基坑双排斜桩模型试验研究

伴随着地下空间开发的开发,基坑开挖深度逐步加大,当开挖深度较大时,单排桩满足不了位移要求时,发展出双排直桩、斜直交替桩等新型支护形式,然而支护效果仍不够理想。为进一步优化基坑工程中的双排支护桩,增大其抗侧刚度,将桩设置为斜桩形成基坑双排斜桩。为了验证双排斜桩的支护效果,基于室内模型试验对双排斜桩在开挖与堆载作用下的桩顶位移和桩身弯矩进行监测,并与单排桩、双排直立桩、小排距前排倾斜双排桩和常规排距前排倾斜双排桩进行对比。研究结果表明:(1)双排直立桩、小排距前排倾斜双排桩、常规排距前排倾斜双排桩和双排斜桩的侧向刚度均优于单排桩;(2)当桩顶排距较小时,前后排形成的空间刚架作用不强,小排距前排倾斜双排桩承载力弱于双排直立桩,当桩顶排距与双排直立桩相同时,前排倾斜双排桩的桩顶位移增长速度比双排直立桩缓慢,承载力提高;(3)双排斜桩在开挖和堆载过程中,位移增长最为缓慢,桩身弯矩较小,相比单排桩、双排直立桩和前排倾斜双排桩有一定优势;(4)对5种工况的桩型布置进行排序,双排斜桩＞常规排距前排倾斜双排桩＞双排直立桩＞小排距前排倾斜双排桩＞单排桩。

Model Test of Double-Row Inclined Piles in Foundation Pit

With the development of underground space, the excavation depth of foundation pit increases gradually. When the excavation depth is large, the single-row piles can't meet the requirements of displacement and settlement, thus, the dual-row vertical piles, oblique-straight piles and other forms of retaining structures are proposed. However, the existing types of retaining structures still can not meet the requirements of deep excavations. In order to optimize the layout of dual-row retaining piles in the foundation pit and increase its lateral stiffness, the inclined pile was employed to form the dual-row inclined piles. To gain full understanding of the behaviors of the dual-row inclined piles, the pile head displacement and pile shaft bending moment under the action of excavation and surcharge loading were monitored in the physical scale model test. The behaviors of the dual-row inclined piles were compared with other four types of pile layouts: the single-row piles, the dual-row vertical piles, the conventional row-spacing dual-row piles with batter pile in the front row, and the small row-spacing dual-row piles with batter pile in the front row. The test results show that: (1) The lateral stiffness of the dual-row vertical piles, the conventional row-spacing dual-row piles with batter pile in the front row, the small row-spacing dual-row piles with batter pile in the front row and the dual-row inclined piles is significantly larger than that of single-row piles. (2) The bearing capacity of the small row-spacing dual-row piles with batter pile in the front row is smaller than that of the dual-row vertical piles. When the row spacing of pile head is inadequate, the spatial effect can not reach its full potential. When the row spacing of pile head of the dual-row piles with batter pile in the front row is equal to that of the dual-row vertical piles, the pile head displacement of the dual-row piles with batter pile in the front row increases more slowly than that of the dual-row vertical piles, and the bearing capacity is improved. (3) During the excavation and surcharge loading process, the displacement of the dual-row inclined piles grows slowest, and the bending moment of the pile shaft is the smallest, comparing to that of the single-row piles, the dual-row vertical piles and the dual-row piles with batter pile in the front row. (4) Priorities are sorted of the arrangement of the five types of piles: dual-row inclined piles > conventional row-spacing dual-row piles with batter pile in the front row > dual-row vertical piles > small row-spacing dual-row piles with batter pile in the front row > single-row piles.