The Upper Cretaceous of Tantou Basin in western Henan has yielded many vertebrate fossils,which are featured by several non-avian dinosaurs.Meanwhile,studies on their eggs were yet inadequate though many eggshells hav...The Upper Cretaceous of Tantou Basin in western Henan has yielded many vertebrate fossils,which are featured by several non-avian dinosaurs.Meanwhile,studies on their eggs were yet inadequate though many eggshells have been reported.The newly discovered material 41HⅤ0199 was excavated from the Upper Cretaceous Qiupa Formation in 2021.The block preserves eight complete eggs arranged in two partial rings that form a partial clutch,and there are some scattered eggshells preserved closely with the block,showing a concave-up to concave-down ratio of 54.5:45.5,which indicates that the scattered eggshells come from the clutch and the clutch had been partially broken before it was buried.Based on morphological and microstructural characteristics,the eggs and eggshells can be assigned to Macroolithus yaotunensis(Elongatoolithidae),an oospecies known to be related to oviraptorids,which leads Yulong mini to be its probable producer.Besides,some eggshells show microstructural signs indicating egg retention,which marks the second example of egg retention in the oofamily Elongatoolithidae.展开更多
[Objective]Implementation of the Ten-Year Fishing Ban policy may alter fish diversity and niche characteristics of dominant species in spawning grounds within the National Nature Reserve for Rare and Endemic Fish in t...[Objective]Implementation of the Ten-Year Fishing Ban policy may alter fish diversity and niche characteristics of dominant species in spawning grounds within the National Nature Reserve for Rare and Endemic Fish in the Upper Yangtze River.This study initiated continuous monitoring of natural spawning habitats from February 2022 to assess these ecological changes.[Methods]Environmental DNA(eDNA)metabarcoding was employed to analyze fish species composition,biodiversity patterns,and niche parameters of dominant species.Water sampling followed the CEN/TS 19461 standard across five monitoring transects(ZT1-ZT5).[Results]The eDNA analysis detected 45 species of fish belonging to 38 genera,13 families,and 3 orders were detected through environmental DNA(eDNA)in this survey,including 10 species endemic to the upper reaches of the Yangtze River,such as Procypris rabaudi and Myxocyprinus asiaticus.The fish community was mainly composed of bottom-dwelling,settling ovum-producing,omnivorous fish.The variation ranges of the Chao1 index,ACE index,Shannon index,and Simpson index are 736~996,719~965,1.58~3.23,and 0.83~0.99,respectively,indicating that fish species in spawning sites are abundant and community distribution uniformity is high.All indexes are highest at ZT1 monitoring points.Cluster analysis showed that,at a certain similarity level,fish community types in spawning sites could be basically divided into two groups:ZT1,ZT3,and ZT5 clustered together,and ZT2 and ZT4 clustered together,indicating similar fish community habitats.There are 9 dominant fish species in typical deep pool habitats in the reserve,with niche widths(Bi)ranging from 1.13 to 3.87.The dominant fish species are broad and medium niche fish,such as Cyprinus carpio and Hemiculter tchangi,with the niche overlap index(Oik)of some dominant fish species reaching more than 0.95.This indicates fierce competition for resources among the fish in this spawning ground.[Conclusion]The Zhutuo spawning ground demonstrates high species richness with homogeneous community structure and intense resource competition.This study establishes an eDNA-based monitoring framework that enhances conventional survey method,providing critical baseline data for adaptive management under the fishing moratorium regime.展开更多
In the practical slope engineering,the stability of lower sliding mass(region A)with back tensile cracks of the jointed rock slope attracts more attentions,but the upper rock mass(region B)may also be unstable.Therefo...In the practical slope engineering,the stability of lower sliding mass(region A)with back tensile cracks of the jointed rock slope attracts more attentions,but the upper rock mass(region B)may also be unstable.Therefore,in this study,based on the stepped failure mode of bedding jointed rock slopes,considering the influence of the upper rock mass on the lower stepped sliding mass,the improved failure model for analyzing the interaction force(F_(AB))between two regions is constructed,and the safety factors(F_(S))of two regions and whole region are derived.In addition,this paper proposes a method to determine the existence of F_(AB) using their respective acceleration values(a_(A) and a_(B))when regions A and B are unstable.The influences of key parameters on two regions and the whole region are analyzed.The results show that the variation of the F_(AB) and F_(S) of two regions can be obtained accurately based on the improved failure model.The accuracy of the improved failure model is verified by comparative analysis.The research results can explain the interaction mechanism of two regions and the natural phenomenon of slope failure caused by the development of cracks.展开更多
Based on the nonlinear failure criterion and the upper bound theorem, the modified tangential technique method was proposed to derive the expression of supporting pressure acting on shallow tunnel. Instead of the same...Based on the nonlinear failure criterion and the upper bound theorem, the modified tangential technique method was proposed to derive the expression of supporting pressure acting on shallow tunnel. Instead of the same stress state, different normal stresses on element boundaries were used. In order to investigate the influence of different factors on supporting pressures, the failure mechanism was established. The solution of supporting pressure, with different parameters, was obtained by optimization theory. The corresponding failure mechanism and numerical results were presented. In comparison with the results using the single tangential technique method, it is found that the proposed method is effective, and the good agreement shows that the present solution of supporting pressure is reliable.展开更多
