Microscopic seepage characteristics are critical for the evaluation of tight sandstone reservoirs.In this study,a digital core approach integrating microscopic seepage simulation and CT scanning was developed to chara...Microscopic seepage characteristics are critical for the evaluation of tight sandstone reservoirs.In this study,a digital core approach integrating microscopic seepage simulation and CT scanning was developed to characterize microscopic seepage and fracture effectiveness(the ratio of micro-fractures that contributes to fluid flow)of tight sandstones.Numerical simulations were carried out for characterizations of tight sandstones.The results show that the axial permeability of the investigated cylindrical tight sandstone from Junggar Basin in China is 0.460μm~2,while the radial permeability is 0.3723μm~2,and the axial and radial effective fracture ratios are 0.4387 and 0.4806,respectively,indicating that cracks are not fully developed and the connectivity between micro-cracks is poor.Directional permeability that is difficult to measure by laboratory experiments can be obtained readily using the proposed method in this paper.The results provide important information for improving the exploration and development of tight sandstone reservoirs.展开更多
A mixture of fault gouge and rubble taken out from a fault zone is used to prepare a S-RM(Soil-Rock Mixture)sample with rock block proportions of 20%,30%,40%,50%,60%and 70%,respectively.A GDS triaxial test system is u...A mixture of fault gouge and rubble taken out from a fault zone is used to prepare a S-RM(Soil-Rock Mixture)sample with rock block proportions of 20%,30%,40%,50%,60%and 70%,respectively.A GDS triaxial test system is used accordingly to measure the seepage characteristics of such samples under different loading and unloading confining pressures in order to determine the variation law of the permeability coefficient.The test results show that:(1)The permeability coefficient of the S-RM samples decreases as the pressure increases,and the decrease rate of this coefficient in the initial stage of confining pressure loading is obviously higher than in the semi-late period;(2)The permeability coefficient at different confining pressure levels presents a common trend as the rock block proportion is increased,i.e.,it decreases first then it increases(the permeability coefficient of the sample with rock block proportion 40%being the smallest,70%the largest);(3)In the stage of confining pressure unloading,the recovery degree of the permeability coefficient grows with the increase of rock block proportion(the recovery rate of S-RM sample with rock block proportion 70%reaches 50.2%);(4)In the stage of confining pressure loading and unloading,the sensitivity of the permeability coefficient to the rock block proportion displays the inverse“Z”variation rule(when rock block proportion reaches 60%,the sensitivity is highest);(5)In the stage of confining pressure loading,the relationship between the permeability coefficient and confining pressure can be described by an exponential relationship.展开更多
Under the effect of eccentric loads,when the suction pressure of the composite bucket foundation is leveled,the seepage failure is very easy to occur.The seepage failure occurrence causes the foundation to settle unev...Under the effect of eccentric loads,when the suction pressure of the composite bucket foundation is leveled,the seepage failure is very easy to occur.The seepage failure occurrence causes the foundation to settle unevenly and impairs the bearing performance.This study uses ABAQUS finite element software to establish a composite bucket foundation model for finite element analysis.The model simulates the seepage of the foundation penetrating process under eccentric load to reveal the induced seepage characteristics of the bucket foundation.The most vulnerable position of seepage failure under the eccentric loading is elucidated.Critical suction formulas for different offset eccentric moment strategies are derived and compared with existing literature formulas.Then the derived formula is supplemented and corrected according to the pressure difference between adjacent cabins.Conclusions can be drawn:(1)Under eccentric loads,the critical suction decreases about 7%−10%.(2)The pressure difference between adjacent cabins impacts significantly on the seepage field,and the critical suction,at most,can be reduced by 17.56%.(3)the offset strategies have little effect on the seepage field.Efficient and appropriate strategies can be selected to meet the requirement of leveling in engineering project.展开更多
In this study,a two-dimensional approach is elaborated to study with the lattice Boltzmann method(LBM)the seepage of water in the pores of a soil.Firstly,the D2Q9 model is selected to account for the discrete velocity...In this study,a two-dimensional approach is elaborated to study with the lattice Boltzmann method(LBM)the seepage of water in the pores of a soil.Firstly,the D2Q9 model is selected to account for the discrete velocity distribution of water flow.In particular,impermeability is considered as macroscopic boundary condition for the left and right domain sides,while the upper and lower boundaries are assumed to behave as pressure boundaries controlled by different densities.The micro-boundary conditions are implemented through the standard rebound strategy and a non-equilibrium extrapolation scheme.Matlab is used for the development of the related algorithm.Finally,the influence of porosity,permeability,osmotic pressure and other factors is assessed with regard to seepage characteristics and the ensuing results are compared with Darcy’s law.The computations show that,for fixed initial conditions,the pore structure has a certain influence on the local velocity of seepage,but the overall state is stable,and the average velocity of each layer is the same.The larger the pore passage is,the faster the flow velocity is,and vice versa.For low permeability,the numerical results are consistent with the Darcy's law.The greater the pressure difference between the inlet and outlet of seepage,the greater the seepage rate.The relationship between them is linear(yet in good agreement with Darcy’s law).展开更多
sing an MTS816.03 test system and self-designed seepage apparatus,seepage tests of saturated broken rocks were conducted,and the influence of lithology,axial stress,grain size distribution and loading rate on seepage ...sing an MTS816.03 test system and self-designed seepage apparatus,seepage tests of saturated broken rocks were conducted,and the influence of lithology,axial stress,grain size distribution and loading rate on seepage characteristics was analyzed.The results show that:(1) Under the same axial stress(12 MPa)the permeability of different lithologic samples increases in the order:gangue < mudstone < sand stone < limestone.The permeability of gangue is 3 magnitudes lower than that of limestone.The absolute value of the non-Darcy coefficient β increases in the order:limestone < sandstone < mudstone < gangue The non-Darcy coefficient β of limestone,which is positive,is 5 magnitudes lower than that of gangue.(2)With increasing axial stress,the permeability of saturated broken sandstone decreases,and the absolute value of the non-Darcy coefficient β increases.After the axial stress exceeds 12 MPa,the curves of perme ability and non-Darcy coefficient β all tend to be stable.(3) With increasing Talbol power exponent,the permeability increases,and the absolute value of the non-Darcy coefficient β decreases.(4) With increas ing loading,the permeability increases,and the absolute value of the non-Darcy coefficient β decreases When the loading rate is 0.5 kN/s,the non-Darcy coefficient β is positive.展开更多
