双向土工格栅处理桥头跳车的试验研究

Experimental Study on Alleviating Bump at Bridge-head Using Biaxial Geogrid

为了研究桥头跳车问题,对采用双向土工格栅加筋与短搭板相结合的方法在武汉阳逻长江大桥接线上进行了实体工程试验研究,对桥头加筋和没有加筋路堤的分层沉降和地基沉降,以及路堤中的土压力进行了对比观测。建立了考虑土工格栅-土界面接触特性的有限元模型,分析了双向土工格栅加筋层数、层间距、格栅的抗拉模量,桥头路堤填土的模量、粘聚力、内摩擦角和地基土的力学性质时桥头路堤沉降的影响规律。结果表明,采用双向土工格栅加筋和短搭板相结合的方法,可以达到消除桥头跳车的目的;从桥头路堤表面向下以一定层间距布设加筋层,随加筋层数的增多(加筋深度随之增大),外荷引起的附加剪应力能向更深处传递,是加筋效果提高以致桥头差异沉降减小的重要原因,但最大有效加筋深度约为2.5～3.6m;当格栅层数一定时,如果采取等间距布置,适中的层间距时桥头路堤沉降最小;增加填土的弹性模量和内摩擦角或土工格栅的刚度,可以有效降低双向土工格栅加筋的桥头路堤沉降。

For conducting experimental study on alleviating bump at bridge-head, a method using biaxial geogrid reinforcement together with a short approach slab was applied in the approach embankment of a bridge in Connecting Expressway of Wuhan Yangluo Bridge across the Yangtze River. The ground settlement, the vertical deformation and earth pressure of the approach embankment with and without geogrid reinforcement were observed for comparison. A finite element model, considering the property of geogrid-soil interface was proposed. Numerical study was carried out to investigate the influence of the parameters, including the number of reinforcement layers, reinforcement spacing and tensile modulus of geogrid, modulus, cohesion and friction angle of the embankment soil, and the properties of the ground earth, on approach embankment settlement respectively. It is concluded that： （ 1 ） Geogrid -reinforced approach embankment with a short slab on it is able to get bump free at bridge-head. （2） Approach embankment with more reinforcement layers, placed from the surface to depth in a certain vertical spacing each other, exhibits less bridge approach relative settlement because of greater transmitting depth of additional shear stress induced by load. However, the maximum of effective reinforcement depth was limited to about 2.5 - 3.6 m beneath the approach embankment surface. （3） When the number of reilfforcement layers was given and they were placed in an equal reinforcement spacing each other, the reinforced approach embankment demonstrates a minimum settlement at a proper reinforcement spacing. （4） The surface settlement of approach embankment reinforced with geogrid decreases while increasing the modulus or friction angle of the fill, or increasing the stiffness of the geogrid.