Anisotropy of Consolidation Yield Stress and Comparison with Anisotropy of Elastic Wave Velocity and Tensile Strength in Sedimentary Soft Rocks

Abstract

Sedimentary soft rocks are one of the foundations of large and important constructions. Because the mechanical properties of the soft rocks control the behavior of the foundations, it is necessary to understand the consolidation characteristics of the sedimentary soft rocks. Particularly, the anisotropy of mechanical property is important, therefore, the relationship between these properties to bedding planes and the stress environment should be considered. In this study, consolidation tests were conducted in three directions using four block samples of Neogene to Quaternary sedimentary soft rocks from the western part of the Boso peninsula, central Japan: orthogonal to the bedding plane (σ₃direction) and two directions within the bedding plane defined by paleo-stresses (σ₁ and σ₂). In comparison with other fundamental physical properties, elastic wave velocity measurements and tensile strength tests were also conducted to investigate their anisotropy. The results show that the consolidation yield stresses in the three directions are almost the same or larger in the past principal stress direction than others, suggesting that they reflect the tectonic stress history experienced in the past. In addition, the anisotropic degree of consolidation yield stress is almost the same as that of tensile strength and higher than that of P-wave velocity. As the degree of anisotropy of consolidation yield stress increases, tensile strength increases negatively. Anisotropy of the internal structure due to lateral compressive stress increases with the action of lateral compressive stress, while anisotropy of the internal structure due to the sedimentation process decreases.