Search

Pre-existing joints within a rock mass has a significant effect on the hydro-mechanical properties of the rock mass. The study investigates the hydro-mechanical properties of rock-like materials with intermittent joints under different confining and hydraulic pressures. Cylindrical specimens containing two sets of parallel pre-existing joints were prepared, and the hydro-mechanical experiments under different hydraulic pressures were carried out using a servo-controlled rock triaxial testing system. The test results show that the strength, permeability and deformation properties of the specimens were influenced by the hydraulic pressure. The four stages of evolution of permeability in the deformation process is closely correlated with the development of joints and cracks within the specimen. The relations between volumetric strain and permeability were analyzed and discussed. It is found that the exponential function describes the permeability and volumetric strain relation well in the contraction stage. When the fluid pressure is high, the fluid pressure has a larger impact on the specimen failure mode than the pre-existing thin joints within the specimen in this test. [ABSTRACT FROM AUTHOR]

The triaxial compression tests under different hydraulic pressures and low confining pressure were carried out to study the hydraulic pressure effect on the mechanical properties and permeabilities of layered rock mass. In general, the results show that the increase of hydraulic pressure reduces the peak strength of layered rock mass and the layer structure changes the mechanical properties of rock mass. With the increase of hydraulic pressure, the peak strength of layered rock mass decreases sharply and then slows down. The peak permeabilities of layered rock mass occurred later than the time when the strength come to the peak. The increase of hydraulic pressure will accelerate the propagation of cracks and significantly enhance the peak permeability of layered rock mass. With the increase of the layer number, the effect of hydraulic pressure becomes more distinct. The initial permeability and the peak permeability increase largely. The increase of hydraulic pressure promotes the expansion and penetration of cracks, so the rock mass develops from tensile failure to the composite failure forms including shear failure and interfacial shear slip failure. [ABSTRACT FROM AUTHOR]

Columnar jointed rock masses (CJRMs) have a complex network structure and, therefore, present a great challenge to geotechnical engineering design. A series of triaxial compression tests is performed on artificial CJRM specimens subjected to a confining pressure of 5 MPa, considering various pore pressures (pw=0 MPa , 2 MPa, and 4 MPa). In this work, the influence of the joint dip angles and pore pressure on the anisotropic strength, deformation, and failure modes of the CJRM is investigated. The anisotropic characteristic stresses, strength parameters (c and φ) and elastic modulus of the CJRM specimens show a U-shaped pattern with increasing joint dip angles (β), while Poisson's ratio changes inversely. The elastic modulus has a stronger anisotropy than Poisson's ratio. Moreover, with increasing pore pressure, the characteristic stresses decrease, while the anisotropy of stresses and deformations increases. Finally, three failure modes of CJRM specimens with different joint dip angles are observed under triaxial compression conditions. [ABSTRACT FROM AUTHOR]

Copyright of Rock Mechanics & Rock Engineering is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper presents an experimental study on the mechanical behavior and permeability evolution of basalt, drilled from the dam foundation of the Baihetan Hydropower Station in China. Two groups of triaxial unloading creep tests under hydro-mechanical coupling conditions were conducted. Based on the experimental results, creep deformation and failure characteristics of basalt were investigated. It was found that the relationship between the confining pressure and steady creep rate could be described satisfactorily by an exponential function. A tensile-shear failure mode was observed for basalt under the action of unloading confining pressure and hydraulic-mechanical coupling. The permeability evolution of basalt in the unloading creep process exhibited phased characteristics: permeability decreased in the initial loading phase and remained stable for a certain range of confining pressure in the steady creep phase. Exponential functions were also used to describe the evolution of permeability and confining pressure. The results of this study can provide a comprehensive understanding for the long-term stability assessment of basalt under coupled hydro-mechanical conditions. [ABSTRACT FROM AUTHOR]

