Experimental study on the influence of prefabricated fissure size on the directional propagation law of rock type-I crack
Introduction
Long-term geological processes result in numerous defects, such as joints and fissures in the rock, which reduce the overall strength of the rock. When disturbed by mining, the stress on the surrounding rock changes, which triggers the initiation, propagation, and coalescence of primary cracks in the rock; in addition, numerous cracks converge to form a macro fracture surface, eventually leading to the instability and failure of the coal and rock mass.1, 2, 3 The instability failure of coal and rock mass is the main factor that causes engineering geological disasters such as rock bursts, large deformations of roadway surrounding rock, and slope landslides.4, 5, 6, 7, 8 Therefore, studying crack propagation in coal and rock mass, including its influencing factors, has an important theoretical guiding significance for predicting the instability of coal and rock mass and preventing engineering geological disasters.
Researchers, home and abroad, have conducted numerous discussions on the crack initiation and propagation law of rock materials containing prefabricated fissures for several years. Subsequently, many static loading tests on fractured rocks have been conducted. The basic mechanical properties and crack propagation mechanism of fractured rocks under different loading conditions have been studied.9, 10, 11, 12 Accordingly, it has been deduced that the fissure shape, geometric size, number, and inclination angle13, 14, 15, 16, 17, 18, 19, 20 of the prefabricated fissure significantly influence the crack evolution process. In practical engineering, the rock mass is subjected to dynamic loads such as impact, earthquakes, and explosions under the action of large-scale excavation.21,22 Hence, it is of practical significance to study crack propagation and coalescence mechanisms under impact loads. Therefore, some researchers have studied the effects of hollow hole23 and prefabricated fissure length24 on the crack coalescence phenomena and mechanical properties of the sample under impact loading, while others have studied the influence of geometric configuration25, 26, 27, 28, 29, 30 on the crack propagation behavior of fractured rock under dynamic loads on the crack propagation behavior of fractured rocks under dynamic load. Based on the fracture mechanics theory, Irwin31 classified cracks into three types: type-I opening, type-II sliding, and type-III anti-plane shear modes. Among these, type-I cracks, which are manifested as cracks subjected to tensile stresses perpendicular to the crack surfaces, produce displacements perpendicular to the crack surfaces. Type-II and III cracks are in-plane and out-of-plane shear cracks in which the surface slip directions are parallel and perpendicular to the crack directions, respectively. In general, the failure of an engineering rock mass is primarily caused by the tensile stress exceeding its ultimate tensile strength to form a tensile fracture surface. Researchers have performed basic mechanical tests such as direct tensile, Brazilian splitting, and three-point bending, to analyze the type-I crack coalescence failure mode under tensile stress.32, 33, 34, 35, 36 AE, digital speckle, infrared imaging, and other monitoring methods37, 38, 39, 40, 41, 42, 43, 44 have been adopted to obtain information on the entire process of crack propagation simultaneously.
Although the aforementioned research experiments mostly analyze the crack initiation and propagation behavior from a qualitative perspective, there are few quantitative studies on the entire process of crack propagation by precisely controlling the direction of crack propagation. A simple device and method for simulating rock crack directional propagation was developed, and the influence of fissure size on the type-I crack directional expansion of sandstone samples was studied. Loading tests of white sandstone samples with different prefabricated fissure lengths and widths were performed, during which the deformation field and AE evolution law throughout the crack propagation were monitored and analyzed by AE and digital image technology, and the effect of prefabricated fissure size on the directional propagation of type I cracks was revealed.
