This paper studies silted algebras,namely,endomorphism algebras of 2-term silting complexes,over path algebras of Dynkin quivers.We describe an algorithm to produce all basic 2-term silting complexes over the path alg...This paper studies silted algebras,namely,endomorphism algebras of 2-term silting complexes,over path algebras of Dynkin quivers.We describe an algorithm to produce all basic 2-term silting complexes over the path algebra of a Dynkin quiver,and use this algorithm to compute some examples.展开更多
Deep excavations in silt strata can lead to large deformation problems,posing risks to both the excavation and adjacent structures.This study combines field monitoring with numerical simulation to investigate the unde...Deep excavations in silt strata can lead to large deformation problems,posing risks to both the excavation and adjacent structures.This study combines field monitoring with numerical simulation to investigate the underlying mechanisms and key aspects associated with large deformation problems induced by deep excavation in silt strata in Shenzhen,China.The monitoring results reveal that,due to the weak property and creep effect of the silt strata,the maximum wall deflection in the first excavated section(Section 1)exceeds its controlled value at more than 93%of measurement points,reaching a peak value of 137.46 mm.Notably,the deformation exhibits prolonged development characteristics,with the diaphragm wall deflections contributing to 39%of the overall deformation magnitude during the construction of the base slab.Subsequently,numerical simulations are carried out to analyze and assess the primary factors influencing excavation-induced deformations,following the observation of large deformations.The simulations indicate that the low strength of the silt soil is a pivotal factor that results in significant deformations.Furthermore,the flexural stiffness of the diaphragm walls exerts a notable influence on the development of deformations.To address these concerns,an optimization study of potential treatment measures was performed during the subsequent excavation of Section 2.The combined treatment approach,which comprises the reinforcement of the silt layer within the excavation and the increase in the thickness of the diaphragm walls,has been demonstrated to offer an economically superior solution for the handling of thick silt strata.This approach has the effect of reducing the lateral wall displacement by 83.1%and the ground settlement by 70.8%,thereby ensuring the safe construction of the deep excavation.展开更多
How the strong segmentation of cascade reservoir dams and the spatiotemporal changes of sediment retention volume affect the river morphology adjustment in the reservoir area is a scientific issue worthy of exploratio...How the strong segmentation of cascade reservoir dams and the spatiotemporal changes of sediment retention volume affect the river morphology adjustment in the reservoir area is a scientific issue worthy of exploration.This study aims to reveal the adjustment mechanism of the thalweg longitudinal profile of cascade reservoirs.This study focuses on the Xiangjiaba and Xiluodu reservoirs located in the lower reaches of the Jinsha River.Utilizing multi-period observational data of thalweg elevation in reservoir reaches both before and after dam construction,the research employs statistical,geomorphological,and sedimentological methodologies to analyze variation characteristics in the measured curves,trend curves,and theoretical fitting curves of the thalweg longitudinal profile.The investigation ultimately reveals two distinct adjustment patterns in the longitudinal profiles of these cascade reservoirs:the concave curve type and the convex curve type.The former is characterized by weak riverbed scouring and silting changed to rapid aggradation in the upstream section of the reservoir area after dam closure,then changed to slow aggradation in the whole reservoir area,which is the common feature of reservoirs that were built earlier and are relatively located in the downstream(such as the Xiangjiaba Reservoir).The latter is characterized by a straight line or concave curve type with weak riverbed scouring and silting before the dam closure changed to a convex curve type with strong siltation after dam closure,which is the characteristic of reservoirs that were built later and are relatively located in the upstream(such as the Xiluodu Reservoir).The adjustment of the cascade reservoir longitudinal profile is controlled by the spatiotemporal changes of the sediment deposition volume and sedimentation rate in the reservoir area,and the alternating changes of the hydrodynamic gradient and regulation mode affect the spatial heterogeneity of the sedimentation rate.The research results are helpful for understanding the adjustment mechanism of the cascade reservoir longitudinal profile in similar areas and have a guiding role in predicting the adjustment trend of the cascade reservoir longitudinal profile without observation data.展开更多
In order to realize the resource utilization of construction waste,industrial waste slag and silt,this paper used Portland cement,mineral waste residue and phosphogypsum composite to make cementing material(CMPS)with ...In order to realize the resource utilization of construction waste,industrial waste slag and silt,this paper used Portland cement,mineral waste residue and phosphogypsum composite to make cementing material(CMPS)with construction waste recycled aggregate to solidify silt.The mechanical properties of the solidified silt were analyzed by laboratory solidification test and microscopic examination respectively.In order to clarify the mineral composition,microscopic morphology and pore characteristics of the regenerated aggregate and CMPS solidified silt,X-ray diffractometer(XRD),scanning electron microscope(SEM),and nitrogen adsorption pore analyzer(NA)were used to further explore and analyze the regenerated aggregate and CMPS solidified silt effectively,and further reveal the internal mechanism of the regenerated aggregate and CMPS solidified silt effectively.The experimental results show that the strength of Portland cement-mineral waste residue phosphogypsum terpolymer system curing agent increases by 107.34%than that of single Port-land cement solidified silt at 56 d,and the strength of CMPS solidified silt increases by 25.68%under the action of recycled aggregate framework.The curing age and moisture content of the silt have a high correlation with the strength of the solidified silt.Therefore,the influence law of the above two influencing factors on its mechanical properties is further explored and the strength prediction is made.The microscopic test results show that,based on the hydration of Port-land cement and the pozzolans reaction of mineral waste residue,the solidified system has produced calcium silicate hydrate gel and ettringite crystals with gelatinous properties,which helps to fill the pores and form a denser structure.展开更多
