| Enduring stability and smoothness of track are very important for high-speed railway due to the high level of speed, comfort, security and contiuous operation, consequently strict settlement after acceptance and differential settlement requirements are proposed. Bridge possesses a significant proportion in the whole line, sometimes larger than 80%, most of which adopt pile foundation. As a result, settlement after acceptance controlling of pile foundation becomes a key technology in design and construction of high-speed railway. Unfortunately, research on settlement after acceptance of pile foundation and relative materials are insufficient, meanwhile, calculation theory remains immature and lagged. Considerring the vigorous construction of high-speed railway, further study on the mechanism and prediction method of settlement after acceptance is of theoretical and practical significance.Aiming at the observation method and development law of long-term settlement of pile foundation, mechanism of the settlement after acceptance, calculation and prediction means, as well as determination of reasonable time for laying tracks which satisfing the settlement after acceptance threshold, field tests, laboratory experiments and theoretical analysis are adopted systematically in this research. Following are some main issues and achievements:(1)Bridge foundation settlement monitoring schemes of Wuhan-Guangzhou and Beijing-Shanghai high speed railway were laid out respectively. The specific implementing technologies of pile foundation deformation monitoring such as the basic requirements, the technical standards, layout of benchmark, re-observation of base point, the leveling line, overall layout of deformation monitoring system and specific measures to obtain reliable field data were proposed through research and practice. Field test results showed that the monitoring method for deformation was effective and the components and instruments were reliable, thus it is worth promoting.(2)The combined monitoring method of precise leveling and hydrostatic leveling was proposed to observe the settlement of bridge pile foundation, which was successfully applied in the typical section of the Wuhan-Guangzhou high-speed railway and the Beijing-Shanghai high-speed railway. Based on reliable settlement and compression data of piles, the law of pile foundation settlement and the axial force, skin friction of pile varying with load were put forward, subsequently the settlement mechanism was explained.(3)Considering location of long and large pile foundation on the soft clay on the Beijing-Shanghai high-speed railway, the joint monitoring method of the settlement gauge and strain gauge was firstly proposed to observe the compression of soil layer under pile foundation. Installing technique of settlement gauge was studied and a reliable technical method for monitoring the thickness of compressible soil layer beneath pile foundation was presented. Based on lots of compression data, the development law of compression of soil layer varying with load and time were illustrated(4)The stress-strain-time curves of soil samples under different load, beneath the long and large pile foundation of the typical section on the Beijing-Shanghai high-speed railway, were obtained through creep test. CPIP, a computer program for creep parameter back-analysis, was developed. The Schiffman viscoelastic model, identified by CPIP, fit the deformation characteristic of soil layer better.(5)By using the Schiffman model, one-dimensional consolidation equation of multi-layered soil was established with single drainage and double drainage under multilevel loading. Moreover, the formulas,used to calculate effective stress and settlement,were derived.(6) Three-dimensional composite analysis methodâ… of the bridge group piles was improved to simulate actual load conditions of pile foundation and to take creep characteristics of soil layer beneath the piles into account. A corresponding program called PG3DSâ…¡was developed. Comparison between calculation and measured data of settlement of pile foundation on Beijing-Shanghai high-speed railway indicated that the method could effectively improve the calculation precision of long-term settlement of pile foundation. (7)Based on the pile foundation settlement of field test and the programme PG3DSâ…¡the main parameters of soil layer were iterated back-analyzed by using coordinate alternation method, and the calculation programe for back-analysis PBAP was developed. Long-term settlement calculation method, which was based on back-analysis results, was presented. Research showed that it was more reliable and accurate than calculation based on lab test.(8)The calculating methods for the settlement after acceptance of pile foundation and the shortest intermittent time to meet the settlement after acceptance threshold were proposed, subsequently the method of determining the reasonable time for laying tracks was presented. In order to improve computational efficiency, the corresponding program called PTLT was developed, which could provide reference in determination of the reasonable time for laying tracks.(9)Through evaluation index analysis, the inadequacy that the expedience evaluation of prediction model was limited to the correlation coefficient index in current guide was pointed out. It was proposed that mean-square error, mean absolute percentage error and mean absolute error should be also introduced as evaluation indexes, furthermore, corresponding reference values were recommended.(10)Weighted combination model for settlement after acceptance prediction of the high-speed railway bridge pile foudation was proposed, based on which the corresponding program named BriFSCF was developed. It was verified that the least-squares criterion optimal combination forecast method should be regarded as the preferred model for its better prediction. This achievement could provide significant references for guide revising.
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