水平力(H)-扭矩(T)组合受荷桩承载特性模型试验研究

Model Testing Investigation on Bearing Behavior of a Single Pile under Combined H-T Loads

为探讨单桩基础在桩顶水平力(H)-扭矩(T)组合作用下的承载特性,研制了H-T组合加载装置.通过室内砂箱模型对比试验,获得了8组H-T组合工况下的桩身内力变形与承载力结果.其表明:相比于单一水平受荷或受扭桩的极限承载力(Hu或Tu),两种荷载的不同大小组合与加载顺序(H→T或T→H)均会导致相应桩身承载力的减小,且H→T组合的影响要比T→H组合明显,如2Tu/3→T时桩身水平承载力减小约12.4%,而2 Hu/3→T组合下桩身扭转承载力减幅达48.5%,故工程设计时不宜基于叠加原理计算HT受荷桩的承载力.在此基础上,采用基于MATLAB编制的可考虑桩周土约束及H-T耦合效应的改进杆系有限元法计算程序求解了不同工况下的H-T组合受荷桩的桩顶扭转角及桩身扭矩与弯矩,并将计算结果与模型试验值进行了对比分析.

In order to study the bearing behavior of a single pile under combined loadings of horizontal force H and torque T, a loading device was first designed to apply H and T on the pile top simultaneously. 8 groups of indoor model were tested to obtain the inner forces and deformation as well as bearing capacities of the pile shaft. The result showed that, compared with the ultimate bearing capacity of pile shaft under pure H or T （i. e. , Hu or Tu）, the H-T load combinations with various magnitudes and sequences （i. e. , H→T or T→H） caused an obvious decrease of the bearing capacity. For example, the application of 2Tu/3 on the pile top reduced the horizontal bearing capacity by 12.4%, while the pre-loading of 2Hu/3 resulted in a reduction of the torsional bearing capacity up to 48.5 %. Therefore, traditional superposition principles can not be used in engineering design to evaluate the bearing capacity of piles under combined loads. Considering the effects of H-T combination and subsoil constraint on the torsional bearing capacity, the torsion angles at the pile top as well as the torque and moment distributions along the pile shaft were calculated by a MATLAB-based FEM program. The predictions were also compared with the model test data.