Papers by Keyword: Rock Mechanics

Abstract: The shear strength of rocks was influenced by internal and external factors whose presence can reduce the shear strength of rocks. Therefore, it was important to analyze the shear strength of rock that has joints in carrying out mining planning in excavations. This study was focused on determining the shear stress of rock samples resulting from direct shear tests by considering the joint roughness coefficient (JRC) so the relationship between the two can be determined and validated using numerical modeling. In this case the author uses the finite element method using Phase2 software. Determination of surface roughness using the Z₂ coefficient, the sample was grouped into several sets based on the roughness value. Other tests carried out are physical properties test, compressive strength test, and Brazilian test, the results of which were used as rock characteristics in modeling. Numerical modeling requires rock characteristics in the form of compressive strength, Young's modulus, Poisson's ratio, tensile strength, internal friction angle, cohesion, normal joint stiffness, and joint shear stiffness. Laboratory test results analyzed using linear regression showed that at peak conditions, JRC’s influences on shear stress was very strong at each loading (R² = 0.93 to 0.97). For the residual condition, a very strong influence occurs only at the highest loading of 640 N (R² = 0.91). The results of the comparison of the weak plane shear test with the modeling results showed the error percentage of 1.4% - 41.7%, this error percentage value was estimated because the analysis used was 2D-based numerical modeling so that the interpretation results only included the cross section of each sample 3D-based laboratory test covering the entire surface of the shear plane.

Abstract: Based on the SHPB (Split Hopkinson Pressure Bar), the dynamic mechanical properties of the granite in the borehole have been tested separately. The data shows that the impact dynamic strength increases as the precompression stress increases and can reach its maximum when the precompression stress is about 50% of the static tension strength. Meanwhile, the coupled static and dynamic strength increases as well, and it could reach about three times of the static precompression stress and one and half times of the dynamic strength respectively. Also, the failure model of the coupled static and dynamic loading is tension failure, which is the same as the static tension and conventional dynamic loading test.

Abstract: For the purpose of researching the freezing-thawing cycle pHysical mechanics properties of sandstone in various chemical solutions, taking the red sandstones from Shandong as the example, freezing-thawing cycles experiments under the condition of H₂SO₄ solution (pH≈1.5), NaOH solution (pH≈12.5), NaCl solution (pH≈7, mass fraction is 4%) and water were conducted. The nuclear magnetic resonance (NMR) technique was used to test the porosity of rock samples after freezing-thawing cycles. Brazilian splitting test was also conducted to test the samples with different times of freezing-thawing cycles and soaking solutions. Results show that the quality change of samples in various solutions is different. The mass of sample in water increased, however, the mass change of the sample in other three solutions showed a firstly increasing and then decreasing tendency. The porosity distribution in rock changed obviously after different time’s freezing-thawing cycles. After 30 times freezing-thawing cycles, the porosity in H₂SO₄ solution, NaOH solution, NaCl solution and water has increased by 151.1%, 85.443%, 39.388%, and 17.976% respectively. With the increase of freezing-thawing cycle’s times, tensile strength of the rock reduced, but the damage properties were different in various solutions. The research can provide some mechanical parameters basis to physical mechanics properties of sandstones.

Abstract: Direct shear tests conducted on the samples containing a central hole and prefabricated cracks are performed to make an analysis on the effects of the inclination angle, the number of prefabricated cracks and the normal stress on shearing characteristics. And the particle flow code in two dimensions (PFC^2D) based on discrete element is applied to carry on simulations on this tests. The micro mechanical parameters of the simulation models are determined by the calibration processes conducted on the shear stress-stain numerical curves of intact samples and the samples containing a pre-existing hole in both experimental tests and simulation tests. And then the micro mechanical parameters obtained above are applied in the simulation models containing prefabricated cracks with varying inclination angles and numbers. Based on the comparisons conducted on simulation curves and experimental curves, investigations of the initiation, propagation and coalescence mechanisms of the prefabricated cracks in both macro and micro scales are performed. And the results may shed lights on the failure mechanism of the surrounding rock involving holes and cracks.

