Kettleman Hills Waste Landfill Slope Failure. I: Liner‐System Properties

A slope‐stability failure occurred in a 15 acre hazardous‐waste landfill (90 ft high) in which lateral displacements of up to 35 ft and vertical settlements of up to 14 ft were measured. Failure developed by sliding along interfaces within the composite, multilayered geosynthetic‐compacted clay liner system beneath the waste fill. The testing, analyses, and related studies made to determine the cause of the failure are the subject of this and a companion paper (Seed et al. 1990). The present paper presents details of a direct shear and pullout testing program undertaken to determine liner‐system‐interface shear‐strength characteristics. The interfaces between the various geosynthetics, and between these materials and the compacted clay in the liner system, are characterized by low frictional resistance, with values of interface‐friction angle as low as 8° for some combinations. The most critical interfaces were determined to be those between high‐density polyethylene (HDPE) geomembrane and geotextile, HDPE geomembrane and geonet, and HDPE geomembrane and saturated compacted clay. Representative values of interface shear‐strength parameters were obtained for use in the stability analyses described in the companion paper. The variations in measured strength parameters for the different interfaces in the liner system indicate the desirability of conducting similar test programs for proposed new facilities to establish design parameters.