Silty clay is widely used as subgrade filler in cold regions,which suffer from frost heave in winter and mud pumping in spring.In this study,polyvinyl alcohol(PVA)and polypropylene(PP)fiber were used to improve the me...Silty clay is widely used as subgrade filler in cold regions,which suffer from frost heave in winter and mud pumping in spring.In this study,polyvinyl alcohol(PVA)and polypropylene(PP)fiber were used to improve the mechanical and frost heave behavior of silty clay in cold regions,and the direct shear test and one-dimensional frost heave test were employed in studying improvement effects.Moreover,improvement mechanisms of PVA and PP fiber were analyzed based on test results.The main findings are as follows.(1)Both PP and PVA can heighten the strength of silty clay and suppress frost heave,but the PVA solution has a more decisive influence on improving mechanical properties than PP fiber.(2)The improvement mechanism of the PVA solution is cementing.The improvement effect of 2%PVA solution is the best,which can increase the shear strength by approximately 40%–60%at different stress levels and decrease the frost heave ratio from 0.89%to 0.16%at optimal water content.(3)For 2%PVA improved samples,0.25%PP fiber can further increase soil cohesion by approximately 20–30 kPa at different stress levels and further decrease the frost heave ratio from 0.16%to 0.07%at optimal water content.The improvement effect is neglectable when the PP fiber content exceeds 0.25%.Overall,2%PVA with 0.25%PP fiber is the optimum combination to improve silty clay in cold regions.展开更多
The complexity of the actual operating environment of EMU trains and the interaction between the reliability of system components have become a huge challenge for the maintenance scheduling of EMU trains. In response ...The complexity of the actual operating environment of EMU trains and the interaction between the reliability of system components have become a huge challenge for the maintenance scheduling of EMU trains. In response to these problems, the evolution of reliability and failure rate under the influence of environmental factors, failure correlations and economy correlations is analyzed. We assume bogie systems form the EMU train in series. The failure correlation matrix of the bogie systems is modeled. With the lowest total maintenance cost as the optimization objective, a decision-making model for EMU train maintenance is established. A dynamic maintenance strategy is proposed for the model, which can improve maintenance plans efficiently. Artificial bee colony algorithm is applied to further iteratively optimize the threshold parameters in the strategy. The results are calculated and verified by a numerical example. The results show the effectiveness of the maintenance decision model. The dynamic maintenance strategy in this paper is compared with the traditional opportunistic maintenance strategy. The proposed maintenance strategy outperforms the traditional opportunistic maintenance strategy in the numerical example.展开更多
In this study,an optimization model of a single machine system integrating imperfect preventive maintenance planning and production scheduling based on game theory is proposed.The costs of the production department an...In this study,an optimization model of a single machine system integrating imperfect preventive maintenance planning and production scheduling based on game theory is proposed.The costs of the production department and the maintenance department are minimized,respectively.Two kinds of three-stage dynamic game models and a backward induction method are proposed to determine the preventive maintenance(PM)threshold.A lemma is presented to obtain the exact solution.A comprehensive numerical study is provided to illustrate the proposed maintenance model.The effectiveness is also validated by comparison with other two existed optimization models.展开更多
Seasonally frozen soil is a four-phase material and its physical-mechanical properties are more complex compared to the unfrozen soil. Its physical properties changes during the freeze-thaw process; repeated freeze-th...Seasonally frozen soil is a four-phase material and its physical-mechanical properties are more complex compared to the unfrozen soil. Its physical properties changes during the freeze-thaw process; repeated freeze-thaw cycles change the characteristics of soil, which can render the soil from an unstable state to a new dynamic equilibrium state. The freezing process changes the structure coupled between the soil particle arrangements, which will change the mechanical properties of the soil. The method of significance and interaction between different factors should be considered to measure the influence on the properties of soil under freeze-thaw cycles.展开更多
Using newly developed dynamic shearing devices, the dynamic shearing strength of frozen soil-concrete interface was studied experimentally. By placing concrete blocks in the lower half of the shear box and frozen soil...Using newly developed dynamic shearing devices, the dynamic shearing strength of frozen soil-concrete interface was studied experimentally. By placing concrete blocks in the lower half of the shear box and frozen soil sample in the upper part, a series of dynamic shear tests on their interfaces were carried out. The obtained results are summarized and the main influencing factors are revealed.展开更多
