This study systematically investigated the pore structure response of kaolin and illite/smectite mixed-layer rich clay in a reconstituted state to one-dimensional (1D) compression by first performing oedometer tests on saturated clay slurries, followed by characterising their pore structure using multi-scale characterisation techniques, with the primary objective of advancing the current understanding of the microstructural mechanisms underlying the macroscopic deformation of such clays. Under 1D loading, the volume reduction observed at the macro level essentially represented the macroscopic manifestation of changes in inter-aggregate porosity at the pore scale. It was the inter-particle pores that were compressed, despite the interlayer pores remaining stable. Two distinct pore collapse mechanisms were identified: kaolin exhibited a progressive collapse of particular larger pore population in an ordered manner, whereas illite/smectite mixed-layer rich clay demonstrated overall compression of inter-aggregate pores. Accordingly, mathematical relationships between the porosity and compressibility parameters for these two soils were proposed, with the two exhibiting opposite trends arising from their distinct microstructural features. Approaching from the unique perspective of pore structure, quantitative analysis of pore orientation and morphology on the vertical and horizontal planes demonstrated some progressively increasing anisotropy during compression. These findings provide important insights into porescale mechanisms governing clay compression behaviour and enrich the limited microporosity database in soil mechanics.

This study presents an enhanced analytical approach for one-dimensional consolidation settlement by introducing a revised AJOP (arc joint via optimum parameters) equation assuming creep and strain rate effects can be neglected for both normally and overconsolidated clays. This modified equation integrates both curved and linear segments within a unified framework, enhancing accuracy across varying stress levels for normally consolidated clay. Additionally, the revised AJOP function, coupled with newly proposed equations for symmetrical and asymmetrical hysteresis, improves the modeling of overconsolidated clay. The findings from a comparative investigation using benchmark datasets and conventional methods, including the linear function (LF) and the curved function (CF), reveal that the revised AJOP method was found to reduce settlement prediction errors by up to 85% compared to LF method (particularly at shallow layers) and by 10-15% compared to the CF method (particularly at deep layers). The revised AJOP equation effectively resolves this error with a wide range of depths. Furthermore, results highlight the crucial impact of clay layering techniques on consolidation settlement predictions. Non-layered models yield lower settlement estimates compared to multilayer approaches, emphasizing the significance of the proper e-log sigma ' v relationship and layering techniques in enhancing prediction reliability.

The salt concentration of the pore solution can alter the micro-pore and particle structure of soil, thereby affecting its engineering properties. To investigate the compression characteristics of marine soil under different salt concentrations, one-dimensional compression and SEM scanning tests were conducted on marine reconstituted clay from the Yellow Sea with varying NaCl concentrations (0-5%). The effects of NaCl concentration on the compression characteristics and microstructure of marine sedimentary clay were analyzed. The results indicate that: (1) Compressibility increases up to a NaCl concentration of 2.5%, after which it declines. At 2.5% NaCl threshold concentration, the coefficient of compression, compressibility index, and consolidation coefficient reach their peak values, and the response becomes more pronounced with increasing compression pressure. During the secondary compression stage, as pore water is expelled, the impact of NaCl concentration on compressibility diminishes, while the rebound characteristics remain unaffected by NaCl concentration; (2) SEM analysis reveals that at a NaCl threshold concentration of 2.5%, the pore fractal dimension, particle fractal dimension, pore anisotropy, and particle anisotropy reach their maximum values, with the most complex shape and pores and particles aligning in the same direction. When the concentration is less than 2.5%, the soil exhibits narrow pores and rounded particles upon compression. When the concentration exceeds 2.5%, the microstructure changes in the opposite direction, confirming the particle rearrangement mechanism driven by surface contact under moderate salinity. At the threshold concentration of 2.5%, a balance between electrostatic forces and attractive forces enables stable surface-to-surface contacts, maximizing compressibility. The findings of this study provide valuable references for the foundation design of marine geotechnical engineering in specific sea areas, thereby enhancing the safety and reliability of related projects.

This paper proposes a semi-analytical solution for one-dimensional consolidation of viscoelastic unsaturated soil considering a variable permeability coefficient under exponential loading. The governing equations of excess pore air pressure (EPAP) and excess pore water pressure (EPWP) were acquired by introducing the Merchant viscoelastic model. By employing Lee's correspondence principle and the Laplace transform, the solutions for EPAP and EPWP were derived under the boundary conditions of the permeable top surface and impermeable bottom surface. Crump's method was then used to execute the inverse Laplace transform, yielding a semi-analytical solution in the time domain. Through typical examples, the dissipation of EPAP and EPWP and the change of the average degree of consolidation over time under the influence of different elastic moduli, viscoelastic coefficients, and air-to-water permeability ratios were studied. The variation of the permeability coefficient and its influence on consolidation were also analyzed. The findings of this research show that the consolidation rate of viscoelastic unsaturated soil is slower than that of elastic unsaturated soil; however, an acceleration in the consolidation of the soil is observed when changes in the permeability coefficient are considered. These discoveries enhance our comprehension of the consolidation behaviors exhibited by viscoelastic unsaturated soil, thereby enriching the knowledge base on its consolidation traits.

