This study examines the performance of coupling the deterministic four-dimensional variational assimilation system （4DVAR） with an ensemble Kalman filter （EnKF） to produce a superior hybrid approach for data assim...This study examines the performance of coupling the deterministic four-dimensional variational assimilation system （4DVAR） with an ensemble Kalman filter （EnKF） to produce a superior hybrid approach for data assimilation. The coupled assimilation scheme （E4DVAR） benefits from using the state-dependent uncertainty provided by EnKF while taking advantage of 4DVAR in preventing filter divergence： the 4DVAR analysis produces posterior maximum likelihood solutions through minimization of a cost function about which the ensemble perturbations are transformed, and the resulting ensemble analysis can be propagated forward both for the next assimilation cycle and as a basis for ensemble forecasting. The feasibility and effectiveness of this coupled approach are demonstrated in an idealized model with simulated observations. It is found that the E4DVAR is capable of outperforming both 4DVAR and the EnKF under both perfect- and imperfect-model scenarios. The performance of the coupled scheme is also less sensitive to either the ensemble size or the assimilation window length than those for standard EnKF or 4DVAR implementations.展开更多
In order to determine whether long-term no-tillage operation in the loess plateau threatens soil fertility and crop yield,a suitable high-yield and efficient tillage technology system was established.In the Changwu lo...In order to determine whether long-term no-tillage operation in the loess plateau threatens soil fertility and crop yield,a suitable high-yield and efficient tillage technology system was established.In the Changwu loess plateau agri-Gecological experiment station of the Northwest A&F University of Changwu County,Shaanxi Province,the no-tillage experimental field for three consecutive years was selected.In September 2015,no-tillage,tillage,and rotary tillage were carried out before winter wheat was sowed.After the harvest of winter wheat in2016,soil organic carbon,total nitrogen and wheat yield in 0-30 cm soil layers under different tillage methods were analyzed.The results showed that the soil organic carbon and total nitrogen contents in the 0-30 cm soil layer decreased along the profile under the three tillage methods.In this study,the soil organic carbon and total nitrogen content in the 0-10 cm soil layer under different tillage methods were no-tillage>rotary tillage>tillage,the actual yield of winter yield in one hectare was tillage>rotary tillage>no-tillage,and there was significant difference in the actual yield of winter wheat only between the no-tillage and tillage.展开更多
Unsaturated loess in natural sites loses stability as the overburden load continuously increases.Traditional soil modifiers such as cement and fly ash affect the surrounding environment.A new type of material,i.e.,lig...Unsaturated loess in natural sites loses stability as the overburden load continuously increases.Traditional soil modifiers such as cement and fly ash affect the surrounding environment.A new type of material,i.e.,lignin,is environmentally friendly and able to increase the strength of loess.However,the engineering characteristics of the improved loess under unsaturated conditions are not yet clear.In this study,the soil-water characteristic curves(SWCCs)of lignin-improved loess samples were determined from 0 kPa to 700 kPa using a pressure plate instrument,and then,they were fitted using the van Genuchten(VG)model and the Fredlund and Xing(FX)model.In addition,the effects of the lignin content and sample preparation methods on the SWCCs were investigated to determine the optimal lignin content and a suitable sample preparation method for loess foundations.As the lignin content increases,the matric suction and residual water content of the improved loess increase.The suction stress increases with the increasing lignin contents of 1%–2%.At lignin contents of 3%–4%,the suction stress begins to decrease and the samples prepared using the slurry method has a lower suction stress than that prepared using the wet mixing method.The air entry value(AEV)increases with increasing lignin content.In addition,scanning electron microscopy(SEM)was used to investigate the microstructural variations.It was found that after the addition of lignin,the entrapment of the loess particles by the lignin fibers created some larger particles and smaller pore diameters,which in turn led to poor connectivity of the loess pores.These changes cause the matric suction of the modified loess to increase.展开更多
