Strengthen safety risk control of open-pit mine slope to prevent collapse accidents

First, strict mine access, reduce the inherent safety risk of slope

(1) Reasonable demarcation of mine boundaries. The newly built and expanded mining scope of the expansion of open pit mines shall strictly implement the "Zhejiang Provincial Department of Land and Resources Zhejiang Province Work Safety Supervision Administration on the Management of sand and gravel mineral development and safety production supervision" (Zhejiang Soil Capital Development [2014] No. 32) the relevant requirements for the establishment of fixed point demarcation of mines, the mountain can be developed as a whole, shall not be divided and demarcation. As far as possible to achieve the whole mountain displacement mining or contour demarcation; Ridgeline should not be used as the mining boundary, and the mining boundary should not be demarcated by "peeling skin" to reduce the final slope height as much as possible, so as to create conditions for the implementation of stepped mining.

(2) Strengthening early geological exploration. The geological exploration data based on joint exploration, safety pre-assessment and safety facility design of open-pit mine construction projects must reach the level of detailed investigation and above, and meet the requirements of relevant design norms, and may not be used as the basis for the establishment of mines. For open-pit mine construction projects with medium or above engineering geology and hydrogeology complexity within the proposed mining scope, the geological exploration data must reach the exploration level. For open-pit mine construction projects with final slope height of 100 meters and above, the Final Slope Stability Study Report shall be prepared; After the slope stability study, and after taking feasible safety technical measures, the final slope is still unable to achieve stability or basically stable, no mine shall be established.

(3) Standardize the general layout. Offices, dormitories for workers, houses and other structures or living facilities with personnel activities shall not be set up within the scope of the hazard of mine slope collapse. No fixed production sites such as crushing and beneficiation shall be set up within 50 meters from the bottom line of the working step slope or the bottom line of the final side slope of a new mine; Where the final slope height is above 50 meters or stratified mining is used, fixed production sites such as crushing and mineral processing shall not be set up within the scope of slope collapse hazards, and the hazards caused by slope collapse shall be strictly controlled.

(4) Strict design review. The "Safety Facilities Design" of mine construction projects should be compiled in strict accordance with the "Safety Regulations for Metal and non-metal mines" and related design manuals, and reasonably determine the height of the step, the working slope Angle and the slope Angle of the final slope, the width of the safety platform and the cleaning platform. The final slope with hard rock and no dangerous structural plane shall not exceed 55 degrees; The final slope with hard rock (medium hard rock) and no dangerous structural plane shall not exceed 42 degrees; The final slope of soft rock without dangerous structural plane shall not exceed 30 degrees. The slope Angle of a slope with a dangerous structural plane shall not be greater than the dip Angle of the dangerous structural plane. For the final slope with a height of more than 90 meters, the slope Angle should be appropriately reduced, and the slope Angle should be reduced by 1 degree every 30 meters.

Second, strengthen technical support to improve slope risk identification ability

(1) Strengthen daily research and judgment of slope safety risks. Open-pit mining enterprises should be equipped with geological engineering technicians in accordance with the requirements of the "Guide for Mine Safety Technical Work in Zhejiang Province", and carry out geological work in a standardized manner. After each operation cycle of mining construction, geological data should be collected in time to investigate and judge the stability of the exposed site slope and put forward countermeasures. It is necessary to strengthen the daily investigation of the dangerous structural plane of the slope. Where it is found that there are adverse geological phenomena in the slope, such as rock strata inclination in the stope, multi-group joint fracture space combination structural plane inclination in the stope, large weak structural plane and weak rock strata cutting slope, the person in charge of the mining enterprise should immediately organize professional and technical personnel to conduct research and judgment. Rectification and control measures must be implemented in accordance with major accident hazards.

(2) Conduct regular research and judgment on slope safety risks. The person in charge of the mining enterprise or the technical person in charge shall hold a technical analysis meeting at least once a month to analyze the dynamic changes of geological conditions and the effectiveness of slope safety risk control measures. The main person in charge of the mining enterprise shall organize a systematic study and judgment of slope safety risks every year, and conduct a systematic analysis and judgment of slope stability and the effectiveness of control measures based on the slope safety production situation, risk events, disclosed geological conditions and safety monitoring data in recent years.

(3) Conduct professional analysis and evaluation of slope stability. Open-pit mining enterprises shall, in accordance with the relevant provisions of the Safety Regulations for Metal and non-metal Mines, conduct slope stability analysis at least once every 5 years and form the Slope Stability Analysis and Evaluation Report. The slope stability analysis and evaluation work should be carried out by the units that have the relevant qualification of geological disaster prevention or have the ability of open-pit slope stability analysis and evaluation. The initial slope stability analysis and evaluation should be completed after the completion of the mine construction project and before the acceptance of the safety facilities.

