This paper presents the experimental investigation carried out for evaluation of the rheological behaviours of Hangzhou soft clay, and proposes a three-dimensional elastic viscoplastic model to describe the rheological characteristics under triaxial condition. Firstly, the time-dependent behaviours of Hangzhou soft clay, such as creep and strain rate effects, were observed and discussed based on the analysis of rheological tests. Subsequently, a constitutive model was formulated under the framework of Perzyna’s overstress theory and incorporates other developments, including: 1) A smooth and continuous egg-shaped yield surface, whose shape can change from an ellipse to a teardrop shape, thus providing greater flexibility for better modelling; 2) An equivalent time concept, which enables the model to describe the time-dependent behaviours under different loading paths. By varying the shape parameter, the newly established model can be degenerated into modified Cam-clay (MCC) model or Yin-Graham elastic viscoplastic model. Finally, the model was solved numerically using the fourth-order convergent iterative method combined with the Runge-Kutta method. Comparison of simulation results and experimental data shows that the newly proposed model has an ability to predict creep characteristics and strain rate effects of soft clay.

To mitigate land occupation and environmental contamination from stockpiled engineering waste slurries (EWS) in coastal areas—while advancing low-carbon and circular economy goals—a novel composite flocculant (FCC) was developed and optimized via the White Shark Optimization (WSO)–support vector machine (SVM) hybrid algorithm to enhance EDS dewatering efficiency. Its mechanism was systematically elucidated using settling column tests, zeta potential measurements, and multi-scale microscopic characterizations (XRD, XRF, SEM, EDS, and MIP), complemented by sensitivity analysis of water type, temperature, and soil texture on flocculation-sedimentation behavior. Settling tests confirmed FCC—formulated with calcium carbide residue (CCR, an industrial by-product) and cationic polyacrylamide (CPAM)—exhibits an optimal mass ratio of 0.149:0.051 via WSO–SVM optimization. At the optimal FCC dosage of 0.2%, the settling rate ( δ) reaches 3.611 × 10 ⁻³ mm/s, representing a 10.67% and 8.80% increase compared to CPAM and CCR alone, respectively. Increasing temperature from 10 to 30 °C enhances δ by approximately 15.6%. Benefiting from synergistic electrostatic neutralization and adsorption bridging, FCC reduces the absolute zeta potential of EWS more effectively than single-component (CCR/CPAM) or untreated EWS. No new mineral phases form, but FCC enriches atomic concentrations of C, O, Ca, Al, and Fe, loosens EWS microstructure, and facilitates formation of coarser particles and pores. Dewatering efficiency follows deionized water > tap water > seawater (inhibited by high ionic content), with elevated temperature enhancing performance via improved molecular mobility. For EWS, sedimentation velocity, dewatering rate, and post-flocculation moisture content are strongly correlated with median particle size ( D ₅₀ ), providing guidance for engineering application.

Purpose: The purpose of this paper is to suggest an implicit integration method for updating the constitutive relationships in the newly proposed anisotropic egg-shaped elastoplastic (AESE) model and to apply it in ABAQUS. Design/methodology/approach: The implicit integration algorithm based on the Newton–Raphson method and the closest point projection scheme containing an elastic predictor and plastic corrector are implemented in the AESE model. Then, the integration code for this model is incorporated into the commercial finite element software ABAQUS through the user material subroutine (UMAT) interface to simulate undrained monotonic triaxial tests for various saturated soft clays under different consolidation conditions. Findings: The comparison between the simulated results from ABAQUS and the experimental results demonstrates the satisfactory performance of this implicit integration algorithm in terms of effectiveness and robustness and the ability of the proposed model to predict the characteristics of soft clay. Research limitations/implications: The rotational hardening rule in the AESE model together with the implicit integration algorithm cannot be considered. Originality/value: The singularity problem existing in most elastoplastic models is eliminated by the closed, smooth and flexible anisotropic egg-shaped yield surface form in the AESE model. In addition, this notion leads to an efficient implicit integration algorithm for updating the highly nonlinear constitutive equations for unsaturated soft clay.