Based on the safety coefficient method,which assigns rock failure criteria to calculate the rock mass unit,the safety coefficient contour of surrounding rock is plotted to judge the distribution form of the fractured ...Based on the safety coefficient method,which assigns rock failure criteria to calculate the rock mass unit,the safety coefficient contour of surrounding rock is plotted to judge the distribution form of the fractured zone in the roadway.This will provide the basis numerical simulation to calculate the surrounding rock fractured zone in a roadway.Using the single factor and multi-factor orthogonal test method,the evolution law of roadway surrounding rock displacements,plastic zone and stress distribution under different conditions is studied.It reveals the roadway surrounding rock burst evolution process,and obtains five kinds of failure modes in deep soft rock roadway.Using the fuzzy mathematics clustering analysis method,the deep soft surrounding rock failure model in Zhujixi mine can be classified and patterns recognized.Compared to the identification results and the results detected by geological radar of surrounding rock loose circle,the reliability of the results of the pattern recognition is verified and lays the foundations for the support design of deep soft rock roadways.展开更多
Geochemical study of Kon Tum（KT） plateau, Sanshui（SS） basin and Daimao（DM） seamount volcanic rocks provides new insight into magmatic processes and characteristics of the mantle source beneath the South China Se...Geochemical study of Kon Tum（KT） plateau, Sanshui（SS） basin and Daimao（DM） seamount volcanic rocks provides new insight into magmatic processes and characteristics of the mantle source beneath the South China Sea（SCS） basin and its surroundings. Geological signature of basaltic lavas from KT, SS and DM indicate rather than a deep-rooted plume derived from the core-mantle boundary, a shallower mantle domain, such as subcontinental lithosphere mantle or asthenospheric mantle, is more likely to be the mantle source region beneath the SCS basin and its adjacent areas. The mantle source beneath the SCS basin has been shown to be more depleted relative to the source regions of the SS basin and the KT plateau, indicating that the magmatism in the SS basin has been interrupted due to the SCS spreading and then recovered in the KT plateau area. The mantle heterogeneity has been sampled and an enriched component that is geochemically comparable to EM2 endmember has been identified in the mantle source region of the SCS basin and its surroundings. This EM2 component was formed by the recycling of Mesozoic subducted proto-SCS slab along with terrigenous sediments.展开更多
The rock mass engineering system （RMES） basically consists ofrock mass engineering （RME）, water system and surroundingecological environments, etc. The RMES is characterized by nonlinearity,occurrence of chaos and...The rock mass engineering system （RMES） basically consists ofrock mass engineering （RME）, water system and surroundingecological environments, etc. The RMES is characterized by nonlinearity,occurrence of chaos and self-organization （Tazaka, 1998;Tsuda, 1998; Kishida, 2000）. From construction to abandonmentof RME, the RMES will experience four stages, i.e. initial phase,development phase, declining phase and failure phase. In thiscircumstance, the RMES boundary conditions, structural safetyand surrounding environments are varied at each phase, so arethe evolution characteristics and disasters （Wang et al., 2014）.展开更多
Based on the discussion on the intracontinental orogenic igneous rocks formed after India-Asia collision (40 or 45 Ma),the intracontinental orogenic processes of Qinghai-Xizang (Tibet )-Himalaya are traced . Muscovite...Based on the discussion on the intracontinental orogenic igneous rocks formed after India-Asia collision (40 or 45 Ma),the intracontinental orogenic processes of Qinghai-Xizang (Tibet )-Himalaya are traced . Muscovite/two mica granite is considered as a petrological record of intracontinental subduction. Volcanic rocks of shoshonite series are believed to be the products of the orogenic and outside cratonic lithosphere convergence . The intracontinental orogenic igneous rocks are developed only on the margins of the orogenic belt. The pairing phe nomenon of the igneous rock zones is regarded as one of the best signs to recognize the special range of orogenic belt . The stage of magmatic activity is a representation and indicator of orogenic episode . Three pairs of the igneous events in Oligocene , Miocene and Pleistocene and their space distribution indicate three corresponding orogenic episodes and the horizontal expansion across the orogenic belt , respectively . On the northern and southern margins of the orogenic belt are always developed the volcanic eruption of the shoshonite series and the muscovite two mica granite intrusion ,indicating the different nature of the margins .In the former case the colder crust and hotter mantle . as well as the double crust resulted from the horizontal shortening are developed , and in the latter case the hotter crust and colder mantle , the double crust by the overlapping of two crusts are formed . During the Pleistocene orogenic episode the interior of the orogenic belt , i. e. the Gandise - Qiangtang might be going to the stage of the orogenic collapse . and the compressional orogeny might occur only at both the mar gins . The orogenic processes mentioned above show that beneath the Qinghai - Xizang (Tibet ) Himalaya,the deeper mantle has been always undergoing a descending convergence , rather than the simple orogeny resulted from the underthrusting of the India continent only . The dynamic forces that results in rapid uplift of the plateau since Pleistocene come from the buoyances caused by the compressional stress and mountain root at the margins and by the lithosphere delamination and mountain root in the interior .展开更多
