Evaluation of Critical Parameters to Improve Slope Drainage System

Table 6

Recommendation between study, European standard, and DID manual.

Parameters	Study	European standard (2005)	DID manual (2009)
Angle of drain installed	5°	None	0.06°
Pipe envelope	Geotextile	Geotextile with at least 5 mm thickness. Comply with ISO 9863, 9864, and 12956 in terms of mass per unit area, pore size index, and wettability	None
Drainage envelope	Geotextile and granular filter material	None	Granular filter material