挤扩支盘桩分布式检测及承载机理研究

Distributed detection and bearing mechanism of squeezed branch piles

基于BOTDR分布式光纤传感技术,研究了桩顶荷载作用下支盘桩桩身轴力的变化规律和桩侧摩阻力的发挥特征。结果表明:当荷载较小时,支盘桩的承载机理与普通直杆桩相似,即随着荷载的增加其桩身轴力逐渐向深部传递。随着桩顶荷载的增加,支盘的作用逐渐显现,并承担了大部分荷载,但桩的沉降和压缩量也增加,使支盘与上部土层间出现离层。随着支盘桩沉降量的增大,支盘与上部土体之间离层面积逐渐增加,在桩土相互作用下使得支盘上部的土体被剪裂,离层上部土层逐渐失去结构的完整性而产生负摩阻力,从而增加了支盘的负担。因此,在支盘桩的设计中,应提高支盘周围的土层性质和桩身强度,减少桩的压缩变形和沉降,从而提高支盘桩的承载能力。

Based on the BOTDR distributed optical fiber sensing technology, the variation laws of branch pile axial force and the action characteristic of the pile side resistance under the action of pile head loads are studied. The result shows that when the load is small, the bearing mechanism of the branch piles is similar to that of the common piles, namely with the increase of the loads, the axial forces of the branch pile are transferring gradually to the deep part. With the increasing pile head loads, the branch of the squeezed branch piles bears most of the pile head loads as the branch function of the squeezed branch piles appears gradually, but the amount of settlement and compression on the branch pile is increased, which gradually brings about the free face between the branch and its overlaying soil layer. With the in creasing settlement of the branch piles, the areas of the free face between the branch and its overlaying soil layer are gradually increased. The upper soil body of the branch is to be shear fracture under the pile-soil interaction, and gradually loses its structural properties, which generates the negative friction and subsequently increases the burdens of the branch. Thus, during the design of the branch piles we should improve the properties of the soil layer around them and the strength of pile body, and reduce compressive deformation and settlement of the branch piles so as to improve their bearing capacity.