The oil and gas stored in deep and ultra-deep carbonate reservoirs is the focus of future exploration and development.Conical PDC(Polycrystalline Diamond Compact)cutter,which is a new kind of PDC cutter,can significan...The oil and gas stored in deep and ultra-deep carbonate reservoirs is the focus of future exploration and development.Conical PDC(Polycrystalline Diamond Compact)cutter,which is a new kind of PDC cutter,can significantly improve the rate of penetration(ROP)and extend PDC bit life in hard and abrasive formations.However,the breakage characteristics and failure mode of the conical PDC cutter cutting carbonate rock is still masked.In this paper,a series of single-cutter cutting tests were carried out with the conical and conventional PDC cutters.The cutting force,rock-breaking process,surface morphology of cutting grooves and cuttings characteristic were analyzed.Based on the derived formula of the brittle fracture index,the failure model of carbonate rock was quantitatively analyzed under the action of conical and conventional cutter.The results show that the average cutting force of the conical cutter is less than that of the conventional cutter,which means greater stability of the cutting process using the conical cutter.Carbonate rock with calcite as the main component tends to generate blocky rock debris by conical cutter.The height of the cuttings generated by the conical cutter is 0.5 mm higher than that generated by the conventional cutter.The conical cutter exhibits enhanced penetration capabilities within carbonate rock.The accumulation of rock debris in front of the conventional cutter is obvious.Whereas,the conical cutter facilitates the cuttings transport,thereby alleviating drilling stickiness slip.At different cutting depths,the conical cutter consistently causes asymmetric jagged brittle tensile fracture zones on both sides of the cutting groove.Calculations based on the brittle fracture index demonstrate that the brittle fracture index of the conical cutter generally doubles that of the conventional cutter.For carbonate rock,the conical cutter displays superior utilization of brittle fracture abilities.The research findings of this work offer insights into the breakage process and failure mode of carbonate rock by the conical cutter.展开更多
The paper presents the advancement and applications of the elasto-plastic cellular automaton （EPCA）, a simulator for rock mechanics and rock engineering. The most significant feature of EPCA lies in its ＇down-top＇...The paper presents the advancement and applications of the elasto-plastic cellular automaton （EPCA）, a simulator for rock mechanics and rock engineering. The most significant feature of EPCA lies in its ＇down-top＇ way of dealing with nonlinear behaviors of rocks. The theory, the basic idea and associated developments, including the definition of cellular automaton, the heterogeneous material model, constitutive relations, failure criteria, the post-yield softening scheme, the thermo-hydro-mechanical coupling process, are described. The applications are presented to show the ability of EPCA to model the rock failure process, fluid flow, heat transfer, and the coupled thermo-hydro-mechanical （THM） process etc.展开更多
Mountain hazards with large masses of rock blocks in motion – such as rock falls, avalanches and landslides – threaten human lives and structures. Dynamic fragmentation is a common phenomenon during the movement pro...Mountain hazards with large masses of rock blocks in motion – such as rock falls, avalanches and landslides – threaten human lives and structures. Dynamic fragmentation is a common phenomenon during the movement process of rock blocks in rock avalanche, due to the high velocity and impacts against obstructions. In view of the energy consumption theory for brittle rock fragmentation proposed by Bond, which relates energy to size reduction, a theoretical model is proposed to estimate the average fragment size for a moving rock block when it impacts against an obstruction. Then, different forms of motion are studied, with various drop heights and slope angles for the moving rock block. The calculated results reveal that the average fragment size decreases as the drop height increases, whether for free-fall or for a sliding or rolling rock block, and the decline in size is rapid for low heights and slow for increasing heights in the corresponding curves. Moreover, the average fragment size also decreases as the slope angle increases for a slidingrock block. In addition, a rolling rock block has a higher degree of fragmentation than a sliding rock block, even for the same slope angle and block volume. Finally, to compare with others' results, the approximate number of fragments is estimated for each calculated example, and the results show that the proposed model is applicable to a relatively isotropic moving rock block.展开更多