The traditional standard wet sieving method uses steel sieves with aperture?0.063 mm and can only determine the particle size distribution(PSD)of gravel and sand in general soil.This paper extends the traditional meth...The traditional standard wet sieving method uses steel sieves with aperture?0.063 mm and can only determine the particle size distribution(PSD)of gravel and sand in general soil.This paper extends the traditional method and presents an extended wet sieving method.The extended method uses both the steel sieves and the nylon filter cloth sieves.The apertures of the cloth sieves are smaller than 0.063 mm and equal 0.048 mm,0.038 mm,0.014 mm,0.012 mm,0.0063 mm,0.004 mm,0.003 mm,0.002 mm,and 0.001 mm,respectively.The extended method uses five steps to separate the general soil into many material sub-groups of gravel,sand,silt and clay with known particle size ranges.The complete PSD of the general soil is then calculated from the dry masses of the individual material sub-groups.The extended method is demonstrated with a general soil of completely decomposed granite(CDG)in Hong Kong,China.The silt and clay materials with different particle size ranges are further examined,checked and verified using stereomicroscopic observation,physical and chemical property tests.The results further confirm the correctness of the extended wet sieving method.展开更多
To ensure the long-term safety and stability of bridge pile foundations in permafrost regions,it is necessary to investigate the rheological effects on the pile tip and pile side bearing capacities.The creep character...To ensure the long-term safety and stability of bridge pile foundations in permafrost regions,it is necessary to investigate the rheological effects on the pile tip and pile side bearing capacities.The creep characteristics of the pile-frozen soil interface are critical for determining the long-term stability of permafrost pile foundations.This study utilized a self-developed large stress-controlled shear apparatus to investigate the shear creep characteristics of the frozen silt-concrete interface,and examined the influence of freezing temperatures(−1,−2,and−5°C),contact surface roughness(0,0.60,0.75,and 1.15 mm),normal stress(50,100,and 150 kPa),and shear stress on the creep characteristics of the contact surface.By incorporating the contact surface’s creep behavior and development trends,we established a creep constitutive model for the frozen silt-concrete interface based on the Nishihara model,introducing nonlinear elements and a damage factor.The results revealed significant creep effects on the frozen silt-concrete interface under constant load,with creep displacement at approximately 2-15 times the instantaneous displacement and a failure creep displacement ranging from 6 to 8 mm.Under different experimental conditions,the creep characteristics of the frozen silt-concrete interface varied.A larger roughness,lower freezing temperatures,and higher normal stresses resulted in a longer sample attenuation creep time,a lower steady-state creep rate,higher long-term creep strength,and stronger creep stability.Building upon the Nishihara model,we considered the influence of shear stress and time on the viscoelastic viscosity coefficient and introduced a damage factor to the viscoplasticity.The improved model effectively described the entire creep process of the frozen silt-concrete interface.The results provide theoretical support for the interaction between pile and soil in permafrost regions.展开更多
The morphological changes in isolated bubbles in gassy silt play a critical role in the microscopic structures between soil particles and bubbles and macroscopic physical properties.Based on X-ray CT scanning experime...The morphological changes in isolated bubbles in gassy silt play a critical role in the microscopic structures between soil particles and bubbles and macroscopic physical properties.Based on X-ray CT scanning experiments under various vertical loads(four levels),self-designed acoustic macro experiments,and a series of formula revisions to the macro-air-bearing silt sound-velocity prediction model,this paper discusses the macro-and micro-scale features of gassy silts from the Yellow River Delta.The samples consisted of different proportions of silt from the Yellow River Delta and porous media,and they were used to form two types of aerosol silts with initial gas contents of 4.23%and 7.67%.The results show that the air bubble content and external load considerably affect the microstructural parameters and acoustic behavior of gassy silt in the Yellow River Delta.The macroscopic sound velocity showed a linear positive correlation with vertical load and relation to microstructural parameters in varying manners and degrees.Based on the traditional Biot-Stoll acoustic model,the gas-phase medium coefficient was introduced for the proper calculation and prediction of the sound velocity of air-bearing silt.The errors of the overall prediction varied between 5.6%and 9.6%.展开更多
Wind erosion is a geomorphic process in arid and semi-arid areas and has substantial implications for regional climate and desertification.In the Columbia Plateau of northwestern United States,the emissions from fine ...Wind erosion is a geomorphic process in arid and semi-arid areas and has substantial implications for regional climate and desertification.In the Columbia Plateau of northwestern United States,the emissions from fine particles of loessial soils often contribute to the exceedance of inhalable particulate matter(PM)with an aerodynamic diameter of 10μm or less(PM10)according to the air quality standards.However,little is known about the threshold friction velocity(TFV)for particles of different sizes that comprise these soils.In this study,soil samples of two representative soil types(Warden sandy loam and Ritzville silt loam)collected from the Columbia Plateau were sieved to seven particle size fractions,and an experiment was then conducted to determine the relationship between TFV and particle size fraction.The results revealed that soil particle size significantly affected the initiation of soil movement and TFV;TFV ranged 0.304-0.844 and 0.249-0.739 m/s for different particle size fractions of Ritzville silt loam and Warden sandy loam,respectively.PM10 and total suspended particulates(TSP)emissions from a bed of 63-90μm soil particles were markedly higher for Warden sandy loam than for Ritzville silt loam.Together with the lower TFV of Warden sandy loam,dust emissions from fine particles(<100μm in diameter)of Warden sandy loam thus may be a main contributor to dust in the region's atmosphere,since the PM10 emissions from the soil erosion surfaces and its ensuing suspension within the atmosphere constitute an essential process of soil erosion in the Columbia Plateau.Developing and implementing strategic land management practices on sandy loam soils is therefore necessary to control dust emissions in the Columbia Plateau.展开更多
