深基坑桩锚支护结构土层预应力锚索工作性能测试分析

On the working performance testing and analysis with the pre-stressed anchor rope in the soil in deep foundation pit

对某深基坑桩锚支护结构土层预应力锚索进行了检测与监测,同时进行了支护结构顶部水平位移的监测。检测结果表明,土层预应力锚索的主要失效模式是注浆体与土层接触面发生剪切破坏,其破坏形式是渐进缓变型;受拔时锚-土界面位移占锚头累计位移的80%-90%,其抗拔承载能力与锚索的二次注浆工艺密切相关。监测成果表明,二次张拉能显著减少预应力损失,同时土层预应力锚索对桩锚支护结构的顶部变形起到了有效的控制作用;锚索锁定后,后续工况引起的顶部变形增加量较小时,不会对锚索锁定荷载产生较大影响。

This paper is inclined to present the results of our study on the working performance investigation and analysis with the prestressed anchor rope in the soil in deep foundation pit. As is often the case for some engineering projects, deep-excavated pile combined anchor rope has been used to retain a system protected with a deep foundation pit, as is shown in our case study, the one in Hengyang, Hunan, in which a slope combined steel tube is locally used with a soil-strengthened wall and double-enhanced pile. In addition, the concrete-enhanced wall is also used as a curtain for preventing the ground water encroachment behind the structure. Besides, since the surrounding conditions around the pit are often complicated, it is necessary to check and monitor the pulling load of the rope in the earth. It is for the above reasons, we have carefully scrutinized the horizontal displacement of the top beam in accordance with the technical data and code required. Here, we have also forwarded the design and construction of the retaining structure for the pit, with the results of inspecting and monitoring for anchor rope and horizontal displacement listed in detail. With the results gained at hand, the working performance of the earth-pre-stressed anchor rope has been analyzed in detail with necessary beneficial conclusions gained, which indicate that the failure mode of pre-stressed anchor rope in the earth is actually caused by a shear force and the interface between the grounding and the earth layer, in turn, producing the breach taking place in a way of slow destruction. The interface movement proves to be of 80% - 90 % of accumulative total displacement of anchorage when the rope is tensioned. Secondary stretch helps to reduce significantly the pre stressed loss to less than 10%. And, the pre-stressed anchor rope in the earth can also prevent the deformation effectively by monitoring the results.