Abstract Soil–structure interaction critically governs the seismic safety of the nuclear power plant (NPP) structure, with pile foundations inducing complex soil–pile–structure interaction (SPSI). We propose a coupled stiffness matrix method–finite-element method scheme for time-domain nonlinear SPSI analysis, simulating wave propagation through nonlinear soils, nonlinear interfaces, and three-dimensional refined pile-supported NPP structure models (including equipment and coolant tanks). Code verification and model validation confirm reliability. Simulations of the pile-founded NPP structure on soil cushions reveal that nonlinear effects at the soil–structure interface significantly alter acceleration spectra and displacement responses of containment vessels and internal structures. Soil nonlinearity amplifies high-frequency components (>5 Hz), thereby increasing equipment vulnerability—a fact that requires critical attention. The reason may be that soil nonlinearity triggers more intense nonlinear behavior at the foundation–soil interface, such as gapping and sliding. Pile foundations attenuate high-frequency responses and reduce superstructure displacements. However, the presence of the superstructure amplifies pile bending moments (241% at the pile head) and shear forces (224% at the pile head). Pile diameter and pile spacing show a significant effect on the response of containment vessels and piles. This work demonstrates that omitting nonlinearities in the SPSI effect would lead to nonconservative designs, providing validated modeling strategies for coastal NPP structure resilience.
Abstract To analyze problems involving creep-driven slow-moving landslides interacting with structures and infrastructure and gain useful information for risk management, numerical modeling is the most comprehensive tool. When resorting to numerical simulations, appropriate constitutive modeling is key to capture the time-dependent behavior of geomaterials. However, a drawback of advanced constitutive models accounting for time dependency is the high number of parameters involved, which are commonly calibrated based on site-scale monitoring data, without accounting for the characteristic creep behavior of the material. This paper describes the implementation of an existing elastoviscoplastic model in a three-dimensional (3D) finite-difference software. The model, called SHELVIP (Stress Hardening Elastic Viscous Plastic), was derived from the classical theory of elastoplasticity by adding a viscoplastic component based on Perzyna’s overstress theory. After illustrating the model and the implementation procedure, the steps to tune the constitutive parameters, especially the viscoplastic ones, are described. First, the viscoplastic parameters are determined at the laboratory scale through an analytical calibration process based on laboratory creep tests. Then, tuning of some parameters at the site scale is performed, while other parameters are kept unchanged from their laboratory-scale value being representative of the intrinsic creep behavior. The final set of parameters can be used to run predictive analyses for problems of engineering relevance. The analytical calibration is exemplified with reference to triaxial creep tests on Palombini clays. Then, the implemented SHELVIP model is validated by comparing numerical, analytical, and experimental creep strains at different deviatoric stress levels. A three-dimensional numerical model of the interaction between a deep-seated landslide and an existing motorway tunnel is developed. The capability of the constitutive framework to catch the time-dependent landslide movement is demonstrated by comparing monitoring data with the corresponding numerical results. The model is then used to run predictive analyses aimed at investigating the slow-moving landslide–infrastructure evolution.
Abstract Accurate characterization of the accelerated creep stage in rock is essential for the long-term stability evaluation of deep geotechnical infrastructures, including deep-buried tunnels, high-dam foundations, and nuclear waste repositories. Traditional creep constitutive models, exemplified by the classical Nishihara model, are mostly established through a phenomenological combination of mechanical elements. These models fail to establish an intrinsic coupling relationship between energy dissipation and damage evolution within a unified thermodynamic framework, resulting in pronounced fitting deviations during the accelerated creep stage. In addition, the physical implication of some empirical parameters in these models remains ambiguous. To address the aforementioned limitations, this paper proposes an accelerated creep damage model for rock based on irreversible thermodynamics and free-energy function. Taking free-energy density as the core state variable, the model establishes a quantitative link between elastic strain energy release and internal microcrack propagation via the damage energy release rate and constructs an energy-driven, damage evolution–coupled constitutive relation. The damage-modified viscoelastic and viscoplastic rheological equations are derived, and a damage-weakening coefficient is introduced to describe the attenuation law of the equivalent viscosity coefficient during the accelerated creep stage. All parameters in the proposed model have explicit physical connotations: energy-damage coupling parameters reflect the rate of development of internal microcrack damage, rheological constitutive parameters characterize the rock’s resistance to viscous deformation, and accelerated creep characteristic parameters quantify the evolution intensity of accelerated deformation induced by damage accumulation. The proposed model is validated against triaxial step-loading creep test data of sandstone and quantitatively compared with the classical Nishihara model using multiple evaluation indicators. The results indicate that the model can fully reproduce the three-stage creep deformation law of rock, i.e., decelerating creep, steady-state creep, and accelerated creep. Under different stress levels, the correlation coefficients ( R 2 ) between fitted curves and experimental data are all above 0.90, and the root mean square error (RMSE) of full-stage creep strain is controlled within 2.1 × 10 − 5. Specifically, for the critical accelerated creep stage, the RMSE of the proposed model is 68%–75% lower than that of the Nishihara model, and the relative fitting error is controlled within 7%. The model can also accurately capture the inflection point where the deformation rate shifts from steady growth to rapid increase. This work reveals the internal mechanism of rock creep damage evolution from the perspective of the essence of energy, and provides a more reliable theoretical tool for long-term stability prediction in deep geotechnical engineering.
