Journal of Geotechnical and Geoenvironmental Engineering

The effects of the initial orientation of principal stress axes and subsequent rotation of principal stresses on liquefaction susceptibility of sands were investigated. Monotonic and cyclic hollow cylinder torsional shear tests were carried out on Fraser River sand specimens consolidated to different initial principal stress orientations and subjected to principal stress rotation during loading. Cyclic loading was applied with constant amplitude cyclic deviator stress, but along stress paths that impose different magnitudes of principal stress rotation. Test results demonstrate that the cyclic resistance ratio (CRR) is influenced by both the initial orientation of principal stresses and the magnitude of stress rotation during dynamic loading. These results suggest that the degree of stress rotation influences CRR more significantly than the initial principal stress orientation. Yet, the effects of the degree of stress rotation are not considered in current liquefaction assessment practice. The only available mechanism to account for principal stress directions is the use of the $K_{\alpha }$ factor, which focuses on the initial principal stress orientation only. Irrespective of the initial inclination of the major principal stress axis, the weakest cyclic resistance was noted in tests with a principal stress rotation of $\pm 45°$. The increased susceptibility to liquefaction is possibly due to factors such as the inclination of the plane of maximum shear stress with the bedding plane, inclination of major principal stress with the bedding plane, the presence of horizontal shear stress, and the nature of the variation of shear stress on the weak bedding plane.

Previous studies have found that pile foundations will be severely damaged when subjected to faulting. However, the pile–soil interaction mechanism is still unclear due to the lack of well-documented field observations and physical model tests. In this study, six centrifuge tests were conducted to investigate the interaction of single piles and sand subjected to dip-slip faulting and to discuss some influential factors, such as fault type, pile location, uplift ratio, pile stiffness, and sand density. The responses of piles are sensitive to fault type, pile location, and uplift ratio. Piles in a reverse fault experience much larger internal forces than those in a normal fault. The fault deformation causes large internal forces on piles located within the fault zone, whereas those out of the fault zone are practically not affected. The outcropping of ruptures is a critical state for the behavior of piles both in reverse and normal faults. After outcropping, further fault movement does not cause the increment of pile bending moment, implying the maximum horizontal load is applied at the time of outcropping.

Microbial-induced calcium carbonate precipitation (MICP) is a bio-mediated technique that may be used to improve the strength and stiffness of soils. Various parameters affect the behavior of MICP-cemented sand, and their effects must be explored before upscaling the MICP treatment technique. The study presented herein investigates the shear response of three types of sand (Ottawa 20-30, Ottawa 50-70, and Nevada) sheared in drained triaxial compression under three effective confining pressures (10, 100, and 400 kPa) at four levels of cementation (untreated, light, moderate, and heavy). Measurements of shear wave velocity were used for process monitoring throughout biotreatment. Shear wave velocity was used as an index to represent the cementation levels. After shearing, the calcium carbonate content was measured directly. Treated specimens showed similar shear responses at a given cementation level, although the number of treatments and the mass of precipitated calcium carbonate varied widely. Bilinear and nonlinear failure envelopes are proposed based on the obtained results to estimate the shear strength of MICP-treated sand. The shear strength parameters are estimated based on the developed bilinear failure envelope. SEM images were used to visually track the evolution of cementation at different cement contents. The predominant crystal phase of precipitated calcium carbonate was visually identified to be calcite.

The shear strength of joints is governed by surface morphology, including roughness and interlocking conditions. Several criteria have been developed in recent decades to assess shear behavior. However, most civil engineering guidelines suggest using the Mohr-Coulomb criterion to evaluate shear strength. The Mohr-Coulomb criterion relies on a friction angle and a cohesion value determined from laboratory tests, the literature, and the engineer’s experience. Two distinct cohesion concepts can be considered: true cohesion, which is a bond between the walls of the joint, and apparent cohesion. Apparent cohesion is obtained by performing a linear regression for the experimental shear strengths obtained in the laboratory for a given normal load interval. For unbounded joints, true cohesion cannot be considered because the walls are not physically bonded. However, apparent cohesion, describing joint roughness, interlocking, and the conditions of the joint walls, can be used with the Mohr-Coulomb criterion. Civil engineering standards are cautious about the use of apparent cohesion during design, and guidelines often recommend considering a null or low value. In this article, we focus on the effects of surface morphology on apparent cohesion, to better appraise the relevance of taking apparent cohesion into account in the Mohr-Coulomb criterion. Direct shear tests were performed on four different rock joint replicas tested under low normal load conditions (0.1–1.0 MPa). The results showed that apparent cohesion increased with roughness. Results also showed that the interlocking and damage state of the joint wall surfaces play a key role in the apparent cohesion value. When the sample is damaged or poorly interlocked, apparent cohesion is significantly reduced.

Tsunamis induce excess pore water pressure gradients in coastal sediment beds. The excess pore water pressure gradient induced during tsunami loading along with the shear stress caused by the tsunami flow can cause significant sediment instability and enhanced scour. Herein, a coupled seepage-deformation model is implemented to estimate the pore water pressure response in the soil during tsunami loading. First, the mechanism of sediment instability during tsunami loading and the delay in the pore water pressure response with depth are investigated. Second, the effect of tsunami height, duration, and impermeable layer depth on the sediment instability and the depth of instability are investigated. Finally, the soil liquefaction potential is evaluated using the effective stress based definition of liquefaction and pressure head gradient viewpoint. The results show that momentary liquefaction with a high excess pore water pressure gradient can occur during a tsunami. The numerical experimentation shows that tsunami properties and impermeable layer depth can significantly affect the excess pore water pressure gradient and the depth of instability during tsunami loading.