Sub Horizontal Drains
Sub horizontal drains are used for drainage and land reclamation, where landslide movements occur during trench excavation work, to consolidate slopes and escarpments subjected to landsliding and in all situations where excess water determines the resistance reduction properties of the terrain. They can also be used with other drainage works or with ground consolidation and support work.
Sub horizontal drainage works by using smooth pvc plastic pipes or perforated pipes wrapped with protective geotextile fabric. Perforation is normally done with a bore diameter of 130-150 mm at a slightly inclined angle from horizontal using the dry rotary drilling method with water and/or mud flushing or rotary percussion drilling using air as the flushing medium with or without temporary casings. When drilling is complete the drainpipe is inserted and once placed the annular space around the pipe in the well bore is sealed allowing for the water to flow freely through the pipe.