Freeze-thaw damage is the most common disease of semi-rigid bases in cold regions, which may greatly affect the durability of roadways. In this study, the compressive strength and frost resistance of four different ty...Freeze-thaw damage is the most common disease of semi-rigid bases in cold regions, which may greatly affect the durability of roadways. In this study, the compressive strength and frost resistance of four different types of semi-rigid bases(lime-fly ash-stabilized sand, cement-stabilized sand, lime-fly ash-stabilized gravel, and cement-stabilized gravel) are assessed by varying the materials content. Based on freeze-thaw and compressive strength tests, this paper presents the performance of the different materials, each having different physical properties, and the optimal amounts of materials contents are proposed.展开更多
Prediction on the coupled thermal-hydraulic fields of embankment and cutting slopes is essential to the assessment on evolution of melting zone and natural permafrost table, which is usually a key factor for permafros...Prediction on the coupled thermal-hydraulic fields of embankment and cutting slopes is essential to the assessment on evolution of melting zone and natural permafrost table, which is usually a key factor for permafrost embankment design in frozen ground regions. The prediction may be further complicated due to the inherent uncertainties of material properties. Hence, stochastic analyses should be conducted. Firstly, Karhunen-Loeve expansion is applied to attain the random fields for hydraulic and thermal conductions. Next, the mixed-form modified Richards equation for mass transfer(i.e., mass equation) and the heat transport equation for heat transient flow in a variably saturated frozen soil are combined into one equation with temperature unknown. Furthermore, the finite element formulation for the coupled thermal-hydraulic fields is derived. Based on the random fields, the stochastic finite element analyses on stability of embankment are carried out. Numerical results show that stochastic analyses of embankment stability may provide a more rational picture for the distribution of factors of safety(FOS), which is definitely useful for embankment design in frozen ground regions.展开更多
Under repeated freezing and thawing in deep seasonal frozen regions, the stability and strength of the soil are imposed in the form of large uneven settlement, instability and strength reduction, which affect the norm...Under repeated freezing and thawing in deep seasonal frozen regions, the stability and strength of the soil are imposed in the form of large uneven settlement, instability and strength reduction, which affect the normal operation of railway lines. This study is to obtain the influencing rules of freeze-thaw on the dynamic properties(dynamic strain, confining pressure and compactness) of silty sand. Based on an amount of inner tests, the dynamic modulus and damping ratio properties of silty soil subjected to repeated freeze-thaw cycles were deeply researched and analyzed. The results are as follows: At the same dynamic strain, the relationship of dynamic stress and freeze-thaw cycles presents negative correlation, and the relationship of dynamic stress, confining pressure and compactness present positive correlation. The dynamic modulus double decreases while the damping ratio double increases with incremental increase in dynamic strain. The dynamic modulus sharply decreases while the damping ratio increases with incremental increase in freeze-thaw cycles, and then the changes level off after six freeze-thaw cycles. The dynamic modulus increases while the damping ratio decreases as the confining pressure and compactness increase at the same strain level.展开更多
To simplify the stability analysis of frozen soil slope, a pseudo-coupled numerical approach is developed. In this approach, the coupled heat transfer and water flow in frozen soils are simulated first, and based on t...To simplify the stability analysis of frozen soil slope, a pseudo-coupled numerical approach is developed. In this approach, the coupled heat transfer and water flow in frozen soils are simulated first, and based on the computed thermal-hydro field, the stability of frozen soil slope is evaluated. Although the shear strength for frozen soil is very complicated and is usually represented by a nonlinear MC failure criterion, a simple linear MC yield criterion is utilized. In this method, the internal friction angle is expressed as a function of volumetric ice content and the cohesion is fitted as a simple bilinear expression of T and volumetric water content. To assess slope stability, the limit analysis is employed in conjunction with the recently developed α-section search algorithm. A frozen soil slope example is used to examine the proposed pseudo-coupled numerical approach, and numerical studies validate its effectiveness. Based on numerical results, it is seen that slope stability may be remarkably influenced by warming air (or ground surface) temperature. With increasing ground surface temperature, slope stability indicated by FOS may reduce to 1.0, implying that warming air temperature could be a trigger of frozen soil slope failure.展开更多
