A method for axial gradient charging of blast holes in a cavern based on ground stress distribution

Abstract

The application provides a hole blasting axial gradient charging method based on ground stress distribution and belongs to the technical field of geotechnical engineering controlled blasting. In view of the problem that the existing uniform charging does not consider the axial distribution of ground stress, which leads to insufficient crushing in the high ground stress area and excessive crushing in the low ground stress area, the application obtains the axial ground stress distribution of surrounding rock and rock mechanics parameters through in-situ measurement, establishes a quantitative mapping relationship between the ground stress and the charging density after normalization, arranges a continuous gradient charging structure without physical separation in the blast hole, uses single-point initiation to make the detonation wave transfer along the charge column, and finally optimizes the charging parameters through monitoring the blasting effect. The application realizes the accurate matching of blasting energy and ground stress distribution, significantly improves the uniformity of surrounding rock crushing, improves the quality of hole contour forming and the utilization rate of blasting energy, and is suitable for the blasting excavation construction of various underground engineering.

Description

Technical Field

[0001] This invention relates to the field of geotechnical engineering and controlled blasting technology, specifically to an axial gradient charging method for blasting boreholes in caverns based on ground stress distribution. It is applicable to blasting excavation construction of various underground projects such as deep-buried tunnels, underground powerhouses, and mine roadways, and is especially suitable for complex geological conditions with high ground stress and uneven axial distribution of ground stress. Background Technology

[0002] Underground cavern blasting excavation is one of the core construction methods in the fields of water conservancy and hydropower, mining, and underground space development. Under complex geological conditions of deep burial and high ground stress, the surrounding rock generally exhibits significant non-uniform stress distribution along the cavern axis, resulting in essential differences in rock mass fracture resistance and failure modes at different axial locations, and thus significant spatial differences in the demand for blasting energy.

[0003] However, in existing cavern blasting construction technologies, the charging parameters, borehole layout, and detonation sequence are mostly determined in advance based on macroscopic geological survey data, engineering experience, or numerical simulation results. Uniform charging or simple segmented charging methods are commonly used, without fully considering the spatial variation characteristics of the surrounding rock stress along the cavern axis, and thus failing to achieve dynamic matching between blasting energy and surrounding rock mechanical conditions.

[0004] In practical engineering applications, the limitations of the above design method are particularly prominent: due to the significant differences in the stress level of the surrounding rock in different axial regions, the use of uniform charge parameters will inevitably lead to insufficient fragmentation and serious under-excavation in high stress areas due to insufficient blasting energy, while excessive fragmentation and expansion of the surrounding rock damage range in low stress areas due to excess energy. Ultimately, this results in a series of problems such as uneven blasting effect, poor quality of tunnel outline formation, large workload of over-excavation and under-excavation repair, and low blasting energy utilization rate.

[0005] More importantly, blasting operations induce the release and redistribution of surrounding rock stress, leading to dynamic changes in the geostress environment of the subsequent excavation area. Current technologies lack differentiated charge control mechanisms tailored to the spatial distribution characteristics of geostress, and have not established an effective dynamic feedback optimization system. Blasting parameters cannot adapt to the evolving mechanical conditions of the surrounding rock in a timely manner, further exacerbating the uncertainty of blasting effects and severely restricting the precision and safety control of tunnel blasting construction.

[0006] Although numerous studies and patent documents both domestically and internationally have proposed various methods for designing and controlling blasting parameters in underground caverns, existing technologies mainly focus on empirical design based on initial geological conditions, blasting vibration prediction and control, or numerical simulation optimization. They generally emphasize the one-time determination of parameters before blasting or local process improvements, and have not fully considered the decisive influence of the spatial distribution characteristics of the surrounding rock stress along the cavern axis on the blasting effect. Nor have they established a differentiated charge control mechanism based on the distribution of ground stress. Therefore, they cannot fundamentally solve the core problem of the mismatch between blasting energy and surrounding rock mechanical conditions. For example, patent CN104596374B discloses a blasting construction method for karst-like tunnel structures, which controls the blasting effect by optimizing the layout of blast holes and the temporary support system. However, its core design lies in the planning of hole positions and the design of the support structure, without considering the influence of the axial distribution of the surrounding rock stress on the charge parameters. The charge method still adopts the traditional uniform charge or empirical adjustment. Patent CN109469487B discloses a drill-blasting construction scheme, which reduces blasting vibration and reduces over- and under-excavation by optimizing the blast hole form and construction process. However, its technical improvement is limited to the blasting structure and construction process, and does not establish a quantitative correspondence between charge intensity and the distribution of surrounding rock stress. Patent CN102607343A discloses a tunnel blasting excavation method, which improves the excavation effect by setting key holes and auxiliary holes and combining delayed detonation technology. However, this method still designs the charge based on traditional empirical parameters and does not zonal control of charge density and charge amount according to the differences in ground stress at different axial positions. Summary of the Invention

[0007] To address the aforementioned deficiencies in existing technologies, this invention provides an axial gradient charging method for blast holes in underground caverns based on ground stress distribution. This method is based on the spatial distribution characteristics of surrounding rock stress during axial excavation of underground caverns and its dynamic evolution under blasting disturbance. By accurately acquiring in-situ ground stress information of the surrounding rock at different axial positions of the blast hole, a quantitative mapping relationship between ground stress and charge density is established, fundamentally achieving a precise match between blasting energy requirements and surrounding rock mechanical conditions.

[0008] Based on this, the explosives inside the borehole are arranged in a continuous gradient along the borehole axis. Higher charge density corresponds to higher ground stress areas, lower charge density to lower ground stress areas, and a smooth, continuous change in charge density in the transition zone. This achieves a differentiated and rational distribution of blasting energy along the borehole axis. Single-point initiation technology is employed to ensure the continuous and stable transmission of the detonation wave along the charge axis. The gradient change in charge density naturally creates a gradient distribution of blasting intensity, ensuring that high ground stress areas receive sufficient rock-breaking energy, low ground stress areas receive moderate energy, and the transition zone experiences a smooth transition of blasting load, thereby guiding the orderly axial expansion of rock fractures.

