Early Warning of Foundation Settlement Deformation for Ballastless High-Speed Railway Tracks

There has been rapid development of high-speed railway lines, especially passenger-dedicated railway lines, in China. Trains are traveling at speeds exceeding 250 km per hour and they require highly smooth tracks to ensure safety. However, there have been no in-depth studies on the early warning of the settlement of high-speed railway lines in China or abroad. Most methods use a simple model based on data processing and decision rules. The core issues of early warning lie in the science and rationality of decision rules. The present paper therefore investigates novel and critical indexes for the warning of settlement under high-speed railway lines according to existing norms and field data, and several essential indexes of deformation warning are suggested through theoretical and experimental analysis.

Settlement Characteristics of Cement Fly-Ash GravelPile-Plate Composite Foundation of High-Speed Railway

Field tests on settlement characteristics were carried out on the cement fly-ash gravel （CFG） pile-plate composite foundation on Beijing-Xuzhou section of Beijing-Shanghai high-speed railway. The settlements of the piles and the soil between pries were measured and analyzed. The results show that the settlement-time dependency experienced three phases： rapid development phase, stable development phase and stable phase. Therefore, surcharge preloading was necessary to reduce the settlement after construction. The finite element software Plaxis was used to calculate the deformations of the pile top and the soil between piles at the embankment center, as well as the settlements of CFG pile reinforcement area and the underlying stratum under surcharge preloading. The calculation results and the field test results were compared and analyzed. Both the results show that the settlement of the composite foundation mainly occured in underlying stratum. The settlement characteristics of pile-plate composite foundation under high embankment are also concluded.

Accumulative deformation in railway track induced by high-speed traffic loading of the trains

Prediction and control of the permanent settlement of a track caused by traffic loading from trains is crucial to high-speed railway design and maintenance. In this study, a unified prediction model of accumulative deformation of geomaterials used in railway construction subjected to cyclic loadings is introduced and calibrated using physical model testing. Based on this versatile model, a calculation approach to determine the track structure settlement under repeated loadings caused by the movement of the wheel axle of the train is proposed. Regression analysis on the physical model testing is adopted to determine the parameters involved in the computational approach. Comparison of model test data and computed results shows that the parameters obtained from the back-analysis are consistent throughout the various testing conditions, and the proposed calculation approach is capable of satisfactorily predicting the accumulative settlement of the railway roadbed and subgrade soil for various axle loads and loading cycles. A case study of a high-speed railway is performed to demonstrate the feasibility of the proposed approach in realistic engineering applications. The computation results from the settlement development of a roadbed and subgrade soil are presented and discussed.

Deformation characteristics and safety assessment of a high-speed railway induced by undercutting metro tunnel excavation

Stratum deformation(settlement) is a challenging issue in tunnel engineering, especially when construction of metro tunnels has to undercut high-speed railway. For this purpose, we used the FLAC30 software to analyze the stratum settlement characteristics of high-speed railway at different crossing angles intersected by metro tunnel, in terms of ground settlement trough, stratum slip line and irregularity of ballastless tracks. According to the evolution of the stratum settlement at different angle regions, an optimized angle is proposed for the actual project design. In order to reduce the influence of stratum settlement on the safety of high-speed railway, an approach of safety assessment is proposed for the shield engineering undercutting high-speed railway, as per Chinese specifications using numerical results and on-site conditions. A case study is conducted for the shield tunnel section crossing the Wuhan-Guangzhou High-speed Railway between the Guangzhou North Railway Station and the Huacheng Road Station, which represents the first metro tunnel project passing below a high-speed railway in China. A series of measures is taken to ensure the safe excavation of the shield tunnel and the operation of the high-speed railway. The results can provide a technical support for performing a safety evaluation between high-speed railways and metro tunnels.

