地裂缝场地地铁隧道地震动力响应的振动台试验研究

SHAKING TABLE MODEL TEST ON SEISMIC RESPONSE OF METRO TUNNEL CROSSING GROUND FISSURE SITE

以西安轨道交通3号线地铁隧道近距离通过地裂缝场地为工程背景,采用几何比1∶30的大型振动台模型试验,研究不同地震波作用下通过地裂缝带上盘场地地铁隧道的地震动力响应。试验结果表明:地裂缝场地上盘加速度响应表现出明显的放大效应;浅埋地铁隧道对地震波在土层中的传播具有一定阻碍作用,而隧道两侧拱腰位置围岩土层加速度放大效应最强;隧道特征部位PGA放大系数拱腰最大,拱底次之,拱顶最小,其中靠近地裂缝侧拱腰的PGA放大系数大于远离一侧;地裂缝附近动土压力增量明显增加,而靠近隧道附近,动土压力增量明显降低;地震作用下隧道通过地裂缝场地上下盘出现差异沉降,地表出现多条与地裂缝近似平行和正交的裂缝;隧道环向受剪切作用在靠近地裂缝一侧的拱肩部位环向应变最大,而隧道轴向受挤压作用在左右拱腰处应变出现最大值。研究结果可为地裂缝场地地铁隧道结构抗震设计与防灾减灾提供重要科学参考与借鉴。

Taking Xi＇ an urban rail transit line 3 crossing the ground fissure site as the targeting project, the shaking table test with a geometrical ratio of 1 ∶ 30 was designed and completed in order to study the seismic dynamic response of metro tunnel crossing the hanging wall site of the ground fissure under the action of different earthquake waves. The results show that the acceleration response of the hanging wall in the ground fissure site has clear elevation amplification effect. Shallow buried metro tunnel has certain obstacles to the propagation of seismic waves in strata. The acceleration amplification effect of strata at hance is strongest on both sides of the tunnel. The PGA amplification coefficient at arch waist of the tunnel is the largest, the second at the arch bottom and the smallest at the arch top. The PGA magnification factor of the tunnel arch waist on one side close to the ground fissure is greater than that far away from the ground fissure. The increment of dynamic earth pressure increases obviously near the ground fissure and but decreases significantly near tunnel. There appears an obviously differential settlement between the hanging and foot wall of the ground fissure site, and so do many cracks which are approximately parallel and perpendicular to the ground fissure under earthquake. The metro tunnel is subjected to circumferential shear action, and the circumferential strain is the largest at the arch shoulder of the tunnel close to one side of the ground fissure, but the axial strain of the tunnel is the biggest at the left and right hances. The research results can provide a scientific basis and reference for anti-seismic design and disaster prevention and mitigation of tunnel crossing ground fissure site.