Through seepage tests under different loading and unloading confining pressures and different hydraulic gradients,the authors studied the effects of stress states and stress history on fracture permeability evolution ...Through seepage tests under different loading and unloading confining pressures and different hydraulic gradients,the authors studied the effects of stress states and stress history on fracture permeability evolution for single granite fracture and sandstone fracture. The results show that there exists a linear relationship between the seepage discharge and osmotic pressure in sandstone fissure under each level of confining pressure. With the increasing in the confining pressure,the permeability of the fracture decreases,but the decreasing rate is changeing. During the unloading process,the fracture seepage velocity cannot be fully recovered to the size of the loading process. Therefore,in the unloading process of the confining pressure,the recovery of fracture permeability shows obvious hysteresis effects. The flow rate of the fracture remains unchanged during five cycles of loading and unloading processes of the confining pressure. In each cycle,the evolution character of the flow rate with the confining pressure remains unchanged. These experiments show that the seepage characteristics of sandstone and granite fractures are not the same under the same stress state.展开更多
The compaction characteristics of gravelly soil are affected by gravel hardness.To investigate the evolution and influencing mechanism of different gravel hardness on the compaction characteristics of gravelly soil,he...The compaction characteristics of gravelly soil are affected by gravel hardness.To investigate the evolution and influencing mechanism of different gravel hardness on the compaction characteristics of gravelly soil,heavy compaction tests and crushing tests were conducted on gravelly soils with gravels originated from hard,soft and extremely soft rocks.According to orthogonal experiments and variance analysis,it was found that hardness has a significant impact on the maximum dry density of gravelly soil,followed by gravel content,and lastly,moisture content.For gravel compositions with an average saturated uniaxial compressive strength less than 60 MPa,the order of compacted maximum dry density is soft gravels>hard gravels>extremely soft gravels.Each type of gravelly soil has a threshold for gravel content,with 60%for hard and soft gravels and 50%for extremely soft gravels.Beyond these thresholds,the compacted dry density decreases significantly.There is a certain interaction between hardness,gravel content,and moisture content.Higher hardness increases the influence of gravel content,whereas lower hardness increases the influence of moisture content.Gravelly soils with the coarse aggregate(CA)between 0.7 and 0.8 typically achieve higher dry densities after compaction.In addition,the prediction equations for the particle breakage rate and CA ratio in the Bailey method were proposed to estimate the compaction performance of gravelly soil preliminarily.The results further revealed the compaction mechanism of different gravelly soils and can provide reference for subgrade filling construction.展开更多
Some of the chemical and physical water qualities of the Graff River in the city of Kut were studied, and for two sites of the river, One was at the Crimea site, the other in the Jihad district, and for the period fro...Some of the chemical and physical water qualities of the Graff River in the city of Kut were studied, and for two sites of the river, One was at the Crimea site, the other in the Jihad district, and for the period from October/2018 to March/2019, Seven variables of river water have been analyzed: temperature PH, electrical conductivity, TDS, turbidity, alkaline, and chloride. The results showed that most of the chemical and physical water properties of the river were in normal proportions and did not rise, except for the turbidity, which was at a very high level, and that the pH values were close to the basal side. The results of the statistical analysis revealed positive significant relationships between the pH and (chloride and TDS). On the other hand, between electrical conductivity and both previous variables as well. And a negative significant connection between temperature and alkaline.展开更多
The microscopic characteristics and mechanical properties of rocks change after the action of acid on deep shale,which affects the fracturing effect.Accordingly,we designed and conducted indoor experiments related to ...The microscopic characteristics and mechanical properties of rocks change after the action of acid on deep shale,which affects the fracturing effect.Accordingly,we designed and conducted indoor experiments related to the changes in macro and microscopic characteristics after the interaction of acid with the shale of Wujiaping Formation,based on which the characteristic law of fracture volume modification after acid fracturing was studied using numerical simulation.The results demonstrate that the pores and fractures are enlarged and the structure is significantly loosened after the acid immersion.And a 15%concentration of hydrochloric acid can effectively dissolve shale.Furthermore,the degree of acid-etching reaction is highly variable because of the different carbonate content,which reveals the strong inhomogeneity of the shale system in the Wujiaping Group reservoir section.After the acid interacted with the shale rock samples,the triaxial compressive strength,elastic modulus,and Poisson’s ratio of shale decreased.Moreover,the evaluation of the effect after acid fracturing simulated by fracturing software revealed that the smaller the value of elastic modulus in shale-based reservoirs,the more favorable the fracture volume modification.This discovery not only provides a theoretical basis for the expansion and extension patterns of acid-fracturing in carbonaceous shale formations but also offers research methods and theoretical insights for the fundamental exploration of other deep-seated oil and gas resources.展开更多
Shaped charge warhead is important for enhancing the damage performance of underwater weapons.This paper used finite element analysis software and based on JPC water penetration experiments to examine the influence of...Shaped charge warhead is important for enhancing the damage performance of underwater weapons.This paper used finite element analysis software and based on JPC water penetration experiments to examine the influence of liner parameters(wall thickness,material),charge aspect ratio,and stand-off distance on the movement characteristics of JPC in water.The findings reveal that the head diameter of the JPC increases and experiences significant erosion after entering the water,the effective length of the JPC in water undergoes two distinct phases:a growth phase and a decrease phase,with the velocity of the JPC decaying exponentially.Increasing the liner thickness,stand-off distance and the charge aspect ratio can improve the erosion resistance and the velocity retention capacity of the JPC.The optimal ranges for liner thickness and stand-off distance are 0.0363D_(k) to 0.0545D_(k)(D_(k) is the charge diameter),the stand-off distance should be within 1.0D_(k).After the charge aspect ratio higher than 1.25,the charge structure exerts minimal influence the movement characteristics of the JPC in water.Material density plays a crucial role in the velocity decay pattern of the JPC during penetration.JPC with higher densities exhibit superior velocity retention capabilities in water,with the velocity decay pattern converging if the densities are similar.Consequently,copper,tantalum and tungsten liners are deemed appropriate for underwater shaped charge warhead.Finally,the results will provide an important reference for the design of underwater shaped charge warhead.展开更多