Settlement mechanism of piled-raft foundation due to cyclic train loads and its countermeasure

In this paper, numerical simulation with soil-water coupling finite element-finite difference（FE-FD） analysis is conducted to investigate the settlement and the excess pore water pressure（EPWP） of a piled-raft foundation due to cyclic high-speed（speed： 300km/h） train loading. To demonstrate the performance of this numerical simulation, the settlement and EPWP in the ground under the train loading within one month was calculated and confirmed by monitoring data, which shows that the change of the settlement and EPWP can be simulated well on the whole. In order to ensure the safety of train operation, countermeasure by the fracturing grouting is proposed. Two cases are analyzed, namely, grouting in No-4 softest layer and No-9 pile bearing layer respectively. It is found that fracturing grouting in the pile bearing layer（No-9 layer） has better effect on reducing the settlement.

The Effect of Traffic on Ballast Settlement

The main factor that contributes to the deterioration of track components is traffic load. Explanations on how the speed, load and repetition of traffic influence the long-term settlement of ballast in a ballasted track are very scarce. Having in mind that tracks subjected to the same load show different settlement behaviors, explanations of track settlements in accordance with the speed, load and repetition are needed. This study is motivated to show how traffic affects the long-term settlement of ballast and how the traffic parameters (speed, load and repetition) contribute to the process. Using finite element modeling software, the three-dimensional track is modeled and analyzed for different values of speed, load and number of repetitions. Drucker Prager plastic model is applied for the ballast and sub-ballast materials of the track. To get the parameters for the Drucker Prager plastic model of granular materials, triaxial test simulation is performed using discrete element software. Hertz’s contact theory is used to model the contact between the wheel and rail. The long-term settlement behavior of ballast material is analyzed by applying 8000 cycles of moving axel load. According to the analyses, a change in the speed and the number of repetitions of train movement changes the permanent settlement of ballast more than the variation in load. Increase in the speed of train movement by 20 km/hr. will increase the stress transferred to the subgrade by up to about 1000 kPa. Speed of train movement is the most contributing parameter in the degradation of ballast material more than the load and number of repetitions. In a conventional ballasted track after about 6000 repetitions of train movement ballast material will start to decrease its performance. The comparison of the effects of the variation of individual traffic parameters speed, load and number of repetitions on the settlement of ballast which is not touched by former researches is well addressed by this study which is very helpful for designing a new railway track and monitoring existing railway tracks. Based on the analysis of the model with the parameters from Ethio-Djibouti standard gauge railway track, the possible maintenance period of ballast material is predicted.

囊袋式注浆对盾构下穿高速铁路路基沉降的控制效果

高铁路基的沉降变形是影响运营安全的重要因素,盾构下穿既有高铁线路施工可诱发高铁路基沉降变形。为有效控制高铁路基沉降,基于数值模拟探究了囊袋式注浆作为高铁路基沉降主动控制措施的有效性。结果表明:注浆囊袋对其周围土体的影响具有局部性,地层等效塑性应变随注浆体埋深的增加而增大,且塑性区厚度通常小于注浆囊袋膨胀厚度的3.0倍。囊袋的埋设深度和膨胀直径对路基抬升整治范围有影响,囊袋埋设越浅其膨胀后对路基抬升的影响效果越明显,且路基表层的隆起变形曲线符合高斯方程。提出了盾构下穿高铁路基时囊袋式注浆控制措施下路基沉降预测模型,可指导盾构下穿高铁路基的沉降控制。

