Q: Why is it required that there be no bridging or trampolining during liner installation at any temperature?
A: Bridging or trampolining is common at breaks in grade at most installation, particularly in cool mornings at a jobsite. If backfilled in this state, the geomembrane would be stressed and could yield or, worse yet, rupture at seams or appurtenances. It is strongly advised that one does not backfill trampolining geomembrane. Please consult EPA/600/R-93/182 document section 3.7.1 “Soil Backfilling of Geomembranes.” It describes a placement of soil backfilling that proceeds from a stable working area in a gradual progression. The soil should be pushed forward in an upward tumbling action in “fingers” with controlled slack being induced into the geomembrane. If a trampolined area is encountered, backfilling should cease until warmer temperatures are experienced and the geomembrane is in intimate contact with the underling material.