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Cohesive soils in nature are created under anisotropic stress and have various stress histories. Embankments generate greater vertical loads underground. Moreover, associated excavation activities can exacerbate the extensional stress state. This study investigated the effects of induced anisotropy on the shear modulus in saturated and unsaturated cohesive soils. A triaxial testing apparatus, equipped with local small strain (LSS) measurement devices and bender elements (BEs), was used to measure the small strain shear modulus. Two series of tests were conducted: (1) LSS and BE tests used specimens normally consolidated under a constant mean effective stress of p' = 300 kPa or net mean stress p net = 300 kPa with different stress ratios to investigate the effects of anisotropic consolidation. The values of the applied stress ratios, represented as K = σ ' h / σ ' v for the saturated soil and K net = (σ h – u a)/(σ v – u a) for the unsaturated soil, were 0.35, 0.43, 0.6, 0.8, 1.0, 1.5, 2.0, 3.0, and 3.5. (2) BE tests used specimens consolidated under various mean effective stresses in the order of p' = 50, 100, 200, 300, 400, 500, and 600 kPa, and swollen in reverse order under K of 0.35, 0.43, 0.6, and 1.0, to elucidate p' and the effects of the overconsolidation ratio (OCR). The results demonstrated that K -consolidation under constant p' produces large differences in initial shear modulus G 0 in saturated cohesive soil, but K net produces only slight differences in unsaturated cohesive soil because of the influence of strong matric suction. Finally, G 0 was normalized successfully considering the effects of void ratio e , K , and OCR. [ABSTRACT FROM AUTHOR]

Grounds subjected to cyclic loading, either continuous or fragmentary, widely exist in natural deposits and at reclaimed sites, e.g., induced by traffic loads, earthquakes, and wave-induced loading environments. Assessing the ground deformation under cyclic loading conditions is necessary for proper design and maintenance planning for traffic services. Accordingly, a testing program, in which vertical, horizontal, and shear stresses are automatically controlled, were newly developed in this study to reproduce the actual cyclic traffic load conditions using a hollow-cylindrical torsional shear apparatus. Estimations based on the results obtained from cyclic triaxial stress conditions were seen to underestimate the ground settlement compared to actual stresses, with combined vertical, horizontal, and shear stresses. Two kinds of vertical strain arose after a certain number of cycles: incremental collapse, in which unstable deformation (failure) is caused, and plastic creep, in which deformation continues to accumulate with the dampened rate (per cycle). The number of cycles of combined vertical, horizontal, and shear stresses necessary to reach a certain vertical strain increased linearly on a logarithmic scale when the magnitude of loading decreased. Moreover, the relationship between vertical strain and excess pore water pressure presented the same trend independent of the magnitude of loading. Practical uses of the obtained results were proposed and discussed. [ABSTRACT FROM AUTHOR]

This paper presents the effects of inherent anisotropy on the shear strength and shear modulus of both saturated and unsaturated sands. Several triaxial compression tests were performed using Toyoura sand with different contents of mica: 0%, 1%, 2.5%, 5%, and 10%. Specimens with various deposition angles α were prepared using the air pluviation (AP) and dry vibration (DV) methods. The shear strength properties were measured by conventional triaxial tests, whereas the small strain stiffness was measured by both local small strain (LSS) tests and bender element (BE) tests. The orientation of the sand particles was assessed based on two-dimensional optical microscopic measurements and mathematical estimation. The results showed that an increase in the mica content brought about a decrease in the degree of anisotropy of the shear strength because of mica particle breakage. However, the degree of anisotropy of the shear modulus became higher with a 0%–10% increase in the mica content. The shear modulus of the unsaturated sand had a slightly higher degree of anisotropy than that of the saturated sand. In addition, the degree of anisotropy of the shear modulus was assessed based on the average orientation angle θ of the sand particles. [ABSTRACT FROM AUTHOR]

The strain rate during shearing has been shown in experimental studies to strongly affect the mechanical behaviour of soil. For saturated soil, sufficient knowledge has been obtained to achieve equilibrium conditions for the pore water pressure. Nevertheless, little is known about unsaturated soil. Therefore, this study used a hollow cylindrical torsional shear apparatus to investigate the rate dependence on the deformation and strength properties of unsaturated soil. First, unsaturated specimens were anisotropically consolidated with different directions of major principal stress to assess the rate dependence of the anisotropic behaviour. Then, the shear stress was removed to produce an isotropic stress state. Shearing was applied using the specimens to evaluate the strain rate effects on the mechanical properties of unsaturated cohesive soil. The results indicate that the secant shear modulus increased with the strain rate in both constant suction (CS) and constant water content (CW) conditions. The shear strength did not change with the strain rate under a CW condition, but it decreased with the strain rate under a CS condition. [ABSTRACT FROM AUTHOR]

Liquefaction resistance is known to increase concomitantly with the increase in time after construction or sedimentation. Nevertheless, the mechanisms of its aging effect on liquefaction have not been completely elucidated. To clarify the mechanisms of aging in sandy soils, the liquefaction resistance (CRR), initial and secant shear moduli (G 0 and G sec), and laboratory penetration resistance of long-term consolidated sand specimens were examined using cyclic undrained triaxial tests, local small strain (LSS) tests equipped with bender elements (BEs), and penetration index tests, respectively. Based on the existing reports, the CRR was inferred from G 0 , G sec , and the laboratory penetration resistance. In the case of Toyoura sand of D r = 40%, the CRR increased by about 14% with a 360-day consolidated specimen in the cyclic undrained triaxial tests. However, increases in the CRR evaluated from G 0 and the laboratory penetration resistance were nothing and only 2%, respectively. G sec started to degrade at greater shear strain in the long-term consolidated specimens. An increase in the CRR, evaluated from the G sec of 0.01% shear strain, had a much better agreement with that obtained from the cyclic undrained triaxial tests. [ABSTRACT FROM AUTHOR]