In order to find out the effects of long-term no-tillage operation on soil available phosphorus and available potassium in the loess plateau, a suitable high-yield and high-efficiency tillage technology system was est...In order to find out the effects of long-term no-tillage operation on soil available phosphorus and available potassium in the loess plateau, a suitable high-yield and high-efficiency tillage technology system was established. In the Changwu loess plateau agri-ecological experiment station of the Northwest A&F University of Changwu County, Shaanxi Province, the no-tillage experimental field for three consecutive years was selected. In September 2015, no-tillage, tillage, and rotary tillage were carried out before winter wheat was sowed. After the harvest of winter wheat in 2016, the contents of available phosphorus and available potassium in 0-30 cm soil layer under three tillage methods were analyzed. The results showed that in the 0-30 cm soil layer, the soil available phosphorus and available potassium decreased with the increase of the soil depth in the three tillage methods. The content of available phosphorus and available potassium in 10-20 cm soil layer and 20-30 cm soil layer decreased by 16.07%, 32.74%, 15.54% and 27.08%, respectively, and there were significant differences ( P <0.05). Under different tillage methods, the soil available phosphorus content in the 0-10 cm soil layer significantly reduced by 11.31% compared with no-tillage. The soil available potassium content under tillage and rotary tillage significantly reduced by 6.16% and 4.97%, respectively ( P <0.05). Compared with no-tillage, the soil available phosphorus content in the 20-30 cm soil layer significantly reduced by 18.12%. The soil available potassium content under tillage and rotary tillage methods significantly reduced by 17.17% and 9.22%, respectively ( P <0.05). Therefore, in the long-term no-tillage dry loess plateau, it is necessary to conduct proper tillage or rotary tillage.展开更多
We evaluate the applicability of an optical transmission measurement method commonly used for the analysis of the Black Carbon (BC) content of aerosol sample, to determine the BC content of loess sediments. A number o...We evaluate the applicability of an optical transmission measurement method commonly used for the analysis of the Black Carbon (BC) content of aerosol sample, to determine the BC content of loess sediments. A number of different sample pretreatment procedures are developed and compared, leading to an optimum preparation process. The results include: 1) Subtraction of the optical attenuation values before and after heating of the sample filters (“ΔATN”) varies linearly with the sample mass. The slope of the regression line provides the best determination of BC concentration. 2) When the sample mass is small, (NaPO3)6 pretreatment is best for BC measurement, and the BC concentration results are given by the slope of the regression between ΔATN and sample mass, for a series of samples of varying mass. 3) HF pretreatment accompanied by centrifugation and rinsing may produce a negative bias on the result. 4) Replicate measurements of BC for loess samples showed a maximum deviation less than 5.6%, suggesting that measurements of the BC concentration of a sequence of loess samples could determine variations to this degree of significance. 5) The overall trends of BC concentration in loess section sequences were similar for all chemical pretreatments. The BC concentration result for replicate samples is comparable when pretreated by the same procedure.展开更多
Check dams are widely constructed on China's Loess Plateau,which had a total number of 58,776 by the end of 2019.Great achievements in check dam construction have been gained regarding the economic and environment...Check dams are widely constructed on China's Loess Plateau,which had a total number of 58,776 by the end of 2019.Great achievements in check dam construction have been gained regarding the economic and environmental impacts.This study reviews the remarkable benefits of check dams on the land reclamation and environmental improvement on the Loess Plateau,and sediment reduction entering the Yellow River.However,the flood incidents on check dams have been frequently reported for the past decades,which has attracted more attention in the context of climate change and extreme rainfall events recently.Advances in the flood migration techniques achieved by the research group led by the first author have been highlighted to migrate the breach risk of check dams due to floods.The“family tree method”has been proposed to determine the survival status and critical rainfall threshold of each check dam in the complicated dam system.An updated dam breach flood evaluation framework and the corresponding numerical algorithm(i.e.,DB-IWHR)have been developed.Moreover,innovative types of water-release facilities for check dams,including geobag stepped spillway and prestressed concrete cylinder pipe in the underlying conduit,have been proposed and developed.Finally,the perspectives concerning the check dam construction on the Loess Plateau have been put forward.展开更多
After expatiating the guiding ideology,contents,standards and principles of eco-environment restoration based on enlarging terrace and de-farming,this paper discussed the planning method and technical flow of enlargin...After expatiating the guiding ideology,contents,standards and principles of eco-environment restoration based on enlarging terrace and de-farming,this paper discussed the planning method and technical flow of enlarging terrace and garden plot in a small catchment of loess hilly region by means of GIS spatial analysis technology,and then the planning method was applied in Yangou catchment.The result showed that it is practicabl,and the areas of newly-built terrace and garden plot in Yangou catchment are at least 295.06 and 4.61 hm2,so that the areas of basic farmland and garden plot reach 359.23 and 622.69 hm2.After the land use structure is regulated,the forest coverage is 48.87%,and the permanent vegetation coverage is about 75% in Yangou catchment,while sediment reduction benefit is above 80% in slope land.In agricultural development,Yangou catchment can yield 1 645.13 tons of food supplies,above 9 340 tons of apples,and can feed 7 500 sheep every year.展开更多