High pressure and water-bearing caverns ahead of a karst tunnel face tend to cause geological disasters, such as water and mud bursts. So, the determination of safe thickness of the reserved rock plug is a key technic...High pressure and water-bearing caverns ahead of a karst tunnel face tend to cause geological disasters, such as water and mud bursts. So, the determination of safe thickness of the reserved rock plug is a key technical problem to be solved for karst tunnel construction. Based on the Hoek-Brown nonlinear failure criterion, the minimum safe thickness of rock plug was investigated in the light of the limit analysis theory. On the basis of the proposed failure mode, the expression of the minimum thickness for rock plug was obtained by means of upper bound theorem in combination with variational principle. The calculation results show the influence of each parameter on safe thickness and reveal the damage range of rock plug. The proposed method is verified by comparing the results with those of the drain cavern of Maluqing Tunnel. The research shows that with the increase of compressive strength and tensile strength as well as constant A of Hoek-Brown criterion, the safe thickness decreases, whereas with the increase of cavern pressure, tunnel diameter, and constant B from Hoek-Brown criterion, the safe thickness increases. Besides, the tensile strength, or constants A and B affect the shear failure angle of rock plug structure, but other parameters do not. In conclusion, the proposed method can predict the minimum safe thickness of rock plug, and is useful for water burst study and prevention measures of tunnels constructed in high-risk karst regions.展开更多
Given the extensive utilization of cantilever retaining walls in construction and development projects,their optimal design and analysis with proper attention to seismic loads is a typical engineering problem.This res...Given the extensive utilization of cantilever retaining walls in construction and development projects,their optimal design and analysis with proper attention to seismic loads is a typical engineering problem.This research presents a new algorithm for pseudo-static analysis of retaining walls employing upper bound method.The algorithm can be utilized to design and check the external and internal stability of the wall based on the proposed mechanism.One of the main features of this algorithm is its ability to determine the critical condition of failure wedges,the minimum safety factor and maximum force acting on the wall,as well as the minimum weight of the wall,simultaneously,by effectively using the multi-objective optimization.The results obtained by the proposed failure mechanisms show that,while using the upper bound limit analysis approach,the active force should be maximized concurrent with optimizing the direction of the plane passing through the back of the heel.The present study also applies the proposed algorithm to determine the critical direction of the earthquake acceleration coefficient.The critical direction of earthquake acceleration coefficient is defined as the direction that maximizes the active force exerted on the wall and minimizes the safety factor for wall stability.The results obtained in this study are in good agreement with those of similar studies carried out based on the limit equilibrium method and finite element analysis.The critical failure mechanisms were determined via optimization with genetic algorithm.展开更多
By combining the results of laboratory model tests with relevant flow rules, the failure mode of shallow unsymmetrical loading tunnels and the corresponding velocity field were established. According to the principle ...By combining the results of laboratory model tests with relevant flow rules, the failure mode of shallow unsymmetrical loading tunnels and the corresponding velocity field were established. According to the principle of virtual power, the upper bound solution for surrounding rock pressure of shallow unsymmetrical loading tunnel was derived and verified by an example. The results indicate that the calculated results of the derived upper bound method for surrounding rock pressure of shallow unsymmetrical loading tunnels are relatively close to those of the existing "code method" and test results, which means that the proposed method is feasible. The current code method underestimates the unsymmetrical loading feature of surrounding rock pressure of shallow unsymmetrical loading tunnels, so it is unsafe; when the burial depth is less or greater than two times of the tunnel span and the unsymmetrical loading angle is less than 45°, the upper bound method or the average value of the results calculated by the upper bound method and code method respectively, is comparatively reasonable. When the burial depth is greater than two times of the tunnel span and the unsymmetrical loading angle is greater than 45°, the code method is more suitable.展开更多
Based on the upper bound theorem of limit analysis,the factor of safety for shallow tunnel in saturated soil is calculated in conjunction with the strength reduction technique.To analyze the influence of the pore pres...Based on the upper bound theorem of limit analysis,the factor of safety for shallow tunnel in saturated soil is calculated in conjunction with the strength reduction technique.To analyze the influence of the pore pressure on the factor of safety for shallow tunnel,the power of pore pressure is regarded as a power of external force in the energy calculation.Using the rigid multiple-block failure mechanism,the objective function for the factor of safety is constructed and the optimal solutions are derived by employing the sequential quadratic programming.According to the results of optimization calculation,the factor of safety of shallow tunnel for different pore pressure coefficients and variational groundwater tables are obtained.The parameter analysis shows that the pore pressure coefficient and the location of the groundwater table have significant influence on the factor of safety for shallow tunnel.展开更多
