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) hasestablished a testing guideline to assess the suitability of geosynthetic or geocomposite drainelements for final landfill cover systems. The BAM guideline uses a uniform procedure fordetermining long-term water flow capacity. For this purpose, it is necessary to produce data forcreep behavior under compressive and shear stresses. The residual long-term thicknesses areextrapolated and the pressures determined that are necessary to enforce the residual thickness in ashort-term experiment. The flow capacities measured under these pressures at the various beddingconditions are defined as long-term water flow capacities. The procedure is described for threedifferent geosynthetic drain materials. Two of them use random arrays of PP strands and the thirda HDPE geonet as drain cores. The extrapolation of creep curves is permissible only when theyfollow a simple functional relation over the envisaged time period (at least 100 years). Thereforeone has to assume that creep will not trigger a stability collapse of the drain core, and that agingdoes not invoke any relevant changes in the material strength, which would alter the course of thecreep curves significantly. The assumption may be proven by the method of long-term, high-pressure creep and long-term, high-temperature shear strength testing, and by measuring antioxidantdepletion in oven-aging tests. The consideration of long-term water flow capacity, given here, issupplemented by a detailed discussion of the structural stability of the drain cores. The long-termaging behavior of the plastic drain cores and the geotextiles will be considered in the second partof the paper.