软土地基上道路桥头跳车缓解工法的设计与工程实践

MITIGATON OF DIFFERENTIAL SETTLEMENT BETWEEN EARTH STRUCTURE AND ROAD ON SOFT CLAYS

针对软土地基上道路行车的“桥头跳车”现象,列举了在日本经常使用的几种桥头接坡过渡段地基处理的方法:(1)设钢筋混凝土连接搭板;(2)沥青混凝土路面的加铺维修;(3)切短桩头的办法重建构筑物。分析了这几种传统的桥头接坡处理方法的优缺点及经济性。在日本佐贺平原有明软粘土地基上的桥头接坡段地基处理工程实例的基础上,介绍了缓解桥头跳车现象的设计施工法——CA工法;给出了CA工法的设计内容及参数确定的方法,包括搅拌桩的长度与接坡段的处理范围;最后通过现场监测结果说明所提出的设计法的有效性。

For low embankment road on soft subsoils,since the traffic loading is cyclically exerted on the soft subsoils,there always exists excess pore pressure at a certain depth in the soft subsoils. Therefore,settlement under the traffic load is continuously developed in the long term. However,the crossing structures such as bridge abutment and box culvert are generally supported by piles and small settlement will happen. Thus,large differential settlement between road and crossing earth structures may occur. The differential settlement will affect or even obstruct vehicle transportations. In order to reduce this differential settlement,many methods have been proposed to provide the transition zone between pile-supported structure and road. In Japan,conventionally,three repairing approaches have been used:(1) to overlay a new pavement on the existing pavement for some periods (overlay repairing);(2) to set a concrete cushion slab under pavement of transition zone;and (3) to cut the pile top and reconstruct the structure. These conventional methods are either not effective or not economic. The effective transition zone treatment is to use piled embankments,which may use different pile types,namely,timber piles, stone columns,sand compaction piles,lime columns,soil-cement columns,and driven or cased in-situ concrete piles. This paper introduces a repairing project of transition zone of a low embankment road on soft Ariake clay, Saga,Japan. In this project the soil-cement columns were used to improve the soft subsoil under the transition zone called column approach (CA) method. The design procedure and parameters are introduced briefly at first. Then,the field case is introduced in detail. The results from field monitoring show that when the differential settlement is over some value,overlay repairing is not economic and the approach cushion does not work well while CA method mitigates the differential settlement more effectively.