In the South Yellow Sea Basin,Mesozoic–Paleozoic marine strata are generally well developed with large thickness,and no substantial breakthroughs have been made in hydrocarbon exploration.Through research,it is belie...In the South Yellow Sea Basin,Mesozoic–Paleozoic marine strata are generally well developed with large thickness,and no substantial breakthroughs have been made in hydrocarbon exploration.Through research,it is believed that the Upper Permian–Lower Triassic can be regarded as a long-term base-level cycle.Based on drilling data,characteristics of the lithology–electric property combination cyclicity,and the special lithology,the long-term base-level cycle was divided into five medium-term base-level cycles(MC1–MC5).On this basis,the Permian–Triassic sedimentary systems and their filling model were analyzed in accordance with the change of base-level cycle and transition of sedimentary environment,as well as characteristics of the drilling sedimentary facies and seismic facies.The results show that there were six sedimentary systems(fluvial,delta,tidal flat,open platform,restricted platform,and continental shelf)developed in the Upper Permian–Lower Triassic,the sedimentary systems were distributed such that the water was deep in the northwest and shallow in the southeast,and there were two base-level cycle filling models(a relatively stable tidal flat facies and a rapidly transgressive continental shelf facies to stable platform facies)developed in the Upper Permian–Lower Triassic.These models can provide a basis for evaluation of the Mesozoic–Paleozoic hydrocarbon geology in the South Yellow Sea Basin.展开更多
To investigate the effective shape of collapsing block in square tunnel subjected to pore water pressure,the analytical solution of detaching curve was derived using upper bound theorem of limit analysis with Hoek-Bro...To investigate the effective shape of collapsing block in square tunnel subjected to pore water pressure,the analytical solution of detaching curve was derived using upper bound theorem of limit analysis with Hoek-Brown failure criterion. The work rate of pore water pressure,which was regarded as an external rate of work,was taken into account in the framework of limit analysis. Taking advantages of variational calculation,the objective function with respect to detaching curve was optimized to obtain the effective shape of collapsing block for square tunnel. According to the numerical results,it is found that the varying pore water pressure coefficient only affects the height and width of the collapsing block,whereas the shape of collapsing block remains unchanged.展开更多
Based on the nonlinear Mohr-Coulomb failure criterion and the associated flow rules,the three-dimensional(3-D)axisymmetric failure mechanism of shallow horizontal circular plate anchors that are subjected to the ultim...Based on the nonlinear Mohr-Coulomb failure criterion and the associated flow rules,the three-dimensional(3-D)axisymmetric failure mechanism of shallow horizontal circular plate anchors that are subjected to the ultimate pullout capacity(UPC)is determined.A derivative function of the projection function for projecting the 3-D axisymmetric failure surface on plane is deduced using the variation theory.By using difference principle,the primitive function of failure surface satisfying boundary condition and numerical solution to its corresponding ultimate pullout capacity function are obtained.The influences of nonlinear Mohr-Coulomb parameters on UPC and failure mechanism are studied.The result shows that UPC decreases with dimensionless parameter m and uniaxial tensile strength increases but increases when depth and radius of plate anchor,surface overload,initial cohesion,geomaterial density and friction angle increase.The failure surface is similar to a symmetrical spatial funnel,and its shape is mainly determined by dimensionless parameter m;the surface damage range expands with the increase of radius and depth of the plate anchor as well as initial cohesion but decreases with the increase of dimensionless parameter m and uniaxial tensile strength as well as geomaterial density.As the dimensionless parameter m=2.0,the numerical solution of UPC based on the difference principle is proved to be feasible and effective through the comparison with the exact solution.In addition,the comparison between solutions of UPC computed by variation method and those computed by upper bound method indicate that variation method outperforms upper bound method.展开更多
In order to reveal the relationship between the penecontemporaneous karstification and sedimentary microtopography in sequence stratigraphy,the sequence stratigraphic framework of Lianglitage formation in Upper Ordovi...In order to reveal the relationship between the penecontemporaneous karstification and sedimentary microtopography in sequence stratigraphy,the sequence stratigraphic framework of Lianglitage formation in Upper Ordovician is studied according to the well drilling,logging,geophysical data,detailed observations of core and the paleontology.The Lianglitage formation belongs to the sequence Ⅳ of Ordovician.The second member of Lianglitage formation is prograde sedimentation in highstand systems tract,and is favorable for developing reef flat.The development scale and thickness of reef flat are controlled by the variation of secondary sea level.The types and characteristics of karst in the highstand systems tract show that the late highstand systems tract is dissolved and cemented by the meteoric fresh water and mixed water.Penecontemporaneous karstification is developed at the top of parasequence and high place of geomorphology.Atmospheric diagenetic lens is formed.The developing regulations and controlling factors of penecontemporaneous karstification can provide new clues to the prediction and exploration of favorable reservoir in this area.展开更多
