注浆长度与套管类型对扩大头锚索性能的影响

扩大头锚索因具有抗拔承载力大、支护效率高等优点在岩土工程中应用广泛，而注浆段落的长度和自由段保护套管的类型将对锚索受力变形特性产生影响。为此，依托实际工程开展了锚固段注浆+PE波纹管(设计方案)、全长注浆+聚乙烯(polyethylene, PE)波纹管(实际施工常用方案)、锚固段注浆+高密度聚乙烯(high density polyethylen, HDPE)套管、全长注浆+HDPE套管等四种不同工况扩大头锚索的现场拉拔试验，对比分析了不同工况下锚索的拉拔荷载-位移(Q-s)曲线、荷载-弹性位移(Q-s_e)曲线与荷载-塑性位移(Q-s_p)曲线、自由段伸长量比例、刚度系数等受力变形特征。试验结果表明，相同注浆长度条件下，采用HDPE套管相比PE波纹管能够更好地发挥对自由段的隔离保护作用，保证自由段的变形性能；而采用相同套管类型时，注浆长度的增加会导致自由段伸长量值的减小，并会增大锚索刚度系数。在试验研究的基础上，提出现场锚索施工采用锚固段注浆+HDPE套管或全长注浆+HDPE套管的建议方案，从而保证锚索受力变形性能均达到设计预期。

Influence of Grouting Length and Casing Tube Type on the Stress and Deformation Characteristics of Underreamed Anchor

The underreamed anchor is widely used in geotechnical engineering because of its advantages of large tensile capacity and high support efficiency.And the grouting length and the type of casing tube for free anchor length will affect the stress and deformation characteristics of anchor. Therefore, field experiments of underreamed anchor under different working conditions were carried out, including fixed anchor length grouting +PE corrugated tube (design scheme), full-length grouting +PE casing tube (common scheme in actual construction), fixed anchor length grouting +HDPE casing tube, full-length grouting +HDPE casing tube. The load-displacement (Q-s) curve, load-elastic displacement (Q-se) curve, load-plastic displacement (Q-sp) curve, elongation ratio of free section and stiffness coefficient of cable under different working conditions were compared and analyzed. The test results show that compared with PE corrugated tube anchor, HDPE casing tube anchor could protect and isolate the free anchor length and ensure the deformation performance of the free anchor length under the same grouting length. When the same casing tube is used, the increase of grouting length will lead to the decrease of free anchor length elongation value, but will increase the stiffness coefficient of the underreamed anchor . On the basis of the experimental study, it is suggested that the scheme of free anchor length grouting +HDPE casing tube or full-length grouting +HDPE casing tube should be adopted in the field construction of anchor cable, so as to ensure that the stress and deformation performance of underreamed anchor meet the design expectation.