Comprehensive evaluation and spatial-temporal evolution characteristics of urban resilience in Chengdu-Chongqing Economic Circle

To clarify the connotations and extensions of urban resilience,this study focuses on the Chengdu-Chongqing Economic Circle with 16 cities as research subjects.A comprehensive evaluation index system was constructed to measure the resilience of each city from 2003 to 2020.The spatial-temporal evolution characteristics were analyzed using Kernel density estimation,standard deviation ellipse,and spatial Markov chain analysis,and the spatial Tobit model was introduced to discover the influencing factors.The results indicate the following:①Urban resilience in the Chengdu-Chongqing Economic Circle displays an upward trend,with the center of gravity moving to the southwest,and the polarization phenomenon intensifying.②The urban resilience level in a region has certain spatial and geographical dependence,while the probability of urban resilience transfer differs in adjacent cities with different resilience levels.③Urban centrality,economic scale,openness level,and financial development promote urban resilience,whereas government scale significantly inhibits it.Finally,this paper proposes countermeasures and suggestions to improve the urban resilience of the Chengdu-Chongqing Economic Circle.

Spatial-temporal evolution of vegetation evapotranspiration in Hebei Province,China

Evapotranspiration （ET） is the sum of soil or water body evaporation and plant transpiration from the earth surface and ocean to the atmosphere, and thus plays a significant role in regulating carbon and water resource cycles. The time-series data set from the remote sensing MOLDS product （MOD16） was used to study the spatial-temporal evolution of vegetation evapotranspiration in salinized areas during 2000-2014 by analyzing the variability, spatial patterns and Mann-Kendall （MK） nonparametric trends for the time series. The results indicate that inter-annual and intra-annual variations of ET across various vegetated areas show seasonal changes, with the abnormal months identified. The Cultivated land displays a greater degree of spatial heterogeneity and the spatial pattern of ET in the area covered by broadleaved deciduous forests corresponds to a higher ET rate and increased water consumption. Awidespread decline of ET is observed only in cultivated areas. However, agricultural cultivation doesn＇t worsen water shortage and soil salinization problems in the region, and water shortage problems are worsening for other vegetated areas. This research provides a basis of reference for the reasonable allocation of water resources and restructuring of vegetation patterns in salinized areas.

Spatial-temporal evolution of gas migration pathways in coal during shear loading

Custom designed and built meso shear test equipment was used to examine the shear crack propagation in gassy coal under different gas pressures.The spatial-temporal evolution of gas migration pathways in the coal during shear loading was also researched.The results show that gas pressure can hasten crack growth at the shear fracture surface,can reduce the shear strength of gassy coal,and can accelerate the shear failure process.Shear failure in gassy coal exhibits five stages:the pre-crack stage;the stable crack growth stage;the unsteady crack growth stage;the fracture stage;and,finally,the friction crack stage.The shear breaking creates two kinds of crack,shear cracks and tensile cracks.Cracks first appear in the shear plane at both ends and then extend toward the center until a shear fracture surface forms.The direction of shear crack propagation diverges from the predetermined shear plane by an angle of about 5°-10°.

Spatial-temporal Evolution of the Urban-rural Coordination Relationship in Northeast China in 1990-2018

To comprehensively understand the law of urban-rural relationship and propose scientific measures of urban-rural coordinated development in Northeast China,this study uses the coupling coordination degree model and geographically and temporally weighted regression(GTWR)model to analyze the spatial-temporal patterns and the corresponding driving mechanisms of its urban-rural coordination since 1990.The results are as follows.First,the urban-rural coupling coordination degree in Northeast China was very low and improved slowly,but its stages of evolution is a good interpretation of the strategic arrangements of China's urbanization.Second,the urban-rural coupling coordination degree in Northeast China had spatial differences and was characterized by central polarization,converging on urban agglomeration,which was high in the south and low in the north.Moreover,the gap between the north and south weakened.Third,the spatial-temporal evolution of the urban-rural coordination relationship in Northeast China was influenced by pulling from the central cities,pushing from rural transformation,and government regulations.The influence intensity of the three mechanisms was weak,but the pulling from the central cities was stronger than that of the other two mechanisms.Furthermore,the spatial difference between the three mechanisms determines the spatial pattern and its evolution of the urban-rural coordination relationship in Northeast China.Fourth,to promote the development of urban-rural coordination in Northeast China,it is essential to advance urban-rural economic correlation,enhance the government^role in regulating and guiding,and adopt different policies for each region in Northeast China.

