To address the issue of extreme thermal-induced arching in CRTS II slab tracks due to joint damage,an optimized joint repair model was proposed.First,the formula for calculating the safe temperature rise of the track ...To address the issue of extreme thermal-induced arching in CRTS II slab tracks due to joint damage,an optimized joint repair model was proposed.First,the formula for calculating the safe temperature rise of the track was derived based on the principle of stationary potential energy.Considering interlayer evolution and structural crack propagation,an optimized joint repair model for the track was established and validated.Subsequently,the impact of joint repair on track damage and arch stability under extreme temperatures was studied,and a comprehensive evaluation of the feasibility of joint repair and the evolution of damage after repair was conducted.The results show that after the joint repair,the temperature rise of the initial damage of the track structure can be increased by 11℃.Under the most unfavorable heating load with a superimposed temperature gradient,the maximum stiffness degradation index SDEG in the track structure is reduced by about 81.16%following joint repair.The joint repair process could effectively reduce the deformation of the slab arching under high temperatures,resulting in a reduction of 93.96%in upward arching deformation.After repair,with the damage to interfacing shear strength,the track arch increases by 2.616 mm.展开更多
Due to space constraints in urban areas,metro tunnels are typically constructed in pairs,with a small clearance.The interaction between twin tunnels leads to a significantly more complex ground deformation and stress ...Due to space constraints in urban areas,metro tunnels are typically constructed in pairs,with a small clearance.The interaction between twin tunnels leads to a significantly more complex ground deformation and stress distribution than that observed in a single tunnel scenario,particularly if the tunnels are excavated in sequence.A series of physical model tests were conducted to investigate soil deformation and stress disturbances caused by the excavation of twin tunnels.The test results indicate that the interaction between the twin tunnels was observed.Due to the soil arching effect,the excavation of Tunnel 2 increases the soil stress acting on Tunnel 1.An analytical method was proposed to determine soil stress considering the soil arching effect and the interaction between twin tunnels.The method categorized the relative locations between twin tunnels into non-influenced,partially influenced,and fully influenced scenarios.For non-influenced and fully influenced scenarios,the soil stresses above twin tunnels were calculated based on a symmetric major principal stress trace.For the partially influenced scenario,however,the soil arch above Tunnel 2 was asymmetric due to the interaction,and the stress distribution was obtained based on a new asymmetric major principal stress trace.The soil stress on Tunnel 1 was influenced by the load transferred from Tunnel 2 and calculated based on the force equilibrium.A comparison of the analytical and test results indicates that the proposed method effectively predicts the soil stress in the cover layer above twin tunnels excavated sequentially,considering the interaction and soil arching effects.展开更多
Introduction Aortic arch anomalies are congenital malformations of the position or branching of the aortic arch,or both.Double aortic arch(DAA)is a very rare malformation,affecting approximately 0.005%~0.007% of fetus...Introduction Aortic arch anomalies are congenital malformations of the position or branching of the aortic arch,or both.Double aortic arch(DAA)is a very rare malformation,affecting approximately 0.005%~0.007% of fetuses[1],and there has been no relevant literature mentioning the prenatal finding DAA in Macao till now.展开更多
The soil arching effect is an important factor affecting the internal load transfer of excavation-induced slopes.Physical model tests are usually used for studying the soil arching effect.Although physical model tests...The soil arching effect is an important factor affecting the internal load transfer of excavation-induced slopes.Physical model tests are usually used for studying the soil arching effect.Although physical model tests can monitor local point loads to demonstrate changes in local stresses,changes in force chains inside slopes are rarely demonstrated by physical modelling,which restricts the understanding of load transfer.To explore overall changes in stresses in slopes from a more microscopic perspective,a numerical simulation of the slope under excavation was carried out.Using built-in code and fish function programming in PFC^(3D),the slope model was developed.Monitoring areas were set up to monitor the changes in stresses and force chains during excavation.The simulation results show that excavation width affects the size of deformation area,and the deformation area expands as excavation width increases.Excavation causes load transfer and the formation of soil arching in the slope.A mechanism is proposed to explain the effect of excavation on soil arching formation and load transfer.The numerical simulation is important for revealing the load transfer of slopes during excavation,and the research results have practical value for the prevention and mitigation of landslides caused by excavation.展开更多
