Due to the relatively different mechanical and physical properties of soils and structures, the interface plays a critical role in the transfer of stress and strain between them. The stability and safety of geotechnical structures are thus greatly influenced by the behavior at the soil–structure interface. It is therefore important to focus on the unique characteristics that set the interface apart from other geomaterials while examining the interface behaviour. Understanding the physical mechanism and modelling principles of these interfaces becomes a crucial step for the secure design and investigation of soil-structure interaction (SSI) issues. Moreover, to deal with this soil-environment interaction problem, the classical soil mechanics formulation must be progressively generalised in order to incorporate the effects of new phenomena and new variables on SSI behaviour. Considering the variety of energy geostructures that are emerging nowadays, it is crucial to comprehend the thermo-hydro-mechanical (THM) behaviour of the interface. The objective of this study is to fill this information gap as concisely as possible. A critical review is provided along with the state-of-the-art information on the thermo-hydro-mechanical behaviour of the soil-structure interface, including testing tools and measurement methods, basic principles and deformation mechanisms, constitutive models, as well as their applications in numerical simulations. This study explains how loading influences the mechanisms at the interface and critically examines the effects of boundary conditions, soil properties, environmental factors, and structure type on the THM behaviour of interface zones between soils and structural elements. The validity and reliability of the interface shear stress-displacement models are also covered in this paper. Lastly, the trends and recent advancements are also recommended for the interface research.

Soil shear strength is the most fundamental property when designing structures in the ground and should be carefully assessed and understood. Several empirical models were introduced to predict the shear strength of unsaturated soils. However, there is uncertainty regarding the applicability and sensitivity of these prediction models. This paper presents a comprehensive verification study to assess the reliability and validity of the existing theoretical models. The results obtained from the prediction models are compared to measured data using thirty experimental data sets. A performance classification program is also conducted to assess the suitability of the analytical models for different soil types as well as over a wide range of matric suctions, saturation degrees, soil densities, soil plasticity, and clay activity. The impact of each single parameter is clarified by the microstructure studies, which also provides insight into the mechanics of unsaturated soils. The results indicated that the applicability of models is more appropriate for sandy soils rather than for clayey ones. The performance of shear strength models tends to decrease with an increase in matric suction, initial density, plasticity index, and clay activity. It is, therefore, recommended that the shear strength estimation models should be carefully selected depending on the soil type and properties. Besides, the analysed results pointed out that the choice to assume the factor $$\chi$$χ in the equation of Bishop equals the saturation degree is only suitable for medium-dense soils with low matric suction. This assumption is particularly not effective for clayey soils, or dense soils with high matric suction.

Geosynthetic-reinforced and pile-supported (GRPS) embankments are becoming more popular as a solution for addressing soil structural instability. The interaction between the geosynthetic-pile-subsoil-embankment elements is crucial to the load transfer mechanism and performance of GRPS embankments. Several analytical models for GRPS embankment design have been proposed, but their performance and applicability still require further validation. This research presents a three-dimensional numerical investigation of the load transfer mechanism of GRPS embankments using the finite difference approach, considering the combined interaction between the soil embankment, geosynthetics, pile, and subsoil. The importance of these crucial aspects in the GRPS embankment design technique is highlighted, as well as their influence and sensitivity. The following elements, in descending order, influence the load and settlement efficacies of the GRPS embankments: soft soil stiffness, embankment height, geosynthetic stiffness, and embankment soil density, according to this research. Furthermore, the use of geosynthetics reduces differential settlements and mitigates soil yielding above the pile heads. The numerical findings are then compared to four well-known design standards, with the subsurface stiffness, geosynthetic stiffness, embankment height, and fill soil density all being varied simultaneously to measure their performance. The findings of the comparison revealed that these techniques differ greatly in their ability to forecast load efficacy and differential settlement. Depending on the geometric properties of the embankment and material properties, all of the selected design methods produce over-predictions or under-predictions.

Geosynthetic-reinforced column-supported system is an economic and effective solution to support embankments constructed on soft soils. In this solution, both end-bearing and floating columns are commonly used in practice. For deep soil foundation depths, floating columns are more economical than end-bearing piles. The design of a floating column foundation involves complex soil–structure interactions and there are still no clear uniform guidelines available for the design of embankments supported by floating columns. The main focus of this paper is to present a design method for the geosynthetic-reinforced floating column-supported (GRFCs) embankments. The main features of the proposed method are combining the bearing capacity theory for the floating columns, the arching theory for fill soils, the tensioned membrane theory for the geosynthetic, and considering interaction models between geosynthetic, soil, and piles. Using the proposed method, the influences of the pile geometry, soft clay, geosynthetic, and embankment fills properties were investigated. It was observed that the geosynthetic membrane inclusion enhances the load transfer mechanism and reduces significantly the differential settlements of floating pile-supported embankments. The floating columns with a higher ultimate bearing capacity cause more soil arching. In general, the soil shear strength properties and column geometry (length, diameter, column spacing) have a strong influence on the GRFCs embankment behaviour. Finally, the proposed method is compared with the BS 8006–1 and EBGEO design standards considering several experimental and numerical models to investigate its validity. The results showed that the proposed method is able of very good prediction performance and allows conducting the design optimization of GRFCs embankment.