Large surface mine slope angle optimization method based on rock mass quality

Abstract

The invention belongs to the technical field of surface mines, and particularly discloses a large surface mine slope angle optimization method based on rock mass quality, which is used for analyzing engineering geological conditions, slope stability conditions and development trends of rock mass by surveying earth surface engineering geology of a mining area. Investigating and counting the mine slope rock mass, and determining a sampling interval and a drilling scheme according to a pre-feasibility research report; drilling and acquiring parameters corresponding to drilling samples, and grading the rock samples in the mining area according to the parameters of the drilling samples and a grading method; carrying out plane and vertical partition on the mining area slope, and calculating rock mass mechanical parameters of each area and lithology; establishing a small slope three-dimensional model according to an open-pit mining boundary, changing a slope angle, and calculating a safety coefficient to meet a predetermined specification so as to determine a maximum slope angle; an overall slope model is established, the maximum slope angle is set, and the safety coefficient is calculated to take the slope angle of the vertical partition which is improved to the maximum degree as the recommended slope angle. The method has the advantages of being simple, high in operability, stable in slope and low in stripping ratio.

Description

Technical Field

[0001] The present invention relates to the technical field of open-pit mines, and particularly relates to an optimization method for the slope angle of a large open-pit mine based on rock mass quality, which has simple method, strong operability, stable slope and low stripping ratio. Background Art

[0002] The slope angle is the angle between the connecting line from the crest line of the uppermost bench to the toe line of the lowermost bench and the horizontal line on the cross-section perpendicular to the slope strike. During the open-pit mine mining process, the smaller the slope angle, the larger the stripping ratio. Although it can improve the slope stability, it will cause waste of mineral resources; while the larger the slope angle, the smaller the stripping ratio. Although it can increase the recovery rate of mineral resources, especially for large slope deep concave open-pit mines, every 1° increase in the slope angle will save huge costs, but it will not only cause an increase in the amount of stripping rock, but also blindly expanding the slope angle will lead to insufficient slope stability, easily resulting in geological disasters such as landslides, which will affect production at least and cause personal injuries and huge property losses of public property at worst.

[0003] At present, the slope angles of most open-pit mine slopes in China are 35 - 45°, and traditionally, the overall design is a unified slope angle. Although it is very difficult to keep the lithology of the overall slope rock stratum consistent, in order to ensure the slope stability, the overall unified design can only select the unified slope angle in the way of taking the lower rather than the higher value in the whole slope rock mass, which will increase the stripping ratio of the mine and lead to waste of mineral resources. Therefore, the traditional overall slope angle design is not reasonable.

[0004] In the prior art, in order to overcome the deficiencies of the existing unified slope angle, a segmented steepening and platform setting scheme has emerged. The slope is divided into several segments (such as the upper, middle, and lower parts), and different stepped slope angles and platform widths are set in different segments, so as to adapt to different rock layer strengths through local optimization to improve the overall stability. Moreover, the wide platform design can effectively isolate the influence of the upper broken zone on the lower slope to reduce the sliding risk; however, it also has the problems that segmentation relies on a large amount of high-precision geological exploration data, the data acquisition cost is high, and the design needs to be frequently adjusted during the dynamic mining process, resulting in high management complexity. In addition, there is also a rock layer grading and differentiation design scheme, which designs different slope angles based on lithological differences (such as sandstone layers and clay layers), reduces the stripping volume by making full use of the characteristics of high-strength rock layers, and the graded steps of the clay layer can disperse stress and reduce the risk of shallow landslides, so as to balance resource recovery and safety; however, complex lithological combinations may lead to conflicts in design parameters, and repeated verification is required, resulting in low determination efficiency. Additionally, there is also a dynamic programming and stage stability analysis scheme, which combines the dynamic programming algorithm to adjust the slope parameters in real time according to the rock mass quality revealed during the mining process, so as to not only dynamically adapt to the changes in geological conditions to improve resource utilization rate, but also reduce the long-term instability risk through stage safety factor checking; however, due to the need for a supporting real-time monitoring system (such as Internet of Things sensors), the initial investment is large, and the algorithm optimization depends on high-performance computing, which is limited in application in medium and small mines. Moreover, there is a risk probability and multi-objective collaborative optimization scheme, which uses probability methods such as Monte Carlo simulation to evaluate the instability risks of different zones, and combines economic indicators (stripping cost, ore recovery rate) for multi-objective optimization, so as to be applicable to mines with high geological uncertainty; however, due to the complex construction of the probability model and the need for a large amount of historical data support, and the multi-objective optimization may lead to result deviations due to the subjectivity of weight allocation, there are also large initial investment and data preparation workloads, making it difficult to apply to medium and small mines.

[0005] Therefore, by deeply controlling the lithological composition and rock mass quality of the slope, studying a method that can scientifically and accurately determine the slope angles of each rock layer in open-pit mines, and maximizing the optimization of the slope angles under the condition of meeting the slope safety performance, is of great significance for reducing the stripping volume during the mining process, improving the resource recovery rate, reducing investment, and lowering production costs. Summary of the Invention

[0006] Aiming at the deficiencies in the prior art, the present invention provides an optimization method for the slope angles of large open-pit mines based on rock mass quality, which is simple in method, strong in operability, has stable slopes, and low stripping ratios.

