| Mineral resources are important to economic construction. For a long time, large-scale and high-strength developing mineral resources has made tremendous contributions to the construction and development of the country. However, exploitation of mineral resources on the environment has not made enough attention; the mine environmental problems have not effectively treated before2006. At present, the mine geo-environmental protection and restoration work has just started. Mine closure lacks up systematic planning and design. Geo-environmental treatment projects and land resource restoration plans have not been implemented in many mines; the environment of mine is deteriorating.For protect the geo-environment of these old abandoned mine effectively, the government has been forcing mining right holders to treat all the environmental problems by establishing laws since2005, and has founded mine geo-environment deposit system. Preparation of mine geo-environmental protection and recovery management plan and mine land reclamation plan must be the pre-conditions of applying or extending mining rights, inspection from2009. In addition, the government finance has invested funds to guide the mine geo-environmental treatment projects which had seriously risks and great ecological damage due to geological disaster by setting up mine geo-environmental treatment projects in a nationwide from2001, and has increased the special funding which annual budget is more than60billion to treat old mine geo-environmental projects which was leaved over before2006, and has deployed a series of treatment projects such as the old mines, resource-exhausted cities and demonstration mine since2010. However, these governance projects still lack the guidance of basic theory and technical methods. So, it is very important to establish a mine geological environment risk assessment and management system, and explore mine geo-environmental engineering theory and technical methods which are suitable for our country.Limestone building mine is the most widely distributed and the largest number, they are most distributed in the exposed limestone mountains. The geological disasters collapse, rockfall often occur within the working face after mining. And the induced geo-environmental problem of limestone mines is typical and representative because of distribution, mining methods in Fengshan county, Guangxi.This article makes a case study in abandoned limestone mine and relies on state finance special project Guangxi Fengshan limestone mine geo-environmental treatment. Through data collection, field surveys and measuring,3D slope laser scanning, infrared scanning, laboratory tests of rock and structure surface, numerical simulation, the research data is obtained. Applying the basic theory:engineering geological analysis, graphical analysis, block theory, rigid body limit equilibrium method, reliability analysis, geological disaster risk analysis, building structural mechanics, geotechnical design theory, the article research on the geo-environmental risk analysis and management of abandoned limestone mine, which not only has demonstration effect and important theoretical significance to national mine geo-environmental risk analysis and management, project treatment but also guides Fengshan mine geo-environmental engineering in the practice. The main contents are as follows.First, the genesis and classification of Limestone mine geo-environmental problems.The article has summed up the domestic mine geo-environment classification firstly. Then based on the characteristics and substance of mine geo-environmental problems and from the mine geo-environmental risk analysis and management perspective, the mine geo-environmental problems are divided into two categories:burst mine geo-environment problems and graded mine geo-environment problems. The hazardous of burst mine geo-environment problems are expressed by the failure probability or reliability, the risk mitigation measures must be deployed before the disaster. The process of graded geo-environmental problems dangerous can be determined by statistics or empirical models. The risk mitigation measures can be deployed in front of the geological environment problems or the development process, without warning or other emergency management measures.In the6abandoned limestone mines around Fengshan county, burst mine geo-environment problems are rockfall, collapse and slag heap unstable slopes, graded mine geological environment problems include occupation of land resources, destruction of ecological resources and damage to the topography landscape. The paper analyses the limestone mine geology background, reveals the relationship between mining activities and mining geology major environmental issues, in-depth study the causes and combined mode of limestone mine geo-environment problems, and then figures out the disasters effects of limestone mine geo-environment to human society.Second, limestone mine geological environment risk analysis1. The main contents and basic risk analysis process of the mine geological environmentAccording to the interaction mechanism of mining and mine geo-environmental issues, the main content and the basic process of mine geo-environmental risk assessment are proposed. The entire system consists of five parts:1) Data capture of mine geo-environmental risk analysisThe data of risk analysis include geological environmental background data, the strength of the existing mine geological environment problems, loss damage surveys, control project status and implementation conditions. And as a case study of abandoned limestone mine in Fengshan, the environmental parameters required of the mine geo-environmental risk assessment for the major acquisition method are explored.2) Mine geo-environment hazard