Through a self-developed model test system,the mechanical properties of silt and the deformation characteristics of airport runways were investigated during the period of subgrade wetting.Based on the test results,the...Through a self-developed model test system,the mechanical properties of silt and the deformation characteristics of airport runways were investigated during the period of subgrade wetting.Based on the test results,the reliability of the numerical simulation results was verified.Numerical models with different sizes were established.Under the same cushion parameter and loading width ranges,the effects of the cushion parameters and loading conditions on the mechanical responses of the cushion before and after subgrade wetting were analyzed.The results show that the internal friction angles of silt with different wetting degrees are approximately 34°.The cohesion is from 8 to 44 kPa,and the elastic modulus is from 15 to 34 MPa.Before and after subgrade wetting,the variation rates of the cushion horizontal tensile stresses with the same cushion parameters and loading width ranges are different under the influence of boundary effects.After subgrade wetting,the difference in the variation rates of the cushion horizontal tensile stresses under the same cushion parameter range decreases compared with that before subgrade wetting;however,this difference increases under the same loading width range.Before and after subgrade wetting,the influence of the boundary effect on the mechanical response evaluation of the cushion is not beneficial for optimizing the pavement design parameters.When the cushion thickness is more than 0.25 m,the influence of the boundary effect can be disregarded.展开更多
The silt soft soil in Nansha District of Guangzhou was the softest soft soil in China. It had the characteristics of high natural water content, high compressibility, long consolidation time, and complex layered distr...The silt soft soil in Nansha District of Guangzhou was the softest soft soil in China. It had the characteristics of high natural water content, high compressibility, long consolidation time, and complex layered distribution of soil layers. These characteristics formed the clogging characteristics of silt soft soil, which greatly increased the construction difficulty and hindered the construction progress. Therefore, based on the basic physical and mechanical properties of silt soft soil in Nansha District of Guangzhou, this paper evaluated the clogging characteristics of three silt soft soil areas in Nansha District of Guangzhou through long-term permeability test, and carried out scanning electron microscope test to explore the influence of different parameters and microstructure on the clogging difficulty of silt soft soil. The results showed that the silt soft soil Zone I and Zone II (shallow layer) in Nansha District of Guangzhou were divided into slight siltation levels, and the silt soft soil Zone III (deep layer) was mild siltation level. Large pores were widely distributed in shallow silt soft soil, while the continuity of large pores in deep silt soft soil was poor. The migration of fine particles that failed to establish contact with surrounding particles in the soil blocks the small pores of seepage and thus produces siltation.展开更多
Uniformitarianism,summarised as‘the present is the key to the past’,has been successfully applied to interpret the geological record.An important variation of this principle is that while the present can be the key ...Uniformitarianism,summarised as‘the present is the key to the past’,has been successfully applied to interpret the geological record.An important variation of this principle is that while the present can be the key to interpreting the past,the past can be useful to more comprehensively and holistically document the present.In this study,for the first time,these principles are explored at two scales:macroscopically/mesoscopically where traditionally Uniformitarianism has been applied(in this paper,using coastal beach-to-dune stratigraphy,and by bubble sand,smallscale sedimentary structures,and silt-sized inter-granular deposits therein),and ultra-microscopically(using patina,a thin crust on weathered glass).The validity of the scalar variation has relevance to interpreting beach sequences where individual lithological,micro-lithological,structural,and micro-structural features in modern beach-to-dune systems are described and compared with‘fossil’sequences.Expression of Uniformitarianism also occurs at ultrasmall-scales in patina using~100-year-old glass found at Cossack,Western Australia and experimentally-produced ultra-microscopic patina.Features of‘mature’patina and glass corrosion have been highlighted through geochemical and hydrochemical processes,and these have been compared with corrosion and incipient,early-stage development of experimentally-produced ultra-microscopic patina.展开更多
[Objective] The research aimed to provide basic files and theoretical guidance for constructing sluicing-siltation dam using soil with high clay content soil.[Method] The soils of Dagou basin near Xiwu Village of Bais...[Objective] The research aimed to provide basic files and theoretical guidance for constructing sluicing-siltation dam using soil with high clay content soil.[Method] The soils of Dagou basin near Xiwu Village of Baishui County,Shaanxi Province were taken as experimental materials.pvc pipes with same height and diameter were used to construct testing model for dynamically determining settlement,shear strength,wet density of grouting bulk under 2 different grouting speeds(15 cm/d and 25 cm/d).[Result] Under different grouting speeds,general change trend was similar during grouting course.The subsidence,deformation,shear strength and wet density increased with the increase of grouting speed.Five or six days after grouting,daily displacement under 25 cm/d grouting speed was fewer than that under 15 cm/d grouting speed.[Conclusion] The increase of grouting speed could shorten the time for reaching the same subsidence,deformation,shear strength and wet density and increased displacement at the initial stage of grouting,however,with the increase of grouting time,lower grouting bulk was bad for displacement at later grouting period because it was near impermeable layer.展开更多
The article analyses the temporal spatial changes of profiles by EOF (Empirical Orthogonal Function) analysis and DTM analysis of GIS. These profiles, which are not affected by engineering, are chosen from the coast w...The article analyses the temporal spatial changes of profiles by EOF (Empirical Orthogonal Function) analysis and DTM analysis of GIS. These profiles, which are not affected by engineering, are chosen from the coast with successive field monitoring data from 1990 to 1999. Temporal and spatial EOF indicates the obvious stability of coast profile parameters in Fengxian tidal flat. In spatial scale, high tidal flats and deep water terraces are in a balance state while upper clino with steep slopes are sensitive and the stability is easy to be destroyed. In temporal scale, the erosion and deposition in this area are kept in balance in a whole. There are almost no change below 8- 9.5m. At the same time, it is the lower limit of tidal affection and the erosion and deposition process from it to high tidal flat keep in balance for many years. So the closure depth is appointed to from 8m to 9.5 m (Wusong datum mark).展开更多
