Pressuremeter tests in municipal solid waste: measurement of shear stiffness

To assess the long-term integrity, and hence adequate performance, of landfill lining systems the designer must consider interaction between lining components and the waste body. Information on typical ranges of waste mechanical properties is required for use in numerical modelling of this interaction. This paper presents results from a programme of pressuremeter testing in municipal solid waste (MSW) carried out to measure shear stiffness properties. An optimum procedure has been developed using a high-pressure dilatometer in a preformed test pocket. Tests have been conducted in fresh and partially degraded MSW deposits. Values of shear moduli for small to intermediate strains have been obtained from series of unload–reload loops, and these show a strong relationship between shear modulus and depth. Stiffness increases with cavity strain owing to drained cavity expansion. A clear linear relationship has been found between shear stiffness and stress level. Results for fresh MSW from two landfill sites show close agreement. Good agreement has been found between shear stiffness values calculated for small strain in pressuremeter tests and shear stiffness values measured using the continuous surface wave method. They also compare well with the limited amount of information in the literature.