The temperature distributions of different parts of a subgrade were analyzed based on the results of three years of monitoring data from the Harbin-Qiqihaer Passenger Dedicated Line, a high-speed railway, including th...The temperature distributions of different parts of a subgrade were analyzed based on the results of three years of monitoring data from the Harbin-Qiqihaer Passenger Dedicated Line, a high-speed railway, including the slope toes, shoulders, and natural ground. The temperature variation with time and the maximum frozen depths showed that an obvious sunny-shady effect exists in the railway subgrade, which spans a seasonal frozen region. Development of frost heave is affected by the asymmetric temperature distribution. The temperature field and the maximum frozen depths 50 years after the subgrade was built were simulated with a mathematical model of the unsteady phase transition of the geothermal field.展开更多
On the basis of on-site measured data of the newly constructed Gonghe-Yushu Highway in a permafrost region, this paper analyzed thermal conditions of the subgrade with XPS insulated board according to different select...On the basis of on-site measured data of the newly constructed Gonghe-Yushu Highway in a permafrost region, this paper analyzed thermal conditions of the subgrade with XPS insulated board according to different selected monitoring sections in various locations. We also summarized the geothermal distribution and change rules of subgrade with XPS insulation board under the asphalt pavement in summarized a high temperature frozen soil region. It is suggested that the shoulder of subgrade with XPS insulation board be widen to a reasonable width so as to keep the subgrade stable.展开更多
Crushed rock subgrade, as one of the roadbed-cooling methods, has been widely used in the Qinghai-Tibet Railway. Much attention has been paid on the cooling effect of crushed rock; however, the mechanical properties o...Crushed rock subgrade, as one of the roadbed-cooling methods, has been widely used in the Qinghai-Tibet Railway. Much attention has been paid on the cooling effect of crushed rock; however, the mechanical properties of crushed rock are somehow neglected. Based on the discrete element method, biaxial compression test condition for crushed rock is compiled in FISH language in PFC2D , and the natural shape of crushed rock is simulated with super particle "cluster". The effect of particle size, crushed rock strength and confining pressure level on overall mechanical properties of the crushed rock aggregate are respectively analyzed. Results show that crushed rock of large particle size plays an essential framework role, which is mainly responsible for the deformation of crushed rock aggregate. The strength of gravel has a great influence on overall mechanical properties which means that strength attenuation caused by the freeze thaw cycles cannot be ignored. The stress-strain curves can be divided into two stages including shear contraction and shear expansion at different confining pressures.展开更多
A coupled water and heat transport mode is established based on the Richards equation to study water flow and heat transport in soil during freezing process. Both the finite difference and finite element method are us...A coupled water and heat transport mode is established based on the Richards equation to study water flow and heat transport in soil during freezing process. Both the finite difference and finite element method are used in the discretization, respectively. Two different computer programs are written and used to simulate an indoor unidirectional frozen test. The freezing depth, freezing rate and temperature variation are compared among lab tests, finite difference calculation simulation and finite element calculation simulation. Result shows that: the finite difference method has a better performance in freezing depth simulation while the finite element method has a better performance in numerical stability in one-dimensional freezing simulation.展开更多
The mechanical property of saline soils varies with moisture and climate in the cold and salt lake region of Qinghai-Tibet Plateau, which influences project construction. In order to improve foundation reinforcement e...The mechanical property of saline soils varies with moisture and climate in the cold and salt lake region of Qinghai-Tibet Plateau, which influences project construction. In order to improve foundation reinforcement effect of the Qarhan-Golmud Highway, Qinghai Province, China, dynamic compaction replacement (DCR) composite foundation was applied in saline soils. A field experiment was conducted in this area, where strength and working mechanism of pier-soil and deformation modulus of the composite foundation was analyzed after reinforcement. This paper presents methods for determining the coefficient on the bearing capacity evaluation and deformation modulus of composite foundation with DCR. Reinforcement case of DCR is highly effective in saline soils of the salt lake regions, which helps the migration of water and salt in saline soils.展开更多