[0007] The present invention is implemented as follows: It includes steps of engineering geological investigation, determination of preliminary schemes, rock mass grading evaluation, acquisition of rock mass mechanical parameters, and slope angle optimization. The specific contents are as follows: A. Engineering geological survey: Conduct an engineering geological survey on the rock masses exposed on the surface of a large open-pit mining area, and investigate the hydrogeological conditions of the mining area. Based on the engineering geological survey, draw a stereographic projection diagram, and analyze the lithology of the rock masses, the engineering geological conditions of the slopes, the slope stability status, the development trend, as well as the number and length of joints according to the stereographic projection diagram. B. Determine the preliminary plan: According to the geological conditions of the mining area obtained from the aforementioned engineering geological survey and hydrogeological condition survey, combined with the mining situation in the mining area, conduct an investigation and statistics on the rock masses of the mine slopes according to the distribution position and combination law of the rock masses. Divide the engineering geological zones according to the investigation and statistics report and specifications, and then determine the sampling interval and drilling plan according to the investigation and statistics report and the pre-feasibility study report. C. Rock mass classification and evaluation: Drill holes and make the drill samples in different zones into the sizes required for various mechanical tests. Through the tests, obtain the uniaxial compressive strength, uniaxial compression deformation, tensile strength, shear strength, and point load strength index corresponding to each drill sample. Then calculate the rock Prandtl coefficient according to the aforementioned uniaxial compressive strength. f , according to f classify the rocks contained in the mining area, then calculate the rock quality designation RQD based on the drilling data and record the drilling positions. Finally, evaluate the RMR value based on five evaluation factors: uniaxial compressive strength / point load strength index, rock quality designation RQD, joint spacing, joint condition, and groundwater condition. Classify the rock samples in the mining area using the Prandtl classification method, the RMR classification method based on the RMR value, and the RQD classification method based on the RQD. f D. Obtain rock mass mechanical parameters: Comprehensively consider the rock sample classification results of the aforementioned classification methods, divide the slopes of the large open-pit mining area into plane zones and vertical zones, divide the large slopes into several small slopes, and then select the intact rock constant mi, blasting influence coefficient D, and geological strength index GSI in the Hoek-Brown criterion according to the rock mechanical parameters obtained from the aforementioned mechanical tests. Import the three parameters into the RocLab analysis software for calculation to obtain the rock mass mechanical parameters of each region and each lithology. E. Slope angle optimization: Based on the open-pit mining boundary determined by the slope design of the mine bench, a small three-dimensional slope model is established, and the previously obtained rock mechanics parameters are set. Then, the initial slope angle of the small slope is changed and numerical simulations are carried out under three combined load intensities. The safety factor obtained from the simulation needs to meet the safety factor of the predetermined specification. Subsequently, the maximum slope angle of each vertical partition is obtained. Then, a cross-section of the plane partition is selected to establish an overall large-scale open-pit mine slope model. The corresponding maximum slope angle calculated above is set for each vertical partition, and the corresponding rock mechanics parameters are set. Finally, numerical simulations are carried out under three load intensities to calculate the safety factor. According to the principle of "meeting the overall first and then the local", the maximum slope angle corresponding to each vertical partition is adjusted. Under the condition that the overall safety factor meets the requirements of the predetermined specification safety factor, the slope angle of each vertical partition is maximized, and the maximum angle mentioned above is used as the recommended slope angle.

[0008] Furthermore, the large open-pit mine slope is a large slope over 500m, and there are differences in the lithology of the rock strata and the development of joints and fissures.

[0009] Furthermore, in step A, for the engineering geological survey of the rock mass exposed on the surface of the large open-pit mining area, survey points are selected on the existing topographic map, and then the development of joints and fissures, rock lithology and weathering degree of the rock mass exposed on the surface of the large open-pit mining area are investigated according to the survey points.

[0010] Furthermore, in step B, the geological conditions of the mining area include the distribution state of the rock mass, geological structure and wall rock alteration; dividing the engineering geological zones according to the investigation and statistical report and specifications means, based on the investigation and statistical report, and according to the requirements of GB 51016-2014 "Technical Code for Slope Engineering of Non-coal Open-pit Mines" and GB 12719-2021 "Code for Hydrogeological and Engineering Geological Exploration of Mining Areas", the geology of the entire large open-pit mining area is preliminarily divided; determining the sampling interval and drilling plan according to the investigation and statistical report and pre-feasibility study report means, according to the investigation and statistical report and pre-feasibility study report, comprehensively considering the economic rationality, technical feasibility of drilling implementation and the safety guarantee for future mine exploitation, formulating a targeted slope drilling plan, and completing the logging and sampling work of the drilling.

[0011] Further, in step C, the sizes of the standard specimens required for the tests of uniaxial compressive strength and uniaxial compression deformation are both φ50mm×H100mm, and the sizes of the standard specimens required for the tests of tensile strength and shear strength are both φ50mm×H50mm; based on the test results and the Protodyakonov grading method, RQD grading method, and RMR grading method, a detailed evaluation of the rock mass quality of each partition and each lithology at different mining depths in the mining area is carried out to complete the grading of the rock mass in the mining area; the rock quality designation RQD is the ratio of the cumulative length of the core with a length equal to or greater than 10 cm to the total drilling length, and its calculation method is as follows: 。

[0012] Further, the rock mass grading based on the Protodyakonov grading method according to the test results is to calculate the Protodyakonov coefficient of the rock based on the uniaxial compressive strength f ,and based on the Protodyakonov coefficient of the rock f the rock mass in the mining area is divided into 10 grades and 15 types; among them, the Protodyakonov coefficient of the rock f is: , wherein, R c is the uniaxial compressive strength of the rock, with the unit of MPa.

[0013] Further, the rock mass grading based on the RMR grading method according to the test results is to use the uniaxial compressive strength / point load strength index, rock quality designation RQD, joint spacing, joint condition, and groundwater condition as evaluation factors, and divide the rock mass in the mining area into 5 grades according to the sum of the scores of the above five evaluation factors.

[0014] Further, in step D, considering comprehensively the grading results of the rock samples by the above grading methods, the rock blocks with different grading results are respectively located in the selected areas, and then the large open-pit mine slope is divided into plane partitions according to the above areas, and then the plane partitions are vertically divided to divide the large slope into several small slopes; the intact rock constant mi in the Hoek-Brown criterion reflects the hardness of the rock, and its value range is 0-25; the blasting influence coefficient D takes 1.0 when conventional blasting is used, 0.7 when mechanical excavation is used, and 0.8-0.9 when controlled blasting is used; the geological strength index GSI is calculated and determined according to the empirical formula GSI = RMR - 5.

