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基于重庆双碑隧道现场测试并采用FLAC~(3D)进行数值模拟,研究富水岩溶地层大断面隧道二次衬砌力学行为。现场测试表明:二衬在混凝土硬化前逐步受力,二次衬砌轴力始终为压力,拱顶承受正弯矩,拱腰边墙承受负弯矩,安全系数拱顶大于边墙;当衬砌背后存在外水压时,外水压对衬砌的环箍效应明显。数值模拟表明:轴力、弯矩随水压增加呈线性增长,轴力下半断面测点不仅数值上高于上半断面而且增长速度也明显高于上半断面,弯矩增长速度拱脚>仰拱>上半断面;当隧道排水能力足够时,排导式衬砌结构基本不承担外水压力,一旦排水能力下降,在外水压力作用下结构的承载能力较弱,拱脚及仰拱为危险区域,极可能产生结构压裂、突水等滞后型危害。
Based on the on-site test of Chongqing Double-Beam Tunnel and the numerical simulation with FLAC 3D, the secondary lining mechanical behavior of large cross-section tunnels in water-rich karst stratum is studied. Field tests show that the second lining is gradually stressed before the concrete is hardened, the axial force of the secondary lining is always under pressure, the crown is subjected to positive bending moment, the arch-waist side wall is subjected to negative bending moment, the safety coefficient is greater than the side wall at the vault; When there is external water pressure, the effect of external water pressure on the lining hoop is obvious. The numerical simulation shows that the axial force and bending moment increase linearly with the increase of hydraulic pressure. The measuring points of the half section under the axial force are not only higher in value than the upper section but also significantly higher than the upper section, Inverted arch> upper half section. When the drainage capacity of the tunnel is sufficient, the drainage lining structure basically does not bear the external water pressure. Once the drainage capacity declines, the bearing capacity of the structure under the external water pressure is weak, and the arch and the back arch are dangerous Region, most likely to produce structural fractures, water jets and other lag-type hazards.