To predict the soil-water characteristic curve(i.e.SWCC)of natural and remoulded Malan loess from soil physical properties,one-point methods for determining the SWCC that are much simpler than experimental methods are...To predict the soil-water characteristic curve(i.e.SWCC)of natural and remoulded Malan loess from soil physical properties,one-point methods for determining the SWCC that are much simpler than experimental methods are proposed.The predicted SWCC is presented in the form of the BRUTSAERT equation,in which the four model parameters can be estimated from soil physical properties using the best correlations obtained in the present study along with one measured data point.The proposed one-point methods are validated using the measured SWCC data reported in the literature.The results of validation studies suggest that the proposed one-point methods can provide reasonable prediction of the SWCC for natural and remoulded Malan loess.The measured data point should be within the transition zone;the measured suction is suggested between25to100kPa for natural loess,while between100to500kPa for remoulded loess.展开更多
It has been a focus of debate for a large time on construction methods for large-span loess tunnel.Reasonable construction method has much effect on stability of tunnel and construction schedule.Deformation and failur...It has been a focus of debate for a large time on construction methods for large-span loess tunnel.Reasonable construction method has much effect on stability of tunnel and construction schedule.Deformation and failure of surrounding rock are quite complex.Associating with the large-span loess tunnel of Zhengzhou- Xi'an high-speed passenger rail line in China,large scale model test with geometric proportion 1:20 is applied to study on dynamic mechanical behavior of various construction methods.They include full-face excavation with support and no support,and benching method with support.It is found that pre-deformation and stress accumulation take place ahead of working face.The effects of three construction methods are further studied,particularly in terms of tunnel displacement and stress changes.It is revealed that benching method transfers load to an unexcavated area,limits horizontal deformation,reduces stress concentration effectively,lengthens the distance between location of peak for stress concentration and working face,and consequently increases stability.The model test results not only supply theoretical foundation for determination of reasonable construction method,but also can act as reference for similar tunnel and underground engineering construction.展开更多
Based on a shallow-buried coal seam covered with thick loose layers in hilly loess areas of western China,we developed a mechanical model for a mining slope with slope stability analysis, and studied the mechanism of ...Based on a shallow-buried coal seam covered with thick loose layers in hilly loess areas of western China,we developed a mechanical model for a mining slope with slope stability analysis, and studied the mechanism of formation and development of a sliding ground fissure by the circular sliding slice method.Moreover, we established a prediction model of a sliding fissure based on a mechanical mechanism,and verified its reliability on face 52,304, an engineering example, situated at Daliuta coal mine of Shendong mining area in western China. The results show that the stress state of a mining slope is changed by its gravity and additional stress from the shallow-buried coal seam and gully terrain. The mining slope is found to be most unstable when the ratio of the down-sliding to anti-sliding force is the maximum, causing local fractures and sliding fissures. The predicted angles for the sliding fissure of face 52,304 on both sides of the slope are found to be 64.2° and 82.4°, which are in agreement with the experimental data.展开更多
Climate change and Land Use/Cover Change（LUCC） have been identified as two primary factors affecting watershed hydrological regime. This study analyzed the trends of streamflow, precipitation, air temperature and po...Climate change and Land Use/Cover Change（LUCC） have been identified as two primary factors affecting watershed hydrological regime. This study analyzed the trends of streamflow, precipitation, air temperature and potential evapotranspiration（PET） from 1962 to 2008 in the Jihe watershed in northwestern Loess Plateau of China using the Mann-Kendall test. The streamflow responses to climate change and LUCC were quantified independently by the elasticity method. The results show that the streamflow presented a dramatic decline with a turning point occurred in 1971, while the precipitation and PET did not change significantly. The results also show that the temperature rose markedly especially since 1990 s with an approximate increase of 1.74°C over the entire research period（1962–2008）. Using land use transition matrix, we found that slope cropland was significantly converted to terrace between 1970 s and 1990 s and that forest cover increased relatively significantly because of the Grain for Green Project after 2000. The streamflow reduction was predominantly caused by LUCC and its contribution reached up to 90.2%, while the contribution of climate change to streamflow decline was only 9.8%. Although the analytical results between the elasticity method and linear regression model were not satisfactorily consistent, they both indicated that LUCC（human activity） was the major factor causing streamflow decline in the Jihe watershed from 1962 to 2008.展开更多
