| The existence of structural plane is the main induced factors of discontinuity and anisotropic of rock mass. Structural plane not only affects the integrity of rock mass, but also reduces the mechanical strength of the rock mass. Therefore the study of the structural plane characteristics has important meaning to analysis the failure mode and failure mechanism of mining slope. Fault, weak intercalation and joint are widely distributed in Huang Shan Limestone Mine, the native or secondary structure surface control the stability of the slope in the great degree. Because the most of slope is bedding slope and had happened a few times bedding landslide along the weak intercalations in the slope, combined with has large exploitation scale and high mining depth and was influenced rainfall or blasting vibration and so on, we should be demonstration and optimization the stability of slope in design and construction to guarantee the safety, economy, scientific and rationality and provide guard for safety production of mine. Firstly, carries out a detailed survey of landslides, the development situation of structural plane, hydrogeological and so on, through the statistical analysis found that the most possible failure mode of working steps is plane sliding destruction, wedge sliding destruction and toppling failure in the process of slope excavation. Researched on the distribution, scale and mechanics characteristics of structural plane. The author has analyzed the destruction mechanism of slope and the boundary conditions, mechanical conditions and its influencing factors which lead to the destruction of slope by the characteristics of distribution and permutation combined with its mechanical property. To establish the calculated model of corresponding failure mode to solve the stability coefficient of slope, so as to guide the safety construction and normal operation of the engineering. The main research contents and results were as follows: (1) By analyzing the existing prospecting and field investigation data, the geological structure, engineering geological and hydrologic condition, mine design parameters, damage in the Huang Shan limestone mine are obtained. Investigation the development of faults, weak intercalation, bedding fault, joint fissure, etc in the mine and the surrounding area. According the extension length, cutting depth, width of fracture zone and its mechanical effects to classification for structural plane and preliminary judge about the stability of work bench slope. Stereographic polar projection method is used to statistical and analysis the measured structural plane, found that the most possible failure mode of work bench slope is plane sliding failure, wedge sliding failure and toppling failure in the process of slope excavation. Combined with laboratory test and in-situ shear test, to determine the mechanical strength value under natural state and saturated state of structure surface and provide the basis for later calculation.(2)The mining slope rock mass consists of multiple strata, based on the saturated uniaxial compressive strength of the rock, rock mass of the slope can be divided into hard rock group, less hard rock group, less soft rock group, hard rock interbedded with soft rock group, soft rock group, loose rock group.The slope structure of Huang Shan limestone mine belongs to the type of alternatively distributed soft and hard rock layers, so bedding sliding failure is easy to be happened in mine. Qualitative expounds the required three failure conditions for bedding sliding of slope without considering the effects of external factors and the cohesion of weak intercalations. Analyzed the main factors which influenced the stability of slope was formation lithology, geology Structure, rock mass structure, function of water and so on. Established two kinds of bedding sliding stability calculation model which have or no posterior margin tension crack of slope, considered the influence of the rainfall and blasting vibration and separately calculated the stability of slope when the dip angle of weak interlayer is 150,21°,24°,28°.No matter what the value of θ, the slope of mine is always stable under the natural state and natural and blasting vibration state. Under the state of natural and blasting vibration, using the pseudo-static method in this paper, the spectrum difference of blasting seismic wave, phase difference and other factors are included in the reduction factor Bb. This approach is easy to operate, but greatly simplified the inertial force of blasting vibration, introduced any uncertain factors, it may bring some errors. Under the natural and rainstorm state, the slope can’t keep stable except when θ=15°. As the θ steepened gradually, the slope gradually can’t satisfy the requirement of safety factor or even damaged. When the θ being kept constant, water level Zw and the depth of trailing edge crack Z has a obvious influence on slope stability. However, the selection of Z and Zw were influenced by artificial factors and does not represent all possible case, but it reflects some regularity, can evaluate the stability of the work bench slope basically. In this state, apart from take into account the effect of hydrostatic pressure, still need to consider softening action of water on the mechanical strength of weak intercalation. Adopting saturated state’s mechanical parameters of weak intercalations to simulate the natural and rainstorm state. The action of water was the main external factor which effects stability of slope. Reasonable measures should be taken to prevent the rain infiltration in the excavation process of mine. (3)The two common types of wedge were analyzed, established the common wedge failure type for calculation model. Analyzed the boundary condition and stress condition which needs to satisfy of wedge failure. Through a large number of trial found that the dip angle of structural plane intersecting line has a great impact on stability of slope wifhout considering the cohesion of structural plane. Using software Swedge which can calculate the stability of slope, considering the influence of the rainfall and blasting vibration, calculating the potential wedge in the mine. Under the natural state and natural and blasting vibration state, wedge sliding destruction will not be occured. However, when faced with heavy rainfall, the stability coefficient will significantly reduced and even wedge failures may be happened of wedge 1,4,5,6,9,10, other wedges can keep stable. Above of all, the function of water is also the main factor which influenced the stability of the wedge.(4) Described the toppling failure occurred in the mine. It was provide a new free face for toppling failure due to the mining and landslides. The potential toppling rocks has been bent mainly under the action of gravity, the tension crack surfaces expanding to the deep constantly and the bottom sliding surface cut-through gradually until the toppling failure happened. Transfer coefficient method is used to calculate the stability of toppling rock in the mine, the affective range of toppling failure mainly influenced by m and m decreased with the increase of the dip angle of failure face. In this way, the range of toppling failure smaller with the decrease of H and increase of 0. With the decrease of H and the increase of 0, plane sliding failure will be happened and toppling failure is less prone to occur. The toppling failure often occurs in the moderately thick layers of limestone and was less affected by external factors. This paper only considers the toppling stability of the rock under the action of gravity and does not take into account of the influence of rainfall and blasting vibration. So still need further research when consider the above factors. In order to verify the calculation result of transfer coefficient method, using the discrete element software 3DEC to calculate the toppling failure. Under the initial parameters, the displacement of rock is small and the slope is in steady state. In order to research the mechanism of toppling failure, reduce the value of structural plane, when φ reduced to 65% of the initial value and c and tensile strength reduced to 30% of the initial value, sliding-toppling failure will be gradually occured. The calculation results of 3DEC are consistent with transfer coefficient method, slope is divided into sliding zone, toppling failure zone and the stable zone and the range of potential toppling failure is also relatively close. It proved the transfer coefficient method is reliable. |
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