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.

Integral bridges have been proposed as a jointless design alternative to the traditional counterparts, possessing copious potential economic and structural advantages. However, due to the monolithic connection at the girder- abutment interface, longitudinal deformations from the superstructure must now be accommodated by the stiffness of the approach backfill and soil surrounding the foundation. Consequently, in addition to traffic loads, integral bridge approaches are subjected to long-term, cyclic loading due to diurnal and seasonal thermal variations. This has resulted in two progressive geotechnical phenomena: an escalation of lateral passive pressures at the abutment-soil interface and accumulated deformations near the bridge approach. Over the last two decades, several investigations on the approach backfill-abutment interaction have been carried out. However, previous reviews on integral bridges have not comprehensively discussed the theoretical aspects of these two complex geotechnical issues. Hence, this paper presents a discussion on the long-term response of stress ratcheting observed from controlled analyses, along with a comparison to that from field monitoring data. Subsequently, the occurrence of accumulated deformations, along with a correlation to the mechanism of the cyclic interaction is explored. The effects of foundation design choice and skew angle on the passive pressure accumulation and soil deformation behavior are then presented. Subsequently, approaches used to mitigate the effects of the backfillabutment interaction are compared. From this review, it is apparent that outcomes based on available experimental and field investigations are yet inadequate to develop analytical models required to predict the long-term response of integral bridge approach backfills under various loading conditions.

This study assesses the performance of a memory surface constitutive model (SANISAND-MS) in capturing vertical cyclic loading on a suction bucket foundation in sand. The model has been calibrated against drained cyclic triaxial responses and validated against corresponding centrifuge experiments on suction buckets. The model was found to satisfactorily capture the effects of increasing accumulated strain with increasing mean stress level and reducing density. The performance of the model was further investigated through a parametric study on suction buckets at different mean stress levels, densities and loading sequences. The insights gained from investigating the strain and stress responses, along with the movement of the memory surface, reveal that the model can satisfactorily capture the strain accumulation and ratcheting effects under different load histories.

This paper investigates the response of Ottawa sand to cyclic loading using virtual oedometer tests and the level-set discrete element method. We study both the macroscopic and the micromechanical behavior, shedding light on the grain-scale processes behind the cyclic response observed in crushable sand, namely stress relaxation under strain control and ratcheting under stress control. Tests without particle breakage first show that asymmetrical frictional sliding during loading-unloading induces these cyclic-loading effects. Then, tests considering particle breakage reveal more pronounced stress relaxation and ratcheting, which decrease in rate over cycles, accompanied by increased frictional sliding and reduced particle contact forces. It is found that the broken fragments unload the most and promote an enhanced cushioning effect. These micromechanical processes contribute to a decrease in breakage potential as the cycles progress, implying that cyclically loaded materials may become more resistant to breakage when compared to the same material loaded monotonically at the same strain level. These new insights highlight the main contributions of the present work, factoring in real particle shapes from 3D X-ray tomography and notably contributing to the existing literature on the topic, where most studies rely on idealized particle shapes and rarely consider crushable grains.

Integral bridges are a low-maintenance form of bridge construction used worldwide. Their jointless structure eliminates bearing and expansion joint replacement bringing a reduction in lifecycle cost, carbon emissions, and socio-economic impact from road and rail disruption, therefore offering a resilient infrastructure solution in the face of a changing climate. By better understanding earth pressure ratcheting in the backfill due to repeated thermal movements of the deck, integral bridge use can increase to greater spans and skews while excessive design conservatism can be reduced. This paper explores the integral bridge problem and design code prescriptions before using analytical, numerical, and centrifuge modeling to show that soil-structure interaction, especially the relative stiffness of soil and structure, can reduce abutment bending moments by 30% and that this is largely unaccounted for in the current U.K. design code PD 6694-1. Preliminary results showed a similar influence of stiffness on seismic response.