Rock damage analysis method and system considering comprehensive action of blasting and ground stress

Abstract

The present application relates to the technical field of surrounding rock damage analysis, especially to a surrounding rock damage analysis method and system considering the comprehensive action of blasting and ground stress, the method comprising the following steps: obtaining the blasting load pressure rise time, the blasting load peak value and the positive pressure action time, and then determining the change process of the blasting load pressure with time, i.e. the blasting load change history; estimating the size, starting time and duration of the ground stress transient unloading, and then determining the ground stress transient unloading change history; considering the blasting and ground stress at the same time, obtaining the comprehensive damage variable of the surrounding rock mass at different positions; reducing the mechanical parameters of the surrounding rock mass according to the comprehensive damage variable, and then obtaining the safety factor of the surrounding rock combined with the surrounding rock stress monitoring result and optimizing the support design. The present application establishes a surrounding rock damage calculation formula considering the comprehensive action of blasting and ground stress, thereby improving the accuracy of the surrounding rock damage evaluation and the safety of the tunnel blasting excavation.

Description

Technical Field

[0001] This invention relates to the field of surrounding rock damage analysis technology, and in particular to a method and system for surrounding rock damage analysis that takes into account the combined effects of blasting and geostress. Background Technology

[0002] Many scholars have conducted in-depth research on the disturbance mechanism of surrounding rock in rock blasting excavation, damage evolution and distribution characteristics, damage detection and prediction, and have achieved certain research results, which have also played a positive guiding and reference role in engineering practice. However, considering the complexity of the damage effect of surrounding rock in rock blasting excavation, current research still has some shortcomings in the following aspects.

[0003] Currently, research on the damage effect of single-hole blasting in deep rock masses mainly considers the combined effect of blasting load and ground stress "inhibition". The excavation unloading effect is generally treated as a quasi-static mechanical process. There is still a lack of a method for analyzing the damage of surrounding rock that comprehensively considers blasting load, ground stress "inhibition" and transient ground stress unloading, which increases the safety hazards in the process of tunnel blasting excavation. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method and system for analyzing surrounding rock damage that considers the combined effects of blasting and ground stress.

[0005] To achieve the above objectives, in a first aspect, this invention provides a method for analyzing surrounding rock damage considering the combined effects of blasting and geostress. The method includes the following steps: obtaining the blasting load intensification time, peak blasting load, and positive pressure duration to determine the blasting load pressure variation over time, i.e., the blasting load variation history; estimating the magnitude, start time, and duration of transient geostress unloading to determine the transient geostress unloading variation history; based on the obtained blasting load variation history and the transient geostress unloading variation history, simultaneously considering blasting and geostress to obtain comprehensive damage variables at different locations on the surrounding rock mass; and reducing the mechanical parameters of the surrounding rock mass according to the comprehensive damage variables to obtain the surrounding rock safety factor and optimize the support design. This method establishes a formula for calculating surrounding rock damage that comprehensively considers the combined effects of blasting and geostress, thereby improving the accuracy of surrounding rock damage evaluation and the safety of tunnel blasting excavation.

[0006] Optionally, the step of obtaining the blast load pressurization time, peak blast load, and positive pressure application time, and then determining the blast load pressure change process over time, i.e., the blast load change history, includes the following steps: Obtain the blast load intensification time, peak blast load, and duration of positive pressure application; Based on the trigonometric function expression, the blast load variation history is established, which includes three parameters: the blast load pressurization time, the peak value of the blast load, and the positive pressure application time.

[0007] Optionally, the blasting load variation history satisfies the following relationship: in, This represents the change of the blasting load pressure P over time t. The duration of the positive pressure application. The peak value of the blasting load is... The time for pressurizing the explosive load.

[0008] Optionally, the transient unloading history of the ground stress satisfies the following relationship: in, Transient unloading pressure of ground stress The process of change with time t The magnitude of the transient unloading of ground stress on the excavation boundary during the blasting of the i-th borehole. This refers to the start time of the transient unloading of the ground stress. This represents the change of the blasting load pressure P over time t. , The stopping time of the transient unloading of the ground stress. The duration of the positive pressure application is denoted as .

[0009] Optionally, the step of obtaining the comprehensive damage variables at different locations on the surrounding rock mass, based on obtaining the blasting load variation history and the transient unloading variation history of the ground stress, while simultaneously considering blasting and ground stress, includes the following steps: Simultaneously considering blasting and in-situ stress, the crack half-length and number of cracks in the surrounding rock mass are calculated, and then the rock mass damage variables under the in-situ stress inhibition are calculated. Based on the rock mass damage variables under the aforementioned in-situ stress suppression, the comprehensive damage variables at different locations on the surrounding rock mass under the combined effects of blasting and in-situ stress are calculated.

[0010] Optionally, the rock mass damage variables under the in-situ stress suppression effect satisfy the following relationship: in, Let r be the rock mass damage variable under the aforementioned stress suppression effect, and r be the distance from the blast source. Poisson's ratio, The number of cracks. Let k be the half-length of the crack, and k be a proportionality coefficient. This represents the peak load on the borehole wall. The radius of the borehole is... The attenuation coefficient is... This refers to geostress.

