| Problems of rock mass fragmentation under strong seismic effect are more andmore revealed and researched, especially a large number of large-scale landslideoccurs after the Wenchuan earthquake, this make geologists have new awareness ofrock mass fragmentation and dynamic origin. But problems of rock massfragmentation of large-scale landslide caused by strong earthquake involveengineering geology, rock mechanics, earthquake engineering and so on, there aremany problems urge to be solved. Daguangbao landslide is a very rare giant landslide,The giant overlying400m thick rock stratum collapsed and slided under the8magnitude earthquake, In the process of earthquake, huge slipe mass vibration androlling compaction, fragmentation is especially striking.This article is based on former research, start from special fragmentation of slidebed residual rock mass, investigate the stratum distribution and continuity features ofthat type of rock. Result shows that this kind of rock continuously exists, average3mthick, it is a weak zone in the Sinian Dengying Formation and is defined asDaguangbao landslide slip zone. Based in this basic cognition, we start fromsketching and scanning the macroscopic features of fragmental rock mass, and dividethe rock mass into three parts:(1)strong vibration, rolling compaction, unloadconfining pressure area;(2) vibration, no rolling compaction, confining pressure area;(3)weak vibration,no rolling compaction, confining pressure area. The existingclassification of rock mass structure cannot cover the extreme fragmentation ofDaguangbao. Aiming at Daguangbao fragmental rock mass, we divide rock mass intofragmental sand shape, fragmental block structure, fragmental splinter shape andcement shape, and define that as fragmental re-cement rock mass. Research inside the rock stratum shows that: the portrait fragmental rock stratums are not contiuous,wefind four stratums that vary significantly in color and hardness from bottom to top inall three zones. And at the bottoms there are all thin mud layers. The investigation offragmental rock mass and areal rock shows that generally there are three types ofstructures, namely: North East, South East, North West, One step closer analysisreveals that, these three groups of structures not only control Daguangbao landslide"glossy" morphological characteristics and also influence the evolution of landformsin this region.Based on the analysis of macro-micro-macro, for fractured rock compositionand structural, analysis and cataclastic structure formation microscopic analysis,concluded that the fractured rock with uneven components、particle size related（tentimes）、diversity of structure（more than6). Cataclastic rock after multiple tectonicmovement by hydrothermal cementation, forming the existing fracture characteristics.According to fracture classification of crystal deformation of rock massdamage,include:(1)intergranular fracture、(2)crystalinterfacefracture、(3)crystaldislocation、(4)crystal plastic deformation、(5) Crystal table impact pits、(6)crystal loosening;According to the pattern classification cataclastic rock crystalfracture mechanics,include:(1)static load of tension fracture、(2)compression-shearfracture、(3)fatigue Tension fracture、(4) fatigue compression-shear fracture、(5)compound fracture； According to the crystal weathering patternclassification,Mainly include:(1)crystal weathering (corrosion)、(2) Intergranularweathering、(3)fracture weathering(shale cementation、 calcareous cementitiousstructural plane)、(4)compound weathering.Quantitative evaluation is a necessary task in the research of rock mass, forsubsequent similar material test, physical simulation, numerical simulation providebasic parameters. Combining with the existing research, based on image processingtechnology and fractal theory, quantitatively statistical analysis of the vein cataclasticrock mass cranny and crumb structure, concluded that The proportion of fracturedrock is less than fifty percent,1cm2distribute110fractures; The fracture roughness,cataclastic fragmentation, degree of fracture fractal dimension valuescalculated,concluded that An average fractal dimension values of fractured rockstructure is1.6, the average fractal dimension values of calcite vein is1.5,and articlecalcite vein with increasing fractal dimension values is into a linear relationship;theaverage fractal dimension values of fractured blocks is2.3.The in-house physical experiment shows that the dense of cataclastic rocks decreases apparently, and the reduction rate is10%.this indicates that the cementingrock mass crevices develop heavily and expand during earthquake, and dilate withvolume range from7.2to50.4million cubic metres during slip and shear. based onthe macro-micro results, the shatter damage and the process of deformation andfailure concept model which has four stages is proposed:(1)the rock shatter to damage,difference structure cracking, the existed fissures reopen.(2)the cracks couple,coalescence, and rock cementation strength deteriorate.(3)the land slide cementingstrength vanishes, slid, crushes, and vibrates.(4)the late unloading, weather and rainflushing.With the basic understanding of cataclastic rocks and based on PFC particles flowdiscrete element analysis of the static and dynamic simulation of structure containingdefects rocks, the result demonstrates that(1) defect structure existed within the rockmass, regardless of the high or low strength will deteriorate the rock overallstrength.(2)the level of defect structure will local influence the rock strength.(3) It isthe local character of rock that change caused the rock deformation within thecoordination, the unharmony decreases gradually with the increase of defect structuredistance.(4)defect structure stiffness and connection strength both significantlyinfluence the incoordinate deformation, Accurate analysis shows that the influencelevel of connection strength is bigger than that of structure stiffness.(5)under thedynamic action, the same character defect degree of effect on rock strength is greaterthan the static effect.(6)the local strength influence of defect structure andincoordinate deformation decide the failure of rock mass containing defect structure,Fracture surface generally generate along the coupling between the weakest surface.The paper established a geology numerical model with weak interlayer foranalyses vibration test. Tests showed that:(1) The rock stress of overlying strata isreducing greatly, strain, vertical and lateral speed are increasing greatly above theweak interlayer,which attract vibration energy.(2) weak interface layer down differentdynamic response strength, lower interface is greater than the The dynamic responsestrength,which in the upper and lower interfaces of weak interlayer,is different,thenon-coordinated deformation in the interface is largest,and Fracture surface forms inlower interface generally.(3) Simulations suggested that weak interlayer is undergoingtensioned and compression-sheared alternative action in the vibration process,thisprocess lead to deformation rate of the weak interlayer to be accelerated greatly andthe damage of it to be exacerbatedThe indoor shear test for the cataclastic rock mass made clear that the shear strength envelope line function of the cataclastic rock mass was a power function, andideally we could calculate the shear strength of the slide belt in the case that there wasthe gravity stress above. Analysis showed that the slide belt strength of Da guang baolandslide changed over time under the power action, and the constitutive parameterswas a function of time. Before and after Da guang bao landslide started, there weremainly the shatter and the shear slide along the fragmentation layer in the South. Thisphenomenon could be abstracted as a natural shear test-the fragmentation layer actedas a shear zone, at the same time10Mpa gravity stress of rock mass above acted asthe positive stress. However, there were two special aspects. For one, the shear need acertain inclination and angle; for another, the load was dynamic load in the process ofshearing. Therefore the shearing process had the characteristics as follows by thesetwo factors:(1) the slide belt strength decreased with the gravity stress strengthincreased;(2) the stability decreased wavily and continuously with time in the processof shearing. |
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