With the continuous development of economy and changes in people’s lifestyle,rural domestic waste brought about serious harm to water,air,human health,ecological landscape and so forth.In this paper,taking Longfang T...With the continuous development of economy and changes in people’s lifestyle,rural domestic waste brought about serious harm to water,air,human health,ecological landscape and so forth.In this paper,taking Longfang Town in Loess Plateau region as example,the source,amount and harms of rural domestic waste were analyzed firstly,as well as the current situation and existing problems of treatment,and then a suitable waste disposal technology for the town was chosen,finally the reasonable treatment methods combining new countryside and non-new countryside with township was summed up,so as to realize the reduction,harmless and resource treatment of rural domestic waste.展开更多
Fiber-reinforced soils have been of great interest to experimenters for building foundations’strength performance,time,and economy.This paper investigates the effects of water content and polypropylene fiber dosage a...Fiber-reinforced soils have been of great interest to experimenters for building foundations’strength performance,time,and economy.This paper investigates the effects of water content and polypropylene fiber dosage and length on loess’s unconfined compressive strength(UCS)according to the central composite response surface design test procedure.The water content is 11%–25%,the mass ratio of fiber to soil is 0.1%–0.9%,and the fiber length ranges from 6–18 mm.The response surface method(RSM)developed full quadratic models of different variables with response values.After analysis of variance(ANOVA),the mathematical model developed in this study was statistically significant(p≤0.05)and applicable to the optimization process.The optimization results showed that the optimal water content values,fiber amount,and fiber length were 16.41%,0.579%,and 14.90 mm,respectively.The unconfined compressive strength of the optimized specimens was increased by 288.017 kPa.The research results can reference the design and construction of fiber-reinforced soil in practical projects such as road base engineering and foundation engineering.展开更多
In order to accurately analyze vibration characteristics and site effects of loess hills under moving load of a highspeed train,four types of loess hill models under railway viaduct was established by ABAQUS of finite...In order to accurately analyze vibration characteristics and site effects of loess hills under moving load of a highspeed train,four types of loess hill models under railway viaduct was established by ABAQUS of finite element analysis software by field test.The dynamic response and stability of loess hills under two different vibration sources under high-speed train load were studied by using two-dimensional equivalent linear response timehistory analysis,and the influence of the mechanical parameters of loess on the vibration of different types of loess hill was analyzed.Results show that there are obvious differences between peak displacement cloud maps of loess hills under the railway viaduct under gravity and train load action.We analyzed the influence of the change of elastic modulus on vibration propagation of soil of foundation and loess knoll,and found that the change of elastic modulus of soil in different position of foundation has more effect on vibration propagation than that of loess knoll soil.At the same time,the vertical acceleration cloud maps of the four types of loess hills are obviously different.展开更多
The successful completion of the Zhengzhou-Xi＇an high-speed railway project has greatly improved the construction level of China＇s large-section loess tunnels, and has resulted in significant progress being made in ...The successful completion of the Zhengzhou-Xi＇an high-speed railway project has greatly improved the construction level of China＇s large-section loess tunnels, and has resulted in significant progress being made in both design theory and construction technology. This paper systematically summarizes the tech- nical characteristics and main problems of the large-section loess tunnels on China＇s high-speed railway, including classification of the surrounding rock, design of the supporting structure, surface settlement and cracking control, and safe and rapid construction methods. On this basis, the key construction tech- niques of loess tunnels with large sections for high-speed railway are expounded from the aspects of design and construction. The research results show that the classification of loess strata surrounding large tunnels should be based on the geological age of the loess, and be determined by combining the plastic index and the water content. In addition, the influence of the buried depth should be considered. During tunnel excavation disturbance, if the