Heavy rain falling on land at the upper reaches of the Kelantan River, Malaysia, on December 2014, had resulted in severe soil erosion and untold damages to croplands. The lower reaches of the river were heavily silte...Heavy rain falling on land at the upper reaches of the Kelantan River, Malaysia, on December 2014, had resulted in severe soil erosion and untold damages to croplands. The lower reaches of the river were heavily silted with infertile materials considered unfit for crop production. A study was conducted to explain why the flood phenomenon occurred, to determine the physico-chemical properties of the sediments silted in the Kelantan Plains and to propose measures for soil mitigation. Results showed that the silted sediments were characterized by the presence of quarts, mica, feldspars, kaolinite, gibbsite and hematite believed to come from the top- and subsoil of the upland areas. The sediments’ pH was very low and Al and/or Fe contents were very high, while nitrogen and carbon contents varied from area to area. Soils in the Kelantan Plains badly affected by this great flood needed to undergo proper ameliorative program. The most appropriate measure would be to apply ground magnesium limestone in combination with bio-fertilizer fortified with beneficial microbes that would increase their pH to a level above 5, which consequently eliminates Al<sup>3+</sup> and/or Fe<sup>2+</sup> that causes toxicity to the crops growing on them. The organic material so added would enhance the formation of soil structures. It is advised that the farming communities in the upper reaches of the Kelantan River would have to follow the advice advocated by the Department of Agriculture, Peninsular Malaysia, via MyGAP initiative, in order to sustain agricultural production on their land.展开更多
In this study, the combined actions of waves and tidal currents in estuarine and coastal areas are considered and a 2D mathematical model for sediment transport by waves and tidal currents has been established in orth...In this study, the combined actions of waves and tidal currents in estuarine and coastal areas are considered and a 2D mathematical model for sediment transport by waves and tidal currents has been established in orthogonal curvilinear coordinates. Non-equilibrium transport equations of suspended load and bed load are used in the model. The concept of background concentration is introduced, and the formula of sediment transport capacity of tidal currents for the Oujiang River estuary is obtained. The Dou Guoren formula is employed for the sediment transport capacity of waves. Sediment transport capacity in the form of mud and the intensity of back silting are calculated by use of Luo Zaosen＇ s formula. The calculated tidal stages are in good agreement with the field data, and the calculated velocities and flow directions of 46 vertical lines for 8 cross sections are also in good agreement with the measured data. On such a basis, simulations of back silting after excavation of the waterway with a sand bar under complicated boundary conditions in the navigation channel induced by suspended load, bed load and mud by waves and tidal currents are discussed.展开更多
Many yellow silt layers have been identified in the Holocene sediments in the last lake of Lop Nur (playa), Xinjiang, northwestern China. Statistics of drill-hole cores have revealed more than one hundred layers, whic...Many yellow silt layers have been identified in the Holocene sediments in the last lake of Lop Nur (playa), Xinjiang, northwestern China. Statistics of drill-hole cores have revealed more than one hundred layers, which exhibit regularity in time sequence. Study has further verified that these yellow silt layers were deposited through eolian processes. The time-frequency distribution diagram shows an obvious peak occurring at about 8200 a B.P., which is consistent with the dry, windy and cold climate event occurring at 8200 a in other places around the world. Therefore, this event is regarded as a response to the global climate change.展开更多
Mechanical behavior such as stress-strain response, shear strength, resistance to liquefaction, modulus, and shear wave velocity of granular mixes containing coarse and fine grains is dependent on intergrain contact d...Mechanical behavior such as stress-strain response, shear strength, resistance to liquefaction, modulus, and shear wave velocity of granular mixes containing coarse and fine grains is dependent on intergrain contact density of the soil. The global void ratio e is a poor index of contact density for such soils. The contact density depends on void ratio, fine grain content （Cv）, size disparity between particles, and gradation among other factors. A simple analysis of a two-sized particle system with large size disparity is used to develop an understanding of the effects of Cv, e, and gradation of coarse and fine grained soils in the soil mix on intergrain contact density. An equivalent intergranular void ratio （ec）oq is introduced as a useful intergrain contact density for soils at fines content of less than a threshold value Crth. Beyond this value, an equivalent interfine void ratio （ef）eq is introduced as a primary intergrain contact density index. At higher values of Cv beyond a limiting value of fine grains content CVL, an interfine void ratio ef is introduced as the primary contact density index. Relevant equivalent relative density indices （Drc）eq and （Drf）eq are also presented. Experimental data show that these new indices correlate well with steady state strength, liquefaction resistance, and shear wave velocities of sands, silty sands, sandy silts, and gravelly sand mixes.展开更多
Frothing is a main disease of highways in Yellow River Flood Field, due to the loss of dynamic strength of roadbed soils under the couple effects of temperature, salt, and vehicle traffic load. This is strongly linked...Frothing is a main disease of highways in Yellow River Flood Field, due to the loss of dynamic strength of roadbed soils under the couple effects of temperature, salt, and vehicle traffic load. This is strongly linked to the dynamic characteristics of silt in this region. To analyze these couple effects on the dynamic characteristics of silt, a series of tests(i.e., freeze-thaw cycling tests, vibration triaxial tests and ultrasonic wave velocity tests) were conducted and two kinds of silt(i.e., salt-free and 3%-salt silt) were designed. The results indicate that the dynamic shear strength and dynamic modulus decrease with increasing freeze-thaw cycles, while the damping ratio simultaneously increases. Furthermore, compared to salt-free silt, the decrement of dynamic shear strength and dynamic modulus of silt with 3% salt is more significant, but the damping ratio of 3%-salt silt is larger. In ultrasonic wave velocity tests, ultrasonic wave velocity of frozen soil specimens decreases as the number of freeze-thaw cycles increases. Based on the results of ultrasonic wave velocity tests, a preliminary model is proposed to evaluate damage of silt through field measurement ultrasonic data. The study could provide a theoretical basis for the treatment of silty soil highway.展开更多
基金National Natural Science Foundation of China(No.11671207).
