山区斜坡桩基地震响应的离心模型试验

为探讨地震对山区桥梁斜坡桩的影响，在土工离心机上进行坡顶平地桩、斜坡上单桩及1×2群桩的振动台试验。通过安装的加速度计、激光位移计及桩身应变片实测在不同加速度峰值的El Centro波作用下，斜坡场地各点的加速度时程、各桩截面的应变量及桩头位移值，由此分析斜坡场地各点的加速度放大系数及位移时程，各桩截面的弯矩及水平变位。然后，结合OpenSees进行数值模拟分析，探讨斜坡场地地震效应、桩与斜坡共同工作特性以及桩基残余变形发展特性等。研究结果表明：在各级地震荷载下，斜坡单桩与1×2群桩在地面处位移约为40 mm，桩顶累积变形量则分别达到90，50 mm，峰值弯矩达到1 120 kN·m；斜坡场地在坡顶位置最为不利，其加速度放大系数最高达到1.8左右，因此在低加速度峰值的输入波作用下，斜坡就会发生侧移，对桩基造成影响；在受地震影响的山区斜坡地段修建桥梁桩基，不能仅考虑边坡安全系数，而应计入地震作用下边坡永久位移对桩基的影响。

Centrifuge Model Tests of Bridge Pile Foundations in Sloping Ground of Mountainous Areas

To study the influence of earthquakes on piles in the sloping ground of mountainous areas, a pile in level ground, a pile and a 1×2 pile group in sloping ground were tested on a centrifugal shaking table. Accelerations at each test point on the slope, strains along each pile shaft, and pile head displacements were measured under the El Centro earthquake of various peak accelerations, using accelerometers, displacement sensors, and strain gauges. Based on these results, numerical analysis was performed in OpenSees, to investigate the site effect of sloping ground, the pile-slope interaction, and residual displacement of each pile. The test and numerical results indicated that for the single pile and the 1×2 pile group, pile displacements at ground level were around 40 mm, while those at the pile head reached 90 mm and 50 mm, respectively. The maximum bending moment reached 1 120 kN·m; the top of the slope underwent the largest amplification factors of acceleration, peaking at around 1.8g. A slope can thus undergo lateral spreading even when encountering low peak acceleration earthquakes, and this has a negative effect on piles. For bridge piles constructed in sloping ground where it is necessary to consider seismic effects, permanent displacement of the slope should be evaluated in addition to global factor of safety.