含软弱夹层场地−桩承桥台−路堤作用体系地震反应分析

Analysis of foundation−piled abutment−embankment interaction system with weak interlayer subjected to seismic load

为研究桥头段震害特征和机理,基于有限差分法,建立含软弱夹层场地−桩承桥台−路堤三维动力分析计算模型,合理考虑地震动输入,着重研究作用体系的地震位移响应,桥台地震土压力、加速度以及桩身弯矩响应等,将计算结果与规范中结果、试验结果以及震害结果对比分析,证实计算模型的合理性。研究结果表明:桩承桥台的震害位移模式为整体滑移后仰式;桥台地震土压力和土压力计算作用点高度较规范计算值大,应适当提高土压力计算作用点高度来进行桥台抗倾覆验算;路堤震害为塌滑下沉、波状起伏变形,距台后5 m内的路堤为重点抗震设防区域,溜坡震害为震陷、上部拉裂、下部鼓张变形;邻近桥台的地基会有不均匀沉陷,并与桥台产生相对滑移;前、后排桩在震中出现桩顶最大正、负弯矩,桩、土相对水平位移最大值位于软弱夹层中,桩的受力状态将在主动桩与被动桩之间变化。

A three-dimensional numerical model of piled abutment with weak interlayer was established by finite difference method to analyze the characteristics and mechanism of seismic damage in the bridge head.Considering the ground motion input reasonably,the main analyses included the seismic displacement responses seismic accelerations,earth pressure response of abutment and moment response of pile foundation.The results of calculation were compared with the results of specification,test and earthquake damage to verify the rationality of the calculation model.The results show that the displacement mode of the piled abutment is the whole sliding back-up type.The calculated height of the seismic earth pressure and earth pressure of abutment is larger than those of the code.The height of earth pressure action point should be increased appropriately to meet the anti-overturning calculation of abutment.The seismic damage of embankment is characterized by collapse and subsidence,undulating deformation.The embankment within 5 m from the platform is a serious seismic damage area.The damage characteristics of sliding slope are seismic subsidence,upper pull crack and lower bulge deformation.The foundation adjacent to the abutment produces uneven subsidence and relative slippage with the abutment.The maximum positive and negative bending moment of the pile top appears in the front and rear piles in the epicenter of the earthquake and the maximum value of the relative horizontal displacement are located in the weak interlayer,and the stress state of pile changes between active pile and passive pile.