[0011] Optionally, the damage to the surrounding rock mass under the combined effects of in-situ stress and blasting is caused by the dynamic effects of the blast stress wave, the quasi-static effects of the blasting gas, the in-situ stress suppression effect, and the quasi-dynamic effects of the transient unloading of in-situ stress.

[0012] Optionally, the comprehensive damage variables satisfy the following relationship: in, For the aforementioned comprehensive damage variable, The damage variable under the dynamic action of the explosion stress wave is... The damage variable is the quasi-static action of the explosive gas. The damage variable is defined as the quasi-dynamic action of transient unloading of ground stress. For dynamic Poisson's ratio, This is the proportionality coefficient under the dynamic action of the explosion stress wave. The number of cracks under the action of the explosion stress wave. The crack half-length activated by the explosion stress wave. For dynamic fracture toughness, The peak load on the borehole wall under the dynamic action of the explosion stress wave is [value missing]. The radius of the borehole is... The attenuation coefficient is... For geostress, The static Poisson's ratio This is the proportionality coefficient under quasi-static action of the explosive gas. and For adjustment coefficients, The number of cracks caused by the explosive gas. The crack half-length activated by the explosive gas, For static fracture toughness, The peak load on the borehole wall under quasi-static action of the explosive gas is [value missing]. This is the proportionality coefficient under the quasi-dynamic action of the transient unloading of ground stress. The peak load on the borehole wall under the quasi-dynamic action of transient unloading of ground stress is given by r, where r is the distance from the blast source. The crack half-length is activated by the transient unloading of the ground stress.

[0013] Optionally, the step of reducing the mechanical parameters of the surrounding rock mass based on the comprehensive damage variables to obtain the surrounding rock safety factor and optimize the support design includes the following steps: Based on the strain equivalence assumption, the mechanical parameters of the surrounding rock mass are reduced using the aforementioned comprehensive damage variables; The safety factor of the surrounding rock is obtained based on the reduced mechanical parameters, and then the support design of the surrounding rock is optimized.

[0014] Secondly, the present invention provides a surrounding rock damage analysis system that considers the combined effects of blasting and geostress. The surrounding rock damage analysis system that considers the combined effects of blasting and geostress includes: a data acquisition device, a data output device, a processor, and a storage device. The storage device includes a computer-readable storage medium storing a computer program. The computer program includes program instructions, which, when executed by the processor, cause the processor to implement the surrounding rock damage analysis method that considers the combined effects of blasting and geostress provided by the present invention.

[0015] The present invention has the following beneficial effects: 1. A calculation formula for surrounding rock damage variables considering the combined effects of blasting and ground stress was established, which can improve the accuracy of surrounding rock damage evaluation in single-hole blasting.

[0016] 2. Based on the calculation of surrounding rock damage variables considering the combined effects of blasting and ground stress, this method reduces the mechanical parameters of the surrounding rock mass according to the calculated damage variables, and then optimizes the support design by combining the surrounding rock stress monitoring results, thereby improving the safety of tunnel blasting excavation.

[0017] 3. A system adapted to this method has been established. This system can operate stably and not only improves the practicality of this method, but also facilitates its promotion. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a flowchart illustrating the surrounding rock damage analysis method considering the combined effects of blasting and ground stress according to an embodiment of the present invention. Figure 2These are the blasting load variation history curves and the transient unloading variation history curves of ground stress in embodiments of the present invention; Figure 3 This is a schematic diagram of the coupling process between blasting load and transient unloading of ground stress in an embodiment of the present invention; Figure 4 This is a fracture mechanics model of crack propagation in the rock mass surrounding the borehole, as described in an embodiment of the present invention. Figure 5 This is a rock mass crack propagation model under in-situ stress conditions, as described in an embodiment of the present invention. Figure 6 These are damage distribution characteristic curves of surrounding rock under different conditions obtained based on the method in this embodiment of the invention; Figure 7 The figures are the damage range variation curves under the in-situ stress conditions with and without transient unloading, obtained based on the method of this invention, according to an embodiment of the present invention. Figure 8 This is a comparison chart of the damage range of the surrounding rock during blasting excavation under different geostress levels calculated by this method according to an embodiment of the present invention, and the numerical simulation results. Figure 9 This is a schematic diagram of the framework of the surrounding rock damage analysis system that considers the combined effects of blasting and ground stress according to an embodiment of the present invention. Detailed Implementation

[0020] Specific embodiments of the present invention will now be described in detail. It should be noted that the embodiments described herein are for illustrative purposes only and are not intended to limit the invention. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that these specific details are not necessary to practice the invention. In other instances, well-known circuits, software, or methods have not been specifically described to avoid obscuring the invention.

[0021] Throughout this specification, references to "an embodiment," "an embodiment," "an example," or "an example" mean that a particular feature, structure, or characteristic described in connection with that embodiment or example is included in at least one embodiment of the invention. Therefore, the phrases "in an embodiment," "in an embodiment," "an example," or "an example" appearing in various places throughout the specification do not necessarily refer to the same embodiment or example. Furthermore, specific features, structures, or characteristics can be combined in one or more embodiments or examples in any suitable combination and / or sub-combination. Moreover, those skilled in the art will understand that the illustrations provided herein are for illustrative purposes and are not necessarily drawn to scale.

