In underground engineering, the fracture dip angle and three-dimensional stress have great influence on the permeability and mechanical properties of fractured rock mass. Firstly, single-fracture ...samples with similar three-dimensional fractal dimensions and different dip angles were selected by using CT scanning technology. Then, the grouting material seepage tests under different dip angles and different three-dimensional stresses were carried out by self-developed single-fracture stress-seepage coupling true triaxial test system. The experimental data of stress-strain curve, grouting pressure, and grouting material flow rate of single-fracture specimen under different fracture dip angles and three-dimensional stress were obtained. The results show that the three-dimensional fractal dimension can be used as an index to measure the influence of fracture factors on grouting seepage test. The third principal stress σ3 had a greater influence on the fracture width than the first principal stress σ1. The larger the fracture inclination, the lower the strength of the single-fracture specimen. As the third principal stress σ3 increases, the grouting pressure increased while the grouting flow decreased. With the increase of the fracture inclination angle, the influence of σ1 on the hydraulic conductivity became larger, while the influence of σ3 on the hydraulic conductivity became smaller. Moreover, the expression of hydraulic conductivity of single-fracture specimen with different dip angles under three-dimensional stress was obtained by nonlinear fitting of hydraulic conductivity data.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
In underground engineering, the complex stress state is the main factor of the permeability characteristics of fractured rock mass. It is of great significance to study the coupling effect of ...three-dimensional principal stress and seepage. Firstly, a large number of single-fracture samples are prepared through splitting test, and the three-dimensional occurrence of single fracture is quantified by taking the three-dimensional fractal dimension as the index. Then, the self-developed single-fracture stress seepage coupling true triaxial test system is adopted to carry out grouting seepage tests of single-fracture specimens under different three-dimensional principal stresses. The experimental data of stress–strain curve, grouting pressure, and slurry velocity of single-fracture specimens under different three-dimensional principal stresses are obtained. The effects of different three-dimensional principal stress states on the anisotropic strain of single-fracture specimens are analyzed. The effects of different three-dimensional principal stress states on grouting pressure and slurry flow are studied. The expression of permeability coefficient of single crack specimen under three-dimensional principal stresses is obtained. Combined with stress–strain curve, grouting pressure, and slurry flow, the application range of three-dimensional principal stresses of permeability coefficient expression is determined.
To study the mechanical and damage characteristics of crushed coal after grouting, self-developed grouting equipment was used to reinforce coal with different particle sizes. A uniaxial compression ...test was carried out on the grouted specimens, and the acoustic emission (AE) and digital image correlation (DIC) techniques were used to monitor the damage and deformation of the specimens during the tests. The experimental results showed that the strength and elastic modulus of specimens with medium particle size (10–15 mm) were the highest, while those with maximum particle size (15–20 mm) were the lowest. The AE events and accumulated AE counts increased with decreasing coal particle size, which indicates more internal damage during the compression process and a larger crack range and damage degree at the macro scale. The test results revealed that the failure mode gradually changed from shear failure to splitting failure with increasing coal particle size, and more coal blocks appeared to crack under compression, which indicated that the skeleton effect of grout became weaker. The DIC results showed that the deformation and local strain increased with decreasing coal particle size, and the region where displacement occurred on the surface of the specimens showed accelerated expansion during the tests.
The argillaceous weakly consolidated rock is a kind of soft rock that will bring great difficulties in the construction process. Specimens of such rock under different moisture contents are taken as ...the research object. By the Hopkinson pressure bar test (SHPB), the structural and mechanical characteristics of the rock under dynamic impact are analysed. With increasing moisture content, the transmitted wave amplitude decreases gradually, which indicates that the higher the moisture content of the rock is, the easier it is to deform under dynamic impact and the greater its plasticity. The boundary between plastic failure and brittle failure is 10% moisture content. Through a mercury injection test, the porosity variation is analysed. The porosity of the rock decreases with increasing moisture content after the same dynamic impact. The porosity curve can be roughly divided into two sections with a moisture content of 15% as the boundary. Based on a uniaxial compression test, the elastic modulus, peak strength, and residual strength of specimens after dynamic impact are analysed, and the mechanical properties of the rock are revealed. Its mechanical properties can be divided into three sections with a moisture content of 9.18% and 15.19%, and each section has obvious differences.
To study the mechanisms and potential control measures for coal mine engineering safety hazards caused by swelling rock, water absorption experiments were performed under different temperature by ...using an independently developed rock water absorption test system. The swelling pressure, expansion amount and water absorption amount of specimens were monitored in real time. Nuclear magnetic resonance and uniaxial compression experiments were performed. The water absorption rate of the swelling rock specimens increases significantly with increasing water absorption time. The water absorption capacity of the specimens differs considerably under different temperatures. The water absorption curve can be divided into three stages: the severe stage, deceleration stage and equilibrium stage. The water absorption amount and water absorption rate are linearly related to temperature. The curve of the swelling pressure depicts a double peak shape. The expansion curve can also be divided into three stages. With increasing temperature, the expansion rate increases, and the time needed to achieve expansion stability is prolonged. There is a negative linear correlation between the uniaxial compressive strength and the moisture content. The higher the temperature is, the higher the moisture content. The increase in the rock porosity after water absorption is one of the important factors driving the strength attenuation.
