黄土地层下预应力锚索荷载传递规律的试验研究

在已有理论推导的基础上,基于现场拉拔试验,分析锚固长度、拉拔荷载及锚索体直径对预应力锚索在特定黄土地层条件下荷载传递规律的影响。分析结果表明:(1)预应力锚索的有效锚固长度以6～8m最为合理,过短不利于锚索极限承载力的充分发挥,过长则易造成锚索材料的浪费;(2)锚索轴力随拉拔荷载增大不断向锚固段远端传递且越来越小,其峰值则不断增大且向远端偏移,该现象与锚固段前端锚索体所受轴力超过其屈服极限而产生局部塑性破坏有关;(3)土体及锚固体具有明显的非均质性和非线性,使得浆体与土层间存在相对薄弱或非连续界面。当拉拔荷载级别增大至一定量值时,这些弱面上即发生锚固力跳跃分布现象;(4)在工程实践中,锚固力分布曲线的始点与锚固段端口并不完全重合,而是相对纵轴均存在不同程度的偏移,导致发挥实际锚固作用的锚固段长度往往较理论设计的偏短;(5)在黄土地层下,部分预应力锚索极限承载力随其直径增加而线性增长,增长系数约为1.1,而与锚索有效锚固长度无关。所得结果为黄土地区锚索支护工程的设计和施工提供参考依据,具有一定的理论和实用价值。

EXPERIMENTAL STUDY OF LOAD TRANSFER LAW OF PRESTRESSED CABLES UNDER LOESS STRATUM

Based on the previous theoretical analysis and the systematic analysis of field pull-out test data，the influence of anchorage length，pull-out load as well as cable diameter on the load transfer law of the prestressed cable under the specific condition of loess stratum are analyzed. The analysis results show that：(1) The most rational effective anchorage length of prestressed cable is 6–8 m. The ultimate bearing capacity of the prestressed cable can not fully be exerted when the anchoring segment is too short；and the prestressed cable is easy to be wasted under the condition that the anchoring segment is too long. (2) The axial force of cable continues to transfer the remote anchorage section getting smaller and smaller whose peak value grows and shifts to the remote with the increase of the pull-out load，which is associated with the fact that the axial force of the front anchorage segment produces local plastic damage when the pull-out load exceeds the anchor¢s ultimate tensile strengths. (3) Soil mass and anchoring body have significant heterogeneity and nonlinearity，which results in being of the relatively weak or noncontinuous interfaces between grout and soil. The distribution of the anchorage force on the weak plane discretes jump while the pull-out load increases to a certain level. (4) In engineering practice，the starting points of anchoring force distribution curves do not overlap with the port anchor absolutely but deviate from the relative vertical axis to varying degrees，which makes the actual length of anchor is usually shorter than the theoretical design length. (5) Under the loess stratum，the ultimate capacity of some prestressed cables increases linearly with their diameters increase，independent to the effective anchorage length. The growth factor is about 1.1. These conclusions with some theoretical and practical values provide a reference for the design and construction of anchor support engineering in the loess region.