Deep shale reservoirs are characterized by elevated breakdown pressures,diminished fracture complexity,and reduced modified volumes compared to medium and shallow reservoirs.Therefore,it is urgent to investigate parti...Deep shale reservoirs are characterized by elevated breakdown pressures,diminished fracture complexity,and reduced modified volumes compared to medium and shallow reservoirs.Therefore,it is urgent to investigate particular injection strategies that can optimize breakdown pressure and fracturing efficiency to address the increasing demands for deep shale reservoir stimulation.In this study,the efficiency of various stimulation strategies,including multi-cluster simultaneous fracturing,modified alternating fracturing,alternating shut-in fracturing,and cyclic alternating fracturing,was evaluated.Subsequently,the sensitivity of factors such as the cycle index,shut-in time,cluster spacing,and horizontal permeability was investigated.Additionally,the flow distribution effect within the wellbore was discussed.The results indicate that relative to multi-cluster simultaneous fracturing,modified alternating fracturing exhibits reduced susceptibility to the stress shadow effect,which results in earlier breakdown,extended hydraulic fracture lengths,and more consistent propagation despite an increase in breakdown pressure.The alternating shut-in fracturing benefits the increase of fracture length,which is closely related to the shut-in time.Furthermore,cyclic alternating fracturing markedly lowers breakdown pressure and contributes to uniform fracture propagation,in which the cycle count plays an important role.Modified alternating fracturing demonstrates insensitivity to variations in cluster spacing,whereas horizontal permeability is a critical factor affecting fracture length.The wellbore effect restrains the accumulation of pressure and flow near the perforation,delaying the initiation of hydraulic fractures.The simulation results can provide valuable numerical insights for optimizing injection strategies for deep shale hydraulic fracturing.展开更多
In order to investigate the effect of water content on the energy evolution of red sandstone, the axial loading–unloading experiments on dry and water-saturated sandstone samples were conducted, and the distribution ...In order to investigate the effect of water content on the energy evolution of red sandstone, the axial loading–unloading experiments on dry and water-saturated sandstone samples were conducted, and the distribution and evolution of elastic energy and dissipated energy within the rock were measured.The results show that the saturation process from dry to fully-saturated states reduces the strength, rigidity and brittleness of the rock by 30.2%, 25.5% and 16.7%, respectively. The water-saturated sample has larger irreversible deformation in the pre-peak stage and smaller stress drop in the post-peak stage.The saturation process decreases the accumulation energy limit by 38.9%, but increases the dissipated energy and residual elastic energy density, thus greatly reducing the magnitude and rate of energy release. The water-saturated sample has lower conversion efficiency to elastic energy by 3% in the prepeak region; moreover, the elastic energy ratio falls with a smaller range in the post-peak stage.Therefore, saturation process can greatly reduce the risk of dynamic disaster, and heterogeneous water content can lead to dynamic disaster possibly on the other hand.展开更多
Besides opening geometry, in situ stress and material properties, opening support also has significant effects on stress redistribution around a roadway. To investigate these effects of rock bolts on the stress redist...Besides opening geometry, in situ stress and material properties, opening support also has significant effects on stress redistribution around a roadway. To investigate these effects of rock bolts on the stress redistribution around a roadway, a series of numerical studies were carried out using the finite difference method. Since the stress changes around a roadway caused by rock bolting is small relative to the in situ stress, they cannot obviously be observed in stress contour plots. To overcome this difficulty, a new result processing methodology was developed using the contouring program Surfer. With this methodology, the effects of rock bolts on stress redistribution can obviously be analyzed. Numerical results show that in the three patterns of rock bolts installed in the roof, in the roof and the two lateral sides, and in all the four sides of the rectangular roadway, the maximum stress magnitude of the increase is 0.931 MPa, 2.46 MPa,and 6.5 MPa, respectively; the bolt number of 5 can form an integrated ground arch; the appropriate length and pre-tensioned force of the rock bolt is 2.0 m and 60 k N, respectively. What is more, the ground arch action under the function of rock bolting is able to be effectively examined. The rock bolts dramatically increase the minor principal stress around a roadway which results in significant increase in material strength. Consequently, the major principal stress that the material can carry will greatly increase.With adequate supports, an integrated ground arch which is critical for the stability of roadway will be formed around the roadway.展开更多
