预应力锚索张拉方式对预应力损失影响探究

Study on Influence of Prestressed Anchor Cable Tensioning Mode on Prestress Loss

预应力锚索结构的预应力损失问题已成为锚固工程界广泛关注的课题,为了研究张拉方式对岩土锚索结构预应力损失的影响,在总结影响预应力损失因素、机理的基础上,通过预应力锚索现场张拉试验,对比分析了预应力锚索在多循环加卸载和单循环加卸载两种加卸载方式下的荷载-位移曲线,得出了两种张拉方式下锚固段岩土体产生的弹性位移和塑性位移。基于塑性位移量计算出了相应的预应力损失值,在此基础上,评价了张拉方式对预应力锚索结构预应力损失的影响。研究表明:两种加卸载方式产生的平均弹性位移量基本一致,但多循环试验产生的塑性位移比单循环试验产生的塑性位移大9.1 mm,占单循环加卸载试验平均塑性位移量的36.1%,说明经过多循环张拉,锚索锚固段岩土体中存在的大量节理、裂隙,在反复循环荷载作用下在短时间被不断压密,起到加速蠕变作用,提前消除了11.3%的由于锚固段岩土体蠕变造成的预应力损失。建议对于地质情况较复杂、节理较发育的工程,在锚索张拉锁定时尽量采用多循环张拉方式,将有助于减小预应力损失,获得更好的长期锚固效果,降低预应力锚索工程安全风险,提高锚索工程的技术经济和社会效益。

Prestress loss of prestressed anchor cable structure has become a widespread concerned topic in the field of anchorage engineering. To study the influence of tensioning mode on the prestress loss of geotechnical anchor cable structure, based on summarizing the factors and mechanism that influence the prestress loss, through the in-situ tension test of the prestressing anchor cable, the load-displacement curves of the prestressing anchor cable under the modes of multi-cycle loading and unloading and single-cycle loading and unloading are compared and analyzed, and the elastic displacement and plastic displacements of rock and soil in anchorage section under 2 tensioning modes are obtained. The corresponding prestress loss values are calculated based on the plastic displacement. On this basis, the influence of tension mode on the prestress loss of the prestressed anchor cable structure is evaluated. The result shows that the average elastic displacements produced by the 2 loading and unloading modes are basically the same. However, the plastic displacement of multi-cycle test is 9.1 mm larger than that of single-cycle test, accounting for 36.1% of the average plastic displacement of single-cycle loading and unloading test. It indicates that after multi-cycle tension, many joints and cracks exist in the rock and soil body of the anchor cable anchorage section, which are continuously compacted in a short time under the repeated cyclic loads, and play a role of accelerating creep, eliminating 11.3% of the prestress loss caused by the creep of the rock and soil body of the anchorage section in advance. It is suggested that the multi-cycle tension mode should be adopted as much as possible when the anchor cable is tensioned and locked in the project with complex geological conditions and developed joints, which will help to reduce the loss of prestressing force, obtain better long-term anchorage effect, reduce the safety risk of the prestressing anchor cable project and improve the technical and economic benefits of the project.