Spatial-temporal Patterns and Evolution History of Rural Settlements from the Perspective of Inheritance——A Case Study of Lianzhou City,Guangdong Province

Formation and evolution of rural settlement patterns in Lianzhou City,Guangdong Province were analyzed from the perspective of space and time,on the basis of its gazetteer and relevant historical data.The results show that Lianzhou was first founded in the sixth year of Yuanding Period of the Western Han Dynasty,and its development could be roughly classified into 6 stages according to the construction of south–north traffic lines and regional development progress,and it witnessed the fastest development in the Ming and Qing Dynasty.In terms of spatial distribution,rural settlements in the local area show spatial continuity,Lianzhou Town is the core of rural settlement growth in the city,and towns with the most concentrated rural settlements in all stages are located in central-west and northeast parts of the city,and those with lower density of rural settlements are mostly located in minority regions in the north and mountainous areas in the east.On the basis of the above facts,the paper studies the influence of natural geological conditions,immigrant,traffic,economic development and ethnic composition on the establishment and development of rural settlements in Lianzhou City.

Spatial-temporal Evolution Analysis on Land Use Multifunctionality in the China-Vietnam Border Area

Exploring the spatial and temporal evolution characteristics of the border land use multifunctionality(LUMF)provides insights for taking advantage of border land use and optimizing border land use policies.Based on the improved Technique for Order Preference by Similarity to an Ideal Solution(TOPSIS)mode,this study identifies and evaluates the LUMFs in the China-Vietnam border area between 2000 and 2018 from the perspectives of agricultural production,social security,ecological service,landscape recreation,and national security.The results show that:1)The comprehensive land use functions in most counties and cities continued to be improved.2)The comprehensive land use function exhibits remarkable spatial divergence and aggregation characteristics.The high-value area of the agricultural production function and social security function evolves from the east to the west.In addition,the spatial evolution of ecological service function is complicated,without an obvious spatial divergence and aggregation pattern.The landscape recreation function shows different spatial differentiation characteristics in the early and middle stage,and forms a large cluster in the later stage.Finally,the spatial evolution pattern of the national security function is significant.3)Designing differentiated border land policies,improving border land use security,and establishing a long-term mechanism for ecological protection and ecological compensation can aid in optimizing the LUMF level in the border area.

The Analysis of Spatial-Temporal Evolution of City Accessibility Based on Highway Network in Henan Province in China

Accessibility is an important tool to evaluate the maturity of a regional traffic network structure which describes the traffic convenience in the traffic network. The paper defines a new accessibility index by using the resident population weighted average value of the sum of inverse of the traveling time distance and time threshold coming from ordinary traffic network, and then uses this accessibility index to analyze the spatial-temporal characteristics of Henan highway network, as well as its evolution patterns from 2005 to 2020. The results show that with the expansion and improvement of Henan highway network, city accessibility level has been significantly improved, spatial convergence is obvious, the cities in the north central are always High-High aggregation area, the cities in the south are always Low-Low aggregation area, gradually forming the characteristics of Northwest high and Southeast low, relative balance between East and West. There is some non-conforming phenomenon in highway mileage growth and improvement of the city accessibility levels, but this situation is being weakened, the highway network layout is gradually rationalized, the spatial distribution of city accessibility and that of population are beginning to converge.

Spatial-temporal Analysis of Daily Air Quality Index in the Yangtze River Delta Region of China During 2014 and 2016

Urban air pollution is a prominent problem related to the urban development in China, especially in the densely populated urban agglomerations. Therefore, scientific examination of regional variation of air quality and its dominant factors is of great importance to regional environmental management. In contrast to traditional air pollution researches which only concentrate on a single year or a single pollutant, this paper analyses spatiotemporal patterns and determinants of air quality in disparate regions based on the air quality index(AQI) of the Yangtze River Delta region(YRD) of China from 2014 to 2016. Results show that the annual average value of the AQI in the YRD region decreases from 2014 to 2016 and exhibit a basic characteristic of ‘higher in winter, lower in summer and slightly high in spring and autumn'. The attainment rate of the AQI shows an apparently spatial stratified heterogeneity, Hefei metropolitan area and Nanjing metropolitan area keeping the worst air quality. The frequency of air pollution occurring in large regions was gradually decreasing during the study period. Drawing from entropy method analysis, industrialization and urbanization represented by per capita GDP and total energy consumption were the most important factors. Furthermore, population agglomeration is a factor that cannot be ignored especially in some mega-cities. Limited to data collection, more research is needed to gain insight into the spatiotemporal pattern and influence mechanism in the future.