Narrow backfill earth pressure estimation is applied to study the stability of supporting structures in the vicinity of existing buildings.Previous narrow backfill earth pressure studies have neglected seismic-unsatur...Narrow backfill earth pressure estimation is applied to study the stability of supporting structures in the vicinity of existing buildings.Previous narrow backfill earth pressure studies have neglected seismic-unsaturated seepage multi-field coupling,resulting in inaccurate estimates.To address these deficiencies,this paper proposed a calculation method for seismic passive earth pressure in unsaturated narrow backfill,based on inclined thin-layer units.It considers the interlayer shear stress,arching effect,and the multi-field coupling of seismic-unsaturated seepage.Additionally,this paper includes a parametric sensitivity analysis.The outcomes indicate that the earthquake passive ground pressure of unsaturated narrow backfill can be reduced by increasing the aspect ratio,seismic acceleration coefficient,and unsaturation parameterα.It can also be reduced by decreasing the effective interior friction angle,soil cohesion,wallearth friction angle,and vertical discharge.Furthermore,for any width soil,lowering the elevation of the action point of passive thrust can be attained by raising the effective interior friction angle,wall-earth friction angle,and unsaturation parameterα.Reducing soil cohesion,seismic acceleration coefficient,and vertical discharge can also lower the height of the application point of passive thrust.展开更多
Determining earth pressure on jacked pipes is essential for ensuring lining safety and calculating jacking force,especially for deep-buried pipes.To better reflect the soil arching effect resulting from the excavation...Determining earth pressure on jacked pipes is essential for ensuring lining safety and calculating jacking force,especially for deep-buried pipes.To better reflect the soil arching effect resulting from the excavation of rectangular jacked pipes and the distribution of the earth pressure on jacked pipes,we present an analytical solution for predicting the vertical earth pressure on deep-buried rectangular pipe jacking tunnels,incorporating the tunnelling-induced ground loss distribution.Our proposed analytical model consists of the upper multi-layer parabolic soil arch and the lower friction arch.The key parameters(i.e.,width and height of friction arch B and height of parabolic soil arch H 1)are determined according to the existing research,and an analytical solution for K l is derived based on the distribution characteristics of the principal stress rotation angle.With consideration for the transition effect of the mechanical characteristics of the parabolic arch zone,an analytical solution for soil load transfer is derived.The prediction results of our analytical solution are compared with tests and simulation results to validate the effectiveness of the proposed analytical solution.Finally,the effects of different parameters on the soil pressure are discussed.展开更多
Hydrogel has developed into a very important platform in solar interface evaporator.However,the current hydrogel evaporators are usually three-dimensional evaporators,which will consume a lot of raw materials.Thus,a n...Hydrogel has developed into a very important platform in solar interface evaporator.However,the current hydrogel evaporators are usually three-dimensional evaporators,which will consume a lot of raw materials.Thus,a new two-dimensional hydrogel evaporator is urgently needed to alleviate this problem.Here,a double layer hydrogel evaporator was designed by twice vacuum filtration.Furthermore,through the arched design and the introduction of concentrated brine drainage system,the hydrogel evaporator has enhanced water transportation and tailored water transportation path.Such a unique drainage evaporation system greatly improves the stability of the evaporator.Thereby,a good balance is established between photothermal conversion and water supply,and solar energy is utilized efficiently.It can remain stable in continuous evaporation for up to 12 h with an excellent evaporation rate of 2.70 kg m^(-2)h^(-1)under 1 sun irradiation.Meanwhile,the drainage system realized the 1.8×10^(-10)mol m^(-2)s^(-1)diffusion flux of concentrated brine.Through one-time freeze-drying preparation,an arch-shaped drainage evaporator was used to prepare an evaporation area of more than 20 cm^(2).With the self-made condensate collecting device in outdoor environment,the fresh water yield reaches 7.5 L m^(-2)d^(-1).This provides a new scheme for building a new hydrogel evaporator and solving the fresh water crisis.展开更多
The stability of underground tunnel roofs is strongly influenced by wedge blocks formed by complex joint networks.The mechanical behavior and failure mechanisms of different roof wedge blocks in arched holes were inve...The stability of underground tunnel roofs is strongly influenced by wedge blocks formed by complex joint networks.The mechanical behavior and failure mechanisms of different roof wedge blocks in arched holes were investigated under biaxial stress conditions.The crack evolution and failure modes of the specimens were analyzed through acoustic emission(AE),digital image correlation(DIC),and discrete element method(DEM).Results show significant variations in mechanical properties:specimens T1(extremely unstable triangular)and T2(extremely unstable quadrilateral)exhibited higher strength than T3(extremely stable triangular)and T4(extremely stable quadrilateral),while support more effectively enhanced the strength of T3 and T4.Failure modes were classified as rock-dominated,wedgedominated,or co-dominated.Cracks typically initiated near the wedge and propagated outward.Unsupported specimens developed tensile cracks at the hole bottom,shear cracks at the sides,and mixed cracks along wedge boundaries,whereas supported specimens mainly exhibited cracks at the roof and sides.Stress analysis indicated that unsupported conditions induced high stress differences,promoting localized shear failure.Wedge geometry significantly affected shear stress redistribution at the roof.These findings highlight the critical role of support and wedge block geometry in controlling stress dis-tribution and failure mechanisms in arched tunnels.展开更多
