加载速率对岩石材料力学行为的影响

 加载速率会造成岩石材料破坏形态的改变,材料破坏过程中存在塑性向脆性转变的临界速率。在颗粒流程序下,通过Fish语言编程,虚拟实现岩石数值试件,并进行0.000 5,0.001 0,0.005 0,0.050 0 m/s四个加载速率下的单轴压缩数值试验。分析加载速率对岩石破裂形态、裂纹数量和扩展、应力–应变曲线和能量转换的影响。发现：加载速率的增加破坏优势剪切带的发展,使得剪切带等速发展,材料呈现锥形破坏;加载速率的增加使得材料的力学性能表现出极大的伪增强,材料更破碎,能量损失增大,这与材料吸收和破坏消散能量的能力有关。     

Three-Dimensional Nonlinear Analysis for the Cooling Characteristics of Crushed-Rock Interlayer Embankment with Ventilated Duct along the Qinghai-Tibet Expressway in Permafrost Regions

The crushed-rock embankment and duct-ventilated embankment have been used as effective cooling measures to protect permafrost underlying the Qinghai-Tibet Railway from thawing in China. These two cooling techniques are not directly applied to the Qinghai-Tibet Expressway, however, due to the large width and higher temperature of pavement surface. Therefore, considering the heat transfer characteristics of crushed-rock interlayer embankments and duct-ventilated embankments, we designed the crushed-rock interlayer embankment with ventilated duct. For cold regions engineering projects, the thermal regime is the most important factor that determines the stability of construction. To investigate the thermal stability of this new type of embankment, a three-dimensional numerical model was developed based on heat and mass transfer theory. The model includes coupled heat transfer between the airflow and the duct wall, air convective heat transfer within the crushed-rock interlayer, and heat conduction with phase change in the soil layer. The computational results indicated that the numerical model can reasonably solve the coupled heat and mass transfer for the crushed-rock interlayer embankment with ventilated duct. Based on an assumption that the mean annual air temperature will increase by 2.6°C in the next 50years, it was determined that in areas where the mean annual air temperature is currently ?4.0°C, the crushed-rock interlayer embankment with ventilated duct can be an effective measure to decrease the underlying ground temperature and ensure the stability of the Qinghai-Tibet Expressway in permafrost regions.     

A simple interpretation of the surface temperature/vegetation index space for assessment of surface moisture status

A simplified land surface dryness index (Temperature–Vegetation Dryness Index, TVDI) based on an empirical parameterisation of the relationship between surface temperature (T_s) and vegetation index (NDVI) is suggested. The index is related to soil moisture and, in comparison to existing interpretations of the T_s/NDVI space, the index is conceptually and computationally straightforward. It is based on satellite derived information only, and the potential for operational application of the index is therefore large. The spatial pattern and temporal evolution in TVDI has been analysed using 37 NOAA-AVHRR images from 1990 covering part of the Ferlo region of northern, semiarid Senegal in West Africa. The spatial pattern in TVDI has been compared with simulations of soil moisture from a distributed hydrological model based on the MIKE SHE code. The spatial variation in TVDI reflects the variation in moisture on a finer scale than can be derived from the hydrological model in this case.     

Uncertainties of thermal boundaries and soil properties on permafrost table of frozen ground in Qinghai-Tibet Plateau

In the permafrost regions of the Qinghai-Tibet Plateau(QTP),the permafrost table has a significant effect on the stability of geotechnical engineering.The thermal boundaries and soil properties are the key factors affecting the permafrost table.Complex geological environments and human activities can lead to the uncertainties of thermal boundaries and soil properties.In this paper,an array of field experiments and Monte Carlo(MC) simulations of thermal boundaries and soil properties are carried out.The coefficient of variation(COV),scale of fluctuation(SOF),and autocorrelation distance(ACD) of uncertainties of thermal boundaries and soil properties are investigated.A stochastic analysis method of the probabilistic permafrost table is then proposed,and the statistical properties of permafrost table on the QTP are computed by self-compiled program.The proposed stochastic analysis method is verified with the calculated and measured temperature observations.According to the relationship between ACD and SOF for the five theoretical autocorrelation functions(ACFs),the effects of ACF,COV,and ACD of soil properties and the COV of thermal boundaries on the permafrost tables are analyzed.The results show that the effects of different ACFs of soil properties on the standard deviation(SD) of permafrost table depth are not obvious.The SD of permafrost table depth increases with time,and the larger the COVs of thermal boundaries and soil properties,the deeper the SD of permafrost table;the longer the ACD of soil properties,the shallower the SD of permafrost table.This study can provide a reference for the stability analysis of geotechnical engineering on the QTP considering the uncertainties of thermal boundaries and soil properties.     