高铁桥墩沉降的通用渐进分解长期预测网络模型

高铁桥墩不均匀沉降是导致轨道不平顺的潜在原因之一,准确预测桥墩沉降对于确保铁路建设和运营的可靠性和安全性具有重要意义。目前,常规时间序列领域的多数预测模型仅在预处理良好且没有缺失的数据集上进行测试,而在高铁桥墩沉降的真实场景中,沉降数据相较于其他领域存在观测频次少且不等时距,以及沉降规律复杂多变的问题,造成长期预测困难。为此,本文提出一种高铁桥墩沉降的通用渐进分解长期预测网络(GPDLPnet),摒弃传统的预处理思想,将预处理过程嵌入网络结构,在网络训练过程中实现渐进预处理。首先,GPDLPnet在每轮迭代中利用改进对角掩码自注意力模块分析沉降数据中的缺失模式。然后,通过改进完全自适应噪声集合经验模态分解模块将沉降数据分解并重构为高频、低频和趋势子分量,将子分量作为BiLSTM-RSA-Resnet预测模块的特征输入。最后,输出递归预测结果,从而实现高铁桥墩沉降的长期预测。结合实际工程数据,将数据划分为高频观测和低频观测两类典型的观测模式进行试验,在3~4个月的预测中GPDLPnet均表现出良好的预测性能,并在精度指标上优于其他7种模型。

盾构下穿高速铁路隧道沉降变形控制标准研究

针对新建盾构下穿高速铁路隧道变形控制难的问题,以石家庄地铁4、5号线以及北京地铁8号线等3个典型的穿越高铁工程为依托,研究下穿高铁隧道沉降变形控制标准.首先,利用有限元软件Midas GTS NX构建精细化的无砟轨道-隧道三维有限元模型,计算盾构下穿整体现浇隧道、盾构法隧道及U型槽段引起的不同沉降工况下的结构内力值,得出满足裂缝宽度限值的结构允许变形值,并且计算了满足规范限值要求的CRTSⅡ型和CRTSⅢ型轨道结构的允许变形值.然后,利用Abaqus软件构建车轨耦合动力模型,计算不同列车速度和沉降工况下车辆的安全性和舒适性指标,得出轨道高低不平顺允许值.最后,汇总各结构的允许变形值,给出结构沉降变形控制标准.研究结果表明:从结构裂缝宽度限值、轨道10 m弦长高低偏差限值和动力学最敏感指标限值方面计算的既有结构允许变形值能够作为盾构下穿高铁隧道沉降变形的控制标准,可作为现行规范的支撑与补充.研究成果可为类似风险大、要求较严的高速铁路穿越工程项目提供隧道及轨道变形控制值参考.

超大直径盾构下穿高铁路基的沉降数值分析

为探究超大直径盾构隧道下穿城际铁路路基沉降规律,以中国武汉两湖隧道工程为例,基于Plaxis有限元软件,建立了铁路路基-土体-隧道的三维精细化数值模型,探讨盾构掘进过程中地层损失率、开挖面支护压力、盾尾注浆压力对隧道上方城际铁路路基沉降的影响.结果显示,盾构下穿复合地层的过程中,高铁路基道砟层表面在盾构掘进方向上会发生不同程度的沉降;当盾构掘进引起的地层损失率从1.0%增加到1.6%时,铁路路基的最大沉降从18.86 mm增加到22.71 mm,增大了20.4%;当开挖面支护力处于隧道拱顶侧向静止土压力的0.7~1.4倍时,不同工况下盾构掘进引起的铁路路基变形差异较小(小于0.67 mm);注浆压力对铁路路基的沉降影响明显,随着注浆压力增大,铁路路基的沉降明显减小.当隧道拱顶注浆压力增大到拱顶侧向静止土压力的3倍(648 kPa)或以上时,沿铁路路基的最大差异沉降未超过规范要求(≤5 mm/10 m).研究结果可为超大直径盾构下穿高铁路基时掘进参数的设置提供参考.