文摘This paper studies silted algebras,namely,endomorphism algebras of 2-term silting complexes,over path algebras of Dynkin quivers.We describe an algorithm to produce all basic 2-term silting complexes over the path algebra of a Dynkin quiver,and use this algorithm to compute some examples.
基金supported by the National Natural Science Foundation of China (Grant Nos.52008039 and 52308425)the Natural Science Foundation of Hunan Province (Grant No.2021JJ40592).
文摘Deep excavations in silt strata can lead to large deformation problems,posing risks to both the excavation and adjacent structures.This study combines field monitoring with numerical simulation to investigate the underlying mechanisms and key aspects associated with large deformation problems induced by deep excavation in silt strata in Shenzhen,China.The monitoring results reveal that,due to the weak property and creep effect of the silt strata,the maximum wall deflection in the first excavated section(Section 1)exceeds its controlled value at more than 93%of measurement points,reaching a peak value of 137.46 mm.Notably,the deformation exhibits prolonged development characteristics,with the diaphragm wall deflections contributing to 39%of the overall deformation magnitude during the construction of the base slab.Subsequently,numerical simulations are carried out to analyze and assess the primary factors influencing excavation-induced deformations,following the observation of large deformations.The simulations indicate that the low strength of the silt soil is a pivotal factor that results in significant deformations.Furthermore,the flexural stiffness of the diaphragm walls exerts a notable influence on the development of deformations.To address these concerns,an optimization study of potential treatment measures was performed during the subsequent excavation of Section 2.The combined treatment approach,which comprises the reinforcement of the silt layer within the excavation and the increase in the thickness of the diaphragm walls,has been demonstrated to offer an economically superior solution for the handling of thick silt strata.This approach has the effect of reducing the lateral wall displacement by 83.1%and the ground settlement by 70.8%,thereby ensuring the safe construction of the deep excavation.
基金National Key R&D Program of China,No.2022YFC3203903National Natural Science Foundation of China,No.42371010,No.41971004。
文摘How the strong segmentation of cascade reservoir dams and the spatiotemporal changes of sediment retention volume affect the river morphology adjustment in the reservoir area is a scientific issue worthy of exploration.This study aims to reveal the adjustment mechanism of the thalweg longitudinal profile of cascade reservoirs.This study focuses on the Xiangjiaba and Xiluodu reservoirs located in the lower reaches of the Jinsha River.Utilizing multi-period observational data of thalweg elevation in reservoir reaches both before and after dam construction,the research employs statistical,geomorphological,and sedimentological methodologies to analyze variation characteristics in the measured curves,trend curves,and theoretical fitting curves of the thalweg longitudinal profile.The investigation ultimately reveals two distinct adjustment patterns in the longitudinal profiles of these cascade reservoirs:the concave curve type and the convex curve type.The former is characterized by weak riverbed scouring and silting changed to rapid aggradation in the upstream section of the reservoir area after dam closure,then changed to slow aggradation in the whole reservoir area,which is the common feature of reservoirs that were built earlier and are relatively located in the downstream(such as the Xiangjiaba Reservoir).The latter is characterized by a straight line or concave curve type with weak riverbed scouring and silting before the dam closure changed to a convex curve type with strong siltation after dam closure,which is the characteristic of reservoirs that were built later and are relatively located in the upstream(such as the Xiluodu Reservoir).The adjustment of the cascade reservoir longitudinal profile is controlled by the spatiotemporal changes of the sediment deposition volume and sedimentation rate in the reservoir area,and the alternating changes of the hydrodynamic gradient and regulation mode affect the spatial heterogeneity of the sedimentation rate.The research results are helpful for understanding the adjustment mechanism of the cascade reservoir longitudinal profile in similar areas and have a guiding role in predicting the adjustment trend of the cascade reservoir longitudinal profile without observation data.
基金Funded by the Jiangsu Province Industry University Research Project(No.BY20231142)the Yangzhou Science&Technology Program(No.YZ2023061)the Zhenjiang Science&Technology Program(No.SH2022018)。
文摘In order to realize the resource utilization of construction waste,industrial waste slag and silt,this paper used Portland cement,mineral waste residue and phosphogypsum composite to make cementing material(CMPS)with construction waste recycled aggregate to solidify silt.The mechanical properties of the solidified silt were analyzed by laboratory solidification test and microscopic examination respectively.In order to clarify the mineral composition,microscopic morphology and pore characteristics of the regenerated aggregate and CMPS solidified silt,X-ray diffractometer(XRD),scanning electron microscope(SEM),and nitrogen adsorption pore analyzer(NA)were used to further explore and analyze the regenerated aggregate and CMPS solidified silt effectively,and further reveal the internal mechanism of the regenerated aggregate and CMPS solidified silt effectively.The experimental results show that the strength of Portland cement-mineral waste residue phosphogypsum terpolymer system curing agent increases by 107.34%than that of single Port-land cement solidified silt at 56 d,and the strength of CMPS solidified silt increases by 25.68%under the action of recycled aggregate framework.The curing age and moisture content of the silt have a high correlation with the strength of the solidified silt.Therefore,the influence law of the above two influencing factors on its mechanical properties is further explored and the strength prediction is made.The microscopic test results show that,based on the hydration of Port-land cement and the pozzolans reaction of mineral waste residue,the solidified system has produced calcium silicate hydrate gel and ettringite crystals with gelatinous properties,which helps to fill the pores and form a denser structure.
