In this paper, a new approach for rotational hardening in elastic-plasticity is formulated. After discussing the standard yield criteria employed for geomaterials and the rotational hardening models proposed in the past, the authors introduce the concept of pure rotational hardening, that is a rigid rotation of the yield surface not implying any distortion of it. In the second part of the paper, a new approach for rotational hardening, based on Householder transformations, is proposed. The method, that allows to reflect vectors with respect to a given hyper-plane, is briefly described since not usually employed in geomechanics. Moreover, the authors clarify that any yield surface or plastic potential rotation, not being a rolling, is a transformation keeping unaltered first and second invariants, but not the third. As a consequence, when rotational hardening is introduced, the use of the third mixed invariant, for defining in the deviatoric plane the yield surface shape, is not appropriate. Finally, the application of the proposed approach in the formulation of anisotropic elastic-plastic strain hardening constitutive models is briefly discussed for the classes of uncoupled and hybrid yield criteria that include a dependence of the yield surface on Lode angle.

The sharp morphological features of lunar dust particles generate significant elastic-plastic contact forces and deformations upon contact with material surfaces, which considerably affect the mechanical properties of lunar dust particles, including their contact, collision, adhesion, transport, and wear characteristics. Despite these severe effects, valid models considering the contact characteristics of typical sharp-featured lunar dust particles are currently lacking. This study proposes an elastic-plastic contact model for nonrotationally symmetric lunar dust particles showing typical sharp features. Detailed derivations of the expressions for various physical responses observed when lunar dust particles establish normal contacts with elastic and elastic-plastic half-spaces under adhesive conditions are also provided. These include derivations for elastic forces, elastic-plastic forces, contact areas, pull-off forces, residual displacements, and plastic deformation areas. Furthermore, the tangential pull-off force during the tangential loading of lunar dust particles is derived, and the tangential contact characteristics are explored. Comparisons of the results of the proposed model with those of previous experiments reveal that the proposed model shows errors of only 6.06 % and 1.03 % in the maximum indentation depth and residual displacement, respectively. These errors are substantially lower than those of conventional spherical models (60.30 % and 60.13 %, respectively), confirming the superior accuracy of the proposed model. Furthermore, the discrete element method is employed to analyze the effects of normal and tangential contacts, dynamic characteristics, and plastic deformations on the considered lunar dust particles. The results are then compared with those of existing contact models. They reveal that maximum elastic-plastic forces under normal contact conditions are positively correlated with the initial velocity but negatively correlated with the lateral angle. Furthermore, the tangential pull-off force is positively correlated with the normal force and surface energy. In addition, the contact duration of lunar dust particles is positively correlated with their initial velocities, while the residual displacement is negatively correlation. For instance, as the initial velocity increases from 10 to 50 m/s, the maximum elastic-plastic force increases from 37.64 to 321.72 mN. Comparisons of the proposed model with other contact models reveal that the maximum elastic-plastic force of the elastic-plastic triangular pyramid model is only 14.93 % that of the cylindrical model, 34.23 % that of the spherical model, and 76.27 % that of the conical model, indicating significant reductions in the maximum elastic-plastic force owing to the plastic deformations of particles with typical sharp features. Overall, the results of this study offer crucial insights into the mechanical characteristics of nonspherical lunar dust particles under various contact conditions, such as elastic-plastic and adhesive contacts, and can guide in situ resource utilization on the lunar surface and for craft landings.

The advantages of constitutive models in energy-conservation frameworks have been widely addressed in the literature. A key component is choosing an appropriate energy potential to derive the hyperelastic constitutive equations. This article investigates the advantages and limitations of different energy potentials found in the literature based on mathematical conditions to guarantee numerical stability, such as the desired order of homogeneity, positive and non-singular stiffness within the application range, and equivalent Poisson's ratio from a constitutive modelling standpoint. Potentials meeting the aforementioned criteria are employed to simulate the response envelopes of Karlsruhe fine sand (KFS). Moreover, the performance of the potentials, in conjunction with plasticity theories, is examined. To achieve this, the hyperelastic constitutive equations have been coupled with the bounding surface plasticity model of Dafalias and Manzari to reproduce the soil response in a hyperelastic-plastic frame. Finally, one of the potentials is modified, whereas recommendations for incorporating other appropriate free energy functions into different soil constitutive models are presented. Furthermore, 100 closed elastic strain cycles have been simulated with the bounding surface plasticity model of Dafalias and Manzari considering the original hypoelastic stiffness and hyperelastic-plastic constitutive equations. Using the hypoelastic framework in the simulation led to stress accumulation after 100 closed elastic strain loops, while a reversible response was predicted using the hyperelastic stiffness tensor.

