The purpose of combined open-pit mining and underground mining is to make effective use of the complementary advantages of open-pit mining and underground mining, and at the same time minimize the coupling influence of both sides. In the process of joint mining, their interaction is mainly manifested in three aspects: first, underground mining weakens the slope rock mass in its affected area, activates the weak structural plane inside the slope system, and makes the slope system which is adjusted for stress state due to open-pit excavation unloading disturbed again, which easily leads to the occurrence of slope instability disasters. Second, the unloading effect of open-pit mining will also have an impact on underground mining, especially the repeated loading of dynamic loads such as open-pit blasting, which will lead to the loosening of rock mass and even the instability of surrounding rock of roadway. Thirdly, due to the overlapping of its influence domains, its mining effects are superimposed, coupled and amplified, leading to disasters.
According to these three aspects, we can analyze the existing or future risk factors that affect safety. In view of these risk factors, detection, testing and risk analysis are carried out to provide basis for the next monitoring, early warning and treatment.
China International Consulting Co., Ltd. conducted a technical consultation study on the stability technology of rock mass (slope) between Anjialing wells in Pingshuo. Through field investigation, the influence of combined open-pit mining on the safety of open-pit slope and surrounding buildings is analyzed. The method of selecting and determining the typical profile is used to check the danger.
You can also use the above investigation methods to investigate the risk factors first, and then determine the typical profile to carry out the work.
Selection principle of (1) typical profile
1) Through field survey, investigation and analysis, select the representative section with poor dynamic stability in the current slope;
2) Analyze and judge the representative sections in the upper kiln dump and open pit slope which are most affected by underground mining and coal mining subsidence;
(three) underground mining and coal mining subsidence may affect and endanger the safety of important buildings on the ground;
4) The representative section with the most unfavorable slope stability under the combined action of underground mining and open-pit mining.
(2) Typical sections selected according to the above principles
1) Typical section (3-3' section) is located in the southwest of Shangyao dump.
This section is located in the southwest of the dump outside the upper kiln, and the strike is NE60. Although there is a certain distance from the first mining area, the ring track is located at the foot of the slope, and there is a powder magazine under the southwest slope. Maximum row height 150m, toe 14, 20m of basement soil, and dip angle of about 8 ~ 10. The slope stability in this section area is directly related to the safety of loop line and powder magazine.
2) Typical section (4-4' section) in the southwest of the upper kiln head.
This section is located in the southwest of the upper kiln dump, southeast of section C-C', and heading for NE60. Due to underground mining subsidence in Shangyaojing mining area, the loop line is located at the foot of the slope, and the high-voltage overhead line passes along the slope. The basement soil layer is 5m thick and the dip angle is about 5.
The main reasons for choosing two sections in the southwest of Shangyao are: the slope is inclined, there are important buildings on the ground near the bottom of the slope, and there is underground mining under the dump, which may endanger the stability of the dump slope after the ground subsidence.
3) Typical section (section C-C') of the slope between belt conveyor lines in the east and west areas of the upper kiln dump.
This section is located in the typical slope section of the transportation line between the eastern dump outside Shangyao, with Shangyaojing mining area on both sides and Xijiejing mining area on the east, with the strike of SW78. West row height 104m, slope angle 16, foundation soil thickness of 23m, and dip angle of about 2; The height of the east row is 67m, the slope angle is 12, and the basement soil layer is inclined. The slope stability in this profile area is very important to the safety of transportation channel and the normal stripping transportation production of open pit mine.
4) Typical section (section F-F') of the upper kiln dump at the southern end of open pit combined mining.
This profile includes the lower slope of the south side slope and the west dump of Shangyao (the lower part is the first mining area of well mining), which is a typical profile with the highest overall slope height and the greatest influence of the joint action of well mining and open pit. Above the floor of No.4 coal seam, it is 220m high from the surface slope, in which the height of the lower slope on the south side of the side pit is 130m, and the dip angle is 29, and the strata are inverted, with a dip angle of about 2; The slope of the west dump is 90m high, with a slope angle of 20 and a soil layer thickness of 18m. No.4 coal seam in Shangyaojing mining area has a buried depth of105 ~165m and a width of 240m ... There are high-voltage overhead lines, strip corridors and railway transportation lines in the south of the profile. Therefore, this section is an important and representative typical section, which has the greatest impact on open-pit mining, and the slope stability is most affected by the combination of open-pit mining and underground mining, and there are important structures on the ground.
