Numerical simulation of dynamic response of subgrade under moving heavy truck in cold regions

This paper reports on the dynamic response of highway subgrade under moving heavy truck in cold regions. Numerical simulations are performed in two stages. In the first stage, the moving heavy truck vibration, induced by road roughness, is calculated through a three-dimensional dynamic interaction model of heavy truck-pavement-subgrade, and the time-histories of nodal loads on the top of the base are calculated through this model. In the second stage, a two-dimensional dynamic finite element model of the base-subgrade-ground system is formulated, using the calculated nodal loads from the first stage as input. The dynamic response of the subgrade is validated by field measurements, and the effects of truck type, axle loading, running speed, and road roughness on the vertical dynamic stress in the unfrozen period and the spring thawing period are analyzed and discussed.     

Stress states of thawed soil subgrade

The article presents the field measurement results of the stress states of roadbed thawed soil subgrade during the passage of trains. The dependences of the vertical and horizontal stresses on the velocity of the rolling stock motion, the axle load, and the distance from the sleeper sole have been obtained.     

Influence of repeated freeze-thaw on dynamic modulus and damping ratio properties of silty sand

Under repeated freezing and thawing in deep seasonal frozen regions, the stability and strength of the soil are imposed in the form of large uneven settlement, instability and strength reduction, which...     

The influence of freeze-thaw cycles on the granulometric composition of Moscow morainic clay

The freeze-thaw cycling process considerably changes the composition,structure,and properties of soils.Since the grain size is the most important factor in determining soil characteristics,our current research primarily aims to investigate dynamic changes of the soil fraction when exposed to freeze-thaw conditions.We observed two series of Moscow morainic clayey specimens(g QmII):(I) the original series,and(II) the remolded series.We subjected each series of soil specimens to different frequencies of freeze-thaw cycles(3,6,20,and 40 cycles),and we used granulometric tests to analyze both series before and after exposure to freeze-thaw conditions.As a result of our experiments,the granulometric compositions tended to be distributed evenly after 40 freeze-thaw processes(i.e.,content of fraction for 0.1–0.05 mm was increased after 40 freeze-thaw cycles) because the division of coarse grains and the aggregation of fine grains were synchronized during the freeze-thaw process.The soil grains in both series changed bi-directionally.In the original series,changes of the sand grains were conjugated with the clay grains,and in the remolded series,changes of the sand grains were conjugated with the silt grains,because potential energy difference caused the division and aggregation processes to relate to the counteraction process.The even distribution of soil grain size indicated the state of equilibrium or balance.The granulometric compositions were altered the most during the sixth freeze-thaw cycle,because the coefficient of the intensity variation of the grain fineness(Kvar) had its maximum value at that time.     

Simulated effect of soil freeze-thaw process on surface hydrologic and thermal fluxes in frozen ground region of the Northern Hemisphere

Soil freeze-thaw process is closely related to surface energy budget,hydrological activity,and terrestrial ecosystems.In this study,two numerical experiments(including and excluding soil freeze-thaw process)were designed to examine the effect of soil freeze-thaw process on surface hydrologic and thermal fluxes in frozen ground region in the Northern Hemisphere based on the state-of-the-art Community Earth System Model version 1.0.5.Results show that in response to soil freeze-thaw process,the area averaged soil temperature in the shallow layer(0.0175?0.0451 m)decreases by 0.35℃in the TP(Tibetan Plateau),0.69℃in CES(Central and Eastern Siberia),and 0.6℃in NA(North America)during summer,and increases by 1.93℃in the TP,2.28℃in CES and 1.61℃in NA during winter,respectively.Meanwhile,in response to soil freeze-thaw process,the area averaged soil liquid water content increases in summer and decrease in winter.For surface heat flux components,the ground heat flux is most significantly affected by the freeze-thaw process in both summer and winter,followed by sensible heat flux and latent heat flux in summer.In the TP area,the ground heat flux increases by 2.82 W/m2(28.5%)in summer and decreases by 3.63 W/m2(40%)in winter.Meanwhile,in CES,the ground heat flux increases by 1.89 W/m2(11.3%)in summer and decreases by 1.41 W/m2(18.6%)in winter.The heat fluxes in the Tibetan Plateau are more susceptible to the freeze-thaw process compared with the high-latitude frozen soil regions.Soil freeze-thaw process can induce significant warming in the Tibetan Plateau in winter.Also,this process induces significant cooling in high-latitude regions in summer.The frozen ground can prevent soil liquid water from infiltrating to deep soil layers at the beginning of thawing;however,as the frozen ground thaws continuously,the infiltration of the liquid water increases and the deep soil can store water like a sponge,accompanied by decreasing surface runoff.The influence of the soil freeze-thaw process on surface hydrologic and thermal fluxes varies seasonally and spatially.     

