落石冲击下单压式拱形明洞的力学响应

Mechanical Responses of Single-Pressure Arch-Shaped Open Tunnel Structure under Rockfall Impaction

为进一步了解结构受力情况,为明洞结构设计提供依据,采用动力有限元方法,对客运专线双线单压式拱形明洞落石冲击下结构力学响应进行了研究.首先,以竖直下落冲击为基本工况,从落石与洞顶回填土的相互作用及运动轨迹入手,分析了结构的应力、应变、应变率、位移、速度、加速度等作用效应响应;其次,根据落石、回填土及结构间能量的转化与传递规律,结合结构及基底应力响应,阐述了回填土和混凝土填充材料对落石冲击的缓冲和对结构的保护作用机理,以及边墙形式对基底及仰拱受力的影响;最后进行了45°斜向冲击响应分析并与基本工况进行了对比.研究结果表明:所设计的明洞结构可以承受竖向700 k J的落石冲击能量,拱顶、拱肩及墙身内侧和耳墙墙址等部位是相对受力不利位置,回填方式和直墙式拱墙形式有待进一步研究优化;冲击引起的结构应变率响应介于1×10^(-3)~1×10^(-2)s^(-1),与地震引起的响应范围相同;在本研究工况下,45°斜向冲击作用效应总体上小于竖直冲击.

To leam the stress state and provide a design basis for open tunnel structures, the mechanical response of a single-pressure arch-shaped open tunnel structure on a double-line passenger dedicated line is analyzed using dynamic finite element method. Firstly, regarding the vertical drop impaction as the basic condition, interactions between rockfall and backfill soil on the tunnel top, as well as the motion trajectory of rock-fall, are analyzed to study responses of the tunnel structure in terms of stress, strain, strain rate, displacement, velocity and acceleration. Secondly, according to the law of energy conversion and transmission among rockfall, concrete backfill materials and tunnel structure, the mechanisms of backfill soils acting as buffering cushions and concrete-filled materials as structure protection to rockfall impaction are explained through stress responses of the side wall and ground basement, and influences of the structural form of the side wall on the mechanical performance of the ground basement and the inverted arch of open tunnel are also discussed. Finally, the dynamic responses of the tunnel structure under 45° oblique rockfall impaction are analyzed and compared with those in the basic condition. The results show that the designed open tunnel can bear 700 kj vertical impaction energy of rockfall while substructures such as apex of arch, spandrel, inner side of the arch wall and comer of the ear wall are relatively weak parts in bearing the stress ; thus the way of backfill and the structural form of the side wall in the open tunnel need to be further optimized. Strain rates of the open tunnel structure caused by rockfall impaction are found limited in the range of 1×10^-3-1×10^2s^-1 , which is the same as that caused by earthquake. Under the condition of this research,the effect on the open tunnel structure from oblique rockfall impaction is generally less than that from vertical drop impaction.