[0022] It should be noted in advance that, in one alternative embodiment, except for independent descriptions, the same symbols or letters appearing in all formulas have the same meaning and value.

[0023] In one optional embodiment, please refer to Figure 1 This invention provides a method for analyzing surrounding rock damage considering the combined effects of blasting and ground stress, the method comprising the following steps: S1. Obtain the blast load pressurization time, blast load peak value and positive pressure action time, and then determine the blast load pressure change process over time, i.e. the blast load change history.

[0024] Step S1 specifically includes the following steps: S11. Obtain the blast load pressurization time, peak blast load, and positive pressure duration.

[0025] Specifically, in this embodiment, after the explosive detonates inside the borehole, the gas pressure on the wavefront can be expressed as: in, The gas pressure on the wavefront; The isentropic exponent of the detonation products is typically taken as 3; The density of the explosive inside the borehole needs to be determined based on the actual type of explosive; VOD is the propagation velocity of the detonation wave, which can be obtained by looking up a table based on the type of explosive or by measuring it through a blasting test.

[0026] For the initial mean pressure of explosive detonation products It can be based on the gas pressure on the wavefront. The calculation is simplified by taking half of the value. For detonation processes under uncoupled charge conditions, the multi-gas equation of state can be used to estimate the peak load pressure of the detonation products before they act on the borehole wall, i.e.: in, This represents the peak load pressure exerted by the detonation products on the borehole wall. For the volume of the explosive, The volume of the borehole is given.

[0027] When detonation products interact with the borehole wall, they increase the peak load pressure acting on the borehole wall, i.e.: in, denoted as , where is the peak value of the blasting load on the borehole wall; n is an amplification factor, typically taken as 8~11. For columnar charge structures, this formula can be further derived as: in, The diameter of the explosive, The diameter of the borehole. The length of the explosive. This represents the length of the borehole.

[0028] The time for the blast load to build up pressure and the time for the barotropic action can be expressed by the rock volumetric compressibility modulus, the distance from the blast center, the borehole radius, the charge amount, and the Poisson's ratio of the rock. in, is the time for the blasting load to build up pressure; K is the volumetric compressibility modulus of rock, determined experimentally; Q is the charge amount; r is the distance from the blast center. The radius of the borehole; The Poisson's ratio for rocks needs to be determined based on the rock type, and is usually taken as 0.2 to 0.3; This refers to the duration of positive pressure application.

[0029] Furthermore, when the explosive detonates from the bottom of the hole, the detonation wave propagates along the explosive towards the hole opening. Because the detonation wave propagates very quickly, the load rise time for the entire process can be approximately equal to the detonation wave propagation time. Therefore, the blasting load pressurization time can be simplified as follows: in, This refers to the length of the explosive charge inside the borehole.

[0030] S12. Based on the trigonometric function expression, establish the blast load variation history, which includes three parameters: the blast load pressurization time, the blast load peak value, and the positive pressure action time.

[0031] Specifically, in this embodiment, to simplify the analysis, a trigonometric function is used to represent the blast load variation history. The trigonometric function expression mainly includes three parameters: blast load inflation time, peak blast load, and barometric pressure duration. The blast load variation history can be expressed as: in, This represents the change of the blast load pressure P over time t. The final blast load change history curve is shown below. Figure 2 As shown.

[0032] S2. Estimate the magnitude, start time and duration of transient unloading of ground stress, and then determine the process of transient unloading of ground stress.

[0033] Specifically, in this embodiment, for underground projects with significant burial depth, the geostress at their location is often substantial, and the rock mass is in a relatively stable state before excavation. When part of the rock mass is excavated, its stable state is disrupted, the initial stress of the rock mass is released to the excavation area, and the stress field is redistributed and adjusted.

[0034] Please see Figure 3, Figure 3 (a) shows a schematic diagram of the blast hole layout before the blasting excavation of a deep-buried circular tunnel. This refers to the radial stress on the excavation boundary during blasting. This refers to the circumferential stress at the excavation boundary during blasting; after the explosive detonates, cracks appear in the rock mass near the blast hole, and the main cracks between adjacent blast holes of the same segment develop preferentially, such as... Figure 3 As shown in (b); when the main cracks penetrate each other, the rock blocks detach from the original rock and are ejected, forming a new excavation face. The in-situ stress within the rock mass near the excavation boundary is also released, as... Figure 3 As shown in (c) in the figure. The transient unloading process of geostress can generally be described by the magnitude, start time and duration of the transient unloading.

[0035] First, estimate the magnitude of the transient unloading of ground stress. Under plane strain and biaxial stress conditions, the stress distribution of the surrounding rock during tunnel blasting excavation can be calculated using the following relationship: in, The radial stress on the excavation boundary during the blasting of the i-th borehole is given. Let be the circumferential stress on the excavation boundary during the blasting of the i-th borehole. Let be the shear stress on the excavation boundary during the blasting of the i-th borehole. Let be the radius of the excavation face formed by the blasting of the i-th blast hole. Let be the radius of the excavation face formed by the blasting of the (i-1)th blast hole. The stress in the original rock in the horizontal direction. This refers to the original rock stress in the vertical direction.