[0015] Further, the specific process of step E is as follows: Based on the open-pit mining boundary determined by the design of the mine bench slope, and the aforementioned slope plane zoning and vertical zoning, establish 3D models of each small slope divided in the MIDAS software, substitute the rock mass mechanical parameters obtained by the Hoek-Brown criterion into the corresponding 3D models of small slopes, and then, on the premise of fully considering the stability of the pre-designed boundary, based on the slope angle designed in the pre-feasibility study report, sequentially increase or decrease by 0.5 - 1.0° in the 3D models of small slopes and conduct numerical simulation calculations under three combined load intensities. The safety factor obtained needs to meet the safety factor requirements of the preset specification for the three load combinations, and finally obtain the maximum slope angle; then select the plane zoning profile, establish an overall large-scale open-pit mining area slope model, set the corresponding maximum slope angle in each vertical zoning, and then conduct numerical simulation calculations for the safety factor under three combined load intensities. If the obtained safety factor meets the safety factor of the preset specification, the aforementioned maximum slope angles are the recommended slope angles; otherwise, sequentially decrease the maximum slope angle of at least one of the aforementioned vertical zonings by 0.5 - 1.0°, and then return to the overall large-scale open-pit mining area slope model for re-simulation calculations until the safety factor of the overall large-scale open-pit mining area slope meets the safety factor of the preset specification. At this time, the maximum slope angles are the recommended slope angles.

[0016] Further, the preset specification is the "Technical Code for Slope Engineering of Non-Coal Open-Pit Mines" GB51016 - 2014, and the three load combinations are respectively: Load combination Ⅰ is self-weight + groundwater, Load combination Ⅱ is self-weight + groundwater + blasting vibration force, and Load combination Ⅲ is self-weight + groundwater + seismic force.

[0017] The beneficial effects of the present invention: 1. The present invention innovatively adopts rock mass quality classification - three-dimensional zoning modeling - multi-load dynamic verification, enabling the optimization of the slope angle to transform from "extensive and unified" to "fine and dynamic"; first, based on the results of engineering geological surveys and drill sample mechanical tests, conduct differential designs for the geological conditions, rock mass characteristics, and mining requirements of each section. Through rock mass quality classification (Prussian, RQD, and RMR classification methods) and three-dimensional model zoning (slope plane zoning + vertical zoning), divide the overall slope into different regions, and in combination with the principle of "first satisfying the whole and then satisfying the part", dynamically adjust the slope angles of each zoning (step size of 0.5 - 1.0°) through numerical simulation, so as to maximize the slope angles of each zoning under the premise of ensuring safety, achieving the balance between the safety and economic benefits of open-pit mine slopes, which can not only significantly reduce the stripping volume of open-pit mines and lower the stripping ratio, but also effectively improve the recovery rate of mine resources.

[0018] 2. The present invention adopts a hierarchical fusion method. By comprehensively considering the Proctor coefficient (uniaxial compressive strength), RQD (rock quality designation), RMR (geological strength index), and multi-dimensional rock mass quality evaluation, it can effectively reduce the error risk caused by a single parameter. Moreover, by using the intact rock constant mi, blasting coefficient D, and GSI index in the Hoek-Brown criterion and combining with RocLab software, the rock mass mechanical parameters can be automatically calculated, reducing manual intervention and experimental costs. And based on the investigation and statistical reports and pre-feasibility study reports, the drilling plan is dynamically adjusted, which can effectively reduce the redundant exploration workload and lower the data acquisition cost. Also, by simplifying the parameter acquisition process (such as the GSI empirical formula) and modular modeling, the dependence on high-performance computing is reduced, and the application cost is lowered. It is applicable to high-steep and deep open-pit mines, complex rock formations, and small and medium-sized mine scenarios, with significant promotion potential.

[0019] 3. The present invention uses MIDAS software to simulate three load combinations for the partitioned small slope model, which can ensure the stability of each partition. And by combining the principle of "meeting the overall first and then the local", the slope angles of each partition are dynamically adjusted, so as to realize the coordinated optimization of the safety and economy of the open-pit mine slope and improve the adaptability of the open-pit mine slope.

[0020] 4. The present invention strictly follows the "Technical Code for Non-coal Open-pit Mine Slope Engineering" GB 51016-2014 and the "Code for Hydrogeological and Engineering Geological Exploration of Mining Areas" GB 12719-2021, which can ensure the design compliance. Moreover, by clarifying the specimen size (such as φ50mm×H100mm) and the value of the blasting coefficient D (D = 0.7 for mechanical excavation, D = 0.8 - 0.9 for controlled blasting), the parameters are made transparent, thereby reducing the human operation deviation. While improving the operability, the optimization process is also simplified.

[0021] In summary, the present invention has the characteristics of simple method, strong operability, stable slope, and low stripping ratio. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is the slope partition and stereographic projection diagram in the embodiment of the present invention; Figure 2 is Figure 1 the top view of the horizontal partition slope of Figure 3 is Figure 2 the grading and sectional view of slope area III before the optimization of the slope angle of Figure 4 is Figure 2 the grading and sectional view III-1 of slope area III after the optimization of the slope angle of DETAILED DESCRIPTION OF THE INVENTION

