【作者】 杨奇；

【导师】 冷伍明；

【作者基本信息】 中南大学 ， 岩土工程， 2011， 博士

【摘要】 高速铁路高速度、高舒适度、高安全性和高密度连续运营的特点,要求轨道结构具有持久稳定的高平顺性,因而对工后沉降和差异沉降提出十分严格的要求。桥梁在整个线路中占的比重很大,有的占到线路总长80%以上,且几乎都采用桩基础。因此桩基工后沉降控制成为了高速铁路设计和施工最为关键的技术之一。但是,目前桥梁基础工后沉降的研究较少,积累的资料不多,计算理论还不成熟,研究滞后于工程实践的需要。面对当前方兴未艾高速铁路建设,确定合理的铺轨时间、保障工后沉降在规定限值内是一项十分重要的工作,因而深入开展桥梁基础工后沉降机理和预测方法研究具有重要的理论意义和工程实用价值。本文针对高速铁路桥梁桩基长期沉降变形观测方法、桩基沉降发展规律、工后沉降产生机理、桩基(长期)工后沉降计算方法、预测理论和满足桥梁基础工后沉降限值的合理辅轨时间等重要问题,应用现场测试、室内试验和理论分析相结合的方法,进行了系统深入地研究。主要的工作和成果如下：(1)编制了武广高速铁路、京沪高速铁路桥梁桩基沉降变形观测方案,通过研究和实践提出了桥梁基础变形沉降监测的具体实施技术,包括基本要求、技术标准、测点布置方法、基点复测、水准路线图、桥墩基础观测系统整体布置方法和保障获得各种可靠监测数据的具体措施。现场试验研究表明变形观测方法行之有效,观测元件和设备可靠,有良好的推广价值。(2)提出了精密水准联合静力水准监测桥梁桩基沉降的方法,并在武广高速铁路和京沪高速铁路典型试验工点得到成功应用。获得了翔实可靠的高速铁路桥梁桩基长期沉降数据、桩身压缩变形数据。基于此揭示了高速铁路桥梁桩基沉降发展规律,桩身轴力、桩侧摩阻力随工况(荷载)的变化规律,探讨了高速铁路桥梁桩基沉降的机理。(3)针对京沪高速铁路典型软土区长大桩基特点,提出了沉降计联合应变计监测桥梁桩基桩底压缩层变形的方法,研究了长大桩桩底压缩层沉降计的安装埋设工艺,为测试桩底压缩层变形提供一种可靠的技术方法。在国内外首次于现场获取了大量长大桩桩底土层压缩变形数据,揭示了深厚软土地段长大桩桩底土层压缩变形随荷载、时间的发展规律。(4)通过室内蠕变试验获取了京沪试验工点长大桩桩底试验土样在各级荷载作用下的应力-应变-时间关系曲线。研制了蠕变参数反演程序(CPIP),对比分析表明Schiffman粘弹性模型能较好地描述桩底土层的变形特性。(5)基于Schiffman模型,建立了多级加载情况下单面和双面透水边界多层粘弹性地基一维固结方程,推导了桩底压缩层在多级加载作用下的有效应力和沉降的计算公式。(6)改进了桥梁群桩沉降计算“三维复合分析方法Ⅰ”使其能模拟高速铁路桥梁桩基实际的受荷情况和考虑桩底压缩层的蠕变特性。编写了相应计算程序PG3DSII,对京沪高速铁路桥梁桩基沉降的计算结果与现场实测值的对比分析表明,该方法能提高桩基长期沉降的计算精度。(7)基于铺轨前桩基沉降观测值与PG3DSII计算程序,运用坐标轮换法分组迭代反演桩基底土层主要参数,编制了桩底土层参数反演计算程序PBAP,提出了基于反演参数的桥梁桩基长期沉降计算方法。对比分析表明,该方法计算的长大桩基沉降误差小,比基于室内土工参数计算的沉降更为“真实”可靠。(8)提出了计算高速铁路桥梁桩基工后沉降和满足桥梁桩基工后沉降限值所需最短休工时间的计算方法,进而提出了最佳铺轨时间的确定方法,研制了相应的计算程序PTLT。可为满足桥梁基础工后沉降限值的合理辅轨时间的确定提供直接参考。(9)通过对常用预测模型预测效果的评价指标分析,指出了客运专线铁路无砟轨道铺设条件评估技术指南中评价预测模型合理性仅局限于相关系数指标的不足,建议引入均方误差MSE、平均绝对误差MAE和平均绝对百分表误差MAPE指标进行综合评价,并提出了这些评价指标的参考值。(10)提出了加权组合预测模型进行高速铁路桥梁工后沉降预测的方法,研制了桥梁桩基沉降加权组合预测程序BriFSCF。通过多个实例验证表明,最小二乘准则下最优组合预测法效果较好,可作为的预测优选模型。研究成果可为客运专线铁路无砟轨道铺设条件评估技术指南的修订、完善提供重要依据。更多还原

【Abstract】 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 methodⅠof 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 PG3DSⅡwas 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 PG3DSⅡthe 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.更多还原