Since mechanical loads exert a significant influence on the life span of wind turbines, the reduction of transient load on drive-train shaft has received more attention when implementing a maximum power point tracking...Since mechanical loads exert a significant influence on the life span of wind turbines, the reduction of transient load on drive-train shaft has received more attention when implementing a maximum power point tracking(MPPT) controller.Moreover, a trade-off between the efficiency of wind energy extraction and the load level of drive-train shaft becomes a key issue. However, for the existing control strategies based on nonlinear model of wind turbines, the MPPT efficiencies are improved at the cost of the intensive fluctuation of generator torque and significant increase of transient load on drive train shaft. Hence, in this paper, a nonlinear controller with variable parameter is proposed for improving MPPT efficiency and mitigating transient load on drive-train simultaneously. Then,simulations on FAST(Fatigue, Aerodynamics, Structures, and Turbulence) code and experiments on the wind turbine simulator(WTS) based test bench are presented to verify the efficiency improvement of the proposed control strategy with less cost of drive-train load.展开更多
In order to improve the engineering stability of saline soil of high chloride content in the Chaerhan salt lake region,six typical characteristics saline soil samples were selected,and tests on their primary physical ...In order to improve the engineering stability of saline soil of high chloride content in the Chaerhan salt lake region,six typical characteristics saline soil samples were selected,and tests on their primary physical properties(total salt content,specific gravity of soil,liquid limit,plastic limit,maximum dry density,and optimal water content) were conducted.The relationships among them were analyzed,a series of variation laws between salt content and these basic physical parameters were determined,and regression equations were derived.This research can improve future engineering design and construction in saline soils and can also help prevent subgrade filler from undermining subgrade stability and producing disease.展开更多
A pile foundation is commonly adopted in geotechnical engineering to support structures, and its application has been extended to cold-regions engineering. In past decades, a host of scholars investigated pile behavio...A pile foundation is commonly adopted in geotechnical engineering to support structures, and its application has been extended to cold-regions engineering. In past decades, a host of scholars investigated pile behaviors and proposed design guidelines for seasonally frozen ground or permafrost. This paper reviews the research with respect to pile performance and engineering practice in cold regions, organized as follows:(1) creep tests and bearing capacity,(2) frost-jacking hazards,(3) laterally loaded piles,(4) dynamic responses,(5) refreezing due to concrete-hydration heat, and(6) improved countermeasures and design methods. We first summarize previous research and recent progress; then, predict the development trend of pile foundations in cold regions and recommend further research.展开更多
The deformation and strength characteristics of roadbed slope under seismic loading in permafrost regions are simulated numerically. The seismic response of roadbed at different positions and inclinations of a slope s...The deformation and strength characteristics of roadbed slope under seismic loading in permafrost regions are simulated numerically. The seismic response of roadbed at different positions and inclinations of a slope section was analyzed.Results show that, roadbed slope damage is mainly led by lateral displacement, and the deformation gradually decreases with increasing depth; roadbed and foundation displacement and plastic strain increases with the magnitude of slope angle,hence the roadbed safety factor will be reduced.展开更多
Frost heave is one of the major complications in highway construction in cold regions. Laboratory experiments are important in the study frost heave behavior of soils, and one-dimensional frost heave experiments are t...Frost heave is one of the major complications in highway construction in cold regions. Laboratory experiments are important in the study frost heave behavior of soils, and one-dimensional frost heave experiments are the easiest way to evaluate the soil frost heave potential. In a one dimensional frost heave test, the deformation in axial direction is non-uniform because of the confining effect of the cutting ring's sidewall. If the effect of confining boundary on soil deformation is ignored, the deformation will be over-estimated. In this paper, the effect of confining boundary on soil deformation is theoretically studied and a volume correction method is developed and applied to the frost heave test of a sulfite saline soil. Test results demonstrate that the sulfite saline soil will expand to a loose, low-density state after several freezing-thawing cycles under the condition of zero axial stress.展开更多
基金supported by the National Natural Science Foundation of China (41731281,42071078)the National Key Basic Research Program of China (No.2012CB026104)Science and Technology Project of Qinghai,China (2021-GX-121).