5) Typical profile (E-E profile) of the north open-pit non-mining area where open-pit mining is combined with open-pit workers.
This profile is the slope profile of the northern end of the open-pit mine in the south side of the underground mining area without open-pit mining area, and it strikes NE0, the floor elevation difference of 9# coal seam from the ground 180m, the slope angle is 29, the soil layer thickness is 4 1m, and the rock stratum dip angle is about 5. The main inclined shaft and auxiliary inclined shaft of production well are near the north slope; The strata at the northern end are inclined along the slope, and the clay layer in the loess layer and the weathering layer in the 4# coal roof are two weak layers. In 2002, cracks appeared in 1300, 1360 and 1375. End-side drift mining; The overall slope angle is 3 1, and the maximum slope angle of local slope is above 40. Therefore, comparatively speaking, it is one of the sections with the worst influence on the stability of the lower slope under the combined action of open pit and underground mining.
Figure 8- 14 open-pit combined mining position and typical profile position
6) Typical profiles (X-X' profile and Y-Y' profile) of inclined shaft wellhead slope in open-pit mining area.
Although the slope in the wellhead area of open-pit mining inclined shaft is not high, it is in an important position, which is the passage for people and materials to enter and leave the inclined shaft. There are important industrial facilities and buildings under the slope, and its stability directly affects the safety of people, equipment and important facilities. This is an important link that must be analyzed and considered for the safety of underground mining in open-pit mining areas.
According to the above typical profile, carry out specific investigation, testing, analysis, monitoring, early warning and safety prevention and control technology research.
8.2. 1.2 survey
The purpose of investigating the risk factors affecting the safety of open-pit combined mining is to find out the engineering geological and hydrogeological conditions of the risk factor area (or the selected typical profile area). This method also adopts the investigation methods of open-pit mining and open-pit mining area, and it is necessary to pay attention to the law of rock mass change in the overlapping area between them. Focus on strengthening the investigation of engineering geological conditions, hydrogeological conditions and the characteristics caused by the comprehensive influence of well opening.
Taking slope engineering geological investigation of open-pit coal mine as an example;
(1) contents of slope engineering geological investigation
1) Rock mass lithology, occurrence, structure, neotectonic movement, regional geological characteristics, rock weathering degree and hydrogeological characteristics of the slope;
2) Mining engineering activities such as hydrological, meteorological and seismic data and blasting in the mining area;
3) Slope stability, slope deformation and landslide survey sum analysis;
4) Rock mass structure type and engineering geological division. The specific contents include:
(1) rock name, color, mineral composition, structural characteristics, rock occurrence and water-bearing state, occurrence, distribution law, contact relationship and contact surface characteristics of weak layer (surface);
(2) Geological structures related to slope stability, including the nature and occurrence of faults, the width and degree of fracture zone, the characteristics of fault plane, fillings and the relationship between faults and groundwater; The nature, occurrence and development degree of the fracture, the width and filler of the fracture zone; Form, type, occurrence and characteristics of folds;
③ Lithology and weathering degree of loose and weathered rocks, contact relationship with hard rocks and contact surface characteristics;
(4) The lithology, thickness, fracture or karst development state and characteristics of the aquifer; Outlet location, flow change, water quality, water source and recharge route;
⑤ Influence degree of groundwater on slope stability.
(2) The slope engineering geological investigation shall be carried out according to the following steps:
1) Collect relevant data on site, including geological, hydrological and climatic data of the slope on site, and determine the rock mass structure, composition and occurrence of the slope;
2) Collect relevant exploration reports, drilling data, geological profiles and previous displacement monitoring data of slopes;
3) determining the position of the slope profile line in combination with the above data, and determining the drilling position on the slope profile line which can represent the nature of the slope rock mass;
4) Slope drilling in open pit mines shall be carried out in strict accordance with the relevant technical requirements in Code for Geotechnical Engineering Investigation (GB5002 1[38]);
5) Collate, analyze and evaluate the slope engineering geological survey data, and prepare the open-pit slope engineering geological survey report.
(3) The change and trend of engineering geological and hydrogeological conditions of slope under the influence of well production.