基于改进土壤冻融水循环的Biome-BGC模型估算青藏高原草地NPP

Biome-BGC模型被广泛用于估算植被净初级生产力（Net Primary Productivity, NPP）,但是该模型未考虑冻土区土壤冻融水循环过程对植被生长的影响。本文基于Biome-BGC模型,改进冻土区活动层土壤冻融水循环,估算了2000—2018年青藏高原高寒草地NPP。通过比较原模型和改进后的模型,并对NPP模拟结果的时空特征进行了分析,结果表明：① 增加冻融循环提高了NPP估算精度,青藏高原草地NPP均值由114.68 gC/(m²·a)提高到128.02 gC/(m²·a)。② 原模型和改进后NPP的空间分布差异较大,时间变化趋势差异不明显。③ 青藏高原草地NPP总量为253.83 TgC/a,呈东南向西北递减的空间格局,年均增速为0.21gC/(m²·a)（P=0.023）,显著增加的占17.85%,主要分布在羌塘高寒草原地带的大部分地区和藏南山地灌木草原地带的西部。④ 该冻融水循环改进方法简单可靠,具有在其他多年冻土区推广的价值。     

河西走廊城市化与生态环境的动态耦合模型及应用

1 Introduction Since the 21stcentury,the urbanization tide has sweptacross the whole China.However,the urbanization in W est China, especially in Hexi Corridor, is severely restricted by eco-environment.There are various kinds of contradictions and intim …     

The dynamic coupling model and its application of urbanization and eco-environment in Hexi Corridor

This paper, taking Hexi Corridor as an example, analyzes the alternating intimidation and the dynamic evolving relation between urbanization and eco-environment in arid area of West China. We argue that the harmonious development system of the urbanization and eco-environment would go through four phases: rudimentary symbiotic phase, harmonious developmental phase, utmost increasing phase and spiral type rising phase. Throughout the four phases, the elements of the system would influence each other, coerce each other, and complete the spiral type rising process from low-grade symbiosis to high-grade harmony together. The study on Hexi Corridor shows that the urbanization level in Hexi Corridor has increased gradually from 1985 to 2003 accompanied with the fluctuations of eco-environment state. The response of eco-environment to urbanization has been evident, but lagged behind the urbanization course. At present, the harmonious development system in Hexi Corridor was in its harmonious developmental phase. However, the coupling degree has increased quickly and approached 90 yet, which is signaling that the system is about to enter the utmost increasing phase, and the ecological crisis will enter the latent period. We have found that the coupling degree can well reflect the interactive coercing and dynamic evolving situation between urbanization and eco-environment in Hexi Corridor. From the temporal change of the coupling degree, it can be concluded that urbanization sometimes needs to pay a certain cost for the damage of the eco-environment in its initial stages, but as the urbanization continues, the state of the eco-environment would be meliorated.     

基于SD和CLUE-S模型的张掖市甘州区土地利用情景分析

近年来,学者们基于不同研究需要开发了很多土地利用变化/覆盖(LUCC)模型.但迄今没有一个单独的模型可在不同时空尺度上揭示所有土地利用变化的关键过程.本文尝试开发一种集成SD模型与CLUE-S模型的建模方法,用以弥补已有LUCC模型缺陷,并将其应用于张掖市甘州区的土地利用情景分析中,得到的LUCC模拟结果可为该区土地利...     

The dynamic response of forest vegetation to hydrothermal conditions in the Funiu Mountains of western Henan Province

This paper uses HJ-1 satellite multi-spectral and multi-temporal data to extract forest vegetation information in the Funiu Mountain region. The S-G filtering algorithm was employed to reconstruct the MODIS EVI (Enhanced Vegetation Index) time-series data for the period of 2000–2013, and these data were correlated with air temperature and precipitation data to explore the responses of forest vegetation to hydrothermal conditions. The results showed that: (1) the Funiu Mountain region has relatively high and increasing forest coverage with an average EVI of 0.48 over the study period, and the EVI first shows a decreasing trend with increased elevation below 200 m, then an increasing trend from 200–1700 m, and finally a decreasing trend above 1700 m. However, obvious differences could be identified in the responses of different forest vegetation types to climate change. Broad-leaf deciduous forest, being the dominant forest type in the region, had the most significant EVI increase. (2) Temperature in the region showed an increasing trend over the 14 years of the study with an anomaly increasing rate of 0.27°C/10a; a fluctuating yet increasing trend could be identified for the precipitation anomaly percentage. (3) Among all vegetation types, the evergreen broad-leaf forest has the closest EVI-temperature correlation, whereas the mixed evergreen and deciduous forest has the weakest. Almost all forest types showed a weak negative EVI-precipitation correlation, except the mixed evergreen and deciduous forest with a weak positive correlation. (4) There is a slight delay in forest vegetation responses to air temperature and precipitation, with half a month only for limited areas of the mixed evergreen and deciduous forest.     

