Use of multi-linear drainage geocomposites for CCP disposal units final cover

摘要

In the event that a final cover is used to close a CCP disposal area, the cover system has to meet or exceed the EPA requirements. Regarding the drainage layer component, the use of Multi-Linear Drainage Geocomposite (MLDG) permits to collect and evacuate the infiltration water. MLDG like Drain Tube have embedded corrugated perforated mini-pipes regularly spaced between two non-woven geotextile layers. They enable water to be evacuated at a higher rate than an homogeneous drainage layer (Del Greco et al., Politecnico di Torino, Italy, 2012) even if the drainage slope is zero. Because differential settlement over time is one of the main concerns for CCP Landfill and Impoundment closures, Drain Tube will drain efficiently water and limit its accumulation even if differential settlements occur thanks to its directional behavior (drainage in the direction of the mini-pipes). The effective drainage capacity of the Drain Tube geocomposite which is a function of the distance between the mini-pipes in the product, is determined using GRI GC15 and ASTM D4716 standards. After Blond et al., 2010 and as per ASTM D7931 standard recommendation, the long-term drainage capacity of tubular drainage geocomposites is not affected by creep in compression nor geotextile intrusion when confined in soil. These two reduction factors RF_(CR) and RF_(IN) must be taken equal to 1.0 in the design of the drainage layer with a MLDG such a Drain Tube. This leads to a cost reduction and a higher factor of safety for the drainage layer.