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类型 其它 预答辩日期 2018-03-26
开始(开题)日期 2013-09-16 论文结束日期 2017-12-04
地点 交通学院大楼323 论文选题来源 其他项目    论文字数 7.06 (万字)
题目 极端地层荷载下埋地刚性管涵与土的相互作用研究
主题词 管土相互作用,接头运动,土阻力,入渗侵蚀,拟沟法
摘要 埋地刚性管涵与土的相互作用,是管涵功能完整性和结构稳定性的主要控制因素之一。在诸如地层沉陷、断层滑移等极端地层荷载作用下,若管涵变形和受力超过相应极限,可能引起管涵密封性能退化甚至结构失稳。国内外学者针对理想荷载条件下的管土相互作用已进行了系统深入的研究,但就极端地层荷载对埋地刚性管涵功能和结构的影响欠缺深入认识,难以指导刚性管涵的结构评估和养护维护。本文以极端地层荷载下埋地刚性管涵与土的相互作用为研究对象,采用模型试验、数值模拟和理论分析结合的方法,分析了地层突变对承插式刚性管涵接头和管身服役性能的影响,发展了相应的理论评估方法;研究了地下水入渗时管周填土的侵蚀机理,建立了管周填料侵蚀空隙随水力条件变化的发展模型;改进了拟沟法管涵上覆土压力和柔性层的设计方法,并探讨了极端地层荷载条件下柔性层的合理布设方式。全文主要研究成果如下: (1)通过足尺试验研究了奇型沉陷分布下(地层突变处位于接头正下方)承插式陶土管的响应机制。研究了接头运动(即接头转角和轴向平移)和管身弯曲随沉陷量的变化规律,探讨了管线密封性和结构稳定性的退化机理。结果表明,管道接头在地层沉陷过程中有明显的转动和平移运动特征,且转动角度和轴向拉伸量随沉陷量的增加而线性增长;接头渗漏时,接头转角远低于规范允许值、而平移和接头剪力则相反;试验条件下,结构失稳方式为承口侧壁拉裂破坏; (2)根据管身弯曲和接头剪力的力学平衡特征,建立了可考虑陶土管承插式接头几何尺寸和构造特征的简化三维有限元模型,模拟分析了奇型和偶型(地层突变处位于管身跨中正下方)分布下接头运动特征随地层沉陷量的发展规律。结果表明,研究条件下,管线不均匀沉降以单管段转动为主;最不利接头为偶型分布下由于管道刚体转动导致的抬升接头,随着埋深减小,该接头的转动和平移特征也相应增大;基于模拟所得管线沉降和刚体运动特征,提出了考虑接头几何特征的轴向平移运动模型,可直观、安全地估算地层沉陷条件下承插式接头的平移特征; (3)通过模型试验研究了地下水沿管底入渗对管周填料的侵蚀机制。分析了侵蚀填料质量通量和地下水入渗速率随水位条件的发展规律,讨论了侵蚀空隙的生成过程和分布特征。结果表明,在升水头边界条件下,侵蚀过程可大致划分为三个阶段:初始渗漏,主侵蚀和亚稳定阶段;在定水头条件下,则仅包括主侵蚀和亚稳定两个阶段;初始空隙高度与填料进气水头高度较为吻合;当破损口尺寸与填料特征粒径之比小于临界条件时,将引起破损口阻塞,降低破损管道-填料系统的相对渗透性;根据侵蚀前后管周地下水位变化及渗流对填料稳定性的影响,提出了细砂填料中最大侵蚀空隙的估算方法。 (4)根据竖向相对位移下的管土相互作用特征,建立了奇型和偶型两种分布特征下分段式刚性管道接头剪力和管身弯曲的理论分析模型。分析了极限土阻力及其对应的极限位移随相对埋深变化的取值特征。结果表明,奇型分布下,管身受力主要由抬升土阻力控制,其作用范围约等于管段全长,最大弯矩约在跨中截面附近;而偶型分布下,管身受力主要由下沉土阻力控制,其作用范围仅为静止区内的1/2管长,最大弯矩约在沿插口至承口方向的3/8跨处。 (5)研究了接头剪力和管身弯矩随地层沉陷量的变化特征。通过与模型试验和数值模拟相对比,验证了理论分析的有效性;揭示了两种分布特征下,相对埋深和地层沉陷量对接头剪力的影响规律。结果表明,随着相对埋深的增大,两种分布下的容许沉陷量均明显减小;当相对埋深较小时,随着地层沉陷量的增加,偶型分布下的接头剪力先达到抗渗和结构稳定极限;当埋深增大时,奇型分布下的接头可能先达到管材的抗渗极限和抗拉强度,导致受拉开裂破坏。 (6)改进了拟沟法管涵上覆土压力的极限平衡解。通过将土单元上覆荷载修正为凹型抛物线分布,并结合管-柔性层-填料的变形协调关系,分析了柔性层几何尺寸和物理参数对拟沟法减载效能的影响规律。结果表明,改进法计算结果与实测值吻合较好;增加柔性层厚度可提高涵顶上覆荷载的减载比例,而增加柔性层和填料的相对刚度则作用相反;提出了改进法的简化设计图,以便工程应用查阅。 (7)探讨了极端地层荷载作用下拟沟法对承插式刚性管减载的有效性。根据奇型和偶型两种分布特征下管道的主要受力特征,提出了单柔性层和双柔性层两种埋设方式,通过数值模拟对其适用性进行了验证。结果表明,在地层沉陷作用下,拟沟法和凸埋式管道的接头转角和轴向平移并无明显差异;在奇型分布下,单柔性层可显著降低管身受弯和接头剪力;在偶型分布下,双柔性层可明显提高管道的容许沉陷量,有效保护承插式刚性管的功能完整性和结构稳定性。
英文题目 INTERACTION BETWEEN SOIL AND RIGID PIPES/CULVERTS UNDER EXTREME GROUND LOADING CONDITIONS
英文主题词 pipe-soil interaction, joint kinematics, soil resistance, ingress erosion, induced trench installation
英文摘要 The soil-structure interaction dominates the performance of buried pipes and culverts. Under extreme ground loading conditions, such as ground subsidence and faulting offset, the deformation and loading subjected by the buried structure might exceed the limit values, and lead to the deterioration of the sealing performance and the structural integrity. Researchers have gained insight into the soil-pipe interaction under idealized loading conditions, but a paucity of understanding still exists in the effects of extreme ground loading conditions on the buried pipes, which limits the assessment and maintenance of buried structures. This study focuses on the interaction between soil and rigid pipes/culverts under extreme loading conditions. With the combination of model tests, numerical simulations, and theoretical analysis, the joint kinematics and the response and serviceability of rigid pipes are discussed, and the corresponding theatrical analysis methods are developed. The ingress erosion mechanism of groundwater on filling materials is investigated, and the forming process of erosion voids associated with the hydraulic conditions is investigated. A modified design method for the induced