## 4 Analysis of Results
### Size Effect of the Mechanical Properties of Basalt Blocks
#### 4.1.2 Size Effects of Stress-Strain Curve Characteristics  
Figure 11 shows the deviatoric stress-strain curves of different-sized basalt samples with hidden cracks under triaxial and uniaxial compression, obtained from FDEM simulations and laboratory tests. As shown in Figure 11a, the pre-peak nonlinear characteristics of the stress-strain curves of intact basalt under uniaxial compression are not evident, and the slope of the stress-strain curve is high, indicating linear elasticity. The post-peak stress drops rapidly, and some samples do not clearly exhibit a post-peak curve, indicative of extremely strong brittleness characteristics. With the increase in the confining pressure, the stress-strain curves of the intact sample still exhibit linear elasticity before the peak and a rapid stress drop after the peak, unlike the brittle-to-ductile transition characteristics of other hard brittle rocks, such as marble and sandstone, under high confining pressures [43]. In other words, although the residual strength of basalt increases significantly with increasing confining pressure, its brittleness is not remarkably influenced by the confining pressure, without evident plasticity and yield platform near the peak under high confining pressures (e.g., \(\sigma_{3}\geq\) 50 MPa). Therefore, intact basalt shows significant elastic-brittle me  
chanical properties, with evident brittle characteristics, and the FDEM results are consistent with the laboratory test results. As shown in Figure 11b,c, the stress-strain curves of basalt with local hidden cracks or many hidden cracks under uniaxial compression are serrated before the peak; that is, there are many evident phenomena in that the stress first enhances and later reduces, and the slope of the stress-strain curve is lower than that of the intact samples, showing significant nonlinear characteristics. The post-peak stress drops gradually, with the decrease in the brittleness degree. With increasing confining pressure, the stress-strain curves of basalt samples still exhibit a pre-peak jagged shape, the post-peak stress drops more gradually, and even an evident yield platform occurs at the post-peak or near the peak stage, with a significant increase in plasticity. Therefore, basalt with local or many hidden cracks exhibits elastoplastic mechanical characteristics, with significantly reduced brittleness and significantly enhanced plasticity. As shown in Figure 11d, the pre-peak stress-strain curve of basalt containing sufficient hidden cracks at the REV size under uniaxial compression is relatively smooth, and the slope of the stress-strain curves is significantly reduced compared with that of intact basalt, indicative of nonlinear and elastoplastic mechanical characteristics. There is an evident yield plateau near the peak, and the post-peak stress decreases more gradually. With increasing confining pressure, the pre-peak nonlinear characteristics of basalt blocks are more significant, and the yield platform range near the peak increases; in particular, there is an evident strain-hardening phenomenon under medium and high confining pressures (i.e., \(\sigma_{3}\geq 20\) MPa), showing a remarkable ductility characteristic. Therefore, the basalt  
Figure 11: Effects of the sample size on the stress–strain curve characteristics of basalt with hidden cracks under different confining pressures. (**a**) Intact specimen at a size of 50 mm; (**b**) specimen with local cracks at a size of 100 mm; (**c**) specimen with many cracks at a size of 300 mm; (**d**) specimen with sufficient cracks at a size of 500 mm. block containing sufficient hidden cracks at the REV size exhibits elastic-ductile mechanical characteristics, with a prominent increase in the plasticity and ductility and a noticeable decrease in the brittleness.