To study the mechanical properties of argillaceous weakly cemented rock under dynamic loading, a sample reconstituted and graded loading scheme is firstly designed, and then the reorganization rock ...sample is used as the research object. Using a Hopkinson pressure bar test, the responses of an argillaceous weakly cemented rock mass under different reorganization loads and different impact velocities is studied, and changes in specimen shape after impact are also analyzed. The study found that with increased of the recombination load, the amplitude of the transmitted wave increases. With increasing impact velocity, the rate of the increase in the incident wave amplitude is much larger than that of the transmission wave amplitude. The dynamic stress–strain curve can be divided into a compaction stage, an approximate linear elastic stage, a microcrack growth stage and a strain softening stage. The larger the reorganization load is, the less obvious the compression stage of the stress–strain curve is, and the greater the elastic modulus is. The peak strength and elastic modulus increase with increasing strain rate before 500 s−1. When the reorganization load is increased, the deformation decreases, and its impact resistance increases. With increasing impact velocity, the deformation of the specimen increases.
Rock materials are often affected by water in underground engineering. In this study, the mechanical and failure characteristics of tuff under different moisture content were studied using laboratory ...tests. The moisture content variation of tuff was studied in water absorption tests, and the mechanical and failure characteristics of tuff under different moisture contents were studied through uniaxial compression tests with a Micro-II acoustic emission (AE) control acquisition system. The results showed that the moisture content of tuff increases rapidly at the initial stage of water absorption tests and stabilizes after 180 h of immersion. According to the results of uniaxial compression tests, both uniaxial compressive strength and elasticity modulus decreased with the increase in moisture content. The AE parameters analyses showed that, when the moisture content increased, the accumulated AE counts and energy gradually decreased, and the “quiet period” at the initial stage of uniaxial compression tests lasted longer, and the RA (rise time⁄amplitude)–AF (AE counts⁄duration) distribution and the failure characteristics verified that the failure patterns evolved from shear failure to tensile failure. Scanning electron microscopy was used to observe the morphology of the fracture surface and analyze the influence of moisture content on the fracture characteristics of the tuff at the mesoscopic level. The results of this research can be used as a basis for studying the influence of water on tuff.
As a high-efficiency and low-consumption mining mode, multi-middle section combined backfilling mining (MMSCBM) is becoming more and more widely used in metal mines. The geological mining conditions ...of Baixiangshan Iron Mine were taken as the simulation prototype. Similar model tests and numerical simulation experiments were used to study the surrounding rock disturbance, stope stability, surrounding rock stress, overburden settlement, and dynamic deformation of the ground surface during the MMSCBM process. The evolution process of the stope instability: the stable stage of the pillar, the large deformation stage of the pillar, the failure of some pillars, and the overall failure of the pillar. MMSCBM effectively buffered the excavation’s disturbance to the surrounding rock, adjusted the stress release mode, and changed the stress concentration area. The dynamic deformation laws of the overburden and the surface were summarized. The method of field monitoring was verified by numerical simulation calculation to study the disturbance degree of MMSCBM to the roadway and evaluate the safety of the roadway. This research has important significance and value for the wider application of the mining model.
Quick-setting grout has time-varying characteristics, and the space porosity of the injected medium changes after being grouted. The above two points need to be considered when loose and broken coal ...rock masses are grouted with rapid-setting grout. In other words, the coupling effect of the slurry-coal rock mass causes the slurry to exhibit the temporal and spatial characteristics of slurry viscosity (TSCSV). Based on the Bingham fluid constitutive model, a capillary group model with a linear increase in diameter was created, and a one-dimensional penetration grout diffusion model was established considering the TSCSV. The one-dimensional visualization splitting-permeation grout diffusion simulation test system was designed to obtain the space porosity of the broken coal rock mass under different final grouting pressures to obtain the law of the changes in grouting pressure and diffusion height with time under the condition of a fixed grouting rate. Furthermore, the mechanism of splitting-permeation grouting in loose and broken coal rock masses is analysed in depth considering the TSCSV. The results showed that the space porosity of coal rock masses increases linearly. In addition, the calculated value of the slurry diffusion distance was 0.93 – 1.1 times the experimental value considering the TSCSV. The calculated value was in good agreement with the experimental value. The calculated value of the final pressure of orifice grouting was approximately 1.5 times the test value without considering the unevenness of the space porosity distribution (USPD). The grouting pressure was overestimated without considering the USPD. Therefore, the TSCSV of the quick-setting slurry should be fully considered in the grouting design.
The Sanshandao Gold Mine is located on a seabed, and the crown pillar is the main barrier to isolating seawater and preventing it from entering the mine. The thickness of the crown pillar and the ...size of the point pillars have a substantial impact on the reduction of resource waste and the economic development of the mine. Therefore, it is very important to determine a reasonable crown pillar thickness and point pillar size. In this paper, theoretical analysis and numerical simulation were performed to determine a reasonable thickness of the crown pillar and the size of the point pillar in the Sanshandao Gold Mine. According to the law of conservation of energy, a theoretical mechanical model was established based on the “crown pillar-point pillar” support system, and the thickness of the crown pillar, which corresponds to different section sizes of the point pillars, was obtained. Numerical simulation was carried out by combining Geologic Object Computer-Aided Design (GOCAD) and Fast Lagrangian Analysis of Continua in 3 Dimensions (FLAC3D). According to the failure criterion of the elastic strain energy density, the limit value of the elastic energy strain density coefficient of the ore body element and crown pillar was analyzed, the thickness of the crown pillar was determined, and the theoretical derivation result was verified. The point pillar with a section size of 4 m × 4 m was selected, and the crown pillar thickness was 50 m.
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