Study on the investigation of cracks identification and spatio-temporal distribution law in cemented sand and gravel materials

To interpret the crack development and evolution characteristics and damage failure mechanism of cemented sand and gravel (CSG) material，uniaxial compression tests were carried out on CSG with different aggregate gradations and water-binder ratios, and the damage process of CSG material was monitored using an acoustic emission (AE) system. The RA-AF and GMM methods were used to comprehensively identify the corresponding crack development mechanisms, while a mesoscale discrete element model of CSG material was established and embedded in the moment tensor theory to simulate the AE process, which further quantitatively describes the damage mechanism of CSG material. The results show that aggregate gradation and water cement ratio have a significant effect on the stress-strain curve and compressive strength of CSG material, and different optimal water cement ratios exist for different aggregate gradations; the damage process is divided into four stages by the characteristics of AE parameters; initial crack closure, new crack expansion, crack coalescence and post-peak damage; the crack initiation, expansion and coalescence processes of CSG material occur before the peak stress, and the crack spatial distribution is mainly decentralized, with sparse distribution of small cracks and dense distribution of large cracks; The GMM crack classification results show tensile cracking at high water-cement ratio and mixed tensile-shear cracking at low water-cement ratio;;during the loading process of numerical simulation, the interfacial cracks around the aggregate show relative slip and extrusion motions, and the expansion of shear and mixed-mode cracks predominates at mesoscale, which ultimately leads to the loss of cohesion between aggregate and cement and the destruction of the material. The results of the study make up for the lack of CSG material mesoscale mechanism study and provide theoretical support for CSG material application.