Coal pyrolysis is a fundamental reaction in the thermal processing and utilization of coal.Investigating the behavior and kinetics of coal pyrolysis is crucial for optimizing,designing,and developing a composite riser...Coal pyrolysis is a fundamental reaction in the thermal processing and utilization of coal.Investigating the behavior and kinetics of coal pyrolysis is crucial for optimizing,designing,and developing a composite riser for the staged pyrolysis gasification process of pulverized coal.In this study,the non-isothermal pyrolysis behavior and kinetics of coal were examined at different heating rates(30,50,100,300,500,700,and 900℃/min)using thermogravimetry(TG)coupled with Fourier-transform infrared spectroscopy.Analysis of the TG/derivative TG(TG/DTG)curves indicated that coal pyrolysis mainly occurred between 300℃ and 700℃.Higher heating rates led to more volatiles being released from the coal,and a higher temperature was required to achieve rapid pyrolysis.Kinetic analysis showed that both the model-free methods(Friedman,Flynn-Wall-Ozawa,and Kissinger-Akahira-Sunose)and the model-based method(Coats-Redfern)effectively describe the coal pyrolysis process.The change in the Ea values between the two kinetic models was consistent throughout the pyrolysis process,and the most probable mechanism was the F2 model(secondary chemical reaction).In addition,the heating rate did not change the overall reaction order of the pyrolysis process;however,a higher heating rate resulted in a decrease in the Ea value during the initial pyrolysis stage.展开更多
Hydraulic jetting is a form of fracturing that involves using a high-pressure jet of water to create fractures in the reservoir rock with a nozzle serving as the central component of the hydraulic sandblasting perfora...Hydraulic jetting is a form of fracturing that involves using a high-pressure jet of water to create fractures in the reservoir rock with a nozzle serving as the central component of the hydraulic sandblasting perforation tool.In this study,the flow behavior of the nozzle is simulated numerically in the framework of a SST k-ωturbulence model.The results show that the nozzle structure can significantly influence the jet performance and related cavitation effect.Through orthogonal experiments,the nozzle geometric parameters are optimized,and the following configuration is found accordingly:contraction angle 20°,contraction segment length 6 mm,cylindrical segment diameter 6 mm,cylindrical segment length 12 mm,spread segment length 10 mm,and spread angle 55°.展开更多
To investigate the influence mechanism of geostress on rockburst characteristics,three groups of gneiss rockburst experiments were conducted under different initial geostress conditions.A high-speed photography system...To investigate the influence mechanism of geostress on rockburst characteristics,three groups of gneiss rockburst experiments were conducted under different initial geostress conditions.A high-speed photography system and acoustic emission(AE)monitoring system were used to monitor the entire rockburst process in real time.The experimental results show that when the initial burial depth increases from 928 m to 1320 m,the proportion of large fracture scale in rockburst increases by 154.54%,and the AE energy increases by 565.63%,reflecting that the degree and severity of rockburst increase with the increase of burial depth.And then,two mechanisms are proposed to explain this effect,including(i)the increase of initial geostress improves the energy storage capacity of gneiss,and then,the excess energy which can be converted into kinetic energy of debris ejection increases,consequently,a more pronounced violent ejection phenomenon is observed at rockburst;(ii)the increase of initial geostress causes more sufficient plate cracks of gneiss after unloading ofσh,which provides a basis for more severe ejection of rockburst.What’s more,a precursor with clear physical meaning for rockburst is proposed under the framework of dynamic response process of crack evolution.Finally,potential value in long term rockburst warning of the precursor obtained in this study is shown via the comparison of conventional precursor.展开更多
Energetic structural materials(ESMs)are a new type of structural materials with bearing and damage characteristics.In this work the microstructure,mechanical properties and energy release characteristics of multi-elem...Energetic structural materials(ESMs)are a new type of structural materials with bearing and damage characteristics.In this work the microstructure,mechanical properties and energy release characteristics of multi-element Ti-Zr-Ta alloys with good casting performance were studied.The microstructure of the Ti_(x)ZrTa alloys gradually change from BCC+HCP to single BCC structure with the increase of Ti.While the Ti_(2)Zr_(y)Ta alloys was still uniform and single BCC structure with the increase of Zr.The evolution of microstructure and composition then greatly affect the mechanical properties and energy-release characteristics of Ti-Zr-Ta alloys.The synergistic effect of dual phase structure increases the fracture strain of Ti_(x)ZrTa(x=0.2,0.5)with the Ti content decreases,while the fracture strain of Ti_(x)ZrTa(x=2.0,3.0,4.0)gradually increase with the Ti content increases caused by the annihilation of the obstacles for dislocation movement.And as Zr content increases,the fracture strain of Ti_(2)Zr_(y)Ta alloys decrease,then the oxidation reaction rate and fragmentation degree gradually increase.The higher oxidation rate and the lager exposed oxidation area jointly leads the higher releasing energy efficiency of Ti_(x)ZrTa alloys with low Ti content and Ti_(2)Zr_(y)Ta alloys with high Zr content.展开更多
The damage evolution process of non-penetrating cracks often causes some unexpected engineering disasters.Gypsum specimens containing non-penetrating crack(s)are used to study the damage evolution and characteristics ...The damage evolution process of non-penetrating cracks often causes some unexpected engineering disasters.Gypsum specimens containing non-penetrating crack(s)are used to study the damage evolution and characteristics under cyclic loading.The results show that under cyclic loading,the relationship between the number of non-penetrating crack(s)and the characteristic parameters(cyclic number,peak stress,peak strain,failure stress,and failure strain)of the pre-cracked specimens can be represented by a decreasing linear function.The damage evolution equation is fitted by calibrating the accumulative plastic strain for each cycle,and the damage constitutive equation is proposed by the concept of effective stress.Additionally,non-penetrating cracks are more likely to cause uneven stress distribution,damage accumulation,and local failure of specimen.The local failure can change the stress distribution and relieve the inhibition of non-penetrating crack extension and eventually cause a dramatic destruction of the specimen.Therefore,the evolution process caused by non-penetrating cracks can be regarded as one of the important reasons for inducing rockburst.These results are expected to improve the understanding of the process of spalling formation and rockburst and can be used to analyze the stability of rocks or rock structures.展开更多
