Structure Change Feature And Research Of Influence Of Strength In The Course Of Shearing Granular Mixtures

Granular mixtures,as a kind of discontinuous medium material,is increasingly used in project construction in recent years.Therefore,research of strength of granular mixtures has extremely practical significance.But presently research of granular mixtures mainly focuses on the influence of strength conducted by granular mixtures static structure.The influence of strength is issued by particle morphology,compactness and gradation of granular mixtures.The present research lacks research of structure change in the course of shearing granular mixtures and can't reveal the influence-of-strength way conducted by granular mixtures structure basically.To explore the influence of strength law conducted by granular mixtures structure change,this article gives quantitative analysis to granular mixtures structure change in the course of shearing granular mixtures through indoor direct shear test and figure simulation test and gives analysis and conclusion to correspondence relationship between structure change and strength.This article verifies main structure change in the course of shearing granular mixtures and the influence of granular mixtures strength conducted by structure change.This article obtains the following research results through this research:(1)Direct shear test has a lot of advantages and is used as a main test method for acquiring granular mixtures shear strength for a long time.But shear boxes loading sample mainly are made of non-transparent rigid material so that granular mixtures structure change in the shear course can't be monitored.Pointing at research requirement,this article finished improvement design work on test facility.We can monitor granular mixtures particle motion state clearly during shearing through improved observable shear box in the indoor direct test,which reached expected effect.(2)Combining research target and test facility,we take strip crushed stone particle(type ?),massive crushed stone particle(type ?)and globular pebble particle(type ?)as research sample.We carry out direct shear test under normal stress of 100 kpa,200kpa and 300 kpa on 3 groups of granular mixtures sample.Through test,we acquire monitoring image of strength parameter and structure change of 3 groups of sample.(3)We utilizes PFC software to respectively establish generalized model of 3 kinds of particle and shear model of corresponding granular mixtures;to simulate course of direct shear of 3 kinds of granular mixtures under normal stress of 100 kpa,200kpa,300 kpa and 400 kpa.Through comparison and analysis of physical test result and simulation test result,we find stress feature and structural change law of both accord with each other,which shows generalized model can reduce physical test course better.Meanwhile,through simulation test,we acquire displacement variable and rotational variable of granular mixtures in the course of shear.(4)This article gives induction and conclusion to main structure changes and strength features of granular mixtures in every shear stage and the shear of granular mixtures course can be divided into 4 stages:(1)stress initial stage.Corresponding structure micro-reduction.(2)shear stress ascendant stage.Drastic dilatancy of corresponding structure;increasing gap between particles;shaping of main chain.(3)shear stress peak value stage.Corresponding dilatancy rate turns and the gap between particles increases to the critical point of cracking of main chain.(4)shear stress decline stage.Dilatancy of corresponding structure becomes slow and the gap between particles doesn't increase any more.(5)Through analysis and comparison of correspondence relationship between structure change feature of three kinds of granular mixtures and respective strength,this article verifies influence of strength way and law conducted by granular mixtures structure change.