The investigation of supporting pressure is of great significance to the design of underground structures.Based on the kinematical approach of limit analysis,an improved failure mechanism is proposed,and the supportin...The investigation of supporting pressure is of great significance to the design of underground structures.Based on the kinematical approach of limit analysis,an improved failure mechanism is proposed,and the supporting pressure is investigated for deep buried cavity.Three failure mechanisms are first introduced according to the existing failure mechanisms of geotechnical structures of limit analysis.A comparison with respect to the optimal failure mechanisms and the upper bound solutions provided among these three mechanisms are then conducted in an attempt to obtain the improved failure mechanism.The results provided by the improved failure mechanism are in good agreement with those by the existing method,the numerical solution and field monitoring,which demonstrates that the proposed failure mechanism is effective for the upper bound analysis of supporting pressure.展开更多
The research activities of the middle and upper atmosphere in China paced abig stride in the recent years. This paper provides an brief overview of theadvances in main aspects of the study in China during the past fou...The research activities of the middle and upper atmosphere in China paced abig stride in the recent years. This paper provides an brief overview of theadvances in main aspects of the study in China during the past four years.展开更多
Considering the variation of cohesion along the depth,the upper bound solution of active earth pressure for a rough inclined wall with sloped backfill is formulated based on a log-spiral failure mechanism.For a more a...Considering the variation of cohesion along the depth,the upper bound solution of active earth pressure for a rough inclined wall with sloped backfill is formulated based on a log-spiral failure mechanism.For a more accurate prediction,the influence of intermediate principal stress is taken into consideration using the unified strength theory.Converting the search for the active pressure to an optimization problem,the most critical failure surface can be located by a natural selection-based gravitational search algorithm(GSA).The proposed method is validated compared with existing methods for noncohesive and cohesive cases and proved to be more accordance with the limit equilibrium solution.The influences of the variation of soil cohesion and intermediate principal stress on active earth pressure coefficient are then fully studied.It can be concluded that both the variations of soil cohesion and intermediate principal stress have a significant influence on the active earth pressure coefficient.展开更多
Convective pore-fluid flow (CPFF) plays a critical role in generating mineral deposits and oil reservoirs within the deep Earth. Therefore, theoretical understanding and numerical modeling of the thermodynamic process...Convective pore-fluid flow (CPFF) plays a critical role in generating mineral deposits and oil reservoirs within the deep Earth. Therefore, theoretical understanding and numerical modeling of the thermodynamic process that triggers and controls the CPFF are extremely important for the exploration of new mineral deposits and underground oil resources. From the viewpoint of science, the CPFF within the upper crust can be treated as a kind of thermodynamic instability problem of pore-fluid in fluid-saturated porous media. The key issue of dealing with this kind of problem is to assess whether a nonlinear thermodynamic system under consideration is supercritical. To overcome limitations of using theoretical analysis and experimental methods in dealing with the CPFF problems within the upper crust, finite element modeling has been broadly employed for solving this kind of problem over the past two decades. The main purpose of this paper is to overview recent developments and applications of finite element modeling associated with solving the CPFF problems in large length-scale geological systems of complicated geometries and complex material distributions. In particular, two kinds of commonly-used finite element modeling approaches, namely the steady-state and transient-state approaches, and their advantages/disadvantages are thoroughly presented and discussed.展开更多
A joined failure mechanism of translation and rotation was proposed for the stability analysis of deep tunnel face, and the upper bound solution of supporting force of deep tunnel was calculated under pore water press...A joined failure mechanism of translation and rotation was proposed for the stability analysis of deep tunnel face, and the upper bound solution of supporting force of deep tunnel was calculated under pore water pressure. The calculations were based on limit analysis method of upper bound theory, with the employment of non-associated Mohr-Coulomb flow rule. Nonlinear failure criterion was adopted. Optimized analysis was conducted for the effects of the tunnel depth, pore water pressure coefficient, the initial cohesive force and nonlinear coefficient on supporting force. The upper bound solutions are obtained by optimum method. Results are listed and compared with the previously published solutions for the verification of correctness and effectiveness. The failure shapes are presented, and results are discussed for different pore water pressure coefficients and nonlinear coefficients of tunnel face.展开更多
文摘The Upper Cretaceous of Tantou Basin in western Henan has yielded many vertebrate fossils,which are featured by several non-avian dinosaurs.Meanwhile,studies on their eggs were yet inadequate though many eggshells have been reported.The newly discovered material 41HⅤ0199 was excavated from the Upper Cretaceous Qiupa Formation in 2021.The block preserves eight complete eggs arranged in two partial rings that form a partial clutch,and there are some scattered eggshells preserved closely with the block,showing a concave-up to concave-down ratio of 54.5:45.5,which indicates that the scattered eggshells come from the clutch and the clutch had been partially broken before it was buried.Based on morphological and microstructural characteristics,the eggs and eggshells can be assigned to Macroolithus yaotunensis(Elongatoolithidae),an oospecies known to be related to oviraptorids,which leads Yulong mini to be its probable producer.Besides,some eggshells show microstructural signs indicating egg retention,which marks the second example of egg retention in the oofamily Elongatoolithidae.
