Development Of Vibration Isolation Device For Dynamic Compaction And Engineering Technology Application

Dynamic compaction technology is a commonly used foundation and subgrade reinforcement technology in highway engineering.It has good engineering effect on improving subgrade density and controlling subgrade settlement.However,the adverse effect of dynamic compaction on surrounding structures seriously restricts the engineering application of dynamic compaction technology.At present,a large number of laboratory and field test researches on dynamic tamping vibration,regarding isolation methods and materials have been carried out at home and abroad.The research on the engineering application technology of dynamic tamping vibration isolation device is insufficiency,therefore;the design and development of dynamic tamping vibration isolation device and its engineering technology application are urgently needed.In this paper,the distribution characteristics of dynamic compaction surface wave on the subgrade side of expressway were analyzed,combined with the expressway reconstruction and extension project.By means of numerical simulation,the vibration isolation effect of air cushion and light cast-in-place vibration isolation material was analyzed.The technical parameters of the two kinds of vibration isolation materials are optimized.The indoor model tests of air cushion,formwork clamped air cushion and lightweight cast-in-place material were carried out.The effects of different vibration isolation depths and frequencies on the vibration isolation efficiency of the material were analyzed,and the related vibration isolation parameters and material design were optimized.According to the characteristics of air cushion vibration isolation material,the special air cushion vibration isolation device and related construction equipment are designed and developed,and the related construction technology is put forward.The conclusions are as follows:(1)The monitoring of dynamic compaction construction site of highway reconstruction and extension project shows that the horizontal and vertical vibration velocity of the foot of roadbed slope at 4.5m from compaction point is 81.4mm/s and 163mm/s,and the horizontal vibration velocity of the hard shoulder at 8.7m from compaction point is 29.13mm/s,and the vertical vibration velocity is 4.87mm/s,the latter is less than the allowable vibration value of 12mm/s.The horizontal and vertical vibration velocities of the test vehicle located in the emergency lane are 8.31mm/s and 2.32mm/s,which meet the allowable value requirements.The horizontal vibration velocity is 29.13mm/s and the vertical vibration velocity is 2.67mm/s in the central separation zone 19.7m away from the tamping point,the former does not meet the allowable value requirements.(2)Numerical simulation of vibration isolation of air cushion and lightweight castin-place materials show that the vibration isolation effect of the two materials is the best when the vibration isolation depth is 6m and 9m,and the vibration frequency is 20Hz and 10Hz.Considering the frequency of dynamic compaction,the optimal vibration frequency is 10Hz and the vibration isolation depth is 9m.At 10Hz vibration frequency and 9m depth,the horizontal and vertical vibration isolation efficiencies of the two vibration isolation materials are respectively 73%and 39%,and 68%and 35%.The elastic modulus(air pressure)has no effect on the vibration isolation efficiency.The density and elastic modulus of lightweight cast-in-situ materials have a significant impact on the vibration isolation efficiency.When the density of lightweight cast-insitu materials increases from 700kg/m3 to 1100kg/m3,the horizontal and vertical vibration isolation efficiency increases by 6%and 5%respectively.When the elastic modulus increases from 348MPa to 1187MPa,the horizontal and vertical vibration isolation efficiency increases by 23%and 20%respectively.The rigidity of lightweight cast-in-place materials has a more significant effect on the improvement of vibration isolation efficiency.(3)The indoor model tests of air cushion,formwork clamped air cushion and light cast-in-place material show that the vibration isolation material of air cushion is basically equivalent to the hollow groove efficiency.Under the working condition of 52kN excitation force and 0.5m vibration isolation depth,the horizontal and vertical vibration isolation efficiency of the former is 73%and 70%,only 4%and 3%lower than that of the latter respectively.Wooden formwork is added on both sides of air cushion vibration isolation material,and the vibration isolation efficiency lost about 5%.The vibration isolation efficiency of lightweight cast-in-place vibration isolation material is about 35%lower than that of air cushion vibration isolation material.Vibration isolation efficiency of three kinds of vibration isolation materials increases with the increase of vibration frequency and decreases with the increase of excitation force.(4)Combined with the results of indoor model test and numerical simulation,the air cushion vibration isolation device is designed,and the special vibration isolation device board device is designed and developed.According to the characteristics of the equipment,the corresponding construction scheme design is carried out,which provides construction technology for the engineering application of air cushion vibration isolation device.