The Karhunen-Loeve （KL） expansion and probabilistic collocation method （PCM） are combined and applied to an uncertainty analysis of rock failure behavior by integrating a self- developed numerical method （i.e., t...The Karhunen-Loeve （KL） expansion and probabilistic collocation method （PCM） are combined and applied to an uncertainty analysis of rock failure behavior by integrating a self- developed numerical method （i.e., the elastic-plastic cellular automaton （EPCA））. The results from the method developed are compared using the Monte Carlo Simulation （MCS） method. It is concluded that the method developed requires fewer collocations than MCS method to obtain very high accuracy and greatly reduces the computational cost. Based on the method, the elasto- plastic and elasto-brittle-plastic analyses of rocks under mechanical loadings are conducted to study the uncertainty in heterogeneous rock failure behaviour.展开更多
A continuous-discontinuous cellular automaton method is developed for rock initiation and propagation simulations, in which the level set method, discontinuous enrichment shape functions and discontinuous cellular aut...A continuous-discontinuous cellular automaton method is developed for rock initiation and propagation simulations, in which the level set method, discontinuous enrichment shape functions and discontinuous cellular automaton are combined. No renmshing is needed for crack growth analysis, and all calculations are restricted to cells without an assembled global stiffness matrix. The frictional contact theory is employed to construct the contact model of normal pressure and tangential shear on crack surfaces. A discontinuous cellular automaton updating rule suitable for frictional contact of rock is proposed simultaneously with Newton＇s iteration method for nonlinear iteration. Besides, a comprehensive fracturing criterion for brittle rock under compression-shear loading is developed. The accuracy and effectivenesss of the proposed method is proved by numerical simulation.展开更多
The rock processing residue(RPR)waste is used for part of the ceramic products.The present work deals with the unused waste useful for making ceramic materials and save the area and the dump space.The residues are ini...The rock processing residue(RPR)waste is used for part of the ceramic products.The present work deals with the unused waste useful for making ceramic materials and save the area and the dump space.The residues are initially analyzed with the chemical and spectroscopic method.The residues are mixed with clay of proportions 0-50 wt%in steps of 10%.The prepared specimens are characterized with Fourier transform infrared(FTIR),X ray fluorescence(XRF)for chemical,mechanical,and physiochemical properties,such as density,compressive strength,weight loss on ignition and porous nature,which are measured through the selective instrument.The thermal stability of the product was tested by firing at 950℃.This says the rock residues are useful for making ceramic and related materials with high concentrations.展开更多
A discontinuous deformation and displacement(DDD) analysis method is proposed for modelling the rock failure process. This method combines the rock failure process analysis(RFPA) method(based on finite element method)...A discontinuous deformation and displacement(DDD) analysis method is proposed for modelling the rock failure process. This method combines the rock failure process analysis(RFPA) method(based on finite element method) and discontinuous deformation analysis(DDA) method. RFPA is used to simulate crack initiation, propagation and coalescence processes of rock during the small deformation state. The DDA method is used to simulate the movement of blocks created by the multiple cracks modelled by the RFPA. The newly developed DDD method is particularly suitable for modelling both crack propagation and block movement during the rock failure process because of the natural and convenient coupling of continuous and discontinuous deformation analyses. The proposed method has been used to simulate crack initiation, propagation and coalescence within a slope as well as the block movement during the landslide process. Numerical modelling results indicate that the proposed DDD method can automatically simulate crack propagation and block movement during the rock failure process without degrading accuracy.展开更多
基金provided by the National Natural Science Foundation of China(Nos.51322401,51309222,51323004,51579239 and 51574223)the Opening Project Fund of Shandong Provincial Key Laboratory of Civil Engineering Disaster Prevention and Mitigation(No.CDPM2014KF03)+2 种基金the State Key Laboratory for GeoMechanics Opening Project Fund of Shandong Provincial Key Laboratory of Civil Engineering Disaster Prevention and MitigationDeep Underground Engineering,China University of Mining&Technology(No.SKLGDUEK1305)China Postdoctoral Science Foundation(Nos.2014M551700and 2013M531424)
