The no-pillar longwall mining method (NPLM) by roof cutting technology (RCT) is an innovative longwall mining method proposed in China. Its essential technology is the employment of RCT to replace ...the chain pillar to safeguard the roadway. In this paper, a novel physical model test method is designed to investigate the protective mechanism of RCT for roadways in greater detail. Furthermore, the physical model test of RCT is conducted in consideration of the effect of broken roof rock bulking. Combined with numerical simulation, the results indicate that RCT can increase the degree of gangue bulking in goaf, hence providing effective support to the overlying strata and maintaining their integrity. Moreover, RCT can significantly reduce the abutment stress of the roadway roof and solid coal side, thereby ensuring the stability of roadway surrounding rock. This paper proposes three protection mechanisms of RCT for roadway based on the findings of the conducted research: I. Reducing the dimensions of roadway roof; II. Utilizing bulking gangue to support the overlying strata; III. Eliminating the cavities in the goaf adjacent to the roadway. The in situ application provides evidence that RCT is effective in controlling roadway deformation. This paper can serve as a reference for no-pillar mining and analogous geotechnical engineering physical model tests.
Highlights
A novel two-dimensional physical model test method is developed that can achieve bulking after failure.
Three protection mechanisms of roof cutting technology for the gob-side roadway are elucidated.
The effect of roof cutting technology on the bulking of broken roof rock is analyzed by experiment.
In conjunction with the in-situ application, the key to no-pillar longwall mining by roof cutting technology is proposed.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Flexible barriers have been widely applied in rockfall mitigation in recent years. However, the behavior of flexible barriers under the impact of boulders is still not fully understood. To ...investigate the interaction between a flexible barrier and a falling boulder, a large-scale physical modeling device has been constructed at a site in Hong Kong. Using this device, large-scale impact tests using boulders with different diameters were conducted. Test results are presented and analyzed in this paper. The motion of the boulder during impact is traced and analyzed. The impact forces on the flexible ring net and the supporting structures are measured and compared. From the comparison, the impact reduction rates (IRR) of boulders with different diameters are calculated. Moreover, a simple approach for estimating the impact loading of a boulder on a flexible barrier is proposed in this study. This approach is calibrated and verified using measured impact forces in the tests.
Central cracking refers to the formation of internal cavities in cross wedge rolling (CWR) products. It occurs in various materials such as aluminium/titanium alloys, steels and plasticine at room or ...elevated temperatures, driven by different central cracking mechanisms. However, these mechanisms are still elusive, and a unified central cracking predictive model is absent due to the complex stress states within the workpiece, including triaxial stress states, cyclic loading and severe shear effects. In this study, the underlying fracture mechanisms were revealed, and a robust unified damage model with sound physical meanings was developed using a lab-scale CWR physical model and finite element models. The physical model with the plasticine billets was built, allowing the CWR dies with different geometries rapidly 3D printed and the billets with various ductility efficiently manufactured. The central cracking transiting from brittle to ductile fracture was experimentally observed for the first time using specifically designed plasticine/flour composite samples at varying ductility. The corresponding physics-based central cracking predictive model was proposed and validated quantitatively with 60 groups of CWR tests and compared with ten existing damage models/fracture criteria. This study effectively solves the long-lasting central cracking problem in the CWR industry and enhances the scientific understanding of fracture mechanics in complex engineering applications.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The paper presents a physical model of energy related processes taking place in a diesel marine generator set. The development of a physical model was preceded by an analysis of the design structure ...of the investigated object and the flow of parameters among the functional modules of the model object. The above was completed by developing of functional and topological models. Only their analysis allowed the development of the proper physical model.
Culvert blockage is a recognized problem known to increase the risk of cross-drainage failure. Presently, the effects of bottom-up inlet blockage can be estimated using the theoretically derived ...energy loss method (ELM) and reduced area method (RAM). Both methods imply that hydraulically efficient inlets are more resilient to blockage effects but have not been verified experimentally for bottom-up blockages. In this study, a physical culvert model was used to determine the entrance loss coefficients and head-discharge relationships for commonly used pipe culvert inlets under different combinations of bottom-up blockage ratio, shape, and roughness. The experimental results confirm that hydraulically efficient inlets are more resilient to bottom-up blockage. Under submerged outlet control conditions, it was found that both blockage ratio and shape significantly influence the entrance loss coefficient and that ELM overestimated the entrance loss coefficient by up to 124%. Under inlet control conditions, it was found that only the blockage ratio significantly influenced the head-discharge relationship and that RAM underestimated the blockage discharge ratio by up to 38%. Comparisons to the experimental results show that ELM and RAM do not account for the increased efficiency of the unblocked part of the inlet under conditions of bottom-up blockage. Comparison to embedded inlets shows that they result in significantly lower entrance loss coefficients than partially blocked inlets under outlet control but yield similar discharge capacity ratios under inlet control. Uncertainties and estimation errors are given for the results, and validity for use in minimum performance design frameworks is evaluated for the different flow types used in hydraulic culvert design.
Based on field geological survey and unmanned aerial vehicle (UAV) photography, this paper studied the inherent causes, intrinsic mechanisms, and kinematic characteristics of a catastrophic landslide ...of dissolved and fractured rock slope in a mountainous area of Southwestern China. The discrete element method (DEM) model of representative volume element of fractured rock mass considering karst existence was developed with its micromechanical parameters calibrated from laboratory element tests. The coupled finite difference and discrete element methods (FDM-DEM) were then employed to simulate deformation and failure evolution and collapse development of the rock slope with both internal and externally triggering factors properly addressed. The kinematic characteristics of mobile collapse debris flow were analyzed, and the numerical simulation results were validated by laboratory physical model test. The results show that the internal causes were mainly manifested in slope structure, lithology combination, karst, and fracture development, among which the unfavorable interaction disintegrated rock masses. The primary external cause was the staged underground coal-mining operations underneath the collapsed body, which led to large cracks appearing at the back edges of the slope. The maximum velocity of mobile collapse debris was about 65 m/s with the maximum travel distance of more than 600 m. Numerical simulation results matched well with both field forensic investigation and laboratory physical model test results. The findings would help further understand the deformation and failure process of fractured rock slope subject to underground mining and provide technical reference for accurate assessment and proper mitigation of similar landslide disasters.