The study of non-axisymmetric fuel dispersal and detonation can provide reference for the prevention of industrial cloud explosion accidents and the design of fuel air explosive(FAE).The concentration and detonation f...The study of non-axisymmetric fuel dispersal and detonation can provide reference for the prevention of industrial cloud explosion accidents and the design of fuel air explosive(FAE).The concentration and detonation fields of 85 kg cylindrical and fan-shaped fuel are investigated by experiments and numerical simulations.A dynamic model of the whole process for fuel dispersal and detonation is built.The concentration distribution of fuel is used as the initial condition to calculate the detonation stage,thus solving the initial value problem of detonation field.The phase and component changes of fuel cloud at different locations are compared.The fuel cloud is divided into directions of 0°,90°,135°and 180°.The results show that the maximum cloud radius is 20.94 m in 135°and the minimum is 12.04 m in 0°.The diameter of the detonation fireball is 53.6 m,and the peak temperature is 3455 K.The highest peak overpressure is 3.44 MPa in 0°and the lowest is 2.97 MPa in 135°.The proportion of liquid phase in 0°is22.90%,and the fuel loss is 11.8% and 9% higher than that in 135°and cylindrical charge,respectively.The stable propagation distance of blast wave in 135°is 42.50% longer than 0°and 28.37% longer than cylindrical charge.展开更多
The dynamic spalling characteristics of rock are important for stability analysis in rock engineering.This paper presented an experimental investigation on the dynamic spalling characteristics of granite with differen...The dynamic spalling characteristics of rock are important for stability analysis in rock engineering.This paper presented an experimental investigation on the dynamic spalling characteristics of granite with different temperatures and strain rates.A series of dynamic spalling tests with different impact velocities were conducted on thermally treated granite at different temperatures.The dynamic spalling strengths of granite with different temperatures and strain rates were determined.A model was proposed to correlate the dynamic spalling strength of granite,high temperature and strain rate.The results show that the spalling strength of granite decreases with increasing temperature.Moreover,the spalling strength of granite with a higher strain rate is larger than that with a lower strain rate.The proposed model can describe the relationship among dynamic spalling strength of granite,high temperature and strain rate.展开更多
The safe and efficient development of natural gas hydrate requires a deep understanding of the deformation behaviors of reservoirs.In this study,a series of triaxial shearing tests are carried out to investigate the d...The safe and efficient development of natural gas hydrate requires a deep understanding of the deformation behaviors of reservoirs.In this study,a series of triaxial shearing tests are carried out to investigate the deformation properties of hydrate-bearing sediments.Variations of volumetric and lateral strains versus hydrate saturation are analyzed comprehensively.Results indicate that the sediments with high hydrate saturation show dilative behaviors,which lead to strain-softening characteristics during shearing.The volumetric strain curves have a tendency to transform gradually from dilatation to compression with the increase in effective confining pressure.An easy prediction model is proposed to describe the relationship between volumetric and axial strains.The model coefficientβis the key dominating factor for the shape of volumetric strain curves and can be determined by the hydrate saturation and stress state.Moreover,a modified model is established for the calculation of lateral strain.The corresponding determination method is provided for the easy estimation of model coefficients for medium sand sediments containing hydrate.This study provides a theoretical and experimental reference for deformation estimation in natural gas hydrate development.展开更多
The Qinghai Nanshan fault is a larger fault in the Northeastern Xizang Plateau.In previous studies,its movement characteristics are mainly investigated with geological and seismic observations,and the tectonic transfo...The Qinghai Nanshan fault is a larger fault in the Northeastern Xizang Plateau.In previous studies,its movement characteristics are mainly investigated with geological and seismic observations,and the tectonic transformation role of the fault on its east is not yet clear.This study uses data fusion to obtain denser GPS observations near the Qinghai Nanshan fault.Based on tectonic characteristics,we establish a block model to investigate the fault slip rate,locking degree,and slip deficit.The results show that the Qinghai Nanshan fault slip rate is characterized by sinistral and convergent movement.Both the sinistral and convergent rates display a decreasing trend from west to east.The locking degree and slip deficit are higher in the western segment(with an average of about 0.74 and 1.1 mm/a)and lower in the eastern segment.Then,we construct a strain rate field using GPS observations to analyze the regional strain characteristics.The results indicate that along the fault,the western segment shows a larger shear strain rate and negative dilation rate.Regional earthquake records show that the frequency of earthquakes is lower near the fault.The joint results suggest that the western segment may have a higher earthquake risk.In addition,the insignificant fault slip rate in the eastern segment may indicate that it does not participate in the tectonic transformation among the Riyueshan,Lajishan,and West Qinling faults.展开更多
In this paper,a detection method combining Cameron decomposition based on polarization scattering characteristics in sea clutter background is proposed.Firstly,the Cameron decomposition is exploited to fuse the radar ...In this paper,a detection method combining Cameron decomposition based on polarization scattering characteristics in sea clutter background is proposed.Firstly,the Cameron decomposition is exploited to fuse the radar echoes of full polarization channels at the data level.Due to the artificial material structure on the surface of the target,it can be shown that the non-reciprocity of the target cell is stronger than that of the clutter cell.Then,based on the analysis of the decomposition results,a new feature with scattering geometry characteristics in polarization domain,denoted as Cameron polarization decomposition scattering weight(CPD-SW),is extracted as the test statistic,which can achieve more detailed descriptions of the clutter scattering characteristics utilizing the difference between their scattering types.Finally,the superiority of the proposed CPD-SW detector over traditional detectors in improving detection performance is verified by the IPIX measured dataset,which has strong stability under short-time observation in threshold detection and can also improve the separability of feature space zin anomaly detection.展开更多
基金financially supported by the National Natural Science Foundation of China(Grant No.41972138)the Technology Major Project of China(Grant No.ZD2019-183007,2016ZX05002-002)。
文摘Microscopic seepage characteristics are critical for the evaluation of tight sandstone reservoirs.In this study,a digital core approach integrating microscopic seepage simulation and CT scanning was developed to characterize microscopic seepage and fracture effectiveness(the ratio of micro-fractures that contributes to fluid flow)of tight sandstones.Numerical simulations were carried out for characterizations of tight sandstones.The results show that the axial permeability of the investigated cylindrical tight sandstone from Junggar Basin in China is 0.460μm~2,while the radial permeability is 0.3723μm~2,and the axial and radial effective fracture ratios are 0.4387 and 0.4806,respectively,indicating that cracks are not fully developed and the connectivity between micro-cracks is poor.Directional permeability that is difficult to measure by laboratory experiments can be obtained readily using the proposed method in this paper.The results provide important information for improving the exploration and development of tight sandstone reservoirs.
