Unlike dynamic properties of municipal solid waste (MSW), the dynamic properties of engineered fill landfill covers at MSW and other landfill sites have not been extensively investigated. The two main reasons for the dearth of research on this topic are: (i) design engineers realize that modern landfill covers are relatively thin (on the order of 1.5 m, or less), and hence, their influence on the overall landfill response is assumed to be small; and (ii) there are readily available sets of dynamic soil properties of cohesive soils that could be assigned to landfill covers soils based upon the results of index testing. However, not all landfill covers are "thin," and the readily available sets of dynamic soil properties may not be applicable for low-plasticity compacted and overconsolidated soils such as landfill covers. At many old landfills and Superfund sites, landfill cover thickness readily exceeds 5 m, and covers can be as thick as 10 to 15 m. These thicker covers may have significant influence on the overall response of landfills, and hence, careful evaluation of cover material properties is warranted. In this paper, results of in-situ nonlinear testing of landfill cover soils was used to develop modulus reduction curves. Shear strains in the cover soils ranging from 10~(-4) % to 2×10~(-2) % were induced by Vibroseis shakers. The material damping curves were estimated from modulus reduction curves by means of a nonlinear constitutive model, Masing rules, and engineering judgement. The modulus reduction and damping curves presented herein may be used for seismic design of landfill covers and other engineered fills constructed of soils of similar plasticity and with similar stiffness (i.e., shear wave velocity) and compaction characteristics.
展开▼
