上海软土地区隧道竖井节点地震摇摆响应研究

Seismic Rocking Behaviour of Tunnel-Shaft Junction in the Soft Soil Area of Shanghai

竖井在剪切地震波作用下会产生水平平动和绕重心转动两种广义位移,后者即为竖井的地震摇摆响应。竖井随场地振动方向的摇摆,会引发隧道竖井节点两种地震响应模式,分别是竖井转动伴隧道绕轴线扭转和竖井转动伴隧道竖向平面内弯曲。以上海软土地区若干典型工程案例为背景,采用隧道竖井节点动力解析模型,对以上两种地震摇摆响应进行研究,重点考察竖井转动位移和隧道地震应力。计算结果表明:竖井地震摇摆响应十分微弱,即使在罕遇地震作用下,其转动位移也仅在10^(-4)rad量级;相比于绕轴扭转,隧道竖向弯曲会造成更剧烈的地震响应,其引发的附加动应力远大于混凝土开裂强度;隧道地震应力总体呈现出横截面直径越大,地震应力越大的规律。

Vertical shafts have two generalized coordinates under seismic S-waves.The first is the horizontal translational displacement,and the second is the rotational displacement about its gravitational center.The latter one causes the seismic rocking behaviour of the tunnel-shaft junction.Determined by the shaking direction of the ground,there are two modes of the seismic rocking behaviour.The first is the rotational displacement of the shaft with the torsional deformation of the tunnel.The second is the rotational displacement of the shaft with the vertical bending deformation of the tunnel.Based on several typical cases in the soft soil of Shanghai,these two modes are studied using a dynamic analytical model of tunnel-shaft junction.The emphasis is placed on the rotational displacement of the shaft and the earthquake-induced stress of the tunnel.The results show that:The seismic rocking behavior of the shaft is minor.Even under rare earthquakes,the rotational displacement of the shaft is at the order of only 10rad.Compared with the torsional deformation,the vertical bending deformation of the tunnel could cause more significant seismic reactions at the junction.The maximum dynamic normal stress of the tunnel cross section is much larger than the tensile strength of ordinary concrete.Generally,the earthquake-induced stress of the tunnel increases with larger cross-section diameter.