基金The work described in this paper was partially supported by grants from the Research Grant Council of the Hong Kong Special Administrative Region,China(Project Nos.HKU 17207518 and R5037-18).
文摘The traditional standard wet sieving method uses steel sieves with aperture?0.063 mm and can only determine the particle size distribution(PSD)of gravel and sand in general soil.This paper extends the traditional method and presents an extended wet sieving method.The extended method uses both the steel sieves and the nylon filter cloth sieves.The apertures of the cloth sieves are smaller than 0.063 mm and equal 0.048 mm,0.038 mm,0.014 mm,0.012 mm,0.0063 mm,0.004 mm,0.003 mm,0.002 mm,and 0.001 mm,respectively.The extended method uses five steps to separate the general soil into many material sub-groups of gravel,sand,silt and clay with known particle size ranges.The complete PSD of the general soil is then calculated from the dry masses of the individual material sub-groups.The extended method is demonstrated with a general soil of completely decomposed granite(CDG)in Hong Kong,China.The silt and clay materials with different particle size ranges are further examined,checked and verified using stereomicroscopic observation,physical and chemical property tests.The results further confirm the correctness of the extended wet sieving method.
基金financial support from the National Natural Science Foundation of China(41902272)Gansu Province Basic Research Innovation Group Project(21JR7RA347).
文摘To ensure the long-term safety and stability of bridge pile foundations in permafrost regions,it is necessary to investigate the rheological effects on the pile tip and pile side bearing capacities.The creep characteristics of the pile-frozen soil interface are critical for determining the long-term stability of permafrost pile foundations.This study utilized a self-developed large stress-controlled shear apparatus to investigate the shear creep characteristics of the frozen silt-concrete interface,and examined the influence of freezing temperatures(−1,−2,and−5°C),contact surface roughness(0,0.60,0.75,and 1.15 mm),normal stress(50,100,and 150 kPa),and shear stress on the creep characteristics of the contact surface.By incorporating the contact surface’s creep behavior and development trends,we established a creep constitutive model for the frozen silt-concrete interface based on the Nishihara model,introducing nonlinear elements and a damage factor.The results revealed significant creep effects on the frozen silt-concrete interface under constant load,with creep displacement at approximately 2-15 times the instantaneous displacement and a failure creep displacement ranging from 6 to 8 mm.Under different experimental conditions,the creep characteristics of the frozen silt-concrete interface varied.A larger roughness,lower freezing temperatures,and higher normal stresses resulted in a longer sample attenuation creep time,a lower steady-state creep rate,higher long-term creep strength,and stronger creep stability.Building upon the Nishihara model,we considered the influence of shear stress and time on the viscoelastic viscosity coefficient and introduced a damage factor to the viscoplasticity.The improved model effectively described the entire creep process of the frozen silt-concrete interface.The results provide theoretical support for the interaction between pile and soil in permafrost regions.
基金supported by the National Natural Science Foundation of China(No.U2006213)the China Post doctoral Science Foundation(No.2022M712989).
文摘The morphological changes in isolated bubbles in gassy silt play a critical role in the microscopic structures between soil particles and bubbles and macroscopic physical properties.Based on X-ray CT scanning experiments under various vertical loads(four levels),self-designed acoustic macro experiments,and a series of formula revisions to the macro-air-bearing silt sound-velocity prediction model,this paper discusses the macro-and micro-scale features of gassy silts from the Yellow River Delta.The samples consisted of different proportions of silt from the Yellow River Delta and porous media,and they were used to form two types of aerosol silts with initial gas contents of 4.23%and 7.67%.The results show that the air bubble content and external load considerably affect the microstructural parameters and acoustic behavior of gassy silt in the Yellow River Delta.The macroscopic sound velocity showed a linear positive correlation with vertical load and relation to microstructural parameters in varying manners and degrees.Based on the traditional Biot-Stoll acoustic model,the gas-phase medium coefficient was introduced for the proper calculation and prediction of the sound velocity of air-bearing silt.The errors of the overall prediction varied between 5.6%and 9.6%.
基金Basic Research Funds for Colleges and Universities directly under the Inner Mongolia Autonomous Region:Desert Ecosystem Protection and Restoration Innovation Team(BR 22-13-03).
文摘Wind erosion is a geomorphic process in arid and semi-arid areas and has substantial implications for regional climate and desertification.In the Columbia Plateau of northwestern United States,the emissions from fine particles of loessial soils often contribute to the exceedance of inhalable particulate matter(PM)with an aerodynamic diameter of 10μm or less(PM10)according to the air quality standards.However,little is known about the threshold friction velocity(TFV)for particles of different sizes that comprise these soils.In this study,soil samples of two representative soil types(Warden sandy loam and Ritzville silt loam)collected from the Columbia Plateau were sieved to seven particle size fractions,and an experiment was then conducted to determine the relationship between TFV and particle size fraction.The results revealed that soil particle size significantly affected the initiation of soil movement and TFV;TFV ranged 0.304-0.844 and 0.249-0.739 m/s for different particle size fractions of Ritzville silt loam and Warden sandy loam,respectively.PM10 and total suspended particulates(TSP)emissions from a bed of 63-90μm soil particles were markedly higher for Warden sandy loam than for Ritzville silt loam.Together with the lower TFV of Warden sandy loam,dust emissions from fine particles(<100μm in diameter)of Warden sandy loam thus may be a main contributor to dust in the region's atmosphere,since the PM10 emissions from the soil erosion surfaces and its ensuing suspension within the atmosphere constitute an essential process of soil erosion in the Columbia Plateau.Developing and implementing strategic land management practices on sandy loam soils is therefore necessary to control dust emissions in the Columbia Plateau.