(4) Carry out "expert consultation" on slope safety with greater risks. Emergency management departments should regularly organize "expert consultation" type safety inspection for open-pit mine slopes with greater risks. For slopes with a height of more than 30 meters and slope angles greater than 30 degrees, the county (city, district) emergency Management Bureau will organize an "expert consultation" every year. On this basis, the municipal emergency management bureau will carry out an "expert consultation" once a year on the final slope with the current height of more than 50 meters and the slope Angle of more than 42 degrees or the current height of more than 100 meters and the slope Angle of more than 30 degrees; The provincial Emergency Management Department organizes an "expert consultation" every year for the final slope of production mines with a current height of more than 200 meters. The "expert consultation" shall evaluate the stability of the slope and the effectiveness of the measures already taken according to the geological report of the mine, the site survey and the slope risk control situation of the enterprise, and form the inspection list of the expert consultation of the open-pit mine slope safety (see Annex 2).

Third, strengthen engineering measures to improve the level of slope risk control

(1) Strengthening slope safety protection. For the overall stable final slope, transportation road slope and other non-working slope, mining enterprises should take engineering and technical measures such as hanging net, setting up safety platform, anchoring and spraying to prevent local collapse and falling blocks. If the slope is found to be unstable or extremely unstable after analysis and evaluation, the design unit shall determine the treatment plan or protective measures. Unstable slope and extremely unstable slope before the completion of governance, stability or basic stability, the dangerous area should take temporary measures such as stopping production and evacuating people, hard isolation, and strictly prohibit personnel from entering.

(2) Standardize the construction of slope engineering. The slope Angle and platform width of open-pit mine must conform to or be better than the design. Controlled blasting or mechanical excavation should be used in the adjacent slope operation to reduce the damage to the slope and maintain the safe slope Angle of the steps. Overdigging the slope bottom is strictly prohibited. To standardize the construction of slope drainage facilities, slope drainage facilities must meet or better than the design requirements; Finally, each step of the slope should be provided with a drain in principle, through which the rainwater can be discharged from the slope.

(3) Precise slope control measures. In the process of mine production and construction, if the engineering geology or hydrogeology type of the mine is found to be inconsistent with the type determined by the original geological report, and is inferior to the original geological report, the slope parameters and risk control measures should be adjusted immediately in accordance with the preliminary geological type. At the same time, it is necessary to timely entrust relevant units to supplement geological exploration, adjust geological types, and revise the "Safety Facilities Design"

Fourth, strengthen safety monitoring, improve slope risk early warning ability

(1) Actively promote slope safety monitoring. The open-pit mine shall entrust the design unit to carry out the overall design of the slope monitoring program according to the final slope boundary, different periods and different mining requirements, and according to the slope safety monitoring grade determined by the Slope Stability Analysis and Evaluation Report in each zone, and clarify the monitoring content and monitoring program by region and stage. When the final slope is not formed, temporary monitoring points should be set up on the stope slope. When the final slope is formed, long-term monitoring points are set up on the final slope. The safety monitoring content shall be implemented in accordance with the relevant provisions of the Technical Specification for Safety Monitoring of High and Steep Slopes in Metal and non-metal open-pit Mines (AQ/T 2063-2018).

(2) Comprehensively carry out online monitoring of slope displacement with large risks. For the final slope whose safety monitoring grade is one or two, the surface displacement must be monitored online. For the final slope with a safety monitoring grade of one, internal displacement online monitoring should also be set up. Considering the variability of geological conditions and calculation error of slope monitoring grade, if the final slope height is more than 200 meters (including 200 meters), it is necessary to establish online displacement monitoring in accordance with the requirements of safety monitoring grade 1. The final slope with a height of 100-200 meters and the final slope with a height of 30-100 meters and complex geological conditions should at least establish an online displacement monitoring system in accordance with the requirements of safety monitoring level 2. Encourage open pit mine to use slope radar to carry out slope surface displacement safety monitoring, improve slope safety monitoring capability; The on-line monitoring system of slope surface displacement can not be built if the radar monitoring of slope meets the requirements of the standard.

(3) Improving the early-warning ability of slope safety. The slope displacement online monitoring system should set three levels of collapse risk warning, yellow, orange and red, reasonably determine the early warning value, clear the corresponding early warning signal, and specify the corresponding emergency disposal measures in the relevant emergency rescue plan. Mining enterprises should carry out at least one targeted slope collapse emergency evacuation drill every six months in combination with the special emergency plan drill for slope collapse accidents.