[0009] Simultaneously, this invention combines a multi-scale monitoring and feedback adjustment mechanism for the failure morphology of the surrounding rock and the in-situ stress response after blasting, dynamically optimizing the charge density distribution and detonation control parameters. Through multiple blasting cycles, the in-situ stress-charge density mapping relationship is continuously corrected, ultimately achieving the optimal match between the axial blasting intensity of the borehole and the in-situ stress distribution of the surrounding rock. This method can effectively control the range of rock mass fracturing and the degree of surrounding rock disturbance, significantly improving the safety, controllability, and contour forming quality of axial excavation construction of underground caverns.

[0010] To achieve the above-mentioned objective, this invention provides a method for axial gradient charging of explosive charges in cavern blasting boreholes based on ground stress distribution, comprising the following steps: S1. In the area to be excavated in the underground cavern, test holes are laid out along the cavern axis to conduct in-situ in-situ in-situ stress measurements on the surrounding rock, obtain the maximum horizontal principal stress, minimum horizontal principal stress and principal stress direction at different axial positions, and analyze the distribution characteristics of in-situ stress along the axis; at the same time, rock mechanical parameter tests are carried out to obtain rock strength, deformation parameters and related physical and mechanical indicators. S2. Based on the ground stress data at different positions along the borehole axis obtained in step S1, the ground stress at each position is quantitatively characterized and normalized, and the correspondence between ground stress and charge density is established to realize the axial gradient mapping of high ground stress area corresponding to charge density higher than the reference charge density and low ground stress area corresponding to charge density lower than the reference charge density. S3. After completing the charge density mapping in step S2, the explosives in the borehole are laid out in a continuous loading manner to form a non-uniform gradient charge structure along the borehole axis. The charge density in the high ground stress area is higher than the reference charge density, the charge density in the low ground stress area is lower than the reference charge density, and the density in the transition zone gradually changes. Through single-point detonation, the detonation wave is smoothly transmitted along the charge column. S4 monitors and analyzes the surrounding rock failure morphology and geostress response after completing gradient charging and detonation, identifies areas of insufficient or excessive fracturing, and optimizes them by adjusting the charge density or detonation sequence; it also adjusts the charge parameters through multiple rounds of feedback.

[0011] Preferably, in step S1, the in-situ stress measurement includes the hydraulic fracturing method and the stress relief method; wherein the deep surrounding rock is measured by the hydraulic fracturing method, and the shallow and surface surrounding rock is supplemented by the stress relief method; the rock mechanical parameters include rock strength, elastic modulus, Poisson's ratio, deformation parameters and dynamic fracture characteristics.

[0012] Preferably, in step S1, the method of measuring in-situ stress by hydraulic fracturing specifically includes: drilling a borehole in the surrounding rock to be tested, sealing a test section with a packer, injecting high-pressure fluid into the sealed section to cause tensile fracturing of the rock mass in the borehole wall; measuring the fracturing pressure, instantaneous closing pressure and re-tensioning pressure, inverting to obtain the maximum and minimum horizontal principal stresses of the surrounding rock, and determining the direction of the principal stress in combination with the fracture orientation.

[0013] Preferably, in step S2, the quantitative characterization and normalization of the geostress at each location specifically includes: Calculate the influence coefficient of geostress k i = s i / s avg ,in s i For the first gun hole i Geological stress at location, s avg The average ground stress; A linear relationship between ground stress and charge density was established based on the ground stress influence coefficient. r i = k i × r avg ,in r i For the first i Explosive density at location, r avg The standard charge density is used.

[0014] Preferably, in step S3, the density distribution of the non-uniform gradient charge structure satisfies: Local stress influence coefficient k i When the value is greater than 1.1, corresponding to high ground stress areas, the charge density should be 1.1 to 1.3 times the baseline charge density; Local stress influence coefficient k i When the value is less than 0.9, corresponding to low ground stress areas, the charge density should be 0.7 to 0.9 times the baseline charge density. Local stress influence coefficient ≤ 0.9 k i When the value is ≤1.1, the corresponding transition region shows that the charge density gradually changes continuously between 0.9 and 1.1 times the reference charge density.

[0015] Preferably, in step S3, no physical partition is set inside the borehole, and the charge density inside the explosive column changes continuously along the axial direction; the detonation point is set at the borehole opening or bottom end, and the detonation wave is transmitted continuously in one direction along the axial direction of the explosive column.

[0016] Preferably, in step S4, the monitoring of the surrounding rock failure morphology includes the distribution of rock mass block size, the morphology of crack propagation, the range of fractured areas, and the quality of the cavern outline; the monitoring of the geostress response includes the residual stress of the surrounding rock, the stress release rate, and the stress disturbance coefficient.

[0017] Preferably, in step S4, the feedback optimization specifically includes: if there is insufficient fragmentation or inadequate stress release in a certain axial region, then increase the charge density, charge density gradient, or adjust the detonation delay time in the corresponding region; if there is excessive fragmentation in a certain axial region, then decrease the charge density in the corresponding region or increase the detonation time interval.

[0018] Preferably, the method is applicable to smooth blasting, pre-splitting blasting and bench blasting construction in deep-buried tunnels, underground powerhouses, mine roadways and underground engineering projects with high ground stress.

