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The objective of this study is to investigate the fracturing characteristics of granite under impact loading. Generation and propagation of cracks from the specimen edge subjected directly to impact loading were captured by the ultrahigh-speed photography. Testing results indicate the existence of a critical impact velocity. At an impact velocity lower than the critical impact velocity, a damage zone will be generated on the edge subjected directly to impact and the damage zone area is varied, depending on the magnitude of impact velocity. At an impact velocity greater than the critical impact velocity, radial cracks appear on the boundary of the damage zone and propagate deep into the rock plate with further increasing impact velocity. The increases in radial crack length and damage zone area are affected by impact velocity and impact angle. However, at some impact velocity, damage zone area decreases while radial crack length increases, demonstrating the existence of an incubation period of crack forming. Comparison between testing and numerical results shows that at a constant impact velocity the fractured zone area and the crater depth are varied, depending on impact angle. The results are helpful to understand the fracturing process in rock subjected to impact loading. [ABSTRACT FROM AUTHOR]

Bolt empowers significant efficacy in reinforcing jointed rock mass, which is mainly embodied in the enhancement of shear performance and the restraint to the dislocation between rock blocks. However, the prevailing assumption that the influencing area of bolt covers the whole joint surface contradicts to the experimental evidence of direct shear tests. In this case, by adopting saw-tooth filling joint samples made of rock-like materials, the direct shear tests were conducted under different normal stresses, and the influencing mechanism of bolt on the shear performance was investigated. Then, the similarities and differences in shear strength, deformation, and failure patterns of unbolted and bolted joints with different filling ratios were analyzed. Besides, based on the assumption of elliptical influencing area of bolt, a new shear strength calculation model of bolted joints was established, and theoretical calculation results show an excellent agreement with test results, verifying the rationality and validity of the proposed model. [ABSTRACT FROM AUTHOR]

The natural rock mass prevailingly exists in the form of a fractured rock mass, and freezing-thawing failure of the fractured rock mass is also frequently encountered during geotechnical projects in cold regions. The previous researches and reports in freezing-thawing field principally focused on intact rocks, while rock joints and fractures were rarely considered, which causes great inconvenience to the safety design and stability assessment of engineering. In response to the special climatic conditions of cold regions, the freezing-thawing damage and degradation mechanism of fractured rock were studied in this paper based on existing laboratory experiments and damage mechanics theory. Primarily, a brief review of the progressive damage process of rock in the conventional triaxial compression experiment was given, as well as the determination methods of four characteristic stresses in the prepeak curve. Then, from the microcosmic perspective, the maximum tensile strain yield criterion was used to reflect the microunit strength which was assumed to statistically satisfy the Weibull distribution, deriving the damage evolution equation of fractured rock under the freezing-thawing cycle and load conditions and quantificationally describing the damage evolution law. Consequently, the statistical empirical constitutive relation of fractured rock considering freezing-thawing and loading damages was established. Ultimately, by combining the existing conventional triaxial compression experimental data of freezing-thawing single fractured rocks with the determination methods of characteristic stresses, the relevant constitutive parameters were solved, and the theoretical constitutive relation curves of the fractured rock after freezing-thawing cycles were obtained, which were compared with the experimental results to verify the validity of the established empirical constitutive relation. The study findings can provide a theoretical basis for revealing the freezing-thawing failure mechanism of the fractured rock mass to some extent. [ABSTRACT FROM AUTHOR]

Geomaterials such as rock mass often have initial damage under the influence of long-term geological action and hydration corrosion environment. The initial damage affects the integrity and stability of the rock mass, resulting in a difference in the mechanical properties of jointed rock mass and intact one. Therefore, the study of the fracture and failure characteristics of the jointed rock mass is of great significance. Most of the previous researches into the fracture behavior of rock with initial damage are based on model testing, theoretical analysis, and numerical simulation of rock mass with preexisting flaws. This review concentrates on the theoretical, experimental, and numerical efforts that have been devoted to the fracture characteristics of rock or rock-like specimens with preexisting flaws under compression. Some suggestions on the future research work in this field are also given. [ABSTRACT FROM AUTHOR]

