青藏铁路多年冻土区桥梁桩基础地震响应的试验研究与数值分析

Test study and numerical analysis of seismic response of pile foundation of bridge at permafrost regions along Qinghai-Tibet Railroad

基于对负温条件下青藏铁路高温不稳定多年冻土区桥梁桩基础的缩尺模型振动台试验,明确了动荷载作用下模型桩-土界面和两桩中间土体存在温度升高响应。在此基础上,考虑天然状态和地震荷载作用下地温升高两种条件,运用动力有限元方法,对青藏铁路清水河特大桥桩基础进行了地震响应分析。计算表明,在高温状态下(-1℃以上),多年冻土的地基及桩基础在地震荷载作用下的动态响应对温度的升高异常敏感;在50年超载概率2%的青藏人工波作用下,因桩基础的相对位移增大了地基与桩基础间的滑移、脱离现象,特别是高温状态下地基与桩基础间的变形出现了明显的不稳定滑移,影响了整个桩基础的稳定性。

Based on shaking table tests for scale model of pile foundation,which belongs to bridges at the unstable permafrost regions of high earth temperatures along the Qinghai-Tibet Railroad,on condition that the soil temperature around pile was below 0 ℃,it discovered that temperature increased at the spot of soil between piles and the interface of the piles and soil under seismic dynamic motions.Moreover,under the conditions of natural state and soil temperature increase,the characteristics of seismic response of pile foundation of the Qingshui River Bridge were analyzed by dynamic finite element analysis.It indicated that seismic response of the permafrost layer and pile foundation,under seismic motions,was obviously sensitive to the increase in temperature,while earth temperature above -1 ℃.Under artificial wave with exceedance probability of 2% in 50 years loading,the slippage and escape,between pile foundation and soil layer around,were enlarged due to relative displacement of pile foundation.Especially,on condition that temperature above -1℃,the slippage was so obvious that it influenced the stability of whole pile foundation.