Xianda Yang

Rock masses in short-term freeze–thaw zones tend to fail under long-term loading. Therefore, investigating the creep damage characteristics of rocks under short-term freeze–thaw cycles is of great significance for the stability evaluation of rock engineering. In this study, white sandstone was used as the research material. Multi-gradient short-term freeze–thaw cycle tests and graded loading creep acoustic emission (AE) tests were performed to investigate the creep behavior and AE response characteristics of sandstone after short-term freeze–thaw action, and a creep damage constitutive model was established. The results show the following: (1) The mass loss rate, P-wave velocity reduction rate, and porosity growth rate of sandstone increase with increasing freeze–thaw cycles and duration. (2) The instantaneous axial strain of specimens increases with the stress level under different freeze–thaw durations and cycle numbers. (3) The cumulative AE event rate decreases significantly with increasing freeze–thaw cycles and duration. (4) Based on the seven-element viscoelastic model, a creep damage constitutive model was developed by introducing the freeze–thaw damage factor (D), with an average goodness-of-fit of 0.964. The findings can provide a theoretical reference for the long-term stability assessment and disaster early warning of geotechnical engineering in short-term freeze–thaw regions.

Rock engineering problems in short-term freeze–thaw zones and short-term freeze–thaw cycles can lead to a reduction in rock strength, thereby inducing engineering disasters. Granite in short-term freeze–thaw zones was selected as the research object. Taking the freezing time (1 h) required for the internal temperature of the rock to reach the target freezing temperature as the reference, freeze–thaw cycle tests with durations of 1 h, 2 h, and 3 h were carried out in sequence. Combined with uniaxial compression acoustic emission (AE) tests, the effects of freeze–thaw duration and freeze–thaw cycle number on the physical and mechanical properties and AE characteristics of the rock were systematically investigated. A multi-index damage characterization system was established. Results show that: (1) Both freeze–thaw duration and cycle number show a positive correlation with the attenuation of peak strength and elastic modulus. (2) With the increase in freeze–thaw duration and cycle number, the AE cumulative ringing count rate and cumulative energy rate show an exponential decay trend. (3) Their proportion shows an increasing trend with the increase in freeze–thaw duration and cycle number. (4) Establishing a multi-index coupled damage variable to replace the traditional single-index characterization can improve the objectivity and reliability of freeze–thaw damage assessment.

Shear slip along structural planes in jointed rock masses is the primary trigger for rock slope instability, threatening geotechnical engineering safety. Direct shear tests were conducted on prefabricated granite specimens with regular sawtooth structural planes (undulation angles: 15°, 30°, 45°; tooth spacing: 10 mm) under 2, 4 and 6 MPa normal stresses, with synchronous acquisition of acoustic emission (AE) and infrasonic signals to explore shear failure characteristics, acoustic spectral features and instability precursors. Results show (1) peak shear stress and stiffness rise significantly with increasing undulation angle and normal stress, and failure modes evolve from sliding friction-dominated to asperity shearing-dominated, finally to composite asperity shearing and compressive crushing. (2) The spectral characteristics of both acoustic emission (AE) and infrasonic signals are closely related to the shear fracture mechanism. (3) Approaching peak shear stress, dominant frequency ratio correlation dimension drops to a minimum and the ib-value rises to a pre-sudden-drop critical point; higher undulation angles align these values with stress closer to the peak, valid as instability precursors. (4) A two-level early warning model (early to imminent warning) is proposed via cross-frequency band AE-infrasonic monitoring, providing a fundamental basis for rock slope stability monitoring using these signals.

Bond strength is one of the most important parameters and can affect the macroscopic mechanical properties and the damage state of rock to some degree. Coarse-grained sandstone was studied using the controlled variable method. The influence of parallel bond strength on the peak strength and failure mode of coarse-grained sandstone was simulated, and the evolution law of peak strength and the failure mode of bond strength were comprehensively analyzed. The results show that the peak strength of the rock was positively correlated with the bond strength; the difference in quantity between the tensile and shear cracks was negatively correlated with tensile bond strength and positively correlated with shear bond strength. With a tensile-shear bond strength ratio of less than 0.5, the peak strength of the rock was usually stable at the certain extreme value under a constant tensile bond strength. The tensile cracks were negatively correlated with the tensile-shear bond strength ratio, and the shear cracks were positively correlated with the tensile-shear bond strength ratio. The main failure mode of the coarse-grained sandstone in the weakly cemented stratum of the Hongqinghe coal mine is shear failure. The research results can be used to guide the ground control of other mine stopes or roadways with weak cementation lithology.

Bond strength is one of the most important parameters and can affect the macroscopic mechanical properties and the damage state of the rock to some degree. The coarse-grained sandstone with strength of less than 40 MPa was studied by the controlled variable method. The influence of parallel bond strength on the peak strength and failure mode of coarse-grained sandstone was simulated, the evolution law of peak strength and failure mode of bond strength were comprehensively analyzed. The results show that the peak strength of rock was positively correlated with the bond strength, the difference value between tensile and shear crack was negatively correlated with tensile bond strength and positively correlated with shear bond strength. Tensile-shear bond strength ratio less than 0.5, the peak strength of the rock was usually stable at the certain extreme value under a constant tensile bond strength. Tensile crack was negatively correlated with the tensile-shear bond strength ratio, shear crack was positively correlated with the tensile-shear bond strength ratio. The failure mode of coarse-grained sandstone is shear failure. The research results can be used to guide the ground control of other mine stopes or roadways with weak cementation lithology.