# Mechanical Behaviour of Rock Samples with Burst Liability Under Different Pre-Cycling Thresholds
## 3 Results
### AF-RA Characteristics of Rock Samples with Burst Liability  
_RA_ was obtained based on rise time (\(T_{1}\)) and AE amplitude (\(F\)). _AF_ was obtained based on AE count (\(Z\)) and duration time (\(T_{2}\)) [46]. _AF-RA_ could characterise the development and evolution of cracks under pre-cycling loading and unloading. When the proportion between low _AF_ and high _RA_ (\(X_{2}\)) was greater than that between high _AF_ and low _RA_ (\(X_{1}\)), shear cracks developed. It caused shear failure. Otherwise, tension failure occurred [47] (Figure 8). Figure 9a,c,e show that _AF-RA_ decreased first and then increased with the increasing time. Additionally, the _AF-RA_ distribution was different in different time periods. It was mainly distributed in stage A and stage D. The distribution form was \"dense-sparse-dense\". In stage A, the _AF-RA_ distribution was concentrated. However, the _AF-RA_ value was small. _AF_ was mainly distributed between 0 and 1500 kHz. _RA_ was mainly distributed between 0 and 1.6 ms/v. The main reasons were friction and slippage between microparticles in rock samples. _AF-RA_ was sparsely distributed in stage B and stage C. It was due to the Kaiser effect. AE signals were not active. _AF-RA_ was widely and intensively distributed in stage D. _AF_ was mainly distributed between 0 and 6000 kHz. _RA_ was mainly distributed between 0 and 2.2 ms/v. In this stage, massive AE signals increased sharply, and highly frequent AE signals were generated. The _AF_ value increased by 75%, and the _RA_ increased by 27.3%. It showed that, with the increasing stress, the plastic deformation characteristics of rock samples became more prominent. Figure 7: Evolution characteristics of the [PERSON] effect: (**a**) pre-cycling threshold was 6 MPa; (**b**) pre-cycling threshold was 12 MPa; (**c**) pre-cycling threshold was 18 MPa. Figure 8: Relationship between _AF-RA_ and crack type. Figure 9: Evolution characteristics of _AF-RA_ and crack types: (**a**) Relationship between _AF-RA_ and time when pre-cycling threshold was 6 MPa; (**b**) Relationship between _AF_ and _RA_ when pre-cycling threshold was 6 MPa; (**c**) Relationship between _AF-RA_ and time when pre-cycling threshold was 12 MPa; (**d**) Relationship between _AF_ and _RA_ when pre-cycling threshold was 12 MPa; (**e**) Relationship between _AF-RA_ and time when pre-cycling threshold was 18 MPa; (**f**) Relationship between _AF_ and _RA_ when pre-cycling threshold was 18 MPa. Additionally, Figure (a)a had the largest _AF-RA_. Figure (c)c had the second largest _AF-RA_. Figure (b)b had the smallest _AF-RA_ value. It indicated that the structural mechanical properties of rock samples were improved when the pre-cycling threshold was 18 MPa. However, AE signals were still not positive when the loading stress increased near the peak stress. Low frequent signals were mostly distributed. However, under this condition, secondary cracks of rock samples could still develop rapidly to form macro failure surfaces. Figure (b)b,d,f show the _AF-RA_ distribution of each pre-cycling threshold. Figure (b)b shows 70.1% > 20.9%. This indicated that shear cracks developed and shear failure occurred. The main reasons were that the weak surface existed in the middle and lower parts of rock samples under pre-cycling loading and unloading. Meanwhile, secondary cracks developed. With the increasing loading stress, secondary cracks of rock samples extended to the upper end to form two macroscopic cracks. Therefore, shear failure was predominant in rock samples. Figure (d)d shows 73.2% > 26.8%. This indicated that the shear crack distribution was concentrated. Therefore, shear failure occurred in rock samples. After rock samples entered the crack generation stage, due to the significant Poisson effect in the middle section of rock samples, secondary cracks were generated first to form low-strength slip zones. When the loading stress was near the peak stress, secondary cracks developed to form a left low-strength slip zone. Shear failure occurred.