抗拔桩承载能力影响因素与群桩变形规律试验研究

Experimental research on influencing factors of uplift pile bearingcapacity and deformation law of group piles

利用自主研发的桩基室内抗拔测试装置,结合数值模拟技术对抗拔桩的承载破坏过程及影响因素、群桩的协同工作特征展开了深入研究。结果表明:抗拔桩的承载破坏经历4个阶段,承载初期,桩顶侧摩阻力最先发挥作用,桩顶土体发生塑性破坏;随上拔荷载不断增大,桩体产生相对位移,桩周土体由于桩身侧摩阻力产生塑性破坏;当桩身轴力自桩顶传递至桩底时,桩身底端产生抗拔“吸附力”,并伴随局部土体塑性破坏;随着桩周土体塑性区的拓展、连通,抗拔桩承载能力达到极限;桩身长径比、桩-土界面摩擦因数、桩侧土体压力与其承载极限呈正相关关系,其中桩身长径比对桩端“吸附力”具有重要影响;群桩抗拔过程中,角桩侧摩阻力发挥最充分,桩身位移量最小,极限承载力最大,中心桩桩身位移最大,极限承载力最低;距径比影响抗拔桩的群桩效应,当距径比从2增大至8时,桩身侧摩阻力提高30%,将距径比8作为群桩工程的推荐值,6~10作为群桩距径比的推荐范围。

The in-depth research on the bearing failure process and influencing factors of uplift piles,as well as the collaborative working characteristics of pile groups,were conducted using a self-developed pile foundation indoor uplift testing device and numerical simulation technology.The results show that the bearing failure of uplift piles goes through four stages.In the initial stage of bearing,the lateral friction resistance at the top of the pile first takes effect,and the soil at the top of the pile undergoes plastic failure.As the uplift load increases,the pile body undergoes relative displacement,and the soil around the pile undergoes plastic failure due to the lateral friction resistance of the pile body.When the axial force of the pile body is transmitted from the top of the pile to the bottom of the pile,an uplift“adsorption force”is generated at the bottom of the pile body,accompanied by local plastic failure of the soil.As the plastic zone of the soil around the pile expands and connects,the bearing capacity of the uplift pile reaches its limit.The length-diameter ratio of the pile body,the friction coefficient of the pile-soil interface,and the soil pressure on the pile side are positively correlated with their bearing capacity.Among them,the length-diameter ratio of the pile body has an important impact on the“adsorption force”at the pile end.During the uplift process of pile groups,the lateral frictional resistance of corner piles is fully utilized,the displacement of the pile body is minimized,and the ultimate bearing capacity is maximized.The displacement of the central pile body is the highest,and the ultimate bearing capacity is the lowest.The distance-diameter ratio affects the pile group effect of uplift piles.When the distance-diameter ratio increases from 2 to 8,the lateral friction resistance of the pile body increases by 30%.Use a distance-diameter ratio of 8 as the recommended value for pile group engineering,and a range of 6-10 as the recommended distance-diameter ratio for pile group engineering.