应力-渗流耦合作用下不同卸荷路径对砂岩损伤特性及能量演化规律的影响研究

岩体灾害发生的本质是能量驱动下的一种失稳现象,受开挖卸荷扰动影响导致的岩体结构破裂失稳是诱发采场突水等动力灾害的主要原因之一。为探究开挖卸荷过程对岩体结构破裂的影响,明晰围岩劣化损伤规律及突水等动力灾害孕育机制,针对应力-渗流耦合因素影响下岩石损伤特性及能量演化规律研究较少的特点,采用Rock Top多场耦合试验仪,在应力-渗流耦合作用下对砂岩开展了常规三轴(C组)、不同初始损伤程度常规卸围压(W组)及循环加卸围压(X组)3种应力路径下的岩石损伤特性及能量演化规律试验研究。试验结果表明:岩石能量演化规律与应力-应变曲线具有明显相关性,基于岩石弹性应变能演化特征,将常规三轴压缩(C组)下岩石应力-应变曲线分为5个阶段,并对每个阶段U_(1)、U_(3)、U_(e)、U_(d)及渗透率变化特点进行了详细阐释(U_(e)为弹性应变能,U_(d)为耗散能,U_(1)为轴向应力对岩石做正功转化的岩石应变能,U_(3)为做负功所释放的应变能);常规卸围压过程中,U_(1)、U_(3)演化规律与C组岩石基本一致,但U_(3)负增长更为显著,岩石输入能逐渐从以U_(e)为主导转变为以U_(d)为主导,初始损伤程度对该规律无明显影响,卸围压过程中渗透率呈波动上升趋势,围压与渗透率呈负相关;循环加卸围压过程中,各能量演化规律与W组岩石基本一致,仅因时间效应而导致能量积累量存有差异。整体来看,无论何种应力路径,峰前阶段岩石均以U_(e)为主导,以能量存储为主,峰后阶段则以能量释放及耗散为主,轴向应力加载是U_(e)得以快速积累的主要影响因素,围压改变不足以引起U_(e)发生较大变化,轴向载荷作用为工程致灾的主要影响因素。此外,岩石损伤变量与围压存在明显负相关,围压越大,岩石U_(e)释放比例越小,岩石损伤越小,围压束缚作用可有效提高岩石储能能力并抑制岩石能量的耗散与释放。

渗流管涌作用下松散堆积层结构演化规律

为揭示渗流管涌作用下松散堆积层结构演化规律,基于颗粒-孔隙尺度流固耦合方法,分别对密实、中密和疏松结构的松散堆积层开展渗流管涌仿真试验,从细观层面分析渗流管涌作用下松散堆积层颗粒迁移特征、颗粒流失量、颗粒间接触力链演化和骨架变形的结构演化特征。结果表明:渗流管涌主要以细颗粒迁移为主,存在局部“堵塞”现象,块石颗粒仅会在细颗粒迁移脱空后自由堆积。细颗粒迁移具有明显的“颗粒堆积”现象,主要集中在出口处,呈“上多下少”的特点。同时,渗流管涌发展过程中相同部位的孔隙率变化具有高度相似性,且结构越疏松越显著。管涌发展过程中,块石颗粒间接触承担主要的应力传递,力链演化的本质是堆积填料内部应力传递结构的改变。此外,下沉量和体应变均随时步增加,呈先急剧增加,后趋于平稳的态势,且随初始渗流速度越大,平稳时刻逐步提前。该研究成果可为从细观角度认识松散堆积层渗流管涌结构演化规律提供一定借鉴。

Study on Spatial-Temporal Evolution of Residential Differentiation in Shanghai from an Employee Perspective

Against a background of deepened globalization, the socio-spatial distribution characteristics of the employed population are one of the important perspectives that reflect the impact of globalization on urban social space. Based on data of the population census of Shanghai in 2000 and 2010, using location quotient and index of dissimilarity, this paper analyzes the residential differentiation evolution in Shanghai from 2000 to 2010. The results show that except the high-end service industry, the residential differentiation of the employees in the other three types of industries has intensified but is not serious. In addition, the proportion of employees in high-end service industry within the Middle Ring has increased, while that of employees in the middle-and low-end service industry beyond the Middle Ring has increased, which further proves that globalization has an increasingly obvious impact on the socio-spatial differentiation in Shanghai. However, the adjustment in spatial development made by the Shanghai municipal government in response to globalization makes the socio-spatial evolution of Shanghai greatly different from the suburbanization of social elites in the West.