[0019] The present invention has the following beneficial effects: 1. This invention establishes a quantitative mapping relationship between ground stress and charge density, achieving dynamic matching between blasting energy and the distribution of ground stress in the surrounding rock. This fundamentally solves the problems of insufficient fragmentation in high-stress areas and excessive fragmentation in low-stress areas inherent in traditional uniform charges. This method enables differentiated and rational spatial distribution of blasting energy, effectively improving the uniformity of surrounding rock fragmentation, significantly enhancing blasting energy utilization efficiency and controllable rock fragmentation capabilities, and greatly improving the targeting and adaptability of underground cavern blasting design.

[0020] 2. This invention employs a continuous gradient charging structure without physical separation, eliminating the need for spacers or segmented charging devices within the borehole. This simplifies the construction process, shortens charging time, and reduces construction costs. Furthermore, the single-point detonation method avoids the safety hazards of misfires and partial explosions that can occur with multi-stage detonation, significantly improving the safety and reliability of blasting operations.

[0021] 3. This invention, through differentiated allocation of blasting energy, ensures sufficient rock-breaking energy in high-stress areas while avoiding energy waste in low-stress areas, effectively reducing ineffective energy consumption. Simultaneously, this method effectively controls blasting vibration intensity, minimizing disturbance to surrounding rock and structures, and contributing to the long-term stability of underground engineering projects.

[0022] 4. This invention establishes a closed-loop feedback optimization mechanism, which can dynamically adjust the charge parameters according to the failure mode of the surrounding rock and the ground stress response after blasting. Through multiple blasting cycles, the ground stress-charge density mapping relationship is continuously optimized, so that the blasting effect is continuously improved. It is particularly suitable for deep underground engineering with complex and variable geological conditions.

[0023] 5. This invention is applicable not only to smooth blasting and pre-splitting blasting, but also to bench blasting and tunneling blasting. It can be widely used in various underground engineering blasting constructions in fields such as water conservancy and hydropower, mining, transportation tunnels, and underground space development. This method can effectively improve the axial continuity and directional controllability of fracture propagation, significantly improve the quality of tunnel profile formation, reduce over- and under-excavation and subsequent finishing work, and provide a new technical means for underground engineering blasting construction under complex geostress conditions. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a technical roadmap for an axial gradient charging method for cavern blasting boreholes based on ground stress distribution, provided in an embodiment of the present invention.

[0026] Figure 2 This is a schematic diagram of a hydraulic fracturing method for monitoring ground stress provided in an embodiment of the present invention.

[0027] Figure 3 The diagram shows the axial stress distribution curve of the borehole provided in an embodiment of the present invention.

[0028] Figure 4 A schematic diagram of an axial gradient charging structure for boreholes based on ground stress distribution, provided for an embodiment of the present invention.

[0029] Figure 5 A comparison diagram of the blasting effects of the method of the present invention and the traditional uniform charge method provided in the embodiments of the present invention. Detailed Implementation

[0030] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0031] Example 1: See Figure 1 This embodiment provides an axial gradient charging method for blasting boreholes in caverns based on ground stress distribution. The method includes the following steps: Step 1, Initial in-situ stress monitoring and axial distribution acquisition of surrounding rock: In the area to be excavated in the underground cavern, test holes are set up along the cavern axis to conduct in-situ in-situ stress measurement of the surrounding rock, obtain the maximum horizontal principal stress, minimum horizontal principal stress and principal stress direction at different axial positions, and analyze the distribution characteristics of in-situ stress along the axis; at the same time, rock mechanical parameter testing is carried out to obtain rock strength, deformation parameters and related physical and mechanical indicators. Specifically, it includes: Within the construction area of ​​the underground cavern to be blasted, boreholes are drilled in the surrounding rock to be tested. A test section is sealed within the borehole using a packer, and high-pressure fluid is injected into this sealed section to induce tensile fracturing in the borehole wall rock mass. Under plane stress conditions, the stress distribution of the rock mass surrounding the borehole is as follows: Radial stress: s r = P w (1); Tangential stress: s θ =( s H + s h )-2( s H - s h cos2 i - P w (2); In the formula: s r Radial stress, in MPa; s θ This is the tangential stress, expressed in MPa. s H The maximum horizontal principal stress is expressed in MPa. s h The minimum horizontal principal stress is expressed in MPa. P w The pressure of the fluid injected into the hole, expressed in MPa; i This represents the polar angle position, in degrees.

[0032] When the tangential stress on the borehole wall reaches the tensile strength of the rock, fracture occurs, and the fracture pressure is: P b =3 s h - s H + s t(3); In the formula: P b This is the burst pressure, expressed in MPa. s H The maximum horizontal principal stress is expressed in MPa. s h The minimum horizontal principal stress is expressed in MPa. s t This represents the tensile strength of the rock, expressed in MPa.

[0033] Record the instantaneous closing pressure when the crack is closed: P s = s h (4); In the formula: P s The instantaneous shut-off pressure is expressed in MPa. s h The minimum horizontal principal stress is expressed in MPa.

[0034] When the fracture reopens, the corresponding re-tension pressure is: P r = s h + s t (5); In the formula: P r The tensile pressure is expressed in MPa. s h The minimum horizontal principal stress is expressed in MPa. s t This represents the tensile strength of the rock, expressed in MPa.

[0035] By measuring the rupture pressure P b Instantaneous pressure shut-off P s and tension P r The maximum horizontal principal stress of the surrounding rock was obtained through inversion. s H With minimum horizontal principal stress s h The direction of principal stress is determined by combining the location of the crack.

[0036] In practical applications, test holes are set up at representative locations or key control areas along the axial direction of the borehole in conjunction with borehole drilling operations. The stress in the surrounding rock is tested by hydraulic fracturing tests, and the stress parameters at each test location are obtained by measuring the fracturing pressure, instantaneous closing pressure, and re-tension pressure.

