液化场地大直径变截面单桩动力响应研究

Study on Dynamic Response of Large Diameter Variable Cross-section Single Pile in Liquefaction Site

为研究不同地震动强度下液化场地大直径变截面单桩的动力响应规律,基于振动台试验,选取5010波,在地震动强度0.10g~0.45g作用下,研究液化场地砂土孔压比和大直径变截面单桩桩顶水平位移、桩身弯矩、桩身加速度时程响应及桩基损伤等变化规律.试验结果表明:饱和砂土孔压比随着地震动强度的增大上升明显,地震动强度≥0.30g时,饱和砂土孔压比稳定值在0.9附近,此时砂土完全液化;在0.45g地震动强度作用下,桩身加速度、桩顶水平位移及桩身弯矩均达到最大;桩身不同位置处加速度峰值出现时刻均滞后于输入地震波加速度峰值出现时刻,且桩顶及变截面的加速度响应比桩端的响应更弱;不同地震动强度作用下,桩身弯矩最大值均出现在液化土层和非液化土层分界处,且变截面处弯矩小于土层分界面处;地震动强度达到0.30g时,大直径变截面单桩桩身发生损伤.因此,液化场地下大直径变截面桥梁单桩基础抗震设计时,应该重点考虑饱和砂土层分界处、变截面处的抗弯能力,以确保单桩桩身强度满足抗震要求.

To study the dynamic response law of large diameter variable cross-section single pile in liquefaction sites under different ground motion intensities,shaking table tests were conducted.Employing the 5010 wave and subjecting the system to ground motion strengths ranging from 0.10g to 0.45g,this study examined the evolution of sand pore pressure ratio,horizontal displacement at the top of the piles,bending moment along the pile body,as well as the time history response of pile acceleration and foundation damage.The test results show that the pore pressure ratio of saturated sand increases obviously with the increase of ground motion strength.The pore pressure ratio of saturated sand increases obviously with the increase of ground motion intensity.When the ground motion intensity is≥0.30g,the stable value of the pore pressure ratio of saturated sand is near 0.9,and the sand is completely liquefied.Under the action of 0.45g ground motion,the acceleration of pile body,the horizontal displacement of pile top and the bending moment of pile body all reach the maximum.The peak acceleration at different positions along the pile body lags behind that of the input seismic wave,and the acceleration response of the pile top and variable cross-section is weaker than that of the pile tip.The maximum bending moment of the pile appears at the boundary between the liquefied soil layer and the non-liquefied soil layer,and the bending moment at variable cross-section is smaller than that at the soil layer interface.When the ground motion strength reaches 0.30g,the damage of a large diameter variable cross-section single pile occurs.Therefore,in the seismic design of the single pile foundation of a large diameter variable cross-section bridge under a liquefaction site,the bending capacity at the boundary of the saturated sand layer and variable section should be considered to ensure that the strength of the single pile meets the anti-seismic requirements.