基金The National Natural Science Foundation of China(No.52008401)the Natural Science Foundation of Hunan Province(No.2021JJ40770)the Open Fund of Hunan Tieyuan Civil Engineering Testing Co.,Ltd.(No.HNTY2022K04).
文摘Through a self-developed model test system,the mechanical properties of silt and the deformation characteristics of airport runways were investigated during the period of subgrade wetting.Based on the test results,the reliability of the numerical simulation results was verified.Numerical models with different sizes were established.Under the same cushion parameter and loading width ranges,the effects of the cushion parameters and loading conditions on the mechanical responses of the cushion before and after subgrade wetting were analyzed.The results show that the internal friction angles of silt with different wetting degrees are approximately 34°.The cohesion is from 8 to 44 kPa,and the elastic modulus is from 15 to 34 MPa.Before and after subgrade wetting,the variation rates of the cushion horizontal tensile stresses with the same cushion parameters and loading width ranges are different under the influence of boundary effects.After subgrade wetting,the difference in the variation rates of the cushion horizontal tensile stresses under the same cushion parameter range decreases compared with that before subgrade wetting;however,this difference increases under the same loading width range.Before and after subgrade wetting,the influence of the boundary effect on the mechanical response evaluation of the cushion is not beneficial for optimizing the pavement design parameters.When the cushion thickness is more than 0.25 m,the influence of the boundary effect can be disregarded.
文摘The silt soft soil in Nansha District of Guangzhou was the softest soft soil in China. It had the characteristics of high natural water content, high compressibility, long consolidation time, and complex layered distribution of soil layers. These characteristics formed the clogging characteristics of silt soft soil, which greatly increased the construction difficulty and hindered the construction progress. Therefore, based on the basic physical and mechanical properties of silt soft soil in Nansha District of Guangzhou, this paper evaluated the clogging characteristics of three silt soft soil areas in Nansha District of Guangzhou through long-term permeability test, and carried out scanning electron microscope test to explore the influence of different parameters and microstructure on the clogging difficulty of silt soft soil. The results showed that the silt soft soil Zone I and Zone II (shallow layer) in Nansha District of Guangzhou were divided into slight siltation levels, and the silt soft soil Zone III (deep layer) was mild siltation level. Large pores were widely distributed in shallow silt soft soil, while the continuity of large pores in deep silt soft soil was poor. The migration of fine particles that failed to establish contact with surrounding particles in the soil blocks the small pores of seepage and thus produces siltation.
文摘Uniformitarianism,summarised as‘the present is the key to the past’,has been successfully applied to interpret the geological record.An important variation of this principle is that while the present can be the key to interpreting the past,the past can be useful to more comprehensively and holistically document the present.In this study,for the first time,these principles are explored at two scales:macroscopically/mesoscopically where traditionally Uniformitarianism has been applied(in this paper,using coastal beach-to-dune stratigraphy,and by bubble sand,smallscale sedimentary structures,and silt-sized inter-granular deposits therein),and ultra-microscopically(using patina,a thin crust on weathered glass).The validity of the scalar variation has relevance to interpreting beach sequences where individual lithological,micro-lithological,structural,and micro-structural features in modern beach-to-dune systems are described and compared with‘fossil’sequences.Expression of Uniformitarianism also occurs at ultrasmall-scales in patina using~100-year-old glass found at Cossack,Western Australia and experimentally-produced ultra-microscopic patina.Features of‘mature’patina and glass corrosion have been highlighted through geochemical and hydrochemical processes,and these have been compared with corrosion and incipient,early-stage development of experimentally-produced ultra-microscopic patina.
基金Supported by National Key Technology R&D Program(2006BAD09)Program for Science and Technology Innovative of Northwest A&F UniversityWarping Dam Management Fund of Department of Water and Soil Conservation~~
文摘[Objective] The research aimed to provide basic files and theoretical guidance for constructing sluicing-siltation dam using soil with high clay content soil.[Method] The soils of Dagou basin near Xiwu Village of Baishui County,Shaanxi Province were taken as experimental materials.pvc pipes with same height and diameter were used to construct testing model for dynamically determining settlement,shear strength,wet density of grouting bulk under 2 different grouting speeds(15 cm/d and 25 cm/d).[Result] Under different grouting speeds,general change trend was similar during grouting course.The subsidence,deformation,shear strength and wet density increased with the increase of grouting speed.Five or six days after grouting,daily displacement under 25 cm/d grouting speed was fewer than that under 15 cm/d grouting speed.[Conclusion] The increase of grouting speed could shorten the time for reaching the same subsidence,deformation,shear strength and wet density and increased displacement at the initial stage of grouting,however,with the increase of grouting time,lower grouting bulk was bad for displacement at later grouting period because it was near impermeable layer.
文摘The article analyses the temporal spatial changes of profiles by EOF (Empirical Orthogonal Function) analysis and DTM analysis of GIS. These profiles, which are not affected by engineering, are chosen from the coast with successive field monitoring data from 1990 to 1999. Temporal and spatial EOF indicates the obvious stability of coast profile parameters in Fengxian tidal flat. In spatial scale, high tidal flats and deep water terraces are in a balance state while upper clino with steep slopes are sensitive and the stability is easy to be destroyed. In temporal scale, the erosion and deposition in this area are kept in balance in a whole. There are almost no change below 8- 9.5m. At the same time, it is the lower limit of tidal affection and the erosion and deposition process from it to high tidal flat keep in balance for many years. So the closure depth is appointed to from 8m to 9.5 m (Wusong datum mark).
