砂土中扩体锚杆承载特性模型试验研究

在25个室内模型试验基础上，研究了均质砂土中竖向拉拔扩体锚杆的几何尺寸及埋深对其承载特性的影响。试验结果表明，根据深径比的不同，扩体锚杆可以分为浅埋与深埋扩体锚杆2种形式，它们在拉拔过程中均经历了土体弹性变形阶段、非扩体锚固段-土界面剪切破坏阶段、土体弹塑性变形阶段以及剪切破坏阶段，破坏特征分别表现为整体剪切破坏与局部剪切破坏。通过扩体锚杆与普通拉力型锚杆模型试验对比发现：与普通拉力型锚杆相比，扩体锚杆极限承载力、承载比与安全性均有大幅度提高。而通过增大扩体锚固段直径的方式提高扩体锚杆承载力的优势较为明显。此外，根据承载比分析，扩体锚杆存在最优扩体锚固段直径，因此，在实际工程中应寻找一个满足需要的最优扩体锚固段尺寸以取得较好的经济效益。

Model test research on bearing capacity characteristics of underreamed ground anchor in sand

The effects of size and embedment depth of underreamed ground anchor under vertical pullout on its bearing capacity characteristics were researched through 25 model tests. The test results exhibited two different modes of underreamed ground anchor depending on depth/diameter ratio, namely shallow and deep underreamed ground anchor. During pullout, the two type underreamed ground anchors experienced several phases, such as soil elastic deformation, shear failure on normal anchor section-soil interface, soil elastoplastic deformation phase and shear failure as well. And they manifested general shear failure and local shear failure. In comparison between underreamed ground anchor and normal tension-type anchor, the test results indicated that in ultimate bearing capacity, bearing capacity ratio and safety, underreamed ground anchor had substantial superiority in comparison with normal tension-type anchor. In order to improve the bearing capacity, expanding diameter of underreamed section had more obvious advantages. Furthermore, there was an optimal diameter of underreamed section by the bearing capacity ratio analysis. So it is highly recommended to seek an optimal dimension of underreamed ground anchor to get more economic benefits in practice.