Experimental Study And Numerical Simulation On Dynamic Compaction Characteristics Of Gravel Soil Foundation

The dynamic compaction method,as a simple,economical and efficient reinforcement treatment method,has been widely used in foundation engineering treatment particularly in the reinforcement of gravel soil.However,due to the fact that the theory of compaction treatment of gravel soil foundation is unmatured,theoretical research still stays far behind of engineering practice.And the improvement of reinforcement effect and compaction parameters in dynamic compaction engineering is mainly based on empirical analysis.In order to cut the construction costs and improve work efficiency,it is necessary to perform model tests and numerical analysis based on the theory of gravel soil foundation reinforcement under dynamic compaction.Based on the theoretical analysis of dynamic compaction and lumped parameters,this study aims on establishing a finite element model of heavy hammer impacted gravel soil foundation under dynamic compaction.In addition,this study aims on verifying the indoor model test results of the soil after dynamic compaction,in order to improve the main design parameters of dynamic pressure and evaluation methods of reinforcement effects.The main results can be summarized as follows:?1?The indoor model experiment of dynamic compaction method was performed based on the similarity principle.This experiment investigated the variation law of the settlement deformation and the porosity of gravel soil foundation under multiple dynamic compaction.The results of indoor model experiment show that:Along with the increase of compaction times,the change curve of pore water pressure and settlement displacement tends to be stable at the 8^th compaction.In a word,the required times of single point compaction were basically in accordance with the engineering reality.?2?By applying the Lumped-parameter method,the settlement deformation of gravel soil was calculated and the dynamic characteristics of three stages?ideal elastic,plastic and elastoplastic stages?was investigated.Specifically,the dynamic response law of dynamic earth pressure,settlement deformation and acceleration with time was analyzed at three stages respectively?ideal elastic,plastic and elastoplastic stages?.In addition,by comparing the results of the Mass-Damp-Spring model?SMD model?and the Mass-Damp-Slider-Spring model?SMSD model?,it can show that SMSD model can better mimic the actual deformation of dynamic compaction.This result indicated that SMSD model has the ability to reflect the real situation of engineering.?3?The experiment of dynamic compaction on gravel soil foundation was performed by conducting field experimental research,with the purpose of exploring the dynamic response law of the sand-gravel soil foundation.The results of these experiments shows that:First,the effects of the first 8^th dynamic compaction is the most obvious;however,the settlement of dynamic compaction is less than 3cm at the last 4compacts.Second,along with the continuously increase of dynamic compaction energy,the average value of dynamic compaction degree at 150kN·m is 0.948;however,it increased to 0.987 at 1200kN·m.Furthermore,the experiments confirmed that the 8^thh dynamic compaction can fulfill the compactness requirements of gravel soil,thus the optimal times of dynamic compaction can be controlled as approximately 8.?4?The dynamic response characteristics of heavy hammer impact soil foundation at 150kN·m and 300kN·m energy levels were analyzed by ABAQUS three-dimensional simulation.The results showed that:Under the same dynamic compaction energy,the compaction of the weight drop was better than that of the light hammer;In addition,the vibration response characteristics of the dynamic compaction were investigated.The trend of the velocity is similar to the double hump distribution,while the acceleration distribution looks like sine distribution.;the porosity reduction increased proportionally at the first 5^th of dynamic compaction,the reinforcement effect has finished 85%at this point,the percentage after the 8^th compaction was basically unchanged.The accumulated settlement and stress have reached about 83%of the total value under the first 5^th compactions,while the click settlement of the eighth strike is still small.Therefore,the optimal number of compaction of this model is 8 times,which can further provide guidance for the actual construction.This paper analyzed and summarized previous empirical formula about effective reinforcement depth;afterwards,in combination with the results of laboratory model test,field test and numerical simulation.Through comprehensively considering of compacted energy level,water content and soil characteristic parameters,the proportional coefficient was established.By fitting the results of numerical simulation and experimental study under dynamic compaction,the improved formula related to effective improvement depth can be obtained as follows:H=?_R?d^M2/3hN_?1-??,which was in agreement with the actual measured results.