A Three-Dimensional Multishear Bounding Surface Model of Granular Soil–Structure Interfaces under Monotonic and Cyclic Loading

Soil-structure is a crucial topic in the building and construction industry. In particular, the deformation process of the soil-structure system has been extensively researched to elucidate the mechanical response and stress transfer characteristics between the soil and structure. The existing literature indicates that the response behavior of soil-structure interface is affected by numerous factors, including the composition, grain size distribution, and relative density, among others. Consequently, several constitutive models for studying the soil-structure interfaces and other bimaterial interfaces have been developed. Unfortunately, most of the existing models are limited to the simulation of two-dimensional soil-structure interface response, which may not be suitable for studying some types of loadings and scenarios, hence the three-dimensional constitutive model is needed.

To this note, Professor Huolang Fang and Mr. Wenjie Wang from Zhejiang University developed a three-dimensional multi-shear bounding surface model for simulating the constitutive response of granular soil-structure interfaces under monotonic and cyclic loadings. The main aim was to predict the constitutive response of interfaces for different soil densities and normal stresses. Their research work is currently published in the journal, Journal of Engineering Mechanics.

In their approach, the bounding surface model was developed based on the plasticity slip theory. Specifically, the overall response of the interface was split into two: macronormal response and a series of oriented micro shear responses in micro-shear structures. The discrete approach provided an effective method for predicting the interface responses by superpositioning the individual responses from all the micro-shear microstructures. The microshear and micronormal responses for the structure were defined using the microstress-strain relation and microstress-dilatancy relation, respectively. The feasibility and effectiveness of the proposed model were validated by simulating the granular soil-structure interface tests under different boundary and loading conditions and comparing the mechanical performance with the experimental results.

The authors reported that the proposed model is suitable for predicting the constitutive response behaviors for soil-structure interfaces subjected to different loadings for both two-dimensional and three-dimensional stress paths. This includes the interaction of multiple shears in different directions and the different cyclic response characteristics of interfaces such as the cyclic hardening, softening and cumulative contraction. This was attributed to the concept of the critical state of the granular soils that accounted for the effect of density and stress on the interface response. The state parameter also ensured that the constitutive model did not only conformed to the critical state theory of the granular soils but also reflected the contractive and dilative behaviors of the granular soil-structure interfaces.

In summary, the study reported the development of a three-dimensional multishear constitutive model for predicting the mechanical responses of granular soil-structure interfaces based on the plasticity theory and concept of the critical state of granular soils. Results showed that the proposed model is suitable for predicting the mechanical response behaviors of soil-structure interfaces subjected to different loadings. The simulation results were also consistent with the experimental results. In a statement to Advances in Engineering, the authors said their findings will advance future studies to address the current challenges in the development of advanced constitutive models for studying the granular-soil structure interfaces.