| The execution of engineering initiatives can induce tensile stress in rock masses,which can cause a series of risks such as slope instability,deformation of adjacent rock in underground chambers,and surface collapse,resulting in incalculable harm to human life and economic property.Moreover,the anisotropic properties of rocks and their tendency to display size effects make it imperative to investigate the impact of size on their tensile strength,as this has significant implications for the safety of rock engineering projects.This article focused on sandstone,a commonly encountered rock in engineering.To investigate the size effect of sandstone’s tensile strength with regard to mechanical properties,acoustic emission signal characteristics in the time and frequency domains,and failure characteristics,Brazilian splitting acoustic emission tests and numerical simulations were the primary research methods employed.The main research content and conclusions are as follows:(1)The splitting tensile strength and strain of sandstone were determined through indoor Brazilian splitting tests performed on three groups of specimens with differing size conditions.The sandstone specimens’ strength decreased as their size increased within the same comparison and diameter groups.Conversely,within the same thickness group,the strength of the sandstone specimens exhibited a trend of decreasing initially and then increasing.By utilizing digital image processing techniques and considering the macroscopic mechanical characteristics,a series of microstructural parameters were derived through an iterative process to correspond with the Brazilian splitting test results of sandstone specimens.(2)By examining the acoustic emission signals obtained while loading sandstone specimens,an investigation was conducted about the impact of size effect on the time-domain and frequencydomain characteristics of acoustic emission.The results indicate that the acoustic emission rate of specimens with different sizes follows a general trend of initially decreasing and then increasing during stages I～III;The cumulative energy and dominant frequency variation of acoustic emission is complex and variable due to changes in specimen size,thickness,and diameter.(3)When investigating crack failure mechanisms,the impact of Brazilian splitting specimen size on parameters such as b-value,RA-AF,and fractal dimension was analyzed.The results revealed that the effects of size alterations on these parameters differed among different sets of specimens.The fluctuation range of the b-value exhibited diverse patterns across the different experimental groups,implying that the impact of varying size conditions on the crack scale within the specimens was intricate.The investigation of RA-AF values revealed that specimens of different dimensions exhibited an escalation in shear crack growth as they approached the point of failure.Within the same comparison and thickness groups,an upward trend in the fractal dimension was observed as the specimen size increased.Conversely,no significant linear correlation existed between the fractal dimension and thickness in the same diameter group.(4)By means of the PFC2 D numerical simulation method,Brazilian splitting specimens of varying sizes were simulated and the resulting failure mode and displacement cloud map of the model were obtained.By comparing and analyzing experimental data,it was confirmed that the PFC2 D simulation method is accurate.Furthermore,it was discovered that the intricate distribution of the displacement field in the model has an inverse relationship with its tensile strength. |
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