| The construction of transportation infrastructure in China is developing rapidly,but the effective construction period is further compressed,which leads to the problem of uneven settlement at the back of bridge and culvert,which leads to the phenomenon of ’ bridgehead jump ’ and seriously affects the comfort and safety of driving.Improving the compaction quality of abutment backfill is an important measure to eliminate uneven settlement.However,due to the narrow working face of abutment,the compaction efficiency of conventional rolling method is limited,and the large mechanical vibration such as dynamic compaction cannot be compacted.High-speed hydraulic ramming is a new type of roadbed compaction technology developed in recent years.It has the characteristics of fast ramming frequency,not easy to produce horizontal and shear waves,and flexibility.It is gradually applied to the roadbed compaction project of bridge and culvert abutment.Because its theoretical research lags far behind engineering application,the reinforcement compaction characteristics and compaction effect of gravel soil subgrade are not clear.However,due to its short application time,the reinforcement effect of gravel soil roadbed is not clear.Therefore,this thesis uses numerical simulation and field test to study the reinforcement mechanism of high-speed hydraulic ramming,analyze the influencing factors of high-speed hydraulic ramming reinforcement effect,optimize the design parameters of high-speed hydraulic ramming,and put forward the calculation formula of effective reinforcement depth,so as to provide theoretical basis and engineering guidance for the design and construction of high-speed hydraulic ramming.The main contents and achievements of this thesis include:(1)According to the composition and working principle of the high-speed hydraulic rammer,the dynamic analysis of the ramming process is carried out,and the energy transfer mechanism in the process of high-speed hydraulic ramming is studied.The reinforcement mechanism of high-speed hydraulic compacted gravel soil subgrade is proposed.(2)The numerical simulation of the reinforcement effect of high-speed hydraulic ramming reinforcement on the backfill soil.The results show that the compactness of subgrade soil particles after tamping is significantly improved,and the reinforcement effect is remarkable.The long axis orientation law of gravel soil particles changes,and the long axis of gravel soil particles after tamping is more inclined to the horizontal direction.The reinforcement of hydraulic ramming makes the porosity of gravel soil particles gradually decrease,and its influence depth can reach 1.8 m.Increasing the diameter of ramming plate can improve the horizontal influence range of hydraulic ramming,but it is not conducive to the reinforcement of deep soil.Keeping the tamping energy unchanged,increasing the quality of the rammer can improve the reinforcement effect of the hydraulic rammer.Increasing the tamping energy can significantly improve the compactness of gravel soil particles and reduce the gap between particles,which is conducive to the reinforcement of subgrade soil.(3)Based on the numerical simulation method,the dynamic characteristics of the subgrade soil during the compaction process are analyzed,and the high-speed hydraulic compaction process is optimized to obtain the effective compaction depth of the hydraulic compaction.The results show that for the reinforcement and compaction of the gravel soil on the back of the platform,the number of ramming is 7-9 times,and the ramming spacing is 1.5times the diameter of the ramming plate.It is appropriate to use three-gear ramming,and the effective reinforcement depth of high-speed hydraulic ramming is 1.75-2m.(4)Based on the field test,the compaction effect and dynamic characteristics of high-speed hydraulic compaction technology are studied,the influence of design parameters such as tamping energy,tamping times and tamping spacing on the compaction quality of subgrade is analyzed,and the influence of tamping construction on abutment structures is evaluated and analyzed.The results show that the settlement of subgrade surface is the largest and the tamping effect is the best in the third tamping.The internal dynamic stress of subgrade increases with the increase of tamping count,and the improvement effect is not produced after9 tampings.With the increase of ramming spacing,the reinforcement effect of subgrade soil gradually weakened;The strain produced by hydraulic compaction is far less than the cracking strain of concrete,and the safety meets the requirements. |
