水平受荷倾斜群桩模型试验及受力机理研究

Study on Model Tests and Stress Mechanism of Inclined Pile Groups Under Horizontal Loading

长期受水平荷载的工程涉及到倾斜桩的应用,其水平承载能力和桩周土体行为受到关注.设计了4组不同布桩方式的室内倾斜群桩水平加荷模型试验,针对6桩承台,对比分析了倾斜群桩的桩身位移、桩身内力及桩周土体变形,相较于群直桩,同向10°、对称10°和对称20°的倾斜群桩水平承载力分别提高了13.3%、28.3%和75.0%,桩顶最大水平位移依次减小了21.3%、35.6%和53.9%,倾斜群桩的桩身内力较小,侧摩阻力较大,桩顶土体水平位移最多减少了48.9%,桩底土体竖向位移最多减小了56.4%.建立了承台-倾斜群桩-土体在水平荷载作用下的精细化有限元模型,进一步分析了足尺条件下不同布桩方式倾斜群桩与土体的相互作用.直桩抵抗水平荷载的作用主要由土体沿桩身法向抗力提供,而倾斜群桩在水平荷载下产生较大的侧摩阻力,且斜桩侧摩阻力水平分量在抵抗水平荷载中发挥重要作用,对称20°倾斜群桩中侧摩阻力水平分量占比高达35%,所以其水平荷载能力更强,显著提高结构的抗侧刚度.承台与桩连接方式的改变没有影响其受力模式,刚接时桩顶存在负弯矩,更有利于减小桩身弯矩和桩顶位移.合理布置的倾斜群桩可以在水平荷载下发挥显著作用.

The engineering projects subjected to long-term horizontal loading involve the applications of inclined piles,and the horizontal capacities of piles and soil behavior are of concern to researchers.In this paper,with symmet-rical and isotropic pile layouts,four testing models which consisted of one cap and six inclined piles under horizontal loading were conducted to compare and analyze the displacements and internal forces of the pile body,as well as the variation in soil around piles.Compared with those of the straight pile group,the horizontal capacities of the isotropic 10°,symmetric 10°and symmetric 20°pile groups were improved by 13.3%,28.3% and 75.0%,respectively,while the maximal horizontal displacements of pile top were reduced by 21.3%,35.6% and 53.9%,respectively.As for inclined pile groups,the internal forces of their pile bodies were smaller,the side frictional resistances were larger,the horizon-tal displacement of soil at the pile top was reduced by 48.9% at most,and the vertical displacement of soil at the pile bottom was reduced by 56.4% at most.The refined finite element models of cap-inclined pile group-soil under horizontal loading were established,and the interaction between inclined pile groups and soil under full-scale conditions and different pile layouts was further analyzed.It was found that the resistance of straight piles to horizontal loading was mainly provided by the soil resistance along the normal direction of the pile body,while a larger side frictional resistance was triggered in inclined pile groups under horizontal loading.In particular,the horizontal component of the side frictional resistance of inclined piles played an important role in resisting horizontal loading.For example,the horizontal component of side frictional resistance in the symmetrical 20°inclined pile group accounted for up to 35%,indicating that its horizontal capacity and stiffness were significantly enhanced.The connections between the cap and piles did not affect the corresponding stress mode.The bending moments at the pile top with a rigid connection were negative,which was helpful in reducing the bending moments of pile body and the pile top displacements.Therefore,a reasonable layout of inclined pile group can play a significant role under horizontal loading.