The High-speed Rail Pile Composite Foundation - Raft (network) Load Sharing Site Testing And Analysis

According to tasks of railway technology projects about "research on Jinghu high-speed rail composite pile foundation for settlement control to reinforce soft foundation"and "Huning inter-city rail construction safety and settlement monitoring technology" and based on field experiment of soft foundation consolidation in Jinghu high-speed rail and zhenjiang section in Huning inter-city rail,this paper makes research on pile-soil load sharing of pile-raft(net) composite foundation in the process of high speed railway filling,standing and preloading and unloading.Through the analysis in lab, theoretical analysis and field experimental datum,this paper carries out a series of research and exploration on pressure distribution,load sharing and pile-soil stress ratio of pile-raft(net) composite foundation.At the same time,this paper give some suggestions to similar projects.Main tasks and conclusions of this paper are displaced as follows:(1)On account of the processing mode of new high-speed railway foundation like pile-raft(net) composite foundation,the author make field experiment on six section chosen reasonably according to geological conditions and design proposal in Jinghu high-speed rail and zhenjiang section in Huning inter-city rail; bury many earth pressure cells on soil between pile top and inter-pile;bury steel bar meter and strain gauge in raft to completely monitor pressure distribution,load sharing ratio,pile-soil stress ratio,raft stress-strain and so on and so forth in pile-top soil of pile-raft(net) composite foundation.(2) By arranging and analysing the data gained from in-site in 182 to 400 days on six section,the author can obtain distributing and developing regulation of soil in cross section of high-speed railway pile-raft(net) composite foundation roadbed, of load sharing ratio in pile-soil,of pile-soil stress ratio in different position,and traits of raft stress-strain in pile-raft(net) composite foundation.Through comparing regulation of load sharing between pile-raft composite foundation and pile-net composite foundation,and regulations among different kinds of pile-raft composite foundations,the paper sums up advantages and disadvantages when this two compostie foundation are used in dealing with high-speed railway soft foundation.(3)Depending on the transversal and vertical action of soil between piles in pile-raft(net) composite foundation,the author selects two calculation models to calculates the pile-soil stress ratio of pile-raft composite foundation and pile-net composite foundation respectively.Through modifing key parameter of cushion thickness, cushion modulus and roadbed load, regulations of development of pile-soil stress ratio of pile-raft(net) composite foundation can be recorded and be compared and analysed with field measurement.(4) According to field test and analysis of load sharing and theoretical analysis of pile-soil stress ratio,some engineering proposal on high-speed railway pile-raft(net) composite foundation are brought forward for reference only.①, intensify design strength of pile on the edge of raft and in the center of roadbed and weaken it in other positions.②, crushed-stone-cast-pile and other pile-raft composite foundations of discrete material should be used firstly in the area where soft soil is bad.③, pile-raft composite foundations should be employed in a thicker soft-soil ground or soft soil foundation with deep dissection.