tensile stress exceeds the soil tensile or shear strength, the surface part of the sliding trend plane can be damaged, and visible cracks can form. The pressure of the surrounding rock of a large-section loess tunnel should be calculated according to the buried depth, using the corresponding formula. A three-bench seven-step excavation method of construction was used as the core technology system to ensure the safe and rapid construction of a large-section loess tunnel, following a field test to optimize the construction parameters and determine the engineering measures to stabilize the tunnel face. The conclusions and methods presented here are of great significance in revealing the strata and supporting mechanics of large-section loess tunnels, and in optimizing the supporting structure design and the technical parameters for construction.展开更多
基金sponsored by the U.S. National Science Foundation (Grant No.ATM0205599)the U.S. Offce of Navy Research under Grant N000140410471Dr. James A. Hansen was partially supported by US Offce of Naval Research (Grant No. N00014-06-1-0500)
文摘This study examines the performance of coupling the deterministic four-dimensional variational assimilation system （4DVAR） with an ensemble Kalman filter （EnKF） to produce a superior hybrid approach for data assimilation. The coupled assimilation scheme （E4DVAR） benefits from using the state-dependent uncertainty provided by EnKF while taking advantage of 4DVAR in preventing filter divergence： the 4DVAR analysis produces posterior maximum likelihood solutions through minimization of a cost function about which the ensemble perturbations are transformed, and the resulting ensemble analysis can be propagated forward both for the next assimilation cycle and as a basis for ensemble forecasting. The feasibility and effectiveness of this coupled approach are demonstrated in an idealized model with simulated observations. It is found that the E4DVAR is capable of outperforming both 4DVAR and the EnKF under both perfect- and imperfect-model scenarios. The performance of the coupled scheme is also less sensitive to either the ensemble size or the assimilation window length than those for standard EnKF or 4DVAR implementations.
文摘In order to determine whether long-term no-tillage operation in the loess plateau threatens soil fertility and crop yield,a suitable high-yield and efficient tillage technology system was established.In the Changwu loess plateau agri-Gecological experiment station of the Northwest A&F University of Changwu County,Shaanxi Province,the no-tillage experimental field for three consecutive years was selected.In September 2015,no-tillage,tillage,and rotary tillage were carried out before winter wheat was sowed.After the harvest of winter wheat in2016,soil organic carbon,total nitrogen and wheat yield in 0-30 cm soil layers under different tillage methods were analyzed.The results showed that the soil organic carbon and total nitrogen contents in the 0-30 cm soil layer decreased along the profile under the three tillage methods.In this study,the soil organic carbon and total nitrogen content in the 0-10 cm soil layer under different tillage methods were no-tillage>rotary tillage>tillage,the actual yield of winter yield in one hectare was tillage>rotary tillage>no-tillage,and there was significant difference in the actual yield of winter wheat only between the no-tillage and tillage.
基金funded by the Natural Science Foundation of the Inner Mongolia Autonomous Region(Grant No.2020BS04003)the Project of High-Level Talent Research in Inner Mongolia University(Grant No.12000-15031942)the National Natural Science Foundation of China(Grant No.51778590,51879131).
文摘Unsaturated loess in natural sites loses stability as the overburden load continuously increases.Traditional soil modifiers such as cement and fly ash affect the surrounding environment.A new type of material,i.e.,lignin,is environmentally friendly and able to increase the strength of loess.However,the engineering characteristics of the improved loess under unsaturated conditions are not yet clear.In this study,the soil-water characteristic curves(SWCCs)of lignin-improved loess samples were determined from 0 kPa to 700 kPa using a pressure plate instrument,and then,they were fitted using the van Genuchten(VG)model and the Fredlund and Xing(FX)model.In addition,the effects of the lignin content and sample preparation methods on the SWCCs were investigated to determine the optimal lignin content and a suitable sample preparation method for loess foundations.As the lignin content increases,the matric suction and residual water content of the improved loess increase.The suction stress increases with the increasing lignin contents of 1%–2%.At lignin contents of 3%–4%,the suction stress begins to decrease and the samples prepared using the slurry method has a lower suction stress than that prepared using the wet mixing method.The air entry value(AEV)increases with increasing lignin content.In addition,scanning electron microscopy(SEM)was used to investigate the microstructural variations.It was found that after the addition of lignin,the entrapment of the loess particles by the lignin fibers created some larger particles and smaller pore diameters,which in turn led to poor connectivity of the loess pores.These changes cause the matric suction of the modified loess to increase.
