. K L =0.164.

[0062] Rockburst tendency zoning map based on loosened zone test results ( Figure 4 It can be seen that, K L =0.164 < 0.3 indicates a strong tendency for rockbursts, meaning the area possesses the conditions for intense rockbursts. Field construction has also verified the high rockburst tendency in this area, with rockburst phenomena already observed in some areas.

[0063] Example 2 Embodiment 2 of this invention provides a method for evaluating rockburst tendency based on loosened zone test results. The specific application environment is as follows: The Sanshandao ultra-deep vertical shaft is located in the Xishan mining area, with a designed depth of 1915m, a net cross-sectional diameter of 10.5m, a shaft excavation cross-sectional diameter of 11.5m, and a designed shaft opening position of +5m. The ultra-deep vertical shaft has now been completed, becoming the deepest vertical shaft in Asia and the fifth deepest in the world. The main lithology of the construction area is granite, with the main faults being F1 and F3, with traversing depths of -960m and -1600m, respectively. Detailed in-situ stress tests have been conducted in the early stages to understand the direction and magnitude of in-situ stress in the deep region. The maximum horizontal principal stress in the -1000m region is 36.37 MPa, with a direction of N 77.31°W, and the minimum horizontal principal stress is 14.77 MPa. In the -1600m region, the maximum horizontal principal stress is 51.88 MPa, with a direction of N 75.18°W, and the minimum horizontal principal stress is 18.46 MPa. In the -2000m region, the maximum horizontal principal stress is 61.53 MPa, with a direction of N 63.17°W, and the minimum horizontal principal stress is 27.50 MPa. At 1000m, the granite is gray monzogranite with a compressive strength of 183 MPa, an elastic modulus of 74.31 GPa, and a tensile strength of 6.73 MPa. At 1600m, the granite is grayish-white monzogranite with a compressive strength of 184.84 MPa, an elastic modulus of 57.73 GPa, and a tensile strength of 9.86 MPa. At 2000m, the granite is white monzogranite with a compressive strength of 57.81 MPa, an elastic modulus of 28.44 GPa, and a tensile strength of 5.04 MPa.

[0064] A loosening zone test was conducted at -1600m using an RSM-SY6 borehole acoustic wave analyzer equipped with a single-transmitter, dual-receiver probe. Figure 7 As shown in the diagram, the on-site acoustic wave test is as follows: Figure 8 As shown.

[0065] Using 5.5 km / s as the longitudinal wave velocity of intact monzogranite, the longitudinal wave velocity of the borehole wall was compared with it, and the integrity coefficient k was calculated using the formula. When the value was less than 0.3, the rock was considered to have broken into a loose zone. The drilling depths were 4.7 m for ZK1590-1, 4.7 m for ZK1590-2, 4.9 m for ZK1590-3, and 2.4 m for ZK1590-4.

[0066] Because water is required as a coupling medium during drilling testing, the borehole has a certain inclination angle during construction. When calculating the test results, it is necessary to convert them into horizontal distances. The specific test results are shown in the table below for the test results and corresponding test curves of SJ1590-1, SJ1590-2, SJ1590-3, and SJ1590-4.

[0067] Table 1 Test Results of SJ1590-1 Table 2 Test Results of SJ1590-2 Table 3 Test Results of SJ1590-3 Table 4 Test Results of SJ1590-4 The extent of surrounding rock damage was detected at the 1590m working face of the vertical shaft. Holes #1, #2, #3, and #4 were drilled in the four directions (N, E, S, W) on the shaft wall. A borehole acoustic wave tester was used to detect the depth of surrounding rock damage. The results showed that the loosened zone ranges were 1.5m for #1, 1m for #2, 1.49m for #3, and 1.59m for #4. Comprehensive calculations indicate that the average range of the loosened zone at -1600m is 1.395m.

[0068] Based on the normalized loosening zone coefficient K L Calculation formula K L = t L / R ; in, t L For the thickness of the loose ring, R This is the equivalent radius of the cavern. This indicator reflects the proportional relationship between the loosened zone thickness and the cavern size, and is used to eliminate the influence of different engineering scales.

[0069] Therefore, substituting the loosened zone depth of 1.395m and the roadway radius of 11.5m into the formula, we can obtain the normalized loosened zone coefficient. K L =0.121.

