Interface resistances among soil and geosynthetic materials for final cover of a hazardous landfill in Thailand

Stability of landfill final cover is controlled mainly by interface resistances among soil and geosynthetic materials, e.g., geonet, geotextile, geomembrane and geosynthetic clay liner (GCL). The present study aims to determine the interface resistance of various materials used in construction of the final cover of a hazardous landfill in Rayong Province (Eastern part of Thailand). Soil used as waste covering layer and protective layer is a coarse sandy soil existing in the area. The friction angles obtained from direct shear tests are about 36 degrees and 42 degrees for samples with dry density of 1.5 and 1.9 t/m(3), respectively. A test setup was arranged to determine resistances among several possible interfaces existing in the final cover. Interfaces between soil and various geosynthetic materials were about only 70 - 80% of the soil friction angle. The interface resistance between geomembrane - geomembrane was the lowest (10 degrees). Fortunately, the case was not actually relevant to the actual landfill. As a consequence, the most critical sliding may occur at the interface between Geotextile - Geomembrane which provided friction angle of no more than 12 degrees. To improve this, it was decided to use the rough surface geomembrane which helped increasing the interface resistance and accommodating the slope with inclination of 1:3 (V:H). The interface resistance between geotextile - geonet obtained from the laboratory test was high due to application of confinement. In actual application, due to much less contact area (depending on aperture and opening ratio of Geonet) during installation, mechanical binders (wires) was required to temporarily fix the geonet to geotextile. Use of Geocomposite was proven to be much more convenient.