To investigate the one-dimensional nonlinear consolidation characteristics of a double-layer foundation under multi-stage loading, a one-dimensional nonlinear consolidation equation for the double-layer foundation was established, and numerical solutions were obtained through the finite difference method. The accuracy of the proposed solution was validated by comparing it with existing analytical solutions and finite element analysis results. Based on these comparisons, the influence of nonlinear parameters, double-layer soil properties, and loading conditions on the consolidation behavior of the double-layer foundation was further examined. The results indicated that, under multi-stage linear loading conditions, an increase in the initial permeability coefficient ratio of the double-layer foundation resulted in a significant reduction in excess pore water pressure and an acceleration of consolidation. The compression index was found to predominantly affect the later stages of consolidation, with minimal impact on the early stages. The consolidation rate was observed to increase as the permeability coefficient ratio decreased. Despite notable differences in early consolidation behavior under varying loading conditions, the findings reveal that these discrepancies are alleviated in the later stages, ultimately resulting in no significant overall difference in the time required for the foundation to achieve complete consolidation.

Soil-rock mixtures are extensively used in geotechnical engineering applications, such as embankment construction, dam engineering, and slope reinforcement, where their compressive deformation characteristics play a crucial role in influencing the stability and settlement behavior of these structures. This study investigates how variations in rock content (W), effective stress (sigma v) and fine-grained soil properties (quartz sand and silty red clay) affect the one-dimensional compression behavior of soil-rock mixtures. Key compression parameters, including the compression index C c and the secondary compression index C a, were obtained and analyzed through one-dimensional consolidation tests to assess the deformation characteristics of these mixtures. Results show that under the same effective stress (sigma v), both the C c and C a exhibit different trends with W, depending on the properties of the fine-grained soil. Soil-rock mixtures with silty red clay demonstrate more pronounced secondary consolidation effects at low rock content, whereas mixtures with quartz sand display weaker secondary consolidation overall. The significantly lower C a /C c values in the quartz sand mixtures suggest that secondary settlement is much smaller in these mixtures compared to those containing silty red clay.

A unified approach for solving the one-dimensional consolidation equation is introduced for the first time in geotechnical engineering. The one-dimensional consolidation partial differential equation is solved through a combined approach employing the complementary functions method (CFM) and Laplace transform. Using the coded program prepared in the FORTRAN, various time-varying loads are applied to different soil types to obtain the response of excess pore water pressure. The comparison demonstrated an excellent agreement, thus proving the effectiveness, applicability, and capability of the proposed approach in solving the governing canonical equations. The study's findings reveal that sand soil (high permeability) exhibits a less pronounced cyclic response under various cyclic loads compared to other soil types, whereas clay soil (low permeability) exhibits significant periodicity in its response. The investigation into the effect of soil properties on one-dimensional consolidation indicates that the dissipation of excess pore water pressure occurs relatively quickly in the case of highly permeable soils and gradually slows down as the soil permeability decreases. Due to the lower permeability of clay soil, the full dissipation of excess pore water pressure takes a much longer time compared to other soil types. Consequently, this process occurs over a more extended period in clay soil.

Since hydraulic conductivity significantly influences the compression and deformation characteristics of granular terrains, this study examines the variations in permeability (k20) of granular soils under one-dimensional compression. Two uniformly graded calcareous soil samples were tested: one with grain sizes of 9.50-12.70 mm, and another of 4.75-9.50 mm. Both samples were subjected to one-dimensional compression and constanthead permeability tests. Key soil properties affecting permeability (k20), including absorption (n), specific surface area (Ss), relative density (Dr), void ratio (e), uniformity coefficient (Cu), effective grain size (d10), and mean grain size (d50), were analyzed. The virgin compression line (VCL) of the soil samples was identified within an oedometric stress (sigma VCL) range of 4.00-14.00 MPa, where the rate of change in soil properties affecting permeability was most pronounced. As oedometric stress increased, the instantaneous absorption (ni) of the soil samples increased linearly, with a slope (alpha n) of 0.055-0.061. Similarly, the instantaneous specific surface area (Ss,i) of the soil samples increased linearly, with a slope (alpha s) of 1.229-1.388. In addition, practical equations were developed to predict the instantaneous relative density (Dr,i), instantaneous grain size distribution curve, and instantaneous permeability (k20,i) of granular soils under one-dimensional compression.

This study introduces a novel methodology to address consolidation under long-term cyclic loading. The approach simplifies analysis by neglecting cyclic load induced fluctuations and by decomposing the cyclic load into a static load and a vibratory load without net tensile or compressive tendency over time. One-dimensional vibration consolidation tests are proposed to investigate the consolidation behavior of normally consolidated soil under vibratory loading. These tests yield a normal vibration consolidation line, which visually represents the consolidation effect of a given vibratory load on normally consolidated soil under different consolidation pressures. Based on these test results, a mathematical model is developed. This model incorporates a constitutive relationship that accounts for both the decrease in effective stress due to the structural damage caused by the vibratory load and the increase in effective stress due to the compression of the soil skeleton. The governing equation, with void ratio and effective stress as dependent variables, comprehensively describes the state change process of soil elements during vibration consolidation. Numerical solutions are then employed to analyze this process in detail.

In uncoupled consolidation analysis, settlement and pore water pressure are solved independently, whereas in coupled analysis, they are solved simultaneously to ensure continuity (i.e., the volume change in soil due to compression must equal the water volume change caused by dissipation). This study investigates the coupling effects of soil deformation and pore water pressure dissipation in the back analysis of soft soil settlements. It further evaluates the suitability of both coupled and uncoupled constitutive models with different types of monitoring data, providing practical guidance for selecting consolidation models and achieving reliable long-term predictions. The one-dimensional governing equations for soft soil consolidation, incorporating prefabricated vertical drains and creep deformation, are first reviewed. A case study of a trial embankment in Ballina, New South Wales, Australia, is then used to demonstrate the impact of coupling effects and monitoring data on settlement predictions. The results show that considering coupling effects not only improves long-term settlement predictions but also reduces uncertainties in the updated soil parameters, especially when both settlement and pore water pressure data are used.