# Research on Mechanical Properties and Failure Mode of Conglomerate Based on Discrete Element Method
## 3 Research Process
### Gravel Content
Effects of different contents of spherical gravel on crack initiation pressure, compressive strength, cumulative fracture number and elastic modulus, as shown in red circular marks in Figure 7a-d, show that the above four parameters all change regularly with the increase in gravel content. The elastic modulus and spherical gravel content show a positive correlation. The cumulative number of fractures increases first and then tends to be flat with the increase in spherical gravel content. The fracture initiation pressure decreases first and then tends to be flat with the increase in gravel content. When the gravel content is more than 50%, the fracture initiation pressure shows an upward trend. According to the distribution map of fractures after failure, there are three main propagation forms of fractures in the conglomerate: crack arrest, bypassing gravels and penetrating gravels. When the content of irregular gravel is 20-35%, cracks are mainly produced by shear force, and the cracks will bypass gravel, which is called bypassing gravel. When the content of irregular gravel is more than 50%, bypassing gravel becomes the major force of crack propagation and is accompanied by penetrating gravel. The fracture propagation morphology of the conglomerate with different gravel content after uniaxial compression is observed, and most of the fractures after failure, are caused by tensile force, as shown in Figure 8a. When the content of spherical gravel is 10%, fractures mainly extend in the conglomerate matrix, and there are few phenomena of penetrating gravel or bypassing gravel. When the content of spherical gravel increases, the phenomenon of penetrating gravel and bypassing gravel increases, which leads to more complex fracture morphology and an increase in the number of shear fractures around gravel. When the gravel content is 55%, the cumulative number of fractures reaches the peak, with a most complex fracture network. When the content of spherical gravel is more than 55%,  
Figure 8: Distribution of cracks with different gravel content. (**a**) Fracture distribution of irregular gravel with different content; (**b**) Fracture distribution of spherical gravel with different content. the cumulative number of fractures decreases, and the fracture shape tends to be single, showing oblique intersecting fractures as shown in Figure 8b. Compared with spherical and irregular gravel with different contents, when the gravel content is high, the fracture network after compression is less complex than spherical gravel because the single particle size of irregular gravel is larger and the fracture is not easy to pass through the larger particle size gravel. In fracturing operation, temporary plugging and other measures can be taken to make fractures produce branch fractures to form a complex fracture network for reservoirs with low gravel content, and cyclic fracturing can be taken to bypass gravel and finally form a complex fracture network with main fractures for conglomerates with high gravel content under low water pressure.