Shattered Rockmass Structure Characteristics Of Slope And Identification System Study On Collapse After Earthquake

Tens of thousands of collapse, landslides and secondary geological disasterstriggered by Wenchuan Earthquake, caused serious harm, and powerful earthquakeforce shook-loose the mountains, it make slope geological disasters takes placeconstantly at long period after earthquake. And the shattered rockmass is the mainreason for cause the secondary geological disasters, the study on the special destroyform is less at present, mainly because of the unpredictable nature of the earthquakeand its complexity, damage range widely, rockmass shattered crack damage occurs inthe mountains, to inspect in site is very difficult, these lead to study on shatteredrockmass is shortage. Frequent the aftershock, heavy rainfall after earthquake is thecauses of shattered rockmass instability, not only large scale and destructive of thedisasters, for example,2009“7.25”CheDiGuan collapse、2010“10.21”12th Crytchcollapse, but also the threat time is long, for example the large-scale collapse ofBaiShaLiu triggered by SongPan earthquake in1976, yet still collapse to now. Basedon the above aspects, firstly the author study on the shattered rockmass structurecharacteristics of slope by combination of precise measurement andengineering geophysical means, make research to the categories、characteristics、lawsof seismic fractures and shattered rockmass feature from macroscopic properties anddeformation characteristics. Through long-term follow-up investigation of collapsealong the highway in earthquake region, master their distribution, categories andinstability modes, and make identification to the collapse after earthquake. The harmtriggered by collapse is mainly caused by the strong impact force of rolling rock,based on the independently developed impact force testing system, make research tothe laws and calculation methods of impact force, the principal results are as follows: (1) Through survey the shatter failure characteristics of blocky structure slope、middle thickness rock layer structure and antidip stratified slope、soft and hard rocklayered slope, the seismic fractures was divided into six types: surface type、transfixing type、strike type、tendency type、closure type、extension type. Seismicfracture was N30o～60oE trending and mainly distributed in seismogenic faults areaor ridge、and steep with slow border area. Seismic fracture was well extension、highopen degree、upper wide and lower narrow of profile morphology, fillings less or no.(2) Shattered rockmass has the characteristics such as open structural planes、fillings less or no、overhead rockmass and so on, then it has the deformationcharacteristics such as low rebound strength、large range of low wave velocity andstrong permeability. Rebound strength of slope surface is between20~30MPa, wavevelocity value common less than3000m/s, concentrated in between2000~3000m/s, integrity coefficient was between0.15and0.5, integrity is poorer, permeabilityis basically high、serious. The partitioning standards of shattered rockmass is based onwave velocity value, divided into three communities: severe shattered rockmass、medium shattered rockmass and slight shattered rockmass.(3) Collapse after earthquake is mainly distributed in the Ⅹ and Ⅺ intensityzone, focused on the slope above40o, the main instability part is in middle-upper.Collapse instability modes could be attributed to five categories: toppling、sliding、buckling、scattering、eccentric-runoff, among them with sliding type and buckling typeprimarily, account for nearly60%of the all, followed by toppling type, scattering typeand eccentric-runoff type instability mode. The sliding type is integrity slip mainly;The toppling type is falling-ripping mainly.(4) Identification system of collapse after earthquake bulit based on interaction ofAHP. Take control discontinuity、gradient of geomorphology、 discontinuitycharacteristics、state of recessed cavity、feature of lithology assemblages、rockmassstructure、degree of seismic damage these seven factors as the basic indicators ofcollapse identification, with AHP, the influence weight of collapse identification andindex importance degree were semi-quantitatively analyzed based on the interactionrelationship between index, put forward the "collapse after earthquake discriminantindex CDI" method of collapse identification, built the identification system ofcollapse after earthquake. Combined with the investigation of slopes along thehighway in quake zones by long-term, based on collapse after earthquakeidentification method, get CDI index of potential collapse-hazards. Relying oncollapse identification index classification interval, the higher the CDI index, the collapse happened has bigger possibility.(5) Original design a set of impact force testing device, including three parts: therolling rock stent、impact resistance device、data acquisition device. Combined withthe system, make research to maximum impact force by simulation test, the force withthe decrease of the rolling rock weight or the lower impact velocity, reduce gradually,the force of2cm buffer layer thickness was reduced by90%than direct. Then itreduced gradually as the incident angle slow, but when the smaller the angle, the littleof lower value of the impact force.(6) Make research to the calculation method of impact force, discuss thesimilarities and differences、rationality、applicability of each calculation formula.Combined with the measured data of impact force, based on impulse theorem, andconsidered the oblique collision conditions, introduced the concept of amplificationcoefficient, set up a maximum impact force calculation method can be used fordifferent impact velocity、different incident angles、 different materials and thicknessof buffer layer(normalimpact η=0). For slow dip (θ＜40°), this paper suggests that impact force is0.7~0.9times of the force under the condition of normal impact.