[0023] In order to make the objectives, technical solutions and advantages of the present invention more clear and understandable, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0024] The present invention includes steps of engineering geological survey, determining a preliminary plan, rock mass classification evaluation, obtaining rock mass mechanical parameters, and slope angle optimization. The specific contents are as follows: A. Engineering geological survey: Conduct an engineering geological survey on the rock masses exposed on the surface of a large open-pit mining area, and investigate the hydrogeological conditions of the mining area. According to the engineering geological survey, draw a stereographic projection diagram, and analyze the lithology of the rock mass, slope engineering geological conditions, slope stability status, development trend, as well as the number and length of joints based on the stereographic projection diagram; B. Determining a preliminary plan: Based on the geological conditions of the mining area obtained from the aforementioned engineering geological survey and hydrogeological condition survey, combined with the mining situation of the mining area, conduct an investigation and statistics on the rock masses of the mine slope according to the distribution position and combination law of the rock masses. Divide the engineering geological zones according to the investigation and statistics report and specifications, and then determine the sampling interval and drilling plan according to the investigation and statistics report and the pre-feasibility study report; C. Rock mass classification evaluation: Drill holes and make the drill samples in different zones into the sizes required for each mechanical test. Through the test, obtain the uniaxial compressive strength, uniaxial compression deformation, tensile strength, shear strength, and point load strength index corresponding to each drill sample. Then calculate the rock's Proctor coefficient according to the aforementioned uniaxial compressive strength f , according to f classify the rocks contained in the mining area, then calculate the rock quality designation RQD based on the drilling data and record the drilling positions. Finally, evaluate the RMR value based on five evaluation factors: uniaxial compressive strength / point load strength index, rock quality designation RQD, joint spacing, joint condition, and groundwater condition. Classify the rock samples in the mining area using the Proctor classification method, the RMR classification method according to the RMR value, and the RQD classification method according to the RQD; f D. Obtaining rock mass mechanical parameters: Comprehensively consider the rock sample classification results of the aforementioned classification methods, conduct plane zoning and vertical zoning on the slopes of the large open-pit mining area. Divide the large slope into several small slopes. Then select the intact rock constant mi, blasting influence coefficient D, and geological strength index GSI in the Hoek-Brown criterion according to the rock mechanical parameters obtained from the aforementioned mechanical tests. Import the three parameters into the RocLab analysis software for calculation to obtain the rock mass mechanical parameters of each region and each lithology; ​E. Optimization of slope angle: Based on the open-pit mining boundary determined by the slope design of the mine bench, a small three-dimensional slope model is established, and the previously obtained rock mechanics parameters are set. Then, the initial slope angle of the small slope is changed and numerical simulations are carried out under three combined load intensities. The safety factor obtained from the simulation needs to meet the safety factor of the predetermined specification. Subsequently, the maximum slope angle of each vertical partition is obtained. Then, a plane partition profile is selected to establish an overall large-scale open-pit mining area slope model. The corresponding maximum slope angles calculated above are set in each vertical partition, and the corresponding rock mechanics parameters are set. Finally, numerical simulations are carried out under three load intensities to calculate the safety factor. According to the principle of "meeting the overall first and then the local", the maximum slope angles corresponding to each vertical partition are adjusted. Under the condition that the overall safety factor meets the requirements of the predetermined specification, the slope angles of each vertical partition are maximally increased, and the aforementioned maximum angle is used as the recommended slope angle.

[0025] The large open-pit mine slope is a large slope exceeding 500 m, and there are differences in the lithology of the rock strata and the development of joints and fissures.

[0026] It should be noted that the stereographic projection is a projection diagram drawn based on data such as the number, distribution density, joint strike, and opening length of engineering joints and fissures. The aforementioned data are obtained through engineering geological survey sampling. The stereographic projection is the visualization of the investigation of joints and fissures and is for facilitating the analysis of engineering conditions. The analysis results obtained from the stereographic projection need to be compared with the partitions of different geological regions according to the actual situation of the project. Areas with more joints are more prone to accidents such as landslides than areas with fewer joints.

[0027] It should be noted that the uniaxial compressive strength / point load strength index means choosing either one. Preferably, when the standard test specimen of uniaxial compression of the rock sample cannot be obtained, the point load strength index can be used for calculation.

[0028] In step A, for the engineering geological survey of the rock mass exposed on the surface of the large open-pit mining area, survey points are selected on the existing topographic map, and then the development of joints and fissures, rock lithology, and weathering degree of the rock mass exposed on the surface of the large open-pit mining area are investigated according to the survey points.

[0029] In the step B, the geological conditions of the mining area include the distribution state of rock masses, geological structures, and wall rock alterations. Dividing the engineering geological zones according to the investigation and statistical reports and specifications means preliminarily zoning the geology of the entire large-scale open-pit mining area based on the investigation and statistical reports and in accordance with the requirements of the Technical Code for Slope Engineering of Non-Coal Open-Pit Mines (GB 51016-2014) and the Exploration Code for Hydrogeology and Engineering Geology of Mining Areas (GB 12719-2021). Determining the sampling intervals and borehole schemes according to the investigation and statistical reports and the pre-feasibility study report means formulating a targeted slope borehole scheme considering the economic rationality, technical feasibility of borehole implementation, and safety guarantee for future mine exploitation based on the investigation and statistical reports and the pre-feasibility study report, and completing the logging and sampling work of the boreholes.

[0030] In the step B, the mining situation in the mining area includes the mining scope, degree, and mining method (manual, mechanical, or blasting mining) of the mining area. Conducting an investigation and statistics on the rock masses of the mine slope according to the distribution position and combination law means investigating and statistically analyzing the lithology, distribution depth, and distribution range of the rock masses in the mining area based on the geological conditions of the mining area and in combination with the mining situation in the mining area.

[0031] In the step C, the sizes of the standard specimens required for the tests of uniaxial compressive strength and uniaxial compression deformation are both φ50mm×H100mm, and the sizes of the standard specimens required for the tests of tensile strength and shear strength are both φ50mm×H50mm. Based on the test results and using the Proctor classification method, RQD classification method, and RMR classification method, a detailed evaluation of the rock mass quality of each zone and each lithology at different mining depths in the mining area is carried out to complete the classification of the rock masses in the mining area. The rock quality designation RQD is the ratio of the cumulative length of rock cores equal to or greater than 10 cm to the total drilling length, and its calculation method is as follows: 。

[0032] Conducting rock mass classification according to the test results and based on the Proctor classification method means calculating the Proctor coefficient of the rock according to the uniaxial compressive strength f , and based on the Proctor coefficient of the rock f the rock masses in the mining area are divided into 10 grades and 15 types as shown in Table 1: Table 1 Rock mass grades determined by the Proctor classification method

[0033] Among them, the Proctor coefficient of the rock f is: , In the formula, R c is the uniaxial compressive strength of the rock, with the unit of MPa.