文摘[Objective]Implementation of the Ten-Year Fishing Ban policy may alter fish diversity and niche characteristics of dominant species in spawning grounds within the National Nature Reserve for Rare and Endemic Fish in the Upper Yangtze River.This study initiated continuous monitoring of natural spawning habitats from February 2022 to assess these ecological changes.[Methods]Environmental DNA(eDNA)metabarcoding was employed to analyze fish species composition,biodiversity patterns,and niche parameters of dominant species.Water sampling followed the CEN/TS 19461 standard across five monitoring transects(ZT1-ZT5).[Results]The eDNA analysis detected 45 species of fish belonging to 38 genera,13 families,and 3 orders were detected through environmental DNA(eDNA)in this survey,including 10 species endemic to the upper reaches of the Yangtze River,such as Procypris rabaudi and Myxocyprinus asiaticus.The fish community was mainly composed of bottom-dwelling,settling ovum-producing,omnivorous fish.The variation ranges of the Chao1 index,ACE index,Shannon index,and Simpson index are 736~996,719~965,1.58~3.23,and 0.83~0.99,respectively,indicating that fish species in spawning sites are abundant and community distribution uniformity is high.All indexes are highest at ZT1 monitoring points.Cluster analysis showed that,at a certain similarity level,fish community types in spawning sites could be basically divided into two groups:ZT1,ZT3,and ZT5 clustered together,and ZT2 and ZT4 clustered together,indicating similar fish community habitats.There are 9 dominant fish species in typical deep pool habitats in the reserve,with niche widths(Bi)ranging from 1.13 to 3.87.The dominant fish species are broad and medium niche fish,such as Cyprinus carpio and Hemiculter tchangi,with the niche overlap index(Oik)of some dominant fish species reaching more than 0.95.This indicates fierce competition for resources among the fish in this spawning ground.[Conclusion]The Zhutuo spawning ground demonstrates high species richness with homogeneous community structure and intense resource competition.This study establishes an eDNA-based monitoring framework that enhances conventional survey method,providing critical baseline data for adaptive management under the fishing moratorium regime.
基金Projects(52208369,52309138,52108320)supported by the National Natural Science Foundation of ChinaProjects(2023NSFSC0284,2025ZNSFSC0409)supported by the Sichuan Science and Technology Program,ChinaProject(U22468214)supported by the Joint Fund Project for Railway Basic Research by the National Natural Science Foundation of China and China State Railway Group Co.,Ltd.
文摘In the practical slope engineering,the stability of lower sliding mass(region A)with back tensile cracks of the jointed rock slope attracts more attentions,but the upper rock mass(region B)may also be unstable.Therefore,in this study,based on the stepped failure mode of bedding jointed rock slopes,considering the influence of the upper rock mass on the lower stepped sliding mass,the improved failure model for analyzing the interaction force(F_(AB))between two regions is constructed,and the safety factors(F_(S))of two regions and whole region are derived.In addition,this paper proposes a method to determine the existence of F_(AB) using their respective acceleration values(a_(A) and a_(B))when regions A and B are unstable.The influences of key parameters on two regions and the whole region are analyzed.The results show that the variation of the F_(AB) and F_(S) of two regions can be obtained accurately based on the improved failure model.The accuracy of the improved failure model is verified by comparative analysis.The research results can explain the interaction mechanism of two regions and the natural phenomenon of slope failure caused by the development of cracks.