盾构隧道下穿对高速铁路CFG桩复合路基影响规律研究

针对城市地铁隧道下穿高速铁路的施工过程中,CFG桩复合路基对地层沉降的响应机理不明确、路基的沉降预测与控制理论缺乏的问题,依托郑州轨道交通8号线盾构区间下穿郑州东站咽喉区工程,提出CFG桩复合路基沉降预测方法 .基于地基加固理论,分析CFG桩对路基的加固效果,并通过物理模型试验,研究盾构隧道下穿对高速铁路CFG桩复合路基的影响规律.研究结果表明:CFG桩可以大幅提升路基压缩模量,盾构隧道下穿不会影响CFG桩复合路基的整体性,复合路基的变形规律符合Peck沉降曲线;CFG桩复合路基能够将地层的等效内摩擦角提高约50%,降低约23%的地层沉降量;盾构隧道下穿引起CFG桩复合路基的沉降量最大值为1.65 mm,在盾构隧道掌子面距离路基中线10 m时地层开始发生显著沉降变形,其中83.6%沉降量发生在盾构穿越阶段;盾构远离阶段,路基沉降量仍会继续增大,建议沉降监测持续到沉降稳定.研究结果可为盾构隧道下穿高速铁路CFG桩复合路基的沉降预测和加固处理提供参考.

边墩沉降致连续简支桥段纵连线桥系统层间联结劣化规律

为研究边墩沉降致纵连板式无砟轨道-连续梁桥系统(纵连线桥系统)层间联结劣化状态,在考虑边墩沉降与层间接触不连续影响的基础上,建立纵连线桥系统非线性空间模型,采用前期提出的理论模型对其进行验证,据此分析边墩沉降下纵连线桥系统典型变形模式,层间联结失效的演化过程、发展规律及出现位置等。结果表明:建立的空间模型准确可靠;边墩沉降下,线桥系统会产生跟随变形、自重变形和悬停分离三种变形模式;沉降墩、与沉降墩临近的简支梁墩及连续梁桥另一侧边墩上方会出现层间联结失效,与沉降墩临近的简支梁墩、连续梁桥全部桥墩上的支座均会发生破坏;边墩沉降处板底脱空高度可用边墩沉降值减去连续梁桥变形限值进行描述;各脱空区长度均随边墩沉降幅值增加而增大,与沉降墩临近的简支梁墩左、右两侧区域脱空长度成正对称分布,连续梁另一边墩处脱空长度值只与连续梁变形有关,始终维持在2.56 m。

新线、帮宽及既有高铁路基系统的沉降及稳定性研究

为指导路基拓宽建设形成新旧路基相互作用系统的设计、分析及评价,以杭台铁路浙江省温岭段新线路基、泡沫混凝土帮宽路基和既有路基系统为工程背景,采用现场监测和有限元仿真相结合的方法,研究该复杂系统的沉降、不均匀沉降和稳定特性。监测表明,新线路基填筑初期,其地基沉降受施工荷载的影响较大,呈现出一定的局部回弹和波动现象;随路基填土厚度增加,该回弹波动逐步减小,仿真沉降与实测沉降最终偏差小于5%。轻质泡沫混凝土帮宽施工期间,既有路基的最大沉降位置逐渐由其路基面中心位置过渡至既有路基与帮宽路基的交接处,且帮宽施工期间既有路基的沉降不足2 mm,其沉降量和沉降速率均远小于报警值。帮宽施工完成后,由于软土层的固结效应,既有路基会经历较长的固结沉降过程,其后续固结沉降占最终沉降的比例可达71.4%。泡沫混凝土帮宽会引起既有路基和帮宽路基产生微量倾斜(倾斜率不足0.05%),不影响既有路基线路和帮宽路基线路的平稳运行及正常排水性能。既有路基和泡沫混凝土帮宽路基的反压护道效应,促使整个路基系统的潜在危险滑动面出现在新线路基的远侧边坡位置。