Abstract: In order to study the deformation mechanism of the weak layer in diabase dikes under long-term loading at a hydropower dam foundation, in situ plate loading tests were performed. A damage creep model which improved the five-parameter generalized Kelvin model was established to describe the creep behavior of the weak layer. In this model, the deterioration effect of the rock parameters is considered and the creep parameters of the rock deteriorate gradually. This model is applied in a slope design for a dam foundation at a hydropower station. Long-term stability of the slope after excavation is evaluated. It shows that when damage creep is considered, the displacement is larger compared with the case of ignoring damage creep. The study shows that the deterioration effect of the rock parameters is of full importance for the project design and construction safety.

Abstract: The basic physical and mechanical characteristics of Clay shale in Bayingobi Basin of Inner Mongolia have been investigated by using supersonic testing system, rock mechanical testing system, and rock triaxial testing system. The results indicate that the deep clay shale of this region is characterized by high density, high mechanical strength, low deformation and strong brittleness. More specifically, according to the tests, because of their relative small particle size, the carbonate grains of clay rocks in this region are distributed more uniformly, and the average clay mineral content is comparatively low, as a result, the deep clay shale of this region are featured by large internal friction angle and high mechanical strength.

Abstract: Seismic rock study aims to clarify the relationship between the rock and the intrinsic nature of seismic attributes contained in the fluid between the paper based on the physical characteristics of the rock, viscoelasticity and anisotropy of systems theory and media rock mechanics model response characteristics, and model simulation, simulation results show that the physical structure of the rocks we build the model can well reflect the characteristics of the seismic response of rock mechanics.

Abstract: Hailar oilfield Nantun Formation is a set of lacustrine sedimentation, the sedimentation dominated by gravity flow,the rock contains a lot of argillaceous components. This paper analyzes the content of mud in mud sandstone in Nantun Formation by means of X-ray diffractometer, the rock mechanics parameters were measured.The results show that mud content increases with the decrease of the young's modulus, mud content increases with the increase of the Poisson's ratio; at the same time, with the increasing of the shale content, the compressive strength of rock reduce, and the tensile strength showed increasing trend; different clay contents of mud sand rock stress strain relationship is not the same, when the clay content ≤20%, rock stress strain is elastic constitutive relation, the shale content 20%-30%, the stress-strain relationship is approximate to the ideal elastic-plastic, shale content ≥30%, stress strain relation of rock strain hardening and softening of two parts including plastic deformation. Fault mud sandstone first with increasing clay content decreases, when the rock is elastic plasticity, fracture little overall change.

Abstract: As a strength parameter less dependent on loading conditions, crack initiation stress is suggested to be used as a lower limit for spalling strength. So far, no suggested methods are given by the ISRM to determine crack initiation stress. In order to understand the physical meaning of the various methods and determine this characteristic stress threshold accurately, we compared the similarities and differences between these methods and then analyzed their applicable scope. It is suggested that a comprehensive consideration be taken to select an appropriate method to identify the crack initiation of rocks in compression.

Abstract: For the purpose of researching the freezing-thawing cycle physical mechanics properties of sandstone in various chemical solutions, taking the red sandstones from Shandong as the example, freezing-thawing cycles experiments under the condition of H₂SO₄ solution (pH≈1.5), NaOH solution (pH≈12.5), NaCl solution (pH≈7, mass fraction is 4%) and water were conducted. The nuclear magnetic resonance (NMR) technique was used to test the porosity of rock samples after freezing-thawing cycles. Brazilian splitting test was also conducted to test the samples with different times of freezing-thawing cycles and soaking solutions. Results show that the quality change of samples in various solutions is different. The mass of sample in water increased, however, the mass change of the sample in other three solutions showed a firstly increasing and then decreasing tendency. The porosity distribution in rock changed obviously after different time’s freezing-thawing cycles. After 30 times freezing-thawing cycles, the porosity in H₂SO₄ solution, NaOH solution, NaCl solution and water has increased by 151.1%, 85.443%, 39.388%, and 17.976% respectively. With the increase of freezing-thawing cycle’s times, tensile strength of the rock reduced, but the damage properties were different in various solutions. The research can provide some mechanical parameters basis to physical mechanics properties of sandstones.