Stability Assessment of Ten Large Landfill Failures

This paper presents and analyzes ten large solid waste landfills. Five are unlined or soil lined, and five are lined with one or more geosynthetic materials. The case histories are analyzed by a 3-D computer code adjusting variables (mainly interface shear strength) to arrive at a factor-of-safety (FS) equal to 1.0. A triggering mechanism, unique to each site, is then applied resulting in an FS less than 1.0. The same variables and triggering mechanisms are then used in a 2-D computer code with FS-values further decreasing by different amounts. The ratio of 3-D to 2-D factors-of-safety is called a wedge factor. Conclusions reached are as follows: (i) Interface shear strengths are the overriding considerations in varying FS-values. Accurate determination cannot be overemphasized. (ii) The triggering mechanisms were all liquid related, i.e., leachate buildup within the waste mass, wet clay beneath the geomembrane, or excessively wet foundation soil. (iii) The average wedge factor of all case histories without, then with, the triggering mechanisms is 1.24.