【作者】 章荣军；

【导师】 郑俊杰；

【作者基本信息】 华中科技大学 ， 桥梁与隧道工程， 2011， 博士

【摘要】 尽管目前很多学者针对土体开挖引起的环境问题开展了大量的研究,但近年来隧道或基坑开挖引起邻近建筑物破坏倒塌的工程事故仍然频发。究其原因,与工程人员和科研人员对土体开挖条件下被动桩的若干问题考虑不周(诸如忽略桩土作用应力历史、界面剪切滑移特性及桩身变形耦合效应等)不无关系,所建立的近接既有桩基开挖条件下地层位移控制标准严重缺乏理论依据和针对性。本文着眼于克服这些缺陷,对土体开挖条件下邻近受荷桩基附加响应预测方法开展了系统的研究。首先,进一步完善了隧道和基坑开挖引起的自由位移场预测方法。考虑到目前基坑深度大、支护结构强及位移控制严格的特点,提出了一种考虑主(被)动区土压力随支挡结构位移发展过程的修正“m”法,并结合Sagaseta解,给出了由围护结构挠曲曲线预测坑外地层位移的解析算法。同时,针对掌子面三维变形问题,开展了近200个工况的数值模拟研究,计算结果表明盾构隧道掌子面水平侵入位移基本服从高斯曲线,且各种不同工况下,最大无量纲化水平侵入位移与稳定系数之间的关系比较统一基本不受隧道埋深、开挖直径及土体不排水抗剪强度等因素影响。基于这些结论,进一步确定出了掌子面侵入位移的归一化模式,并提出了一种预测掌子面前方三维变形引起的等效间隙参数的半解析方法。验证实例表明,所提出的隧道和基坑开挖引起的自由位移场预测方法是可靠的。其次,建立了考虑变形耦合效应及桩基实际受荷历史的被动单(群)桩分析方法。首先针对被动单桩的特性,提出了一种改进的非线性两阶段分析方法,该法能够更合理地考虑桩土作用非线性特征、桩土荷载传递应力历史及桩身纵横向变形耦合效应等,并编制了相应的MATLAB程序。参数分析表明,先期工作荷载对被动阶段桩身竖向响应影响显著,且对于被动桩而言,有必要考虑变形耦合效应,完全解耦算法的计算结果与实际值之间的偏差可能超过25%。随后,考虑被动群桩内桩一桩相互作用特性,建立了遮拦效应的位移传递系数法求解思路,成功地将被动单桩的改进两阶段分析方法推广至无承台群桩和刚性高承台群桩。利用编制的程序进行参数化分析,结果显示竖直方向上桩身遮拦效应明显,必须予以考虑,而水平方向上桩身的遮拦效应相对较小,土体刚度较大时可不予考虑,承台影响区域之外的桩身弯矩可直接按单桩进行计算。然后,建立了考虑桩土界面剪切滑移特性的被动桩分析方法。在全面总结结构—土界面试验成果的基础上,提出了考虑界面往返剪切特性的修正双曲线模型及损伤模型,建立了一种能够全面适用于各类桩—土界面的“双弹簧—地基梁”模型,并编制了考虑桩土界面滑移特性的被动桩分析方法的计算程序。结果显示,当界面强度系数小于0.7时,无论桩顶是否受荷,都应如实考虑界面的剪切滑移特性；考虑界面剪胀软化效应是必要的,采用理想弹塑性模型来近似代替可能会产生25%以上的误差。最后,提出了盾构掘进与邻近受荷被动桩相互作用的精细模拟思路及实现方法。首先针对目前商业程序中处理桩土界面的缺陷,提出了各种界面模型的统一数值实现方法,并采用FISH语言编制了相应的子程序。随后,全面考察了盾构隧道施工的各个细节,给出了盾构掘进的精细模拟方法。分析实例表明,所提出的精细模拟方法能够较好地适应不同的分析工况,并能有效地考虑砂土中桩身环箍应力的深度效应。更多还原

