光纤光栅传感技术在大直径灌注桩承载力自平衡法测试中的应用

Application of FBG sensors in self-balanced test method for bearing capacity of large-diameter cast-in-place piles

基于自平衡试验方法和FBG传感器测试基本原理,分别采用FBG传感器和传统钢筋计对桩基承载力进行现场测试,分析了桩身轴力和桩侧摩阻力传递规律的差异性.结合实际工程案例,分析了大直径灌注桩桩身轴力和桩侧摩阻力的传递规律,并采用规范简化转换法、Kwon法和Kim法3种等效转换方法确定桩基承载力.结果表明:与传统钢筋计相比,FBG传感器可剔除温度变化和混凝土膨胀产生的预应力;由2种传感器得到的桩身应变和桩侧阻力变化规律相一致,其中荷载箱附近误差均在10%以内;由FBG传感器实测值得到的桩身轴力和桩侧摩阻力,能够满足自平衡测试规律性和精度的要求,为工程应用推广提供参考依据;对比了自平衡测试结果的3种等效转换方法,验证了规范简化转换法所确定的桩基承载力偏安全,满足设计要求.

Based on the principles of self-balanced test method and fiber Bragg grating (FBG) sensor test,the FBG sensors and the traditional steel bar meters were used to measure the bearing capacity of the pile foundation,and the difference in the law of transmission between the axial force and the side friction was analyzed.Combined with the actual engineering case,the transmission laws of axial force and pile side friction of large diameter cast-in-place piles were analyzed,and three equivalent equivalent conversion methods,i.e.the code simplified conversion method,Kwon method and Kim method,were used to determine the bearing capacity of the pile foundation.The results show that FBG sensors can remove the prestress effects of temperature changes and concrete expansion,compared with the tranditional steel bar meters.The vibration of strain and side friction of pile is consistent with each other by two kinds of sensors,in which the error near the load cell is less than 10%.The axial force and pile side friction obtained from the measured data of FBG sensors can meet the requirements of self-balanced test regularity and accuracy.This method can provide a reference for engineering application.By comparing the three equivalent conversion methods of the self-balanced test results,it is verified that the bearing capacity of the pile foundation determined by the code simplified conversion method is more secure and meets the design requirements.