analysisThe core of burst geo-environmental hazard analysis is to establish the scale of the disaster, the intensity (speed, impact, etc.) and the relationship between the frequencies of occurrence. The graded geo-environmental including two parts:the status and trends in risk prediction. Through historical data statistical or empirical models, the risk trends are predicted.3) Mine geo-environmental vulnerability assessmentVulnerability comes from three parts:the vulnerability of physical entities, such as personnel and building social; economic and ecological fragility; ecology and socio-economic lack resilience. In the vulnerability assessment, vulnerability is classified into two categories, the first category used to evaluate the extent of the potential damage to human loss and physical entities; the second category used to evaluate impact harm degree of the potential social, ecological and environmental to human society.4) Mine geo-environment risk assessmentRisk assessment make acceptable level and tolerance as a standard to to determine whether the risk is accepted, tolerated or not tolerated.5) Mine geo-environment risk managementRisk management Includes risk decisions, risk control and risk enforcement. Risk control measures include three categories:engineering measures to reduce the risk of mine geo-environmental problems; soft measures to reduce hazard bearing body vulnerability and the consequences disasters; decentralized disaster consequences.2. Theory and Methods of burst mine geo-environment risk analysisThe hazard bearing bodies of burst mine geo-environment problems are building and the crowd. Its risk assessment include pre-disaster risk assessment and disaster damage assessment. From the perspective of the loss of the building, the process and development trend of collapse and rockfall in the limestone mine geo-environment problems, and the basic processes and methods of risk assessment have researched by research on the4th Fengshan limestone mine.1) Data acquisition and analysis of limestone mine geo-environment.Based on the collection of mine geo-environment background information, the exploitation of the working face, waste dumps, mining slag heaps and abandoned buildings are investigated in detail; Through topographic survey, site surveys, laser scanning, infrared detection, and rock mechanical testing and other investigation methods, as well as block theory, rigid limit balance, reliability analysis and numerical simulation analysis theory and method, the physical mechanical properties of the rock and soil and the data of structure surface are obtained. Then the tunnel face mine geological environment is partitioned.2) Hazard analysis(1) Rockfall hazard AnalysisApplication of block theory, the structure and rockfall instability mode is determined, and then based on the physical and mechanical properties of the sliding surface, all the key block are determined in the excavation works surface. Specific analysis process is:Specific analysis process is:block theory'geometric analysis'remove stable block'identify potential instability blocks under engineering force and weight force'determine key block by sliding surface shear strength,'stereographic projection and vector analysis'determine unstable mode and rockfall volume. The results show there is rockfall hazards in Fengshan the4th limestone mine except Ⅱ, Ⅷ.By using structural surface scale (trace length) function, the probabilities of different sizes rockfall occurrence are analyzed. The results indicate the probabilities of rockfall occurrence are different among Ⅰ, Ⅱ, Ⅴ, Ⅵ and Ⅶ in the4th limestone mine, and the probabilities of rockfall occurrence is higher.The reliability index and the failure probability of the block are calculated by using the checking point method. the danger of falling rocks is expressed by reliability and failure probability. The dangerous value of Ⅰ, Ⅲ, Ⅴ and Ⅵ zone respectively is0.53,0.004,0.279and0.5in Guangxi4th limestone mine.By using software RockFall to simulate the rockfall intensity, the rockfall horizontal position, velocity distribution, jumping height are obtained, which are used in the next vulnerability research.(2) Collapse hazard analysisFengshan limestone NO.4mine of collapse are mainly distributed in II area, a potential collapse body boundary is made of the two large dipping fractures and slope, exists strewn at random type collapses and dump collapsed two failure modes. Strewn at random type collapse is volume of3695m3, in1/3,1/2and2/3full water conditions, the failure probability respectively is0.571,0.618and0.864.Dumping collapse is volume of4682m3, In full water under the condition, the failure probability respectively is0.28,0.28and0.728, the collapse body risk is extremely high.3) Vulnerability AnalysisVulnerability degree (value) of the building have relations with disasters strength and structural damage of mutant geo-environmental problems. Considering the specific parameters of intensity rockfall hazards, such as speed, power and trajectory, and the interaction between the structure and the building structure in response to falling rocks, the vulnerability of buildings caused by falling rocks and collapses are analyzed. Building structure response is closely related to rockfall impact intensity and position, which directly determines the initial injury and the overall stability of the main load-bearing building components. By quantifying structural damage of rocks and collapse to buildings falling and using the relative maintenance costs, the vulnerability is calculated.(1) Impact possibilityRockfall impact with building have a total of40kinds independent different program, the probability of each scenario building load-bearing columns collision is calculated.