Effect Of Particle Size Distribution And Wetting-drying Cycles On Shear Mechanical Properties Of Red-bed Soil-rock Mixture

The construction of highway in Sichuan and Chongqing areas,often required to pass through red-bed area of Sichuan Basin.At this point,nearby choose tunnel or cutting excavation of the red-bed soil-rock mixture（RB-SRM）as subgrade filling materials are environmental and economic.Therefore,RB-SRM were used in subgrade filling of highway,such as Chengdu-Anyue-Chongqing expressway and Chengdu-Mianyang expressway.However,particle size of RB-SRM differences apparently,and affected by the distribution of it.In addition,under the action of hydraulic coupling,the hard rock of red-bed crushing,soft rock avalanche soil solution,and has significant structural evolution characteristics.Red-bed soil-rock embankment operation a few years later,prone to collapse and deformation of subgrade disease.However,the particle size distribution and the wetting-drying cycles of RB-SRM were not study systematically.Based on this,this paper took RB-SRM from Mabian-Zhaojue section 1 of Leshan-Xichang expressway as materials,and studied the effect of particle size distribution on shear mechanical properties of RB-SRM through the large-scale direct shear test,the laminated shear test and the screening test.Taking two particle size distribution levels,the shear mechanical properties of RB-SRM under wetting-drying cycles were studied by the laminated shear test and the static disintegration test.Three levels of particle size distribution,wetting-drying cycles and fill height were taken to design the orthogonal numerical tests,and FLAC3D was used to simulate the sensitivity of influencing factors on stability of high-fill red-bed embankment.The results show that:（1）Based on the non-uniformity coefficient（C_u）and curvature coefficient（C_c）of the existing evaluation parameters,the relative content of medium sized rock（C_m）is proposed,which can further refine the evaluation of the particle size distribution of soil-rock mixture.Four particle size distribution levels ofC_u=22.47 andC_c=1.40 were proposed,and the correspondingC_m values were 0.143,0.343,0.543 and 0.743,respectively.Among the existing wetting-drying cycles methods,Saturated Water-natural Air drying is feasible and meets the tests needs.Staggered deformation occurs between laminated layers in the laminated shear test,compared with the large-scale direct shear test,the influence range of shear zone is wider,and the shear plane is not fixed by human,which weakens the defect that the shear plane decreases with the increase of shear displacement.In the laminated shear test,the deformation of particles in the RB-SRM along the shear direction is more sufficient,and the shear strength and its parameters measured are less than that of the large direct shear test,which makes laminated shear test more suitable for the laboratory large-scale physical test of RB-SRM.（2）With the increase of C_m,the cohesion（c）of RB-SRM first decreases and then increases,and the internal friction angle（?）first increases and then decreases,both of which have extreme values at C_m=0.543,and the shear strength is the maximum at this point.In the shear process,the content of large and medium sized rock decreases due to self-crushing,the content of small sized rock fluctuates due to self-crushing and the supplement of larger sized lump stone,and the soil content increases due to the supplement of larger sized rock.The particle size distribution affects the bearing body of the skeleton and the degree of deformation difficulty,and the normal constraint（?_n）affects the failure mode and the amount of energy released during the failure.The relative particle breakage rate（B_r）decreases first and then increases with the increase of C_m and?_n.When?_n is lower than the shear strength,the RB-SRM shows the characteristics is shrinking first,and then dilating later.When?_n is higher than the shear strength,the shear shrinkage is continuous.The RB-SRM with the same particle size evaluated by traditional methods can form a skeleton-dense structure with better load bearing characteristics,lower particle breakage rate,higher strength and higher anti-deformation ability after the reasonable setting of C_m（C_m=0.543 in this paper）.In the laminated shear tests,with the increase of C_m,B_r,c and dilation ratioηof RB-SRM decrease first and then increase,while?and shear modulus G_0.02 increase first and then decrease.The influence weight of C_m on effect parameters is as follows:?>B_r>c>η>G_0.02.（3）The disintegration of red-bed soft rock can be divided into three parts:severe section,transitional section and stable section.When the number of cycles n?2,the disintegration is severe,and the content of grain group changes obviously.The disintegration characteristics are closely related to the size of rock.The strength of RB-SRM decreases with the increase of n,and tends to be stable when n（29）2.When n（28）6,the strength deterioration of RB-SRM has no effect on the cycles.Electrostatic attraction and cementation have positive effects on the bonding strength of RB-SRM under wetting-drying cycles.After the collapse of red-bed soft rock,the mechanical bite between blocks weakens and the apparent cohesion decreases,which has a negative effect on the bonding strength.The friction between particles of RB-SRM decreases under wetting-drying cycles,but the sliding friction and the reorientation of particles increase with the disintegration of red-bed soft rock.Reasonable setting of grain size distribution refinement parameter C_m can weaken the strength deterioration of RB-SRM in red-bed under wetting-drying cycles.The dilating of RB-SRM decreases with increasing n and?_n.The shear modulus G_{0.0 2} decreases with the increase of n and tends to be stable when n（29）2.The displacement difference between laminated layers decreases with the increase of n,and the critical failure surface tends to be smooth with the increase of n.When C_m=0.143,the influence weight of n on effect parameters is as follows:η>c>G_{0.0 2}>?.When C_m=0.543,the influence weight of n on effect parameters is as follows:η>c>?>G_0.02.（4）Under the action of gravity stress field,the settlement of high-filled red-bed soil-rock embankment is distributed along the filling height in strips,and the settlement is the largest at the center line of the embankment top.The sensitivity of the three factors to embankment settlement is as follows:filling height>wetting-drying cycles>particle size distribution.There are arc-shaped potential slip surfaces in embankment slope,and the sensitivity degree of the influence of the three factors on slope safety factor is as follows:wetting-drying cycles>fill height>particle size distribution.The horizontal displacement of the critical failure state of embankment slope presents a step-like distribution,the displacement value decreases successively from the foot of slope to the top of slope,and the potential slip surface cuts out from the foot of slope.The sensitivity degree of the influence of three factors on the maximum horizontal displacement of embankment in critical failure state is as follows:particle size distribution>wetting-drying cycles>filling height.