Seismic Isolation Materials for Bored Rock Tunnels: A Parametric Analysis

Ahmed Elgamal, Nissreen Elfaris
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Abstract

Most recent tunnel designs rely on more thorough analyses of the intricate rock interactions. The three principal techniques for excavating rock tunneling are drill-and-blast for complete or partial cross-sections, TBM only for circular cross-sections with full faces, and road header for small portions. Tunnel-boring machines (TBM) are being utilized to excavate an increasing number of tunnels. Newer studies have demonstrated that subterranean structures such as tunnels produce a variety of consequences during and after ground shaking, challenging the long-held belief that they are among the most earthquake-resistant structures. Consequently, engineering assessment has become crucial for these unique structures from both the geotechnical and structural engineering standpoints. The designer should evaluate the underground structure’s safety to ensure it can sustain various applied loads, considering both seismic loads and temporary and permanent static loads. This paper investigates how adding elastic, soft material between a circular tunnel and the surrounding rock affects seismic response. To conduct the study, Midas/GTS-NX was used to model the TBM tunnel and the nearby rock using the finite element (F.E.) method to simulate the soil–tunnel interactions. A time–history analysis of the El Centro (1940) earthquake was used to calculated the stresses accumulated in the tunnels during seismic episodes. Peak ground accelerations of 0.10–0.30 g, relative to the tunnel axis, were used for excitation. The analysis utilized a time step of 0.02 s, and the duration of the seismic event was set at 10 s. Numerical models were developed to represent tunnels passing through rock, with the traditional grout pea gravel vs. isolation layer. A parametric study determined how isolation material characteristics like shear modulus, Poisson’s ratio, and unit weight affect tunnel-induced stresses. In the meantime, this paper details the effects of various seismic isolation materials, such as geofoam, foam concrete, and silicon-based isolation material, to improve protection against seismic shaking. The analysis’s findings are discussed, and how seismic isolation affects these important structures’ performance and safety requirements is explained.
钻孔岩石隧道的隔震材料:参数分析
最近的隧道设计大多依赖于对错综复杂的岩石相互作用进行更全面的分析。岩石隧道开挖的三种主要技术是:钻爆法用于整个或部分断面;隧道掘进机仅用于全断面的圆形断面;掘进机用于小断面。隧道掘进机(TBM)被用于挖掘越来越多的隧道。最新研究表明,隧道等地下结构在地震动期间和之后会产生各种后果,这对人们长期以来认为隧道是抗震能力最强的结构之一的看法提出了挑战。因此,从岩土工程和结构工程的角度对这些独特的结构进行工程评估变得至关重要。设计人员应评估地下结构的安全性,确保其能够承受各种外加荷载,同时考虑地震荷载以及临时和永久静态荷载。本文研究了在圆形隧道和围岩之间添加弹性软材料对地震响应的影响。在研究过程中,使用 Midas/GTS-NX 对 TBM 隧道和附近的岩石进行建模,采用有限元(F.E.)方法模拟土壤与隧道之间的相互作用。通过对埃尔森特罗(1940 年)地震的时间历史分析,计算了地震发生时隧道内累积的应力。相对于隧道轴线的峰值地面加速度为 0.10-0.30 g,用于激励。分析中使用的时间步长为 0.02 秒,地震事件持续时间设定为 10 秒。建立了数值模型来表示隧道穿过岩石时,传统的灌浆豌豆砾石与隔离层的对比。参数研究确定了剪切模量、泊松比和单位重量等隔离材料特性对隧道诱导应力的影响。同时,本文还详细介绍了各种隔震材料(如土工泡沫、泡沫混凝土和硅基隔震材料)对改善地震震动防护的影响。本文讨论了分析结果,并解释了隔震材料如何影响这些重要结构的性能和安全要求。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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