渗流作用下多级配土石混合填料的结构演化规律

渗流是引起土石混合填料中细颗粒流失,致使土体结构变化引起路基变形及失稳的关键因素。采用自行研发的颗粒流失试验装置,对不同级配的土石混合填料进行渗流试验,监测渗流作用下填料的透水质量、细颗粒流失量和沉降量的变化过程,分析土体结构演变过程;采用PFC^(3D)(Particle Flow Code in 3D)对细颗粒流失过程进行数值模拟,分析填料孔隙和粒径动态变化特性。研究结果表明:透水质量和细颗粒流失率可以反映土石混合填料结构对水分的敏感程度。填料骨架结构对水分的敏感程度越低,可及时有效地排出水分,渗流对结构的破坏越小。渗流条件下土石混合填料的结构演化过程可分为细颗粒快速流失、骨架重塑和相对稳定3个阶段,其中骨架重塑阶段是引起其结构演化的关键阶段。细颗粒快速流失阶段,每小时透水量增长速率较快,细颗粒大量流失,沉降量很小;骨架重塑阶段,每小时透水量变化速率减缓,细颗粒流失量减少,但骨架结构重组导致颗粒产生明显的相对位移,沉降量增长较快;相对稳定阶段,每小时透水量变化缓慢,沉降量基本保持不变。颗粒流失数值模拟的过程表明细颗粒组分的迁移引起填料孔隙率产生变化,致使土体结构发生改变。上述结果表明,在所研究的几种填料中,n=0.55级配下土石混合填料的骨架结构最稳定,对水分的敏感性最弱。

中间主应力影响下含瓦斯复合煤岩体变形渗流及能量演化特征研究

深部环境中,复合煤岩体处于三向不等应力状态,中间主应力的存在对煤岩体变形、强度特性及能量演化特征有着重要影响。本文利用真三轴气固耦合煤岩渗流试验装置,开展了不同中间主应力条件下含瓦斯复合煤岩体变形-渗流试验研究。结果表明:(1)随着中间主应力的增大,当达到峰值强度时,试件最大主应力方向应变呈现先增大后减小的变化,中间主应力方向应变和最小主应力方向应变之间的差值越来越大;(2)低中间主应力下试件中间主应力方向呈现出膨胀变形,中间主应力较大时,ε_(2)-Δσ曲线达到峰值后发生回弹,中间主应力方向最终表现为压缩变形;(3)随着中间主应力的增大,试件相对渗透率系数谷值降低,相对渗透率系数曲线峰值拐点与ε_(1)-Δσ曲线的拐点一致;(4)达到应力峰值时,试件总输入能量先增大后减小,与试件强度变化趋势类似,弹性应变能先增大后减小,耗散能持续增大,U_(e)/U先升高后降低,U_(d)/U先降低后升高。

高温蒸汽作用油页岩孔隙-裂隙结构演化规律实验研究

油页岩孔隙裂隙演化规律是影响对流加热方式原位流态化开采油页岩的关键影响因素。选取新疆巴里坤油页岩试样,首先利用自主研制的高温蒸汽作用实验系统对试样进行加热,然后采用显微CT和扫描电镜对不同温度作用后的油页岩的孔隙裂隙特征进行测试,并利用Avizo软件,对油页岩孔裂隙结构、内部渗流场特征以及表面微观特征随温度的演化规律进行了详细地研究,结果表明:1)原始状态下油页岩内部裂隙以微裂隙(100~500μm)为主,随着水蒸汽作用温度不断提高,微裂隙数量呈指数形式增长,同时孔径较小的小孔逐步转变为孔径较大的中大孔。2)随着水蒸汽作用温度增加,油页岩孔隙度显著增加,由常温状态下的2.7%增加到555℃时的16.2%,是常温下的6倍。3)随着热解温度的升高,油页岩内部连通的孔隙也不断增多,为高温水蒸汽以及热解产物的运移提供了良好通道,总体上平行层理方向的渗透率总是大于垂直层理方向的渗透率。4)油页岩渗透性存在明显的各向异性特征,当热解温度为314℃时,油页岩在平行层理方向与垂直层理方向的渗透率差异性最大,渗透率各向异性系数量级可达103.研究结论对调控水蒸汽对流加热原位开采油页岩油气的工艺参数具有重要意义。

