Study on Siphon Drainage Capacity of Slopes with Long-Horizontal Pipe Sections

Abstract

Siphon drainage, which is applicable in engineering as one of the effective methods to maintain slope stability, has many advantages, including no additional power requirements, simple construction, and low construction cost. However, due to topographic constraints and high farmland occupation costs, most projects inevitably use pipes with a total length of more than 100 m and horizontal sections of more than 50 m for drainage. The increase in pipe length has serious adverse effects on the siphon drainage process, limiting its drainage capacity and long-term applicability. Therefore, in slope siphon drainage, drainage efficiency and long-term effectiveness are critical factors in determining whether a particular pipe size can be used effectively for slope drainage management. This paper investigates the performance of different pipe diameters in drainage capacity, flow regime, and restarting ability under different head and pipe length combinations through theoretical analysis and extensive foot-scale model tests. It was found that a 5 mm pipe diameter, as a transitional pipe diameter between capillary and typical pipe diameter, has both capillary and gravity-dominated characteristics under different capillary and Reynolds number conditions, which can form a stable segmental plug flow while maintaining the presence of liquid film and preventing increased frictional losses along the course.