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五星形混凝土桩是一种新型截面异形桩,由圆截面均匀内切5个圆弧形成,其截面参数主要有被切割圆半径R、切割圆半径r、切割圆弧所对应的外包圆圆心角2x、外包圆弧对应圆心角θ。经截面尺寸优化分析,推导出周长最大化五星形桩和周长面积比最大化五星形桩。为进一步掌握五星形桩承载性能,以砂雨法制作土样,在干砂中进行了4根单桩对比模型试验研究,4根单桩为:周长面积比最大化五星形桩F_2、周长最大化五星形桩F_1、与F_2等截面周长圆桩C_1、与F_2等截面面积圆桩C_2。试验结果表明:与F_1相比,F_2的桩侧表面积与其相近,极限承载力大致相同,但F_2混凝土用量是F_1混凝土用量的0.75倍,单位体积混凝土承载力更高,F_2为最优的截面尺寸;与等截面面积小圆桩C_2相比,F_2桩侧表面积是其1.53倍,极限承载力是其2.4倍,显示出在相同混凝土用量下五星形桩F_2具有良好的承载性能,截面异性扩大效应明显;与相同截面周长的大圆桩C_1相比,F_2桩截面面积是其0.44倍,极限承载力是其0.96倍,但F_2桩单位体积混凝土承载力是C_1桩的2.21倍,显示出更高的承载性价比。各级荷载作用下五星形桩侧摩阻力所占比例在80%以上,特别是F_2桩,在90%以上,表现出摩擦桩的特性。研究成果可对五星形桩的工程应用提供一定理论支持。
The five-star shaped concrete pile is a new type of cross-section shaped pile, which is formed by uniformly cutting five circular arcs in a circular cross section. The cross-sectional parameters of the five-star shaped concrete pile include the radius R of the cutting circle, the radius r of the cutting circle, 2x, Outsourcing arc corresponds to central angle θ. According to the optimization of cross-sectional dimensions, the five-star shaped piles that maximize the perimeter of five-star shaped piles and the perimeter area ratio are derived. In order to further understand the bearing capacity of five-star shaped piles, soil samples were made by the sand and rain method. Four single-pile comparative models were tested in dry sand. Four single piles were found: the circumference area ratio maximized five- Length maximized five-star pile F_1, F_2 circular cross-section cylindrical pile C_1, and F_2 cross-sectional area of cylindrical pile C_2. The experimental results show that compared with F_1, the lateral surface area of F_2 is similar to that of F_1, and the ultimate bearing capacity is almost the same. However, the F_2 concrete content is 0.75 times the F_1 concrete content, the unit volume concrete load capacity is higher and F_2 is the optimal cross-sectional dimension ; Compared with C_2 with equivalent cross-sectional area, the lateral surface area of F_2 pile is 1.53 times and the ultimate bearing capacity is 2.4 times, which shows that F_2 with five-star shape has good bearing capacity and heterosexual expansion effect Obviously, the cross-sectional area of F_2 pile is 0.44 times that of the great circular pile C_1 with the same section circumference, and the ultimate bearing capacity is 0.96 times, but the carrying capacity of F_2 pile unit volume concrete is 2.21 times that of C_1 pile, showing higher The bearing cost. The frictional resistance of the five-star shaped pile under all loadings accounts for more than 80%, especially for the F_2 pile, which is above 90%, showing the characteristics of the friction pile. The research results can provide certain theoretical support for engineering application of five-star pile.