基金This work was supported by the Key Laboratory of Safety and High-Efficiency Coal Mining,Ministry of Education,Anhui University of Science and Technology(JYBSYS2020209)the Natural Science Research Project of Anhui Provincial Department of Education(KJHS2020B13)the Huangshan University School Level Talent Launch Project(No.2020XKJQ001).
文摘A mixture of fault gouge and rubble taken out from a fault zone is used to prepare a S-RM(Soil-Rock Mixture)sample with rock block proportions of 20%,30%,40%,50%,60%and 70%,respectively.A GDS triaxial test system is used accordingly to measure the seepage characteristics of such samples under different loading and unloading confining pressures in order to determine the variation law of the permeability coefficient.The test results show that:(1)The permeability coefficient of the S-RM samples decreases as the pressure increases,and the decrease rate of this coefficient in the initial stage of confining pressure loading is obviously higher than in the semi-late period;(2)The permeability coefficient at different confining pressure levels presents a common trend as the rock block proportion is increased,i.e.,it decreases first then it increases(the permeability coefficient of the sample with rock block proportion 40%being the smallest,70%the largest);(3)In the stage of confining pressure unloading,the recovery degree of the permeability coefficient grows with the increase of rock block proportion(the recovery rate of S-RM sample with rock block proportion 70%reaches 50.2%);(4)In the stage of confining pressure loading and unloading,the sensitivity of the permeability coefficient to the rock block proportion displays the inverse“Z”variation rule(when rock block proportion reaches 60%,the sensitivity is highest);(5)In the stage of confining pressure loading,the relationship between the permeability coefficient and confining pressure can be described by an exponential relationship.
基金supported by the National Natural Science Foundation of China(Grant No.51779171)the Tianjin Municipal Natural Science Foundation(Grant No.18JCYBJC22800).
文摘Under the effect of eccentric loads,when the suction pressure of the composite bucket foundation is leveled,the seepage failure is very easy to occur.The seepage failure occurrence causes the foundation to settle unevenly and impairs the bearing performance.This study uses ABAQUS finite element software to establish a composite bucket foundation model for finite element analysis.The model simulates the seepage of the foundation penetrating process under eccentric load to reveal the induced seepage characteristics of the bucket foundation.The most vulnerable position of seepage failure under the eccentric loading is elucidated.Critical suction formulas for different offset eccentric moment strategies are derived and compared with existing literature formulas.Then the derived formula is supplemented and corrected according to the pressure difference between adjacent cabins.Conclusions can be drawn:(1)Under eccentric loads,the critical suction decreases about 7%−10%.(2)The pressure difference between adjacent cabins impacts significantly on the seepage field,and the critical suction,at most,can be reduced by 17.56%.(3)the offset strategies have little effect on the seepage field.Efficient and appropriate strategies can be selected to meet the requirement of leveling in engineering project.
文摘In this study,a two-dimensional approach is elaborated to study with the lattice Boltzmann method(LBM)the seepage of water in the pores of a soil.Firstly,the D2Q9 model is selected to account for the discrete velocity distribution of water flow.In particular,impermeability is considered as macroscopic boundary condition for the left and right domain sides,while the upper and lower boundaries are assumed to behave as pressure boundaries controlled by different densities.The micro-boundary conditions are implemented through the standard rebound strategy and a non-equilibrium extrapolation scheme.Matlab is used for the development of the related algorithm.Finally,the influence of porosity,permeability,osmotic pressure and other factors is assessed with regard to seepage characteristics and the ensuing results are compared with Darcy’s law.The computations show that,for fixed initial conditions,the pore structure has a certain influence on the local velocity of seepage,but the overall state is stable,and the average velocity of each layer is the same.The larger the pore passage is,the faster the flow velocity is,and vice versa.For low permeability,the numerical results are consistent with the Darcy's law.The greater the pressure difference between the inlet and outlet of seepage,the greater the seepage rate.The relationship between them is linear(yet in good agreement with Darcy’s law).
基金provided by the National Basic Research Program of China (No.2013CB227900)the Ordinary University Graduate Student Research Innovation Project in Jiangsu Province for 2014 (No.KYLX_1370)the National Natural Science Foundation of China (Nos.11502229 and 51404266)
文摘sing an MTS816.03 test system and self-designed seepage apparatus,seepage tests of saturated broken rocks were conducted,and the influence of lithology,axial stress,grain size distribution and loading rate on seepage characteristics was analyzed.The results show that:(1) Under the same axial stress(12 MPa)the permeability of different lithologic samples increases in the order:gangue < mudstone < sand stone < limestone.The permeability of gangue is 3 magnitudes lower than that of limestone.The absolute value of the non-Darcy coefficient β increases in the order:limestone < sandstone < mudstone < gangue The non-Darcy coefficient β of limestone,which is positive,is 5 magnitudes lower than that of gangue.(2)With increasing axial stress,the permeability of saturated broken sandstone decreases,and the absolute value of the non-Darcy coefficient β increases.After the axial stress exceeds 12 MPa,the curves of perme ability and non-Darcy coefficient β all tend to be stable.(3) With increasing Talbol power exponent,the permeability increases,and the absolute value of the non-Darcy coefficient β decreases.(4) With increas ing loading,the permeability increases,and the absolute value of the non-Darcy coefficient β decreases When the loading rate is 0.5 kN/s,the non-Darcy coefficient β is positive.
