This paper presents a study of flow characteristics in high-lift siphon drains. A laboratory test was conducted to investigate the effects of hose diameter and flow velocity on siphon drainage. Three types of water flow were observed and analyzed. The experimental results show that the flow characteristics of siphon drainage are significantly influenced by the hose diameter. Water flows in the form of a wall pressing flow in a large diameter siphon hose (e.g., larger than 5.0 mm) under low flow velocity, which leads to discontinuous siphon drainage. However, water flows in the form of an integral slug flow in a small diameter siphon hose (e.g., smaller than 4.0 mm) under low flow velocity, which leads to continuous siphon drainage. Based on experimental observations, a thermodynamic derivation of the threshold of siphon hose diameter for continuous siphon drainage was analytically conducted. In slope engineering, a 3.6 mm polyurethane (PU) hose is recommended for siphon drainage. 从实验及理论角度阐述边坡高扬程虹吸排水容易断流造成虹吸中断的原因, 并提供解决方案, 实现虹吸排水的长期有效。 利用物理模型实验, 结合理论解析推导, 得到了高扬程虹吸排水管顶部流态特征及其与管径的关系, 解决了高扬程虹吸排水容易断流造成虹吸中断问题, 保证了虹吸排水技术在边坡治理工程中的长期有效性。 通过物理模型试验, 揭示虹吸水流经过管顶区段的三种流型特征(见图4); 利用热力学理论推导, 得到了虹吸水流经过管顶区段由贴壁流向弹状流转变的临界管径, 见公式(23)。 管中形成气液共同移动的完整弹状流是实现虹吸排水长期稳定的关键, 虹吸水流经过管顶区段由贴壁流向弹状流转变时存在临界管径。 保证边坡工程中虹吸排水长期稳定的管径以3.6 mm为宜。