[0037] To achieve multi-scale acquisition of geostress in the surrounding rock of the cavern, in addition to the hydraulic fracturing method for measuring deep surrounding rock, a stress relief method was used to supplement the measurements of shallow and surface surrounding rock. In the shallow surrounding rock near the cavern surface and borehole openings, the stress relief method was used for geostress testing. Specifically, small-diameter boreholes were drilled in the test area, and the original geostress was released through local grooving or borehole unloading. Strain gauges were then deployed to measure the rock mass strain response. Based on the strain change results and combined with the rock mass elastic parameters, the in-situ geostress values ​​of the shallow surrounding rock were obtained through inversion, thus supplementing and verifying the deep geostress results obtained by hydraulic fracturing.

[0038] Simultaneously, the longitudinal wave velocity of the rock was obtained using ultrasonic testing, and the elastic modulus and Poisson's ratio of the rock were determined using triaxial compression tests. Based on the above test results, the initial geostress field distribution characteristics and rock mechanical parameter system of the surrounding rock in the construction area were established, providing a basis for subsequent inward progressive blasting parameter design and dynamic evolution analysis of surrounding rock geostress.

[0039] Step 2, Axial charge density mapping of boreholes: Based on the ground stress data at different locations along the borehole axis obtained in Step 1, the ground stress at each location is quantitatively characterized and normalized, and the correspondence between ground stress and charge density is established to achieve axial gradient mapping where high ground stress areas correspond to charge densities higher than the benchmark charge density, and low ground stress areas correspond to charge densities lower than the benchmark charge density. Specifically, it includes: Based on the ground stress data at different locations along the borehole axis obtained in step 1, the ground stress level at each location is quantitatively characterized, and the charge parameters are designed accordingly.

[0040] First, the in-situ stress at each axial measuring point is normalized to obtain the in-situ stress influence coefficient: k i = s i / s avg (6); In the formula: k i For the first gun hole i Location-related stress influence coefficient; s i For the first gun hole i The geostress at a given location, expressed in MPa; savg This represents the axial average ground stress of the borehole, or the representative reference ground stress, such as the design reference stress or the average value of measuring points, in MPa.

[0041] Based on the relationship between in-situ stress and rock mass fracture resistance, the in-situ stress influence coefficient is converted into the corresponding target blasting energy requirement: E i = k i × E avg (7); In the formula: E i For the first gun hole i The target's explosive energy at location, measured in J; E avg The average target blast energy or the baseline design energy is expressed in J.

[0042] Furthermore, during the blasting process, the energy released by the explosive acts on the surrounding rock through detonation pressure, and the interaction can be expressed as follows: (8); In the formula: P i Let be the detonation pressure at position i of the borehole, in Pa; V This is the volume parameter, in m³.

[0043] At the same time, the detonation pressure satisfies the following relationship with the explosive density and detonation velocity: (9); In the formula: r i For the first gun hole i The charge density at the location, expressed in g / cm³; The detonation velocity of the explosive is expressed in m / s. This is an empirical constant related to the type of explosive.

[0044] Under the condition that the type of explosive is determined and the detonation velocity is basically constant, the detonation pressure is mainly determined by the charge density, thus realizing the direct control of the blasting intensity by the charge parameters. Based on this, the ground stress influence coefficient is mapped to the detonation pressure adjustment coefficient, and further applied to the charge density control, achieving the following relationship: r i = k i× r avg (10); In the formula: r avg The reference charge density is expressed in g / cm³.

[0045] As can be seen from the above relationship, the charge density at different positions along the borehole axis varies with the ground stress level, achieving the goal of a higher charge density in high ground stress areas and a lower charge density in low ground stress areas, thus providing a design basis for subsequent specific charge methods and detonation control.

[0046] Step 3, continuous gradient charging and detonation control in boreholes: After completing the charge density mapping in Step 2, the explosives in the boreholes are continuously loaded to form a non-uniform gradient charge structure along the borehole axis. The charge density in high-stress areas is higher than the reference charge density, and the charge density in low-stress areas is lower than the reference charge density. The density gradually changes in the transition zone. Through single-point detonation, the detonation wave is successfully transmitted along the explosive column. Specifically, it includes: After completing the design of the borehole axial charging parameters in step 2, based on the calculated charge density and charge per unit length at each axial position, the explosives in the borehole are continuously loaded to form a non-uniform gradient charge structure distributed along the borehole axis. No physical separators are installed within the borehole, allowing the charge density within the explosive column to continuously vary along the axis, matching the stress distribution characteristics of the surrounding rock.

[0047] Based on the mapping relationship between axial ground stress and charge density, the charge density at different locations of the borehole varies with the ground stress level according to the following pattern: when k i When the value is greater than 1.1, corresponding to high ground stress areas, the charge density increases by 10% to 30% compared to the baseline charge density. That is, the charge density in high ground stress areas is: r i =(1.1~1.3) r avg (11); when k i When the value is less than 0.9, corresponding to low ground stress areas, the charge density is reduced by 10% to 30% compared to the baseline charge density. Therefore, the charge density in low ground stress areas is: r i =(0.7~0.9) r avg (12); When 0.9≤ k iWhen the value is ≤1.1, the charge density in the corresponding transition region is adjusted in a gradual manner.

[0048] Through the above mapping relationship, higher detonation pressure and higher charge density are corresponding to high ground stress areas, and lower detonation pressure and lower charge density are corresponding to low ground stress areas, thereby realizing the gradient distribution and spatial matching control of the axial blasting intensity of the borehole.

[0049] During initiation, only one initiation point is set, and the detonation wave is smoothly transmitted along the explosive charge through appropriate initiators or detonators, thus naturally forming a gradient blasting effect. Since the detonation pressure is proportional to the charge density, the high charge density area can preferentially act on the high-stress surrounding rock during detonation, improving the local crack initiation and fragmentation capabilities; the low charge density area releases less energy, which can avoid excessive fragmentation of the low-stress surrounding rock; the charge density in the transition area is designed in a continuously gradual manner, so that the blasting load transitions smoothly along the borehole axis, slowing down the sudden change of stress wave and improving the continuity and stability of crack propagation.