基金National Natural Science Foundation of China(No.41372239)Graduate Innovation Fund of Jilin University(No.2015096)
文摘Through seepage tests under different loading and unloading confining pressures and different hydraulic gradients,the authors studied the effects of stress states and stress history on fracture permeability evolution for single granite fracture and sandstone fracture. The results show that there exists a linear relationship between the seepage discharge and osmotic pressure in sandstone fissure under each level of confining pressure. With the increasing in the confining pressure,the permeability of the fracture decreases,but the decreasing rate is changeing. During the unloading process,the fracture seepage velocity cannot be fully recovered to the size of the loading process. Therefore,in the unloading process of the confining pressure,the recovery of fracture permeability shows obvious hysteresis effects. The flow rate of the fracture remains unchanged during five cycles of loading and unloading processes of the confining pressure. In each cycle,the evolution character of the flow rate with the confining pressure remains unchanged. These experiments show that the seepage characteristics of sandstone and granite fractures are not the same under the same stress state.
基金supported by the National Natural Science Foundation of China(No.51878127)the Fundamental Research Funds for the Central Universities(N180104013).
文摘The compaction characteristics of gravelly soil are affected by gravel hardness.To investigate the evolution and influencing mechanism of different gravel hardness on the compaction characteristics of gravelly soil,heavy compaction tests and crushing tests were conducted on gravelly soils with gravels originated from hard,soft and extremely soft rocks.According to orthogonal experiments and variance analysis,it was found that hardness has a significant impact on the maximum dry density of gravelly soil,followed by gravel content,and lastly,moisture content.For gravel compositions with an average saturated uniaxial compressive strength less than 60 MPa,the order of compacted maximum dry density is soft gravels>hard gravels>extremely soft gravels.Each type of gravelly soil has a threshold for gravel content,with 60%for hard and soft gravels and 50%for extremely soft gravels.Beyond these thresholds,the compacted dry density decreases significantly.There is a certain interaction between hardness,gravel content,and moisture content.Higher hardness increases the influence of gravel content,whereas lower hardness increases the influence of moisture content.Gravelly soils with the coarse aggregate(CA)between 0.7 and 0.8 typically achieve higher dry densities after compaction.In addition,the prediction equations for the particle breakage rate and CA ratio in the Bailey method were proposed to estimate the compaction performance of gravelly soil preliminarily.The results further revealed the compaction mechanism of different gravelly soils and can provide reference for subgrade filling construction.
文摘Some of the chemical and physical water qualities of the Graff River in the city of Kut were studied, and for two sites of the river, One was at the Crimea site, the other in the Jihad district, and for the period from October/2018 to March/2019, Seven variables of river water have been analyzed: temperature PH, electrical conductivity, TDS, turbidity, alkaline, and chloride. The results showed that most of the chemical and physical water properties of the river were in normal proportions and did not rise, except for the turbidity, which was at a very high level, and that the pH values were close to the basal side. The results of the statistical analysis revealed positive significant relationships between the pH and (chloride and TDS). On the other hand, between electrical conductivity and both previous variables as well. And a negative significant connection between temperature and alkaline.
基金This study is supported by a Scientific Research Project of Sinopec(Program No.P21087-2)the Open Fund of Key Laboratory of Marine Oil&Gas Reservoirs Production,Sinopec(Grant No.33550000-22-FW2099-0004).
文摘The microscopic characteristics and mechanical properties of rocks change after the action of acid on deep shale,which affects the fracturing effect.Accordingly,we designed and conducted indoor experiments related to the changes in macro and microscopic characteristics after the interaction of acid with the shale of Wujiaping Formation,based on which the characteristic law of fracture volume modification after acid fracturing was studied using numerical simulation.The results demonstrate that the pores and fractures are enlarged and the structure is significantly loosened after the acid immersion.And a 15%concentration of hydrochloric acid can effectively dissolve shale.Furthermore,the degree of acid-etching reaction is highly variable because of the different carbonate content,which reveals the strong inhomogeneity of the shale system in the Wujiaping Group reservoir section.After the acid interacted with the shale rock samples,the triaxial compressive strength,elastic modulus,and Poisson’s ratio of shale decreased.Moreover,the evaluation of the effect after acid fracturing simulated by fracturing software revealed that the smaller the value of elastic modulus in shale-based reservoirs,the more favorable the fracture volume modification.This discovery not only provides a theoretical basis for the expansion and extension patterns of acid-fracturing in carbonaceous shale formations but also offers research methods and theoretical insights for the fundamental exploration of other deep-seated oil and gas resources.
基金supported by the National Natural Science Foundation of China(Grant No.11672278)。
文摘Shaped charge warhead is important for enhancing the damage performance of underwater weapons.This paper used finite element analysis software and based on JPC water penetration experiments to examine the influence of liner parameters(wall thickness,material),charge aspect ratio,and stand-off distance on the movement characteristics of JPC in water.The findings reveal that the head diameter of the JPC increases and experiences significant erosion after entering the water,the effective length of the JPC in water undergoes two distinct phases:a growth phase and a decrease phase,with the velocity of the JPC decaying exponentially.Increasing the liner thickness,stand-off distance and the charge aspect ratio can improve the erosion resistance and the velocity retention capacity of the JPC.The optimal ranges for liner thickness and stand-off distance are 0.0363D_(k) to 0.0545D_(k)(D_(k) is the charge diameter),the stand-off distance should be within 1.0D_(k).After the charge aspect ratio higher than 1.25,the charge structure exerts minimal influence the movement characteristics of the JPC in water.Material density plays a crucial role in the velocity decay pattern of the JPC during penetration.JPC with higher densities exhibit superior velocity retention capabilities in water,with the velocity decay pattern converging if the densities are similar.Consequently,copper,tantalum and tungsten liners are deemed appropriate for underwater shaped charge warhead.Finally,the results will provide an important reference for the design of underwater shaped charge warhead.