The rotational-translational loess landslides are widely distributed in northwest China, usually posing threats to the surrounding residents and infrastructure. These loess landslides are characterized by the formation of multiple slip surfaces during the run-out process, and the mechanisms of this phenomenon in loess landslides have not been sufficiently investigated. Therefore, in this paper, we integrated the elastic-plastic strain softening constitutive law into the original DualSPHysics code to extend its application in simulating rotational-translational loess landslides. Two benchmark cases are studied to validate the model, the failure process of a cohesive soil slope without strain softening and that of a sensitive clay slope with strain softening. The results illustrate that our model can effectively predict large deformation. Then, the run-out process of the Caijiapo landslide in northwest China is analyzed by the modified model to investigate its failure mechanism. The results illustrate that the failure pattern of the Caijiapo loess landslide is very different from the typical retrogressive failure of clay landslides. The main slip surface of the Caijiapo landslide is controlled by the pre-existing structural plane. The second and third slip surfaces of this landslide are formed inside the sliding mass due to stress redistribution during the run-out process. Three scarps are formed in the landslide deposit because of the formation of multiple slip surfaces. This deposition morphology can be well reproduced by the SPH model taking strain softening into account, while the results using an SPH model without considering strain softening cannot capture this essential deformation characteristic.

Ice cementation and ice-substrate adfreeze force are the primary contributors to the high bearing capacity of pile foundations in cold regions and the stability of frozen walls in areas subjected to artificial freezing. Given the significant temperature sensitivity of ice's shear rheology, engineering structures in ice or ice-rich soils continue to deform even under constant external loads. A thorough understanding of shear creep and the long-term adfreeze force at the ice-substrate interface is essential for predicting the continuous deformation of these structures. However, research into the shear creep behavior at frozen interfaces has historically been constrained by the precision of temperature control in experimental settings and the complexity of load paths in shear testing devices. In this study, a temperature- and stress-control device for interface shear creep is assembled firstly, and multilevel loading-unloading creep tests on steel pipes embedded in layered frozen ice were conducted. Through the decoupling of deformation progression, the viscoelastic and viscoplastic shear behaviors at the steel-ice interface under various temperatures and shear stresses were characterized, the principle of sustainable interfacial shear creep along with its underlying physical mechanism were proposed. Subsequently, with the aid of a modified nonlinear Burger model, various interfacial shear creep parameters were derived. Results reveal that the interfacial generalized shear modulus continuously improves but with a gradually weakening degree until a point of accelerating creep is reached. Additionally, the long-term adfreeze force is found to be less than half of the short-term strength, which significantly decreases as the temperature approaches the water phase transition zone. Interestingly, the stress exponent associated with the interfacial steady creep rate is considerably smaller than that predicted by Glen's law. This research provides a theoretical basis instrumental in the engineering design in cold regions and those structures employing artificial freezing techniques.

In this paper, the tunnelling-induced deformation in anisotropic stiff soils is analysed using FE modelling. The influence of material description is investigated rather than an advanced simulation of the tunnelling method. A new hyperelastic-plastic model is proposed to describe the anisotropic mechanical behaviour of stiff highly overconsolidated soil. This model can reproduce the superposition of variable stress-induced anisotropy and constant inherent cross-anisotropy of the small strain stiffness. Additionally, a Brick-type framework accounts for the strain degradation of stiffness. Formulation of the novel model is presented. The tunnelling-induced deformation is first investigated in plane strain conditions for a simple boundary value problem of homogeneous ground. The influence of initial stress anisotropy and inherent cross-anisotropy is inspected. Later, the results of 2D simulations are compared with the analogous results of 3D simulations considering different excavated length of the tunnel sections. The tunnelling process is reproduced by introduction of a supported excavation and a lining contraction stage in undrained conditions. Finally, the tunnelling case study at St James Park is back analysed using the proposed material model in plane strain conditions. The obtained calculation results are compared with the field measurements and discussed.