The existing analytical models for umbrella arch method(UAM)based on elastic foundation beams often overlook the influence of the surrounding soil beyond the beam edges on the shear stresses acting on the beam.Consequ...The existing analytical models for umbrella arch method(UAM)based on elastic foundation beams often overlook the influence of the surrounding soil beyond the beam edges on the shear stresses acting on the beam.Consequently,such models fail to adequately reflect the continuity characteristics of soil deformation.Leveraging the Pasternak foundation-Euler beam model,this study considers the generalized shear force on the beam to account for the influence of soil outside the beam ends on the shear stress.An analytical model for the deformation and internal forces of finite-length beams subjected to arbitrary loads is derived based on the initial parameter method under various conditions.The mechanical model of the elastic foundation beam for advanced umbrella arch under typical tunnel excavation cycles is established,yielding analytical solutions for the longitudinal response of the umbrella arch.The reliability of the analytical model is verified with the existing test data.The improved model addresses anomalies in existing models,such as abnormal upward deformation in the loosened segment and maximum deflection occurring within the soil mass.Additionally,dimensionless characteristic parameters reflecting the relative stiffness between the umbrella arch structure and the foundation soil are proposed.Results indicate that the magnitude of soil characteristic parameters significantly influences the deformation and internal forces of the umbrella arch.Within common ranges of soil values,the maximum deformation and internal forces of the umbrella arch under semi-logarithmic coordinates exhibit nearly linear decay with decreasing soil characteristic parameters.The impact of tunnel excavation height on the stress of unsupported sections of the umbrella arch is minor,but it is more significant for umbrella arch buried within the soil mass.Conversely,the influence of tunnel excavation advance on the umbrella arch is opposite.展开更多
The influence of rockbolt pretension on bolting has not been well addressed,despite its critical importance in drift support systems.In this study,laboratory and numerical simulations of gravel bolting are conducted t...The influence of rockbolt pretension on bolting has not been well addressed,despite its critical importance in drift support systems.In this study,laboratory and numerical simulations of gravel bolting are conducted to investigate the effects of varying rockbolt pretensions.The simulations are developed using the particle flow code(PFC3D),enabling detailed analysis of contact forces between gravel particles under low and high rockbolt pretensions.The results indicate that bolted gravel can maintain stability even without pretension,though bearing capacity is significantly enhanced under high pretension.Two distinct bolting behaviors are identified:a pressure arch structure is formed under low pretension,while high pretension creates a compression zone characterized by intensified particle interlocking and superior load-bearing capacity.Based on these findings,a concept for drift support is proposed,integrating rockbolts and cables to stabilize both shallow and deep rocks.This study advances our understanding of bolting behaviors and provides theoretical guidance for designing effective drift support systems in practical applications.展开更多
Failure tests were conducted on two concrete-filled steel tubular(CFST)truss arch bridges with a span of approximately 12 m to investigate the influence of initial geometric defects on the in-plane bearing capacity of...Failure tests were conducted on two concrete-filled steel tubular(CFST)truss arch bridges with a span of approximately 12 m to investigate the influence of initial geometric defects on the in-plane bearing capacity of CFST truss arch bridges.The effects of antisymmetric defect on the ultimate bearing capacity,failure mode,structural response,and steel–concrete confinement effect of CFST truss arch bridges under quarter-point loading were analyzed.On this basis,numerical simulations were conducted to investigate the in-plane bearing capacity of CFST truss arch bridges further under different scenarios.The initial defect formof the archwas obtained by using theoretical deduction,and the theoretical basis for the weakening of the ultimate bearing capacity of the arch bridge caused by geometric defects was clarified.Results indicate that the antisymmetric defect does not change the four-hinge failure mode of the model arch under quarter-point loading but increases the local cracking area and crack density of the concrete inside the pipe.The sine geometric defect with an amplitude of L/250 resulted in a 44.4%decrease in the yield load of the single hinge of the model arch,a 10.5%decrease in the failure load of the four hinges,and a 40.9%increase in themaximum vertical deformation during failure.At the initial stage of loading,the steel pipe and the concrete inside the pipe were subjected to relatively independent forces.After reaching 67%of the ultimate load,the catenary arch ribs began to produce a steel pipe concrete constraint effect.The initial geometric defects resulted in a decrease in the load when the constraint effect occurred.The antisymmetric defects with the same amplitude have a greater impact on the in-plane bearing capacity of the CFST arch bridge than the initial geometric defects with symmetry.The linear deviation at L/4 caused by constructionmust be controlled to be less than L/600 to ensure that the internal bearing capacity of the CFST arch bridge reaches 95%of the design bearing capacity.The structural deformation caused by geometric initial defects increases linearly with the increase in defect amplitude.The bearing capacity is weakened because the structural deflection and bending moment are amplified by initial defects.展开更多