基金the financial support from the National Natural Science Foundation of China(Grant No.21576293 and 21576294)。
文摘Coal pyrolysis is a fundamental reaction in the thermal processing and utilization of coal.Investigating the behavior and kinetics of coal pyrolysis is crucial for optimizing,designing,and developing a composite riser for the staged pyrolysis gasification process of pulverized coal.In this study,the non-isothermal pyrolysis behavior and kinetics of coal were examined at different heating rates(30,50,100,300,500,700,and 900℃/min)using thermogravimetry(TG)coupled with Fourier-transform infrared spectroscopy.Analysis of the TG/derivative TG(TG/DTG)curves indicated that coal pyrolysis mainly occurred between 300℃ and 700℃.Higher heating rates led to more volatiles being released from the coal,and a higher temperature was required to achieve rapid pyrolysis.Kinetic analysis showed that both the model-free methods(Friedman,Flynn-Wall-Ozawa,and Kissinger-Akahira-Sunose)and the model-based method(Coats-Redfern)effectively describe the coal pyrolysis process.The change in the Ea values between the two kinetic models was consistent throughout the pyrolysis process,and the most probable mechanism was the F2 model(secondary chemical reaction).In addition,the heating rate did not change the overall reaction order of the pyrolysis process;however,a higher heating rate resulted in a decrease in the Ea value during the initial pyrolysis stage.
基金The authors gratefully acknowledge the financial support by the Marine Economy Development Foundation of Guangdong Province“Technical Support for Stimulation and Testing of Gas Hydrate Reservoirs”(GDNRC[2022]44).
文摘Hydraulic jetting is a form of fracturing that involves using a high-pressure jet of water to create fractures in the reservoir rock with a nozzle serving as the central component of the hydraulic sandblasting perforation tool.In this study,the flow behavior of the nozzle is simulated numerically in the framework of a SST k-ωturbulence model.The results show that the nozzle structure can significantly influence the jet performance and related cavitation effect.Through orthogonal experiments,the nozzle geometric parameters are optimized,and the following configuration is found accordingly:contraction angle 20°,contraction segment length 6 mm,cylindrical segment diameter 6 mm,cylindrical segment length 12 mm,spread segment length 10 mm,and spread angle 55°.
基金support from the National Natural Science Foundation of China(No.41941018,No.52074299)the Fundamental Research Funds for the Central Universities(No.2023JCCXSB02)the China Geological Survey Project(DD20221816,DD20211376)are gratefully acknowledged.
文摘To investigate the influence mechanism of geostress on rockburst characteristics,three groups of gneiss rockburst experiments were conducted under different initial geostress conditions.A high-speed photography system and acoustic emission(AE)monitoring system were used to monitor the entire rockburst process in real time.The experimental results show that when the initial burial depth increases from 928 m to 1320 m,the proportion of large fracture scale in rockburst increases by 154.54%,and the AE energy increases by 565.63%,reflecting that the degree and severity of rockburst increase with the increase of burial depth.And then,two mechanisms are proposed to explain this effect,including(i)the increase of initial geostress improves the energy storage capacity of gneiss,and then,the excess energy which can be converted into kinetic energy of debris ejection increases,consequently,a more pronounced violent ejection phenomenon is observed at rockburst;(ii)the increase of initial geostress causes more sufficient plate cracks of gneiss after unloading ofσh,which provides a basis for more severe ejection of rockburst.What’s more,a precursor with clear physical meaning for rockburst is proposed under the framework of dynamic response process of crack evolution.Finally,potential value in long term rockburst warning of the precursor obtained in this study is shown via the comparison of conventional precursor.
基金supported by the National Natural Science Foundation of China(Grant Nos.52171166,11972372 and U20A20231)supported by Sinoma Institute of Materials Research(Guang Zhou)Co.,Ltd。
文摘Energetic structural materials(ESMs)are a new type of structural materials with bearing and damage characteristics.In this work the microstructure,mechanical properties and energy release characteristics of multi-element Ti-Zr-Ta alloys with good casting performance were studied.The microstructure of the Ti_(x)ZrTa alloys gradually change from BCC+HCP to single BCC structure with the increase of Ti.While the Ti_(2)Zr_(y)Ta alloys was still uniform and single BCC structure with the increase of Zr.The evolution of microstructure and composition then greatly affect the mechanical properties and energy-release characteristics of Ti-Zr-Ta alloys.The synergistic effect of dual phase structure increases the fracture strain of Ti_(x)ZrTa(x=0.2,0.5)with the Ti content decreases,while the fracture strain of Ti_(x)ZrTa(x=2.0,3.0,4.0)gradually increase with the Ti content increases caused by the annihilation of the obstacles for dislocation movement.And as Zr content increases,the fracture strain of Ti_(2)Zr_(y)Ta alloys decrease,then the oxidation reaction rate and fragmentation degree gradually increase.The higher oxidation rate and the lager exposed oxidation area jointly leads the higher releasing energy efficiency of Ti_(x)ZrTa alloys with low Ti content and Ti_(2)Zr_(y)Ta alloys with high Zr content.
基金supported by the National Natural Science Foundation of China(Nos.52204092 and 52274203).
文摘The damage evolution process of non-penetrating cracks often causes some unexpected engineering disasters.Gypsum specimens containing non-penetrating crack(s)are used to study the damage evolution and characteristics under cyclic loading.The results show that under cyclic loading,the relationship between the number of non-penetrating crack(s)and the characteristic parameters(cyclic number,peak stress,peak strain,failure stress,and failure strain)of the pre-cracked specimens can be represented by a decreasing linear function.The damage evolution equation is fitted by calibrating the accumulative plastic strain for each cycle,and the damage constitutive equation is proposed by the concept of effective stress.Additionally,non-penetrating cracks are more likely to cause uneven stress distribution,damage accumulation,and local failure of specimen.The local failure can change the stress distribution and relieve the inhibition of non-penetrating crack extension and eventually cause a dramatic destruction of the specimen.Therefore,the evolution process caused by non-penetrating cracks can be regarded as one of the important reasons for inducing rockburst.These results are expected to improve the understanding of the process of spalling formation and rockburst and can be used to analyze the stability of rocks or rock structures.