The Muzhailing tunnel is located in the plateau and mountainous areas. Under the combined action of strong earthquakes, large fault zones and dense and huge tectonic stresses, the weak surrounding ...rock of the tunnel is usually fissured. Repeated, irregular and asymmetric large deformation and damage accidents often occur during the construction process. To explore the asymmetric large deformation and failure characteristics of the surrounding rock caused by asymmetric stress, this paper considers the equal straight wall arch tunnel as the research object and explores the deformation mechanism of a carbonaceous slate tunnel under asymmetric stress by applying the physical model experiment. Initially, based on the actual geometric characteristics, spatial distribution characteristics and engineering geological conditions of the tunnel, the optimal similarity ratio is determined, and the tunnel physical model under asymmetric stress is established. Afterward, by analyzing the variation laws of displacement, surrounding rock strain anchor cable axial force under asymmetric load, the deformation mechanism of the tunnel surrounded by carbonaceous slate under asymmetric load is revealed. The influence mechanism and control countermeasures of asymmetric stress on the tunnel surrounded by carbonaceous slate are explored by integrating the macro failure characteristics and failure forms of the tunnel. Finally, the 1G-NPR anchor cable characterized by constant resistance and large deformation with a negative Poisson's ratio and the 2G-NPR bolts with long and short combination support are selected to propose control measures for carbonaceous slate tunnels affected by asymmetric stress. The asymmetric support measures are verified by on-site support tools. The research results indicate that with the loading of asymmetrical stress, obvious asymmetrical deformation occurs in the carbonaceous slate tunnel model due to stress concentration, such as bending deformation, block falling and surface peeling of the sidewall and the bottom. The deformation can be effectively controlled by a combination of long and short bolts and cables, which provides a theoretical basis and practical guidance for the design of tunnel asymmetric support with a similar engineering background.
Highlights
The failure in the study area represents a parallel or small angle oblique fault mode, leading to severe, non-uniform pressure failure.
The sudden increase of the axial force of the monitoring anchor bolt can be used as a monitoring and early warning tool for detecting tunnel deformations.
The effect of 2G-NPR large deformation bolt support in controlling asymmetric large deformation failure of tunnel is verified on the geomechanical model experiment and field.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
An activated carbon (AC) deriving from sludge is used in this research for the adsorption of two water pollutants, namely Reactive Black 5 (RB5) and Green Alizarin (GA) dyes, at different ...temperatures. The adsorption capacities varied from 277.2 to 312.69 mg/g for GA and from 225.82 to 256.02 mg/g for RB5. Comparatively, this adsorbent presents good performances in removing these dyes from wastewater. The application of physical models to adsorption experiments is advantageous to provide new insights into the dyes’ adsorption mechanism. A dedicated physical adsorption model suggests that RB5 and GA dyes are adsorbed in a monolayer. Moreover, the orientation of RB5 and GA dyes on AC resulted in an angled position, determining a multi-molecular process. In addition, both dyes are adsorbed by the occurrence of an aggregation process, forming a dimer. The impact of temperature can be also interpreted, allowing concluding that it plays a relevant role in removing these dyes. The calculation and interpretation of adsorption energies show that the dyes are removed via an endothermic process, and physical forces are involved.
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CEKLJ, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Decoupled cylindrical charge structure is widely used in contour blasting to reduce overbreak and control rock damage, which is critical to the safety and efficiency of rock excavation. The blasting ...effect strongly depends on the blasting stress acting on the rock to generate cracks along the connecting line of boreholes. The blasting stress decays with distance in rock mass, so its attenuation significantly affects the blasting effect. The attenuation characteristics of blasting stress under different decoupled cylindrical charge structures are, accordingly, necessary to be investigated. In this study, physical model blasting tests under different filling mediums and decoupling ratios were conducted, and strain gages and a sonic tester were used to evaluate the blasting stress response and block damage. A numerical model was developed and verified to simulate the same tests and some other tests with additional decoupling ratios. The results show that filling medium and decoupling ratio play important roles in the attenuation characteristics of stress peak, which are analyzed and attributed to the different peak pressures and loading rates of the borehole wall pressures. A modified numerical model combined with response surface method was then developed to study the independent and interactive effects of static pressure, peak pressure (
P
b
), loading rate (
L
r
), and velocity of detonation (
v
d
) on the stress attenuation index (
α
). The results indicate that static stress has little effect on
α
in the elastic stage.
α
decreases with increasing
P
b
and
v
d
, and decreases with decreasing
L
r
. The effects of
P
b
and
L
r
on
α
are weakened with increasing
v
d
. Finally, based on a theoretical model of cylindrical charge, the results are further analyzed. The results show that the blasting stress for water decays more slowly than that for air, especially in low
v
d
.
Highlights
Decoupled cylindrical charge blasting tests under different filling mediums and decoupling ratios are conducted.
The effects of decoupling ratio and filling medium on stress attenuation is attributed to the borehole wall pressure (BWP).
A numerical model combined with response surface method is proposed to study the interactive effects of BWP and velocity of detonation (VOD) on stress attenuation.
The effects of BWP on the stress attenuation are weakened with increasing VOD.
The stress attenuation for water medium is slower than that for air medium.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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