The steel tube arch rib in a large-span concrete-filled steel tube arch bridge has a large span and diameter,which also leads to a larger weld seam scale.Large-scale welding seams will inevitably cause more obvious we...The steel tube arch rib in a large-span concrete-filled steel tube arch bridge has a large span and diameter,which also leads to a larger weld seam scale.Large-scale welding seams will inevitably cause more obvious welding residual stress(WRS).For the purpose of studying the influence of WRS from large-scale welding seam on the mechanical properties of steel tube arch rib during arch rib splicing,test research and numerical simulation analysis on the WRS in arch rib splicing based on the Guangxi Pingnan Third Bridge,which is the world’s largest span concrete-filled steel tube arch bridge,were conducted in this paper,and the distribution pattern of WRS at the arch rib splicing joint was obtained.Subsequently,the WRS was introduced into the mechanical performance analysis of joints and structures to analyze its effects.The findings reveal that the distribution of WRS in the arch rib is greatly influenced by the rib plate,and the axial WRS in the heat-affected zone are primarily tensile,while the circumferential WRS are distributed in an alternating pattern of tensile and compressive stresses along the circumferential direction of the main tube.Under the influence of WRS,the ultimate bearing capacity of the joint is reduced by 29.4%,the initial axial stiffness is reduced by 4.32%,and the vertical deformation of the arch rib structure is increased by 4.7%.展开更多
Support and maintenance of tunnel excavations during operation are critical to ensure the safety and stability of tunnels.This study proposes a specialized support technology for a railroad tunnel in western China,cha...Support and maintenance of tunnel excavations during operation are critical to ensure the safety and stability of tunnels.This study proposes a specialized support technology for a railroad tunnel in western China,characterized by substantial deformation and a limited inherent self-stabilizing capacity.The method involves the application of a foam concrete compressible layer at the inverted arch of the tunnel.The effectiveness of the foam concrete layer in mitigating the effect of the surrounding rock on the tunnel inverted arch structure is investigated by a combination of indoor tests and numerical simulations.The laboratory test results show that the train load has little effect on the compressive performance of the foamed concrete compressible layer,which indicates that the foamed concrete compressible layer can be applied in the tunnel invert.By analyzing the support effect of the established model,it is found that the foam concrete compressible layer can effectively absorb the deformation pressure generated by the surrounding rock and protect the secondary lining structure,when the compressible layer density is 500 kg/m^(3) and the thickness is set to 20 cm,the supporting effect is the best.展开更多
BACKGROUND Although acute pancreatitis and walled-off necrosis(WON)are rare complications following aortic surgery,they are serious risk factors for postoperative mortality.Considering the poor general condition of th...BACKGROUND Although acute pancreatitis and walled-off necrosis(WON)are rare complications following aortic surgery,they are serious risk factors for postoperative mortality.Considering the poor general condition of the postoperative patient,more effective and less invasive treatments are favorable.CASE SUMMARY A 67-year-old man was referred to our hospital for the treatment of WON after acute pancreatitis.He had undergone total aortic arch replacement due to aortic arch aneurysm and coronary artery bypass grafting due to angina pectoris 6 weeks prior in another hospital.On the second postoperative day,laboratory data and computed tomography showed that the patient had developed acute pancreatitis.Although conservative management(antibiotics,hydration,etc.)had helped in relieving the symptoms of acute pancreatitis,peripancreatic fluid collection(PFC)persisted,accompanied by duodenal obstruction and vomiting.Contrastenhanced computed tomography showed that the heterogeneous enhancement and fluid collection in the pancreatic body and tail had increased,consistent with walled-off WON.We therefore performed endoscopic ultrasound-guided transluminal drainage for the PFC.As a result,the WON resolved gradually,resulting in improved oral intake.CONCLUSION Acute pancreatitis is a rare gastrointestinal complication following thoracic and thoracoabdominal aortic aneurysm surgery.To the best of our knowledge,this is the first case of WON after aortic arch surgery treated with endoscopic ultrasound-guided transluminal drainage for PFC.展开更多
基金Project(K2022G038)supported by the Science Technology Research and Development Program of China State Railway Group Co.,LtdProject(52178405)supported by the National Natural Science Foundation of China。
文摘To address the issue of extreme thermal-induced arching in CRTS II slab tracks due to joint damage,an optimized joint repair model was proposed.First,the formula for calculating the safe temperature rise of the track was derived based on the principle of stationary potential energy.Considering interlayer evolution and structural crack propagation,an optimized joint repair model for the track was established and validated.Subsequently,the impact of joint repair on track damage and arch stability under extreme temperatures was studied,and a comprehensive evaluation of the feasibility of joint repair and the evolution of damage after repair was conducted.The results show that after the joint repair,the temperature rise of the initial damage of the track structure can be increased by 11℃.Under the most unfavorable heating load with a superimposed temperature gradient,the maximum stiffness degradation index SDEG in the track structure is reduced by about 81.16%following joint repair.The joint repair process could effectively reduce the deformation of the slab arching under high temperatures,resulting in a reduction of 93.96%in upward arching deformation.After repair,with the damage to interfacing shear strength,the track arch increases by 2.616 mm.
