高喷插芯组合桩荷载传递机制足尺模型试验研究

高喷插芯组合桩(简称JPP)是由高压旋喷桩和预应力混凝土芯桩构成的一种新型组合桩,为了对其荷载传递机制有更深入的认识,以自行开发的大型土工试验模型槽为依托,进行了JPP桩、灌注桩和高压旋喷水泥土桩静载荷对比试验。通过埋设在JPP桩中的监测仪器对桩身轴力、桩端阻力以及桩体沉降等进行了直接量测,进而分析了JPP桩中管桩与水泥土轴力的分布和内外侧摩阻力的分布。试验结果表明,JPP桩与同桩长、同桩经灌注桩相比承载力高30%以上;JPP桩变形由芯桩控制,管桩轴力分布与水泥土轴力分布规律不一致,但同一截面上管桩和水泥土的轴力比值约为其弹性模量的比值;内外摩阻沿桩身的分布规律类似,内摩阻是外摩阻的1.62倍左右,约为JPP桩直径和管桩直径的比值;桩侧摩阻力与桩土相对位移近似双曲线分布,桩端阻力和桩端位移也近似双曲线分布。

Full-scale model test on load transfer mechanism for jet grouting soil-cement-pile strengthened pile

Jet grouting soil-cement-Pile strengthened Pile (JPP) is a new kind of composite pile composed of high pressure jet grouting pile and prestressed concrete core pile. In order to make a further research on load transfer mechanism of JPP under vertical loads, the full-scale model test of JPP, cast-in-place pile and jet grouting soil-cement pile have been done in the test room which is developed for this test. With the pre-arranged instrument in JPP, the axial stress, dip resistance and settlement of pile have been measured; and distribution of axial force and friction resistance are also analyzed. Experimental results show that: bearing capacity of JPP is thirty percent higher than that of cast-in-place pile which has the same length and diameter with JPP. The deformation of JPP is controlled by core pile; axial force distribution of PHC is different with soil-cement; and their axial force ratio in same section is their elastic modulus ratio. Distribution of inner and outer friction resistance is similar; and the inner friction is about 1.62 times of the outer one; it is about the ratio of JPP diameter and PHC diameter. Furthermore, the relation between friction resistance and relative displacement is similarly hyperbolic; and the relation between dip resistance and displacement is also hyperbolic.