[0034] The rock mass classification based on the test results and the RMR classification method uses the uniaxial compressive strength / point load strength index, rock quality designation RQD, joint spacing, joint condition, and groundwater condition as evaluation factors. The rock mass in the mining area is divided into 5 grades as shown in Table 2 according to the sum of the scores of the above five evaluation factors: Table 2 Rock Mass Grades Determined by the RMR Classification Method .

[0035] In step D, considering the rock sample classification results of the above classification methods comprehensively, the rock blocks with different classification results are respectively located in the selected area. Subsequently, the large open-pit mine slope is divided into plane partitions according to the above area, and then the plane partitions are vertically partitioned, and the large slope is divided into several small slopes; the intact rock constant mi in the Hoek-Brown criterion reflects the hardness of the rock, and its value range is 0-25, where the ideal intact hard rock mass takes 25; the blasting influence coefficient D takes 1.0 for conventional blasting, 0.7 for mechanical excavation, and 0.8-0.9 for controlled blasting; the geological strength index GSI is calculated and determined according to the empirical formula GSI = RMR - 5.

[0036] The specific process of step E is as follows: According to the open-pit mining boundary determined by the design of the mine bench slope and the above-mentioned slope plane partition and vertical partition, a three-dimensional model of each small slope is established in the MIDAS software. Substitute the rock mass mechanical parameters obtained by the Hoek-Brown criterion into the corresponding three-dimensional model of the small slope. Then, considering the stability of the pre-designed boundary, based on the slope angle designed in the pre-feasibility study report, increase or decrease by 0.5-1.0° in turn in the three-dimensional model of the small slope and perform numerical simulation calculations under three combined load intensities. The safety factor obtained needs to meet the safety factor requirements of the preset specification for the three load combinations, and finally obtain the maximum slope angle; then select the plane partition profile, establish an overall model of the large open-pit mine slope, set the corresponding maximum slope angle in each vertical partition, and then perform numerical simulation calculations for the safety factor under the three combined load intensities. If the obtained safety factor meets the safety factor of the preset specification, the above maximum slope angles are the recommended slope angles; otherwise, decrease the maximum slope angle of at least one of the above vertical partitions by 0.5-1.0° in turn, and then return to the overall large open-pit mine slope model for re-simulation calculation until the safety factor of the overall large open-pit mine slope meets the safety factor of the preset specification. At this time, the maximum slope angles are the recommended slope angles.

[0037] The pre-set specification is GB51016-2014, "Technical Specification for Slope Engineering in Non-Coal Open-Pit Mine," and the three load combinations are: Load Combination I (deadweight + groundwater), Load Combination II (deadweight + groundwater + blasting vibration), and Load Combination III (deadweight + groundwater + seismic force). The safety factor requirements for the three load combinations are shown in Table 3. Table 3 Design safety factors of overall slope under different load combinations .

[0038] Example S100: A total of 15 survey points were selected on the existing topographic map of the slope of the large open-pit mine area for investigation. The hydrogeological conditions of the mining area were investigated. Then, the development of rock joints and fissures exposed on the surface of the large open-pit mine area was investigated based on the survey points. A total of 357 joints and fissures were found. Based on the above investigation results, a stereographic projection map was drawn ( Figure 1 ), and then analyze the rock properties, slope engineering geological conditions, slope stability, development trend, and the number and length of joints based on the stereographic projection map.

[0039] S200: Based on the geological conditions of the mining area obtained from the aforementioned engineering geological survey and hydrogeological condition survey, combined with the mining conditions such as the scope, degree, and mining method (manual, mechanical or blasting mining) of the mining area, the rock mass of the mine slope was investigated and statistically analyzed according to the distribution position and combination law of the rock mass. It was found that the main rock types of the slope include andesite, quartz sandstone, and porphyry, and the failure mode is mainly arc and wedge-shaped, with overall joints and fissures developed and the rock is broken; according to the aforementioned survey and statistical report and GB 51016-2014 "Technical Specifications for Slope Engineering of Non-coal Open-pit Mines" and GB According to the requirements of 12719-2021 "Specifications for Hydrogeological and Engineering Geological Exploration in Mining Areas", the slope of the mining area was divided into four zones; then, based on the survey and statistical report and the preliminary feasibility study report, the economic rationality, technical feasibility and safety guarantee of drilling implementation were comprehensively considered, and 49 exploration drilling holes were planned to complete resource survey work within the mining area. Later, in order to meet the exploration needs, 21 exploration holes were arranged more densely, and a drilling workload of 13,984.577 m was completed. Finally, the cataloging and sampling of the drill holes were completed.

[0040] S300: Drill holes and make the drilled samples in different zones into the required sizes for each mechanical test (the sizes of the standard test specimens for uniaxial compressive strength and uniaxial compression deformation are both φ50mm×H100mm, and the sizes of the standard test specimens for tensile strength and shear strength are both φ50mm×H50mm). The test obtains the corresponding uniaxial compressive strength, uniaxial compression deformation, tensile strength, shear strength and point load strength index of each rock sample, and then calculates the rock Proctor coefficient based on the aforementioned uniaxial compressive strength. f ,according tof Classify the rocks contained in the mining area, then calculate the Rock Quality Designation (RQD) based on the borehole data and record the borehole positions. Finally, evaluate the Rock Mass Rating (RMR) value according to five evaluation factors: uniaxial compressive strength / point load strength index, Rock Quality Designation (RQD) of core rocks, joint spacing, joint condition, and groundwater condition (as shown in Table 4), and classify the rock mass of the mining area according to the Protodyakonov coefficient f Adopt the Protodyakonov classification method, the RMR classification method based on the RMR value, and the RQD classification method based on the RQD to conduct a detailed rock mass quality evaluation for each subarea and each lithology at different mining depths in the mining area, and complete the classification of the rock mass in the mining area.

[0041] Table 4 RMR system classification table

[0042] Among them, for the rock mass classification based on the test results and the Protodyakonov classification method, the Protodyakonov coefficient of the rock is calculated according to the uniaxial compressive strength f , and based on the Protodyakonov coefficient of the rock f The rock mass in the mining area is divided into 10 grades and 15 types as shown in Table 1.

