Study On The Dynamic Stability Of Baihua Bridge Bedding Rock Slope In Yingxiu

5.12Wenchuan earthquake is the most extensive of the affected areas suffered and the most damaging earthquake in China since the founding, secondary disasters caused by earthquakes such as landslides, avalanches, landslides, dammed lake had large number, affected a very wide range, and were devastating, had brought great losses to the country and the people. Studies on rock slope have focused on the response characteristics and stability analysis of the slope under static loading, very little research work has been done on the Slope stability under seismic load. It has been a hot and difficult issue need to be resolved. In this paper, the analysis of Baihua Bridge rock slope stability in the Wenchuan earthquake has a very important theoretical and practical significance.This thesis is essentially based on the author’s research work during joining the research project of evaluation of the rock dynamic safety in Wenchuan earthquake area sponsered by China Geology Survey. I followed the project team to Yingxiu area which was one of severely affected areas during the Wenchuan earthquake twice in August2009and July2010. A detailed survey on secondary disasters by the earthquake-induced in the region was carried out,then author selected Baihua Bridge bedding rock slope in Yingxiu Town, Dujiangyan City for a typical object of study. Baihua Bridge slope stability under strong earthquake was studied. The key findings include the following:(1) engineering geological conditions of the Baihua Bridge bedding slope were ascertained,including physical geography,topography,geological structure,lithology,earthquake activity, hydro-geological conditions, climate and other environmental features.then the basic characteristics of Baihua Bridge bedding rock slope were analysised, Lithology of Baihua Bridge Rock Slope is hard, exposed lithology is sericite siltstone and fine sandstone of the Triassic Xujiahe (Tx1). Bedding and joints develop, there is a group of well-developed bedding which is rough and free filled,most of it is open at the same time a small number of bedding is slightly open. The form of Bedding is mostly flat, a small number of it is irregular-shaped and jagged, it has a certain bond strength. The body of slope has developed two sets of joints,which are rough and free filled. Most of them are open at the same time a small number of bedding is slightly open. The shape of the joints are mostly irregular, jagged or wavy, a few of them are straight. (2) The surface geometry characteristics of Baihua Bridge slope rock mass structure were analyzed. According to the measurement data of the structure, initial probability model parameters such as structure orientation, inclination, diameter, gap width, bulk density are calculated. The occurrence of the joints group I is137°∠73°,its diameter is2.49m,its gap width is5.54mm,its bulk density is1m-1; The occurrence of bedding group Ⅱ is302°∠33°, its diameter is1.58m,its gap width is4.41mm,its bulk density is4.3m-1; The occurrence of the joints group Ⅲ is27°∠Z74°, its diameter is0.88m,its gap width is1.30mm,its bulk density is4m-1. the slope failure mode is determined according to the stereographic projection. Bedding group Ⅱ plays a controlling role in the destruction of the slope. Joints group Ⅰ and bedding group Ⅱ cut each other and cut the landslide into numerous blocks. Joints group Ⅰ plays a role in promoting slope failure. Landslide slided along the sliding surface formed by bedding group Ⅱ in the seismic forces and gravity.(3) Slope rock mass classification and rock mass quality assessment can give correct and timely qualitative or semi-quantitative macroscopic evaluation to the stability of engineering slope rock mass.RMR classification method is used to categorize Baihua Bridge Slope rock mass.The rock quality designation RQD is one of important parameters in the RMR classification method,but traditional methods to access RQD do not meet the practical application of rock anisotropy requires,therefore,three-dimensional discontinuity network simulation method-. the volume RQD method、the statistical measurement method of discontinuity are used to calculate the rock RQD.The advantages and disadvantages of the three methods and calculation accuracy are contrasted.Using the RQD got by the three ways to carry out RMR rock mass classification.The RMR rating values are approximate, rock mass classification results are poor rock, preliminary evaluation results of the stability by RMR classification descirbe the quality of the rock really and objectively.the results are also consistent with the engineering geological investigation.(4) Basing on Baihua Bridge slope engineering geological plans and sections, on the basis of restoring the original topography, the appropriate geometrical parameters are selected for the model. Binding discontinuity analysis data.Basing on the division requirements of the grid size and the corresponding parameters in the model; the mesh size of the upper part of the model where the bedding and joint developed is6m; the grid size of the lower part of the model is25m; The bottom boundary of the model is the viscous boundary, surrounded boundary by borders is the free-field boundary; The bottom boundary of the model is the viscous boundary, so when the power is input,it must be converted to stress time,and then the shear and normal stress is brought to bear to the bottom of the model. Local damping calculation is chosen, and its damping value is0.125. In order to facilitate the modeling calculation, a certain angle is existing between the coordinate system in the model and the real coordinate system,the calculation parameters related to the angle should be carried out the coordinate transformation;when the seismic waves are input,the first20s of the May12earthquake seismic wave data is intercepted,then seismic waves handling software Seismosignal software are used to baseline correction and low-pass filter the seismic waves.(5) Strength reduction method and discrete element software3DEC are binded to calculate the numerical simulation of the Baihua Bridge slope.The simulation is divided into two parts,the frist part is to calculate the stability coefficient of Baihua Bridge slope in the natural state;the second part is to calculate the stability coefficient of Baihua Bridge slope in the role of the Wenchuan earthquake.The potential slip surface AB can be determined by studying of rate and displacement vector field when the slope is unstable and fail; Five monitoring points a#,b#,c#,d#e#are located in the upper part of the potential slip surface AB. the critical state of the slope is determined by the trend of monitoring points’displacement-time curves and speed-time curve. The Baihua Bridge slope stability coefficient in the natural state is1.13while stability coefficient in the Wenchuan earthquake stability coefficient is0.58.(6) Baihua Bridge slope failure mechanism and failure process in the two project status are studied and compared.the displacement vector maps of Baihua Bridge slope in the Wenchuan earthquake are studied, and the slope leading part and block part are enlarged, It is got that the slope failure mechanism in the Wenchuan earthquake is divided into four stages.①、The landslide progressive failure stage②、landslides start-up stage③、the landslide movement stage④The landslide stabilization stage.The failure mechanism of Baihua Bridge slope in the natural state are as follows:by reducing the shear strength of structure, bond strength decreased.when the reduction factor K=1.14, the leading edge of the slope form plastic zone due to shearing, the tension crack appear in the slope trailing edge of the slope.over time,the leading edge of the plastic zone continues to expand, the tensile cracks in the trailing edge of slope darken wider,the plastic zone has also been expanding, clavicle force in the leading edge of the slope gradually reduce to zero,and ultimately the sliding plane formed along bedding,the decline force is greater than the stabilizing force,the overall slope slide failure along the sliding surface, blocks squeez and collision each other in the sliding process, resulting the block fragmentation, and ultimately the formation of accumulation bodies pile at the foot of the slope.