Analysis Of Response To Dynamic Compaction Of Soil-rock Mixture Fill And Related Investigations Of Testing Technique

Dynamic compaction is one of main compaction methods of high fill airport construction.The soil-rock mixture,obtained from blasting,is always used as original fill material for airport construction,the particle size of the filler usually varies greatly and the content of giant grains is high.In view of the fact that the relevant standards and techniques of dynamic compaction of such fillers are imperfect,this paper focuses on the mechanism and effect of soil-rock mixture strengthened by dynamic compaction.By layered burying of speed and stress sensors during high platform construction in airport of Chengde,the development and attenuation law of vibration velocity and dynamic stress in gravel soil during dynamic compaction was obtained,which provided useful advice for compaction quality control.According to the experience of Chengde test,this paper continued to study the vibration testing technique of dynamic compaction and an improved monitoring method was proposed by calibration tests in Beijing New Airport.Based on the experimental results above,finite element software ABAQUS was used to simulate and analyze the soil reinforcement and influence scope under different tamping energies.The results of field tests and numerical analysis show that:(1)Dynamic compaction will produce two kinds of different vibration waves inside the soil,combined with analysis of corresponding displacement curves,it is found that elastic and plastic zones both exist in the soil,and according to the wave characteristics,the impact reinforcement area and vibration reinforcement area are formed in plastic zone.(2)The plastic boundary of soil under dynamic compaction has a critical elastic vibration velocity.Through the relationship of vibration velocity and the tamping times,the standard and method of determining the range of reinforcement with the critical vibration velocity is established.Analysis show:the plastic region is about 7.5m deep and 3.5m wide while the tamping energy is 1000kN m.The coefficient in the modified Menard formula used in mountainous airport can be 0.7.(3)The calibration tests accomplished in Beijing New Airport show:Fixing the sensors on the tube wall of PVC to measure the vibration response of the soil instead of directly burying is feasible.This improved method can effectively measure the relative attenuation law of the energy and the wave’s velocity of propagation in soil under every compaction.(4)Compaction Degree of 94～95%(corresponding plastic strain is about 10%)is used as a parameter to control the quality of airport runway,and the reinforcement range of soil under four different dynamic energy levels are obtained through numerical method.Results show:When the tamping energy is between 1000-1500kN·m,the suggested layered thickness is 3m and the tamping point spacing should be 2 times the diameter of the hammer;when the energy is between 2000-3000kN·m,the suggested layered thickness is 3m and the spacing should be 3 times.