[0036] The magnitude of the transient unloading of ground stress on the excavation boundary during the blasting of the i-th borehole It can be estimated by the change in radial stress at the excavation boundary before and after blasting excavation, that is... , This refers to the radial stress on the excavation boundary before blasting.

[0037] Next, we estimate the start time and duration of the transient unloading of in-situ stress. The process of transient unloading of in-situ stress can be divided into two stages: 1. The initial steady-state stage: Before rock mass excavation, the stress constraint of the excavated rock mass on the surrounding rock can be regarded as applying a reverse load equal to the initial in-situ stress to the surrounding rock; 2. The excavation unloading stage: After the rock mass is removed, the reverse load rapidly decays to zero. In fact, during the rock mass blasting excavation process, when the main crack between the boreholes forms and the rock blocks detach from the original rock, the pressure within the cracks is still greater than the initial in-situ stress, and the stress constraint still exists. Only when the pressure of the explosive gas in the borehole decays to the level of the in-situ stress will the transient unloading phenomenon occur. When the pressure of the explosive gas in the borehole is the same as the atmospheric pressure, the blasting load process and the transient unloading of in-situ stress are completed simultaneously. In the process of transient unloading of in-situ stress, the attenuation of the blasting load is equal to the amount of in-situ stress removed at the tunnel excavation boundary. It can be seen that the process of transient unloading of in-situ stress is the same as the process of blasting load change after the start of unloading.

[0038] Therefore, the start time of transient stress unloading is the moment when the blasting load decays to be equal to the ground stress at the excavation face, and the duration of transient stress unloading is the difference between the termination time of the blasting load and the start time of transient stress unloading. The duration of transient stress unloading is estimated below by refining the blasting load and transient stress unloading processes.

[0039] The process from the detonation of the explosive to the completion of the transient unloading of ground stress can be roughly divided into the following three stages: In the first stage, after the explosive detonates, the detonation wave propagates rapidly along the explosive, the blasting load pressure inside the borehole increases rapidly, and the velocity generated in the surrounding rock of the borehole is... The stress wave caused the crack to initiate and continue to crack. The rate of propagation continues until the main crack between adjacent boreholes is completely connected. During this stage, as the detonation products continuously penetrate the crack, and the initial pressure of the detonation products far exceeds the in-situ stress in the surrounding rock of the borehole, the in-situ stress cannot be unloaded. However, the rate at which the detonation products penetrate the crack is lower than the crack propagation rate. Therefore, there will be partial release of in-situ stress in the local area of ​​the crack. However, compared with the entire process of transient unloading of in-situ stress, the stress unloading effect at this stage is negligible.

[0040] In the second stage, after the main crack is completed and the filler material is ejected, the high-pressure detonation products escape, generating a beam with a velocity of... Furthermore, the sparse wave propagates in the reverse direction, and the pressure inside the borehole gradually decreases. During this stage, although the blasting load pressure inside the borehole decreases rapidly, its value is still higher than the magnitude of the ground stress, and the ground stress cannot be fully unloaded.

[0041] In the third stage, when the back-propagating rarefaction wave reaches the bottom of the aperture, it is reflected and... The velocity propagates along the borehole towards the orifice, further reducing the pressure inside the borehole until it reaches the same level as atmospheric pressure. During this stage, the pressure of the detonation products typically drops to the tens of megapascals, and the ground stress begins to be fully unloaded. Once the blast load pressure has completely decayed, the transient unloading of the ground stress is also complete.

[0042] The timeframes encompassed in the three stages mentioned above include the time for the blast load to increase pressure, the time for the main crack to penetrate between holes, the time for the rarefaction wave to propagate from the borehole opening to the bottom of the hole, and the time for the rarefaction wave to propagate from the bottom of the hole to the opening. The time for the main crack to penetrate between holes, the time for the rarefaction wave to propagate from the borehole opening to the bottom of the hole, and the time for the rarefaction wave to propagate from the bottom of the hole to the opening can be calculated sequentially using the following formulas: in, S represents the time it takes for the main crack to penetrate between holes, and S represents the distance between holes. Let be the time it takes for a rarefaction wave to propagate from the orifice to the bottom of the orifice. This refers to the length of the explosive packing section. The time it takes for a rarefaction wave to propagate from the bottom of the hole to the opening is denoted as .

[0043] Based on the above analysis, the start time of transient unloading of ground stress is after the completion of the second stage and before the completion of the third stage, that is: Duration of transient unloading of ground stress It can be represented as: In summary, the transient unloading history of ground stress satisfies the following relationship: in, Transient unloading pressure of ground stress The process of change with time t This represents the start time of the transient unloading of ground stress. , The stopping time of transient unloading of ground stress. This refers to the duration of positive pressure application.