基金supported by the National Natural Science Foundation of China(Grant No.52308463)the Shanghai Rising-Star Program(Grant No.23YF1449100)the Fundamental Research Funds for the Central Universities(Grant No.2023-2-ZD08).
文摘Due to space constraints in urban areas,metro tunnels are typically constructed in pairs,with a small clearance.The interaction between twin tunnels leads to a significantly more complex ground deformation and stress distribution than that observed in a single tunnel scenario,particularly if the tunnels are excavated in sequence.A series of physical model tests were conducted to investigate soil deformation and stress disturbances caused by the excavation of twin tunnels.The test results indicate that the interaction between the twin tunnels was observed.Due to the soil arching effect,the excavation of Tunnel 2 increases the soil stress acting on Tunnel 1.An analytical method was proposed to determine soil stress considering the soil arching effect and the interaction between twin tunnels.The method categorized the relative locations between twin tunnels into non-influenced,partially influenced,and fully influenced scenarios.For non-influenced and fully influenced scenarios,the soil stresses above twin tunnels were calculated based on a symmetric major principal stress trace.For the partially influenced scenario,however,the soil arch above Tunnel 2 was asymmetric due to the interaction,and the stress distribution was obtained based on a new asymmetric major principal stress trace.The soil stress on Tunnel 1 was influenced by the load transferred from Tunnel 2 and calculated based on the force equilibrium.A comparison of the analytical and test results indicates that the proposed method effectively predicts the soil stress in the cover layer above twin tunnels excavated sequentially,considering the interaction and soil arching effects.
文摘Introduction Aortic arch anomalies are congenital malformations of the position or branching of the aortic arch,or both.Double aortic arch(DAA)is a very rare malformation,affecting approximately 0.005%~0.007% of fetuses[1],and there has been no relevant literature mentioning the prenatal finding DAA in Macao till now.
基金supported by the National Key Scientific Instrument and Equipment Development Projects of China(No.41827808)the Major Program of National Natural Science Foundation of China(No.42090055)+2 种基金the National Natural Science Foundation of China(Nos.42077268)the National Natural Science Foundation of China(No.42107194)the Fundamental Research Funds for the Central Universities(No.CUGL190810)。
文摘The soil arching effect is an important factor affecting the internal load transfer of excavation-induced slopes.Physical model tests are usually used for studying the soil arching effect.Although physical model tests can monitor local point loads to demonstrate changes in local stresses,changes in force chains inside slopes are rarely demonstrated by physical modelling,which restricts the understanding of load transfer.To explore overall changes in stresses in slopes from a more microscopic perspective,a numerical simulation of the slope under excavation was carried out.Using built-in code and fish function programming in PFC^(3D),the slope model was developed.Monitoring areas were set up to monitor the changes in stresses and force chains during excavation.The simulation results show that excavation width affects the size of deformation area,and the deformation area expands as excavation width increases.Excavation causes load transfer and the formation of soil arching in the slope.A mechanism is proposed to explain the effect of excavation on soil arching formation and load transfer.The numerical simulation is important for revealing the load transfer of slopes during excavation,and the research results have practical value for the prevention and mitigation of landslides caused by excavation.