文摘Silty clay is widely used as subgrade filler in cold regions,which suffer from frost heave in winter and mud pumping in spring.In this study,polyvinyl alcohol(PVA)and polypropylene(PP)fiber were used to improve the mechanical and frost heave behavior of silty clay in cold regions,and the direct shear test and one-dimensional frost heave test were employed in studying improvement effects.Moreover,improvement mechanisms of PVA and PP fiber were analyzed based on test results.The main findings are as follows.(1)Both PP and PVA can heighten the strength of silty clay and suppress frost heave,but the PVA solution has a more decisive influence on improving mechanical properties than PP fiber.(2)The improvement mechanism of the PVA solution is cementing.The improvement effect of 2%PVA solution is the best,which can increase the shear strength by approximately 40%–60%at different stress levels and decrease the frost heave ratio from 0.89%to 0.16%at optimal water content.(3)For 2%PVA improved samples,0.25%PP fiber can further increase soil cohesion by approximately 20–30 kPa at different stress levels and further decrease the frost heave ratio from 0.16%to 0.07%at optimal water content.The improvement effect is neglectable when the PP fiber content exceeds 0.25%.Overall,2%PVA with 0.25%PP fiber is the optimum combination to improve silty clay in cold regions.
基金Sponsored by the National Natural Science Foundation of China(Grant No. 72061022)。
文摘The complexity of the actual operating environment of EMU trains and the interaction between the reliability of system components have become a huge challenge for the maintenance scheduling of EMU trains. In response to these problems, the evolution of reliability and failure rate under the influence of environmental factors, failure correlations and economy correlations is analyzed. We assume bogie systems form the EMU train in series. The failure correlation matrix of the bogie systems is modeled. With the lowest total maintenance cost as the optimization objective, a decision-making model for EMU train maintenance is established. A dynamic maintenance strategy is proposed for the model, which can improve maintenance plans efficiently. Artificial bee colony algorithm is applied to further iteratively optimize the threshold parameters in the strategy. The results are calculated and verified by a numerical example. The results show the effectiveness of the maintenance decision model. The dynamic maintenance strategy in this paper is compared with the traditional opportunistic maintenance strategy. The proposed maintenance strategy outperforms the traditional opportunistic maintenance strategy in the numerical example.
基金Sponsored by the National Natural Science Foundation of China(Grant Nos.72061022 and 72171037).
文摘In this study,an optimization model of a single machine system integrating imperfect preventive maintenance planning and production scheduling based on game theory is proposed.The costs of the production department and the maintenance department are minimized,respectively.Two kinds of three-stage dynamic game models and a backward induction method are proposed to determine the preventive maintenance(PM)threshold.A lemma is presented to obtain the exact solution.A comprehensive numerical study is provided to illustrate the proposed maintenance model.The effectiveness is also validated by comparison with other two existed optimization models.
基金the support and motivation provided by National 973 Project of China (No. 2012CB026104)the Fundamental Research Funds for the Central Universities (No. 2011JBZ009)
文摘Seasonally frozen soil is a four-phase material and its physical-mechanical properties are more complex compared to the unfrozen soil. Its physical properties changes during the freeze-thaw process; repeated freeze-thaw cycles change the characteristics of soil, which can render the soil from an unstable state to a new dynamic equilibrium state. The freezing process changes the structure coupled between the soil particle arrangements, which will change the mechanical properties of the soil. The method of significance and interaction between different factors should be considered to measure the influence on the properties of soil under freeze-thaw cycles.
基金supported by the National Natural Science Foundation of China (Grant No. 41171064)the National Basic Research Program of China (973 Program Grant No. 2012CB026104)
文摘Using newly developed dynamic shearing devices, the dynamic shearing strength of frozen soil-concrete interface was studied experimentally. By placing concrete blocks in the lower half of the shear box and frozen soil sample in the upper part, a series of dynamic shear tests on their interfaces were carried out. The obtained results are summarized and the main influencing factors are revealed.