考虑参数随机性的砂浆脱空长度对行车的影响

研究目的:高速铁路无砟轨道砂浆脱空病害直接影响线路运营速度和行车性能。本文以某六跨简支梁桥-CRTSⅡ型无砟轨道系统,CRH2C、CRH3和CRH380A高速动车组为研究对象,基于ANSYS开展无砟轨道-桥梁子模型模态分析,获取整体质量、刚度和阻尼矩阵。结合HBMAT命令和PYTHON语言将整体矩阵转换为稀疏矩阵,并与节点自由度映射文件一起导入多体动力学软件中。通过轮轨接触关系最终建立考虑砂浆脱空的车轨桥耦合系统动力学模型,并进行验证。以中国轨道谱为初始不平顺,基于前期开发的桥轨通用表征模型求得桥墩沉降引起的轨道变形为附加不平顺。考虑扣件刚度、砂浆弹性模量和桥墩沉降的随机性,基于Design-Expert软件,采用Box-Behnken法设计试验点,分别开展耦合动力学模型计算,评估不同类型高铁列车在不同砂浆脱空工况和力学参数随机性下的走行性能。研究结论:(1)建立的考虑砂浆脱空的车轨桥耦合动力学模型与文献模型计算结果吻合良好;(2)同一砂浆脱空值下,对安全性指标强弱影响依次为CRH380A>CRH2C>CRH3,对舒适性指标影响强弱依次为CRH2C>CRH3>CRH380A,对平稳指标性影响,三种型号的列车基本一致;(3)考虑参数随机性后,安全性、舒适性及平稳性指标值均呈现上下波动情况,各指标控制限值呈上、下界值,取上界值作为控制限值较不考虑参数随机更安全可靠;(4)本研究结果可为高铁简支梁桥上行车设计及验算提供一定参考。

近运营线高铁站房施工沉降变形智能监测研究

高速铁路运营环境安全、可靠是列车高效运行的前提。以海南环岛高铁某邻近运营线路站房工程为研究对象,通过变形监测系统选型研究,确定采用基于静力水准仪的自动化智能监测系统,在高铁站房施工阶段进行施工区域以及站台和线路沉降变形监测。全过程、全时段的智能监测相较人工监测,可即时采集多种监测项目数据,并同步分析处理、及时预警。静态液位系统的实时高精度测量,为邻近高速运营线的运行安全提供重要保证。研究结果可为类似站台限界工程提供技术参考。

基于GB-RAR的高速铁路桥梁变形监测研究

提出一种地基真孔径雷达(Ground-Based Real Aperture Radar,GB-RAR)变形信息估计方法,将该方法应用于上海某地铁线路盾构隧道下穿E大桥的安全监测与分析。基于GB-RAR数据进行分析推导,得到桥梁的沉降变形时间序列,并通过水准测量进行了验证,精度优于0.27 mm。通过功率谱分析和最大似然估计,去除彩色噪声比,不考虑彩色噪声影响的变形监测信息更准确,与水准测量结果更加吻合。研究结果表明,该方法在本次工作中具有可靠性和有效性,桥梁在监测期内稳定、安全。

高速铁路沉降自动化监测系统研发与应用

目前铁路沉降观测仍依靠传统的测量仪器,其存在着观测效率低、实时性差等缺点。为了解决以上问题,研发了一套高速铁路沉降观测自动化系统,该系统包括6大子系统。将该系统成功应用于沪昆高速铁路沉降监测中,实现了路肩、线路、轨面和电气化柱的不均匀沉降观测与评估分析。经过实际应用验证,证明了该系统在实际工作中的可行性和有效性。

高速铁路沉降变形预测方法研究与分析

为了降低传统GM(1,1)模型在变形预测时受到的外界环境的影响,提升沉降变形预测精度,本文在传统GM(1,1)模型的基础上,结合相对误差与时间距离,对原始序列进行定权,同时,引入新陈代谢思想,提出一种新的加权GM(1,1)模型。将本文提出模型应用于复杂的高速铁路变形监测数据预测中,并对比不同模型的预测效果。实验结果表明,本文提出模型较传统GM(1,1)模型、加权GM(1,1)模型的拟合预测精度更高,更加适用于复杂变形监测序列的预测,对于高速铁路的沉降监测、保障安全有序运营具有重要意义。

邻近既有运营高铁深大基坑变形监测

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