基金Project(42277175)supported by the National Natural Science Foundation of ChinaProject(NRMSSHR-2022-Z08)supported by the Key Laboratory of Natural Resources Monitoring and Supervision in Southern Hilly Region,Ministry of Natural Resources,China。
文摘Narrow backfill earth pressure estimation is applied to study the stability of supporting structures in the vicinity of existing buildings.Previous narrow backfill earth pressure studies have neglected seismic-unsaturated seepage multi-field coupling,resulting in inaccurate estimates.To address these deficiencies,this paper proposed a calculation method for seismic passive earth pressure in unsaturated narrow backfill,based on inclined thin-layer units.It considers the interlayer shear stress,arching effect,and the multi-field coupling of seismic-unsaturated seepage.Additionally,this paper includes a parametric sensitivity analysis.The outcomes indicate that the earthquake passive ground pressure of unsaturated narrow backfill can be reduced by increasing the aspect ratio,seismic acceleration coefficient,and unsaturation parameterα.It can also be reduced by decreasing the effective interior friction angle,soil cohesion,wallearth friction angle,and vertical discharge.Furthermore,for any width soil,lowering the elevation of the action point of passive thrust can be attained by raising the effective interior friction angle,wall-earth friction angle,and unsaturation parameterα.Reducing soil cohesion,seismic acceleration coefficient,and vertical discharge can also lower the height of the application point of passive thrust.
基金Project(2022YJS073)supported by the Fundamental Research Funds for the Central Universities,ChinaProject(2024YFE0198500)supported by the National Key Research and Development Program of China:Intergovernmental International Science and Technology Innovation CooperationProject(U2469207)supported by the National Natural Science Foundation Railway Innovation and Development Joint Fund Project,China。
文摘Determining earth pressure on jacked pipes is essential for ensuring lining safety and calculating jacking force,especially for deep-buried pipes.To better reflect the soil arching effect resulting from the excavation of rectangular jacked pipes and the distribution of the earth pressure on jacked pipes,we present an analytical solution for predicting the vertical earth pressure on deep-buried rectangular pipe jacking tunnels,incorporating the tunnelling-induced ground loss distribution.Our proposed analytical model consists of the upper multi-layer parabolic soil arch and the lower friction arch.The key parameters(i.e.,width and height of friction arch B and height of parabolic soil arch H 1)are determined according to the existing research,and an analytical solution for K l is derived based on the distribution characteristics of the principal stress rotation angle.With consideration for the transition effect of the mechanical characteristics of the parabolic arch zone,an analytical solution for soil load transfer is derived.The prediction results of our analytical solution are compared with tests and simulation results to validate the effectiveness of the proposed analytical solution.Finally,the effects of different parameters on the soil pressure are discussed.
基金the financial support of the National Natural Science Foundation of China(No.52075309)the Youth Innovation Team of Shaanxi Universities(21JP021)。
文摘Hydrogel has developed into a very important platform in solar interface evaporator.However,the current hydrogel evaporators are usually three-dimensional evaporators,which will consume a lot of raw materials.Thus,a new two-dimensional hydrogel evaporator is urgently needed to alleviate this problem.Here,a double layer hydrogel evaporator was designed by twice vacuum filtration.Furthermore,through the arched design and the introduction of concentrated brine drainage system,the hydrogel evaporator has enhanced water transportation and tailored water transportation path.Such a unique drainage evaporation system greatly improves the stability of the evaporator.Thereby,a good balance is established between photothermal conversion and water supply,and solar energy is utilized efficiently.It can remain stable in continuous evaporation for up to 12 h with an excellent evaporation rate of 2.70 kg m^(-2)h^(-1)under 1 sun irradiation.Meanwhile,the drainage system realized the 1.8×10^(-10)mol m^(-2)s^(-1)diffusion flux of concentrated brine.Through one-time freeze-drying preparation,an arch-shaped drainage evaporator was used to prepare an evaporation area of more than 20 cm^(2).With the self-made condensate collecting device in outdoor environment,the fresh water yield reaches 7.5 L m^(-2)d^(-1).This provides a new scheme for building a new hydrogel evaporator and solving the fresh water crisis.
基金the National Natural Science Foundation of China(No.52374150)the Key Science and Technology Project of Ministry of Emergency Management of the People’s Republic of China(No.2024EMST141405).
文摘The stability of underground tunnel roofs is strongly influenced by wedge blocks formed by complex joint networks.The mechanical behavior and failure mechanisms of different roof wedge blocks in arched holes were investigated under biaxial stress conditions.The crack evolution and failure modes of the specimens were analyzed through acoustic emission(AE),digital image correlation(DIC),and discrete element method(DEM).Results show significant variations in mechanical properties:specimens T1(extremely unstable triangular)and T2(extremely unstable quadrilateral)exhibited higher strength than T3(extremely stable triangular)and T4(extremely stable quadrilateral),while support more effectively enhanced the strength of T3 and T4.Failure modes were classified as rock-dominated,wedgedominated,or co-dominated.Cracks typically initiated near the wedge and propagated outward.Unsupported specimens developed tensile cracks at the hole bottom,shear cracks at the sides,and mixed cracks along wedge boundaries,whereas supported specimens mainly exhibited cracks at the roof and sides.Stress analysis indicated that unsupported conditions induced high stress differences,promoting localized shear failure.Wedge geometry significantly affected shear stress redistribution at the roof.These findings highlight the critical role of support and wedge block geometry in controlling stress dis-tribution and failure mechanisms in arched tunnels.
