地下隧道轴向地震动土作用分析

Seismic Soil Pressure on an Underground Tunnel in the Axial Direction

以弹性基岩上覆层状场地中刚性衬砌隧道为模型,采用间接边界元方法求解衬砌隧道所受的沿轴向地震动土作用,通过参数分析揭示轴向动土作用的幅值大小、空间分布等基本规律。研究表明,土-隧道动力相互作用对地震动土作用的空间分布形式影响较小,但对地下隧道所受地震动土作用峰值大小具有显著影响,隧道主要位置点的地震动土作用峰值与隧道相应位置处自由场土层应力相比放大1.7~2.4倍。论文最后提出一个轴向地震动土作用的简化计算方法。

Considering that seismic soil pressure is the key to an efficient seismic design of an un- derground tunnel, seismic soil pressure on an underground tunnel in the axial direction is studied by indirect boundary element method. First, the time domain problem is transformed to discrete frequency domain problem by Fourier transform. Next, the free-field ground motion is calculat- ed, and the scattered field is simulated by a set of fictitious loads combined with the Green＇ s functions of uniformly distributed load acting on an inclined line. The values of these fictitious loads are determined from the displacement boundary conditions of the underground tunnel. Then, the seismic soil pressure in the axial direction is obtained by utilizing these fictitious loads. Finally, the seismic soil pressure is transformed back to time domain by inverse Fourier trans- form. The proposed method is verified by comparing its results with those of the analytical solu- tion. Based on the model of a rigid underground tunnel soil layers over elastic bedrock, the ampli- tude and distribution of the seismic soil pressure are analyzed through parametric studies. Several findings are obtained. （1） For the underground tunnel, the kinematic interaction plays a major role while the inertial interaction has little effect. （2） The dynamic soil-tunnel interaction （SSI） only has minimal effect on the distribution of the seismic soil pressure, but it can significantly af-fect the amplitude of the seismic soil pressure; moreover, the peak of the seismic soil pressure can be significantly amplified compared with the relevant free-field soil stress. （3） The distribu tion of the seismic soil pressure is similar with that of the free field soil stress, which is nearly linear distribution. Furthermore, the seismic soil pressures on the top and the bottom of the un- derground tunnel are in opposite direction, whereas the seismic soil pressure on the bottom of the underground tunnel is large. （4） Finally, the burial depth of the underground tunnel affects the amplitude and the distribution of the seismic soil pressure. Furthermore, the amplitude of the seismic soil pressure increases with the augmentation of the burial depth. A simplified estimation method is proposed for analyzing seismic soil pressure in accordance with its basic law. The sire plified method is based on free-field seismic response analysis, which does not require the calcula- tion of the dynamic soil-tunnel interaction. The method can be utilized to estimate the design load for underground tunnel seismic design in the axial direction.