文摘Based on the safety coefficient method,which assigns rock failure criteria to calculate the rock mass unit,the safety coefficient contour of surrounding rock is plotted to judge the distribution form of the fractured zone in the roadway.This will provide the basis numerical simulation to calculate the surrounding rock fractured zone in a roadway.Using the single factor and multi-factor orthogonal test method,the evolution law of roadway surrounding rock displacements,plastic zone and stress distribution under different conditions is studied.It reveals the roadway surrounding rock burst evolution process,and obtains five kinds of failure modes in deep soft rock roadway.Using the fuzzy mathematics clustering analysis method,the deep soft surrounding rock failure model in Zhujixi mine can be classified and patterns recognized.Compared to the identification results and the results detected by geological radar of surrounding rock loose circle,the reliability of the results of the pattern recognition is verified and lays the foundations for the support design of deep soft rock roadways.
基金The National Natural Science Foundation of China under contract Nos 41276047 and 41030853
文摘Geochemical study of Kon Tum（KT） plateau, Sanshui（SS） basin and Daimao（DM） seamount volcanic rocks provides new insight into magmatic processes and characteristics of the mantle source beneath the South China Sea（SCS） basin and its surroundings. Geological signature of basaltic lavas from KT, SS and DM indicate rather than a deep-rooted plume derived from the core-mantle boundary, a shallower mantle domain, such as subcontinental lithosphere mantle or asthenospheric mantle, is more likely to be the mantle source region beneath the SCS basin and its adjacent areas. The mantle source beneath the SCS basin has been shown to be more depleted relative to the source regions of the SS basin and the KT plateau, indicating that the magmatism in the SS basin has been interrupted due to the SCS spreading and then recovered in the KT plateau area. The mantle heterogeneity has been sampled and an enriched component that is geochemically comparable to EM2 endmember has been identified in the mantle source region of the SCS basin and its surroundings. This EM2 component was formed by the recycling of Mesozoic subducted proto-SCS slab along with terrigenous sediments.
基金funded by the National Natural Science Foundation of China(Grant Nos.51274110,51304108,U1361211)
文摘The rock mass engineering system （RMES） basically consists ofrock mass engineering （RME）, water system and surroundingecological environments, etc. The RMES is characterized by nonlinearity,occurrence of chaos and self-organization （Tazaka, 1998;Tsuda, 1998; Kishida, 2000）. From construction to abandonmentof RME, the RMES will experience four stages, i.e. initial phase,development phase, declining phase and failure phase. In thiscircumstance, the RMES boundary conditions, structural safetyand surrounding environments are varied at each phase, so arethe evolution characteristics and disasters （Wang et al., 2014）.
基金This study is supported by the Ministry of Geology and Mineral Resources and the National Natural Science Foundation of China
文摘Based on the discussion on the intracontinental orogenic igneous rocks formed after India-Asia collision (40 or 45 Ma),the intracontinental orogenic processes of Qinghai-Xizang (Tibet )-Himalaya are traced . Muscovite/two mica granite is considered as a petrological record of intracontinental subduction. Volcanic rocks of shoshonite series are believed to be the products of the orogenic and outside cratonic lithosphere convergence . The intracontinental orogenic igneous rocks are developed only on the margins of the orogenic belt. The pairing phe nomenon of the igneous rock zones is regarded as one of the best signs to recognize the special range of orogenic belt . The stage of magmatic activity is a representation and indicator of orogenic episode . Three pairs of the igneous events in Oligocene , Miocene and Pleistocene and their space distribution indicate three corresponding orogenic episodes and the horizontal expansion across the orogenic belt , respectively . On the northern and southern margins of the orogenic belt are always developed the volcanic eruption of the shoshonite series and the muscovite two mica granite intrusion ,indicating the different nature of the margins .In the former case the colder crust and hotter mantle . as well as the double crust resulted from the horizontal shortening are developed , and in the latter case the hotter crust and colder mantle , the double crust by the overlapping of two crusts are formed . During the Pleistocene orogenic episode the interior of the orogenic belt , i. e. the Gandise - Qiangtang might be going to the stage of the orogenic collapse . and the compressional orogeny might occur only at both the mar gins . The orogenic processes mentioned above show that beneath the Qinghai - Xizang (Tibet ) Himalaya,the deeper mantle has been always undergoing a descending convergence , rather than the simple orogeny resulted from the underthrusting of the India continent only . The dynamic forces that results in rapid uplift of the plateau since Pleistocene come from the buoyances caused by the compressional stress and mountain root at the margins and by the lithosphere delamination and mountain root in the interior .