基金Projects(52008403,52378421)supported by the National Natural Science Foundation of ChinaProject(2022-Key-10)supported by the Science and Technology Research and Development Program Project of China Railway Group LimitedProject(202207)supported by the Hunan Provincial Transportation Science and Technology,China。
文摘The existing analytical models for umbrella arch method(UAM)based on elastic foundation beams often overlook the influence of the surrounding soil beyond the beam edges on the shear stresses acting on the beam.Consequently,such models fail to adequately reflect the continuity characteristics of soil deformation.Leveraging the Pasternak foundation-Euler beam model,this study considers the generalized shear force on the beam to account for the influence of soil outside the beam ends on the shear stress.An analytical model for the deformation and internal forces of finite-length beams subjected to arbitrary loads is derived based on the initial parameter method under various conditions.The mechanical model of the elastic foundation beam for advanced umbrella arch under typical tunnel excavation cycles is established,yielding analytical solutions for the longitudinal response of the umbrella arch.The reliability of the analytical model is verified with the existing test data.The improved model addresses anomalies in existing models,such as abnormal upward deformation in the loosened segment and maximum deflection occurring within the soil mass.Additionally,dimensionless characteristic parameters reflecting the relative stiffness between the umbrella arch structure and the foundation soil are proposed.Results indicate that the magnitude of soil characteristic parameters significantly influences the deformation and internal forces of the umbrella arch.Within common ranges of soil values,the maximum deformation and internal forces of the umbrella arch under semi-logarithmic coordinates exhibit nearly linear decay with decreasing soil characteristic parameters.The impact of tunnel excavation height on the stress of unsupported sections of the umbrella arch is minor,but it is more significant for umbrella arch buried within the soil mass.Conversely,the influence of tunnel excavation advance on the umbrella arch is opposite.
基金supported by the National Natural Science Foundation of China(Grant Nos.52274124,52274123)funding of the Coal Mining and Designing Department,Tiandi Science&Technology Co.,Ltd.(Grant No.2022-2-TD-QN008).
文摘The influence of rockbolt pretension on bolting has not been well addressed,despite its critical importance in drift support systems.In this study,laboratory and numerical simulations of gravel bolting are conducted to investigate the effects of varying rockbolt pretensions.The simulations are developed using the particle flow code(PFC3D),enabling detailed analysis of contact forces between gravel particles under low and high rockbolt pretensions.The results indicate that bolted gravel can maintain stability even without pretension,though bearing capacity is significantly enhanced under high pretension.Two distinct bolting behaviors are identified:a pressure arch structure is formed under low pretension,while high pretension creates a compression zone characterized by intensified particle interlocking and superior load-bearing capacity.Based on these findings,a concept for drift support is proposed,integrating rockbolts and cables to stabilize both shallow and deep rocks.This study advances our understanding of bolting behaviors and provides theoretical guidance for designing effective drift support systems in practical applications.
基金National Natural Science Foundation of China(Grant No.52408314)Science and Technology Project of Sichuan Provincial TransportationDepartment(GrantNo.2023-ZL-03)Science and Technology Project of Guizhou Provincial Transportation Department(Grant No.2024-122-018).
文摘Failure tests were conducted on two concrete-filled steel tubular(CFST)truss arch bridges with a span of approximately 12 m to investigate the influence of initial geometric defects on the in-plane bearing capacity of CFST truss arch bridges.The effects of antisymmetric defect on the ultimate bearing capacity,failure mode,structural response,and steel–concrete confinement effect of CFST truss arch bridges under quarter-point loading were analyzed.On this basis,numerical simulations were conducted to investigate the in-plane bearing capacity of CFST truss arch bridges further under different scenarios.The initial defect formof the archwas obtained by using theoretical deduction,and the theoretical basis for the weakening of the ultimate bearing capacity of the arch bridge caused by geometric defects was clarified.Results indicate that the antisymmetric defect does not change the four-hinge failure mode of the model arch under quarter-point loading but increases the local cracking area and crack density of the concrete inside the pipe.The sine geometric defect with an amplitude of L/250 resulted in a 44.4%decrease in the yield load of the single hinge of the model arch,a 10.5%decrease in the failure load of the four hinges,and a 40.9%increase in themaximum vertical deformation during failure.At the initial stage of loading,the steel pipe and the concrete inside the pipe were subjected to relatively independent forces.After reaching 67%of the ultimate load,the catenary arch ribs began to produce a steel pipe concrete constraint effect.The initial geometric defects resulted in a decrease in the load when the constraint effect occurred.The antisymmetric defects with the same amplitude have a greater impact on the in-plane bearing capacity of the CFST arch bridge than the initial geometric defects with symmetry.The linear deviation at L/4 caused by constructionmust be controlled to be less than L/600 to ensure that the internal bearing capacity of the CFST arch bridge reaches 95%of the design bearing capacity.The structural deformation caused by geometric initial defects increases linearly with the increase in defect amplitude.The bearing capacity is weakened because the structural deflection and bending moment are amplified by initial defects.
