反射波法检测桥梁灌注桩的桩底特征研究

Research on the Characteristics of Pile Bottom of Bridge Perfusion Piles by Reflectance Wave Method

研究目的:我国南方在建的某高速铁路桥梁灌注桩,其桩身完整性检测采用反射波法,按《铁路工程基桩检测技术规程》(TB 10218—2019)4.4.5条文说明:柱桩(端承桩)桩底反射波与入射波反相位,摩擦桩桩底反射波与入射波正相位;而现场所测嵌岩桩桩底反射波与入射波有反相位也有正相位、摩擦桩桩底反射波与入射波有正相位也有反相位,由此对其桩底特征进行研究。研究结论:(1)灌注桩施工应严格按端承桩桩底沉渣厚度不大于50 mm、摩擦桩桩底沉渣厚度不大于200 mm实施;(2)用抗压强度P替代波阻抗ρVA进行分析,当桩体抗压强度P1大于桩底岩土抗压强度P2,其桩底反射波曲线呈正向特征,反之呈反向特征;(3)嵌岩桩采用冲击法施工,桩底直径不变;摩擦桩采用反循环法或正循环法施工,桩底直径变扩;(4)冲击法施工的桩长不变,反循环法和正循环法施工的桩长要超长1.5 m;(5)灌注桩反射波速与钻芯芯样反射波速一致;(6)本研究成果可为铁路、公路等领域桥梁灌注桩的桩底特征研究提供参考。

Research purposes:For the perfusion pile of a high-speed railway bridge under construction in the south of China,the method of reflection wave is used to test the pile integrity of the perfusion pile.According to 4.4.5 Provisions state of Technical Specification for Testing of Railway Piles(TB 10218-2019):the reflection wave at the bottom of rock-embedded piles is in the inverse phase with incident wave,and the reflection wave at the bottom of friction pile is in positive phase with the incident wave.The reflection wave and incident wave at the bottom of the embedded pile have inverse phase and positive phase,the reflection wave and incident wave of the pile bottom of the friction pile have positive phase and inverse phase in the field.Therefore,the characteristics of pile bottom were studied.Research conclusions:(1)The construction of infusion pile should be carried out strictly in accordance with that the bottom sediment thickness of end-bearing pile is not more than 50 mm and the sediment thickness at the bottom of friction pile is not more than 200 mm.(2)The pressure strength P is used instead of the wave impedanceρVA for analysis.When the pile pressure strength P1 is greater than the rock soil pressure strength P2 at the bottom of the pile,the reflection wave curve of the pile bottom of the reflected wave is positive.Conversely,it is reversed.(3)The bottom diameter of rock-socketed pile remains unchanged with impact method while that of friction pile expands with reverse circulation method or positive circulation method.(4)The pile length of the impact method construction is unchanged,and the pile length of the anti-circulation method and the positive circulation method construction should be over 1.5.(5)The reflected wave velocity of infusion pile is consistent with that of core sample.(6)The research results can provide reference for the study of the pile bottom characteristics of bridge perfusion piles in railways and highways.