文摘In order to find out the effects of long-term no-tillage operation on soil available phosphorus and available potassium in the loess plateau, a suitable high-yield and high-efficiency tillage technology system was established. In the Changwu loess plateau agri-ecological experiment station of the Northwest A&F University of Changwu County, Shaanxi Province, the no-tillage experimental field for three consecutive years was selected. In September 2015, no-tillage, tillage, and rotary tillage were carried out before winter wheat was sowed. After the harvest of winter wheat in 2016, the contents of available phosphorus and available potassium in 0-30 cm soil layer under three tillage methods were analyzed. The results showed that in the 0-30 cm soil layer, the soil available phosphorus and available potassium decreased with the increase of the soil depth in the three tillage methods. The content of available phosphorus and available potassium in 10-20 cm soil layer and 20-30 cm soil layer decreased by 16.07%, 32.74%, 15.54% and 27.08%, respectively, and there were significant differences ( P <0.05). Under different tillage methods, the soil available phosphorus content in the 0-10 cm soil layer significantly reduced by 11.31% compared with no-tillage. The soil available potassium content under tillage and rotary tillage significantly reduced by 6.16% and 4.97%, respectively ( P <0.05). Compared with no-tillage, the soil available phosphorus content in the 20-30 cm soil layer significantly reduced by 18.12%. The soil available potassium content under tillage and rotary tillage methods significantly reduced by 17.17% and 9.22%, respectively ( P <0.05). Therefore, in the long-term no-tillage dry loess plateau, it is necessary to conduct proper tillage or rotary tillage.
文摘We evaluate the applicability of an optical transmission measurement method commonly used for the analysis of the Black Carbon (BC) content of aerosol sample, to determine the BC content of loess sediments. A number of different sample pretreatment procedures are developed and compared, leading to an optimum preparation process. The results include: 1) Subtraction of the optical attenuation values before and after heating of the sample filters (“ΔATN”) varies linearly with the sample mass. The slope of the regression line provides the best determination of BC concentration. 2) When the sample mass is small, (NaPO3)6 pretreatment is best for BC measurement, and the BC concentration results are given by the slope of the regression between ΔATN and sample mass, for a series of samples of varying mass. 3) HF pretreatment accompanied by centrifugation and rinsing may produce a negative bias on the result. 4) Replicate measurements of BC for loess samples showed a maximum deviation less than 5.6%, suggesting that measurements of the BC concentration of a sequence of loess samples could determine variations to this degree of significance. 5) The overall trends of BC concentration in loess section sequences were similar for all chemical pretreatments. The BC concentration result for replicate samples is comparable when pretreated by the same procedure.
基金National Natural Science Foundation of China,Grant/Award Number:42330719National Natural Science Foundation of China,Grant/Award Number:U2443228+1 种基金Power Construction Corporation of China,Grant/Award Number:DJ-ZDXM-2021-51China Institute of Water Resources and Hydropower Research,Grant/Award Number:GE121003A0042022。
文摘Check dams are widely constructed on China's Loess Plateau,which had a total number of 58,776 by the end of 2019.Great achievements in check dam construction have been gained regarding the economic and environmental impacts.This study reviews the remarkable benefits of check dams on the land reclamation and environmental improvement on the Loess Plateau,and sediment reduction entering the Yellow River.However,the flood incidents on check dams have been frequently reported for the past decades,which has attracted more attention in the context of climate change and extreme rainfall events recently.Advances in the flood migration techniques achieved by the research group led by the first author have been highlighted to migrate the breach risk of check dams due to floods.The“family tree method”has been proposed to determine the survival status and critical rainfall threshold of each check dam in the complicated dam system.An updated dam breach flood evaluation framework and the corresponding numerical algorithm(i.e.,DB-IWHR)have been developed.Moreover,innovative types of water-release facilities for check dams,including geobag stepped spillway and prestressed concrete cylinder pipe in the underlying conduit,have been proposed and developed.Finally,the perspectives concerning the check dam construction on the Loess Plateau have been put forward.