Section snippets
Test method
The white sandstone samples used in the experiments were obtained from a mine in Zizhong County, Neijiang City, Sichuan Province, China. The sampling depth was 80 m at the excavation face, and the sampling direction was perpendicular to the rock deposition direction. The obtained rock samples were grayish white (Fig. 1a). Fig. 1b shows the X-ray diffraction result of a white sandstone sample. The white sandstone sample is mainly composed of elements such as silicon, sodium, aluminum, potassium,
Load curve and failure mode
The load-time curves of the samples with different lengths of prefabricated fissures are presented in Fig. 4. The change rate of the load curve initially increased, and then decreased with an increase in load. When the load increases to the peak load, the tensile stress in the prefabricated fissure area reaches the limit value, which controls the main crack formation, and the sample fracture leads to a rapid reduction in the load. Meanwhile, the peak load of the sample decreases with an
Load curve and failure mode
The load–time curves of the samples with different widths of prefabricated fissures are presented in Fig. 11. The rate of change of the load curve initially increases, and then decreases as the load increases. When the load increases to the peak load, the formation of the main crack triggers a decrease in the bearing capacity of the sample and a rapid decrease in the load. At the post-peak stage, the rate of the curve gradually decreases from rapid to steady. Meanwhile, the peak load and the
Discussion on mechanism and engineering guidance of rock crack directional propagation under the influence of fissure size
Fig. 17 presents a diagram of crack directional propagation. When the maximum bending stress at the fissure tip exceeds the tensile strength of the rock, microcracks began to appear at the prefabricated fissure tip, and the microcracks aggregate to form the fracture process zone (FPZ). Because some cohesion still exist between the two crack surfaces, in equivalent elastic fracture mechanics, FPZ is considered a crack with closed cohesion, and it is regarded as an effective crack Le together
Conclusion
To investigate the influence of prefabricated fissure size on the directional propagation law of rock type-I cracks, a simple device for simulating rock crack directional propagation was developed. Subsequently, loading tests for white sandstone samples with different prefabricated fissure lengths and widths were performed. The evolution laws of the deformation field and AE were analyzed during the entire crack propagation process. Finally, the influence of fissure size on the crack directional
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
The research described in this paper was financially supported by National Natural Science Foundation of China (No. 52274086, No. 51904165), Major Program of Shandong Provincial Natural Science Foundation(No. ZR2019ZD13).
References (54)
- et al.
An experimental investigation of the fracturing behaviour of rock-like materials containing two V-shaped parallelogram flaws
Int J Min Sci Technol
(2020) - et al.
Mechanical behavior of coal under different mining rates: a case study from laboratory experiments to field testing
Int J Min Sci Technol
(2021) - et al.
Modified semi-circular bend test to determine the fracture toughness of anisotropic rocks
Eng Fract Mech
(2019) - et al.
Potential fracture paths for cracked rocks under compressive-shear loading
Int J Rock Mech Min Sci
(2020) - et al.
Experimental and numerical study on splitting failure of brittle solids containing single pore under uniaxial compression
Mech Mater
(2006) - et al.
Investigation of crack dynamic parameters and crack arresting technique in concrete under impacts
Construct Build Mater
(2019) - et al.
Influence of thermal treatment on mode I fracture toughness of certain Indian rocks
Eng Geol
(2016) - et al.
Comprehensive sandstone fracturing characterization: integration of fiber Bragg grating, digital imaging correlation and acoustic emission measurements
Eng Geol
(2018) - et al.
Experimental investigation on infrared radiation features of fracturing process in jointed rock under concentrated load
Int J Rock Mech Min Sci
(2021) - et al.
Modified semi-circular bend test to determine the fracture toughness of anisotropic rocks
Eng Fract Mech
(2019)
Comprehensive sandstone fracturing characterization: integration of fiber Bragg grating, digital imaging correlation and acoustic emission measurements
Eng Geol
A fracture toughness criterion for concrete
Eng Fract Mech
Biaxial shear crack propagation modes of rock-like samples with prefabricated fissures and their strength characteristics
Shock Vib
The effect of fracture growth rate on fracture process zone development in quasi-brittle rock
Engineering Fracture Mechanice
Apparent-depth effects of the dynamic failure of thick hard rock strata on the underlying coal mass during underground mining
Rock Mech Rock Eng
Coal rib burst mechanism in deep roadway and “stress relief-support reinforcement” synergetic control and prevention
J China Coal Soc
Case studies of rock bursts under complicated geological conditions during multi-seam mining at a depth of 800 m
Rock Mech Rock Eng
Rock failure modes under uniaxial compression, Brazilian, and point load tests
Bull Eng Geol Environ
Experimental study on crack propagation and the coalescence of rock-like materials with two preexisting fissures under biaxial compression
Bull Eng Geol Environ
The effect of sample shape and strain rate on uniaxial compressive behavior of rock material[J]
Bull Eng Geol Environ
Experimental and numerical study of the influence of prefabricated crack width on the fracture toughness of NSCB samples
Rock Mech Rock Eng
Triaxial discrete element simulation of soil-rock mixture with different rock particle shapes under rigid and flexible loading modes
Int J GeoMech
Micro-failure process and failure mechanism of brittle rock under uniaxial compression using continuous real-time wave velocity measurement
J Cent S Univ
The length of pre-existing fissure effects on the dilatancy behavior, acoustic emission, and strength characteristics of cracked sandstone under different confining pressures
Environ Earth Sci
Failure and mechanical behavior of transversely isotropic rock unde compression-shear tests: laboratory testing and numerical simulation
Eng Fract Mech
Mechanical properties and failure behavior of rock with different flaw inclinations under coupled static and dynamic loads
J Cent S Univ
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