The behavior of soft soils distributed in coastal areas usually exhibits obvious time-dependent behavior after loading. To reasonably describe the stress-strain relationship of soft soils, this paper establishes a viscoelastic-viscoplastic small-strain constitutive model based on the component model and the hardening soil model with small-strain stiffness (HSS model). First, the Perzyna's viscoplastic flow rule and the modified Hardin-Drnevich model are introduced to derive a one-dimensional incremental Nishihara constitutive equation. Next, the flexibility coefficient matrix is utilized to extend the one-dimensional model to three-dimensional conditions. Then, by combining the HSS elastoplastic theory with the component model, the viscoelastic-viscoplastic small-strain constitutive model is subsequently established. To implement the proposed model for numerical analysis, the corresponding UMAT subroutine is developed using Fortran. After comparing the results of numerical simulations with those of existing literature, the reliability of the constitutive model and the program written in this paper is verified. Finally, numerical examples are designed to further analyze the effects of small-strain parameters and viscoelastic-viscoplastic parameters on the time-dependent behavior of soft soils.

The September 19, 2017 earthquake (Mw = 7.1) struck M & eacute;xico between the states of Puebla and Morelos. The ground motion damaged buildings near the epicenter and in Mexico City, with 44 collapsed buildings and many more experiencing some level of damage. The study gathers and statistically analyzes all available information, identifying characteristics in the plan and elevation of the damaged structures. The analysis identified structural issues typically associated with damage, such as buildings with soft or flexible ground floors and corner buildings supported by reinforced concrete frames. Corner buildings often have infill walls on two sides adjacent to neighboring properties, which, when connected to columns, cause significant torsional effects. The corner effect, combined with other structural pathologies such as soft-story, irregular building shapes, and seismic amplification effects in some city regions, significantly contributed to the damage and building collapses presented during the earthquake. The results, in addition to showing damage statistics for buildings located in a corner with infill walls, showed that the facade walls in the corner provide very little lateral stiffness comparatively to the stiffness of the perimeter walls situated on the other two sides of the building, which causes significant torsion in the building. The study also revealed that corner buildings with infill walls next to low-rise buildings were significantly more at risk than those surrounded by buildings of similar heights. A non-linear analysis of a case study showed that the observed earthquake damages in corner buildings were indeed expected, given the building's seismic demands obtained with the numerical model.

Whole-life geotechnical design accounts for the evolution of geotechnical properties due to the actions imparted on the infrastructure during the design life to improve design outcomes. In fine-grained soils, geotechnical properties evolve as a result of cyclic softening from excess pore pressure generation under undrained cyclic loading, and hardening during subsequent dissipation. Traditionally geotechnical design has focused on reduced strength and stiffness from softening, overlooking beneficial effects of hardening leading to increases in strength and stiffness. This paper presents a surrogate model that can capture the evolution of geotechnical properties of normally and lightly over consolidated clays through episodes of undrained pre-failure cyclic loading with intervening consolidation, validated against laboratory element test results. The surrogate model is shown to capture the essential elements of the whole-life soil-structure interaction, which include: (i) the excess pore pressure generated during undrained cyclic loading and the associated soil softening; (ii) the reduction in void ratio caused by the dissipation of excess pore pressured during the consolidation process; and (iii) the evolution of undrained shear strength and stiffness through these processes. The surrogate model allows rapid estimation of evolving soil properties in design, enabling automated optimization of geotechnical design calculations (such as required size of foundations or anchors), and use in probabilistic analyses such as Monte Carlo approaches, to quantify the influence of uncertainty in loading history and geotechnical parameters on system reliability.

Electroosmosis and surcharge preloading represent two effective soil consolidation methodologies. Their combined application has been proven to be effective in shortening the consolidation period and mitigating the degradation of electroosmotic consolidation performance due to crack generation. In this study, an axisymmetric free-strain consolidation analytical model incorporating a continuous drainage top boundary was established. A semi-analytical solution was then derived utilizing Laplace-Hankel transform and boundary condition homogenization. The validity of the proposed solution was confirmed by comparing it with three cases documented in the existing literature. Additionally, a comparison with indoor model box test results demonstrated the rationality of setting the top boundary as a continuous drainage boundary. Parameter analysis revealed several key insights: firstly, under the free strain assumption, the spatiotemporal distribution of excess pore water pressure aptly captured the coupled effects of the radial electric field. Secondly, the combination of electro-osmosis and preloading technology significantly improved consolidation efficiency, with this effect becoming more pronounced as the applied voltage increased. Lastly, the general solution based on the continuous drainage boundary proved to be suitable for addressing the consolidation of soft soils enhanced by vertical drainage, applicable to real foundation consolidation problems with top boundaries exhibiting different permeabilities.

This study characterises the effects of naturally varying organic content on the compression and shear behaviour of a marine silty-clay from the Netherlands. Index properties and mechanical properties are determined through laboratory tests, including oedometer and multistage loading-unloading triaxial stress paths. The results indicate a significant impact of the organic content on the compression response, with both the loading and reloading indexes increasing as the loss on ignition increases from 3% to 7%. Additionally, the study suggests a directional response of the compression behaviour, with the loading index increasing with the stress ratio. The influence of the organic content on shear strength appears to be less significant. No brittle response is observed during shearing, and a similar ultimate stress ratio is attained by all samples. However, a unique critical state line can only be identified for samples with similar organic content, as its intercept and slope are found to increase with increasing organic content. The experimental results from stress paths at constant stress ratio reveal an anisotropic prefailure plastic deformation mode, which depends on the previous stress history and loading direction. This suggests that the stress-dilatancy relationship cannot be formulated as a unique function of the stress ratio. The high-quality experimental data presented in the study enlarge the database on soft organic soils in view of the development of advanced constitutive models.

Prefabricated horizontal drains and vacuum preloading have advantages in the consolidation of ultra-soft dredged sludge and soils for maintenance dredging, reclamation, and ground improvement in coastal regions. While laboratory tests and field trial projects have been reported, a convenient analysis and design method is still unavailable. This study proposes a new simple method for the settlement analysis of soft soils considering horizontal drains, vacuum preloading, creep, and large-strain effects. A unified equation is constructed to account for various layouts of horizontal drains in consolidation. A new explicit method is developed to consider the large-strain deformation with the nonlinear evolution of permeability and compressibility of ultra-soft soils under vacuum preloading. The viscous compression is taken into account using a simplified Hypothesis B method. The proposed solution also facilitates convenient consideration of multiple layers of soils and drains subjected to staged loading. The proposed method is examined by a series of physical model tests with different horizontal drain dimensions. Finally, the method is applied in the analysis of two well-documented field cases in Hong Kong and Japan, which confirms its effectiveness and accuracy.

The paper is dedicated to developing a comprehensive analysis method of the criteria for defining the compressible thickness critical for estimating long-term settlements in buildings and structures situated on soft soils, focusing on their creep behavior. This study introduces an engineering method grounded on the criterion of soil's undrained condition within the mass, considering both elastic and residual deformations through equivalent creep deformations. Unlike previous methodologies, the proposed method facilitates the assessment of long-term settlements by incorporating creep effects over time, employing undrained shear strength for both normally consolidated and overconsolidated soils. The method enables settlement calculations based on static-sounding data, enhancing predictions' accuracy and reliability. This research endeavors to broaden the application of numerical and analytical calculations in real-world practices, employing elastoviscoplastic soil models to design structures on weak foundations.