Stress-strain behavior of two different soil specimens subjected to cyclic compressive loading are studied herein, the goal being to present a simple dynamic uniaxial mem-modeling approach that aids physical insight and enables system identification. In this paper, mem stands for memory, i.e., hysteresis. Mem-models are hysteresis models transferred from electrical engineering using physical analogies. Connected in series, a mem-dashpot and mem-spring are employed to model inter-cycle strain ratcheting and intra-cycle gradual densification of the two soil specimens. Measured time histories of stress and strain are first decomposed so that the two modeling components, mem-dashpot and mem-spring, can be identified separately. This paper focuses on the mem-dashpot, a nonlinear generalization of a linear viscous damper. A mem-spring model is also devised built on an extended Masing model. Nonlinear dynamic simulations (with inertia) employing the identified mem-dashpot and mem-spring demonstrate how well the identified mem-models reproduce the measured early-time data (first 200 cycles of loading). Choices of state variables inherited from bond graph theory, the root of mem-models, are introduced, while MATLAB time integrators (i.e., ode solvers) are used throughout this study to explore a range of contrasting damper and spring models. Stiff solver and the state event location algorithm are employed to solve the equations of motion involving piecewise-defined restoring forces (when applicable). Computational details and results are relegated to the appendices. This is the first study to use single-degree-of-freedom (SDOF) system dynamic simulations to explore the consistency of mem-models identified from real-world data.

Important unsaturated soil mechanics topics for all geotechnical engineers and geotechnical engineering students are reviewed. These key topics include: (1) Soil is an elastoplastic material for which the macro-level response, in general, is controlled by two separate stress variables: total stress (net stress) and negative pore water pressure (suction). (2) Pore water pressures are always negative above the groundwater table-and should not be conservatively assumed zero; (3) shear strength and volume change of unsaturated soils are dependent on soil suction, as well as confining stress, and therefore geotechnical site investigations and testing must account for both stress variables; (4) water flow follows Darcy's law, but hydraulic conductivity is a strong function of water content such that fine-grained soil can have a higher conductivity than course-grained soil, leading to unexpected results when using saturated flow thinking processes; (5) unsaturated soil response is complex and difficult to intuit in the absence of laboratory testing and simulation. Features of unsaturated soil behavior most frequently encountered in geotechnical practice are highlighted, with discussion and demonstration from existing literature. Suggestions are given for relatively simple approaches for first steps in taking unsaturated soil mechanics principles into consideration in site investigation, laboratory testing, and design-related decisions.

In this study, a hypoplastic model is developed to describe the mechanical behaviors of cemented sand under both monotonic and cyclic loading conditions. A state variable is proposed to qualify the bonding strength, and it is incorporated into the model to reflect the influence of cementation on the strength, stiffness, and dilatancy of sand. To reflect the bonding degradation, this variable evolves during the shearing following a simple evolution rule and may vanish after large deformation. The critical void ratio and friction angle are related to the initial cemented content to consider the variation of the critical state induced by the cementation. The model is subsequently extended to account for cyclic loading by incorporating the intergranular strain, fabric change effect, and semifluidized state. The capability of the model is demonstrated by simulating the behavior of cemented sand under both monotonic and cyclic loading conditions.

This study presents a novel formulation for incorporating anisotropy into the generalized plasticity constitutive model. Generalized plasticity is a hierarchical framework allowing for extensibility, in order to encompass new phenomena and improve its predictive capabilities. Anisotropy formulation is based experimentally on the phase transformation state and considers explicitly the direction of the maximum principal stress and the magnitude of the intermediate principal stress, through an anisotropy state variable that contributes to the state parameter. Additionally, the model incorporates the fabric using an evolving fabric variable that reflects initial fabric due to sample preparation method for granular soils. The formulation is simple and introduces three constitutive parameters, allowing for straightforward implementation into the constitutive model and direct application in finite element analysis. The model is validated with undrained triaxial tests conducted on Toyoura sand, covering a wide range of initial conditions with a unique set of constitutive parameters, and yielding overall satisfactory results despite some limitations.