[0070] Rockburst tendency zoning map based on loosened zone test results ( Figure 4 It can be seen that, K L =0.121<0.3 indicates a strong tendency for rockbursts, meaning the conditions for a strong rockburst are present.

[0071] Subsequent indoor mechanical experiments were conducted to verify the theory, selecting four rockburst tendency characterization indicators for verification, namely the impact energy index representing its own lithology. W cf and elastic strain energy index W et Rock mass quality index (RQD) indicates rock mass integrity, and geostress index (S) characterizes the environment.

[0072] The impact energy index refers to the ratio of the elastic strain energy stored in the rock specimen before the peak load to the energy consumed during the process from the peak load until complete failure. Figure 9 As shown, the calculation formula is as follows: ; in, W cf E1 is the impact energy index; E2 is the elastic strain energy, the recoverable energy stored before reaching peak strength during loading; E3 is the plastic deformation energy, the energy consumed by the rock during the failure process, including the energy consumed by irreversible deformation such as microcracks and friction slip.

[0073] Uniaxial compression curves are obtained through mechanical experiments, such as Figure 10 As shown, the impact energy index is calculated. Table 5 shows the discrimination criteria, and Table 6 shows the experimental calculation results.

[0074] Table 5. Criteria for Determining Rockburst Level by Energy Storage Index Table 6 Calculation results of impact energy index The elastic energy index (elastic strain energy index), also known as the impact tendency index, indicates the amount of energy released upon failure. A higher value indicates greater energy release during rockburst and its intensity. Its calculation formula is: ; in, It is the strain energy storage index (elastic strain energy index); The retained elastic strain energy (kJ); The strain energy lost is (kJ).

[0075] Cyclic loading and unloading curves are obtained through mechanical experiments, such as... Figures 11 to 12 As shown, the elastic energy index is calculated. Table 7 shows the discrimination criteria, and Table 8 shows the experimental calculation results.

[0076] Table 7 Elastic Strain Energy Index Rockburst Level Judgment Criteria Table 8 Calculation results of elastic strain energy index Generally, rock masses with well-developed fissures have poor integrity and are less prone to high stress concentration and energy accumulation. Therefore, the degree of fissure development in a rock mass reflects, to some extent, its tendency to produce rockbursts. The rock mass quality factor (RQD) is a simple and practical indicator for describing the integrity of a rock mass; the RQD value can be used to approximately analyze and understand the rockburst tendency of a rock mass.

[0077] The criteria for judging the rockburst level of RQD value are shown in Table 9, and Table 10 shows the experimental calculation results.

[0078] Table 9. RQD Value Rockburst Level Judgment Criteria Table 10 RQD Value and Rockburst Level Determination In areas of high geostress, rocks possess significant elastic strain energy and are most prone to rockburst. This is generally expressed as maximum geostress. The greater the maximum geostress, the greater the accumulated elastic strain energy in the rock. When the elastic strain energy reaches the critical elastic energy for rockburst before the rock reaches its peak strength, a rockburst is imminent. The geostress index S refers to the maximum geostress. Uniaxial compressive strength of rock The ratio, that is: .

[0079] The criteria for judging rockburst level based on ground stress index are shown in Table 11, and Table 12 shows the experimental calculation results.

[0080] Table 11. Criteria for Determining Rockburst Grade Based on Geostress Index Table 12 Results of Rockburst Judgment Based on Geostress Index Calculations using four characterization indices revealed that the rockburst tendency in this area is characterized by a strong rockburst tendency, consistent with the normalized loosened zone coefficient. K L The calculation results are the same, both showing a strong tendency for rockburst.

[0081] The calculations in the above embodiments, as well as the on-site construction verification and indoor mechanical theory calculations, all agree with the normalized loosening zone coefficient. K L The calculation results are similar to those of other methods, which proves that the evaluation method provided by this invention is highly scientific and reliable.

[0082] In summary, this invention provides a rockburst tendency evaluation method based on loosened zone test results, belonging to the field of rockburst disaster prediction in underground engineering. Addressing the problem that existing rockburst tendency evaluation methods rely on laboratory tests and neglect the actual damage state of the surrounding rock after excavation, this invention proposes obtaining the thickness of the loosened zone and the equivalent radius of the cavern through field testing, constructing a normalized loosened zone coefficient to characterize the remaining energy storage capacity of the surrounding rock. The smaller the normalized loosened zone coefficient, the more intact the surrounding rock, the stronger its elastic energy accumulation capacity, and the higher the rockburst tendency. Based on the comparison between the normalized loosened zone coefficient and a preset threshold, the rockburst tendency is divided into four levels: strong, medium, weak, and none. This invention is entirely based on field non-destructive testing, requiring no laboratory mechanical tests or empirical parameters. It has advantages such as simple operation, low cost, clear physical meaning, and intuitive classification results. It can effectively explain the engineering phenomenon of no rockburst in high-stress areas but rockburst in low-stress areas, providing a scientific basis for rapid assessment and prevention of rockburst risks in deep underground engineering.

