Tunnelling and its effects on piles and piled structures
Tunnelling and its effects on piles and piled structures
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发表时间：
2017-07
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通讯作者：
A. Franza
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作者：
A. Franza
目前城市地区对基础设施和服务的需求往往需要建造可能影响现有地表和地下结构的隧道。一般而言，在深基础附近建造新隧道会引起与桩体破坏和相关结构损坏（上部结构和基础）有关的问题。尽管其实际的重要性，很少有研究调查的全球隧道桩结构相互作用（TPSI），因此，工程师通常弥补缺乏理解与过于保守的设计方法。为了深入了解TPSI的相互作用机制，本研究采用土工离心试验作为主要的调查方法，以获取相关的格林菲尔德在沙地上的隧道开挖和桩下隧道开挖和桩基建筑物。特别是，开发了一种新的方法，通过实时耦合的数值模拟和离心模型，提高离心模型的能力，研究TPSI问题。此外，经验和封闭形式的解决方案被用来研究隧道引起的位移场和简化的弹性分析被用来提供洞察全球TPSI机制。格林菲尔德试验的结果表明，砂土中的地表移动预测非常复杂，因为土壤侵蚀效应和隧道从相对较浅深度过渡到较深深度时发生的变化，导致高度非线性位移机制。结果还说明了垂直和水平位移机制之间的相关性。特别是，土壤的相对密度和体积损失的变形模式的影响是高度依赖于隧道的相对深度。为了给工程实践提供简单的工具，提出了经验和封闭形式的解决方案。预测的地面运动为初步评估提供了足够的准确性，但应考虑这些方法的局限性。TPSI的离心试验提供了试验证据，隧道施工引起的桩位移受[i]桩安装方法的影响（位移桩与非位移桩），影响隧道开挖前的土壤状态和桩身与基底之间的荷载分布，[ii]桩基的初始安全系数，与桩承载力和上部结构自重有关，以及[iii]上部结构刚度和结构，这会导致桩荷载重新分配，同时最大限度地减少结构变形。此外，结果表明，潜在的桩故障是一个关键方面的桩与相对较低的初始安全系数和桩故障可以防止有限的相对减少桩荷载由于上部结构。最后，上部结构的刚度和自重的隧道引起的结构变形的重要性进行了确认。桩基建筑物对桩尖深度以下的隧道开挖的弯曲变形反应很大。在一般情况下，它表明，[iv]桩增加结构变形相比，浅基础和[v]的上部结构刚度和自重减少和增加隧道施工造成的上部结构变形，分别。结果也进行了评估内的修改系数的方法;弹性土桩结构相互作用的参数分析用于开发简单的设计图表，可用于估计水平应变和挠度比修改系数的基础上，新定义的相对轴向和弯曲刚度参数。包络线与离心试验测得的挠度比修正系数比较良好。在这些设计图表中，需要进一步研究土壤塑性、建筑物自重、上部结构配置和隧道结构偏心的影响。本文着重介绍了地下建筑设计的改进，可以实现地面和结构工程相结合。
Current needs for infrastructure and services in urban areas often require the construction of tunnels that may affect existing surface and buried structures. In general, the construction of new tunnels in the proximity of deep foundations raises concerns related to pile failure and associated structural damage (in both the superstructure and the foundation). Despite its practical importance, few studies have investigated the global tunnel-pile-structure interaction (TPSI) and, thus, engineers generally compensate for the lack of understanding with an overly conservative design approach. To provide insights into the interaction mechanisms of TPSI, this research used geotechnical centrifuge testing as the main investigation method to acquire data related to both greenfield tunnelling in sands and tunnel excavations beneath piles and piled buildings. In particular, a novel method was developed to study TPSI problems through the real-time coupling of numerical and centrifuge modelling, enhancing centrifuge modelling capabilities. Furthermore, empirical and closed-form solutions were used to study the tunnelling-induced displacement fields and simplified elastic analyses were used to provide insights into the global TPSI mechanisms. Results from the greenfield tests illustrate that ground movement prediction in sands is very complex because of soil arching effects and changes that occur as tunnels transition from relatively shallow to deep depths, resulting in highly non-linear displacement mechanisms. Results also illustrate the correlation between vertical and horizontal displacement mechanisms. In particular, the influence of soil relative density and volume loss on deformation patterns is highly dependent on the tunnel relative depth. To provide simple tools for engineering practice, empirical and closed-form solutions are proposed. Predicted ground movements provide sufficient accuracy for preliminary assessments, though limitations of these methods should be considered. The centrifuge tests on TPSI provide experimental evidence that tunnelling-induced pile displacements are affected by [i] pile installation method (displacement versus non-displacement piles), which affects the pre-tunnelling soil state and the distribution of loads between pile shaft and base, [ii] initial safety factor of the pile foundation, which is related to pile bearing capacity and superstructure self-weight, and [iii] superstructure stiffness and configuration, which results in pile load redistribution while minimising structural distortions. In addition, results show that potential for pile failure is a critical aspect for piles with relatively low initial safety factors and that pile failure may be prevented by a limited relative reduction in the pile load due to the superstructure. Finally, the importance of superstructure stiffness and self-weight on tunnelling-induced structural distortions is confirmed. Piled buildings respond critically to tunnelling beneath the pile tip depth in terms of flexural deformations. In general, it is shown that [iv] piles increase structural distortions compared to shallow foundations and that [v] the superstructure stiffness and self-weight decrease and increase the superstructure distortions resulting from tunnelling, respectively. Results are also evaluated within the modification factor approach; parametric analyses of elastic soil-pile-structure interaction are used to develop simple design charts that can be used to estimate horizontal strains and deflection ratio modification factors based on newly defined relative axial and bending stiffness parameters. The envelopes compare well with deflection ratio modification factors measured from centrifuge tests. Further research is needed to include the effects of soil plasticity, building self-weight, superstructure configuration and tunnel-structure eccentricity in these design charts. This dissertation highlights the improvements in the design of underground constructions that can be achieved by combining ground and structural engineering.