基金Projects(2013CB0360042011CB013800)supported by the National Basic Research Program of China+1 种基金Project(51178468)supported by the National Natural Science Foundation of ChinaProject(2011G013-B)supported by the Science and Technology Development of Railways Department in China
文摘Based on the nonlinear failure criterion and the upper bound theorem, the modified tangential technique method was proposed to derive the expression of supporting pressure acting on shallow tunnel. Instead of the same stress state, different normal stresses on element boundaries were used. In order to investigate the influence of different factors on supporting pressures, the failure mechanism was established. The solution of supporting pressure, with different parameters, was obtained by optimization theory. The corresponding failure mechanism and numerical results were presented. In comparison with the results using the single tangential technique method, it is found that the proposed method is effective, and the good agreement shows that the present solution of supporting pressure is reliable.
基金Project(2013CB036004)supported by the National Basic Research Program of ChinaProject(51378510)supported by the National Natural Science Foundation of ChinaProject(CX2014B069)supported by Hunan Provincial Innovation Foundation for Postgraduate,China
文摘High pressure and water-bearing caverns ahead of a karst tunnel face tend to cause geological disasters, such as water and mud bursts. So, the determination of safe thickness of the reserved rock plug is a key technical problem to be solved for karst tunnel construction. Based on the Hoek-Brown nonlinear failure criterion, the minimum safe thickness of rock plug was investigated in the light of the limit analysis theory. On the basis of the proposed failure mode, the expression of the minimum thickness for rock plug was obtained by means of upper bound theorem in combination with variational principle. The calculation results show the influence of each parameter on safe thickness and reveal the damage range of rock plug. The proposed method is verified by comparing the results with those of the drain cavern of Maluqing Tunnel. The research shows that with the increase of compressive strength and tensile strength as well as constant A of Hoek-Brown criterion, the safe thickness decreases, whereas with the increase of cavern pressure, tunnel diameter, and constant B from Hoek-Brown criterion, the safe thickness increases. Besides, the tensile strength, or constants A and B affect the shear failure angle of rock plug structure, but other parameters do not. In conclusion, the proposed method can predict the minimum safe thickness of rock plug, and is useful for water burst study and prevention measures of tunnels constructed in high-risk karst regions.
文摘Given the extensive utilization of cantilever retaining walls in construction and development projects,their optimal design and analysis with proper attention to seismic loads is a typical engineering problem.This research presents a new algorithm for pseudo-static analysis of retaining walls employing upper bound method.The algorithm can be utilized to design and check the external and internal stability of the wall based on the proposed mechanism.One of the main features of this algorithm is its ability to determine the critical condition of failure wedges,the minimum safety factor and maximum force acting on the wall,as well as the minimum weight of the wall,simultaneously,by effectively using the multi-objective optimization.The results obtained by the proposed failure mechanisms show that,while using the upper bound limit analysis approach,the active force should be maximized concurrent with optimizing the direction of the plane passing through the back of the heel.The present study also applies the proposed algorithm to determine the critical direction of the earthquake acceleration coefficient.The critical direction of earthquake acceleration coefficient is defined as the direction that maximizes the active force exerted on the wall and minimizes the safety factor for wall stability.The results obtained in this study are in good agreement with those of similar studies carried out based on the limit equilibrium method and finite element analysis.The critical failure mechanisms were determined via optimization with genetic algorithm.
基金Project(2014M560652)supported by China Postdoctoral Science FoundationProjects(2011CB013802,2013CB036004)supported by the National Basic Research Program of China
文摘By combining the results of laboratory model tests with relevant flow rules, the failure mode of shallow unsymmetrical loading tunnels and the corresponding velocity field were established. According to the principle of virtual power, the upper bound solution for surrounding rock pressure of shallow unsymmetrical loading tunnel was derived and verified by an example. The results indicate that the calculated results of the derived upper bound method for surrounding rock pressure of shallow unsymmetrical loading tunnels are relatively close to those of the existing "code method" and test results, which means that the proposed method is feasible. The current code method underestimates the unsymmetrical loading feature of surrounding rock pressure of shallow unsymmetrical loading tunnels, so it is unsafe; when the burial depth is less or greater than two times of the tunnel span and the unsymmetrical loading angle is less than 45°, the upper bound method or the average value of the results calculated by the upper bound method and code method respectively, is comparatively reasonable. When the burial depth is greater than two times of the tunnel span and the unsymmetrical loading angle is greater than 45°, the code method is more suitable.
基金Project(51178468) supported by the National Natural Science Foundation of ChinaProject(2010bsxt07) supported by the Doctoral Dissertation Innovation Fund of Central South University,China
文摘Based on the upper bound theorem of limit analysis,the factor of safety for shallow tunnel in saturated soil is calculated in conjunction with the strength reduction technique.To analyze the influence of the pore pressure on the factor of safety for shallow tunnel,the power of pore pressure is regarded as a power of external force in the energy calculation.Using the rigid multiple-block failure mechanism,the objective function for the factor of safety is constructed and the optimal solutions are derived by employing the sequential quadratic programming.According to the results of optimization calculation,the factor of safety of shallow tunnel for different pore pressure coefficients and variational groundwater tables are obtained.The parameter analysis shows that the pore pressure coefficient and the location of the groundwater table have significant influence on the factor of safety for shallow tunnel.