(2) The response of individual structural members to rockfallThe response of individual structural members to rockfall is related to rockfall and structure, such as quality, speed, the area, stiffness, load, collision geometry feature. According to the linear shear failure model of reinforced concrete components, initial energy of Rockfall crashed one, two, three or more columns is calculated. Finally, collision damage characteristic curve of rockfall impact columns is obtained.(3) Building progressive collapse analysisThrough the impact pattern analysis of rock falls to frame structure buildings, applying software SAP2000numerical simulation to analyze the damage degree of structures under the action of rockfalls.(4) Damage index calculation of building structureThe grading standard of building structure can be set up according to the damage indexes of40independent programs. Then considering the collision location, the probability of each program and the relative repair costs (RRC), the building vulnerability assessment matrix including different volume rock falls and speeds reaching the building can be set up.In the Guangxi Fengshan limestone NO.4mine, for1m diameter rock falls, the building vulnerability is0.01when the speed is less than4m/s,0.09when the speed is4-6m/s,0.17when the speed is6-7.5m/s and0.33when the speed is more than8m/s. For2m diameter rock falls, the building vulnerability is0.01when the speed is less than1.5m/s,0.53when the speed is3-8m/s. For4m diameter rock falls, when the speed is more than1m/s, the building can be damaged totally and the vulnerability is1.0.4) Risk assessment of buildingsThe risk of burst mine geo-environment problems can be expressed as the multiply of the possibility of geological environment problems and the damage of the problem. The risk of real mine geo-environment problem is the summation of each problems with the use the index model. Based on the method, the calculated result shows:the risk of building NO.1is from the rock falls damage, the highest level of risk and the value of it is0.188; The risk of building NO.2is from the comprehensive function of rock falls and collapse, the middle level of risk and the value of it is0.042; the risk of building NO.3is from the rock falls damage, the low level of risk and the value of it is0.002. 3. The risk analyses of gradient mine geo-environment problemThe bearers of gradient mine geo-environment problems are environment and ecology and the assessment of the problem majors in the process of it. From the impact on society and the environment and recoverability, this paper explores the assessment technology and methods of gradient mine geo-environment problems in abandoned mine. The risk assessment include four respects:land resources destruction、landforms and landscape devastation、ecological resources destruction environmental pollution.1) Hazard assessment of gradient mine geo-environment problemThe hazard of gradient mine geo-environment problems is the comprehensive analysis of the hazard under current conditions and the tendency of the problems within t time. The problems needed to solve include:the distribution range and impact of the present geo-environment problems, and the change processes of the problems’range and impact during the time t. According to the above, the evolution model of five different application range and impact factors can be established to predict the risk of geo-environment problems in the short term, the risk probability is1.2) Vulnerability assessment of gradient mine geo-environment problemThe vulnerability assessment of gradient mine geo-environment problems refers to the social, economic, and ecological vulnerability, and evaluation about the recoverability of ecological and social economy.For a single mine, its vulnerability assessment of gradient mine geo-environment problems refers to the value of the social, ecological and environmental vulnerability within time under its effect, is the function about the social impact, ecological destruction and loss, environmental damage and loss, which can be called the vulnerability function.(1) Vulnerability of land resources destructionThe vulnerability of land resources destruction is decided to influence index of land resources impact on social and economic and the feasibility of land restoration decision, and its social influence index bases on the influence of population; The feasibility of recovery index bases on the difference of farming land and construction land, the former uses the environmental sensitive area index model, and the latter uses the geo-environment suitability evaluation model of different function construction land. Then establish the vulnerability degree standard of land resources destruction in the Fengshan limestone NO.4mine, and calculate every mine’s regional vulnerability of the destruction of land resources.(2) The damage vulnerability of landform and landscapeThe damage vulnerability of landform and landscape is determined by breaking strength、 social and economic influence and recovery feasibility index. It is divided into four level of vulnerability. The breaking strength can be determined by the area destroyed, the degree of terrain damage and the landscape contrast before and after mining. Social and economic impacts include mining zone location and socio-economic development planning two parameters. Recovery feasibility index include the type of mines, slope height, visual buffer and policies four indicators.(3) The vulnerability of ecological resources destructionThe vulnerability of ecological resources destruction is composed of six categories of index: natural environmental index, land index, biodiversity index, ecological system dynamic balance index, landscape ecological index and ecological restoration case index.