Experimental Study On The Effect Of Particle Shape On Mechanical And Liquefaction Characteristics Of Manufactured Sand

In recent years,the rapid development of domestic infrastructure projects has led to a large consumption of natural sand resources.In addition,the unrestrained mining of the river sand causes hidden risks to the safety of the riverbed and ecological environment.As the substitution for natural quartz sand,manufactured sand has been widely used for infrastructure projects.It not only relieves the shortage of natural sand resources,but also shows a promising market and greener nature of manufactured sand in the future.However,little attentions are paid to the mechanical properties of manufactured sand.Investigating the shear and liquefaction characteristics of manufactured sand as well as its mechanism,which is of theoretical and reference significance for the application of manufactured sand in backfilling projects,such as artificial island and pipe layer.One of the noticeable distinctions between manufactured sand and natural sand is their particle shape,which has a significant effect on their shear and liquefaction behaviors under the monotonic and cyclic shear stresses and needs to be further investigated.In this study,four kinds of manufactured sand produced in Lishui city,Zhejiang province,as well as a kind of natural quartz sand(Leighton Buzzard sand)were used as testing materials.The particles’ morphology representative parameters are assessed in terms of sphericity,roundness and regularity with microscopic observation and image processing.A number of basic physical properties tests and geotechnical tests were carried out to investigate the static and dynamic characteristics of quartz sand sample and four kinds of manufactured sand samples.The effects of particle shape parameters on the evaluation of relevant mechanical indexes were proposed by regression analysis.The main contents and conclusions are as follows:(1)The particle morphology of quartz sand sample and four kinds of manufactured sand samples were derived and analyzed by microscope and image processing software.The results show that the particles of manufactured sand are more irregular,the edges and corners are more developed compared with quartz sand.(2)The maximum and minimum dry density of the testing samples were evaluated,and the corresponding minimum and maximum void ratio were calculated.The minimum and maximum void ratio of the samples decrease with the increasing particle shape parameters,indicating that manufactured sand particles with angularity have better compressibility.(3)Considering different particle shape parameters(sphericity,roundness,regularity)and different normal stress(50 k Pa,100 k Pa,200 k Pa,400 k Pa),the interface friction characteristics and shear strength of sand samples with various particle shape parameters were studied by direct shear apparatus.It is found that the shear strength and internal friction angle decrease with higher particle regularity.The liner regression formula between internal friction angle and shape factors was established.Moreover,the MohrCoulomb strength formula was optimized based on this liner regression.(4)In order to investigate the stress-strain behavior of these five sandy soils,a series of undrained monotonic shear tests were conducted by dynamic cyclic simple shear system.The shear strength of quartz sand and manufactured sand samples were compared,the influence of particle shape factors on the gradient of flow liquefaction line were analyzed as well.(5)The undrained dynamic cyclic single shear test was carried out through the dynamic cyclic single shear system.The evolution laws of cyclic shear stress,dynamic shear modulus,shear stiffness and other dynamic characteristics of sand under different cyclic shear strain amplitudes and different particle shape parameters were discussed.The correlation regression formulas for these dynamic characteristics were also established.(6)Undrained monotonic shear tests were carried out for the liquefied sand samples to explore the coupling effects of cyclic shear history and particle shape on the postliquefaction behavior.For a specific sand sample,the shear strength increases linearly with the increasing cyclic shear strain amplitudes,while the peak pore pressure decreases as the cyclic shear strain amplitudes increases.The shear strength of quartz sand with relative round particles is obviously lower than those of manufactured sand,The peak pore pressure of quartz sand is higher than those of manufactured sand in the same testing condition,demonstrating the samples with round particles are more unstable.According to the experimental results,the undrained shear strength and peak pore pressure interrelated with cyclic shear history and particle shape were proposed.The research findings could provide theoretical and technical supports for the application of manufactured sand in the backfilling of foundation and offshore engineering.In addition,the findings also could serve as references for the selection of manufactured sand in engineering and the deformation prediction of the corresponding backfilling layers.