The development trend of urban underground space towards deep and large three-dimensional foundation pit projects in complex environments faces the challenges of deformation and instability of supporting structures, strong sensitivity of the surrounding environment, and significant limitations of the traditional design theory. Based on the ultra-long/deep foundation pit project at the Shenzhen Airport East Station, a refined three-dimensional finite element simulation is used to systematically study the deformation mechanism of the supporting structures of deep and large foundation pits under a complex environment and investigate the influence on the neighbouring buildings. In this study, a three-dimensional finite element model is constructed considering the soil–structure coupling effect, and the mechanical response law of the foundation pit under the compliant–inverse combination method is revealed. Based on ABAQUS 6.14, a 10 m wide strip-shaped model of the central island area and an environmental risk source model including an underground station and group pile foundation are established. The analysis shows the following: the lateral shift in the ground wall is distributed in a ‘convex belly’ shape, with a maximum displacement of 29.98 mm; the pit bottom is raised in the shape of the bottom of a rebutted pot, and the settlement behind the wall has an effect ranging up to 3.8 times the depth of the excavation; the lateral shift in the side wall of the neighbouring underground station and the differential settlement of the group piles validate the predictive ability of the model on the complex-environment coupling effect. The research results can provide guidance for the design and construction of support structure projects and similar projects.

This study aims to investigate the compressive and microstructural properties of loess before and after treatment with a new permeable polymer. To enhance the compressive properties of loess, specimens were infused with the new polymer, and one-dimensional consolidation tests were performed to assess the compressibility of solidified loess (SL) and unsolidified loess (UL) at different water contents. Additionally, the microstructure and pore morphology of UL and SL were examined using a scanning electron microscope (SEM) and the Particles (Pores) and Cracks Analysis System (PCAS). Statistical methods were employed to analyze the relationships between microstructural parameters and compression modulus. The experimental results demonstrate a significant improvement in the compressibility of loess when treated with the polymer. The complexity of pore structure and variability in pore size are reduced, leading to a more uniform pore distribution. Moreover, all microstructural parameters exhibit a strong correlation with the compression modulus. The results pertaining to the compressive and microstructural properties of loess reinforced with permeable polymer grouting can provide insights into the variations in the curing effect, serving as a theoretical foundation for the application of permeable polymer in loess treatment.

The issue of interfacial shear damage has been a significant challenge in the field of geotechnical engineering, particularly in the context of diaphragm walls and surrounding soils. Polymer grouting is a more commonly used repair and reinforcement method but its application to interface repair and reinforcement in the field of geotechnical engineering is still relatively rare. Consequently, this paper presents a new polymer grouting material for use in grouting reinforcement at the interface between concrete and soils. The bonding characteristics and shear damage mode of the interface after grouting were investigated by the direct shear test, and the whole process of interface shear damage was investigated by digital image correlation (DIC) technology. Finally, the reinforcement mechanism was analyzed by microscopic analysis. The results demonstrate that the permeable polymer is capable of effectively filling the pores of soil particles and penetrating into the concrete-soil interface. Through a chemical reaction with water in the soil, the polymer cements the soil particles together, forming chemical adhesion at the interface and thereby achieving the desired reinforcement and repair effect. In the shear process, as the normal stress increased, the horizontal displacement and horizontal compressive strain at the distal end of the loading end decreased, while the maximum vertical displacement and maximum vertical strain of the cured soil also decreased. The results of scanning electron microscopy (SEM) demonstrated that the four groups of test polymers exhibited a reduction in soil porosity of 53.47%, 58.79%, 52.71%, and 54.12%, respectively. Additionally, the form of concrete-soil interfacial bonding was observed in the concrete-cohesive layer-cured soil mode. The findings of this study provide a foundation for further research on diaphragm wall repair and reinforcement.

The interface between asphalt and aggregate acts as a key link in load transfer and damage development; its shear mechanical behaviour has a decisive influence on the fatigue cracking and durability of bituminous pavements. In this study, SBS-modified asphalt and limestone aggregate were selected. By precisely controlling the moulding load, asphalt film thicknesses ranging from 23 μm to 219 μm were achieved. Systematic shear tests were conducted within a temperature range of 10 °C to 40 °C to systematically investigate the evolution of interfacial shear strength, stress–displacement curve characteristics, shear fracture energy and failure modes. Two primary failure modes were identified: adhesive failure, defined as debonding at the asphalt–aggregate interface with minimal residual asphalt on the aggregate surface; and cohesive failure, defined as internal rupture within the asphalt film with asphalt residue covering both fracture surfaces. The results indicate that temperature has a significant deteriorating effect on interfacial shear strength; as temperature rises, shear strength decays rapidly at first and then more slowly before gradually approaching zero, whilst shear fracture energy decreases monotonically, with the rate of decay being more pronounced at lower temperatures; the thickness of the bituminous film exerts a monotonically decreasing influence on interfacial shear strength, whilst shear fracture energy remains at a relatively high level within the intermediate film thickness range; bituminous films that are either too thin or too thick are detrimental to the effective dissipation of interfacial energy. An analysis of interfacial failure modes reveals that, under low-temperature conditions, failure occurs primarily at the interface between the asphalt and the aggregate, manifesting as adhesion failure; under high-temperature conditions, the failure path shifts to within the asphalt film, manifesting as cohesion failure. An increase in asphalt film thickness promotes a shift towards cohesion failure, whilst a decrease in film thickness tends to favour adhesion failure; between these two extremes, a coupled and competitive relationship is observed. Based on interfacial thermodynamics and phase transition theory, this study provides an interpretation of how temperature governs the migration of failure modes through alterations in asphalt cohesion, intermolecular forces and interfacial surface tension, and reveals the pivotal role of film thickness in restructuring the distribution of interfacial weak points by regulating the ratio of structural asphalt to free asphalt.