沉管隧道干坞基坑可回收锚索力学特性研究

Mechanical Properties Resaearch on the Recyclable Anchor Cable of Dry Dock Foundation Pit in Immersed Tunnel

为理清沉管隧道干坞基坑开挖使用过程可回收锚索的力学特性,以典型工程实例为背景,简析干坞基坑可回收锚索的作用机制,借助数值法建立可回收锚索精细仿真模型,计算揭露干坞基坑支护体系受力变形特征,开展与普通锚索受力特性对比分析,并提出可回收锚索修正设计思路。研究表明:实例干坞基坑支护结构位移和锚索轴力均小于规范限值,基坑处于安全稳定状态;可回收锚索轴力呈均匀的“矩形”分布,而非现有研究提出的单调递减曲线分布;坞内蓄、排水过程,在往复水压作用下,土层与可回收锚索力学特性受到了显著的影响,实际工程应充分考虑;蓄、排水作用诱发的变形为可恢复的弹性变形,引起的锚索内力变化幅值由上往下逐渐增加;可回收锚索抑制基坑侧移能力较普通锚索差,内力比普通锚索总体更大,且两者分布规律不同,普通锚索锚固段轴力呈“阶梯形”分布;实际工程可回收锚索应用设计时,内力可参照常规锚索设计思路,通过修正满足承载力要求。

To clarify the mechanical properties of recyclable anchor cable of dry dock foundation pit in immersed tunnel during excavation and operation process, the action mechanism of recyclable anchor cable of dry dock foundation pit was analyzed based on a typical engineering example. The fine simulation model of recyclable anchor cable was established by numerical method. The stress and deformation characteristics of the pit supporting system were calculated and revealed. The mechanical properties of anchor cable were compared with that of ordinary anchor cable, and revised design ideas of recyclable anchor cable were proposed. The results show that the displacement of supporting structure and the axial force of anchor cable are both less than the standard limit, so the foundation pit is in a safe and stable state. The recyclable anchor cable axial force presents a uniform "rectangular" distribution, rather than the monotone decreasing curve distribution proposed by existing researches. In the process of storage and drainage in the dry dock, the effect of the reciprocating water pressure on mechanical properties of soil and anchor cable is significant, which should be fully considered in actual engineering. The deformation induced by storage and drainage is recoverable elastic deformation, and the amplitude of the internal force of the anchor cable increases gradually from top to bottom. Compared with the ordinary anchor cable, the recyclable anchor cable has weaker ability to restrain the lateral movement of foundation pit and meanwhile internal force is greater than that of ordinary anchor cables as well as the distribution law of the axial force is different. The axial force in the anchorage section of ordinary anchor cable distributes in the form of "ladder". In practical engineering, the internal force design of recyclable anchor cable can refer to the conventional design idea, and then meet the bearing requirements through modification.