Landfill lining stability and integrity: the role of waste settlement

Design of landfills must consider stability both within and between elements of the lining system, within the waste and involving the sub-grade. However, the design must also consider the long-term integrity of the lining system. Stresses, and hence deformations, in both mineral and geosynthetic lining materials must be controlled to ensure preferential flow paths are not formed. An assessment of integrity requires knowledge of the interaction between components of the lining system and the waste body as it settles. This paper considers assessment of both global stability and local failure that could result in loss of lining integrity. Results are presented that demonstrate traditional limit equilibrium techniques cannot be used to assess local failure. Factors of safety relate to global stability failure (i.e. development of a continuous failure surface) and not local failure that can lead to loss of integrity. Numerical analysis techniques can be used to assess local instability. Example results are presented for typical landfill cell geometries. These demonstrate the mechanism of local failure and sensitivity of behaviour to waste properties. Local factors of safety are introduced to illustrate the likelihood of integrity failure due to loss of geomembrane protection.