Propagation of vibrations in thawing deep seasonally frozen soils in railway subgrade

In this study, in-situ testing results are given, and the analytical relationship of the vibrations' amplitudes inside an embankment by the thawing of the subgrade surface of seasonably deep frozen soils is provided. The peculiarities of the vibration waves' propagation during the springtime thawing of soils compared to those during the summertime period and the correlation of the vibrations with the under-rail basement modulus of elasticity are defined.     

Study on the sunny-shady slope effect on the subgrade of a high-speed railway in a seasonal frozen region

The temperature distributions of different parts of a subgrade were analyzed based on the results of three years of monitoring data from the Harbin-Qiqihaer Passenger Dedicated Line, a high-speed railway, including the slope toes, shoulders, and natural ground. The temperature variation with time and the maximum frozen depths showed that an obvious sunny-shady effect exists in the railway subgrade, which spans a seasonal frozen region. Development of frost heave is affected by the asymmetric temperature distribution. The temperature field and the maximum frozen depths 50 years after the subgrade was built were simulated with a mathematical model of the unsteady phase transition of the geothermal field.     

A method used to determine the upper thermal boundary of subgrade based on boundary layer theory

In the numerical simulation of long-term subgrade temperature fields, the daily variation of soil temperature at a certain depth h is negligible. Such phenomenon is called the "boundary layer theory."Depth h is defined as the boundary layerthickness and the soil temperature at h is approximately equal to a temperature increment plus the average atmosphere temperature. In the past, the boundary layer thickness and temperature increment were usually extracted from monitored data in the field. In this paper, a method is proposed to determinate the boundary layer thickness and temperature increment. Based on the typical designs of highway or railway, the theoretical solution of boundary layer thickness is inferred and listed. Further, the empirical equation and design chart for determining the temperature increment are given in which the following factors are addressed, including solar radiation, equivalent thermal diffusivity and convective heat-transfer coefficient. Using these equations or design charts, the boundary layer thickness and temperature increment can be easily determined and used in the simulation of long-term subgrade temperature fields. Finally, an example is conducted and used to verify the method. The result shows that the proposed method for determining the upper thermal boundary of subgrade is accurate and practical.     

东北黑土区土壤剖面地温和水分变化规律

东北黑土区土壤侵蚀的结果使土壤在坡面上发生再分配,土壤腐殖质层厚度的空间变异增大。腐殖质层厚度的变化又引起地温和土壤水分等土壤物理性质的变化,地温和水分是影响和反映冻融侵蚀作用的重要因子,也是影响地表和土壤剖面物质运移的重要因素。本文通过实测不同厚度腐殖质层剖面的地温和土壤水分,分析了地温和水分随时间和土壤剖面深度的变化规律。结果显示腐殖质层厚度对土壤温度和含水量有显著影响,腐殖质层较厚的剖面解冻速度比薄层黑土区要慢,不同深度土层温度到达0℃的日期也不相同,腐殖质层较厚的剖面冻结时间要滞后1周左右。同时,腐殖质层较厚的黑土区土壤含水量明显大于薄层黑土区,土壤水分运移的深度范围也大。     

Neumann stochastic finite element method for calculating temperature field of frozen soil based on random field theory

To study the effect of uncertain factors on the temperature field of frozen soil, we propose a method to calculate the spatial average variance from just the point variance based on the local average theory of random fields. We model the heat transfer coefficient and specific heat capacity as spatially random fields instead of traditional random variables. An analysis for calculating the random temperature field of seasonal frozen soil is suggested by the Neumann stochastic finite element method, and here we provide the computational formulae of mathematical expectation, variance and variable coefficient. As shown in the calculation flow chart, the stochastic finite element calculation program for solving the random temperature field, as compiled by Matrix Laboratory (MATLAB) software, can directly output the statistical results of the temperature field of frozen soil. An example is presented to demonstrate the random effects from random field parameters, and the feasibility of the proposed approach is proven by comparing these results with the results derived when the random parameters are only modeled as random variables. The results show that the Neumann stochastic finite element method can efficiently solve the problem of random temperature fields of frozen soil based on random field theory, and it can reduce the variability of calculation results when the random parameters are modeled as spatially random fields.     