[0043] Among them, the Protodyakonov coefficient of the rock f is: , In the formula, R c is the uniaxial compressive strength of the rock, with the unit of MPa.

[0044] For the rock mass classification based on the test results and the RMR classification method, the uniaxial compressive strength / point load strength index, Rock Quality Designation (RQD) of core rocks, joint spacing, joint condition, and groundwater condition are used as evaluation factors. According to the RMR value (the sum of the scores of the five evaluation factors) evaluated by the above five evaluation factors, the rock mass in the mining area is divided into 5 grades as shown in Table 2.

[0045] As Figure 2 shown, taking Subareas III and IV in the mining area as examples, the final height of the slope of the main profile in Subarea III is 975 m. The overall lithology is mainly quartz sandstone, containing a small amount of porphyry; the joint fissures are developed, the rock is relatively broken, and the RQD value of the rock mass is about 18.6 - 20.5; after conducting mechanical tests on the rock samples in this area, the uniaxial compressive strength of the quartz sandstone in this area is 32.7 - 51.8 MPa. Before detailed subarea classification, the overall slope angle of the slope is 34.5°.

[0046] The final height of the slope of the main profile in the IVth partition area is 1110 m. The overall lithology is mainly quartz sandstone, including a small part of porphyry. Joints and fissures are developed, the rock is relatively fragmented, and the RQD value of the rock mass is about 9.8 - 29.0. After carrying out mechanical tests on the rock samples in this area, the uniaxial compressive strength of the quartz sandstone in this area is 15.9 - 54.7 MPa. Before detailed zoning and grading, the overall slope angle of the slope is 37°.

[0047] S400: Considering comprehensively the grading results of rock samples by the aforementioned Prandtl grading method, RQD grading method and RMR grading method, the rock blocks with different grading results are respectively located in the selected area. Subsequently, the slope of the large open-pit mining area is divided into plane partitions according to the aforementioned area, and then the plane partitions are vertically divided to divide the large slope into several small slopes. Subsequently, according to the rock mechanics parameters obtained from the aforementioned mechanical tests, the complete rock constant mi (the value range is 0 - 25, and 25 is taken for the ideal complete hard rock mass), the blasting influence coefficient D (1.0 is taken when conventional blasting is used, 0.7 is taken when mechanical excavation is used, and 0.8 - 0.9 is taken when controlled blasting is used), and the geological strength index GSI (determined according to the empirical formula GSI = RMR - 5) in the Hoek - Brown criterion are selected, and the three parameters are imported into the RocLab analysis software for calculation to obtain the rock mass mechanics parameters of each area and each lithology.

[0048] As Figure 3 shown, according to the Prandtl grading method, RQD grading method, RMR grading method and the position of the rock stratum distribution, the plane of the IIIrd partition area is divided into two areas, which are respectively designated as III - 1 and III - 2 (according to the lithology position selected by the drill samples, the position of the lithology in the mine can be accurately located. The boundary line between the poorer lithology and the better lithology is the partition line. In this embodiment, there are a total of four boundary lines from the better rock stratum to the relatively better rock stratum in the whole mine. In the four areas, it can be further refined into two areas according to the quality of the lithology), and the parameters determined by the Hoek - Brown criterion are substituted into RocLab for calculation and analysis, and the cohesion c of the quartz sandstone and porphyry in the IIIrd area are 0.627 - 1.408 MPa and 0.95 MPa respectively, and the internal friction angles are 20.39 - 35.47° and 27.24° respectively.

[0049] According to the Prandtl grading method, RQD grading method, RMR grading method and the position of the rock stratum distribution, the plane of the IVth partition area is divided into three areas, which are respectively designated as IV - 1, IV - 2, and IV - 3, and the parameters determined by the Hoek - Brown criterion are substituted into RocLab for calculation and analysis to obtain that the cohesion c of the quartz sandstone, andesite and porphyry in the IVth area are 0.624 MPa, 0.439 - 1.374 MPa and 0.935 MPa respectively, and the internal friction angles are 34.37°, 15.70 - 35.00° and 26.99° respectively.

[0050] S500: Based on the open-pit mining boundary determined according to the design of the mine bench slope, as well as the aforementioned plane zoning and vertical zoning of the slope, establish 3D models of each small slope divided in the MIDAS software. Substitute the rock mass mechanical parameters obtained by the Hoek-Brown criterion into the corresponding 3D models of small slopes. Then, on the premise of fully considering the stability of the pre-designed boundary, based on the slope angle designed in the pre-feasibility study report, increase or decrease by 0.5 - 1.0° successively in the 3D models of small slopes and conduct numerical simulation calculations under three combinations of load intensities. The safety factors obtained should meet the safety factor requirements for the three load combinations in the "Technical Code for Non-coal Open-pit Mine Slope Engineering" GB51016-2014, and finally obtain the maximum slope angle of each vertical zoning. Then select the plane zoning section, establish an overall large-scale open-pit mining area slope model, set the corresponding maximum slope angles obtained above in each vertical zoning, and then conduct numerical simulation calculations for the safety factor under three combinations of load intensities. If the obtained safety factor meets the safety factor of the predetermined code, the aforementioned maximum slope angles are the recommended slope angles; otherwise, decrease the maximum slope angle of at least one of the aforementioned vertical zonings by 0.5 - 1.0° successively, and then return to the overall large-scale open-pit mining area slope model for re-simulation calculation until the safety factor of the overall large-scale open-pit mining area slope meets the safety factor in the "Technical Code for Non-coal Open-pit Mine Slope Engineering" GB51016-2014. At this time, the maximum slope angles are the recommended slope angles.

[0051] Among them, the three load combinations are respectively: Load combination I is self-weight + groundwater; Load combination II is self-weight + groundwater + blasting vibration force; Load combination III is self-weight + groundwater + seismic force. The safety factor requirements of the preset code for the three load combinations are shown in Table 3.