trench installation is proposed, and its effectiveness under extreme loading conditions are studied. The main conclusions can be drawn as following: (1) A full-scale laboratory model test is conducted to investigate the kinematics of bell-spigot joints and the bending behavior of the vitrified clay pipeline under odd subsidence configuration in which the abrupt location is directly under the joint. The variations of joint kinematics and barrel bending with the subsidence displacement are investigated, and the joint leaking and structural failure behaviors are analyzed. Results show that significant joint kinematics occurs during the subsidence process. The joint rotation and axial extension are increased proportional to the increment of the subsidence displacement. Leakage is detected at a rotation response much lower than the allowable value regulated by the ASTM standard. Under the tested condition, the pipeline is breaking by the spilt failure of the bell. (2) Based on the equilibrium condition of barrel bending and joint shear loading, a simplified three-dimensional finite element model for the bell-spigot joint is proposed. The pipe-soil interaction under both odd and even configurations, i.e., the shear band passes through the joint and through the mid-span of a pipe barrel, respectively, are simulated. Results show that the pipe displacement is close to the single pipe rotation model. The worst joint kinematic condition occurs in the even configuration at the joint which is uplifted due to the rigid rotation of the pipe segment. Its kinematic response is more remarkable under a shallower burial depth. Based on the pipeline displacement and its rigid motion behavior, a kinematic model is developed, which can provide straightforward and safety assessment on the axial translation of bell-spigot joint. (3) The erosion mechanism of ingress of groundwater through the pipe invert on the filling material is investigated using model tests. The mass flux of eroded sand and inflow speed of groundwater are analyzed. The forming process of erosion voids is discussed. Results show that under a rising head hydraulic boundary condition, the erosion process can be divided into three stages: the initial leakage, the main erosion and the metastable stage. In a constant head condition, it contains the main erosion and the metastable stage only. The height of initial visible voids is in accordance with the air-entry head of the sand around the pipe. When the size ratio between the aperture and the eroded particles reaches the critical condition, sand bridging will be formed, and the aperture will be blocked, which can reduce the relative permeability of the soil-pipe system. Based on the effect of groundwater and the seepage stability of the sand, an empirical method is proposed to estimate the size of maximum erosion void. (4) Based on the pipe-soil interaction under vertical relative displacement condition, the theoretical analysis method for the joint shear load and barrel bending behavior of segmented rigid pipes connected by flexible joints under both odd and even configurations are established. The change of the ultimate soil resistance and the corresponding pipe-soil relative displacement with the burial depth is studied. Results show that in the odd configuration, the pipe response is dominated by the uplift soil resistance, which was loaded nearly on the entire span of the pipe barrel. The maximum bending appears nearly at the mid-span of the barrel. Whereas