旋挖成孔工艺在川南长江古河道桩基施工中的应用

Rotary Drilling Method in Bored Pile at an Ancient Yangtze Riverbeds in Southern Sichuan

根据宜宾某桩基工程实例,分析了湿法作业下旋挖成孔灌注桩泥浆护壁及长护筒工艺的施工技术要点,进而选取合适的泥浆配比,采用膨润土泥浆护壁工艺减小塌孔发生的概率;通过加设长护筒解决串孔、泥浆上返困难及混凝土面达不到设计标高问题,并对桩头处理、长护筒拔出困难等工程问题的处理提出建议措施;采用改变桩型的处理方式对桩头较低的情况进行处理,进而提出采用孔口围堰及永临分离式钢护筒保证成桩质量,对类似项目的桩基施工起到一定的借鉴作用。

This paper presents a case history of a deep foundation installation in Yibin City of southern Sichuan Province. The bored pile installation techniques, such as, rotary drilling of the bored concrete pile under wet conditions, slurry method and long casing method for the maintenance of the borehole stability are introduced in the paper. Then the optimum mud-water ratio was selected, bentonite slurry borehole stability technology was utilized to minimize the probability of borehole caving. The use of long casing effectively resolved defects in the bored pile installations, such as, connecting of adjacent bored piles, difficulties of slurry circulation return, and dirty concrete at the pile head so that the strength of the concrete at pile head lower than the required. The paper also proposes some bored pile installation suggestions such as, pile head treatment, difficulties encountered in the long casing withdrew. The improved pile head treatment methods, such as, temporary cofferdam and/or splitable short casing at bored pile head are proposed for the low pile head issues and improved the bored pile head installation quality.