| In order to guarantee the steadiness,security and passenger comfort of high-speed train in operation,the requirement for the stability of high-speed railway subgrade has become more and more strict.At present,using composite foundation structure to reinforce soft foundation is widely recognized in engineering.As a new method of soft foundation treatment,CFG pile-net composite foundation has been studied deeply by many researchers and has accumulated rich experience in practice.However,the theoretical research on the settlement deformation of pile-net composite foundation is insufficient and still lags behind the engineering practice.In particular,there is little research on CFG pile-net composite foundation under dynamic load.However,the number of high-speed railway construction in China is large,and there are many bad geological conditions such as soft foundation.Bad geological conditions,such as weak ground,will bring about problems such as running safety of trains.Therefore,it is particularly important to study the influence of pile-net composite structure on the settlement of the foundation under the action of train dynamic load.Based on the engineering background of Chang-Gan passenger dedicated line,a single pile static load test is carried out in the pile test section,and settlement data of the single pile static load test are collected in this paper.On the basis of the test,the CFG pile net is used to reinforce the weak foundation of the whole weathered phyllite in this section.By means of numerical method,the effects of different factors such as train speed,pile length,cushion thickness,bed surface,cushion layer and pile stiffness on settlement and deformation of phyllite soft ground are analyzed,The suggestion of CFG pile net to improve the weak foundation of phyllite is obtained,which can provide a reference for similar projects.The main points are as follows:(1)The calculation method of composite foundation settlement is analyzed and summarized.A single pile static load test was carried out in a test pile section of Chang-Gan passenger dedicated line,and settlement data of the test pile were collected to provide a basis for verifying the reliability of the numerical results.(2)Application of finite difference software FLAC3 D,Combined with the engineering geological data of Chang-Gan passenger dedicated line,the simulation model of CFG pile-net composite foundation is established,the settlement of the foundation under static load is simulated,and the maximum settlement value of the target pile is obtained.The reliability of the numerical analysis model is verified by comparing the settlement data of the test pile section.(3)On the basis of fully considering the mechanism of vibration load generation,the dynamic response of train dynamic load to subgrade structure is simulated with five excitation functions at different vehicle speeds,and the dynamic response of train dynamic load to subgrade structure is calculated and analyzed.The results show that the dynamic response of subgrade is mainly concentrated on the surface layer of subgrade.(4)Considering the speed at 150 km/h,200 km/h,250 km/h,300 km/h and 350 km/h,by simulating method,this paper analyzed the settlement characteristics of the pile-net composite foundation soil and pile under the dynamic load.Taken 300km/h as an example,the paper analyzed the influences of pile length,pile modulus,the structure stiffness and thickness on settlement value.Three different stiffness conditions were designed,and the settlement characteristics of composite foundation under three working conditions were compared and analyzed.Finally,some valuable conclusions for design and construction are obtained. |
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