三轴应力对单裂隙砂岩渗流特性的影响试验研究

针对渗流作用下裂隙岩体的失稳机制复杂、难以完全揭示的问题,文章开展了不同裂隙倾角单裂隙砂岩的渗流试验,从力学特性、能量耗散规律和渗透特性三个方面分析砂岩破坏特性,并探讨能量耗散过程对渗流特性的影响规律。结果表明:不同裂隙倾角砂岩的偏应力、应变能、渗透率随应变的演化过程基本一致,而不同加载阶段的变化规律差异性明显。在裂隙非水平和竖直情况下,裂隙倾角越大,脆性特征越弱,越难破坏;而对于水平和竖直裂隙而言,水平裂隙尖端的应力集中强于竖直裂隙,脆性特征更显著。此外,单裂隙砂岩的渗透率与应力的关系同样符合Louis负指数方程。不同裂隙倾角砂岩的能量耗散过程对渗流特性的影响规律大致相同,耗散能的增加均可增大渗透率,但在加载初期和末期,能量耗散反而会降低渗透率。

煤体瓦斯吸附渗流过程及声发射特性实验研究

对原煤试样瓦斯吸附渗流过程的声发射信号进行了监测,并基于声发射信号特征,分析了煤体损伤演化及瓦斯吸附渗流的动态特征。实验发现,在吸附过程的初期,声发射强度最大,而且随着吸附量的逐渐增加,声发射信号逐渐减弱;吸附过程中声发射信号在时域上呈现阵发性,即密集段与间歇段相连的特征。实验结果表明:瓦斯是由煤体最外层开始逐层向内部吸附渗流的;在瓦斯逐层渗流过程中,当瓦斯压力梯度大于可导致煤体局部微观结构破坏的临界压力梯度时,瓦斯表现为具有动力效应的破坏式渗流,对应着声发射的密集段;煤体受到破坏后,渗流阵面的压力急剧降低,瓦斯表现为无破坏能力的渗流,同时也进入蓄能阶段,对应着声发射间歇段;随着煤体内部瓦斯压力的增大,吸附过程趋于平衡,煤体内产生的声发射信号也逐渐减弱。

裂隙岩体渗流-损伤-断裂耦合分析与工程应用

综合运用岩体结构力学、几何损伤力学及岩石流体力学理论,建立裂隙岩体渗流–损伤–断裂耦合数学模型(扩展FLAC3D模型),在FLAC现有计算模块的基础上,通过Fish研制了其分析程序。该模型的耦合机理:渗透水力梯度作为渗透体积力作用于损伤应力计算单元,裂隙渗透压作为面力作用于裂纹张开部分引起断续岩石裂纹的起裂,扩展导致岩体损伤演化;岩体裂纹的扩展引起岩体渗透系数的增加,导致渗流场的改变。对一复杂裂隙岸坡蓄水加载过程进行渗流–损伤–断裂耦合分析,得到不同蓄水时期,裂隙岸坡渗流场分布、损伤场的演化,初步探讨了水库蓄水过程中岸坡山体变形机制。耦合分析认为:山体变形是增量渗透力和增量浮托力共同作用于岸坡的结果;对蓄水相对高程较大的裂隙岸坡而言,库水位上升,裂隙渗透水压增加导致岩体裂纹起裂扩展,岩体损伤区增大且向岸坡深部扩展。高渗透压诱发岸坡不利断层带损伤区扩展,甚至贯通,可能是导致岸坡失稳的重要原因。

降雨对裂隙型岩溶含水系统演化影响的数值模拟研究

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在连续损伤力学理论基础上,将塑性损伤演化及渗流相互耦合的概念引入Mohr-Coulomb破坏准则,用于分析在孔隙压力和塑性损伤演化共同作用下岩石损伤演化机制,建立了相应的有限元损伤数值分析模型,并应用于比利时核废料库开挖过程中泥岩隧道附近围岩发生损伤演化、渗流场和应力场耦合过程分析中,得到了开挖引起的围岩损伤特性、孔隙压力以及渗透性的变化规律,为进一步研究隧道流变过程水力耦合特性合理的数值计算模型建立方法提供基础。