8.2. 1.3 test
The purpose of the test is to determine the physical and mechanical properties of rock and soil in the dangerous affected area or typical section, including the physical and mechanical properties, changing laws and development trends of rock and soil before the impact and under the interaction with open pit mining. This method also adopts the method of testing the physical and mechanical properties of rock mass by open-pit mining and underground mining, which increases the changing law and development trend of the physical and mechanical properties of rock mass under the joint influence of open-pit mining and underground mining.
Taking the test of geotechnical physical and mechanical properties of open pit slope as an example.
(1) Test content of geotechnical physical and mechanical properties of slope
1) shear strength test, including direct shear or triaxial compression shear strength test of rock sample, in-situ rock mass and loose rock and soil. Direct shear instrument is used for direct shear of geotechnical samples; Triaxial instrument is used for triaxial shear resistance of geotechnical samples; In-situ rock mass direct shear test adopts in-situ rock mass direct shear test system; Large-scale triaxial apparatus test system is used for large-scale triaxial test of granular rock and soil;
2) Determine the physical properties of rock and soil, including density, water content, specific gravity, boundary water content, compression, consolidation and permeability.
3) Determination of compressive strength, point load strength and deformation parameters (elastic modulus, Poisson's ratio, etc.). ) geotechnical samples;
4) Soft rock or argillaceous laminar rheological test, in which the long-term strength and various rheological parameters are measured by direct shear rheometer;
5) Physical and mechanical properties test of rock and soil with different water content.
(2) Test method of geotechnical physics and mechanics of slope
The physical and mechanical properties of the slope shall be tested according to relevant national standards (such as Standard of Geotechnical Test Methods and Standard of Test Methods for Engineering Rock Mass GB/T50 123[4 1] and GB/T50266[40]). ), coal rock test standard (MT) in coal industry and rock test and geotechnical test standard in water conservancy and hydropower industry.
(3) Rock mass strength evaluation
Rock mass strength evaluation is mainly to determine the index parameters used for slope stability analysis. Combined with the above test results, the appropriate rock mass strength evaluation theory, landslide back analysis results and geotechnical properties analogy results are selected to comprehensively determine the physical and mechanical properties indexes, especially the shear strength indexes, which affect the open-pit joint mining slope, and select them for slope stability analysis.
(4) Slope simulation test
According to the needs of slope stability analysis, landslide mode and failure mechanism analysis of open pit mine, and according to the actual occurrence conditions, geological profile and geotechnical engineering properties of slope rock mass, bottom friction model method or similar material model method should be used to carry out slope simulation test to obtain slope deformation and failure and landslide mode. The test method is carried out according to MT/T675 "Simulation Test Method for Slope of Open-pit Coal Mine".
(5) The above test and evaluation contents should include the physical and mechanical properties of rock mass before and after the joint open-pit mining, especially the changing law and development trend of the properties.
8.2. 1.4 Analysis of risk factors affecting safety
The main purpose of risk factor analysis is to analyze the types, time-space relationship, influence and harm degree of risk factors affecting the safety of open-pit mining, and put forward preliminary suggestions such as monitoring, early warning and preventive countermeasures. The analysis method can adopt the following two methods:
(1) With reference to Guidelines and Methods for Preparing Emergency Plans for Coal Mining Enterprises, conduct scenario simulation for risk analysis. Through investigation and investigation, analyze the types, scope (space-time relationship), size and harm degree of risk factors, monitor the early warning system, and take technical and management measures to effectively control and reduce the probability of accidents. On this basis, an emergency plan for joint mining of open-pit workers and workers that affects safety risk factors can also be worked out.
Risk factor analysis and corresponding emergency plan should be targeted, operable, scientific, coordinated, mandatory and normative.
(2) According to the Geological Hazard Exploration, Design and Risk Assessment Method of the Ministry of Land and Resources, the geological hazard risks caused by geological environmental conditions and influencing factors are analyzed and classified. For example, Fushun West Open-pit Mine introduced in 2.5. 1, the geological environment classification of open-pit slope affected by Shengli Mine mining (collapse slip zone) and the corresponding geological disaster danger zone and safety zone. On the basis of classification, this paper analyzes the category, scope, size and harm of risk factors and puts forward preliminary preventive measures.