(4) Environmental pollution vulnerability calculationThe vulnerability of environmental pollution set the risk of pollutants on human health as the goal.3) The risk assessment of gradient geo-environmentThe hazard of geo-environment problems can be predicted, so the hazard probability is1.That is to say, risk is equal to vulnerability. And the gradient mine geo-environment risk assessment includes two parts.(1) Risk assessment of single gradient mine geo-environmentEvery part of the gradient mine geo-environment risk can be regarded respectively as a risk assessment parameters including land resources destruction、landforms and landscape devastation、ecological resources destruction、environmental pollution. Then the single gradient mine geo-environment risk assessment should be finished.(2) Comprehensive risk assessment of multiple geo-environment problems.After determining the weight of the risk that every geo-environment problem brings, linear exponential model is in application to the comprehensive risk assessment better when choosing the sensitivity of the model and the comprehensive index model.(3) Risk assessment of gradient mine geo-environment in Guangxi Fengshan limestone NO.4mine.According to the landform、the location and the relevant policy, the damage vulnerability of landform is3.46,which means it is of high risk.In the paper, five indicators are considered for the Fengshan limestone NO.4mine ecological risk assessment. And scored them from1～4, the higher the score, the higher the vulnerability. The score of natural environmental conditions is2; land border index is4; ecological system homeostasis index is4; ecological landscape index is4, and ecological restoration case is3. Based on above, the vulnerability degree is4, belonging to high-risk areas of ecological resource damage.According to the sensitive factor+index model, combing the mine risk assessment results of landscape topography damage and results of the ecological resource damage, we can concluded that the mine belongs to the high-risk areas of geo-environment problem. The evaluation results indicate that we should not only consider the ecological restoration measures and should be combined with local social and economic development.Third, research on risk management of abandoned limestone mine geo-environmentThe paper set up the multi-objective decision tree, summarized the composition of mine geo-environment risk control engineering, and studied how to choose the management project scientifically from the point of risk management. Taking the Fengshan instance, the paper completed a practice of mine geo-environment of risk management and control.1. Research about risk management methods of mine geo-environmentRisk management includes risk decision-making, risk control planning,(determination of the risk control measures) and implementation plan (supervision). The paper proposes3main steps for the multi-objective decision,3class one objects,7class two objects and the assessment criteria. And then put forward the main measures for the problem.In the paper, the main characteristics of burst geo-environment problem and gradient geo-environment problem have been analyzed. And the paper pointed out that mine geo-environment risk control is a comprehensive process applying economic instruments, administrative and legal means and technical means to reduce the risk.2. Technical solution selection of mine geo-environment risk control-taking the mine geo-environment treatment in Fengshan instanceTechnical methods to mine geo-environment of risk management including the development of technical standards, norms and regulations adapted to the mine geo-environment protection and management measures, implementation in the mine geo-environment investigation, monitoring and treatment recovery. Thus effectively reduce negative impact on the environment caused by the geological development of mineral resources. Mine geo-environment treatment project is an important aspect of the mine geo-environment of risk management, belongings to technical means. Also tend to be the ultimate risk control measures in the economic, administrative and legal means of control after, but also the largest investment, the most difficult means of control and its effectiveness depends mainly on the engineering design of science and rationality.Mine geo-environment is complex and diverse, and the dangers of it are large. We need to consider the geological environment problems; the feasible of treatment project, effectiveness and social demand four major factors.Based on the mine geo-environment risk analysis and management, the management solutions can be determined by using analytical hierarchy model:P11(cutting slope, cleaning dangerous rock, slope anchorage)+P12(catchwater, rock fall platform, monitoring)+P13(slope plastic+rock carvings, slope ecological recovery)+P14(risk education). The carved shallow of the slope surface increased the risk of falling rocks, so we need to decrease the rock fall distance by planting grass in the slope toe accumulation zone and rock fall platform.In the future, with the national targets of ecological civilization and beautiful China, carrying out mine geo-environment risk research is particularly important. We need to explore suitable mine geo-environmental risk assessment and management for China; strengthen the vulnerability study about graded mine geo-environment risks. The basic theory presented in this paper about the geo-environment risk assessment and management and technical methods also need to be used in other minerals, mining methods and mining application areas. So the assessment indicators and quantitative models can be further improved and the suitable mine geo-environment risk analysis and management model for China can be formed. |
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