软土地基正循环钻孔灌注桩二次清孔工艺选择及其最佳清孔时间研究

软土地基钻孔灌注桩在终孔清孔至开始灌注水下混凝土期间，孔底沉渣厚度往往会超出规范要求，必须进行二次清孔。通过对顺德快速干线高富路南华分离式立体交叉隧道工程的正循环钻孔灌注桩施工进行研究，找出了适合正循环钻孔灌注桩二次清孔的换浆法清孔工艺，并对该工艺下二次清孔的最佳时间进行研究，总结出计算二次清孔时间的经验公式。对软土地基等多种地质条件下采用换浆法进行二次清孔的钻孔灌注桩的施工具有一定的指导意义。

Secondary Cleaning Technology of Boreholes Made by Normal Circulation in Soft Sub-soil and Its Optimal Cleaning Duration

Secondary cleaning must be made for the boreholes of cast-in-situ bored piles in soft sub-soil before underwater concrete is cast, because the thickness of the mucks on the bottom of the boreholes always exceeds the limit values specified in relevant specifications. Taking the construction of the bored piles of a tunnel in Shunde, China as an example, the author determines to adopt the slurry replacement method in the secondary cleaning of the boreholes of the bored piles. The author studies on the optimum duration of the secondary cleaning of the boreholes and achieves the empirical formula to calculate the secondary borehole cleaning duration. This paper can provide guidance for the secondary cleaning of boreholes of cast-in-situ bored piles in soft sub-soil in the future.