Many factors influence the shear resistance of rock joints. Among them, the above overburden load is the most important factor. The uneven thickness of the overburden causes the joints to be subjected to the nonuniform distribution load. While the peak shear strength shows nonlinear relationship with normal stress, linear superposition cannot be used to calculate the overall shear resistance of joint under nonuniform normal stress distribution. In this paper, the nonlinear shear strength model, JRC-JCS model, is applied to study the overall shear resistance of the joint under four nonuniform distribution patterns of normal stress. The results show that when the normal stress is distributed in a nonuniform way, the shear resistance provided by rock joint as a whole decreases with the increase of the normal stress distribution interval. Given the nonuniform distribution of normal stress along the joint, the shear resistance obtained by the Mohr-Coulomb linear model is overestimated. In order to give full play to the overall shear performance of the joint, the shear strength at different positions on the joint should be as close as possible. Then, the shear strength of joint parts can enter peak state condition simultaneously, at which time the shear strength is fully exerted. [ABSTRACT FROM AUTHOR]

Highlights • An equivalent Burgers model for rock crack rheological fracture subjected to hydraulic pressure and far field stresses was proposed. • In theory, wing crack propagation is divided into the two parts: the transient crack propagation with at very high velocity and the subcritical crack propagation at extreme low velocity. Abstract Mathematical modelling of rheological fracture of rock cracks under the combined effect of hydraulic pressure and far field stresses has not been fully studied so far. The objectives of this study are to investigate the rheological fracture behavior and to establish a simple and practical model for rheological fracture of rock cracks under the combined effect of hydraulic pressure and far field stresses. Research results show that rheological fracture behavior of rock cracks is similar to the rock rheological process and can be decomposed into two stages: the decay and steady creep stages. By conducting a series of calculation analyses of the crack rheological fracture under different hydraulic pressures, it is found that wing crack propagation can be divided into two parts: the transient crack propagation at very high velocity and subcritical crack propagation at extreme low velocity. Moreover, both the transient crack propagation and subcritical crack propagation increase with an increase in the hydraulic pressure. Based on the introduction of an equivalent stress, an equivalent Burgers model for rock crack rheological fracture is proposed. The proposed equivalent Burgers model curves agree well with the theoretical curves under various hydraulic pressures, and generate a crack rheological propagation rate that is comparable to the theoretical analysis results. The proposed equivalent Burgers model lays the foundations for revealing the rheological behavior of fractured rock mass subjected to the combined action of hydraulic pressure and stresses. [ABSTRACT FROM AUTHOR]

Blast induced rock mass damage and crack propagation play important roles in structure safety and stability in mining, quarrying, and civil constructions. This paper focuses on the effect of small blasthole diameter blast on crack propagation and damage accumulation in water-bearing rock mass containing initial damage composed of inherent geological discontinuities and previous multiblast induced damage. To elucidate this effect, theoretical analysis of calculation method for several important blast influencing factors is firstly presented. Secondly, definition of a practical damage variable using ratio of longitudinal wave velocity in rock mass before blast occurrence to that after blast occurrence and derivation of a damage accumulation calculation equation accounting for initial damage and blasting effect are described. Lastly, a detailed description of the conducted in situ blast tests and plan layout of the sonic wave monitoring holes is reported. The results indicate that blast activates and then extends the initial cracks in rock mass, leading to accumulation of rock mass damage. The rock mass damage accumulation can be conveniently quantified using the proposed damage variable. When the damage variable reaches its threshold of 0.19, occurrence of damage in the surrounding rock mass is indicated. It is also found that the blast induced rock mass damage extent and the blast induced vibration velocities decrease nonlinearly with increasing the distance between blast source and monitoring position. [ABSTRACT FROM AUTHOR]