基金supported by the NSFC Key International(Regional)Cooperative Research Projects(No.52020105001)National Natural Science Foundation of China(52304014)+2 种基金China Postdoctoral Science Foundation funded project(2023M733873)the Science Foundation of China University of Petroleum,Beijing(No.2462023SZBH003)General Program of National Natural Science Foundation of China(52374016,52274016)。
文摘The oil and gas stored in deep and ultra-deep carbonate reservoirs is the focus of future exploration and development.Conical PDC(Polycrystalline Diamond Compact)cutter,which is a new kind of PDC cutter,can significantly improve the rate of penetration(ROP)and extend PDC bit life in hard and abrasive formations.However,the breakage characteristics and failure mode of the conical PDC cutter cutting carbonate rock is still masked.In this paper,a series of single-cutter cutting tests were carried out with the conical and conventional PDC cutters.The cutting force,rock-breaking process,surface morphology of cutting grooves and cuttings characteristic were analyzed.Based on the derived formula of the brittle fracture index,the failure model of carbonate rock was quantitatively analyzed under the action of conical and conventional cutter.The results show that the average cutting force of the conical cutter is less than that of the conventional cutter,which means greater stability of the cutting process using the conical cutter.Carbonate rock with calcite as the main component tends to generate blocky rock debris by conical cutter.The height of the cuttings generated by the conical cutter is 0.5 mm higher than that generated by the conventional cutter.The conical cutter exhibits enhanced penetration capabilities within carbonate rock.The accumulation of rock debris in front of the conventional cutter is obvious.Whereas,the conical cutter facilitates the cuttings transport,thereby alleviating drilling stickiness slip.At different cutting depths,the conical cutter consistently causes asymmetric jagged brittle tensile fracture zones on both sides of the cutting groove.Calculations based on the brittle fracture index demonstrate that the brittle fracture index of the conical cutter generally doubles that of the conventional cutter.For carbonate rock,the conical cutter displays superior utilization of brittle fracture abilities.The research findings of this work offer insights into the breakage process and failure mode of carbonate rock by the conical cutter.
基金supported by the National Basic Research Program of China (No. 2010CB732006)the National Natural Science Foundation of China (Nos. 10972231, 50709036 and 11002154)
文摘The paper presents the advancement and applications of the elasto-plastic cellular automaton （EPCA）, a simulator for rock mechanics and rock engineering. The most significant feature of EPCA lies in its ＇down-top＇ way of dealing with nonlinear behaviors of rocks. The theory, the basic idea and associated developments, including the definition of cellular automaton, the heterogeneous material model, constitutive relations, failure criteria, the post-yield softening scheme, the thermo-hydro-mechanical coupling process, are described. The applications are presented to show the ability of EPCA to model the rock failure process, fluid flow, heat transfer, and the coupled thermo-hydro-mechanical （THM） process etc.
