Study On Performance Of Particle Breakage And Resilient Modulus Of UGM Under Dynamic Load

Unbound granular materials(UGM)is a typical flexible base with engineering characteristics such as high shear strength,strong water permeability,and small permanent deformation.However,under the effects of construction compaction and vehicle load on the UGM,the particle crushing situation and the influence of mechanical properties require indepth and systematic research.The main research goal of this paper is to quantitatively evaluate the vibration compaction characteristics of graded crushed stone and the particle crushing before and after the test based on the traditional indoor test method combined with the developed coarse aggregate image acquisition equipment and analysis method,using the indoor rebound modulus test method(AASHTO-T307),to study the impact of particle breakage and mechanical properties of flexible base graded gravel due to vehicle load.Firstly,Based on the developed coarse aggregate image acquisition equipment and analysis method,this paper analyzes the gradation of this kind of tuff gravel,and the results show that the determined coarse aggregate gradation error is in the range of-2% to 6%.Compared with the traditional screening test,this equipment and method can quickly and accurately determine the coarse aggregate gradation,simple operation,and no noise and dust pollution in the whole process.Secondly,for the study of particle crushing caused by vibration compaction of graded crushed stone,this paper selects a kind of tuff crushed stone in Gansu area as the research object.Based on the Taibo formula,7 sets of target gradations(n=0.3～0.6,interval 0.05)are selected.)Carry out indoor experimental research.The indoor vibration compaction test is used to simulate the vibration compaction load of the graded crushed rock during the on-site construction stage,and the gradation change of the specimen before and after the vibration compaction test is quantitatively analyzed,and the vibration pressure of this material during the on-site construction stage is evaluated.Actually lead to particle fragmentation.The results show that this kind of tuff material crushed stone will produce larger particles in the indoor vibratory compaction test,resulting in a change in the gradation of UGM and an increase in fine aggregates.The maximum particle crushing rate can reach 11%.In the test process,the particle crushing rate is significantly correlated with the crushed stone gradation and moisture content.The material particle crushing increases with the gradation n value from 0.3 to 0.6;the material particle crushing increases from 0% to the moisture content.8% has a clear downward trend.And based on the experimental results,this paper established a prediction model for the particle crushing rate of this material based on gradation and moisture content(R~2=0.816).Finally,in order to study the impact of particle crushing and mechanical properties of graded crushed stone due to vehicle load,this paper uses indoor rebound modulus test to simulate the vehicle load of graded crushed stone in the use stage,and compare the rebound modulus of the specimen.Quantitative analysis of gradation changes before and after the test is carried out to evaluate the impact of particle breakage caused by vehicle load on this material and the influence of gradation changes on its resilience modulus during the use phase.The results show that in the indoor resilience modulus test of this kind of tuff material,the resilience modulus has obvious stress-dependent characteristics;the maximum axial stress,confining pressure and the resilience modulus of graded crushed stone are positively correlated;relative to the maximum axial The change of the directional stress and confining pressure can more affect the change of the rebound modulus of UGM.However,the particle breakage produced by the indoor resilience modulus test of UGM is not obvious,and the maximum particle breakage rate is only 3%;the gradation change of UGM(n is 0.3-0.6,the interval is 0.05)has an effect on the resilience modulus.There is no obvious effect.Therefore,some particles of graded crushed stone were broken during construction and use,but the mechanical properties did not change significantly.This paper compares three commonly used rebound modulus prediction models and finds that for this tuff material,the NCHRP1-28 rebound modulus prediction model has the best prediction effect,followed by the modified k-θ model,and the NI model has the worst fitting effect.