Numerical Investigation on the Hydraulic Fracture Evolution of Jointed Shale

Joints are a common structure of heterogeneous shale rock masses, and in situ stress is the environment in which heterogeneous rock masses can be found. The existence of joint plane and confining pressure difference influences the physical properties of shale and propagation of fractures. In this study, jointed shale specimens were simulated under different confining pressures to explore the failure patterns and fracture propagation behavior of hydraulic fracturing. Different from the common research of hydraulic fracturing on signal parallel joint rock mass, the simulations in this study considered three points (parallel joint, multi-dip angle joint, and no-joint points). The effects of the single-dip angle joint, multi-dip angle joint, and confining pressure difference on the hydraulic fracture evolution and stress evolution of the jointed shale were studied comprehensively. The confining pressure difference coefficient proposed in this study was used to accurately describe the confining pressure difference. Results indicate that the larger is the confining pressure difference, the stronger is the control of the maximum principal stress on fracture evolution; by contrast, the smaller is the confining pressure difference, the stronger is the control of the joint plane on fracture evolution. Under the same confining pressure difference, the hydraulic fracture propagates more easily along the small dip angle joint plane. As the value of the confining pressure difference coefficient moves closer to zero, the hydraulic fracture propagates randomly, the tensile stress region around the fracture tip widens, and the joint planes fractured by tensile increase. This study can offer valuable guidance to the design of unconventional reservoir reconstruction.

Experimental Study on the Deterioration Rules of Anchoring Performance of Rock Mass under Different Joints Distribution

In order to analyze the influence of damage caused by corrosion on anchoring performance of a rock mass with different joints, the anchored rock mass specimens with different joints distribution were prepared. An electrochemical accelerated corrosion test of specimens was carried out, and the mechanical test of them under different corrosion time was also investigated. The results showed that the pitting corrosion is the main form of the anchor bar corrosion of an anchoring rock mass with different joints, and the shape of the etch pit is reverse semi-ellipse. With the increase of pitting ratio, the ultimate bond strength and the corresponding slide distance decrease gradually. The effects of pitting ratio on the slide distance of the anchor bar in an anchored joint rock mass are insignificant, but these on the bond strength of it are significant. The bond-slide model of the anchored joint rock mass with different pitting ratios was established. The research results of this paper can provide reference for analyzing the corrosion damage of a complex anchored joint rock mass in practical engineering and a theoretical basis for the design optimization of anchoring support in the complex jointed rock mass.

Research on Rock Mass Blasting of Weak Plane by High Dynamic Strain Test

when explosive blasts in the rock, the stress wave of impact produced appears all kinds of phenomena, such as reflection, refraction, and transmission in the process of transmission on the joint surface because of discontinuity, heterogeneity and anisotropy of rock mass of weak plane in physics, which lead to extremely complex on rock blasting process. Through conducting on high dynamic strain test of blasting process on joint rock mass model, it researches dynamic load characteristics of joint rock mass and joint-planes effect on extension of critical raw crack and attenuation law of stress wave, analyzes the strain waveform of strain gages which locate in the different direction between initial crack of blasting and joint, and figures out the impact of joint plane on the stress wave transmission, which provide an important theoretical basis on the relevant parameters design in the process of blasting engineering of joint mass existing in actual.

Application of D-CRDM Method in Columnar Jointed Basalts Failure Analysis

Columnar jointed basalt is a type of joint rock mass formed by the combined cutting effect of original joints and aphanitic microcracks. After excavation unloading, such rock mass manifested distinct mechanical properties including discontinuity, anisotropy, and proneness of cracking. On the basis of former research findings, this paper establishes a D-CRDM method applicable to the analysis of columnar jointed basalt, which not only integrates discrete element and equivalent finite-element methods, but also takes into account the coupling effect of original joints and aphanitic microcracks. From the comparative study of field monitoring data and strain softening constitutive model calculated results, it can be found that this method may well be used for the simulation of mechanical properties of columnar jointed basalts and the determination of rock failure mechanism and failure modes, thus providing references for the selection of supporting measures for this type of rock mass.

Study on Finite Element Algorithm of Jointed Rock Mass in Tunnel in Blasting and Model Building

It is a kind of effective way to study blasting to joint rock mass using the finite element method, in which the key is algorithm and model building. Comparing the relationship of explosive and blasting structure simulated by adopting Lagrange method and ALE method, the paper considers that Lagrange method is more close to practice, and could finish numerical simulation analysis of the intact rock blasting.

Research on the Cavern Stability and Rock Fracture with Different Joint Groups

The numerical simulation using DDARF was carried out to analysis the rock samples with two and four cracks under uniaxial loading condition. Contrastive research was made about the fracture process analysis of rock mass with joints sets at the three different angles. The rock stability with difference of joint rock mass was compared when the lateral coefficient of initial stress varied. It is shown that distribution of joint groups will bring effects on rock surroundings in controlling deformation, stress status and stability.

Structural Plane of Rock Mass Strength Characteristics and its Impact on Groundwater

The strength characteristic of discontinuity is one of the most important mechanical characteristics of rock mass, and its strength dominates the strength and deformation of joint rock mass. The underground water has an important influence on the strength of discontinuity. In this paper, the strength theory of joint rock mass was summarized and analyzed; further, two kinds of failure mode of joint rock mass which are joint shear failure and rock shear failure were proof. Considering the impact of underground water, the effective stress principle was introduced, and base on it, the joint shear failure strength rule of the saturated rock mass was built. When the influence of underground water on joint strength is studied, the shear strength formula has important theoretical and realistic significance.

Research of Inclination Angle Effect on Joint Rock Macromechanical Parameters

The joint of rock mass influences and controls the rock mass intensity, deformation characteristics and instability failure in the rock engineering to a great extent. Using the similar material simulation is of different inclination angle of non-penetration jointing and non-jointing rock mass, through using rigid servo compression machine to carry uniaxial compression test, we get a nearly same trend of joint rock mass stress-strain curve of different angle, the curve of inclination angle of 45 is analyzed, the test result shows that the compressive strength first decreases and then increases gradually with the increase of rock inclination angle. The compression intensity is its minimum when of the inclination angle of 45°, and the deformation modulus first decreases and then increases, but deformation modulus of 30° is its minimum. In addition, through the use of developed RFPA2D system to simulate on trial uniaxial compression value based on microscopic damage mechanics, we get the conclusion that the numerical analysis and test result is fitting approximately, it is validated that the numerical model can simulate joint rock well. Keywords: joint rock mass, inclination angle, uniaxial compression, compressive intensity, deformation modulus