[0044] The final obtained transient unloading history curve of in-situ stress is as follows: Figure 2 As shown. From Figure 2 It is evident that when using the drill-and-blast method for deep rock excavation, both the blasting load and the transient unloading of in-situ stress affect the surrounding rock damage, differing only in the duration of their effects. Furthermore, at the instant of blasting, the release of in-situ stress at the excavation boundary leads to a rock mass unloading strain rate that is... Within this range, it belongs to a quasi-dynamic mechanical process, therefore the transient unloading effect of ground stress cannot be ignored.

[0045] S3. Based on the obtained blasting load change history and the transient unloading change history of the ground stress, and considering both blasting and ground stress, obtain the comprehensive damage variables at different locations on the surrounding rock mass.

[0046] Analysis in steps S1 and S2 reveals that the damage to the surrounding rock caused by blasting excavation is a result of the coupling effect of blasting load and transient unloading of ground stress. Therefore, when blasting excavation of rock under ground stress conditions, it is necessary to simultaneously consider the dynamic effect of the blasting stress wave, the quasi-static effect of the blasting gas, and the quasi-dynamic effect of transient unloading of ground stress. All three effects will cause varying degrees of damage to the rock mass, but with slight differences in their duration. In other words, when analyzing the damage to the surrounding rock during blasting excavation under ground stress conditions, the combined effects of blasting and ground stress must be considered.

[0047] Step S3 specifically includes the following steps: S31. Simultaneously considering blasting and in-situ stress, calculate the crack half-length and number of cracks in the surrounding rock mass, and then calculate the rock mass damage variables under the action of in-situ stress inhibition.

[0048] Specifically, in this embodiment, deep rock masses generally have good integrity and relatively uniform structure. Therefore, the rock mass can be considered as a linear elastic body with uniformly and randomly distributed microcracks within it. According to the theory of micromechanical damage, the rock mass damage variable D can be defined as: in, This represents the elastic modulus of the rock mass after being subjected to load. Let N be the initial elastic modulus of the rock mass, and N be the number of cracks per unit volume of rock mass. The crack is half its length.

[0049] Without considering geostress conditions, the crack half-length can be determined based on the stress intensity factor at the crack tip. To calculate. When Not greater than the fracture toughness of the rock mass At that time, the crack stops cracking. Therefore, it is generally considered that... As the critical value for solving the crack half-length, that is: Where Y is the shape factor; The nominal stress is equal to the peak stress at the crack tip, i.e., the stress at the distance from the hole wall. Peak stress at that location.

[0050] For borehole blasting, the nominal stress satisfies the following relationship: in, This represents the peak load on the borehole wall. For proportional distance, This is the attenuation coefficient. For relatively intact rock masses, For rock masses containing fractures, The value is not less than 2.

[0051] Finally, without considering geostress, the crack half-length can be solved using the following formula: Assuming that the crack half-length is L without considering geostress conditions, such as Figure 4 As shown in (a) above. Further, as... Figure 4 As shown in (b), increasing ground stress At this time, due to the "inhibition" effect of geostress, the crack half-length will shorten to Furthermore, under the same fracture toughness and peak borehole load, the greater the in-situ stress, the shorter the crack half-length, meaning the crack half-length is inversely proportional to the in-situ stress. Therefore, when considering in-situ stress, referring to the wedge-shaped crack propagation mechanical model, the peak stress at the crack tip is... Therefore, the relationship for solving the crack half-length under in-situ stress can be obtained, namely: When cracks generated by rock blasting are under bidirectional pressure (horizontal and vertical), their crack propagation model is as follows: Figure 5 As shown. At this point, the in-situ stress at the crack can be expressed as: in, The first principal stress, i.e. and The larger one; The third principal stress, i.e. and The smaller one; The angle between the crack and the maximum principal stress.

[0052] and The stress field can be measured at the blasting site. For situations where the actual stress field cannot be obtained experimentally, it can be calculated using the following formula: Where h is the burial depth.

[0053] The number of cracks is directly proportional to the peak load on the borehole wall, that is: Where k is the proportionality coefficient.

[0054] Due to the influence of ground stress, the number of cracks developed in the rock mass after blasting will decrease. The number of cracks is inversely proportional to the ground stress, that is: Finally, the rock mass damage variable considering the "inhibition" effect of geostress can be solved using the following relationship: S32. Based on the rock mass damage variables under the aforementioned in-situ stress suppression, calculate the comprehensive damage variables at different locations on the surrounding rock mass under the combined effects of blasting and in-situ stress.

[0055] Specifically, in this embodiment, step S31 obtains the rock mass damage variables under the action of in-situ stress suppression. However, the rock mass blasting damage under in-situ stress conditions is caused by the dynamic action of the blast stress wave, the quasi-static action of the blasting gas, and the quasi-dynamic action of the transient unloading of in-situ stress. The contribution of each of these three actions to the damage differs at different stages; in reality, their effects are coupled. When multiple actions jointly cause rock mass damage, the rock mass damage variables under each action can be derived individually first, and then the comprehensive damage variable under the coupled action can be obtained using the following formula: in, To integrate damage variables, The damage variable is the result of the dynamic action of the explosion stress wave. For damage variables under quasi-static action of explosive gas, It represents the damage variable under quasi-dynamic action of transient unloading of ground stress.