城市水环境分析模型系统的国际化与本土化研究

人类生态环境的退化是新世纪全球可持续发展所面临的重大问题，而城市水环境污染治理的中心业已从发达国家转移到发展中国家。我们在参与上海市水环境污染治理研究中认识到；在借鉴国际上先进的水环境分析模型系统的同时，必须运用先进的地理信息系统技术，开发本土化的空间模拟系统，才能使模型分析更有效的应用于我国城市水环境治理的决策中。本文结合作者近期研发成果，重点介绍国际上著名的水环境分析模型从数值处理，图表显示，空间可视化到动态模拟系统的发展态势及其我们的模型本土化开发中创建的方法与技术特点。     

基于动态空间面板模型的中国港口竞争与合作关系研究

港口之间的竞争与合作关系是港口资源整合所要理顺和优化的关键问题,关系着港口体系的健康可持续发展。本文采用动态空间面板模型,研究了2000年以来中国港口整体及沿海和内河各区域港口群的竞争与合作关系,并探讨其影响因素。研究表明：中国港口货物吞吐量和集装箱吞吐量存在空间正相关性,且呈现逐渐增强的趋势;从货物吞吐量看,全国范围内的港口和内河港口之间不存在显著的竞争效应,沿海港口之间竞争态势显著,而三者在集装箱运输方面均为竞争关系;五大沿海港口群在货物吞吐量方面的竞争激烈程度排序为环渤海港口群>珠江三角洲港口群>长江三角洲港口群>西南沿海港口群>东南沿海港口群,内河港口群中,仅珠江水系港口群呈竞争态势;珠江三角洲港口群、东南沿海港口群、长江三角洲港口群、长江水系和珠江水系港口在集装箱运输中竞争激烈;港口供求关系、港口规模结构、港口职能结构、港口规划与管理等是影响竞争与合作关系及竞争激烈程度的重要因素。本研究有助于丰富港口地理学的理论研究,并为港口资源整合提供思路和方向。     

经济体制转轨下的无锡市城乡地域结构演变响应

城乡地域结构与经济体制响应关系研究,是从体制变革出发剖析中国城乡地域空间演变规律的重要视角。对比1978-2010年长三角地区无锡市城乡地域结构演变和中国经济体制转轨进程,发现二者变化阶段具有一致性,城—郊—乡地域结构向城乡一体化地域结构演变,响应计划经济体制向社会主义市场经济体制转轨。通过选取经济体制核心要素(固定资产投资所有制结构)为体制变量、地域结构要素(城乡地域范围)为空间变量,建立基于向量自回归(VAR)模型的脉冲响应函数(IRF),刻画城乡地域空间对体制变量的响应状态,并利用方差分解函数(VD)进一步分析体制变量对城乡地域结构演变的贡献率。结果表明: ① 城乡地域结构中,城乡过渡地域对体制变量的响应强度最高;② 城乡地域各个空间对私有经济投资变化均表现出响应强度相对较大、持续时间长的特征,城市建成区扩展对国有经济投资变化响应迅速,并呈负响应关系,而乡村建设用地增加主要响应集体经济投资变化;③ 在体制影响下,城市建成区和乡村自身发展状态的惯性对其演变依然长期起着重要作用,而城乡过渡地域的自身发展状态惯性在经济体制转轨影响下很快失去主导作用。     

互联网对中国城市内部就业分布的动态影响

本文旨在揭示互联网影响城市内部就业分布的净效应及其动态变化。首先,将互联网分散力与集聚力的相对变化纳入互联网动态影响的分析框架并提出相应理论假说;其次,利用中国2004年、2008年、2013年3次经济普查中289个地级市的2247万个企业的微观数据,以“邮区”为基本空间单元构建了城市内部就业集聚指数;最后,构造工具变量以缓解内生性问题。结果显示,平均而言,互联网能显著促进城市内部的就业集聚,但随互联网渗透率的提高,其促进作用呈现“边际递减”趋势,而城市就业的空间多中心性不断提升,即就业向远离城市主中心的次中心集聚;对于高发展水平的城市,互联网渗透率的提高促进了就业先短暂分散,而后“边际递增”式集聚。本文研究发现对于预判未来城市中经济活动的空间分布和指导空间规划具有重要意义。     