基金funded by the Science and Technology Research Program of the Chongqing Municipal Education Commission(grant number KJQN202403002).
文摘The steel tube arch rib in a large-span concrete-filled steel tube arch bridge has a large span and diameter,which also leads to a larger weld seam scale.Large-scale welding seams will inevitably cause more obvious welding residual stress(WRS).For the purpose of studying the influence of WRS from large-scale welding seam on the mechanical properties of steel tube arch rib during arch rib splicing,test research and numerical simulation analysis on the WRS in arch rib splicing based on the Guangxi Pingnan Third Bridge,which is the world’s largest span concrete-filled steel tube arch bridge,were conducted in this paper,and the distribution pattern of WRS at the arch rib splicing joint was obtained.Subsequently,the WRS was introduced into the mechanical performance analysis of joints and structures to analyze its effects.The findings reveal that the distribution of WRS in the arch rib is greatly influenced by the rib plate,and the axial WRS in the heat-affected zone are primarily tensile,while the circumferential WRS are distributed in an alternating pattern of tensile and compressive stresses along the circumferential direction of the main tube.Under the influence of WRS,the ultimate bearing capacity of the joint is reduced by 29.4%,the initial axial stiffness is reduced by 4.32%,and the vertical deformation of the arch rib structure is increased by 4.7%.
基金supported by the National Natural Science Foundation of China under grant number 52179113Open Research Fund of State Key Laboratory of Geomechanics and Geotechnical Engineering Safety Grant No.SKLGME 022022,SKLGME-JBGS2401.
文摘Support and maintenance of tunnel excavations during operation are critical to ensure the safety and stability of tunnels.This study proposes a specialized support technology for a railroad tunnel in western China,characterized by substantial deformation and a limited inherent self-stabilizing capacity.The method involves the application of a foam concrete compressible layer at the inverted arch of the tunnel.The effectiveness of the foam concrete layer in mitigating the effect of the surrounding rock on the tunnel inverted arch structure is investigated by a combination of indoor tests and numerical simulations.The laboratory test results show that the train load has little effect on the compressive performance of the foamed concrete compressible layer,which indicates that the foamed concrete compressible layer can be applied in the tunnel invert.By analyzing the support effect of the established model,it is found that the foam concrete compressible layer can effectively absorb the deformation pressure generated by the surrounding rock and protect the secondary lining structure,when the compressible layer density is 500 kg/m^(3) and the thickness is set to 20 cm,the supporting effect is the best.
文摘BACKGROUND Although acute pancreatitis and walled-off necrosis(WON)are rare complications following aortic surgery,they are serious risk factors for postoperative mortality.Considering the poor general condition of the postoperative patient,more effective and less invasive treatments are favorable.CASE SUMMARY A 67-year-old man was referred to our hospital for the treatment of WON after acute pancreatitis.He had undergone total aortic arch replacement due to aortic arch aneurysm and coronary artery bypass grafting due to angina pectoris 6 weeks prior in another hospital.On the second postoperative day,laboratory data and computed tomography showed that the patient had developed acute pancreatitis.Although conservative management(antibiotics,hydration,etc.)had helped in relieving the symptoms of acute pancreatitis,peripancreatic fluid collection(PFC)persisted,accompanied by duodenal obstruction and vomiting.Contrastenhanced computed tomography showed that the heterogeneous enhancement and fluid collection in the pancreatic body and tail had increased,consistent with walled-off WON.We therefore performed endoscopic ultrasound-guided transluminal drainage for the PFC.As a result,the WON resolved gradually,resulting in improved oral intake.CONCLUSION Acute pancreatitis is a rare gastrointestinal complication following thoracic and thoracoabdominal aortic aneurysm surgery.To the best of our knowledge,this is the first case of WON after aortic arch surgery treated with endoscopic ultrasound-guided transluminal drainage for PFC.