古尔班通古特沙漠季节性冻土入渗特性试验研究

以古尔班通古特沙漠南缘融雪期冻结土壤入渗试验为依据,分析了沙漠地区季节性冻土水分入渗特性及主要影响因素.结果表明:沙漠地区季节性冻土具有较高的入渗能力,沙漠冻结风沙土的稳渗率为0.26～0.30 mm/min,是田间冻结壤土的10～20倍,可以保证融雪水及时入渗进入土壤,为融雪水的高效储存创造了有利条件.入渗能力随着土壤含水率的升高而减小.沙地土壤初始的低含水率、土壤大孔隙结构特征是沙地冻结土壤具有较高入渗能力的主要原因.研究结果为进一步研究春季融雪水在沙地的再分配过程奠定了基础.     

Study on potential evapotranspiration and wet-dry condition in the seasonal frozen soil region of northern Tibetan Plateau

This study was based on the CEOP/CAMP-Tibet observed data at AWS (Automatic Weather Station) of MS3478 in the seasonal frozen soil region of northern Tibetan Plateau from March 2007 to February 2008. The variation characteristics of PE (potential evapotranspiration) were analyzed based on the Penman-Monteith method recommended by FAO (the Food and Agriculture Organization of the United Nations). The contributions of dynamic, thermal and water factors to PE were discussed, and the wet-dry condition of the plateau region was further studied. The results indicated that daily PE was between 0.52 mm and 6.46 mm for the whole year. Monthly PE was over 107 mm from May to September, but decreased to less than 41 mm from November to February. Annual PE was 1,037.8 mm. In the summer, thermal PE was significantly more than dynamic PE, but conversely in the winter. Annual variation of thermal PE was of sine wave pattern. In addition, drought and semi-drought climate lasted for a long time while semi-humid climate was short. The effect of water and dynamic factors on PE varied considerably with the seasons. Annual variation of thermal PE was of sine wave pattern.     

Study on temperature field and settlement of thawing soil under static and dynamic loading

A series of tests were conducted to analyze temperature field distribution and thawing settlement of a thawing soil under static and dynamic loading at various cooling and thawing temperatures. The res...     

In-situ testing study on convection and temperature characteristics of a new crushed-rock slope embankment design in a permafrost region

For the purpose of enhancing air convection and controlling solar radiation, a new crushed-rock slope embankment design combined with a sun-shade measure is proposed. A newly designed embankment was constructed in the Tuotuohe section of the Qinghai-Tibet Railway and a field-testing experiment was carried out to determine its convection and temperature characteristics. The results show that distinct air convection occurred in the crushed-rock layer of the new embankment, especially in cold seasons, which was enhanced when it flowed upwards along the slope. This preliminarily indicated that the new design of the embankment slope was good for reinforcing air convection in the crushed-rock layer. The frequent fluctuations of the convection speed and the environmental wind speed were in good agreement, suggesting that the convection in the crushed rock primarily came from the ambient wind. It was also preliminarily determined that the new embankment had a better cooling effect and sun-shade effect for decreasing the temperature of the embankment slope compared with a traditional crushed-rock slope embankment, and the mean temperature difference between them was up to 1.7 °C. The mean annual temperature at the bottom boundary of the crushed-rock layer was obviously lower than that at the top boundary, and heat flux calculation showed that the shallow soil beneath the embankment slope was weakly releasing heat, all of which indicated that the new embankment slope design was beneficial to the thermal stability of the embankment. This study is helpful in providing some references for improved engineering design and maintenance of roadbeds in permafrost regions.     