基金supported by the National Natural Science Foundation of China (Nos. 51378057 and 41371081)
文摘Freeze-thaw damage is the most common disease of semi-rigid bases in cold regions, which may greatly affect the durability of roadways. In this study, the compressive strength and frost resistance of four different types of semi-rigid bases(lime-fly ash-stabilized sand, cement-stabilized sand, lime-fly ash-stabilized gravel, and cement-stabilized gravel) are assessed by varying the materials content. Based on freeze-thaw and compressive strength tests, this paper presents the performance of the different materials, each having different physical properties, and the optimal amounts of materials contents are proposed.
基金supported by the National 973 Project of China (No. 2012CB026104)the National Natural Science Foundation of China (No. 51378057)
文摘Prediction on the coupled thermal-hydraulic fields of embankment and cutting slopes is essential to the assessment on evolution of melting zone and natural permafrost table, which is usually a key factor for permafrost embankment design in frozen ground regions. The prediction may be further complicated due to the inherent uncertainties of material properties. Hence, stochastic analyses should be conducted. Firstly, Karhunen-Loeve expansion is applied to attain the random fields for hydraulic and thermal conductions. Next, the mixed-form modified Richards equation for mass transfer(i.e., mass equation) and the heat transport equation for heat transient flow in a variably saturated frozen soil are combined into one equation with temperature unknown. Furthermore, the finite element formulation for the coupled thermal-hydraulic fields is derived. Based on the random fields, the stochastic finite element analyses on stability of embankment are carried out. Numerical results show that stochastic analyses of embankment stability may provide a more rational picture for the distribution of factors of safety(FOS), which is definitely useful for embankment design in frozen ground regions.
基金funded by the National Key Basic Research Development Plan of China (Grant No. 2012CB026104)the National Natural Science Foundation (NSFC) of China (Grant Nos.51208320 and 51171281)
文摘Under repeated freezing and thawing in deep seasonal frozen regions, the stability and strength of the soil are imposed in the form of large uneven settlement, instability and strength reduction, which affect the normal operation of railway lines. This study is to obtain the influencing rules of freeze-thaw on the dynamic properties(dynamic strain, confining pressure and compactness) of silty sand. Based on an amount of inner tests, the dynamic modulus and damping ratio properties of silty soil subjected to repeated freeze-thaw cycles were deeply researched and analyzed. The results are as follows: At the same dynamic strain, the relationship of dynamic stress and freeze-thaw cycles presents negative correlation, and the relationship of dynamic stress, confining pressure and compactness present positive correlation. The dynamic modulus double decreases while the damping ratio double increases with incremental increase in dynamic strain. The dynamic modulus sharply decreases while the damping ratio increases with incremental increase in freeze-thaw cycles, and then the changes level off after six freeze-thaw cycles. The dynamic modulus increases while the damping ratio decreases as the confining pressure and compactness increase at the same strain level.
基金supported in part by the Scientific Research Foundation for the 973 Program of China (No. 2012CB026104)Research Fund of Young Teachers for the Doctoral Program of Higher Education of China (No. 20110009120020)the Fundamental Research Funds of the Central Universities (No. 2013JBM059)
文摘To simplify the stability analysis of frozen soil slope, a pseudo-coupled numerical approach is developed. In this approach, the coupled heat transfer and water flow in frozen soils are simulated first, and based on the computed thermal-hydro field, the stability of frozen soil slope is evaluated. Although the shear strength for frozen soil is very complicated and is usually represented by a nonlinear MC failure criterion, a simple linear MC yield criterion is utilized. In this method, the internal friction angle is expressed as a function of volumetric ice content and the cohesion is fitted as a simple bilinear expression of T and volumetric water content. To assess slope stability, the limit analysis is employed in conjunction with the recently developed α-section search algorithm. A frozen soil slope example is used to examine the proposed pseudo-coupled numerical approach, and numerical studies validate its effectiveness. Based on numerical results, it is seen that slope stability may be remarkably influenced by warming air (or ground surface) temperature. With increasing ground surface temperature, slope stability indicated by FOS may reduce to 1.0, implying that warming air temperature could be a trigger of frozen soil slope failure.
