Stiffness parameters of municipal solid waste

Abstract

This paper presents results of the deformability parameters of municipal solid waste (MSW) determined through laboratory (oedometer and triaxial tests) and in situ tests [standard penetration tests (SPT) and cone penetration tests (CPT)], as well as by a monitoring system including topographic control marks, open-tube piezometers, earth and pore pressure cells and inclinometer tubes with magnetic settlement plates and spiders. The studied landfill is located in a textile industry area, and was landfilled with some direct waste (10 %) and mostly pre-treated waste (90 %, from composting and triage). The influence of: the waste age, construction phase of the landfill and confining stress on the results of stiffness modulus, lateral waste pressure coefficient at-rest (K0) and Poisson’s ratio (ν) are presented, as well as an attempt to establish correlations to estimate MSW stiffness modulus from SPT and CPT tests. The results indicate the increases of K0 and ν with the average effective confining stresses during the first 2 years of the post-construction phase, reaching maximum values of 0.7 for K0 and 0.4 for ν, and then decreasing gradually until stabilizing at values of around 0.23–0.48 for K0 and around 0.19–0.32 for ν. The stiffness modulus values determined by different methods are consistent with each other and corroborate the fact that typical values for MSW are low. These values are between 0.4 and 2 MPa for a mean confinement stress of about 50 kPa, and tend to increase linearly with the increase of the confinement stress. The correlations established with SPT and CPT tests are of the same type as usually proposed for granular soils; however, the constant values are significantly lower than the lowest values reported for normally consolidated sandy soils.