砂土中支盘桩抗拔承载特性模型试验研究

Experimental Studies of the Uplift Capacity of Expanded Shaft Piles in Sand

采用了PIV(Particle Image Velocimetry)技术,对竖向荷载作用下支盘桩桩周土体变形特性进行非介入式测量,考虑了埋深率、砂土密实度以及支盘桩盘径的影响,研究了支盘桩在上拔时刻的承载性能,分析表明:密实度是影响支盘桩的承载力的主要因素,密砂中支盘桩承载性能为松砂中的3倍以上。为了提高单支盘桩在松砂中的承载力和减少桩基位移,根据试验综合考虑后,单支盘桩直径宜取2.5d。对于密砂,单支盘桩在竖向荷载作用下是一个剪切伴随剪胀的过程,支盘处剪应力较为集中,随着支盘直径的增大,支盘上部位移影响区不断扩大,支盘上部土体沿支盘底面产生的滑动范围增大。为提高支盘桩在密砂中的承载力,单支盘桩的盘径以3d为佳。

The current studies on the expanded shaft piles are concentrated on the axial resistance characteristics and very few research on the mechanism of the uplift characteristics and ultimate uplift capacity theoretical estimations are reported. Therefore, an un-intrusive testing method, Particle Image Velocimetry(PIV), was used to measure the deformation of the surrounding soils surrounding the expanded shaft pile. The influence of the embedment depth, relative density of sand and the diameter of expanded shaft piles on the uplift capacity are evaluated. The analytical results show that the relative density is a major factor that affects the uplift capacity of the expanded shaft piles. The uplift performance of the expanded shaft piles in the dense sand is more than three times that of in the loose sand. The test results also indicate that, due to the low relative density and high compressibility of the loose sand, in order to improve the uplift capacity of the single expanded shaft piles and reduce pile displacement, the diameter of the expanded shaft portion should be 2.5 times of the shaft diameter. For piles in dense sand, the performance of the expanded shaft pile is a process of shearing and dilatancy under the action of vertical uplifting load. The shear stress at the expanded plate is relatively concentrated. As the diameter of the expanded plate increases, the displacement in the upper soil influence zone of the expanded plate continues to be affected. With the increase of the diameter, the sliding range of the upper part of the plate along the bottom surface of the expanded plate increases. In order to improve the uplift capacity of the expanded shaft pile in the dense sand, the diameter of the expanded plate of the expanded shaft pile is optimized to be the three times of the shaft diameter.