基金supported by the National Natural Science Foundation of China(Nos.51378057 and 41371081)Scientific and Technological Research and Development Plan of Chinese Railway Corporation(2014G003-A)
文摘The temperature distributions of different parts of a subgrade were analyzed based on the results of three years of monitoring data from the Harbin-Qiqihaer Passenger Dedicated Line, a high-speed railway, including the slope toes, shoulders, and natural ground. The temperature variation with time and the maximum frozen depths showed that an obvious sunny-shady effect exists in the railway subgrade, which spans a seasonal frozen region. Development of frost heave is affected by the asymmetric temperature distribution. The temperature field and the maximum frozen depths 50 years after the subgrade was built were simulated with a mathematical model of the unsteady phase transition of the geothermal field.
基金supported by the National Key Basic Research Program of China 973 Project(No.2012CB026104)National Natural Science Foundation of China(No.41271072 and No.51378057)Service Performance Evaluation of the Subsidiary Structure in The Permafrost Regions of the Qinghai Tibet Plateau(2014-07-01)
文摘On the basis of on-site measured data of the newly constructed Gonghe-Yushu Highway in a permafrost region, this paper analyzed thermal conditions of the subgrade with XPS insulated board according to different selected monitoring sections in various locations. We also summarized the geothermal distribution and change rules of subgrade with XPS insulation board under the asphalt pavement in summarized a high temperature frozen soil region. It is suggested that the shoulder of subgrade with XPS insulation board be widen to a reasonable width so as to keep the subgrade stable.
基金supported by National 973 Project of China (No. 2012CB026104)National Natural Science Foundation of China (Nos. 41171064, 41371081)the Fundamental Research Funds for the Central Universities (No. 2011JBZ009)
文摘Crushed rock subgrade, as one of the roadbed-cooling methods, has been widely used in the Qinghai-Tibet Railway. Much attention has been paid on the cooling effect of crushed rock; however, the mechanical properties of crushed rock are somehow neglected. Based on the discrete element method, biaxial compression test condition for crushed rock is compiled in FISH language in PFC2D , and the natural shape of crushed rock is simulated with super particle "cluster". The effect of particle size, crushed rock strength and confining pressure level on overall mechanical properties of the crushed rock aggregate are respectively analyzed. Results show that crushed rock of large particle size plays an essential framework role, which is mainly responsible for the deformation of crushed rock aggregate. The strength of gravel has a great influence on overall mechanical properties which means that strength attenuation caused by the freeze thaw cycles cannot be ignored. The stress-strain curves can be divided into two stages including shear contraction and shear expansion at different confining pressures.
基金the support and motivation provided by National 973 Project of China (No. 2012CB026104)National Natural Science Foundation of China (No. 41171064)
文摘A coupled water and heat transport mode is established based on the Richards equation to study water flow and heat transport in soil during freezing process. Both the finite difference and finite element method are used in the discretization, respectively. Two different computer programs are written and used to simulate an indoor unidirectional frozen test. The freezing depth, freezing rate and temperature variation are compared among lab tests, finite difference calculation simulation and finite element calculation simulation. Result shows that: the finite difference method has a better performance in freezing depth simulation while the finite element method has a better performance in numerical stability in one-dimensional freezing simulation.
基金the support and motivation provided by National 973 Project of China (No. 2012CB026104)National Natural Science Foundation of China (No. 41171064) and (No. 41271072)
文摘The mechanical property of saline soils varies with moisture and climate in the cold and salt lake region of Qinghai-Tibet Plateau, which influences project construction. In order to improve foundation reinforcement effect of the Qarhan-Golmud Highway, Qinghai Province, China, dynamic compaction replacement (DCR) composite foundation was applied in saline soils. A field experiment was conducted in this area, where strength and working mechanism of pier-soil and deformation modulus of the composite foundation was analyzed after reinforcement. This paper presents methods for determining the coefficient on the bearing capacity evaluation and deformation modulus of composite foundation with DCR. Reinforcement case of DCR is highly effective in saline soils of the salt lake regions, which helps the migration of water and salt in saline soils.
