| For strong demand of mineral resources and through consideration of the safety and environmental protection during mining activities, fundamental and applied research topics toward deep-level ore deposits have become the active research directions to make progress in the mining science and technology. For this reason, the research project "Multi-Phase & Multi-Field Coupling and Disaster Mechanism and its Prevention in Deep Level Rock Mass (No. 50490274)" was brought forward and was supported as a key project by the national nature science fund. The investigation of this project will greatly influence on the traditional mining techniques and will produce a new demand and new progress to mining activities. Backfill is an important technology that is often used in noble metal mines and the mines of which ore deposits are difficult to exploitation. Therefore, the backfill technology becomes an important research topic and is very significant both in theory and application for deep level mining of ore bodies.However, there are many existing problems at present in the backfill technology in Chinese mines, such as low strength of filling mass, high consumption of cement material, poor reliability of the backfill system which causes many accidents. Meanwhile, few investigations were conducted by researchers in reliability of the backfill system. After considering the presented problems of the backfill technology and the research status in the area, and based on the data collected from many technical improvement cases of pipeline backfill system with gravity in Chinese mines, the author completed a series of reliability analysis and assessment for the pipeline system with gravity and put forward the correspondent strategies for improving the system reliability with the help of safety system engineering, theories of reliability and fuzzy evaluation approach. The main research contents and results in the dissertation are as follows:1. A complete risk assessment system considering multi-factors was put forward for evaluating the excavation engineering under deep level with multi-field coupling conditions and for explaining the relationship between the reliability and the backfill system. In the assessing process, the noble risk assessment system of DOW's Chemical Company was integrated with the existing research results in deep rock mass with multi-field coupling, the testing results in rock excavation engineering and Q method and RMR method in rock mass stability classifications. In the assessing system, risk assessment indexes of the underground excavation engineering were given by determining each hazard index and its weight in the model from considering macro reaction.2. Based on the data collected from Xiaotieshan Mine of Baiyin Nonferrous Metals Corporation, Hubei Sanxin Gold & Copper Limited Company and Fenghuangshan Copper Mine, the theoretical framework for evaluation of a backfill system was established and the internal reaction regulations in the backfill system was discovered. A deep level backfill system is divided into three parts, and the connection among the parts and the logic relationship among all elements within each part are deduced. The objective necessary for evaluation of the system with reliability theory was addressed, and correspondingly the method and its emphasis for the evaluation of the backfill system were put forward.3. With reference of the research fruits of long distance slurry transportation system and oil-gas pipeline system, the deep level backfill system failure from possibility to impossibility was set up to resolve the presented puzzle that appears in the design and the evaluation of the backfill system. A method for calculation of fault probability in different backfill systems was brought forward with fuzzy comprehensive evaluation method. The logic relationships among the factors which influence on the deep level backfill system failure were established systematically, with the application of FMEA, FTA, fault effect propagation diagraph and fuzzy probability. It is shown that the main system failure reasons are the high frequency of filling process, bad quality of filling materials and slurry loss. The calculation of probability value of basic events has been conducted through the conversion from fuzzy probability estimation of basic event failure probability to probability estimation calculation. The quantitative puzzle is resolved without the failure database, the degree of reliability can be judged through the comparison of occurrence probability and project failure probability which are calculated by fault tree.4. The model for a pipeline backfill system has been established and analyzed, the utmost state function for bearing capacity has been established which is used for the analysis of failure possibility of the pipe. Hence it is concluded that residual head and slurry flow are the main factors which influence the reliability of deep level backfill system. The reliability analysis of in-service pipeline with defect which is a puzzle for years is resolved with the model for supply and demand. By analyzing the influence of density, concentration, flux of slurry on the effective slurry height of deep level pipe and by analyzing the effective mean value and standard value for slurry highness and the means of central-point method (mean value), that is Taylor series expansion method, the reliability of the designed pipe height can be calculated with the application of the reliability index as a result. It is demonstrated that the reliability of the system with 93% and 99% can be insured when the height of slurry is increased with 10 mm and 20 mm on the designedheight. However, the reliability with only 50% can be insured if the design is conducted under mean condition.5. The scheme for improving the backfill system reliability was based on the modifications in technology and filling material. In respect of the technology, variable diameter pipe for dissipated energy and isometric flow distribution technology which can improve the reliability of operation and the quality of the backfill material are recommended. In respect of the backfill materials, flocculants settlement approach was successfully conducted, and the quality of the filling materials is improved, and the improvement of dewatering effect is obtained. Applied multi-factor classification method, a solution to the subjective weight, objective weight and decision-making priority was found. The effect of the non-clinker blast furnace slag cementing material in the mining filling is good, which illustrates that the strategy method is correct, so more reliable cementing materials can be supplied to deep mines.
|
PDF Full Text Request