基金supported by the National Key Research and Development Program of China (Grant No.2021YFC3001204)。
文摘The study of non-axisymmetric fuel dispersal and detonation can provide reference for the prevention of industrial cloud explosion accidents and the design of fuel air explosive(FAE).The concentration and detonation fields of 85 kg cylindrical and fan-shaped fuel are investigated by experiments and numerical simulations.A dynamic model of the whole process for fuel dispersal and detonation is built.The concentration distribution of fuel is used as the initial condition to calculate the detonation stage,thus solving the initial value problem of detonation field.The phase and component changes of fuel cloud at different locations are compared.The fuel cloud is divided into directions of 0°,90°,135°and 180°.The results show that the maximum cloud radius is 20.94 m in 135°and the minimum is 12.04 m in 0°.The diameter of the detonation fireball is 53.6 m,and the peak temperature is 3455 K.The highest peak overpressure is 3.44 MPa in 0°and the lowest is 2.97 MPa in 135°.The proportion of liquid phase in 0°is22.90%,and the fuel loss is 11.8% and 9% higher than that in 135°and cylindrical charge,respectively.The stable propagation distance of blast wave in 135°is 42.50% longer than 0°and 28.37% longer than cylindrical charge.
基金supported by the Beijing Natural Science Foundation,China(Grant No.JQ20039)National Natural Science Foundation of China(Grant No.12172019).
文摘The dynamic spalling characteristics of rock are important for stability analysis in rock engineering.This paper presented an experimental investigation on the dynamic spalling characteristics of granite with different temperatures and strain rates.A series of dynamic spalling tests with different impact velocities were conducted on thermally treated granite at different temperatures.The dynamic spalling strengths of granite with different temperatures and strain rates were determined.A model was proposed to correlate the dynamic spalling strength of granite,high temperature and strain rate.The results show that the spalling strength of granite decreases with increasing temperature.Moreover,the spalling strength of granite with a higher strain rate is larger than that with a lower strain rate.The proposed model can describe the relationship among dynamic spalling strength of granite,high temperature and strain rate.
基金supported by the Qingdao Natural Science Foundation(No.23-2-1-54-zyyd-jch)the National Natural Science Foundation of China(Nos.42076217,41976074)+1 种基金the Laoshan Laboratory(No.LSKJ202203506)the Key Laboratory of Geotechnical and Underground Engineering of Ministry of Education,Tongji University(No.KLE-TJGE-G2202).
文摘The safe and efficient development of natural gas hydrate requires a deep understanding of the deformation behaviors of reservoirs.In this study,a series of triaxial shearing tests are carried out to investigate the deformation properties of hydrate-bearing sediments.Variations of volumetric and lateral strains versus hydrate saturation are analyzed comprehensively.Results indicate that the sediments with high hydrate saturation show dilative behaviors,which lead to strain-softening characteristics during shearing.The volumetric strain curves have a tendency to transform gradually from dilatation to compression with the increase in effective confining pressure.An easy prediction model is proposed to describe the relationship between volumetric and axial strains.The model coefficientβis the key dominating factor for the shape of volumetric strain curves and can be determined by the hydrate saturation and stress state.Moreover,a modified model is established for the calculation of lateral strain.The corresponding determination method is provided for the easy estimation of model coefficients for medium sand sediments containing hydrate.This study provides a theoretical and experimental reference for deformation estimation in natural gas hydrate development.
基金supported by the National Natural Science Foundation of China(41874011,42074007)the Fundamental Research Funds for the Central Universities(2042023kfyq01)。
文摘The Qinghai Nanshan fault is a larger fault in the Northeastern Xizang Plateau.In previous studies,its movement characteristics are mainly investigated with geological and seismic observations,and the tectonic transformation role of the fault on its east is not yet clear.This study uses data fusion to obtain denser GPS observations near the Qinghai Nanshan fault.Based on tectonic characteristics,we establish a block model to investigate the fault slip rate,locking degree,and slip deficit.The results show that the Qinghai Nanshan fault slip rate is characterized by sinistral and convergent movement.Both the sinistral and convergent rates display a decreasing trend from west to east.The locking degree and slip deficit are higher in the western segment(with an average of about 0.74 and 1.1 mm/a)and lower in the eastern segment.Then,we construct a strain rate field using GPS observations to analyze the regional strain characteristics.The results indicate that along the fault,the western segment shows a larger shear strain rate and negative dilation rate.Regional earthquake records show that the frequency of earthquakes is lower near the fault.The joint results suggest that the western segment may have a higher earthquake risk.In addition,the insignificant fault slip rate in the eastern segment may indicate that it does not participate in the tectonic transformation among the Riyueshan,Lajishan,and West Qinling faults.
基金supported by the National Natural Science Foundation of China(62201251)the Natural Science Foundation of the Jiangsu Higher Education Institutions of China(22KJB510024)the Open Fund for the Hangzhou Institute of Technology Academician Workstation at Xidian University(XH-KY-202306-0291)。
文摘In this paper,a detection method combining Cameron decomposition based on polarization scattering characteristics in sea clutter background is proposed.Firstly,the Cameron decomposition is exploited to fuse the radar echoes of full polarization channels at the data level.Due to the artificial material structure on the surface of the target,it can be shown that the non-reciprocity of the target cell is stronger than that of the clutter cell.Then,based on the analysis of the decomposition results,a new feature with scattering geometry characteristics in polarization domain,denoted as Cameron polarization decomposition scattering weight(CPD-SW),is extracted as the test statistic,which can achieve more detailed descriptions of the clutter scattering characteristics utilizing the difference between their scattering types.Finally,the superiority of the proposed CPD-SW detector over traditional detectors in improving detection performance is verified by the IPIX measured dataset,which has strong stability under short-time observation in threshold detection and can also improve the separability of feature space zin anomaly detection.
