层状地基中PHC管桩的静压残余应力试验研究

静压桩贯入过程中，因桩顶卸荷残留于桩身的应力较为显著。通过成层土地基中5根桩身预埋准分布式FBG光纤传感器的静压桩足尺试验，对开口PHC管桩沉桩过程中施工残余应力性状、沉桩结束17 d内桩身残余应力的发展变化情况及其对后续静载荷试验影响进行了阐述。试验表明，开口PHC管桩桩身残余应力及桩侧平均残余摩阻力随贯入深度呈折线型分布，中性面深度与贯入桩长比值介于0.66～0.92之间，其大小与桩端持力层密实度及桩端残余应力呈正相关关系。土塞效应成为制约开口PHC管桩桩端残余应力不同于其他桩型的主要因素之一；休止期内桩身残余应力逐渐趋于稳定，中性面处桩身残余应力降低幅度介于3.2%～29.88%之间，桩端残余应力降低幅度介于10.78%～32.39%之间；静载荷试验过程中不考虑施工残余应力将高估中性面以上桩侧摩阻力约53.46%，低估中性面以下桩侧摩阻力及桩端阻力分别56.62%，10%。研究成果可为进一步研究开口PHC管桩施工残余应力性状提供依据。

Field performance of residual stresses in jacked PHC pipe piles in layered ground

The residual stress along piles after unloading at pile tip is significant during installation. The full-scale tests are conducted on 5 piles inserted with quasi distributed FBG optical fiber sensors jacked into stratified soils. The post-installation residual stress in opened PHC pipe piles during installation, the variations in residual stress during 17 d after installation and the effect on static load tests are elaborated. The results indicate that the distribution of residual stresses and average residual shaft friction in opened PHC pipe piles during installation resemble a folded line, and the ratio of neutral point depth to pile penetration is between 0.66 and 0.92, which is positively related with the bearing stratum compactness at pile tip and residual point resistance. The plugging effect becomes one of the main factors to restrict the residual point resistance in opened PHC pipe piles, and it is different from that of other pile types. The residual stresses tend to decay to a stable value gradually after installation, and the reduction of residual stress in neutral point is between 3.2% and 29.88%, while that of the residual point resistance is between 10.78 % and 32.39%. It will overestimate the side friction above neutral point by about 53.46%, and underestimate the side friction below neutral point by about 53.46% and the tip resistance by 10% separately without regard to the post-installation residual stresses during the static load tests. The research results can provide the basis for the post-installation residual stresses in opened PHC pipe piles further.