Columnar jointed rock masses (CJRM), characterized by regular arrays of polygonal prisms or columns, are exposed in the dam foundation of the Baihetan hydropower station and pose a challenge to the stability of the project. To understand the hydro-mechanical behaviour of Baihetan CJRM, triaxial compression experiments are carried out on artificial CJRM specimens with regular arrays of hexagonal columns, which are similar to the actual CJRM. Based on the experimental results, mechanical and hydraulic behaviour of CJRM is studied. It is found that the compressive strength of CJRM varies in a typical U-shape with the joint inclination angle. Three failure modes associated with the angle of joint inclination are observed. The evolution of permeability with stress exhibits distinct phased characteristics: initial compression stage, linear elastic stage, yield stage, and strain-softening stage. The results of this study provide helpful information for the design and construction of the Baihetan project involving CJRM. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this paper is to investigate the mechanical behavior and propagation of cracks of numerical granite samples through the Brazilian split test and to provide a reference for predicting the behavior of real granite samples. Design/methodology/approach: The numerical models of granite containing two fissures are established using the parallel bond model (PBM) and the smooth joint model (SJM) in PFC2D. The peak stresses, number of cracks and anisotropic ratios are obtained to study the influence of the mineral composition and the angle of inclination of rock bridge on the strength, failure mode and deformation characteristics. Findings: The numerical results obtained show that the mineral composition has a marginal influence on the peak stress. When the angle of inclination of rock bridge β increases, the peak stress drops to its minimum value at β = 90° and then gradually increases to a relatively low level. The behavior of cracks falls into three categories based on the distribution of cracks. By analyzing the stress–strain curve and the process of crack propagation for sample No. 4 with β = 60°, it is found that the process of failure can be divided into four stages and tensile cracks dominate. The anisotropic ratios of peak stress and a number of cracks obtained show that the peak stress is low anisotropic and the number of cracks is medium anisotropic. Originality/value: This paper presents a numerical simulation method to analyze mechanical behavior and propagation of cracks under different conditions. The proposed method and the results obtained are useful for predicting the behavior of real granite samples in laboratory and engineering projects. [ABSTRACT FROM AUTHOR]

• Performed triaxial compression and multi-level cyclic loading tests on artificial CJRM specimens. • Analyzed the effect of fatigue effect on the anisotropic mechanical characteristics of the CJRM specimens. • Revealed the evolution of energy of the CJRM specimens under triaxial compression and multi-level cyclic loading. • Conducted EDS tests to discuss the failure mechanism of the CJRM specimens. Columnar jointed rock masses (CJRM) are natural geological structures with regular and irregular polygons. Because of the joints throughout, the rock mass mechanical properties are severely degraded. This study focused on the effect of joint dip angle, fatigue effect, and stress level on the anisotropic strength, deformation behavior, energy evolution characteristics, and failure mode of CJRM specimens. Triaxial compression and multi-level cyclic loading tests were performed on artificial CJRM specimens with a similar geological structure under a 7 MPa confining pressure. Energy dispersive spectroscopy (EDS) tests were performed on the hexagonal prism and joint structure to investigate the failure mechanism of the CJRM specimens. The experimental results show that the relationship between the characteristic stress and the joint dip angle is a typical U-shaped pattern. The anisotropy of characteristic stresses decreases gradually under triaxial compression. The fatigue effect increases peak strength's anisotropy and decreases residual strength's anisotropy. The plastic strain and strain energy depend on stress level, fatigue effect, and joint dip angle. Three failure modes were observed. Disintegration and fracture of hexagonal prisms, and joint cracking result in the failure of CJRM specimens. Overall, the fatigue effect increases the number and distribution of cracks in CJRM specimens. [ABSTRACT FROM AUTHOR]

In order to investigate the anisotropic mechanical behaviour of the columnar jointed rock masses (CJRM) under cyclic loading, triaxial cyclic loading-unloading tests are conducted on artificial CJRM specimens with a geological structure similar to the actual CJRM under the confining pressures of 5 MPa. In this work, particular attention is paid on the influence of joint dip angles on the anisotropic deformation behaviour, strength, mechanical properties, and failure modes of the CJRM. The experimental results show that the relationship between characteristic stress thresholds and joint dip angles is exhibited as a typical U-shape. Crack unstable growth (σ cu) and crack damage (σ cd) stress thresholds are more anisotropic than the crack stable growth stress threshold (σ cs), peak stress (σ p) and residual stress (σ r). The CJRM anisotropy mechanical parameters induced by stress gradually increases. Three main failure modes are observed throughout the loading process with respect to the joint dip angles. The results presented in this paper are significant for understanding the mechanical behavior of anisotropy in rock engineering. [ABSTRACT FROM AUTHOR]