桩长对桩与桩相互作用影响的试验研究

为明确桩长对静压沉桩全过程中桩与桩之间相互作用产生影响的机理,通过室内模型试验,在中密实砂土中以2倍桩径为间距沉入双桩,研究了桩长对端阻力、卸除顶压后的桩周土压力以及双桩承载力特性的影响。结果表明:沉入过程中先沉桩和后沉桩的压入端阻力均随沉桩深度的增加而近似线性增大,当桩长(沉桩完成后沉入的总长度)为600 mm时,后沉桩仅比先沉桩的端阻力高0.2%左右,即此深度处2根桩的压桩端阻力基本达到极值;后压桩沉入前先沉桩的桩周土压力为后沉桩的90%左右,而后沉桩卸除顶压后先沉桩的桩周土压力总体为后沉桩的2~3倍,且随土压力盒埋深的增加而增大;相同深度桩周土压力均随桩长增大而降低;单桩试验时桩体极限承载力略高于先沉桩极限承载力2%~5%,提高的幅度随桩长增加而降低;不考虑桩间土作用双桩系统极限承载力约为单桩试验时极限承载力的2倍。研究成果对于进一步明确桩与桩相互作用机理和改善双桩承载力特性等均具有重要的工程意义。

Influence of Pile Length on the Interaction Between Piles

The impacts of pile length on end resistance of jacking pile, surrounding earth pressure after unloading, and bearing capacity of double piles were investigated through indoor model test of jacking double piles in modera-tely dense sand. Pile length in this paper is defined as the total length buried in sand when pile jacking is finished.Results demonstrated that the pressed end’s resistance of both piles increased approximately linearly with the deepening of pile jacking; at depth 600 mm at the finish of pile jacking, the end resistance of pile 1^# (which is pressed firstly) was larger than that of pile 2^# (referring to the pile pressed later) by about 0.2%, indicating that the end resistance of two piles reached the extreme value at this depth. Given the same pile length, the surrounding earth pressure of pile 1^# before the sinking of pile 2^# was about 90% of that of pile 2^#; after the unloading of pile 2^#, the surrounding earth pressure of pile 2^# was about 2~3 times of that of pile 1^#, and in the meantime increased with the increasing of embedded depth of pressure gauge. However, at the same buried depth, the surrounding earth pressure of the two piles both decreased with the increase of pile length. The ultimate bearing capacity of pile in single pile test was higher than that of pile 1^# in double pile test by about 2%~5%, but such increment attenuated with the increasing of pile length. The ultimate bearing capacity of double pile system in no consideration of pile interaction was about twice times of single pile. The research findings are of engineering significance in further clarifying the interaction mechanism between piles and improving the bearing capacity of double piles.