Research on the temperature field of a partially freezing sand barrier with groundwater seepage

To study the distribution characteristics and variation regularity of the temperature field during the process of seepage freezing,a simulated-freezing test with seepage of Xuzhou sand was completed by using a model test developed in-house equipment.By means of three group freezing tests with different seepage velocities,we discovered the phenomenon of the asymmetry of the temperature field under the influence of seepage.The temperature upstream was obviously higher than that downstream.The temperature gradient upstream was also steeper than that downstream.With a higher seepage velocity,the asymmetry of the temperature field is more pronounced.The asymmetry for the interface temperature profile is more strongly manifest than for the main surface temperature profile.The cryogenic barrier section is somewhat"heartshaped".With the increasing velocity of the seepage flow,the cooling rate of the soil decreases.It takes much time to reach the equilibrium state of the soil mass.In our study,seepage flow velocities of 0 m/d,7.5 m/d,and 15 m/d showed the soilcooling rate of 4.35°C/h,4.96°C/h,and 1.72°C/h,respectively.     

基于MODIS和CloudSat的京津冀降水冰云季节分布特征

利用2008年9月～2016年8月Aqua MODIS和CloudSat卫星数据,筛选出京津冀地区的降水冰云,同时将其分为4个区域讨论,得到关于该地区降水冰云4个季节的分布特征,为该地区的人工影响天气提供依据。结果表明:京津冀整个地区的降水冰云在夏季的发生率都较高,且发生率有上升的趋势。从整个地区看来,京津冀地区的降水冰云的云顶高度在冬季最低、夏季最高,云顶温度的最小值在冬季最高、夏季最低;京津冀地区的降水冰云在春夏秋3季均以单层云为主,而在冬季则以双层云为主;京津冀地区的降水冰云的类型按春夏秋冬分别为7种、7种、6种和5种,且在夏季该地区的降水冰云以深对流云为主(占48.3%),而其他季节以雨层云为主;京津冀地区降水冰云微物理量(包括冰水含量、粒子数浓度、粒子有效半径)主要分布高度分别为0～13.5 km(春季)、3.5～17.0km(夏季)、1.0～14.0km(秋季)、0～11.0km(冬季)。冰水含量、粒子有效半径和粒子数浓度的分布高度和最大值均在夏季最高,但粒子有效半径在秋季最低,冰水含量和粒子数浓度在冬季最低。这3种微物理量随高度的分布特征夏季在京津冀各分区较为一致,都呈单...     

Simulation of frozen ground distribution in northeast China based on a surface frost number model

Journal of Geographical Sciences - Against the background of global warming, environmental and ecological problems caused by frozen ground degradation have become a focus of attention for the...     

三个全球气候模式对中国气温季节变化模拟能力的空间差异特征分析

针对第五次国际耦合模式比较计划（CMIP5）中3个全球气候模式对中国气温季节变化模拟能力的空间差异特征进行具体分析。结果表明：BCC-CSM1.1（m）模式和GFDL-CM3模式能够再现中国气温的季节性变化,在中国东部地区模拟能力较强,平均绝对误差和均方根误差均较小,在中国西部地区模拟能力较弱,平均绝对误差和均方根误差较大。与BCC-CSM1.1（m）和GFDL-CM3模式相比,HADGEM2-ES模式再现中国地区气温季节变化的能力最弱,平均绝对误差和均方根误差在西部部分地区、内蒙古地区和东北地区较大,在华南地区南部较小。在相同模式下,日平均气温模拟效果最好,其次是日最低气温,日最高气温模拟效果最差。纬度、经度、海拔和坡度对气候模式模拟效果的影响存在模式间的差异,而坡向和地形遮蔽度对模式的模拟效果无明显影响。     

