Strength characteristics of the sliding zone soil of bedding deep cutting slopes and early warning analysis of the reserved thickness of the base

Objective Bedding deep cutting slopes containing weak interlayers are commonly found in slope engineering, whose stability is influenced by two key factors: The strength of the sliding zone soil and the reserved thickness of the base (the distance from the base of an excavated slope to the weak interlayer). Methods In this research, taking the K42 cutting slope of the Yang-Xuan Expressway as an example, the evolution process of slope deformation was analyzed, especially the characteristics of basal heave deformation. The properties of the deep sliding zone soil in the slope were revealed by ring shear tests, which are suitable for studying the shear strength of soil that has experienced large shear displacements. Moreover, the residual strength parameters of the saturated sliding zone soil were applied to analyze the reserved thickness of the base. Results The results show that sliding zone soils exhibit obvious strain softening characteristics, which become more evident as the normal stress decreases. As the soil shear strength transitions from peak strength to residual strength, both the cohesion force and internal friction angle decrease, with the cohesion force decreasing to a greater extent than the internal friction angle. The residual cohesion force of sliding zone soil varies slightly with the shear rate, while the relationship between the residual internal friction angle and shear rate varies as a logarithmic function. When the shear rate is less than 2 mm/min, the residual shear strength parameter of sliding zone soil is more sensitive to the shear rate and vice versa. Conclusion Furthermore, according to the regression equations of the critical states of slope stability, the reserved thickness of the base under different slope rates was divided into four zones: A (extremely unstable zone), B (unstable zone), C (basically stable zone) and D (stable zone), and based on this, the criterion and early warning model of the reserved thickness of the base for slope excavation were established.