High pre-tension reinforcing technology and design for ultra-shallow buried large-span urban tunnels

IF 7 1区 工程技术 Q1 ENGINEERING, GEOLOGICAL International Journal of Rock Mechanics and Mining Sciences Pub Date : 2024-09-02 DOI:10.1016/j.ijrmms.2024.105891
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Abstract

Due to the thin overlying formation of ultra-shallow buried large-span urban tunnels, the surrounding rock can be easily loosened and damaged after excavation. High prestressed anchoring support can improve the self-bearing capacity of the surrounding rock. However, traditional bolts often undergo necking fracture after the yield stage and strengthening stage, and the designed pre-tension is low, generally not exceeding 50 % of the yield strength of the bolt. To this end, our research group developed a new NPR bolt. After comparing the mechanical properties of the NPR bolt and the traditional bolt, the high strength, high elongation, and high prestressed properties of the NPR bolt are revealed. Subsequently, the constitutive relationship of the CABLE element in FLAC3D is modified, and the constitutive model of the NPR bolt is established, which can describe the whole process of bolt. Furthermore, a numerical comparison of prestressed control for ultra-shallow large-span tunnels is carried out. Compared with non-prestress, when the prestress of bolt reaches 100 kN, the area of tensile stress zone and plastic zone of surrounding rock are reduced by 79.6 % and 73.7 %, respectively. At the same time, the settlement of surface and roof is reduced by 66.7 % and 64.1 %, respectively. The control mechanism of the prestressed NPR bolt support is explored, and the design method for ultra-shallow large-span tunnels is proposed. The field application and monitoring results show that the surface and roof settlement of the tunnel supported by NPR bolts are 3.2 mm and 6.3 mm, respectively. The safe and effective stability control of the tunnel surrounding rock is achieved.

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超浅埋大跨度城市隧道的高预应力加固技术与设计
由于超浅埋大跨度城市隧道的上覆地层较薄,开挖后围岩容易松动和破坏。高预应力锚杆支护可以提高围岩的自承载能力。然而,传统螺栓在屈服阶段和加固阶段后往往会出现缩颈断裂,且设计预拉力较低,一般不超过螺栓屈服强度的 50%。为此,我们的研究小组开发了一种新型 NPR 螺栓。在比较了 NPR 螺栓和传统螺栓的机械性能后,发现 NPR 螺栓具有高强度、高伸长率和高预应力性能。随后,修改了 FLAC3D 中 CABLE 元素的构成关系,建立了 NPR 螺栓的构成模型,该模型可描述螺栓的全过程。此外,还对超浅埋大跨度隧道的预应力控制进行了数值对比。与非预应力相比,当螺栓预应力达到 100 kN 时,围岩的拉应力区面积和塑性区面积分别减少了 79.6 % 和 73.7 %。同时,地表和顶板的沉降量也分别减少了 66.7% 和 64.1%。探讨了预应力 NPR 螺栓支护的控制机理,提出了超浅埋大跨度隧道的设计方法。现场应用和监测结果表明,采用 NPR 螺栓支护的隧道表面沉降和顶板沉降分别为 3.2 毫米和 6.3 毫米。实现了对隧道围岩安全有效的稳定性控制。
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来源期刊
CiteScore
14.00
自引率
5.60%
发文量
196
审稿时长
18 weeks
期刊介绍: The International Journal of Rock Mechanics and Mining Sciences focuses on original research, new developments, site measurements, and case studies within the fields of rock mechanics and rock engineering. Serving as an international platform, it showcases high-quality papers addressing rock mechanics and the application of its principles and techniques in mining and civil engineering projects situated on or within rock masses. These projects encompass a wide range, including slopes, open-pit mines, quarries, shafts, tunnels, caverns, underground mines, metro systems, dams, hydro-electric stations, geothermal energy, petroleum engineering, and radioactive waste disposal. The journal welcomes submissions on various topics, with particular interest in theoretical advancements, analytical and numerical methods, rock testing, site investigation, and case studies.
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