[0050] Through the above-mentioned continuous gradient charge and single-point detonation control, the axial blasting energy of the blast hole can be continuously distributed in space and dynamically matched with the surrounding rock stress, thereby significantly improving the rock breaking efficiency in high stress areas, while reducing energy waste and excessive fragmentation risk in low stress areas, and achieving a controllable and balanced gradient blasting effect.

[0051] Step 4, monitoring and feedback optimization of blasting effect: After the gradient charge and detonation are completed, the failure mode of the surrounding rock and the ground stress response are monitored and analyzed to identify areas of insufficient or excessive fragmentation, and optimization is carried out by adjusting the charge density or detonation sequence; the charge parameters are adjusted through multiple rounds of feedback.

[0052] Specifically, it includes: After the gradient charging and detonation are completed, the damage effect on the surrounding rock and the ground stress response after blasting are monitored and analyzed at multiple scales to assess the degree of matching between the blasting energy release process and the original ground stress field.

[0053] Specifically, through on-site investigation, image recognition, or numerical reconstruction methods, the distribution of rock mass blocks, the morphology of fracture propagation, and the spatial range of the fractured area after blasting are obtained to form the evaluation results of blasting fracture morphology, including indicators such as average block size, maximum fracture radius, fracture density, and damage impact range.

[0054] Meanwhile, the residual stress or stress release degree of the surrounding rock around the blast hole and in the key monitoring area was tested. By comparing the changes in ground stress before and after blasting, the ground stress release rate or stress disturbance coefficient was obtained, which was used to characterize the control effect of blasting on the original ground stress field.

[0055] Furthermore, by combining the blasting fragmentation results with the ground stress response results, a continuous spatial evaluation of the blasting effect at different locations along the borehole axis is conducted to identify whether there are local insufficient fragmentation, excessive fragmentation, or uneven energy release phenomena, and to conduct a correlation analysis with the ground stress level and charge density distribution at the corresponding locations.

[0056] If the test results indicate that there is insufficient fragmentation or inadequate stress release in a certain axial region, the charge density or charge density gradient in the corresponding region will be increased, or the detonation delay time will be adjusted. If there is excessive fragmentation in a local area, the charge density in the corresponding region will be reduced, or the detonation time interval will be increased, thereby achieving optimized adjustment of the blasting parameters.

[0057] Furthermore, through multiple blasting cycles and feedback corrections, the mapping relationship between ground stress, detonation pressure, and charge density is gradually corrected, so that the continuous gradient charge structure and the ground stress distribution characteristics of the surrounding rock tend to be in an optimal matching state, thus forming an adaptive gradient charge optimization method based on ground stress feedback.

[0058] By adopting the above methods, closed-loop control of the blasting process can be achieved, enabling blasting parameters to be continuously optimized according to the actual response of the surrounding rock. This improves the rock breaking efficiency in high-stress areas and reduces the ineffective energy consumption and risk of uncontrolled damage to the surrounding rock in low-stress areas.

[0059] Example 2: The following is in conjunction with the embodiments and appendices Figure 1-5 The technical solution of the present invention is described in detail, but this does not constitute a limitation on the scope of protection of the present invention.

[0060] This embodiment uses a smooth blasting test of a deep-buried granite water diversion tunnel as an example. The tunnel is buried at a depth of 800–1200 m, and the surrounding rock is hard granite with a uniaxial compressive strength of 80–120 MPa. The implemented technical route is as follows: Figure 1 As shown.

[0061] Step 1: Monitoring and Obtaining Initial Geostress and Axial Distribution of Surrounding Rock Within the construction area of ​​the underground cavern to be blasted, boreholes are drilled in the surrounding rock to be tested. A test section is sealed within the borehole using a packer. High-pressure fluid is injected into this sealed section to induce tensile fracturing in the borehole wall rock mass. Specific application methods are detailed below. Figure 2 Under plane stress conditions, the stress distribution of the rock mass surrounding the borehole is as follows: Radial stress: s r = P w (1); Tangential stress: s θ =( s H + s h )-2( s H - s h cos2 i - P w (2); In the formula: s r Radial stress, in MPa; s θ This is the tangential stress, expressed in MPa. s H The maximum horizontal principal stress is expressed in MPa. s h The minimum horizontal principal stress is expressed in MPa. P w The pressure of the fluid injected into the hole, expressed in MPa; i This represents the polar angle position, in degrees.

[0062] In this example, the maximum horizontal principal stress measurements for several representative boreholes ranged from approximately 20.8 MPa to 45.2 MPa, and the minimum horizontal principal stress ranged from approximately 14.9 MPa to 35.3 MPa. The average direction of the maximum horizontal principal stress was approximately 65° northwest.

[0063] When the tangential stress on the borehole wall reaches the tensile strength of the rock, fracture occurs, and the fracture pressure is: P b =3 s h - s H + s t (3); In the formula: P b This is the burst pressure, expressed in MPa. s H The maximum horizontal principal stress is expressed in MPa. s h The minimum horizontal principal stress is expressed in MPa. s t This represents the tensile strength of the rock, expressed in MPa.

[0064] Record the instantaneous closing pressure when the crack is closed: P s = sh (4); In the formula: P s The instantaneous shut-off pressure is expressed in MPa. s h The minimum horizontal principal stress is expressed in MPa.

[0065] When the fracture reopens, the corresponding re-tension pressure is: P r = s h + s t (5); In the formula: P r The tensile pressure is expressed in MPa. s h The minimum horizontal principal stress is expressed in MPa. s t This represents the tensile strength of the rock, expressed in MPa.

