注浆微型钢管桩体轴向承载特性的试验研究

Test Study on Axial Mechanical Properties of Grouted Micro-steel-pipe-piles

针对注浆微型钢管桩用于桩基工程时的承载与变形性能的研究相对较少,借助室内试验研究钢管直径d和壁厚t、桩体长H、浆体水灰比、钢管表面布孔直径r和间距s等因素对微型钢管桩轴向承载、变形和破坏模式的影响。结果表明:钢管直径和壁厚是影响微型钢管桩轴向极限荷载的主要因素,随着钢管直径和壁厚增加,极限荷载近似呈线性增加,破坏模式由脆性破坏向延性破坏发展;增加桩长或注浆体水灰比,极限荷载呈减少趋势;当钢管直径与桩径之比增至0.59≤d/D≤0.72时,试验桩长、注浆水灰比和钢管表面布孔形式对轴向极限荷载的影响较小;进而基于桩体轴向承载特性及钢管受力与应变分析,提出了合理桩径比值为0.59≤d/D≤0.72,并提出了微型钢管桩轴向极限荷载计算公式。

Studies on mechanical and deformation performance of grouted micro-steel-pipe-piles(MSPP)in pile engineering are relatively rare. In this paper,a series of tests were carried out to investigate the effect of the parameters,such as diameter d and wall thickness t of steel pipe,the length of pile specimen H,the water-cement ratio,and the layout mode of holes in steel pipes,on axial bearing capacity,deformation and failure mode of MSPP. The tests results showed that the diameter and the wall thickness of steel pipe play dominant roles in enhancing axial bearing capacity of MSPP. With the increase of diameter and wall thickness of steel pipe,the ultimate axial load of MSPP tends to increase linearly,and the failure mode of MSPP shifts from brittle failure to ductile fracture. Increasing the length of MSPP specimen or improving the water-cement ratio results in a decrease of axial ultimate bearing capacity;when the diameter ratio of steel pipe to MSPP,d/D,increases and falls in the range of 0.59 to 0.72,the length of MSPP specimen,the water-cement ratio and the layout of holes do not significantly affect the axial ultimate bearing capacity of MSPP. Furthermore,on the basis of comprehensive consideration on axial load characteristics and mechanical behavior and strain of steel pipe,a reasonable diameter ratio range of steel pipe to MSPP,0.59≤d/D≤0.72,is presented herein,and an empirical expression on calculating the axial bearing capacity of grouted MSPP is put forth as well. The analytical results in this paper will be helpful in guiding design of MSPP in practical projects.