[0083] It should be noted that the present invention is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments that have the same structure and perform the same effects as the technical concept within the scope of the present invention are included within the scope of the present invention. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of the present invention, are also included within the scope of the present invention.

Claims

1. A method for evaluating rockburst tendency based on loosened zone test results, characterized in that, Includes the following steps: S1, based on field tests in the area to be evaluated, the thickness of the loosened zone of the surrounding rock after excavation is obtained; S2, determine the equivalent radius of the cavern in the area to be evaluated; S3, construct a normalized loosening ring coefficient, wherein the normalized loosening ring coefficient is the ratio of the loosening ring thickness to the equivalent radius; S4. Determine the rockburst tendency level of the surrounding rock based on the normalized loosening zone coefficient. In step S4, the rockburst tendency level is determined as follows: When the normalized loosening zone coefficient is less than or equal to the first threshold, it is determined to be a strong rockburst tendency; When the normalized loosening zone coefficient is greater than the first threshold and less than or equal to the second threshold, it is determined to be a moderate rockburst tendency. When the normalized loosening zone coefficient is greater than the second threshold and less than or equal to the third threshold, it is determined to be a weak rockburst tendency; When the normalized loosening zone coefficient is greater than the third threshold, it is determined that there is no tendency for rockburst. The first threshold is 0.30, the second threshold is 0.60, and the third threshold is 1.00; The normalized loosening zone coefficient is negatively correlated with rockburst tendency. The smaller the normalized loosening zone coefficient, the higher the integrity of the surrounding rock, the stronger the elastic energy accumulation capacity, and the higher the rockburst tendency.

2. The method for evaluating rockburst tendency based on loosened zone test results according to claim 1, characterized in that, The process of obtaining the thickness of the loosened ring in step S1 includes: Test holes are arranged in the surrounding rock, and at least one of the following methods, namely acoustic logging, cross-hole acoustic testing, and seismic testing, is used to obtain the data sequence of test signals as the hole depth changes. The wave velocity change curve is analyzed based on the data sequence, and the thickness of the loosening ring is determined according to a preset rule.

3. The method for evaluating rockburst tendency based on loosened zone test results according to claim 2, characterized in that, The preset rules include: When the wave velocity value is significantly lower than the average wave velocity in the deep stable zone, and the wave velocity change rate is greater than the preset threshold and exists continuously within a certain depth range, the corresponding section is identified as a loosened surrounding rock zone. The depth from the orifice to the wave velocity recovery to the stable zone is defined as the loosening zone thickness.

4. The method for evaluating rockburst tendency based on loosened zone test results according to claim 2, characterized in that, The data sequence includes at least one of the following: longitudinal wave velocity, transverse wave velocity, and wave velocity attenuation coefficient.

5. The method for evaluating rockburst tendency based on loosened zone test results according to claim 1, characterized in that, In step S2, determining the equivalent radius of the cavity includes: When the cross-section of the cavern is circular, the equivalent radius is half the diameter of the cavern, and the equivalent radius R = D / 2, where D is the diameter of the cavern; When the cross-section of the cavern is not circular, the equivalent radius is determined according to the principle of equivalent area, which is R=A / π, where A is the cross-sectional area.

6. The method for evaluating rockburst tendency based on loosened zone test results according to claim 1, characterized in that, The method further includes: S5, output the rockburst tendency evaluation result, which includes the numerical result of the normalized loosening zone coefficient and / or the classification result of the rockburst tendency level, to guide the adjustment of support design, pressure relief measures or construction methods.

7. The method for evaluating rockburst tendency based on loosened zone test results according to claim 1, characterized in that, The normalized loosening zone coefficient is used to eliminate the influence of different engineering scales on the rockburst tendency evaluation and to characterize the relative relationship between the integrity of the surrounding rock and the elastic energy accumulation capacity.

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