大通河源区冻土地温模拟与分类特征分析

以大通河源区为研究区域,分析了植被对多年冻土分布的影响.以等效高程为基础,根据实测的多年冻土地温数据和植被调查数据,建立了不同植被类型条件下的冻土地温-等效高程关系模型.借助于TM遥感数据、DEM数据和GIS技术模拟了大通河源区植被覆盖区的多年冻土地温分布特征.以地温数据为基础,参照青藏高原多年冻土分带方案,对多年冻土的分类特征进行了研究.结果表明:大通河源区多年冻土年均地温为-8.66～1.72℃,多年冻土和季节冻土的面积比例分别为95%和5%,其中极稳定型、稳定型、亚稳定型、过渡型和不稳定型多年冻土各类型的面积比例依次为1%,12%,31%,35%和16%.     

Orchard identification using landform and landscape factors based on a spatial–temporal classification framework

Ecological restoration measures have been undertaken in loess hilly and gully regions since the 1970s to prevent soil loss and to improve the ecological environment in those regions. Orchard construction was the main ecological measure undertaken in the Luo-Yu-Gou watershed, and in this article we propose a coupled maximum a posteriori decision rule and Markov random field (MAP-MRF) framework for orchard identification based on landform and landscape factors. Support vector machine (SVM) classification was first performed to obtain initial classification results for the years 2003 and 2008. A series of factors including landform factor, landscape factor, and the spatial–temporal neighbourhood factor are used to obtain land-cover change information including the change in orchard class. Finally, field experiments were carried out in the case study region of the Luo-Yu-Gou watershed, and based on the experimental results, it was found that the quantity error and the allocation error of the classification results for 2008 were 0.0441 and 0.1037, respectively.     

Cooling processes and effects of crushed rock embankment along the Qinghai–Tibet Railway in permafrost regions

Crushed rock embankment (CRE) was most prevalent embankment structure with cooling measures along the Qinghai–Tibet Railway in permafrost regions. Ground temperature dataset from embankment construction (in 2002) to 2010 at nine monitoring sites along the railway were compiled to study long term cooling processes and cooling effects of CRE. Monitoring results indicated that the heat stored in filling materials could dissipate out in two cold seasons after embankment construction. Under cooling effect of CRE, permafrost tables beneath CRE moved upwards significantly during the first three years after embankment construction and then maintain almost constant. But underlying permafrost experienced different thermal process in relative warm and cold permafrost regions. In cold regions, underlying permafrost up to 14 m in depth experienced considerable cooling trends during the first five to sixth years after embankment construction. While in warm regions, the uppermost permafrost layer warmed after upwards movement of permafrost table, and underlying deep permafrost had no obvious cooling trends with time. Finally, differences in freezing and thawing seasons of, and differences in ground thermal regimes of cold and warm permafrost regions were investigated based on ground temperature from natural borehole. Then, the different cooling effects of CRE in two regions were interpreted based on these differences.     

青藏冻结黏土滞回曲线形态特征的定量研究

 滞回曲线的形态特征包括不闭合程度、宽窄程度、向应变轴的整体倾斜程度、密集程度和面积,采用残余应变?p、滞回曲线的短轴与长轴之比?、滞回曲线长轴的斜率k、相邻滞回曲线中心点之间的距离d和滞回曲线所围成的面积S五个参数定量表征滞回曲线的上述形态特征。对不同负温条件下的冻结青藏黏土进行动三轴试验,分析滞回曲线的形态特征,结果表明：同一级动荷载下,?p,?,k,d和S随振次的增加变化不大,因此,可以采用各参数的平均值来反映各级加载下滞回曲线的形态特征;随着动应变幅的增加,?p,?,d和S逐渐增大,k逐渐减小,即滞回曲线越来越不闭合、越来越宽、向应变轴整体越来越倾斜、越来越疏松、面积也越来越大,表明土的残余塑性应变、黏滞性、细观损伤程度和能量耗散越来越大,刚度越来越小。     

Layered titanosilicates JDF-L1 and AM-4 for biocide applications

JDF-L1 and AM-4 are porous layered titanosilicates that can be modified by ion exchange while keeping the crystallinity. In this study, JDF-L1 and AM-4 were exchanged with Ag⁺, Zn²⁺ and Cu²⁺ ions and characterized by XRD and TEM. JDF-L1 exchanged titanosilicate preserved the crystalline structure while AM-4 exchanged titanosilicate showed a certain loss of crystallinity. In the case of Ag-exchanged samples, the Ag nanoparticles were distributed at the edges of the JDF-L1 crystals whereas they were distributed around the AM-4 particles. The antimicrobial activity was tested with Staphylococcus aureus. All the exchanged titanosilicates showed good antimicrobial activity against the bacteria and the most active was Ag–AM-4.