Study On Shear Properties And Rock Block Breakage Characteristics Of Soil-rock Mixtures

With the implementation of the Western Development strategy and the construction of the Silk Road Economic Belt,the southwest China airport construction has been developing rapidly and the scale has been expanding continuously,so many superhigh fill slopes have been formed.For example,the maximum fill height of Chongqing Jiangbei International Airport expansion project is up to 130 m.In the process of filling,the Soil-Rock Mixtures with pretty engineering properties such as good compaction performance,high density of filling,high shear strength and small settlement deformation is widely used as filling materials.Shear properties,as a strength characteristic of Soil-Rock Mixtures,is an important physical-mechanical parameter to control high fill slope's stability and deformation.And the serious particle breakage problem of the high fill slope under high stress have a significant influence on the shear properties.The shear properties of Soil-Rock Mixtures considering particle breakage will be an important theoretical-practical significance for stability and foundation uneven settlement of high hill slope in the construction of the southwestern airport.Based on the four extension project of Chongqing Jiangbei International Airport,this paper studies the shear properties of Soil-Rock Mixtures with the consideration of particle breakage.The on-site trenching and laboratory direct shear test are producted to obtain the basic physical and mechanical properties of Soil-Rock Mixtures.Through the add-on development of FISH language in PFC2D,the particle flow model of Soil-Rock Mixtures considering rock breakage is constructed.The influence of rock block content on shear properties is analyzed,and the rock block breakage characteristics are studied.Some other numerical direct shear test models are constructed to enlarge the scale of research of discussing the influence of block size,block shape,grain size distribution and initial porosity on shear properties and particle breakage degree of Soil-Rock Mixtures.The main research results are as follows:?1?First of all,the shear and breakage characteristics of Soil-Rock Mixtures with different rock block content and rock lithologies are studied through laboratory large scale direct shear tests and sieve tests.With the increase of rock block content,the shear curve of Soil-Rock Mixtures develops from strain hardening to plastic strain,and finally develops to strain softening.With the increase of rock block uniaxial compressive strength,the shear curve develops from strain softening to strain hardening.With the increase of normal stress,the fine particles of Soil-Rock Mixtures after shear increase,the coarse particles decrease and the intermediate particles change.With the increase of rock block content,the particle breakage is more common,and grading curve is bigger.The greater the uniaxial compressive strength and elastic modulus of rock block is,the less likely it is to break,and the smaller the rock block breakage degree of Soil-Rock Mixtures is.?2?Based on labratory direct shear test,the Soil-Rock Mixtures particle flow model which can truly describe Soil-Rock Mixtures morphological character and accurately reflect features of particle breakage in the shearing process of discrete element numerical model is constructed through the add-on development of FISH language in PFC2D on the basis of Soil-Rock Mixtures particle size composition and the law of block form statistics.The random breaking process of random polygonal rock block with particle size greater than 5mm is realized by using Cluster particle cluster,which can better reflect the breaking effect of rock block.Based on uniaxial compression test and direct shear test,the microscopic parameters of the particle flow model of Soil-Rock Mixtures are calculated and calibrated.And the microscopic parameters that can better reflect the shear properties of Soil-Rock Mixtures and the characteristics of rock block breakage are finally selected.?3?The numerical direct test model is constructed,to discuss shear properties of Soil-Rock Mixtures with the consideration of rock block breakage.The influence of rock block content on the shear strength index and rock block breakage rate is revealed,and Soil-Rock Mixtures shear surface evolution law in the process of shearing from the micro perspective is analyzed.The shear process of Soil-Rock Mixtures can divide into 4 stages,including elastic deformation stage,local shear stage,shear failure stage and residual deformation stage.The higher the rock block content,the higher the shear strength of Soil-Rock Mixtures,which is basically in accordance with the mole Kulun strength criterion in the range of 200kPa⁸00kPa normal stress.In the course of shearing,the breakage forms of rock block can be classified into 4 categories:surface grinding,partial breakage,complete rupture and complete breakage.For quantitative analysis of rock block which particle size is greater than 5mm,a breakage index based on the relative breakage rate Br of Hardin which called block relative breakage rate B_r-5 is proposed.The relative breakage index B_r-5 increases with rock block content and normal stress increasing.The B_r-5 of Soil-Rock Mixtures which rock block content is P₅ under the normal stress?_n is fitted,to roughly forecast breakage rate under different working conditions in practical engineering.The final shear surface of Soil-Rock Mixtures is not smooth but deviates from the preset shear surface.With the increase of rock block content,the shear surface is more undulating and the"shear oblique"phenomenon is more obvious.?4?The multiscale numerical direct shear test models are constructed and the influence of four intrinsic factors,such as block size,block shape,particle size distribution and initial porosity,on the shear properties and particle breakage degree of Soil-Rock Mixtures is discussed.The shear strength of Soil-Rock Mixtures increases with increase of block size,and the difference shows an increasing trend with the normal stress increases.As the block size increases,B_r-5 increases.The block shape has no obvious effect on the shear strength of Soil-Rock Mixtures,but with the block roundness increases,B_r-5 will decrease.The more uniform the particle gradation,the more complete the contact between particles is,the closer the bite is,and the higher the shear strength.As the particle gradation tends to be good,B_r-5 decreases.The initial porosity has no significant effect on the shear strength of Soil-Rock Mixtures.With the increase of initial porosity,the number of contact points around the stone particles is relatively small,the stress at the contact point will increase,and the B_r-5 will increase.