[0052] The slope height of the III-1 section is about 975m. In the area of the slope in the shallow part with a height of about 557m, the lithology is poor (positioned according to drill samples and test data, the lithology of the entire slope shows differences at 557m. The part above 557m has relatively better lithology. This poor is relative and has nothing to do with good or bad in the code, that is, the RMR value evaluated by three methods in this area is lower than that of the area above 557m. In numerical simulation, there will be different situations when changing the slope angle with such rock mass mechanical parameters). Therefore, the slope section can be optimized and analyzed, and the local slope angle of this area of the slope can be reduced. Finally, the slope angle of the non-shallow slope area is selected as 41.5°, and the slope angle of the shallow slope area is selected as 34.5°. The slope height of the III-2 section is about 945m. In the area of the slope in the shallow part with a height of about 512m, the lithology is poor. Therefore, the slope section can be optimized and analyzed. By reducing the local slope angle of this area of the slope, finally, the slope angle of the non-shallow slope area is selected as 42°, and the slope angle of the shallow slope area is selected as 36°.

[0053] After the plane partition and vertical partition, the overall slope safety factor of the III-1 partition is 1.244 under load combination I, 1.198 under load combination II, and 1.158 under load combination III; the overall slope safety factor of the III-2 partition is 1.235 under load combination I, 1.192 under load combination II, and 1.155 under load combination I, all meeting the requirements described in Table 3.

[0054] The slope height of the IV-1 section is about 1080 m, the overall optimized slope angle of the IV-1 section is 38.5°, and the average safety factors of the slope in the area with a height of about 246 m in the shallow area under two load combination conditions are both less than the allowable value of the specification (the safety factor is the standard for evaluating the stability of a slope in the numerical simulation software. Applying different loads will cause changes in the lithology, so the slope safety factor will change. The slope safety factor needs to meet the specification requirements. If the slope safety factor does not meet the specification requirements, there are potential safety hazards, and the slope needs to be flattened or cut to improve the slope safety factor). Therefore, the optimization analysis of this slope section can be carried out. Lower the local slope angle of the slope in this area. The safety factors of each plan and the final optimized plan during the optimization process are as follows: According to the calculation results, the slope angle of the shallow area of the IV-1 section is finally selected as 39°. The slope height of the IV-2 section is 1110 m, the designed overall slope angle is 40°, and the safety factors all meet the specification requirements. The slope height of the IV-3 section is about 1005 m, and the overall optimized slope angle of the IV-1 section is 41.5°, and the safety factors all meet the specification requirements.

[0055] After the plane partition and vertical partition, the overall slope safety factor of the IV-1 partition is 1.236 under load combination I, 1.194 under load combination II, and 1.157 under load combination III; the overall slope safety factor of the IV-2 partition is 1.233 under load combination I, 1.190 under load combination II, and 1.154 under load combination III; the overall slope safety factor of the IV-3 partition is 1.231 under load combination I, 1.190 under load combination II, and 1.156 under load combination III, all meeting the requirements described in Table 3.

[0056] The above is only the preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. An optimization method for the slope angle of large open-pit mines based on rock mass quality, characterized in that: It includes engineering geological investigation, determining the preliminary scheme, rock mass classification evaluation, obtaining rock mass mechanical parameters, and slope angle optimization steps. The specific contents are as follows: A. Engineering geological investigation: Conduct an engineering geological investigation on the rock masses exposed on the surface of a large open-pit mining area, and investigate the hydrogeological conditions of the mining area. According to the engineering geological investigation results, draw a stereographic projection diagram, and analyze the lithology of the rock mass, slope engineering geological conditions, slope stability status, development trend, as well as the number and length of joints based on the stereographic projection diagram; B. Determining the preliminary scheme: Based on the geological conditions of the mining area obtained from the aforementioned engineering geological investigation and hydrogeological condition investigation, combined with the mining situation in the mining area, conduct an investigation and statistics on the rock masses of the mine slope according to the distribution position and combination law of the rock masses. Divide the engineering geological zones according to the investigation and statistics report and specifications, and then determine the sampling interval and drilling scheme according to the investigation and statistics report and pre-feasibility study report; C. Rock mass classification and evaluation: Drill holes and make drill samples from different zones into the sizes required for various mechanical tests. Obtain the uniaxial compressive strength, uniaxial compression deformation, tensile strength, shear strength, and point load strength index corresponding to each drill sample through tests. Then calculate the rock Prandtl coefficient based on the aforementioned uniaxial compressive strength f , according to f classify the rocks contained in the mining area, then calculate the rock quality designation RQD based on the drill hole data and record the drill hole positions. Finally, evaluate the RMR value based on five evaluation factors: uniaxial compressive strength / point load strength index, rock quality designation RQD, joint spacing, joint condition, and groundwater condition. According to the Prandtl coefficient f classify the rock samples in the mining area using the Prandtl classification method, the RMR classification method based on the RMR value, and the RQD classification method based on the RQD D. Obtaining rock mass mechanical parameters: Comprehensively consider the rock sample classification results of the aforementioned various classification methods, divide the slope of the large open-pit mining area into plane partitions and vertical partitions. Divide the large slope into several small slopes, and then select the intact rock constant mi, blasting influence coefficient D, and geological strength index GSI in the Hoek-Brown criterion according to the rock mechanical parameters obtained from the aforementioned mechanical tests. Import the three parameters into the RocLab analysis software for calculation to obtain the rock mass mechanical parameters of each region and each lithology; E. Slope angle optimization: According to the open-pit mining boundary determined by the design of the mine bench slope, establish a three-dimensional model of the small slope, set the aforementioned obtained rock mechanical parameters, and then change the initial slope angle of the small slope and conduct numerical simulations under three combined load intensities. The safety factor obtained from the simulation needs to meet the safety factor of the predetermined specifications. Subsequently, obtain the maximum slope angle of each vertical partition; then select the plane partition profile, establish an overall model of the large open-pit mining area slope, set the corresponding maximum slope angle calculated above in each vertical partition, and set the corresponding rock mechanical parameters. Finally, conduct numerical simulation calculations of the safety factor under three load intensities, and adjust the maximum slope angle corresponding to each vertical partition according to the principle of "meeting the overall first and then the local". When the overall safety factor meets the requirements of the predetermined specification safety factor, maximize the slope angle of each vertical partition, and use the aforementioned maximum angle as the recommended slope angle.