基金Projects(41506080,41702162)supported by the National Natural Science Foundation of ChinaProjects(DD20160152,DD20160147,GZH200800503)supported by China Geological Survey+1 种基金Projects(XQ-2005-01,2009GYXQ10)supported by China Ministry of Land and ResourcesProject(201602004)supported by the Postdoctoral Innovation Foundation of Shandong Province,China
文摘In the South Yellow Sea Basin,Mesozoic–Paleozoic marine strata are generally well developed with large thickness,and no substantial breakthroughs have been made in hydrocarbon exploration.Through research,it is believed that the Upper Permian–Lower Triassic can be regarded as a long-term base-level cycle.Based on drilling data,characteristics of the lithology–electric property combination cyclicity,and the special lithology,the long-term base-level cycle was divided into five medium-term base-level cycles(MC1–MC5).On this basis,the Permian–Triassic sedimentary systems and their filling model were analyzed in accordance with the change of base-level cycle and transition of sedimentary environment,as well as characteristics of the drilling sedimentary facies and seismic facies.The results show that there were six sedimentary systems(fluvial,delta,tidal flat,open platform,restricted platform,and continental shelf)developed in the Upper Permian–Lower Triassic,the sedimentary systems were distributed such that the water was deep in the northwest and shallow in the southeast,and there were two base-level cycle filling models(a relatively stable tidal flat facies and a rapidly transgressive continental shelf facies to stable platform facies)developed in the Upper Permian–Lower Triassic.These models can provide a basis for evaluation of the Mesozoic–Paleozoic hydrocarbon geology in the South Yellow Sea Basin.
基金Project(09JJ1008) supported by Hunan Provincial Science Foundation, ChinaProject(CX2009B043) supported by Hunan Provincial Postgraduate Innovation Program, China
文摘To investigate the effective shape of collapsing block in square tunnel subjected to pore water pressure,the analytical solution of detaching curve was derived using upper bound theorem of limit analysis with Hoek-Brown failure criterion. The work rate of pore water pressure,which was regarded as an external rate of work,was taken into account in the framework of limit analysis. Taking advantages of variational calculation,the objective function with respect to detaching curve was optimized to obtain the effective shape of collapsing block for square tunnel. According to the numerical results,it is found that the varying pore water pressure coefficient only affects the height and width of the collapsing block,whereas the shape of collapsing block remains unchanged.
基金Project(51478477)supported by the National Natural Science Foundation of ChinaProject(2016CX012)supported by the Innovation-driven Project of Central South University,ChinaProject(2014122006)supported by the Guizhou Provincial Department of Transportation Foundation,China
文摘Based on the nonlinear Mohr-Coulomb failure criterion and the associated flow rules,the three-dimensional(3-D)axisymmetric failure mechanism of shallow horizontal circular plate anchors that are subjected to the ultimate pullout capacity(UPC)is determined.A derivative function of the projection function for projecting the 3-D axisymmetric failure surface on plane is deduced using the variation theory.By using difference principle,the primitive function of failure surface satisfying boundary condition and numerical solution to its corresponding ultimate pullout capacity function are obtained.The influences of nonlinear Mohr-Coulomb parameters on UPC and failure mechanism are studied.The result shows that UPC decreases with dimensionless parameter m and uniaxial tensile strength increases but increases when depth and radius of plate anchor,surface overload,initial cohesion,geomaterial density and friction angle increase.The failure surface is similar to a symmetrical spatial funnel,and its shape is mainly determined by dimensionless parameter m;the surface damage range expands with the increase of radius and depth of the plate anchor as well as initial cohesion but decreases with the increase of dimensionless parameter m and uniaxial tensile strength as well as geomaterial density.As the dimensionless parameter m=2.0,the numerical solution of UPC based on the difference principle is proved to be feasible and effective through the comparison with the exact solution.In addition,the comparison between solutions of UPC computed by variation method and those computed by upper bound method indicate that variation method outperforms upper bound method.