[0056] Based on the formula for calculating rock mass damage variables under in-situ stress suppression, the damage variables under the dynamic action of explosive stress waves can be expressed as: in, For dynamic Poisson's ratio, This is the proportionality coefficient under the dynamic action of the explosion stress wave. The number of cracks under the action of explosive stress wave. , The crack half-length activated by the explosion stress wave, For dynamic fracture toughness, The peak load on the borehole wall under the dynamic action of the explosion stress wave. This is the adjustment coefficient.

[0057] The peak load on the borehole wall under the dynamic action of the explosion stress wave is: After the rock mass is subjected to the dynamic action of the explosive stress wave, initial cracks are generated inside. The explosive gas expands and enters the initial crack, causing it to propagate further. Assuming the explosive gas instantaneously enters the crack and is uniformly distributed along its length, the explosive gas begins to exert its quasi-static effect. Based on the formula for calculating the rock mass damage variable under in-situ stress suppression, the damage variable under the quasi-static action of the explosive gas can be expressed as: in, The static Poisson's ratio This is the proportionality coefficient under quasi-static action of explosive gas. For adjustment coefficients, The number of cracks caused by explosive gases. , For crack half-length activated by explosive gases, For static fracture toughness, The peak load on the borehole wall under quasi-static action of explosive gas.

[0058] Assuming the expansion process of the detonation products is an isentropic adiabatic expansion process, then according to the adiabatic instantaneous detonation theory, the peak load on the borehole wall under quasi-static action of the detonating gas satisfies the following relationship: in, This refers to the critical pressure of the explosive. is the isentropic exponent for the gas, taken as 1.4.

[0059] According to CJ theory, the critical pressure of explosives It can be calculated using the following formula: in, , These are the specific volumes of the detonation products at the detonation wave front and the so-called conjugate point, respectively. The explosive is heated.

[0060] Based on the elastic unloading assumption, when the in-situ stress in the rock mass is transiently unloaded, it will generate elastic stress waves within the rock mass and propagate outwards. These unloading stress waves will also cause damage to the rock mass. The peak value of the transient unloading stress is equal to the magnitude of the in-situ stress at the excavation boundary, i.e. Based on the calculation formula for rock mass damage variables under in-situ stress suppression, the damage variables under quasi-dynamic action of transient in-situ stress unloading can be expressed as: in, This is the proportionality coefficient under quasi-dynamic action of transient unloading of ground stress. The peak load on the borehole wall under quasi-dynamic action of transient unloading of ground stress. The crack half-length is activated by transient unloading of ground stress.

[0061] By solving the simultaneous equations provided in this step, we can obtain the rock mass damage variables caused by the dynamic effects of the explosion stress wave, the quasi-static effects of the explosive gas, the ground stress suppression effect, and the quasi-dynamic effects of the transient unloading of ground stress at different explosion center distances during single-hole or single-initiation detonation.

[0062] Furthermore, this method is validated for its accuracy in calculating comprehensive damage variables through a two-dimensional numerical simulation experiment of blasting damage during deep tunnel excavation.

[0063] In a two-dimensional numerical simulation experiment of blasting damage during deep tunnel excavation, the rock mass was under hydrostatic stress, with a static Poisson's ratio of 0.25 and a static fracture toughness of approximately 0.71–1.35 MPa·m. 1 / 2 The borehole diameter is 45 mm, the explosive used is 32 mm diameter emulsion explosive, the detonation velocity is 3600 m / s, and the explosive density is 1000 kg / m³. 3 The heat of explosion is approximately 1,820,000 J / kg, and the stress levels of the rock mass are taken as 0 MPa, 5 MPa, 10 MPa, 15 MPa, 20 MPa, 25 MPa and 30 MPa respectively.

[0064] By solving the simultaneous equations of the damage variables using this method, we finally obtain the damage distribution characteristic curves of the surrounding rock under different in-situ stress conditions, without considering transient unloading of in-situ stress, as shown below. Figure 6 As shown in (a); considering the transient unloading of in-situ stress, the damage distribution characteristic curves of the surrounding rock under different in-situ stress conditions are as follows. Figure 6 As shown in (b); the damage range variation curves under in-situ stress conditions with and without transient unloading, as shown in (b). Figure 7 As shown.

[0065] exist Figure 6 In the diagram, the dashed line corresponding to D=0.19 intersects the curves corresponding to geostresses of 30 MPa, 25 MPa, 20 MPa, 15 MPa, 10 MPa, 5 MPa, and 0 MPa along the direction of increasing r. Figure 6 It can be observed that after blasting, the damage variable D decreases exponentially with increasing surrounding rock depth, gradually approaching 0. Currently, a damage variable D = 0.19 is generally used as the standard for determining whether the rock mass is damaged; when D ≥ 0.19, the rock mass is considered damaged. This embodiment also uses D = 0.19 as the threshold to determine the extent of rock mass damage. Figure 7As can be seen, when only the effects of explosive stress wave and explosive gas are considered, the degree and extent of damage to the surrounding rock gradually decrease with the increase of ground stress due to the effect of ground stress suppression, but the rate of decrease gradually decreases. When the effects of explosive stress wave, explosive gas and transient unloading of ground stress are considered simultaneously, the transient unloading effect is enhanced with the increase of ground stress, and its role in the development of surrounding rock damage gradually increases, gradually offsetting the reduction in the degree of damage caused by the effect of ground stress suppression. Therefore, after exceeding a certain ground stress threshold, the overall degree and extent of damage will change from a decreasing trend to an increasing trend.

