The Research And Application Of Pipe Pile Composite Foundation In Soft Foundation Treatment

The Chinese railway gets speed from2007,a large number of bullet train workingin existed railway and has built Beijing to Tianjin,Wuhan to Guangzhou,Beijing toShanghai,Zhengzhou to Wuhan high-speed railway,and so on,to further improveChina’s railway network, has brought great convenience for people’stravel.However,the high-speed railway must meet the requirements of ballastlesstrack’s settlement. The high speed railway roadbed and the foundation are importantparts of the railway,are the foundations to bear the track structure and train load,it isthe most unstable one among the railway project,settlement control is very important toensure the quality of railway engineering. Chinese high-speed railway across more softsoil section, treatment of soft soil foundation is an important part of high speed railwayengineering. There are many methods for ground treatment,which include thereplacement method, the drainage consolidation method, the compaction method,thecementation method and the reinforcement method and so forth.It is very important tochoose the method of foundation treatment,according to the specific engineeringconditions.However, the traditional way of soft foundation treatment is limited to theprocessing depth,on the treatment of deep soft foundation which depth more than25m,using long pile treatment frequently.But these treatment methods exists someproblems in high price and larger constraint by construction conditions,its long-termreinforcement effect needs to be strengthened. our country is widely used compositefoundation in deep soft soil foundation at present.This paper focuses on the application of PHC pile net composite foundation indeep soft foundation treatment.Firstly, introduced the Mechanism of PHC pile netcomposite foundation, from four aspects which are the soil squeezing effect,theplugging effect,cushion effect,the pile group effect.The settlement influence factors ofPHC pile net composite foundation settlement are analyzed through theoretical andnumerical analysis method,analysis of cushion thickness, pile length and pile spacingeffect on the settlement of composite foundation.Secondly, introduced the applicationof PHC pile net composite foundation in deep soft foundation treatment through adetailed engineering design.The Xuchang east station roadbed of Shijiazhuang to Wuhan high-speed railway is soft and liquefacient soil foundation,which need special treatment.Its treatment is usethe PHC pile, concrete pile cap,the gradation crushed stone and geogrid composed ofpile net composite foundation.There are a simple introduction of the PHC pile netcomposite foundation construction process and a detailed introduction to the testingand the settlement observation of the composite foundation.The detec method ofcomposite foundation mainly contain the low strain test and the static load test.Thefunction of low strain reflection wave method is detect the integrity of pile,determinethe type,the extent and the location of defects.The function of static load test is todeterminate the vertical ultimate bearing capacity of PHC pile net compositefoundation.After testing,all the piles is first class and the value of subgrade bearingcapacity greater than design value.For analysis and calculate the final settlement andpost-construction settlement,determine the time of railway ballastless track layingrationally, made settlement observation and data analysis.In this paper have a introduceto the settlement observation technical requirements, observation section’sselection,components buried, evaluation method, settlement evaluation.Thedeformation measurement level and accuracy according to the two measurementregulations.In order to meet the settings on the observation section of"The detailedrules for the implementation of Settlement Deformation Observation and Evaluation ofShijiazhuang to Wuhan high-speed railway"selected eleven monitoring sectionsintroduced.All the monitoring sections were set up observation components such assettlement plate, settlement monitoring pile, section settlement tube,layered settlementgauge and so forth.To analyze the observation data which collected from constructionprocess, this paper introduces the settlement evaluation of three kinds of commonlyused assessment methods, and analysis the single point settlement and postconstruction settlement prediction.Finally, in order to further judgment the rationality and validity of compositefoundation testing and the settlement observation datas,use finite element analysissoftware MIDAS GTS modeled and analyzed,calculation of settlement data and fieldmeasured data are basically consistent with software, further verify the feasibility andeffectiveness of PHC pile net composite foundation.