工程科学与技术 (Nov 2024)
Damage Strength Model of Soil–Structure Interface Based on Equivalent Damage
Abstract
Objective Pile-soil interaction plays a critical role in slope support engineering. Since the contact surface represents the weakest link in the system, analyzing the influence of the soil shear area on the mechanical properties and the constitutive model of the contact surface between soil and structure enhances the understanding of pile-soil interactions.Methods Three sets of ring-shaped samples are initially cast to evaluate the impact of the soil shear area on the interface strength characteristics between soil and structure. Each sample has a height of 1.00 cm, an outer diameter of 6.12 cm, and inner diameters of 0 cm, 3.50 cm, and 4.98 cm, respectively. Subsequently, corresponding segments of 300-mesh sandpaper are adhered to the sample surfaces using a robust adhesive. The remolded soil is then dried, pulverized, sieved through a 2 mm mesh, and adjusted to a moisture content of 20%. It is cured for 24 hours prior to sample preparation. Different soil-structure interface samples with varying soil shear areas are then fabricated using specially designed equipment, and shear tests are conducted using the electric ZLB-1 strain-controlled direct shear apparatus manufactured by Nanjing Soil Instrument Co., Ltd. The test employs the fast shear method, with a shear rate of 0.8 mm/min and a shear displacement of 7 mm. During the tests, the soil shear area ratio (ρ) at the interface between soil and structure is controlled at 0, 0.33, 0.66, and 1.00, with normal stresses of 100, 200, 300, and 400 kPa, respectively.Results and Discussions The peak strength of the soil-structure interface increases linearly with increasing normal stress and soil shear area ratio. The shear area ratio of soil significantly influences the stress-strain curve of the sample. When the soil shear area ratio is ρ = 0 or ρ = 1.00, the shear stress-displacement curve of the sample exhibits a hardening behavior. Conversely, when the shear area ratio is 0 < ρ < 1.00, the curve demonstrates a softening behavior. This primarily occurs because the soil strength exceeds the interface strength between the soil and the structure. Under various soil shear area conditions, the strength at the soil-structure interface initially derives from the soil itself. Once the soil’s shear strength reaches its maximum, the sample’s shear stress is substantially reduced, exhibiting a stress-softening phenomenon. As the soil shear area ratio at the soil-structure interface gradually increases, the shear strength at the interface approaches that of the soil. Consequently, the interface effect leads to a decrease in shear strength compared to that of the soil shear surface. The shear strength of the soil shear surface primarily arises from the interactions between soil particles, including rotation, interlocking, and biting. In contrast, the shear strength at the soil-structure interface comprises two components: one part is generated by the friction, interlocking, and biting between the soil particles and the structure’s surface, while the other arises from the interactions among soil particles near the shear zone on the structure’s surface. During the shear process of the specimen, the proportion of shear strength is contributed by inter-particle shear resistance within the soil, and the interface shear resistance undergoes dynamic changes, exhibiting variability in the shear strength mechanism at the soil-structure interface. The total damage to the soil shear surface results from loading damage, whereas the total damage at the soil-structure interface is divided into equivalent initial damage, loading damage, and coupling damage caused by the interaction of the two. The smaller the soil shear area ratio ρ, the greater the equivalent initial damage at the soil-structure interface. By establishing a damage evolution relationship between the soil shear surface and the soil-structure interface, the latter is equated to the soil shear surface with initial damage, describing the influence of soil shear area on the strength characteristics of the interface. Based on the assumption that the strength of both the soil-structure interface and the soil shear surface follows a two-parameter Weibull probability distribution during the shear process of the sample, a damage strength model of the soil-structure interface based on equivalent damage is proposed using statistical damage theory. This model primarily consists of the fitting parameter B, which controls peak strength, and the fitting parameter C, which controls softening characteristics. Compared to the soil shear plane, the pre-set interface leads to significant changes in pores and microcracks during the shear process of the soil-structure interface. Consequently, the total damage to the soil-structure interface is considerably higher than that of the soil shear plane initially, and the macroscopic performance is that the strength of the soil-structure interface is significantly lower than that of the soil shear plane. The proposed model is validated by comparing it with experimental data, demonstrating that it accurately represents both softening and hardening stress-strain behaviors at the soil-structure interface.Conclusions This study explores how the soil shear area influences the mechanical properties of the soil-structure interface and proposes a zero-thickness interface model to predict this behavior, supported by experimental evidence. This model effectively fits the nonlinear relationship at the soil-structure interface under different soil shear area ratios, making it suitable for programmed calculations in finite element software.