in the even configuration, the pipe response is mainly controlled by the downward soil resistance, which was exerted on the half-length of the pipe barrel located in the stationary zone. The maximum bending appears to be at about 3/8L along the barrel from the spigot end to the bell end. (5) The variation of joint shear loading the barrel bending behavior with the subsidence displacement is theoretically analyzed. The validity of analysis solution is verified with the results of the full-scale test and the numerical simulation. The effects of the relative burial depth and the subsidence displacement are examined. Results show that with the augment of relative burial depth, the allowable subsidence displacement for both configurations are remarkably diminished. Under relatively small burial depth, the shear load in the even configuration reaches first to the ultimate sealing and failure loading. With the increment of burial depth, the joint in the odd configuration could reach to its leakage resistance and tensile strength first, and then cause the split failure of the bell. (6) A modified limit equilibrium solution for vertical pressure on top of induced trench rigid pipes is proposed. In the modified method, the stress above the soil element is assumed to be distributed in a parabolic pattern. Based on the deformation compatibility of the pipe, the soft layer and the fill material, the effect of the geometry and the physical property of the soft layer on load reduction is calculated. Results show that the modified method can provide estimates comparable to the field measurements. The increment of the thickness of the soft layer is beneficial to improve the load reduction, but the increase of the relative stiffness between the soft layer and the surrounding soil would have an adverse effect. The simplified design charts are proposed, which can facilitate the use of the modified method. (7) The effectiveness of the induced trench installation on rigid pipes with bell-spigot joints under extreme ground loadings are analyzed. Based on the loading behaviors of the pipeline in both odd and even configurations, two arrangements of the soft layer, i.e., the single layer above the pipe, and the double layers at the top and invert of the pipe, respectively, are introduced and validated using numerical simulations. Results show that under extreme loading conditions, no significant difference is observed for the joint kinematics in both the induced trench condition and the projection condition. However, in the odd configuration, the single soft layer can obviously reduce the barrel bending moment and the joint shear loading, whereas in the even configuration, only the double layers arrangement can remarkably increase the allowable subsidence displacement, and effectively protect the functionality and the structural integrity of bell-spigot jointed rigid pipes.
学术讨论
主办单位时间地点报告人报告主题
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学术会议
会议名称时间地点本人报告本人报告题目
美国交通工程年会(TRB) 20170108 美国华盛顿 An Improved Analytical Solution to Estimate Vertical Stress on Top Of Induced Trench Culverts
北美非开挖年会 20140406 美国奥兰多 Infiltration erosion around defective pipes
加拿大岩土灾害年会 20140618 加拿大金斯顿
     
代表作
论文名称
Improved analytical solution of vertical pressure on top of induced trench rigid culverts
电石渣改良过湿黏土的物理力学试验研究
 
答辩委员会组成信息
姓名职称导师类别工作单位是否主席备注
刘松玉 正高 教授 博导 东南大学
唐朝生 正高 教授 博导 南京大学
孔纲强 正高 教授 博导 河海大学
章定文 正高 教授 博导 东南大学
蔡国军 正高 教授 博导 东南大学
童立元 副高 副教授 博导 东南大学
      
答辩秘书信息
姓名职称工作单位备注
吴恺 其他 讲师 东南大学