High groundwater levels and lasting intense rainfall usually lead to rapid flow rates.

For high-lift drainage, exhaust devices are usually applied at the tops of the drains to prevent air accumulation (Shu and Zhang, 2005 Yang et al., 2009). Currently, most siphon applications are associated with low-lift siphons. The water lift of an on-site low-lift siphon is a great deal lower than its maximum level. As a result, we conclude that there are fundamental differences in physical conditions between high and low lift siphons. In high-lift siphon drainage, the dramatic pressure change brings intensive air precipitation. According to previous experiments (Sun et al., 2013), bubbles can be easily observed when the water-lift is higher than 5.4 m, which can be defined as high-lift siphon drainage. Thus, during siphon processes, the air dissolved in the liquid separates out and generates bubbles, as a consequence of which, air accumulates at the tops of hoses leading to interruption of the siphon process. In siphon drainage, the pressure of liquid gradually decreases with the increasing elevation over the liquid surface of the nozzle. Generally, the solubility of a gas dissolved in liquid is proportional to the pressure acting on the liquid surface (Mao, 1987). However, the management of long-term operation of siphon techniques has not been fully explored yet.ĭue to their non-persistence, siphon techniques have not yet been used widely. Associated engineering applications have also been developed (Zhang and Zhang, 1999a 1999b Yang et al., 2009 Shu and Zhang, 2005). Studies have been conducted on slope siphon drainage since the 1990s, such as those on the initial siphon forming method, the maximum height limit of siphon drainage, the maintenance of siphon and management requirements.

Currently, siphon drainage combined with electropneumatic drainage is a key method for discharging ground water in Europe, especially in France (Bertolini et al., 2005 Clark et al., 2007 Bomont, 2008 Gillarduzzi, 2008 Mrvik and Bomont, 2012). Govi ( 1989) and Cambiaghi and Schuster ( 1989) introduced a system using a siphon technique as an emergency drainage treatment for landslides. During the siphon process, flow velocity can be controlled by automatically changing water levels. Siphon drainage can be used in slope drainage for its powerful water delivery capacity.

Therefore, the study of effective drainage techniques, such as siphon drainage, is essential for engineering geology and disaster prevention. Consequently, reducing pressure is usually a main goal in achieving engineering safety. This is particularly true in the case of earth flows or earth slides where clay content plays a significant role. Positive pore pressure is the main factor governing the evolution of the entire landslide body. Most landslides are triggered or influenced by the rising of groundwater levels because of rainfall infiltration (Sassa, 2005 Sun et al., 2012 Shrestha et al., 2013).

Water syphoner