基金Project(2008ZX05004-004)supported by the State Key Scientific Research Programs,ChinaProject(SZD0414)supported by the Sichuan Province Key Discipline Construction Project,ChinaProject(KZCX2-YW-Q05-01)supported by the Chinese Academy of Sciences Innovation Engineering Directional Project
文摘In order to reveal the relationship between the penecontemporaneous karstification and sedimentary microtopography in sequence stratigraphy,the sequence stratigraphic framework of Lianglitage formation in Upper Ordovician is studied according to the well drilling,logging,geophysical data,detailed observations of core and the paleontology.The Lianglitage formation belongs to the sequence Ⅳ of Ordovician.The second member of Lianglitage formation is prograde sedimentation in highstand systems tract,and is favorable for developing reef flat.The development scale and thickness of reef flat are controlled by the variation of secondary sea level.The types and characteristics of karst in the highstand systems tract show that the late highstand systems tract is dissolved and cemented by the meteoric fresh water and mixed water.Penecontemporaneous karstification is developed at the top of parasequence and high place of geomorphology.Atmospheric diagenetic lens is formed.The developing regulations and controlling factors of penecontemporaneous karstification can provide new clues to the prediction and exploration of favorable reservoir in this area.
基金Project(51674115)supported by the National Natural Science Foundation of ChinaProject(51434006)supported by the Key Program of the National Natural Science Foundation of ChinaProject(2015JJ4024)supported by the Natural Science Foundation of Hunan Province,China
文摘The investigation of supporting pressure is of great significance to the design of underground structures.Based on the kinematical approach of limit analysis,an improved failure mechanism is proposed,and the supporting pressure is investigated for deep buried cavity.Three failure mechanisms are first introduced according to the existing failure mechanisms of geotechnical structures of limit analysis.A comparison with respect to the optimal failure mechanisms and the upper bound solutions provided among these three mechanisms are then conducted in an attempt to obtain the improved failure mechanism.The results provided by the improved failure mechanism are in good agreement with those by the existing method,the numerical solution and field monitoring,which demonstrates that the proposed failure mechanism is effective for the upper bound analysis of supporting pressure.
文摘The research activities of the middle and upper atmosphere in China paced abig stride in the recent years. This paper provides an brief overview of theadvances in main aspects of the study in China during the past four years.
基金Project(2016YFC0800200)supported by the National Key Research Plan of China。
文摘Considering the variation of cohesion along the depth,the upper bound solution of active earth pressure for a rough inclined wall with sloped backfill is formulated based on a log-spiral failure mechanism.For a more accurate prediction,the influence of intermediate principal stress is taken into consideration using the unified strength theory.Converting the search for the active pressure to an optimization problem,the most critical failure surface can be located by a natural selection-based gravitational search algorithm(GSA).The proposed method is validated compared with existing methods for noncohesive and cohesive cases and proved to be more accordance with the limit equilibrium solution.The influences of the variation of soil cohesion and intermediate principal stress on active earth pressure coefficient are then fully studied.It can be concluded that both the variations of soil cohesion and intermediate principal stress have a significant influence on the active earth pressure coefficient.
基金Project(11272359)supported by the National Natural Science Foundation of China
文摘Convective pore-fluid flow (CPFF) plays a critical role in generating mineral deposits and oil reservoirs within the deep Earth. Therefore, theoretical understanding and numerical modeling of the thermodynamic process that triggers and controls the CPFF are extremely important for the exploration of new mineral deposits and underground oil resources. From the viewpoint of science, the CPFF within the upper crust can be treated as a kind of thermodynamic instability problem of pore-fluid in fluid-saturated porous media. The key issue of dealing with this kind of problem is to assess whether a nonlinear thermodynamic system under consideration is supercritical. To overcome limitations of using theoretical analysis and experimental methods in dealing with the CPFF problems within the upper crust, finite element modeling has been broadly employed for solving this kind of problem over the past two decades. The main purpose of this paper is to overview recent developments and applications of finite element modeling associated with solving the CPFF problems in large length-scale geological systems of complicated geometries and complex material distributions. In particular, two kinds of commonly-used finite element modeling approaches, namely the steady-state and transient-state approaches, and their advantages/disadvantages are thoroughly presented and discussed.
基金Project(2013CB036004)supported by National Basic Research Program of ChinaProjects(51178468+2 种基金51378510)supported by the National Natural Science Foundation of ChinaProject(2015zzts061)supported by the Fundamental Research Funds for the Central UniversitiesChina
文摘A joined failure mechanism of translation and rotation was proposed for the stability analysis of deep tunnel face, and the upper bound solution of supporting force of deep tunnel was calculated under pore water pressure. The calculations were based on limit analysis method of upper bound theory, with the employment of non-associated Mohr-Coulomb flow rule. Nonlinear failure criterion was adopted. Optimized analysis was conducted for the effects of the tunnel depth, pore water pressure coefficient, the initial cohesive force and nonlinear coefficient on supporting force. The upper bound solutions are obtained by optimum method. Results are listed and compared with the previously published solutions for the verification of correctness and effectiveness. The failure shapes are presented, and results are discussed for different pore water pressure coefficients and nonlinear coefficients of tunnel face.
