A comparative study of the effects of particle grading and compaction effort on the strength and stiffness of earth building materials at different humidity levels

This paper presents an investigation of the mechanical properties of three different earth building materials manufactured by compacting two soils with distinct particle size distributions under two markedly different efforts. Multiple samples of each material have been equalised either inside a climatic chamber at different humidity levels or oven-dried, before being subjected to shearing inside a triaxial cell to measure the corresponding levels of strength and stiffness. Triaxial shearing has been performed under different levels of radial stress to investigate the effect of material confinement inside thick walls. Consistent with previous research, the study has indicated that strength and stiffness increase as ambient humidity reduces and degree of saturation decreases, though the actual variation of these properties strongly depends on the dry density and clay content of the material. Most importantly, particle grading has emerged as a key material parameter, whose impact on earth building has often been overlooked. Particle grading appears to influence strength and stiffness even more than compaction effort, dry density and average particle size, which are usually quoted as the most important variables for the design of earth building materials.