[0066] pass Figure 8 It can be seen that when D=0.19 is used as the threshold, under the same working conditions, whether based on the calculation results of this method or the numerical simulation results ( Figure 8 The damage range of the surrounding rock, calculated using the borehole wall load method, equivalent load method, and NDIL method, initially decreases rapidly and then increases slowly with increasing in-situ stress, with an inflection point of 5 MPa. The calculation results of this method show the same trend as the numerical simulation results. Furthermore, the damage range calculated by this method is close to the numerical simulation results, with a maximum error of 0.29 m. Therefore, the calculation results of this method are relatively accurate and reliable, and have good applicability.

[0067] Figure 8 The borehole wall load method, equivalent load method, and NDIL method are numerical simulation methods used by Luo Sheng et al. (Luo Sheng, Yan Peng, Lu Wenbo et al. Numerical simulation and damage mechanism study of blasting damage in deep buried tunnel excavation [J]. Chinese Journal of Rock Mechanics and Engineering, 2021, 40(S1):2760-2772.).

[0068] S4. Based on the comprehensive damage variables, the mechanical parameters of the surrounding rock mass are reduced to obtain the surrounding rock safety factor and optimize the support design.

[0069] Step S4 specifically includes the following steps: S41. Based on the strain equivalence assumption, the mechanical parameters of the surrounding rock mass are reduced using the comprehensive damage variables.

[0070] Specifically, in this embodiment, the mechanical parameters of the surrounding rock mass include the internal friction angle and cohesion. Based on the strain equivalence assumption, that is, the strain of the damaged material under nominal stress is equivalent to the strain of the undamaged material under effective stress, the mechanical parameters of the surrounding rock mass can be reduced using the following relationship: in, This is the reduced internal friction angle. The initial internal friction angle, is the reduced cohesive force, is the initial cohesive force.

[0071] S42. Acquire the surrounding rock safety factor based on the reduced mechanical parameters, so as to optimize the surrounding rock support design.

[0072] Specifically, in this embodiment, first, the comprehensive damage variables at different positions on the rock mass are calculated by adjusting the blasting center distance r, and the and at the corresponding positions are reduced according to the relational expression given in step S41, to obtain and . Then, the FLAC3D software is used to construct a numerical model of the tunnel. In this model, the Mohr-Coulomb model is adopted as the constitutive model, and the calculated reduced internal friction angle and cohesive force at each position are taken as input parameters and substituted into the numerical model. Finally, based on the strength reduction method, the safety factor FoS at different positions of the surrounding rock is calculated.

[0073] Further, for any position, when FoS > 1.3, the surrounding rock is considered to be stable; when 1.0 < FoS ≤ 1.3, the surrounding rock is in a basically stable or under-stable state and requires close attention; when FoS ≤ 1.0, the surrounding rock is considered to be unstable, the current support design is insufficient, and the support needs to be strengthened.

[0074] It should be noted that, in some cases, the actions recorded in the specification may be performed in different sequences and still achieve the desired result. In this embodiment, the given sequence of steps is only for making the embodiment clearer and easier to illustrate, rather than a limitation thereto.

[0075] In an optional embodiment, please refer to Figure 9 , in order to improve the practicability of the present method and facilitate the popularization of the present method, the present invention further provides a surrounding rock damage analysis system considering the combined effect of blasting and in-situ stress. The surrounding rock damage analysis system considering the combined effect of blasting and in-situ stress includes: a data acquisition device 1, a data output device 2, a processor 3 and a memory 4. The memory 4 includes a computer-readable storage medium, and a computer program is stored in the computer-readable storage medium. The computer program includes program instructions, which when executed by the processor 3, cause the processor 3 to implement the contents described in steps S1 to S4.

[0076] In summary, this invention has at least the following beneficial effects: This method comprehensively considers the dynamic effects of explosive stress waves, the quasi-static effects of explosive gases, the suppression effect of ground stress, and the quasi-dynamic effects of transient unloading of ground stress, establishing a calculation formula for surrounding rock damage variables considering the combined effects of blasting and ground stress. In single-hole blasting, this improves the accuracy of surrounding rock damage evaluation. Based on the calculation of surrounding rock damage variables considering the combined effects of blasting and ground stress, this method reduces the mechanical parameters of the surrounding rock mass according to the calculated damage variables, and then optimizes the support design by combining the surrounding rock stress monitoring results, thus improving the safety of tunnel blasting excavation. A system adapted to this method has been established. This system can operate stably, which not only improves the practicality of this method but also facilitates its promotion.

