广东地区超长旋挖灌注桩桩端注浆试验

Experimental Research on Bearing Capacity of the Super-Long Rotary Excavating Post-Grouting Bored Pile Utilized in the Guangdong Region

目的分析常规桩和注浆桩的荷载传递特性,对比常规桩和注浆桩在不同桩顶位移下承载力的提高幅度,提出了设计大直径超长单桩极限承载力的建议方法,并验证其适用性.方法通过广东某大桥大直径超长旋挖灌注桩桩端注浆现场试验得出荷载-沉降曲线,根据预埋的应力计测出桩身侧摩阻力值,通过计算得到桩身轴力、桩土相对位移以及桩端位移.结果注浆桩S2的桩端阻力比常规桩S1发挥较早,浆液技术更有利于侧阻和端阻的同步发挥;注浆桩总承载力、侧摩阻力和端阻力提高系数随桩顶位移呈先增大后减小趋势,总承载力和侧摩阻力的提高系数变化平稳,增加速率远远小于端阻力.结论桩端注浆不仅有利于端阻的发挥,还有效减小了桩顶沉降,从而提高单桩极限承载力;常规桩下部土层侧摩阻力和端阻力未达到极限,建议计算时乘以折减系数;桩端注浆桩桩端附近土层的侧摩阻力和桩端阻力均乘一定的增大系数.

This paper analyzed load transfer characteristics of the normal pile and the grouting pile, studied the beating capacity increase rate of the post-grouting pile under different top displacements and proposed a new computing method for ultimate bearing capacity of the large-diameter super- long rotary bored pile. Load-settlement curves of a large-diameter and super-long rotary excavatingbored pile used in a bridge in Guangdong were obtained by field tests. Side friction forces were measured by embedded stress detectors. The axial force, the relative displacement between the pile and soil and the displacement on the pile top were calculated. Results show that the tip resistance of the post-grouting pile $2 develops earlier than the normal pile S1, which benefits synchronous plays of the side resistance and tip resistance. Increase coefficients of the total bearing capacity, the side resistance and the tip resistance increase firstly, and then decrease with the increase of the dis- placement on top pile. Increase coefficients of the total bearing capacity and side friction change smoothly and their rates are far less than that of the tip resistance. Conclusion is that using the post- grouting can increase the bearing capacity of the pile and decrease its top settlement effectively. The computational results for the normal pile should be multiplied by a reduction factor, because side and top resistances of lower soil layer are not reach to the limits. But for the post-grouting, the side and top resistance of the soil layer should be multiplied by a magnify factor.