Studies On The Stability Of Tailings Dam

With the increasing of domestic mining, the large number of constructions for tailing zone result tailing dam safety evaluation and prediction become a more serious problem. Upstream, midstream and downstream dams are three main types of tailing dams. About80%of the tailing dams are upstream dams in China. The main issue of tailing dam safety evaluation is to prevent failure and collapse during the construction process and after closing.The current paper firstly concerns about the effects of sedimentation, consolidation and chemical actions to the stability of tailing dams. Then according to the engineering characteristics of tailing dams and traditional method for stability analysis, the author obtains the following results regarding the stability analysis of tailing dams:1. Based on the analysis of the tailing slurry accumulation process in the tailing dams, it can be found that the deposition process of tailing sand has three main stages as presented:1) punctuated deposition at the nest-like pilestage which is located at the discharge nozzle position in front of the dam;2) tailing dam ray flow deposition zone according to the existing slope characteristics of the tailing dams;3) static deposition zone at the tailwater pool. The types of the deposition, energy consumption of the deposition process, and deposition paths have been detailed discussed, including discussion on the interation among the three deposition stages and the alternating deposition due to multi-tubes in the lateral direction.2. According to the Terzaghi consolidation theory and the large strain consolidation theory, the proposal of consolidation stress analysis at different stages based on the growth model has been established, analyzing the effects of vertical seepage and clogging to the consolidation tailing dams. It has been discovered that the vertical seepage and clogging is the reason of the differences between the horizontal and vertical permeability coefficients. When the particle size is at very different conditions in the vertical direction, infiltration clogging makes the porosity remains stable, inducing the unsaturated infiltration coefficient at the infiltration line keep stable. 3. The chemical actions are also investigated, finding Eh-pH conditions are the key issues of controlling the hydrochemistry for the tailing dams. According to the redox theory, a tailing dam can be divided into three parts, including oxidation zone, alternating regions, and restore the area. Combined with the dynamic growth model of the tailing dams, the characteristic of hydrochemistry at different stages is also discussed and an iron ore mine is analyzed as an example.4. On the basis of practical engineering, the effects of the water level and infiltration line to the stability of the tailings dam are discussed.5. As the saturated silver sand or the silt in the dam foundation and dam body could have over pore water pressure when earthquake happens, it is particularly important to analyze the liquefaction properties under different seismic intensity. The research shows that:after the earthquake, the tailing dam locally liquefies, and with the increasing of the seismic intensity, the level of the liquefaction increases. The dynamic results indicate that the tailing dam safety factor decreases as the seismic intensity increases, and the range is between0.3and0.4.6. Different finite element models are used to do the analysis and compared.7. The proposed model for analyzing the stability of tailings dams can be used to develop the package for on-site stability analysis.