岩石非线性黏弹性蠕变特性的时温等效效应     

朱元广  刘泉声  张程远  时凯 《岩土力学》2012,33(8):2303-2309

岩石的时温等效效应是指岩石在低温、长时间尺度下与在高温、短时间尺度下的流变力学特性等效的效应。利用岩石的时温等效效应,可以通过提高试验温度方法得到岩石在相对低温下的长期流变力学特性。为研究岩石在非线性黏弹性条件下的时温等效效应,基于Schapery单积分型的非线性本构方程,得到了岩石非线性黏弹性蠕变力学特性时温等效效应的数学表示。根据不同应力及温度下花岗岩的蠕变试验结果,设定20 ℃为参考温度,考虑温度改变对岩石瞬时蠕变柔量的影响,得到了垂直移位因子随温度的变化规律及修正后的蠕变柔量的时间对数曲线;对修正后的曲线进行水平移位使得相邻温度曲线之间相交于一点,得到不同应力下蠕变柔量的主曲线及水平移位因子的变化规律;主曲线中相邻温度曲线之间的一致性较好,进一步验证了花岗岩时温等效效应的存在性。通过对不同应力下的垂直移位因子和水平移位因子的变化规律分析,发现应力为40～60 MPa之间的非线性并不明显,但到87 MPa,非线性特性明显增强。  相似文献   

微型抗滑桩土拱效应空间特征的细观力学分析   总被引：1，自引：0，他引：1  

姜春林  李晋 《岩土力学》2012,33(6):1754-1760

目前研究中大多将土拱效应简化为平面应变问题,而微型抗滑桩由于桩径小,在承担滑坡推力时将发生较大的变形,其土拱效应的产生和发展具有明显的三维空间特征,目前的研究方法难以考虑这一问题。为此采用基于离散单元法的颗粒元程序PFC3D,利用平行黏结模型建立微型抗滑桩进行分析。模拟结果显示,微型抗滑桩系统中土拱主要出现在接近滑面的深部和中部土体中,浅部土体中土拱受到桩身位移的影响无法成型,且桩间以水平土拱为主,桩长和桩身刚度对微型抗滑桩系统的土拱分布影响不大;随着桩间距的增加,土拱的形成受到显著影响。  相似文献   

基于自平衡试桩法大直径嵌岩桩尺寸效应分析   总被引：2，自引：0，他引：2  

龚成中  何春林  龚维明  戴国亮 《岩土力学》2012,33(8):2403-2407

基于自平衡测试技术,通过现场的原位测试方法,对大直径嵌岩桩的尺寸效应进行了研究,内容包括桩径尺寸和嵌岩深度变化以及桩端阻力尺寸效应的影响分析等。从测试结果来看,嵌岩桩也存在一定程度的尺寸效应现象。当其他条件一定时,随着桩径的增大,桩侧阻力存在着减小现象;在同一种岩层的情况下,随着嵌岩深度的增大,桩侧阻力发挥也并不相同,嵌岩深度越大,桩侧阻力发挥也越小。实测结果表明,桩周岩石的特性变化对桩侧阻力影响最大,岩石抗压强度越高,桩侧阻力也越大。此外,桩径的变化对桩端阻力的影响更为明显。因此,在大直径嵌岩桩的设计中应注意尺寸效应对桩基承载力的影响。  相似文献   

Variability and management patterns of range resources in the Baro River plain, Ethiopia     

Daniel Kassahun  Soloman Afsaw 《Area》2008,40(1):108-116

The biophysical environment of rangelands in the arid and semi-arid lowland parts of Africa is customarily viewed as a homogenous entity. Such notion has encouraged employing a blanket management approach. However, there are perceptible variations within them which necessitate site-specific range management. This study has attempted to identify the variability of soil and forage attributes and assess the existing management practices of those resources in the Baro River plain, Ethiopia. Sample transects, representing pre- and post-fire conditions, were used to collect composite soil samples and vegetation attributes. Alongside the physical survey, a household survey was undertaken to validate the laboratory-generated information. The result showed significant differences of soil and forage attributes among different management regimes, distances from river course and dominant cover types. In general, the distribution of soil nutrients showed a 'distance decay effect', while the distribution of pH showed the reverse pattern. Application of heavy fire load and congested grazing are the principal range management related factors. About 80 per cent of sample pastoralists employ heavy fire without due consideration for the sustainability of the range resource and without considering the local variability. Recognition of site-specific information is the key to effective management of range resources in the study area.  相似文献   

广西崇左市可持续综合发展及对策初探   总被引：2，自引：0，他引：2  

张健  濮励杰 《地理研究》2008,27(4):938-948

以我国西部新兴边贸城市崇左市为研究区域,根据社会经济发展、资源—能源消耗及环境污染的相互关系,结合生态学表现,利用三角模型工具分析评估区域经济可持续发展状况和长期趋势。探求崇左市1985~2005年可持续综合利用情况,对研究区经济发展现状问题的解决具有实用价值,对区域经济的可持续综合利用具有方法论意义。结果表明2005年崇左市可持续综合发展处于一般可持续性状态,且区域内7个行政子单元可持续综合发展水平介于弱可持续性到一般可持续性状态,东南部可持续综合发展状况优于西北部。崇左市可持续综合发展水平1985~1990年呈一般可持续性趋势;1991~1995年呈强可持续性趋势;1996~2000年呈一般可持续性趋势;2001~2005年呈一般可持续性趋势,但较前一阶段有下降趋势。这些状况和趋势与近20年间崇左市大力发展经济,加大环境保护力度有一定关系。  相似文献   