基金Supported by National Natural Science Foundation of China(41171449)Key Project of Chinese Academy of Sciences(KZZD-EW-06-01)
文摘After expatiating the guiding ideology,contents,standards and principles of eco-environment restoration based on enlarging terrace and de-farming,this paper discussed the planning method and technical flow of enlarging terrace and garden plot in a small catchment of loess hilly region by means of GIS spatial analysis technology,and then the planning method was applied in Yangou catchment.The result showed that it is practicabl,and the areas of newly-built terrace and garden plot in Yangou catchment are at least 295.06 and 4.61 hm2,so that the areas of basic farmland and garden plot reach 359.23 and 622.69 hm2.After the land use structure is regulated,the forest coverage is 48.87%,and the permanent vegetation coverage is about 75% in Yangou catchment,while sediment reduction benefit is above 80% in slope land.In agricultural development,Yangou catchment can yield 1 645.13 tons of food supplies,above 9 340 tons of apples,and can feed 7 500 sheep every year.
基金Project(41372329) supported by the National Natural Science Foundation of ChinaProject(2014CB744701) supported by the National Basic Research Program of China
文摘To predict the soil-water characteristic curve(i.e.SWCC)of natural and remoulded Malan loess from soil physical properties,one-point methods for determining the SWCC that are much simpler than experimental methods are proposed.The predicted SWCC is presented in the form of the BRUTSAERT equation,in which the four model parameters can be estimated from soil physical properties using the best correlations obtained in the present study along with one measured data point.The proposed one-point methods are validated using the measured SWCC data reported in the literature.The results of validation studies suggest that the proposed one-point methods can provide reasonable prediction of the SWCC for natural and remoulded Malan loess.The measured data point should be within the transition zone;the measured suction is suggested between25to100kPa for natural loess,while between100to500kPa for remoulded loess.
基金the National Natural Science Foundation of China(Nos. 50978172 and 51078318)the New Century Excellent Talents in University(No. 10-0667)
文摘It has been a focus of debate for a large time on construction methods for large-span loess tunnel.Reasonable construction method has much effect on stability of tunnel and construction schedule.Deformation and failure of surrounding rock are quite complex.Associating with the large-span loess tunnel of Zhengzhou- Xi'an high-speed passenger rail line in China,large scale model test with geometric proportion 1:20 is applied to study on dynamic mechanical behavior of various construction methods.They include full-face excavation with support and no support,and benching method with support.It is found that pre-deformation and stress accumulation take place ahead of working face.The effects of three construction methods are further studied,particularly in terms of tunnel displacement and stress changes.It is revealed that benching method transfers load to an unexcavated area,limits horizontal deformation,reduces stress concentration effectively,lengthens the distance between location of peak for stress concentration and working face,and consequently increases stability.The model test results not only supply theoretical foundation for determination of reasonable construction method,but also can act as reference for similar tunnel and underground engineering construction.
基金Projects funded by the National Key Basic Research Development Program(No.2013CB227904)the National Natural Science Foundation of China(No.41272389)+1 种基金China Postdoctoral Science Foundation(No.2014M561931)the Natural Science Foundation of Hebei Province(No.D2014402007)
文摘Based on a shallow-buried coal seam covered with thick loose layers in hilly loess areas of western China,we developed a mechanical model for a mining slope with slope stability analysis, and studied the mechanism of formation and development of a sliding ground fissure by the circular sliding slice method.Moreover, we established a prediction model of a sliding fissure based on a mechanical mechanism,and verified its reliability on face 52,304, an engineering example, situated at Daliuta coal mine of Shendong mining area in western China. The results show that the stress state of a mining slope is changed by its gravity and additional stress from the shallow-buried coal seam and gully terrain. The mining slope is found to be most unstable when the ratio of the down-sliding to anti-sliding force is the maximum, causing local fractures and sliding fissures. The predicted angles for the sliding fissure of face 52,304 on both sides of the slope are found to be 64.2° and 82.4°, which are in agreement with the experimental data.
基金funded by the National Natural Science Foundation of China (41501025, 51609083, 41401038, 51509089)the 2016 Key Scientific Research Projects for Universities of Henan Province (16A170014)
文摘Climate change and Land Use/Cover Change（LUCC） have been identified as two primary factors affecting watershed hydrological regime. This study analyzed the trends of streamflow, precipitation, air temperature and potential evapotranspiration（PET） from 1962 to 2008 in the Jihe watershed in northwestern Loess Plateau of China using the Mann-Kendall test. The streamflow responses to climate change and LUCC were quantified independently by the elasticity method. The results show that the streamflow presented a dramatic decline with a turning point occurred in 1971, while the precipitation and PET did not change significantly. The results also show that the temperature rose markedly especially since 1990 s with an approximate increase of 1.74°C over the entire research period（1962–2008）. Using land use transition matrix, we found that slope cropland was significantly converted to terrace between 1970 s and 1990 s and that forest cover increased relatively significantly because of the Grain for Green Project after 2000. The streamflow reduction was predominantly caused by LUCC and its contribution reached up to 90.2%, while the contribution of climate change to streamflow decline was only 9.8%. Although the analytical results between the elasticity method and linear regression model were not satisfactorily consistent, they both indicated that LUCC（human activity） was the major factor causing streamflow decline in the Jihe watershed from 1962 to 2008.