基金supported by the National Natural Science Foundation of China(61203129,61174038,61473151,51507080)the Fundamental Research Funds for the Central Universities(30915011104,30920130121010,30920140112005)
文摘Since mechanical loads exert a significant influence on the life span of wind turbines, the reduction of transient load on drive-train shaft has received more attention when implementing a maximum power point tracking(MPPT) controller.Moreover, a trade-off between the efficiency of wind energy extraction and the load level of drive-train shaft becomes a key issue. However, for the existing control strategies based on nonlinear model of wind turbines, the MPPT efficiencies are improved at the cost of the intensive fluctuation of generator torque and significant increase of transient load on drive train shaft. Hence, in this paper, a nonlinear controller with variable parameter is proposed for improving MPPT efficiency and mitigating transient load on drive-train simultaneously. Then,simulations on FAST(Fatigue, Aerodynamics, Structures, and Turbulence) code and experiments on the wind turbine simulator(WTS) based test bench are presented to verify the efficiency improvement of the proposed control strategy with less cost of drive-train load.
基金the support and motivation provided by the Gansu Province Natural Science Foundation(No.145RJZA054)Lanzhou Jiaotong University Young Scientific Research Fund Project(No.2012032)
文摘In order to improve the engineering stability of saline soil of high chloride content in the Chaerhan salt lake region,six typical characteristics saline soil samples were selected,and tests on their primary physical properties(total salt content,specific gravity of soil,liquid limit,plastic limit,maximum dry density,and optimal water content) were conducted.The relationships among them were analyzed,a series of variation laws between salt content and these basic physical parameters were determined,and regression equations were derived.This research can improve future engineering design and construction in saline soils and can also help prevent subgrade filler from undermining subgrade stability and producing disease.
基金supported by the National Natural Science Foundation of China(Grant Nos.41731281and 41771073)
文摘A pile foundation is commonly adopted in geotechnical engineering to support structures, and its application has been extended to cold-regions engineering. In past decades, a host of scholars investigated pile behaviors and proposed design guidelines for seasonally frozen ground or permafrost. This paper reviews the research with respect to pile performance and engineering practice in cold regions, organized as follows:(1) creep tests and bearing capacity,(2) frost-jacking hazards,(3) laterally loaded piles,(4) dynamic responses,(5) refreezing due to concrete-hydration heat, and(6) improved countermeasures and design methods. We first summarize previous research and recent progress; then, predict the development trend of pile foundations in cold regions and recommend further research.
基金National 973 Project of China (No.2012CB026104)National Natural Science Foundation of China (No.41171064)
文摘The deformation and strength characteristics of roadbed slope under seismic loading in permafrost regions are simulated numerically. The seismic response of roadbed at different positions and inclinations of a slope section was analyzed.Results show that, roadbed slope damage is mainly led by lateral displacement, and the deformation gradually decreases with increasing depth; roadbed and foundation displacement and plastic strain increases with the magnitude of slope angle,hence the roadbed safety factor will be reduced.
基金supported by the State Key Development Program of Basic Research of China (Project No.2012CB026104)a Chinese National Key Technology R&D Program of the Ministry of Science and Technology Project(2012BAH10B01)an open fund sponsored by Qinghai Research and Observation Base, Key Laboratory of Highway Construction & Maintenance Technologyin Permafrost Regions, Ministry of Transport
文摘Frost heave is one of the major complications in highway construction in cold regions. Laboratory experiments are important in the study frost heave behavior of soils, and one-dimensional frost heave experiments are the easiest way to evaluate the soil frost heave potential. In a one dimensional frost heave test, the deformation in axial direction is non-uniform because of the confining effect of the cutting ring's sidewall. If the effect of confining boundary on soil deformation is ignored, the deformation will be over-estimated. In this paper, the effect of confining boundary on soil deformation is theoretically studied and a volume correction method is developed and applied to the frost heave test of a sulfite saline soil. Test results demonstrate that the sulfite saline soil will expand to a loose, low-density state after several freezing-thawing cycles under the condition of zero axial stress.
