Long-term water flow capacity of geosynthetic drains and structural stability of their drain cores

摘要

ABSTRACT: The German Federal Institute for Materials Research and Testing (BAM) hasnestablished a testing guideline to assess the suitability of geosynthetic or geocomposite drainnelements for final landfill cover systems. The BAM guideline uses a uniform procedure forndetermining long-term water flow capacity. For this purpose, it is necessary to produce data forncreep behavior under compressive and shear stresses. The residual long-term thicknesses arenextrapolated and the pressures determined that are necessary to enforce the residual thickness in anshort-term experiment. The flow capacities measured under these pressures at the various beddingnconditions are defined as long-term water flow capacities. The procedure is described for threendifferent geosynthetic drain materials. Two of them use random arrays of PP strands and the thirdna HDPE geonet as drain cores. The extrapolation of creep curves is permissible only when theynfollow a simple functional relation over the envisaged time period (at least 100 years). Thereforenone has to assume that creep will not trigger a stability collapse of the drain core, and that agingndoes not invoke any relevant changes in the material strength, which would alter the course of thencreep curves significantly. The assumption may be proven by the method of long-term, high-npressure creep and long-term, high-temperature shear strength testing, and by measuring antioxidantndepletion in oven-aging tests. The consideration of long-term water flow capacity, given here, isnsupplemented by a detailed discussion of the structural stability of the drain cores. The long-termnaging behavior of the plastic drain cores and the geotextiles will be considered in the second partnof the paper.