厚淤泥地层灌注桩深长护筒受力特性理论分析

Theoretical analysis on mechanical characteristics of deep and long pile casing for cast-in-place piles in deep soft clay

本文针对厚淤泥地层灌注桩深长护筒受力问题,建立了护筒打设与起拔力学模型。基于小孔扩张理论,分析了护筒打设时的挤土作用,考虑灌注桩混凝土参数随时间的变化,分别分析了护筒的几何尺寸和起拔时间对打设贯入和成桩后拔出时护筒的受力大小与演化规律。研究结果表明,当护筒长度小于20 m时,打设时的贯入阻力在50 t以内,主要靠护筒自重施沉,且随着护筒长度增加,贯入阻力急剧增加。护筒的起拔时间对起拔力的影响显著,特别是在浇筑3 h后,混凝土界面的胶结力剧增,起拔力显著增大。建议现场施工中护筒起拔时间以不超过3 h为宜。本文提出的计算模型可为厚淤泥地层灌注桩深长护筒优化设计与施工提供理论依据和指导。

A mechanical model for the calculation of push-in and pull-out resistances of the deep and long pile casing for cast-in-place piles in deep soft clay is established in this paper.Based on the theory of small hole expansion,the earth squeezing effect of the pile casing is analyzed.Considering the changes of concrete parameters of cast-in-place pile with time,the effects of geometric size and lifting time of pile casing on the stress and evolution of pile casing during installation and pull-out stages are analyzed respectively.The results show that when the length of the pile casing is less than 20 m,the penetration resistance during installation is less than 50 t force,which mainly depends on the self-weight of the pile casing,and the penetration resistance increases sharply with the increase of the length of the pile casing.The pull-out time of pile casing has a significant impact on the pull-out force,especially after pouring for 3 hours,the cementation force at the concrete interface increases sharply,and the pull-out force increases significantly.It is suggested that the lifting time of pile casing should not exceed 3 hours during on-site construction.The mechanical model proposed in this paper can provide theoretical basis and guidance for the optimal design and construction of deep and long pile casing of cast-in-place pile in thick silt stratum.