[0066] By measuring the rupture pressure P b Instantaneous pressure shut-off P s and tension P r The maximum horizontal principal stress of the surrounding rock can be obtained by inversion. s H With minimum horizontal principal stress s h The direction of principal stress is determined by combining the fracture orientation. In this case, calculations and field tests show that the fracture pressure of some boreholes is approximately 13 to 19 MPa, the instantaneous closure pressure is approximately 7 to 9.7 MPa, and the re-tension pressure is approximately 8 to 9.3 MPa.

[0067] In practical applications, test holes can be set up at representative locations or key control areas along the axial direction of the borehole in conjunction with borehole drilling operations. The stress in the surrounding rock can be tested by hydraulic fracturing tests, and the stress parameters at each test location can be obtained by measuring the fracturing pressure, instantaneous closing pressure, and re-tension pressure.

[0068] To achieve multi-scale acquisition of geostress in the surrounding rock of the cavern, in addition to the hydraulic fracturing method for measuring deep surrounding rock, a stress relief method was used to supplement the measurements of shallow and surface surrounding rock. The stress relief method was employed to test geostress in the shallow surrounding rock near the cavern surface and borehole openings. Specifically, small-diameter boreholes were drilled in the test area, and the original geostress was released through local grooving or borehole unloading. Strain gauges were then deployed to measure the rock mass strain response. Based on the strain change results and combined with the rock mass elastic parameters, the in-situ geostress values ​​of the shallow surrounding rock were obtained through inversion, thus supplementing and verifying the deep geostress results obtained from hydraulic fracturing. In this example, the geostress at the borehole opening was approximately 10 to 15 MPa.

[0069] Simultaneously, ultrasonic testing was used to obtain the longitudinal wave velocity of the rock, and triaxial compression tests were employed to determine the rock's elastic modulus and Poisson's ratio. Based on these test results, the initial in-situ stress field distribution characteristics and rock mechanical parameter system of the surrounding rock in the construction area were established, providing a fundamental basis for subsequent inward progressive blasting parameter design and dynamic evolution analysis of surrounding rock stress. In this example, the rock's dynamic tensile strength was 12 MPa, the longitudinal wave velocity was 4800 m / s, the elastic modulus was 45 GPa, and the Poisson's ratio was 0.23.

[0070] Step 2, Axial charge density mapping of boreholes Based on the ground stress data at different locations along the borehole axis obtained in step 1, the ground stress level at each location is quantitatively characterized, and the charge parameters are designed accordingly.

[0071] First, the in-situ stress at each axial measuring point is normalized to obtain the in-situ stress influence coefficient: k i = s i / s avg (6); In the formula: k i For the first gun hole i Location-related stress influence coefficient; s i For the first gun hole i The geostress at a given location, expressed in MPa; s avg This represents the axial average ground stress of the borehole, or the representative reference ground stress, such as the design reference stress or the average value of measuring points, in MPa.

[0072] Based on the relationship between in-situ stress and rock mass fracture resistance, the in-situ stress influence coefficient is converted into the corresponding target blasting energy requirement: E i =k i × E avg (7); In the formula: E i For the first gun hole i The target's explosive energy at location, measured in J; E avg The average target blast energy or the baseline design energy is expressed in J.

[0073] Furthermore, during the blasting process, the energy released by the explosive acts on the surrounding rock through detonation pressure, and the interaction can be expressed as follows: (8); In the formula: P i Let be the detonation pressure at position i of the borehole, in Pa; V This is the volume parameter, in m³.

[0074] At the same time, the detonation pressure satisfies the following relationship with the explosive density and detonation velocity: (9); In the formula: r i For the first gun hole i The charge density at the location, in g / cm³; The detonation velocity of the explosive is expressed in m / s. This is an empirical constant related to the type of explosive.

[0075] Under the condition that the type of explosive is determined and the detonation velocity is basically constant, the detonation pressure is mainly determined by the charge density, thus realizing the direct control of the blasting intensity by the charge parameters. Based on this, the ground stress influence coefficient is mapped to the detonation pressure adjustment coefficient, and further applied to the charge density control, to achieve the following relationship: r i = k i × r avg (10); In the formula: r avg The reference charge density is expressed in g / cm³.

[0076] As can be seen from the above relationships, the charge density at different positions along the borehole axis varies with the ground stress level, and the corresponding ground stress distribution is shown in the figure. Figure 3 This achieves the goal of having a higher charge density in high-stress areas than the benchmark charge density and a lower charge density in low-stress areas than the benchmark charge density, providing a design basis for subsequent specific charge methods and detonation control.

[0077] In this example, the mean axial stress of the borehole was calculated. s avg =32MPa, No. 2 rock emulsion explosive was selected as the blasting material, and its reference charge density is 32MPa. r avg =1.0g / cm³, explosion velocity =3600m / s.

[0078] Step 3, Continuous gradient charging and detonation control in boreholes After completing the design of the borehole axial charging parameters in step 2, based on the calculated charge density and charge per unit length at each axial position, the explosives in the borehole are continuously loaded to form a non-uniform gradient charge structure distributed along the borehole axis. No physical separators are installed within the borehole, allowing the charge density within the explosive column to continuously vary along the axis, matching the stress distribution characteristics of the surrounding rock.

[0079] Based on the mapping relationship between axial ground stress and charge density, the charge density at different locations of the borehole varies with the ground stress level according to the following pattern: when k i When the value is greater than 1.1, corresponding to high ground stress areas, the charge density increases by 10% to 30% compared to the baseline charge density. That is, the charge density in high ground stress areas is: r i =(1.1~1.3) r avg (11); when k i When the value is less than 0.9, corresponding to low ground stress areas, the charge density is reduced by 10% to 30% compared to the baseline charge density. Therefore, the charge density in low ground stress areas is: r i =(0.7~0.9) r avg (12); When 0.9≤ k i When the value is ≤1.1, the charge density in the corresponding transition region is adjusted in a gradual manner.

