Numerical Analysis Of Coarse-grained Soil Compaction Response Under Dynamic Compaction

Dynamic compaction method has been widely used in the construction of expressway,railway and airport.Using dynamic compaction to strengthen coarse-grained soil can not only improve the strength of soil foundation,but also effectively control the late foundation settlement.However,in the existing studies,the reinforcement mechanism of dynamic compaction is mainly focused on the macroscopic response of soil under dynamic compaction,while the research on the mesoscopic dynamic response of soil under dynamic compaction is insufficient.Moreover,the influence of particle breakage on the consolidation effect of dynamic compaction is rarely considered.Therefore,To fully understand the physical and mechanical process of dynamic compaction,and reveal the mechanism of dynamic compaction reinforcement.Coarse-grained soil is the research object in this thesis and is commonly used in geotechnical engineering.Using discrete element software PFC3D(Particle Flow Code in 3 Dimensions),the macro and micro dynamic response of quartz sand under dynamic compaction was studied and analyzed.The influence of particle breakage on dynamic stress response and reinforcement effect is revealed.The main research contents are as follows:(1)Based on the theory of scale and dimensional analysis,a laboratory scale model of dynamic compaction is established.Physical properties of test soil samples were tested and dynamic compaction tests were carried out.The response law of soil compaction under dynamic compaction is obtained.These provide the data basis for the establishment and verification of the subsequent numerical model.(2)The numerical model of dynamic compaction was established by using discrete element software PFC3D.Numerical tests of dynamic compaction were carried out.The results of numerical test and laboratory test were compared and analyzed.The results show that the numerical model of dynamic compaction is reliable.(3)Numerical tests of dynamic compaction with different hammer weights and falling distances were carried out.The macro and micro dynamic response of soil under dynamic compaction was monitored and analyzed by means of particle ergodic technique and measuring element method.The compaction mechanism of soil under dynamic compaction is revealed.From the aspects of compaction,dynamic stress,porosity,coordination number and contact force,the rationality of the optimal value of α(α is the weight coefficient of the impact of falling distance on the consolidation effect of dynamic compaction)is explained as 0.3.(4)The criterion and method of particle crushing were established and introduced into numerical test of dynamic compaction.The influence of soil particle breakage on dynamic consolidation was studied.It is found that the fragmentation of soil particles will weaken the consolidation effect of dynamic compaction in the early stage of dynamic compaction,but will effectively accelerate the consolidation rate of soil.The purpose of this study is to provide scientific basis for further research on dynamic compaction theory and fully reveal the mechanism of dynamic compaction.Moreover,it can provide reference for engineering application and technology upgrading of dynamic compaction.