基金supported by the National Natural Science Foundation of China (41472272, 41225011)the Youth Science and Technology Fund of Sichuan Province (2016JQ0011)the Opening Fund of the State Key Laboratory of Geohazard Prevention and Geoenvironment Protection (Chengdu University of Technology) (SKLGP2013K015)
文摘Mountain hazards with large masses of rock blocks in motion – such as rock falls, avalanches and landslides – threaten human lives and structures. Dynamic fragmentation is a common phenomenon during the movement process of rock blocks in rock avalanche, due to the high velocity and impacts against obstructions. In view of the energy consumption theory for brittle rock fragmentation proposed by Bond, which relates energy to size reduction, a theoretical model is proposed to estimate the average fragment size for a moving rock block when it impacts against an obstruction. Then, different forms of motion are studied, with various drop heights and slope angles for the moving rock block. The calculated results reveal that the average fragment size decreases as the drop height increases, whether for free-fall or for a sliding or rolling rock block, and the decline in size is rapid for low heights and slow for increasing heights in the corresponding curves. Moreover, the average fragment size also decreases as the slope angle increases for a slidingrock block. In addition, a rolling rock block has a higher degree of fragmentation than a sliding rock block, even for the same slope angle and block volume. Finally, to compare with others' results, the approximate number of fragments is estimated for each calculated example, and the results show that the proposed model is applicable to a relatively isotropic moving rock block.
基金supported by the National Natural Science Foundation of China(NSFC)(Grant Nos.42377156,42077251 and 42202305).
文摘Deep shale reservoirs are characterized by elevated breakdown pressures,diminished fracture complexity,and reduced modified volumes compared to medium and shallow reservoirs.Therefore,it is urgent to investigate particular injection strategies that can optimize breakdown pressure and fracturing efficiency to address the increasing demands for deep shale reservoir stimulation.In this study,the efficiency of various stimulation strategies,including multi-cluster simultaneous fracturing,modified alternating fracturing,alternating shut-in fracturing,and cyclic alternating fracturing,was evaluated.Subsequently,the sensitivity of factors such as the cycle index,shut-in time,cluster spacing,and horizontal permeability was investigated.Additionally,the flow distribution effect within the wellbore was discussed.The results indicate that relative to multi-cluster simultaneous fracturing,modified alternating fracturing exhibits reduced susceptibility to the stress shadow effect,which results in earlier breakdown,extended hydraulic fracture lengths,and more consistent propagation despite an increase in breakdown pressure.The alternating shut-in fracturing benefits the increase of fracture length,which is closely related to the shut-in time.Furthermore,cyclic alternating fracturing markedly lowers breakdown pressure and contributes to uniform fracture propagation,in which the cycle count plays an important role.Modified alternating fracturing demonstrates insensitivity to variations in cluster spacing,whereas horizontal permeability is a critical factor affecting fracture length.The wellbore effect restrains the accumulation of pressure and flow near the perforation,delaying the initiation of hydraulic fractures.The simulation results can provide valuable numerical insights for optimizing injection strategies for deep shale hydraulic fracturing.
基金provided by the Fundamental Research Funds for the Central Universities(No.2014QNA80)the Project funded by China Postdoctoral Science Foundation(No.2014M550315)+2 种基金a Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutionsthe National Natural Science Foundation of China(No.11202108)the Natural Science Foundation of Jiangsu Province(No.BK20140189)
文摘In order to investigate the effect of water content on the energy evolution of red sandstone, the axial loading–unloading experiments on dry and water-saturated sandstone samples were conducted, and the distribution and evolution of elastic energy and dissipated energy within the rock were measured.The results show that the saturation process from dry to fully-saturated states reduces the strength, rigidity and brittleness of the rock by 30.2%, 25.5% and 16.7%, respectively. The water-saturated sample has larger irreversible deformation in the pre-peak stage and smaller stress drop in the post-peak stage.The saturation process decreases the accumulation energy limit by 38.9%, but increases the dissipated energy and residual elastic energy density, thus greatly reducing the magnitude and rate of energy release. The water-saturated sample has lower conversion efficiency to elastic energy by 3% in the prepeak region; moreover, the elastic energy ratio falls with a smaller range in the post-peak stage.Therefore, saturation process can greatly reduce the risk of dynamic disaster, and heterogeneous water content can lead to dynamic disaster possibly on the other hand.