基于MODIS的新疆地表温度时空变化特征分析

地表温度（LST）作为陆地环境相互作用过程研究中的重要地学参量,其时空分异与下垫面属性、地形地貌格局等息息相关。本文基于2000—2020年MOD11C3数据,采用GIS空间分析、空间重心模型及改进的半径法等手段,对新疆地区月、季、年及昼夜等序列时空尺度LST的分布特征及变化趋势进行研究,并借助LUCC、DEM等多源遥感数据进一步探讨各类下垫面、不同地貌单元及部分典型区域的LST垂直递减率、增减温及热（冷）岛效应等地理特征。结果表明：① 研究期间新疆年均LST为9.45 ℃,呈减温和增温趋势的区域分别占研究区面积的13.3%和86.7%,增温区域占绝大部分,故近20年研究区整体呈升温趋势（0.024 ℃·a^-1）,较全国高出约0.01 ℃·a^-1,其中春季增幅最大,冬季次之;夜间LST变化明显强于白天,春、夏两季昼夜温差均大于23.7 ℃,而冬季最小（约15 ℃）;研究区年际高、低温重心迁移轨迹大多分布于LST变幅较大区域,各月LST空间分布及高低温重心转移轨迹均表现出以7月为中点的年内强对称性规律。② 不同下垫面地表冷热环境空间分布差异较显著。其中以荒漠和裸土为主的未利用地年均LST最高（13.42 ℃）且昼夜温差最大（23.6 ℃）,高寒区冰川年均LST最低（-7 ℃）且昼夜温差（14.3 ℃）最小,其他下垫面年均LST在2.6~11 ℃之间,昼夜温差较小且较一致（平均16.75 ℃）。③ 东西走向的“三山夹两盆”地貌结构,使新疆LST的纬度地带规律被大幅削弱。研究区各山区（群）LST垂直递减率不尽相同,地处较高纬的阿尔泰山递变（0.63 ℃/100 m）最明显,山体高大的帕喀昆阿山群递变（0.57 ℃/100 m）次之,天山山脉递变（0.54 ℃/100 m）最小。另外各山区（群）山麓处均出现了不同程度的逆温现象,而山腰处LST垂直递减率线性拟合效果最佳。④ 本研究所选取的部分典型城市大都表现出不同程度的热岛效应。其中乌鲁木齐市热岛效应最为强烈,伊宁市其次,哈密市最微弱,而阿克苏市则表现出绿洲城市冷岛效应,但各城市热（冷）岛效应均存在一定环数（8环）范围的冷、热岛足迹。     

不同时间尺度、季节的气温数据空间平稳特征及其对插值结果的影响

不同时间尺度、季节的气温数据表现出不同的空间平稳特征。为探讨分析空间平稳性对气温插值的影响规律,采用趋势线法对气温数据进行空间平稳性探索,并对比分析不同空间平稳性条件下,普通线性回归、普通克里格、回归克里格的气温插值精度及插值结果的空间分布特点。结果显示：冬季日均、月均气温与年均气温呈现空间非平稳,插值精度随时间序列的增长而提高,随着气温数据逐渐趋于稳定,精度提高的幅度逐渐下降;夏季日均、月均气温呈现空间平稳,随时间序列的增长,插值精度的提高并不显著;夏季日均气温各插值方法的插值精度普遍高于冬季日均气温。与普通克里格相比,回归克里格能有效提高空间非平稳数据的插值精度。时间序列的增长削弱了不同插值算法之间的插值精度差异和插值结果空间分布差异。     

基于植被覆盖与生产力视角的亚喀斯特区域生态环境特征研究——以黔中部分地区为例

为了研究亚喀斯特区域的生态环境特征,以黔中部分地区为研究区,利用2010年的TM影像数据和MODIS-NPP影像数据,通过NDVI像元二分模型法和格网计算法,对比分析亚喀斯特与喀斯特区域的植被覆盖和净第一生产力,探讨不同区域的植被状况、土地承载力等生态特征.研究发现亚喀斯特区域有着不同于传统喀斯特区域的生态特征,在相同的土地利用类型条件下,前者具有更好的植被覆盖水平和净第一生产力,但其生态环境更易受到人类活动的干扰.因此区域的生态环境问题需要引起关注,并应采取针对性措施进行生态恢复和保护,提出生态发展策略,旨在对区域的生态环境研究更加深入,促进人地和谐发展.