Rock engineering especially deep rock engineering undergoing long-term effects of external loading and gravity all or most may gradually damage deformation or creep deformation accumulation, leading rock structures to damage, crack, such as severe plastic deformation or even progressive failure. In this paper, based on the nonlinear damage creep characteristics of rock and damage variable, a new nonlinear damage creep constitutive model of high-stress soft rock is defined in series with the improved Burgers model, Hooke model and St. Venant model. This new nonlinear damage creep constitutive model can work out fairly reasonably explanations for the soft rock creep deformation. A series of uniaxial compression creep tests were performed to study the creep damage characteristics of typical soft rock in Jinchuan No.2 Mine in the northwest of China. Using the increment step loading and single-step loading, the results of creep experiments and nonlinear damage creep constitutive model results are very consistent in this study. The new model not only can reflect the whole course of creep deformation, but also can reasonably describe the soft rock under different initial creep stage, steady-state creep stage and accelerated creep stage. Therefore, the new nonlinear creep damage model is a reasonable reference model for the research of soft rock creep. [ABSTRACT FROM AUTHOR]

Describes the sodium-rich dacites and albite porphyries rock of Permian in the Awulale Mountain of west Tianshan. Details on adakites; Geology and petrography; Analytical data of major and trace elements of Awulale sodium-rich dacites and albite porphyries.

A schematic drawing of strain-time curves during freeze-thaw cycles and the curve fitted by the elasto-visco-plastic model, which shows the deformation and damage of water-saturated rocks. • A new elasto-visco-plastic model based on stress functions is proposed. • The characteristics of plastic strain show a unique process of damage development of saturated rocks. • The data of strain-time relationship of sandstone are well fitted by the new model. Rocks can be used as building materials. In this study, based on the effect of freeze-thaw cycles (FTC) on the properties of water-saturated rocks and the theory of rheology, an elasto-visco-plastic model based on stress functions is proposed, which consists of the elastic, viscoelastic and viscoplastic submodels. The elastic strain shows obvious time dependence and is different from the traditional one in the theory of creep. Although the Kelvin model can be used to fit the relationship between elastic strain and time during the freezing process, but not suitable for thawing process. A threshold element obtained by improving the classical plastic element in rheology is applied to improve the Kelvin model to simulate the viscoelastic behavior of rocks, which only has the action of a valve without any plastic flow and does not work during the thawing process. The viscoelastic strain will be generated after the frost heave stress is greater than σ f t ev , after thawing, it will not recover until time tends to infinity. The viscoplastic strain will be developed when the frost heave stress exceeds σ f t vp , which can be divided into two substages during the freezing process, namely the substages of stress growth (t vp ⩽ t ⩽ t cf ) and stress constancy (t cf ⩽ t ⩽ t n). The viscoplastic strain will continue to develop until the frost heave stress is reduced to σ f t vp after thawing. Thus it can be seen that the characteristics of viscoplastic strain show a unique process of damage development of water-saturated rocks during the freeze-thaw (FT) process. Finally, the model is simplified by a piecewise linear function and adopted to fit the strain-time data of water-saturated red sandstone samples during the freezing process. [ABSTRACT FROM AUTHOR]

Existing research on rock freeze-thaw mainly focuses on a single freeze-thaw process, while little attention is paid to the cumulative effect of cyclic freeze-thaw on rock mass joints. However, the accumulated freeze-thaw effects are precisely the leading cause of rock mass deterioration and damage in severe cold regions. This study aims to investigate the use of a novel laboratory testing method, i.e., membrane pressure sensors in the joint, to demonstrate the impact of cyclic frost-thaw on jointed rocks. With the sensors, the change of frost-heaving pressure in the joint under cyclic process is continuously monitored. The measurements indicate that under freeze-thaw cycles, the initiation of frost-heaving pressure is critical, which is followed by an explosion, stability, and ablation stages. In these stages, the maximum frost-heaving pressure is observed to emerge at the early stage of the freeze-thaw cycle. Based on the experimental observations, frost-heaving pressure evolution law and damage mechanism of jointed rock masses are analyzed. For example, the peak frost-heaving pressure increases exponentially with the decrease of temperature and decreases exponentially with the increase of freeze-thaw cycles. Also, the pressure has a positive linear relationship with the geometric size of the joint. In essence, the deterioration of freeze-thaw cycles on jointed rock masses is mainly due to crack propagation caused by the frost-heaving pressure. [ABSTRACT FROM AUTHOR]