环渤海地区港口与城市关系的动态测度及驱动模式研究

港城交互作用是港口城市形成、演化并实现可持续发展的关键因素,因此,如何测定港城关系并从中揭示港城交互作用的模式是港口城市研究的一个难点问题.一直以来,港城关系中港口功能与城市功能定量分析方法以及港城互动关联机制的研究比较薄弱.在RCI基础上,提出DCI的概念、内涵及其算法,并以此为基础,对环渤海地区主要海港城市的港城关系状况及DCI值动态变化趋势进行定量测度,并运用脉冲响应函数对港城驱动模式进行系统分析,揭示不同港口城市在港城相互作用方面的具体差别与联系,丰富地理学对于港城关系内在机理的认识.结果显示:环渤海地区12个海港城市港城关系状况可以分为港口驱动型、城市驱动型和港城稳定型三类;变动趋势可以分为持续上升型、持续下降型及波动型三类;港城交互作用机制及稳定性存在明显差别.港城关系的强弱或倾向性与港口或城市规模没有直接关系,而是与港口或城市发展阶段、港口与腹地的关系等深层次问题密切相关.     

Modeling dynamic assessment of ecosystem services based on remote sensing technology: A sampling of the Gansu grassland ecosystem

The ecosystem is important because it is the life sustaining system for human survival.Three ecosystem characteristics are:regional particularities,ecosystem complexity and conventional cultural particularities.This paper develops a remote sensing based dynamic model to assess grassland ecosystem service values involving multidisciplinary knowledge.The ecological value of grassland ecosystems is focused on using a remote sensing technique in the model,and setting up the framework for a dynamic assessing model.The grassland ecological services condition and value in 1985 is used as the benchmark.The dynamic model has two adjusting indicators:biomass and price index.The biomass is simulated using the CASA(Carnegie-Ames-Stanford Approach) model.The price index was obtained from statistics data published by the statistical bureau.Results show that the grassland ecosystem value in Gansu Province was 28.36 billion Chinese Yuan in 1985,140.37 billion in 1999 and 130.86 billion in 2002.     

西部省区旅游经济效率与区域经济水平的重心耦合及互动响应研究

在新一轮西部大开发背景下,旅游业是推动西部区域经济发展的重要动力。基于此,文章综合运用非径向超效率DEA模型、综合线性加权法、非参数Kernel核密度估计、重心模型、重心耦合模型以及VAR模型等方法分析旅游经济效率与区域经济水平的重心耦合与互动响应。研究结果表明：（1）西部旅游经济效率与区域经济水平均处于较低水平,前者经历了从“川-黔-渝”三核到“滇-黔”双核的演变,后者则始终以四川为唯一增长极;（2）旅游经济效率核密度曲线形状从相对平稳发展为陡峭,区域经济水平则相对稳定,前者两极化态势更为严峻;（3）旅游经济效率与区域经济水平重心迁移距离最大方向分别为“南偏西”和“南偏东”,均呈现“西北-东南”极化格局,极化方向分别以顺时针转动了3.41°和1.41°;（4）空间重叠性数值呈“U”型演化,重心耦合态势先“优化”后“劣化”;（5）脉冲响应多呈平滑型响应,响应多集中在前3~4期,区域经济水平对旅游经济效率的方差贡献度较低,旅游经济效率对区域经济水平的方差贡献度较高。     

旅游社会—生态系统的运行机制——以西安市上王村为例

乡村旅游人地关系研究迫切需要新的视角。将乡村视作以旅游发展为基础的局域社会—生态系统,认为其本质是将乡村自然环境、社会经济和旅游发展联接起来,构建一种"全景式"审视村域人地关系的分析框架。借鉴社会—生态系统的相关理论,以陕西秦岭北麓上王村为例,构建乡村旅游社会—生态系统模型,通过实地调查和访谈获取数据,以游客分类为基础,辨识了乡村旅游社会—生态系统获得稳态的关键变量,分析系统内部运行的动力机制。主要结论:1划分出生态旅游者和大众旅游者,通过识别不同游客的旅游偏好,结合生态系统商品与服务的质量,以及资本变量,构建旅游社会—生态系统的四维模型,理清指标的关键变量。2通过模型计算,得到维持系统稳态的阈值(退化系数)ω在0.2587~0.3605之间,各子系统的关键变量包括与生态旅游者相关的"娱乐方式"、"景区内部道路完善性"、"景区旅游接待设施的完善"和"人类是世界的主宰",与大众旅游者相关的"便宜的住宿"、"人类需要和环境和谐共处"和"景区旅游接待设施的完善",与环境相关的"发展旅游的条件",与资本相关的"景区基础设施的退化程度"。3景区管理者在政策制定方面,应根据游客行为的特征和反馈,做出调整和改变,以应对和减缓当地社会—生态系统的负面影响,促进乡村旅游发展的"可持续性"。