Drained response of municipal solid waste in large-scale triaxial shear testing.

A comprehensive laboratory investigation was performed on municipal solid waste (MSW) from a landfill located in northern California using a large-scale triaxial (TX) apparatus. An improved, standardized waste specimen preparation method was developed and used to prepare 27 large-scale TX specimens (d=300 mm, h=600-630 mm). The effects of waste composition, confining stress, unit weight, loading rate, and stress path on the drained stress-strain response of MSW were investigated. Waste composition has a significant effect on its stress-strain response. The commonly observed upward curvature of the stress-strain response of specimens composed of larger-sized waste materials results from the fibrous constituents (primarily paper, plastic and wood) reinforcing the waste matrix. This effect is greatest when the MSW specimen is sheared across the long axis of the fibrous particles. Due to this significant strain hardening effect and waste's in situ stress state, a limiting strain failure criterion of 5% axial strain from the K(o) field consolidation state is judged to be most appropriate. Results from this test program and data from the literature indicate that the TX compression secant friction angle of MSW varies from 34° to 44°, with 39° as a best estimate, at a confining stress of one atmosphere (assuming c=0). The friction angle decreases as confining stress increases. The friction angles measured in this testing program are representative of failure surfaces that are oriented at an angle to the predominant orientation of the long axis of the fibrous waste particles. These friction angles are higher than those obtained in direct shear tests where shearing typically occurs parallel to the orientation of the fibrous waste particles.

Evaluating effectiveness of liquefaction remediation measures for bridges

To effectively retrofit a bridge foundation sited on liquefiable soil deposits, it is necessary to determine the location and lateral extent of the soil block which should be treated by ground improcement techniques. Adequacy of a given treatment plan depends on limiting deformations to some tolerable level. Because the stability and deformation issues involved in such cases can be complex, the most sophisticated analysis methods may lie beyond the engineering budget and expertise available for smaller jobs. The current study focuses on developing simplified guidelines complexity for a typical liquefiable site. By examining the results of these analyses, preliminary conclusions have been reached regarding suitable methods of analysis, and the optimal location for ground treatment in similar cases.(AU)

Observed effects of testing conditions on the residual strength of loose, saturated sands at large strains

Undrained residual strengths (or "steady state" strengths) are useful in assessing the potential for large ground deformations in deposits of loose, saturated sands due to the strain-softening behavior of these materials in undrained loading. Extensive research over the past decade has raised numerous issues regarding the effects of various testing conditions on these strengths when measured in the laboratoey. In this paper, the authors present the results of a testing program which invetsigated the possible effects of consolidation stress level, the effective stress path during shearing, and the drainage conditions on the steady state strengths of Monterey #0 sand. The data suggests thatthe mode of deformation, or strain path during shearing, may be an important factor affecting the steady state strengths of cohesionless soils.(AU)