[0077] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A method for analyzing surrounding rock damage considering the combined effects of blasting and geostress, characterized in that, Includes the following steps: The blast load pressure rise time, peak blast load, and positive pressure action time are obtained to determine the blast load pressure change process over time, i.e., the blast load change history. The blasting load variation history satisfies the following relationship: in, This represents the change of the blasting load pressure P over time t. The duration of the positive pressure application. The peak value of the blasting load is... The pressurization time of the explosive load; The magnitude, start time, and duration of transient unloading of ground stress are estimated, thereby determining the history of transient unloading of ground stress. The transient unloading history of the ground stress satisfies the following relationship: in, Transient unloading pressure of ground stress The process of change with time t The magnitude of the transient unloading of ground stress on the excavation boundary during the blasting of the i-th borehole. This refers to the start time of the transient unloading of the ground stress. This represents the change of the blasting load pressure P over time t. , The stopping time of the transient unloading of the ground stress; Simultaneously considering blasting and in-situ stress, the crack half-length and number of cracks in the surrounding rock mass are calculated, and then the rock mass damage variables under the in-situ stress inhibition are calculated. The rock mass damage variables under the in-situ stress suppression effect satisfy the following relationship: in, Let r be the rock mass damage variable under the aforementioned stress suppression effect, and r be the distance from the blast source. Poisson's ratio, The number of cracks. Let k be the half-length of the crack, and k be a proportionality coefficient. This represents the peak load on the borehole wall. The radius of the borehole is... The attenuation coefficient is... For geostress, For rock mass fracture toughness; Based on the rock mass damage variables under the aforementioned in-situ stress suppression, calculate the comprehensive damage variables at different locations on the surrounding rock mass under the combined effects of blasting and in-situ stress. The comprehensive damage variables satisfy the following relationship: in, For the aforementioned comprehensive damage variable, The damage variable is the result of the dynamic action of the explosion stress wave. For damage variables under quasi-static action of explosive gas, The damage variable is the quasi-dynamic action of transient unloading of ground stress. For dynamic Poisson's ratio, This is the proportionality coefficient under the dynamic action of the explosion stress wave. The number of cracks under the action of explosive stress wave. The crack half-length activated by the explosion stress wave, For dynamic fracture toughness, The peak load on the borehole wall under the dynamic action of the explosion stress wave. The radius of the borehole is... The attenuation coefficient is... For geostress, The static Poisson's ratio This is the proportionality coefficient under quasi-static action of explosive gas. and For adjustment coefficients, The number of cracks caused by explosive gases. For crack half-length activated by explosive gases, For static fracture toughness, The peak load on the borehole wall under quasi-static action of explosive gas. This is the proportionality coefficient under quasi-dynamic action of transient unloading of ground stress. Let r be the peak borehole wall load under quasi-dynamic action of transient unloading of ground stress, and r be the distance from the blast source. The crack half-length is activated by transient unloading of in-situ stress; The mechanical parameters of the surrounding rock mass are reduced based on the comprehensive damage variables to obtain the surrounding rock safety factor and optimize the support design. The mechanical parameters of the surrounding rock mass include the internal friction angle and cohesion. These parameters can be reduced using the following formula: in, This is the reduced internal friction angle. The initial internal friction angle, The reduced cohesion. This represents the initial cohesive force.

2. The method for analyzing surrounding rock damage considering the combined effects of blasting and geostress according to claim 1, characterized in that, The process of obtaining the blast load pressurization time, peak blast load, and positive pressure duration, and then determining the change process of blast load pressure over time, i.e., the blast load change history, includes the following steps: Obtain the blast load intensification time, peak blast load, and duration of positive pressure application; Based on the trigonometric function expression, the blast load variation history is established, which includes three parameters: the blast load pressurization time, the peak value of the blast load, and the positive pressure application time.

3. The method for analyzing surrounding rock damage considering the combined effects of blasting and geostress according to claim 1, characterized in that: Damage to the surrounding rock mass under the combined effects of in-situ stress and blasting is caused by the dynamic effects of blast stress waves, the quasi-static effects of blasting gases, the suppression effects of in-situ stress, and the quasi-dynamic effects of transient unloading of in-situ stress.

4. The method for analyzing surrounding rock damage considering the combined effects of blasting and geostress according to claim 1, characterized in that, The step of reducing the mechanical parameters of the surrounding rock mass based on the comprehensive damage variables to obtain the surrounding rock safety factor and optimize the support design includes the following steps: Based on the strain equivalence assumption, the mechanical parameters of the surrounding rock mass are reduced using the aforementioned comprehensive damage variables; The safety factor of the surrounding rock is obtained based on the reduced mechanical parameters, and then the support design of the surrounding rock is optimized.

5. A surrounding rock damage analysis system considering the combined effects of blasting and ground stress, characterized in that, The surrounding rock damage analysis system considering the combined effects of blasting and in-situ stress includes: a data acquisition device, a data output device, a processor, and a storage device. The storage device includes a computer-readable storage medium storing a computer program. The computer program includes program instructions, which, when executed by the processor, cause the processor to implement the surrounding rock damage analysis method considering the combined effects of blasting and in-situ stress as described in any one of claims 1-4.

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