Study On CFG Pile Composite Foundation In The Road-culvert Transition Section Of Passenger Line Railway

With the development of high speed railway construction in the world, there puts forward more and more requirements to the stability of subgrade, and requires a very rigorous post-construction settlement control standard. As a new method for treating high-speed railway transition section, the pile-net composite foundation can effectively control post-construction settlement of subgrade so that reduce the foundation settlement difference of transition section as far as possible, and it saves cost. As its technical and economic benefits are more apparent comparing to other treatments, people are paying more and more attention to this method.Although pile-net composite foundation has been applied in engineering practice, but its study home and broad is far from mature, and there is no effective theory or design method which is recognized by people. This paper bases on the existing research and application results of the pile-net composite foundation home and abroad obtained through comprehensive study, and combined with the Tianjin-Qinhuangdao Passenger Line Railway engineering practice, then undertakes three areas of work on the road-culvert transition section of high speed railway ballastless track pile-net composite foundation focusing on theoretical analysis, field experiment and numerical simulation as follows:1This paper introduces the problems in the transition section of high speed railway and how they happened and summaries the major treatment measures home and abroad, includes:increasing the track rigidity, increasing the subgrade bed rigidity and improving the line structure bridge head. This paper expounds the meaning and composition of the post-construction settlement systematically and gives the post-construction settlement control standard of Chinese high-speed railway ballastless track.2This paper presents the concept of pile-net composite foundation, development history and research status, expounds the action mechanism and failure mode of reinforced soil, cushion and pile-soil reinforced area which is the component systematically.3This paper analyzes the principle of the post-construction settlement of the pile-net composite foundation, includes several important factors:embankment height, pile spacing, length and radius of the pile, replacement rate, bearing capacity of soil between pile, replacement rate and net’s tensile modulus. This paper deduces pile-soil ratio formula and the post-construction settlement of the pile-soil reinforced area formula of the pile-net composite foundation.4This paper monitor the deformation and stress(includes foundation settlement, pile-soil stress, strain of geogrid) of the typical section selected in the Tianjin-Qinhuangdao Passenger Line Railway, also arranges, calculates and analyzes the collect data. This paper draws the change trend of settlement and stress in the typical section according to the calculation results, and analyzes and researches the law of settlement in the road-culvert transition section.5This paper conducts a modeling study using the large-scale finite element numerical analysis software ABAQUS. CFG pile-net composite foundation settlement was studied by the finite element model, as well as how every parameter effect settlement and stress.