汶川地震中道路边坡工程震害分析

SEISMIC DAMAGE ANALYSIS OF ROAD SLOPES IN WENCHUAN EARTHQUAKE

发生在山区的地震对边坡工程所造成的危害,在致灾机制和破坏形式方面具有鲜明的特征。结合汶川地震灾区道路边坡工程震害实例,分析路堑、路堤以及与桥隧相连的各类边坡及相应支挡结构的震害机制和破坏形式。锚索(杆)地梁或预应力锚索抗滑桩加固的边坡具有较好的抗震性能,其原因是这些结构已与坡体联接在一起而形成一个整体,在地震波作用下结构与坡体的位移和变形能够很好地协调一致。铺设土工格栅或施加加筋材料的路堤边坡工程具有较好的抗震性能,一般填筑路堤特别是高路堤,其抗震性能较差。根据沙土液化和软弱黏性土层震陷造成的震害实例,提出含水沙质地层路堤边坡应注意坡脚沙土液化造成的震害,应采取措施防止软弱黏性土层地基震陷造成路面破坏以及坡脚震陷造成的边坡失稳。山区隧道洞口边、仰坡的抗震设计应重视支挡结构的耐震性。建于坡体上的桥台、桥基和桥路过渡段的安全性与坡体稳定性直接相关,应切实加强这些结构所在边坡的抗震设计。对于依山傍水而建的顺河桥,相关边坡的失稳危害桥梁时,应对其采取抗震措施。目前公路、铁路工程抗震规范涉及边坡工程及支挡结构的内容极少,研究成果可为规范的修改和补充提供有益的参考。

Seismic damages of road slopes in mountainous areas have different characteristics in mechanism and types from those in rain. Based on cases of damaged road slopes in the Wenchuan earthquake, failure mechanisms and types of the road slopes for cutting and embankment slope and slopes around bridge and tunnel, as well as retaining structures, are analyzed. Slopes stabilized by using anchored foundation beams or lateral loaded piles with prestressed anchors have better performance in the earthquake. The reason is that these structures make both structures and soils become integral, and so deformation between structures and soil is consistent. Geogrid or other reinforced embankment slopes have better performance in the earthquake; but the aseismic performance of embankments without reinforcement, particularly high embankments, is poor. Based on the cases of liquefaction or soft soil layer-induced settlement, it is suggested that engineers in aseismic design should pay attention to liquefaction-induced settlement at the toe of the slopes constructed on sandy soil layers and take measures to prevent from pavement failure caused by the settlement on soft soil layers and slope instability caused by the settlement at the toe of the slope. At tunnel portals and portal slopes, engineers should strengthen aseismic design of retaining structures. Safety and stabilization of bridge abutment, foundation and transition between abutment and embankment constructed on slopes are dependent of the slope stability; and so aseismic design of the slope, on which those structures are constructed, should be strengthened. For bridges constructed along the bank of river, unstable slope can damage the bridges, some measures in aseismic design should, therefore, be taken into consideration. At present, codes for aseismic design of roads and railway have few contents for how to design slope and retaining structures; and so the achievements obtained will be helpful to revision and supplementary of the codes.