考虑冲刷深度变化的桩基小型振动台试验研究

岷江3号桥遭遇2008年“5.12”8级强烈地震,又面临令人震撼的严重冲刷。为了弄清楚该桥实际工况,按照实际桥梁墩桩的1:20模型,采用小型振动台试验的方法,分析在不同冲刷深度、不同地震波作用下桥梁墩桩的抗震性能。试验结果表明:模型桩基冲刷深度在15 cm(相当于桩长1/8)左右时,桩顶弯矩、轴力达到最大值;随着冲刷深度的加大桩身弯矩也随之增大,桩身最大弯矩位置(即最不利位置)随之下移,墩顶弯矩不变而墩底弯矩逐渐减小。岷江3号桥存在继续加剧冲刷的趋势,桩基承载力将继续下降,抗震性能将逐渐降低,需要进行墩桩加固。研究可为强震区受严重冲刷桥梁的抗震设计与加固提供参考依据,对类似工程有较强的借鉴意义。

Experimental Study on Small Vibration Table of Pile Foundation Consideringthe Scour Depth Change

The pile foundations of Minjiang River Bridge No.3 have experienced the “5/12” earthquake registered 8 on the Richter magnitude scale in 2008,and have been facing severely scour over the years.In order to find out the actual working conditions of the bridge,here,based on the 1:20 model of the actual bridge pier pile,a small shaking table test was carried out to analyze the seismic performance of the bridge pier pile under the action of different scour depths and seismic waves.The results indicated that the bending moment and axial force of the pile top reach the maximum value when the scour depth of the model pile foundation is about 15 cm(equivalent to 1/8 of the pile length);the bending moment of the pile body increases with the increase of the scour depth,and the position of the maximum bending moment of the pile body(namely the most unfavorable position) moves down,and the bending moments at the tops of piles remains constant while that at the bottom of the pier decreases gradually.The piers and piles need to be strengthened,because Minjiang River Bridge No.3 is still facing a trend of intensified erosion,and its bearing capacity and seismic performance will continue to decline.This paper can provide an important reference for bridge design and reinforcement in earthquake-prone areas and river erosion areas,especially the similar projects.