[0080] Through the above mapping relationship, higher detonation pressure and higher charge density are corresponding to high ground stress areas, and lower detonation pressure and lower charge density are corresponding to low ground stress areas, thereby realizing the gradient distribution and spatial matching control of the axial blasting intensity of the borehole.

[0081] During initiation, only one initiation point is set, and the detonation wave is smoothly transmitted along the explosive charge through appropriate initiators or detonators. Since the detonation pressure is proportional to the charge density, the high charge density area can preferentially act on the high-stress surrounding rock during detonation; the low charge density area releases less energy; the charge density in the transition area is designed in a continuously gradual manner to ensure a smooth transition of the blasting load along the borehole axis.

[0082] Through the aforementioned continuous gradient charging and single-point detonation control, the axial blasting energy of the borehole can be continuously distributed along space and dynamically matched with the surrounding rock stress. The basic layout is shown in [reference needed]. Figure 4 .

[0083] In this example, the smooth blasting boreholes have a diameter of 42mm, a depth of 3.5m, and a borehole spacing of 50cm. Based on the ground stress distribution, the boreholes are divided into three zones: Orifice section (0–1.0 m): Influence coefficient of geostress k i =0.7~0.9, corresponding to low ground stress areas, the charge density is 0.7~0.9g / cm³, and the charge per unit length is 100~125g / m; Middle section (1.0–2.5 m): Influence coefficient of ground stress k i =0.9~1.1, corresponding to the transition region, the charge density is 0.9~1.1g / cm³, and the charge per unit length is 125~150g / m; Bottom section of borehole (2.5–3.5 m): Influence coefficient of ground stress k i =1.1~1.3, corresponding to high ground stress areas, the charge density is 1.1~1.3g / cm³, and the charge per unit length is 150~175g / m.

[0084] A detonation point was set at the borehole opening, and an No. 8 industrial electric detonator was used for initiation. The detonation wave propagated smoothly along the axis of the explosive charge towards the bottom of the borehole.

[0085] Step 4: Monitoring and Optimizing the Explosion Effect After completing the continuous gradient charging and detonation, the damage effect on the surrounding rock and the ground stress response after blasting are monitored and analyzed at multiple scales to assess the degree of matching between the blasting energy release process and the original ground stress field.

[0086] Specifically, through on-site investigation, image recognition, or numerical reconstruction methods, the distribution of rock mass blocks, the morphology of fracture propagation, and the spatial range of the fractured area after blasting are obtained to form the evaluation results of blasting fracture morphology, including indicators such as average block size, maximum fracture radius, fracture density, and damage impact range.

[0087] Meanwhile, the residual stress or stress release degree of the surrounding rock around the blast hole and in the key monitoring area was tested. By comparing the changes in ground stress before and after blasting, the ground stress release rate or stress disturbance coefficient was obtained, which was used to characterize the control effect of blasting on the original ground stress field.

[0088] Furthermore, by combining the blasting fragmentation results with the ground stress response results, a continuous spatial evaluation of the blasting effect at different locations along the borehole axis is conducted to identify whether there are local insufficient fragmentation, excessive fragmentation, or uneven energy release phenomena, and to conduct a correlation analysis with the ground stress level and charge density distribution at the corresponding locations.

[0089] If the test results indicate that there is insufficient fragmentation or inadequate stress release in a certain axial region, the charge density or charge density gradient in the corresponding region will be increased, or the detonation delay time will be adjusted. If there is excessive fragmentation in a local area, the charge density in the corresponding region will be reduced, or the detonation time interval will be increased, thereby achieving optimized adjustment of the blasting parameters.

[0090] Furthermore, through multiple blasting cycles and feedback corrections, the mapping relationship between ground stress, detonation pressure, and charge density is gradually corrected, so that the continuous gradient charge structure and the ground stress distribution characteristics of the surrounding rock tend to be in an optimal matching state, thus forming an adaptive gradient charge optimization method based on ground stress feedback.

[0091] In this case, three-dimensional laser scanning technology was used to measure the tunnel outline after blasting. The results showed that the tunnel outline flatness was 8-12 cm, the average over-excavation was 12 cm, the maximum over-excavation was 18 cm, and the under-excavation was less than 3 cm. On-site sieving revealed that the average rock mass block size was 20-30 cm, with a large block rate of less than 8%. Simultaneously, the residual stress in the surrounding rock was tested using a stress relief method, yielding a stress release rate of 75%-85%. Based on the monitoring results, the charge density at the bottom of the borehole was fine-tuned to 1.2-1.3 g / cm³.

[0092] Comparison of effects of each example The axial gradient charging blasting method for caverns based on ground stress distribution, as described in this invention, allows blast-induced fractures to expand relatively stably along the cavern axis under the influence of the spatial distribution of surrounding rock stress, and forms a well-continuous and effective fractured zone under the control of gradient charging energy. For example... Figure 5 As shown, the rock fragmentation effect of axial gradient charge blasting in caverns was compared with that of traditional single-charge or uniform charge blasting.

[0093] Compared with traditional uniform charge blasting methods, this method adjusts the charge density and unit charge amount at different axial positions according to the distribution characteristics of the surrounding rock stress along the axial direction, so as to match the blasting energy with the stress state of the surrounding rock. This effectively improves the problem of uneven local energy distribution, suppresses insufficient fragmentation in high-stress areas and excessive fragmentation in low-stress areas, and significantly improves the quality of the tunnel outline and the smoothness of the boundary.

