PC工法桩围堰施工受力及变形特性研究

Research on Stress and Deformation Characteristics of PC Method Pile Cofferdam Construction

为研究PC工法桩围堰结构在施工过程中的受力及变形特性,本文以某工程的深水基础施工为背景,采用有限元软件建立围堰空间整体模型,考虑土压力、静水压力、水流力以及波浪力等荷载组合对围堰的作用,按照不同的施工阶段,划分为六种工况进行加载计算,得出最不利工况,并对围堰的结构应力、位移变形等进行分析。结果表明:该围堰结构的强度和刚度均满足要求,结构安全可靠。在施工前期,围堰各个侧面中心位置处的位移变形随着深度的增加呈现出逐渐减小的趋势,而在施工后期,位移变形呈现出先增大后减小的变化趋势,且在整个过程中,迎水面的位移变形始终大于侧水面和背水面。随着围堰坑内开挖深度的增加,最大侧向位移对应的位置越来越深,但无论在任何施工阶段,钢板桩底端插入风化岩后其侧向位移变形几乎都很小。下层围檩及内支撑的应力大于上层,横撑中间位置处的应力大于两端处的应力,围堰开挖面的四角是最薄弱的受力点,应力集中现象明显。因此,在围堰设计过程中,需加强四角位置的连接,下层围檩及内支撑可选择截面惯性矩和屈服强度较大的型钢,也可根据实际情况,在底层围檩的中心位置处加设钢管,避免围堰发生失稳现象。

In order to study the stress and deformation characteristics of the PC construction method pile cofferdam structure during the construction process, this paper takes the deep-water foundation construction of a certain project as the background, uses finite element software to establish a comprehensive spatial model of the cofferdam, considers the effects of load combinations such as soil pressure, static water pressure, water flow force, and wave force on the cofferdam, divides it into six working conditions according to different construction stages for loading calculation, obtains the most unfavorable working condition, and analyzes the structural stress and displacement deformation of the cofferdam. The results show that the strength and stiffness of the cofferdam structure meet the requirements, and the structure is safe and reliable. In the early stage of construction, the displacement and deformation at the central position of each side of the cofferdam showed a gradually decreasing trend with the increase of depth, while in the late stage of construction, the displacement and deformation showed a trend of first increasing and then decreasing. In the whole process, the displacement and deformation of the facing surface were always greater than that of the side and back water surfaces. With the increase of excavation depth in cofferdam pit, the position corresponding to the maximum lateral displacement becomes deeper and deeper, but the lateral displacement and deformation of steel sheet pile after the bottom end is inserted into weathered rock are almost small in any construction stage. The stress of the lower enclosing purlin and the inner support is greater than that of the upper layer, and the stress in the middle position of the transverse support is greater than that at both ends. The four corners of the cofferdam excavation face are the weakest stress points, and the stress concentration is obvious. Therefore, in the process of cofferdam design, it is necessary to strengthen the connection of the four corners. The lower enclosing purlin and the inner support can choose the section steel with larger section moment of inertia and yield strength, or according to the actual situation, the steel pipe can be installed at the center of the bottom enclosing purlin to avoid the instability of the cofferdam.