文摘With the continuous development of economy and changes in people’s lifestyle,rural domestic waste brought about serious harm to water,air,human health,ecological landscape and so forth.In this paper,taking Longfang Town in Loess Plateau region as example,the source,amount and harms of rural domestic waste were analyzed firstly,as well as the current situation and existing problems of treatment,and then a suitable waste disposal technology for the town was chosen,finally the reasonable treatment methods combining new countryside and non-new countryside with township was summed up,so as to realize the reduction,harmless and resource treatment of rural domestic waste.
文摘Fiber-reinforced soils have been of great interest to experimenters for building foundations’strength performance,time,and economy.This paper investigates the effects of water content and polypropylene fiber dosage and length on loess’s unconfined compressive strength(UCS)according to the central composite response surface design test procedure.The water content is 11%–25%,the mass ratio of fiber to soil is 0.1%–0.9%,and the fiber length ranges from 6–18 mm.The response surface method(RSM)developed full quadratic models of different variables with response values.After analysis of variance(ANOVA),the mathematical model developed in this study was statistically significant(p≤0.05)and applicable to the optimization process.The optimization results showed that the optimal water content values,fiber amount,and fiber length were 16.41%,0.579%,and 14.90 mm,respectively.The unconfined compressive strength of the optimized specimens was increased by 288.017 kPa.The research results can reference the design and construction of fiber-reinforced soil in practical projects such as road base engineering and foundation engineering.
基金supported by Science and Technology Project of State Grid Corporation of China(Grant No.5200-202230098A1-1-ZN)。
文摘In order to accurately analyze vibration characteristics and site effects of loess hills under moving load of a highspeed train,four types of loess hill models under railway viaduct was established by ABAQUS of finite element analysis software by field test.The dynamic response and stability of loess hills under two different vibration sources under high-speed train load were studied by using two-dimensional equivalent linear response timehistory analysis,and the influence of the mechanical parameters of loess on the vibration of different types of loess hill was analyzed.Results show that there are obvious differences between peak displacement cloud maps of loess hills under the railway viaduct under gravity and train load action.We analyzed the influence of the change of elastic modulus on vibration propagation of soil of foundation and loess knoll,and found that the change of elastic modulus of soil in different position of foundation has more effect on vibration propagation than that of loess knoll soil.At the same time,the vertical acceleration cloud maps of the four types of loess hills are obviously different.
文摘The successful completion of the Zhengzhou-Xi＇an high-speed railway project has greatly improved the construction level of China＇s large-section loess tunnels, and has resulted in significant progress being made in both design theory and construction technology. This paper systematically summarizes the tech- nical characteristics and main problems of the large-section loess tunnels on China＇s high-speed railway, including classification of the surrounding rock, design of the supporting structure, surface settlement and cracking control, and safe and rapid construction methods. On this basis, the key construction tech- niques of loess tunnels with large sections for high-speed railway are expounded from the aspects of design and construction. The research results show that the classification of loess strata surrounding large tunnels should be based on the geological age of the loess, and be determined by combining the plastic index and the water content. In addition, the influence of the buried depth should be considered. During tunnel excavation disturbance, if the tensile stress exceeds the soil tensile or shear strength, the surface part of the sliding trend plane can be damaged, and visible cracks can form. The pressure of the surrounding rock of a large-section loess tunnel should be calculated according to the buried depth, using the corresponding formula. A three-bench seven-step excavation method of construction was used as the core technology system to ensure the safe and rapid construction of a large-section loess tunnel, following a field test to optimize the construction parameters and determine the engineering measures to stabilize the tunnel face. The conclusions and methods presented here are of great significance in revealing the strata and supporting mechanics of large-section loess tunnels, and in optimizing the supporting structure design and the technical parameters for construction.