基金Financial support for this work provided by the National Key Scientific Apparatus Development of Special Item (No.2012YQ24012705)is deeply appreciated
文摘Besides opening geometry, in situ stress and material properties, opening support also has significant effects on stress redistribution around a roadway. To investigate these effects of rock bolts on the stress redistribution around a roadway, a series of numerical studies were carried out using the finite difference method. Since the stress changes around a roadway caused by rock bolting is small relative to the in situ stress, they cannot obviously be observed in stress contour plots. To overcome this difficulty, a new result processing methodology was developed using the contouring program Surfer. With this methodology, the effects of rock bolts on stress redistribution can obviously be analyzed. Numerical results show that in the three patterns of rock bolts installed in the roof, in the roof and the two lateral sides, and in all the four sides of the rectangular roadway, the maximum stress magnitude of the increase is 0.931 MPa, 2.46 MPa,and 6.5 MPa, respectively; the bolt number of 5 can form an integrated ground arch; the appropriate length and pre-tensioned force of the rock bolt is 2.0 m and 60 k N, respectively. What is more, the ground arch action under the function of rock bolting is able to be effectively examined. The rock bolts dramatically increase the minor principal stress around a roadway which results in significant increase in material strength. Consequently, the major principal stress that the material can carry will greatly increase.With adequate supports, an integrated ground arch which is critical for the stability of roadway will be formed around the roadway.
基金supported by the National Natural Science Foundation of China(Nos.51322906 and 41272349)the National Basic Research Program of China(No.2013CB036405)Youth Innovation Promotion Association of CAS(No.2011240)
文摘The Karhunen-Loeve （KL） expansion and probabilistic collocation method （PCM） are combined and applied to an uncertainty analysis of rock failure behavior by integrating a self- developed numerical method （i.e., the elastic-plastic cellular automaton （EPCA））. The results from the method developed are compared using the Monte Carlo Simulation （MCS） method. It is concluded that the method developed requires fewer collocations than MCS method to obtain very high accuracy and greatly reduces the computational cost. Based on the method, the elasto- plastic and elasto-brittle-plastic analyses of rocks under mechanical loadings are conducted to study the uncertainty in heterogeneous rock failure behaviour.
基金supported by the National Key Technologies R&D Program of China(No.2013BAB02B01)the National Natural Science Foundation of China(Nos.41272349,41172284 and 51322906)
文摘A continuous-discontinuous cellular automaton method is developed for rock initiation and propagation simulations, in which the level set method, discontinuous enrichment shape functions and discontinuous cellular automaton are combined. No renmshing is needed for crack growth analysis, and all calculations are restricted to cells without an assembled global stiffness matrix. The frictional contact theory is employed to construct the contact model of normal pressure and tangential shear on crack surfaces. A discontinuous cellular automaton updating rule suitable for frictional contact of rock is proposed simultaneously with Newton＇s iteration method for nonlinear iteration. Besides, a comprehensive fracturing criterion for brittle rock under compression-shear loading is developed. The accuracy and effectivenesss of the proposed method is proved by numerical simulation.
文摘The rock processing residue(RPR)waste is used for part of the ceramic products.The present work deals with the unused waste useful for making ceramic materials and save the area and the dump space.The residues are initially analyzed with the chemical and spectroscopic method.The residues are mixed with clay of proportions 0-50 wt%in steps of 10%.The prepared specimens are characterized with Fourier transform infrared(FTIR),X ray fluorescence(XRF)for chemical,mechanical,and physiochemical properties,such as density,compressive strength,weight loss on ignition and porous nature,which are measured through the selective instrument.The thermal stability of the product was tested by firing at 950℃.This says the rock residues are useful for making ceramic and related materials with high concentrations.
基金supported by the National Basic Research Program of China("973"Project)(Grant No.2014CB047100)the National Natural Science Foundation of China(Grant Nos.51421064,51474046 & 51174039)the Fundamental Research Funds for the Central Universities(Grant No.DUT14LK21)
文摘A discontinuous deformation and displacement(DDD) analysis method is proposed for modelling the rock failure process. This method combines the rock failure process analysis(RFPA) method(based on finite element method) and discontinuous deformation analysis(DDA) method. RFPA is used to simulate crack initiation, propagation and coalescence processes of rock during the small deformation state. The DDA method is used to simulate the movement of blocks created by the multiple cracks modelled by the RFPA. The newly developed DDD method is particularly suitable for modelling both crack propagation and block movement during the rock failure process because of the natural and convenient coupling of continuous and discontinuous deformation analyses. The proposed method has been used to simulate crack initiation, propagation and coalescence within a slope as well as the block movement during the landslide process. Numerical modelling results indicate that the proposed DDD method can automatically simulate crack propagation and block movement during the rock failure process without degrading accuracy.