Reservoir geologic fluid-bearing granular materials are characterized by multiscale nonuniformity and coupled multiphysical mechanisms, for which conventional poroelastic theory cannot accurately portray wave dispersion and attenuation characteristics. To design a suitable dielectric wave propagation model to characterize the dispersion and attenuation laws of dynamic waves in geologic reservoirs, first, the branching functions of frequency-dependent dynamic permeability and dynamic tortuosity are derived by considering the effects of the geometry and fractal structure of fluid-bearing granular materials on the high-frequency properties of permeability and tortuosity. Second, the stress-strain relationship of the fluid-particle system is redrawn by the viscoelastic-plastic constitutive relation, and the dynamic wave propagation model of fluid-containing granular materials at a unified frequency is constructed by an integrated dissipation mechanism including frictional dissipation, internal dissipation, and plastic energy dissipation-wave propagation model based on viscoelasticplastic constitutive relation and dynamic permeability (WVPDP model). Finally, the reliability of the WVPDP model is verified by carrying out wave velocity tests on saturated dolomite and sandstone, and the effects of different parameters on the wave velocity dispersion amplitude and attenuation peak are analysed. The results show that the WVPDP model can accurately characterize the dispersion and attenuation of dynamic waves in granular media under uniform high and low frequencies and can invoke different dissipation mechanisms at different excitation frequency intervals, which is shown by the fact that internal dissipation and the plastic mechanism play the main role in the low-frequency interval, and frictional dissipation gradually replaces internal dissipation and plastic dissipation to become the main dissipation mechanism with increasing excitation frequency. Parameters such as fluid viscosity, reference angular frequency and reference quality can have different effects on the dispersion amplitude and transition band range of the fast P-wave and S-wave, the two mechanical response mechanisms in the medium of fluid-containing granular materials.

In order to optimize the efficiency and safety of gas hydrate extraction, it is essential to develop a credible constitutive model for sands containing hydrates. A model incorporating both cementation and damage was constructed to describe the behavior of hydrate-bearing cemented sand. This model is based on the critical state theory and builds upon previous studies. The damage factor Ds is incorporated to consider soil degradation and the reduction in hydrate cementation, as described by plastic shear strain. A computer program was developed to simulate the mechanisms of cementation and damage evolution, as well as the stress-strain curves of hydrate-bearing cemented sand. The results indicate that the model replicates the mechanical behavior of soil cementation and soil deterioration caused by impairment well. By comparing the theoretical curves with the experimental data, the compliance of the model was calculated to be more than 90 percent. The new state-dependent elasto-plastic constitutive model based on cementation and damage of hydrate-bearing cemented sand could provide vital guidance for the construction of deep-buried tunnels, extraction of hydrocarbon compounds, and development of resources.

With the widespread application of large- quasi-rectangular pipe-jacking tunnels in urban road traffic engineering in China, higher requirements have been put forward to control the influence of their construction on the surrounding environment. To scientifically evaluate the stability of large- quasi-rectangular pipe-jacking tunnels under-passing existing box culverts, we proposed a novel viscoelastic-plastic model coupling Biot consolidation with non-stationary parameter shear creep (NPSCBCVPM) to fully characterize the coupling effect of consolidation and rheology of saturated soft soil. NPSCCBVPM was developed in Fortran as an ABAQUS user material subroutine. In addition, the NPSCBCVPM was compared with the creep tests of undisturbed soft soil and the generalized Nishihara creep model (GNCM). Finally, the proposed model was applied to the large- quasi-rectangular pipe-jacking tunnel under-passing existing box culverts of Songhu Road in Shanghai. The results show that NPSCBCVPM are in good agreement with the creep tests of soft soil, and NPSCBCVPM can better reflect the nonlinear rheological characteristics of soft soil than GNCM. Furthermore, the proposed model can scientifically evaluate the viscoelastic-plastic stability analysis of large- quasi-rectangular pipe-jacking tunnel under-passing box culvert. Further research should focus on developing three-dimensional NPSCBCVPM to better evaluate the spatial response of the box culvert structure and surrounding soil to the entire construction process of large- quasi-rectangular pipe-jacking tunnels.