| Earthquake-induced rock slope failure is a common earthquake disaster, including sliding and collapse, especially in mountainous and hilly areas,which has characteristics of greatness of distribution, quantity, and hazard. In China, seismic activity has features of high degree of frequency, intensity, shallow focal, wide distribution; there are many earthquake examples of slope failure, which does serious harm to life and property security. China's recent large-scale earthquake was "5?12" Wenchuan earthquake, which induced tens thousands of landslide hazard, and formed relatively large-scale of 136 barrier lake, that brought huge injury to people of disaster area. So, Study on slope deformation and failure mechanism under earthquake action, can further evaluate of slope dynamic stability, meanwhile back-stepping seismic characteristic, can provide a good foundation for landslide prediction, above research allows us to take protective measures, nip in the bud, effectively reduce the economic loss caused by earthquake-induced slope failure, which is very important significance for Chinese socialist modernization construction.Landslide is usually formed by bedding rock slope. Bedding rock slopes can be classified into different kinds according different research purposes. Classifying according to parameters of structural slope: According to angle of slope ,bedding rock slopes can be divided into gentle slope, sloping ground,steep slope,steep gradient,hang slope,adverse slope. According to angle of slope can be divided into gentle inclined outward layer structure, medium dip outward layer structure, steep dip outward layer structure, nearly vertical layer structure, angle-tilt outward layer structure. According to slope height can be divided into ultra-high slope, high slope, middle slope, low slope; According to slope structure can be divided into single-layer structure, multi-layer structure, and inter-layer structure. According to layered rock-mass degree of broken , it can be divided into broken layered rock-mass, relatively complete layered rock-mass; According to formation lithology can be divided into extrusive rock slope, carbonatite slope, sedimentary rock slope with weak intercalated layers, incompetent bed slope, metamorfic rock slope. According to degree of rock weathering can be divided into completely weathered, highly weathered, weakly weathered, slightly weathered, non-weathered; According to groundwater dynamic condition can be divided into the motive mechanism of hydrodynamic pressure and dynamic pore pressure, the motive mechanism of excess pore pressure; According to deformation and failure characteristics , one of them can be divided into unloading resilience and slope creep by the mode of slope deformation, the other can be divided into caving(collapse), creep down (landslide), side displacement by type of slope failure.6 According to the geomechanical patterns of the slope deformation and failure can be divided into creep (sliding)and fracturing,sliding and compression cracking,bending and fracturing,plastic flowing and fracturing,sliding and bending; According to the velocity of gliding mass movement can be divided into high speed, fast, medium-speed, slow. We can set up structure model of rock bedded slopes and stability mathematical model according to classified scheme, This has laid foundations of bedding slopes stability analysis.Study on the rock mechanics characteristic by earthquake loading, In this paper, Factors analysis on stability of bedding slopes under earthquake,including geologic background, formation lithology of geological environment and their combinatory, terrain landform, rock mass structural plane, structure types, hydrology conditions, earthquake loading conditions and so on. Then system research on mechanism of rock bedded slopes deterioration under earthquake loading, which by slopes fluctuation oscillation cause sliding failure, the deformation and failure process will produce three effects: progressive failure effect, priming effect, starting accelerated effect; the slopes deformation process under earthquake loading can be divided into deformed slow action stage, severe loading stage, instability violent slide stage.Discrete element method is established by Cundall who is from the United States in the 20th century 70's.It is an important method for numerical analysis applied to solve problems of discontinuous body. Interface (such as Discontinuity) is introduced in this method which is based on the finite element method to be the boundary between continuous bodies (intact rock). Continuum mechanics method is used for describing the mechanics behavior of continuous body and non-continuum mechanics for interface. This paper gives an in-depth research on problems encountered in the application of discrete element method and UDEC program, such as damping treatment, constitutive model selection, Time-stepping choosing, mesh generation, seismic loading and boundary condition determination. Conclusion of the research is advantageous to solve practical problems and issues. Dynamic deformation and failure rule of slope is researched by the way of numerical simulating deformation and destruction rule of bedding rock slope under earthquake condition with UDEC program , taking into account discontinuous joints and changing slope angle, height, bed angle, materials components and the seismic load conditions separately .Then get the following conclusions: (1)The maximum speed and displacement increase with height, and when the slope is higher than 80m, slope deformation and destruction increased obviously. (2) Bedding dip aggravates slope deformation. When it increases from 20°to 80°, the maximum displacement appears rapid growth, while block maximum speed decreases when the angle is 80°. This demonstrates that earthquake plays an important part in destroying the slope when bedding dip is 40°.Yet when bedding dip is bigger than slope angle, seismic load reduce the damage on slope. At the same time, slope failure mode will transit from slippage to toppling. (3)With the increase of the slope Angle, slope deformation increases at first, and then decreases. When the Angle is smaller than 60°, slope deformation is influenced seriously by earthquake. When slope angle is bigger than 60°, seismic load effect decreases. (4) The maximal displacement of slope increases with the amplitude and the increasing degree increases with the amplitude. Slope displacement under the intensity of VI ~, VIII degrees are respectively 2.2, 6.3, 19.2 times to that under V degrees. When it is 0.8s, maximum speed of block increases with the amplitude, and the slip velocity changes from fast to top speed. (5) There is a critical value for the effect of dynamic load cycle on slope. (6) Duration has significant effects on slope deformation and destruction. The maximal displacement increases with duration. As a result, if earthquake lasts longer, slope will be destroyed more seriously. (7) Under earthquake, the rock mass strength has a great effect on slope deformation and failure. Slope made up of rock of lower strength is easier to destroy. Conversely, slope comprised of rock of higher strength is more difficult to destroy. Slope destruction by dynamic loads is inversely proportional to the strength of rock mass.Based on the above analysis and investigation, this paper did discrete element numerical simulation on slide slope I-I at Tangjiashan's trailing edge which caused Tangjiashan barrier lake in "5?12" Wenchuan earthquake, completely simulated the 30s' whole process of landslide sliding from the slope to the Tongkou river and forming a weir dam,and obtained displacement vector graph, velocity vector graph and stress-strain diagram of landslide body after 29s'loading. From the velocity vector graph of landslide body we are told that there could be three stages in the process of slide deformation and failure: leading edge shearing, trailing edge cracking-rapid decline, forming air waves, leading edgeriver eroding riverbed-slope at the trailing edge collapse and damming, we could also calculate the downslide velocity of landslide body and the result is up to 30 m/s, belonging to typical superhigh-speed landslides. This is consistent with the actual formation process of Tangjiashan landslide in the "5?12" Wenchuan earthquake, therefore it is of important practical significance for the investigation of landslide process of bedding rock slope under the action of earthquakes, the dynamic stability analysis, and mechanism of landslides blocking river system. |
