The reinforcing action of soil nails is governed by its interaction with the surrounding soil generally investigated in terms of interface friction. The reported literature depicts that increase in interface friction enhances the reinforcing action of a soil nail. Thus, with the aim of utilizing additional interface friction from internal surface of a hollow pipe and bearing resistance from helical plates attached to it, the present work investigates the pullout behavior of newly developed open-ended pipe helical soil nails. The novel open-ended pipe helical soil nails are installed and subjected to pullout force in a test tank filled with frictional soil using installation/pullout machine. The present study also examined the effect of varying soil nail diameter, number of helices and phenomenon of soil plugging on pullout capacity. Additionally, torsional and axial strains developed during pullout are also observed. The installation torque and pullout capacity are correlated using a dimensionless factor called as ‘Torque factor (Kt)’ with values ranging from 27 to 55 m−1 in compression and 28.12–53.3 m−1 in tension. A theoretical torque model for open-ended helical soil nails is also developed and is verified by the laboratory test results. The test results indicate that soil plug contributes about 11.5% of the total mobilized skin friction during pullout. The pullout capacity increases with increase in the number of helices and nail shaft diameter. However, soil plug length is independent of number of helices. Besides, higher torsional and axial strains are found for helical nails with smaller diameter.

中文翻译：

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新型开口管螺旋土钉在摩擦土中的水平拔出性能

土钉的加固作用受其与周围土壤的相互作用控制，通常根据界面摩擦进行研究。报道的文献描述了界面摩擦的增加增强了土钉的加固作用。因此，为了利用空心管内表面的额外界面摩擦和附着在其上的螺旋板的轴承阻力，本工作研究了新开发的开口管螺旋土钉的拔出行为。使用安装/拔出机将新型开口管螺旋土钉安装在充满摩擦土的试验罐中并承受拔出力。本研究还研究了不同的土钉直径、螺旋数和土壤堵塞现象对拔出能力的影响。此外，还观察到在拔出过程中产生的扭转和轴向应变。安装扭矩和拉出能力使用称为“扭矩系数 (Kt)”的无量纲系数相关联，压缩范围为 27 到 55 m-1，拉伸范围为 28.12–53.3 m-1。还开发了开口螺旋土钉的理论扭矩模型，并通过实验室测试结果进行了验证。测试结果表明，在拔出过程中，土塞贡献了总动员皮肤摩擦的 11.5%。拔出能力随着螺旋数和钉轴直径的增加而增加。然而，土塞长度与螺旋数无关。此外，直径较小的螺旋钉会产生更高的扭转和轴向应变。安装扭矩和拉出能力使用称为“扭矩系数 (Kt)”的无量纲系数相关联，压缩范围为 27 到 55 m-1，拉伸范围为 28.12–53.3 m-1。还开发了开口螺旋土钉的理论扭矩模型，并通过实验室测试结果进行了验证。测试结果表明，在拔出过程中，土塞贡献了总动员皮肤摩擦的 11.5%。拔出能力随着螺旋数和钉轴直径的增加而增加。然而，土塞长度与螺旋数无关。此外，直径较小的螺旋钉会产生更高的扭转和轴向应变。安装扭矩和拉出能力使用称为“扭矩系数 (Kt)”的无量纲系数相关联，压缩范围为 27 到 55 m-1，拉伸范围为 28.12–53.3 m-1。还开发了开口螺旋土钉的理论扭矩模型，并通过实验室测试结果进行了验证。测试结果表明，在拔出过程中，土塞贡献了总动员皮肤摩擦的 11.5%。拔出能力随着螺旋数和钉轴直径的增加而增加。然而，土塞长度与螺旋数无关。此外，直径较小的螺旋钉会产生更高的扭转和轴向应变。