Failure Machanism Of Stratiform Rock Slope Under Strong Earthquake

Lots of landslides have been triggered by the Wenchuan earthquake, whileprovides plenty of sample for mechanism analysis in the strong earthquake area.In thispaper.The studied on the rock slope failure machanism of the strong earthquake area isimported to the disaster prevention work of the similar area.Based on field investigation data of the four basin(Jushuihe River, ChapingheRiver, Mianyuanhe River and Shitingjiang River), the author studied the distributionlaw of the landslides in the study area, with further analysis of the key factor whichinfluenced on it. While typical stratiform rock slope has been studied and modeled forshaking table test. Thought out the data collected from the test, a comparative analysisof slope with different lithology and structure has been carried on.Besides, withnumerical simulation and mechanics theory calculation of the slope under strongearthquake, the failure development location, the rupture expansion direction andslide behavior after failure also was analysed. Main conclusions are as follows:(1)The distribution law of the peak value of ground acceleration(PGA) analysiswas carried on based on strong motion records of the digital strong earthquakenetwork in sichuan and its neighbouring region. The analysis proved that the PGAcontour line is an elliptic whose major axis is parallel to the fault belts ofLongmenshan. The vertical seismic wave reduction is more significant that thehorizontal direction.And in the upfaulted district of the seismogenic faults betweenWolong to Qingping, the PGA value of vertical direction is close or even bigger thatthe horizontal direction. The author also proposes a method to describe landslidedensity with peak value of the ground velocity.(2)Thought out imagery interpretation, distribution law of the landslides was explained, and the key factor which has significant influence on it has beenselected.The research discovered that the PGA value controlled the regionaldistribution of the landslides, while the structure of the slope controlled the type of thelandslides itself.(3)Based on failure patten field investigation of the typical landslides in thestudy area, the author summarized the mechanism of different slope structure. Theanti-dip slope were crack-slide(dip angle>50) and crack-cut through(dip angle<20),while the dip slope were simply slide(dip angle <slope gradient) and slide-buck.(4)Large scale shaking table test is used to analyze the dynamic response of theslope with different lithology and structure.Four different types were tested, includinghard rock dip slope, hard rock anti-dip slope, soft rock dip slope and soft rock anti-dipslope.Thought PGA amplification analysis, structural damage recognition analysis,modal analysis, the conclusions were as following:①The lithology and structure of the slope has a significant influence on themechanism of a landslide. After cracking in the rear edge of the slope top, there is abucking at the the bottom of the dip slope, while malposition at the middle position.②PGA amplification is larger on the upper half parts of the slope, and theamplification factor of horizontal vibration is larger than the vertical one. The dipslope has a significant amplification on the shallow surface, while the anti-dip one isinfluenced in the deeper parts.③Damage identification base on HTT method shows that the damage depth ofthe hard dip slope is not as deeper as the anti-dip one, even more longer in thevertical direction.Due to the better deformational properties, the soft rock slope canpartly repair its damage in the process.④The damping ratio variety which calculated from the modal analysis canexpress the natural property change of the slope in the whole process. The moreacute variety of the hard rock slope than the soft rock means the former one hasexperienced more structural change than the latter.(5) Numerical simulation and mechanics theory calculation are used to explainthe unique phenomenon of the landslides triggered by the strong earthquake.As thefailure development location of different type of slope, the rupture expansiondirection and slide behavior after failure can be explained.①Based on stress increase magnitude results which are calculated with DiscreteElement Method, failure development parts of the dip slope and anti-dip slope aredifferent.The dip slope is in the foot section, while the anti-dip slope is in the middle section.②Fracture mechanics and finite element analysis are used to obtain the ruptureexpansion direction inside the slope. The relationship between which and the PGAmagnitude is built to explain the form of steep back-wall and gentle shear outlets.③Based on mechanism analysis of the blocks system of the landslide on thestrong earthquake, equations are deduced, with further inversely calculation using thetypical landslides of the strong earthquake region. The author proposed that afterformation of sliding surface, the landslide movement is more likely in a "Jumping"way.