2. The large open-pit mine slope angle optimization method based on rock mass quality according to claim 1, characterized in that: The large open-pit mine slope is a large slope exceeding 500m, and there are differences in the lithology of the rock strata and the development of joint fissures.

3. The large open-pit mine slope angle optimization method based on rock mass quality according to claim 1, characterized in that: In step A, when conducting an engineering geological investigation on the rock masses exposed on the surface of the large open-pit mining area, investigation points are selected on the existing topographic map, and then the development of joint fissures, rock lithology, and weathering degree of the rock masses exposed on the surface of the large open-pit mining area are investigated according to the investigation points.

4. The large open-pit mine slope angle optimization method based on rock mass quality according to claim 1, characterized in that: In the step B, the geological conditions of the mining area include the distribution state of rock masses, geological structures, and wall rock alteration. Dividing the engineering geological zones according to the investigation and statistical report and specifications means, based on the investigation and statistical report, and in accordance with the requirements of the Technical Code for Slope Engineering of Non-Coal Open-Pit Mines (GB51016-2014) and the Exploration Code for Hydrogeology and Engineering Geology of Mining Areas (GB12719-2021), preliminarily dividing the geology of the entire large-scale open-pit mining area; determining the sampling interval and borehole scheme according to the investigation and statistical report and the pre-feasibility study report means, based on the investigation and statistical report and the pre-feasibility study report, comprehensively considering the economic rationality, technical feasibility of borehole implementation, and safety guarantee for future mine exploitation, formulating a targeted slope borehole scheme, and completing the logging and sampling work of the boreholes.

5. The large open-pit mine slope angle optimization method based on rock mass quality according to claim 1, characterized in that: In the C step, the sizes of the standard specimens required for the tests of uniaxial compressive strength and uniaxial compression deformation are both φ50mm×H100mm, and the sizes of the standard specimens required for the tests of tensile strength and shear strength are both φ50mm×H50mm; according to the test results and based on the Proctor classification method, the RQD classification method and the RMR classification method, a detailed evaluation of the rock mass quality of each partition and each lithology at different mining depths in the mining area is carried out to complete the classification of the rock mass in the mining area; the rock quality designation RQD is the ratio of the cumulative length of the core with a length equal to or greater than 10 cm to the total drilling length, and its calculation method is as follows: .

6. The method for optimizing the slope angle of a large open-pit mine based on rock mass quality according to claim 5, characterized in that: The rock mass classification is carried out according to the test results and based on the Protodyakonov grading method, and the Protodyakonov coefficient of the rock is calculated according to the uniaxial compressive strength. f , and according to the Protodyakonov coefficient of the rock f , the rock masses in the mining area are divided into 10 grades and 15 types; among them, the Protodyakonov coefficient of the rock f is as follows: ， In the formula, R c is the uniaxial compressive strength of the rock, with the unit of MPa.

7. The method for optimizing the slope angle of a large open-pit mine based on rock mass quality according to claim 5, characterized in that: The rock mass classification based on the RMR classification method according to the test results means using the uniaxial compressive strength / point load strength index, rock quality designation RQD, joint spacing, joint condition, and groundwater condition as evaluation factors, and classifying the rock masses in the mining area into 5 grades according to the sum of the scores of the above five evaluation factors.

8. The large open-pit mine slope angle optimization method based on rock mass quality according to claim 1, characterized in that: In the step D, comprehensively considering the rock sample classification results of the above classification methods means positioning the rock blocks with different classification results in the selected areas respectively, then dividing the slope of the large-scale open-pit mining area into plane zones according to the above areas, and then dividing the plane zones vertically, dividing the large slope into several small slopes; the intact rock constant mi in the Hoek-Brown criterion reflects the hardness of the rock, and its value range is 0-25; the blasting influence coefficient D takes 1.0 for conventional blasting, 0.7 for mechanical excavation, and 0.8-0.9 for controlled blasting; the geological strength index GSI is calculated and determined according to the empirical formula GSI = RMR - 5.

9. The method for optimizing the slope angle of a large open-pit mine based on rock mass quality according to any one of claims 1 to 8, characterized in that: The specific process of step E is as follows: Based on the open-pit mining boundary determined by the design of the mine bench slope, and the aforementioned slope plane zoning and vertical zoning, establish 3D models of each small slope divided in the MIDAS software. Substitute the rock mass mechanical parameters obtained by the Hoek-Brown criterion into the corresponding 3D models of small slopes. Then, considering the stability of the pre-designed boundary, based on the slope angle designed in the pre-feasibility study report, increase or decrease by 0.5 - 1.0° in turn in the 3D models of small slopes and conduct numerical simulation calculations under three combined load intensities. The safety factor obtained needs to meet the safety factor requirements of the preset specification for the three load combinations, and finally obtain the maximum slope angle. Then, select the plane zoning profile, establish an overall large open-pit mining area slope model, set the corresponding maximum slope angle in each vertical zoning, and then conduct numerical simulation calculations of the safety factor under three combined load intensities. If the obtained safety factor meets the safety factor of the preset specification, the aforementioned maximum slope angles are the recommended slope angles; otherwise, decrease the maximum slope angle of at least one of the aforementioned vertical zonings by 0.5 - 1.0° in turn, and then return to the overall large open-pit mining area slope model for re-simulation calculation until the safety factor of the overall large open-pit mining area slope meets the safety factor of the preset specification. At this time, the maximum slope angles are the recommended slope angles.

10. The large open-pit mine slope angle optimization method based on rock mass quality according to claim 9, characterized in that: The preset specification is the "Technical Code for Slope Engineering of Non-coal Open-pit Mines" GB51016 - 2014. The three load combinations are: Load combination Ⅰ is self-weight + groundwater; Load combination Ⅱ is self-weight + groundwater + blasting vibration force; Load combination Ⅲ is self-weight + groundwater + seismic force.

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