文摘Heavy rain falling on land at the upper reaches of the Kelantan River, Malaysia, on December 2014, had resulted in severe soil erosion and untold damages to croplands. The lower reaches of the river were heavily silted with infertile materials considered unfit for crop production. A study was conducted to explain why the flood phenomenon occurred, to determine the physico-chemical properties of the sediments silted in the Kelantan Plains and to propose measures for soil mitigation. Results showed that the silted sediments were characterized by the presence of quarts, mica, feldspars, kaolinite, gibbsite and hematite believed to come from the top- and subsoil of the upland areas. The sediments’ pH was very low and Al and/or Fe contents were very high, while nitrogen and carbon contents varied from area to area. Soils in the Kelantan Plains badly affected by this great flood needed to undergo proper ameliorative program. The most appropriate measure would be to apply ground magnesium limestone in combination with bio-fertilizer fortified with beneficial microbes that would increase their pH to a level above 5, which consequently eliminates Al<sup>3+</sup> and/or Fe<sup>2+</sup> that causes toxicity to the crops growing on them. The organic material so added would enhance the formation of soil structures. It is advised that the farming communities in the upper reaches of the Kelantan River would have to follow the advice advocated by the Department of Agriculture, Peninsular Malaysia, via MyGAP initiative, in order to sustain agricultural production on their land.
基金This work was supported bythe National Basic Research Program(973) of China (Grant No.2003CB415206) andthe National Natural Science Foundation of China (Grant No.50379027 and No.50479004)
文摘In this study, the combined actions of waves and tidal currents in estuarine and coastal areas are considered and a 2D mathematical model for sediment transport by waves and tidal currents has been established in orthogonal curvilinear coordinates. Non-equilibrium transport equations of suspended load and bed load are used in the model. The concept of background concentration is introduced, and the formula of sediment transport capacity of tidal currents for the Oujiang River estuary is obtained. The Dou Guoren formula is employed for the sediment transport capacity of waves. Sediment transport capacity in the form of mud and the intensity of back silting are calculated by use of Luo Zaosen＇ s formula. The calculated tidal stages are in good agreement with the field data, and the calculated velocities and flow directions of 46 vertical lines for 8 cross sections are also in good agreement with the measured data. On such a basis, simulations of back silting after excavation of the waterway with a sand bar under complicated boundary conditions in the navigation channel induced by suspended load, bed load and mud by waves and tidal currents are discussed.
基金supported by the Orientated Fund Project (DKD95-22)of the former Ministry of Geology and Mineral Resources of Chinathe"305"Project(96-916-08-05)of the Ministry of Science and Technology of China
文摘Many yellow silt layers have been identified in the Holocene sediments in the last lake of Lop Nur (playa), Xinjiang, northwestern China. Statistics of drill-hole cores have revealed more than one hundred layers, which exhibit regularity in time sequence. Study has further verified that these yellow silt layers were deposited through eolian processes. The time-frequency distribution diagram shows an obvious peak occurring at about 8200 a B.P., which is consistent with the dry, windy and cold climate event occurring at 8200 a in other places around the world. Therefore, this event is regarded as a response to the global climate change.
文摘Mechanical behavior such as stress-strain response, shear strength, resistance to liquefaction, modulus, and shear wave velocity of granular mixes containing coarse and fine grains is dependent on intergrain contact density of the soil. The global void ratio e is a poor index of contact density for such soils. The contact density depends on void ratio, fine grain content （Cv）, size disparity between particles, and gradation among other factors. A simple analysis of a two-sized particle system with large size disparity is used to develop an understanding of the effects of Cv, e, and gradation of coarse and fine grained soils in the soil mix on intergrain contact density. An equivalent intergranular void ratio （ec）oq is introduced as a useful intergrain contact density for soils at fines content of less than a threshold value Crth. Beyond this value, an equivalent interfine void ratio （ef）eq is introduced as a primary intergrain contact density index. At higher values of Cv beyond a limiting value of fine grains content CVL, an interfine void ratio ef is introduced as the primary contact density index. Relevant equivalent relative density indices （Drc）eq and （Drf）eq are also presented. Experimental data show that these new indices correlate well with steady state strength, liquefaction resistance, and shear wave velocities of sands, silty sands, sandy silts, and gravelly sand mixes.
基金Project(2018YFB1600100) supported by the National Key Research and Development Project of ChinaProjects(51778346, 51508310) supported by the National Natural Science Foundation of ChinaProject(2019GSF111007) supported by Key Research and Development Project of Shandong Province, China。
文摘Frothing is a main disease of highways in Yellow River Flood Field, due to the loss of dynamic strength of roadbed soils under the couple effects of temperature, salt, and vehicle traffic load. This is strongly linked to the dynamic characteristics of silt in this region. To analyze these couple effects on the dynamic characteristics of silt, a series of tests(i.e., freeze-thaw cycling tests, vibration triaxial tests and ultrasonic wave velocity tests) were conducted and two kinds of silt(i.e., salt-free and 3%-salt silt) were designed. The results indicate that the dynamic shear strength and dynamic modulus decrease with increasing freeze-thaw cycles, while the damping ratio simultaneously increases. Furthermore, compared to salt-free silt, the decrement of dynamic shear strength and dynamic modulus of silt with 3% salt is more significant, but the damping ratio of 3%-salt silt is larger. In ultrasonic wave velocity tests, ultrasonic wave velocity of frozen soil specimens decreases as the number of freeze-thaw cycles increases. Based on the results of ultrasonic wave velocity tests, a preliminary model is proposed to evaluate damage of silt through field measurement ultrasonic data. The study could provide a theoretical basis for the treatment of silty soil highway.