长三角地区经济极化过程与空间演变分析   总被引：2，自引：0，他引：2  

叶磊  欧向军 《地理科学进展》2012,31(12):1668-1677

在经济极化研究的基础上, 首先利用ER指数和TW指数对长三角1990-2010 年的经济极化趋势进行测度, 从整体上把握区域经济极化的演变过程;其次, 选取1997、2001、2006 和2010 年这4 个典型年份, 从极化效应与扩散效应的角度对长三角地区的经济极化过程进行科学分析, 总结其空间格局的演化规律。研究发现:①从极化指数的动态演变过程来看, 长三角地区的经济极化水平在1990-2010 年间呈现出波动上升的变化趋势, 并通过极化的初始定义对上述论断进行了验证;②从极化理论的两大效应来看, 长三角地区的极化效应在研究时段内经历了一个先扩大再缩小的变化过程, 而其扩散效应在研究时段内是逐渐增强的;③从经济极化的空间格局来看, 长三角地区在近10 多年的时间里呈现出“箭头”型-“Z”字型-“M”字型-“区”字型的变化过程, 未来借助相关基础设施束扩散效应的增强, 本地区空间格局有望向网络型转变。  相似文献   

曲率半径对大温差地区小半径曲线梁桥地震响应影响分析          下载免费PDF全文

丁万鹏  虞庐松  李子奇  王力 《地震工程学报》2022,44(1):93-99

为研究曲率半径和近断层脉冲效应对大温差地区小半径曲线梁桥在地震作用下的动力响应和碰撞效应的影响规律,以某大温差地区曲线梁桥为研究对象,建立不同曲率半径的全桥非线性有限元模型,考虑温度变化对支座性能和伸缩缝间距的影响,开展桥梁地震响应分析.结果表明:随着主梁曲率半径增大,墩底内力响应逐渐增加,邻梁间碰撞效应逐渐增强;温度...  相似文献   

A qualitative study of seismic-ionospheric precursor phenomena monitored by a very close to the epicenter VLF and LF receiver     

《Physics and Chemistry of the Earth》2015

This work investigates the occurrence of disturbances across a wide range of VLF and LF frequencies received prior to a seismic event (Mw = 4), that took place on May 12th 2012, the epicenter of which was very close (14 km) to the VLF/LF station. The signals analyzed were emitted from five VLF and five LF European transmitters. This seismic event produced precursory ionospheric disturbances, identified as spectral distortion, three days before its occurrence, providing a distinct pattern open to further investigation. Although the basis of the ionosphere interaction with seismic phenomena has been well documented in previous studies, the close proximity of the receiver to the seismic event provides a new perspective to this study. The monitored signals have undergone normalization and then they have been processed by means of the Hilbert-Huang Transform. Diagrams of the signals relevant to the phenomena are presented and the disturbances that are present in the raw data are accentuated through further processing.  相似文献   

Application of Advanced Oxidation Processes for Polycyclic Aromatic Hydrocarbons Removal from Municipal Treatment Sludge          下载免费PDF全文

Gizem Karaca  Yücel Tasdemir 《洁净——土壤、空气、水》2015,43(2):191-196

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Radiofluorescence of quartz: A review     

《Quaternary Geochronology》2015

Radiofluorescence (RF) is the luminescence emitted during exposure to ionizing radiation. Charged particles or high-energy photons can be used as stimulation sources, and different designs for measurement equipment have been published. Only few studies have successfully used the quartz RF signal for dosimetry and dating. However, RF is a valuable tool in deciphering charge trafficking in quartz crystals, and also provides information for identifying types of defects causing specific luminescence emissions. Based on models for charge transfer in quartz, RF is seen as resulting from direct recombination of electrons with holes captured in recombination centers (or vice versa) during ionizing irradiation. Competition between reservoir and luminescent centers explains the initial decay of the modeled RF curve followed by a steady rise and also the observed ‘pre-dose’ effect. Emission spectra have been found to be similar to thermoluminescence (TL) spectra, with prevalent emissions in the UV and further emissions for some samples in the blue-green and red range. The high intensity levels and the possibility of choosing longer accumulation times compared to TL and OSL are advantages of RF for spectral measurements. Relative peak intensities in the emission spectra change with dose and absolute intensities with dose rate. Investigating the RF signal with changing measurement temperature allows calculating physical parameters of individual emissions that control thermal quenching. The degree of thermal quenching varies between the emissions, with most intense quenching in the UV. Sensitization of RF by several orders of magnitude has been observed after annealing at 500 °C.  相似文献