[0094] Under the action of axial gradient charge, the rock-breaking ability is enhanced by increasing the charge strength in high ground stress areas, while energy excess is avoided by reducing the charge strength in low ground stress areas. This achieves a reasonable distribution of blasting energy along the axial direction, thereby improving the overall blasting and breaking efficiency and reducing over- and under-excavation and subsequent repair work. As a result, the safety and forming quality of tunnel excavation under complex ground stress conditions are optimized.

[0095] Experimental and numerical simulation results show that this method is superior to traditional uniform charge or one-time design blasting methods in terms of crack propagation direction control, blasting energy utilization efficiency, and surrounding rock damage control.

[0096] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for axial gradient charging of explosive charges in cavern blasting boreholes based on ground stress distribution, characterized in that, Includes the following steps: S1. In the area to be excavated in the underground cavern, test holes are laid out along the cavern axis to conduct in-situ in-situ in-situ stress measurements on the surrounding rock, obtain the maximum horizontal principal stress, minimum horizontal principal stress and principal stress direction at different axial positions, and analyze the distribution characteristics of in-situ stress along the axis; at the same time, rock mechanical parameter tests are carried out to obtain rock strength, deformation parameters and related physical and mechanical indicators. S2. Based on the ground stress data at different positions along the borehole axis obtained in step S1, the ground stress at each position is quantitatively characterized and normalized, and the correspondence between ground stress and charge density is established to realize the axial gradient mapping of high ground stress area corresponding to charge density higher than the reference charge density and low ground stress area corresponding to charge density lower than the reference charge density. S3. After completing the charge density mapping in step S2, the explosives in the borehole are laid out in a continuous loading manner to form a non-uniform gradient charge structure along the borehole axis. The charge density in the high ground stress area is higher than the reference charge density, the charge density in the low ground stress area is lower than the reference charge density, and the density in the transition zone gradually changes. Through single-point detonation, the detonation wave is smoothly transmitted along the charge column. S4 monitors and analyzes the surrounding rock failure morphology and geostress response after completing gradient charging and detonation, identifies areas of insufficient or excessive fracturing, and optimizes them by adjusting the charge density or detonation sequence; it also adjusts the charge parameters through multiple rounds of feedback.

2. The method for axial gradient charging of blast holes in caverns based on ground stress distribution according to claim 1, characterized in that, In step S1, the in-situ stress measurement includes the hydraulic fracturing method and the stress relief method; The deep surrounding rock was measured using the hydraulic fracturing method, while the shallow and surface surrounding rock was measured using the stress relief method. The rock mechanical parameters included rock strength, elastic modulus, Poisson's ratio, deformation parameters, and dynamic fracture characteristics.

3. The method for axial gradient charging of blast holes in caverns based on ground stress distribution according to claim 1, characterized in that, In step S1, the method of measuring in-situ stress by hydraulic fracturing specifically includes: drilling a borehole in the surrounding rock to be tested, sealing a test section with a packer, injecting high-pressure fluid into the sealed section to cause tensile fracturing of the rock mass in the borehole wall; measuring the fracturing pressure, instantaneous closing pressure and re-tensioning pressure, inverting to obtain the maximum and minimum horizontal principal stresses of the surrounding rock, and determining the direction of the principal stress in combination with the fracture orientation.

4. The method for axial gradient charging of blast holes in caverns based on ground stress distribution according to claim 1, characterized in that, Step S2, which involves quantitatively characterizing and normalizing the geostress at each location, specifically includes: Calculate the influence coefficient of geostress k i = σ i / σ avg ,in σ i For the first gun hole i Geological stress at location, σ avg The average ground stress; A linear relationship between ground stress and charge density was established based on the ground stress influence coefficient. ρ i = k i × ρ avg ,in ρ i For the first i Explosive density at location, ρ avg The standard charge density is used.

5. The method for axial gradient charging of blast holes in caverns based on ground stress distribution according to claim 4, characterized in that, In step S3, the density distribution of the non-uniform gradient charge structure satisfies: Local stress influence coefficient k i When the value is greater than 1.1, corresponding to high ground stress areas, the charge density should be 1.1 to 1.3 times the baseline charge density; Local stress influence coefficient k i When the value is less than 0.9, corresponding to low ground stress areas, the charge density should be 0.7 to 0.9 times the baseline charge density. Local stress influence coefficient ≤ 0.9 k i When the value is ≤1.1, the corresponding transition region shows that the charge density gradually changes continuously between 0.9 and 1.1 times the reference charge density.

6. The method for axial gradient charging of blast holes in caverns based on ground stress distribution according to claim 1, characterized in that, In step S3, no physical partitions are set inside the borehole, and the charge density inside the explosive column changes continuously along the axial direction; the detonation point is set at the borehole opening or bottom end, and the detonation wave is transmitted continuously in one direction along the axial direction of the explosive column.

7. The method for axial gradient charging of blast holes in caverns based on ground stress distribution according to claim 1, characterized in that, In step S4, the monitoring of surrounding rock failure morphology includes rock mass block size distribution, fracture propagation morphology, fractured area range, and cavern outline quality; the monitoring of geostress response includes surrounding rock residual stress, stress release rate, and stress disturbance coefficient.

8. The method for axial gradient charging of blast holes in caverns based on ground stress distribution according to claim 1, characterized in that, In step S4, the feedback optimization specifically includes: if there is insufficient fragmentation or inadequate stress release in a certain axial region, then increase the charge density or charge density gradient of the corresponding region or adjust the detonation delay time; if there is excessive fragmentation in a certain axial region, then decrease the charge density of the corresponding region or increase the detonation time interval.

9. The method for axial gradient charging of blast holes in caverns based on ground stress distribution according to claim 1, characterized in that, The method is applicable to smooth blasting, pre-splitting blasting, and bench blasting in deep-buried tunnels, underground powerhouses, mine roadways, and underground engineering projects with high ground stress.

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