【Abstract】 During the past few years, a large number of researches have been conducted to investigate soil excavation-induced environmental problems. However, in recent years, buiding collapse accidents induced by tunnelling or deep excavation happened again and again. Most often, the reason for these accidents is that some aspects about this problem are not well understood or considered by researchers and engineers, for example, pile-soil load transfer history, interface slip characteristics and coupling effect of longitudinal and lateral deformations of the pile shaft etc. And previous displacement control standards adopted by most unban underground structures lack of theoretical basis and pertinency. In order to overcome these deficiencies, systemic researches are carried out in this dissertation to establish more accurate and applicable methods for predicting soil excavation-induced responses of adjacent on-service pile foundations.Firstly, methods for predicting the free-field soil movement due to tunnelling and deep excavation are further improved. In consideration of the actual features of modern deep excavations, such as great excavation depth, strong support structure and strict control standard of soil displacement etc., a modified "m" method is presented to calculate the deflection of the enclosure structure. This modified "m" method can take into account the development processes of earth pressures within the active and passive regions with the deflection of the enclosure structure. Then by utilizing Sagaseta’s solution, an analytical method is proposed to evaluate the diaplacement of the outside soil on the basis of the deflection curve of enclosure structure. Meanwhile, almost 200 analysis conditions are performed to investigate the three-dimentional (3D) deformation of the soil ahead of the tunnel face using the elastoplastic numerical simulation method. The results show that the horizontal intrusive displacement of the tunnel face basically follows Gaussian distribution. The relationship between the maximum dimentionless intrusive displacement of the tunnel face and the stability number is almost unique for different conditions, and it will not be influenced by the embedded depth of the tunnel, excavation diameter and undrained shear strength of the soil. Based on these conclusions, a normalized mode of intrusive displacement of the tunnel face is established and a semi-analytical method is proposed for estimating the equivalent gap parameter due to 3D deformation of the tunnel face. The results of verification examples domenstrate that the proposed methods for predicting the free-field movements induced by soil excavations are reliable.Secondly, analysis methods applicable to passive single piles and pile groups are focused on. According to the mechanical characteristics of passive single piles, an improved nonlinear two stage analysis method (TSAM) is proposed. This improved method can more factually take into account the nonlinear characteristics of the pile-soil interaction, load history of the pile-soil interface and deformation coupling effect of the pile shaft etc. And a MATLAB program is compiled to implement the proposed method. Through a series of parametric studies, it can be found that the influence of the prophase working load on vertical response of the pile shaft in the passive stage is significant. Also, for the passive piles, it is necessary to consider the deformation coupling effect, and the relative error between the results from the decoupled and coupled methods may be up to 25%. Then, in consideration of pile-pile interaction within pile groups, a solving approach is put forward for the shield effect of the pile groups by using the displacement transfer coefficients. Subsequently, the method for passive single piles is successfully extended to those for passive pile groups with and without rigid elevated caps. These methods are then employed to carry out some parametric studies. The calculated results indicate that the shield effect in the vertical direction is evident and must be considered. In contrast, the shield effect in the horizontal direction is not obvious, it can be neglected when the soil is not very soft, and accordingly, the bending moment of the pile shaft beyond the influence range of the pile cap can be calculated by treating it as a single pile.Thirdly, analysis methods for the cases that slip displacement is possible at pile-soil interface are discussed. On the basis of achievements of structure-soil interface tests, modified hyperbolic and damage model, which can rationally consider the cyclic shear behaviour of the interface, are proposed. Subsequently, a "double springs"-"elastic foundation beam" model is established. This model is applicable to any pile-soil interface model. According to this "double springs"-"elastic foundation beam" model, a calculation program which can factually deal with the potential slip effect of the pile-soil interface is developed. The results of case studies show that when the interface strength factor is less than 0.7, the interface slip effect should be considered regardless of whether there is working load on the pile head or not. Also, it is necessary to take into account the shear dilatancy effect of interface. If an elastic-perfect plastic is adopted to substitute the damage model, the relative deviation may exceed 25%.Finally, the elaborate simulation measures and implement methods for the interaction problem between the on-service pile foundations and soil excavations are concentrated on. Existing numerical simulation methods tend to neglect some details of pile-soil interface. Aiming at these deficiencies, an numerical implement method is developed, and the corresponding subprogram is compiled by using FISH language embedded in FLAC3D. This subprogram is applicable to all the interface models. Then, after comprehensively investigating the construction details of shield tunnels, an elaborate simulation method is proposed to simulate the advancing of shield machines. The results of case studies domenstrate that the proposed elaborate simulation method can well consider the depth effect of the confining stress along the pile shaft in sand and be applicable to different analysis conditions.更多还原