承压螺旋桩斜向荷载试验与极限荷载判定分析

桩基础所受外载荷并不是单一方向的载荷,如输电塔结构,在承受竖向压力的同时承受着水平载荷作用,导致基桩受到斜向压荷载作用,该种条件的桩基础极限载荷的确定对结构设计的安全性极为重要.为此,开展承压螺旋桩基础斜向荷载的试验研究工作.模型试验采用1#(叶片距宽比为3.14)和2#(叶片距宽比为5)2种桩型,1#桩型试验5次,2#桩型试验4次,2组共计9次试验.承压螺旋桩斜向荷载试验表明:①本次试验桩顶水平位移较竖向位移大了1个数量级,螺旋桩基础的竖向承载能力并未得到充分发挥,竖向分量限制了背载侧叶片对地基向上的压缩作用,从而提高了基础抗水平载荷的能力.②叶片间距增大时(1#<2#),荷载-位移曲线表现出更为明显的非线性特征,1#和2#桩受载侧地基表面均出现放射性裂纹;1#桩背载侧地基表面沿桩体外径开裂,2#桩的背载侧出现似"拔出体".③可采用F-ΔX0/ΔF方法、S-LogP方法,并根据荷载量变化、桩土相互作用和桩周材料的变形阶段确定螺旋桩基础的斜向极限载荷;本次试验1#桩的判定极限荷载为327.93 N,2#桩为348.06 N.

Analysis of Estimating Ultimate Loading and Static Test of Screw Pile Under Inclined Loading

The loading type of pile foundation is not single direction, such as transmit electricity tower, which bears the vertical press and horizontal load at the same time. Under this condition, it is very important to estimate the ultimate inclined load of pile for the security of structural design, so the model test of screw pile under inclined load is done in this paper. Two types of pile, 1#(RPDD=3.14,RPDD is the ratio of the pitch of screws or distance between laminas to the net diameter) and 2# (RPDD=5), is used in the model test, and the test number of 1# and 2# are 5 and 4 respectively, total of two groups are 9. The static test shows that:① the horizontal displacement is more than 10 times to the vertical displacement, and the compressed effect of ground upside POL (the pullout part of lamina) is restricted by vertical component, so the capacity of horizontal loading is increased; ② at the condition of increasing RPDD, 1#＜2#, the non-linear characteristic of load-displacement curves are more obviously, and the radicalized crack are appeared on the surface ground of PL (the pressed part of lamina) of 1# and 2#, at the POL ground surface, the elliptical crack on surface ground upside the lamina diameter occur at the side of POL of 1#, but pullout body occur at POL of 2#; ③ on the base of the method of F-ΔX_0/ΔF and S-Log P, the changing load, pile-soil interaction and the deformation phase of soil, the ultimate load of screw pile are estimated, i.e. the ultimate load of 1# and 2# screw pile are 327.93 N and 348.06 N respectively.