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在岩石电阻率随压力变化的不同阶段,部份地减低轴向压力后再加压(每回总压降约为破坏应力的10%).研究这种特殊的加载方式下,即所谓应力反复对电阻率的影响.结果如下:(1)对高水饱和度岩石,随压力不断增加电阻率变化的总趋势为上升——平稳——下降的变化形态(包括饱和度为100——70%).对低饱和度岩石(实验中饱和度为70%和50%),电阻率变化的总趋势已改变.(2)对高饱和度岩石共作了十一次应力反复实验.除了水饱和度为71%的岩石在压力为30MPa 处,应力反复时电阻率无明显变化外,其余均呈现电阻率的负异常(下降幅度约2%左右),我国地电台在震前观测到的地电阻率变化以负异常为主.实验结果为解释这种负异常提供一种新的可能机制.(3)在电阻率随压力变化的下降段,特别是接近岩石破坏时,应力反复所引起的电阻率负异常与一般情况下出现的负异常相比,有以下三个特征:a)负异常的幅度要大一个数量级(约-20%);b)不仅应力下降时电阻率下降,而且应力恢复时电阻率仍然下降;c)各个方向电阻率变化的差别很大(约10%).以上这三个特征可作为岩石临近破坏的标志.而一般的电阻率负异常可能只与应力反复有关,并不意味着岩石处于临近破裂的危险状态.(4)低饱和度岩石,应力反复可能引起电阻率的正异常.作者还用 相似文献
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单轴压力下有补给水岩石电阻率变化各向异性研究 总被引:18,自引:1,他引:18
将两种规格的长方体水饱和花岗岩标本,以标本一个面的中心点为中心,对称布置成互成45°角的4条对称四极法电阻率测线。标本电极面和相邻面的一小部分用防水环氧胶密封,使标本在装有水的承压水箱中,沿标本长轴方向受压,观测标本视电阻率随压力的变化。实验结果为:(1)有补给水实验与无补给水实验,电阻率变化整体形态相似,即电阻率随压力的变化先上升,后下降,但有补给水实验的电阻率下降幅度要大一些。(2)电阻率变化出现明显的方向性,可以用电阻率变化最大的各向异性主轴方向表示;实验中,用4条测线、4种组合(每3条测线组合可以确定1个视电阻率变化各向异性主轴方向)方法确定的4个电阻率变化各向异性主轴方向基本一致。(3)加压期间,电阻率各向异性主轴方向随压力增加发生变化,这种变化不是渐变和乱变,而是有规律的跃变,即整个实验过程,多数标本只跃变1—3次,每次跃变形成一个主方向,在主方向内,角度变化不大。(4)有补给水岩石电阻率变化整体形态与美国Brace等(1968)所作的围压和孔隙压的岩石电阻率变化形态相似。 相似文献
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从电阻率的角度研究岩石裂隙介质的各向异性特征是一种方便而有效的方法,但多限于空间单个点上的测量数据分析.通过在砂岩岩样上的饱水与排水实验以及同步进行的高密度电阻率成像监测,探讨了应用高密度电阻率成像法获得图像研究岩石各向异性特征的可能性,分析了饱水与排水过程中岩石电阻率在不同方向上的响应特性.结果表明,电阻率成像法在分析岩石裂隙介质的各向异性方面具有多方向成像和动态监测的优点,可以通过对不同方向上获得的电阻率图像的分析,提取出岩石沉积结构的空间分布模式,清晰地反映出岩石在饱水和排水过程中电阻率变化空间分布模式的各向异性特征. 相似文献
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在3种非含岩成分造成的岩石原始电阻率各向异性标本(在采集和加工过程中,标本完整性遭 到破坏的标本),和一种由含岩成分形成的 岩石原始电阻率各向异性标本上,布设多个电极,并将标本用水饱和. 然后用多电极组合法 ,将己布电极组合成不同方向、不同极距的电阻率各向异性测线. 采用单轴压缩、低围压 三 轴压缩和剪切3种加载方式,对标本进行动态电阻率变化实验. 观测标本电阻率随承载力的 变化. 实验结果表明∶对于岩石原始电阻率各向异性标本,在电阻率变化各向异性方面,与 岩石 原始电阻率各向同性标本相似,即∶裂隙和破碎带通过区域的测点,视电阻率变化各向异性 结果好,4种组合求得的4个各向异性主轴方向趋向一致,且与破碎带方向基本吻合;裂隙 和破碎带不经过区域的测点,4个视电阻率变化各向异性主轴方向不一致,或者根本求不出 各向异性解. 这后一种情况,在裂隙面平行测量面时,表现最为明显. 相似文献
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我国50多年的视电阻率连续观测结果表明,大地震前近震中区域的视电阻率呈现出与主压应力方位有关的各向异性变化,即:垂直于主压应力方向观测的变化幅度最大,平行方向最小或不明显,斜交方向介于二者之间.目前我国定点台站视电阻率观测的探测范围主要在浅层沉积层以内,通常含有较多的含水裂隙.本文将地下岩土介质简化为由固体基质和含流体/气体裂隙组成的固液气三相介质,且基质、流体和气体具有标量形式的电阻率,推导出了包含基质和流体电阻率、裂隙率、饱和度和裂隙面积率因子的电阻率张量表达式.以裂隙的扩展/闭合表示应力作用下裂隙的变化,得到了电阻率随裂隙变化的微分形式,电阻率变化对裂隙体积变化放大系数的表达式和裂隙横向变化对纵向电阻率影响的横向权系数的表达式.在此基础上得到了介质电阻率和视电阻率的各向异性变化特征:对于含水裂隙介质,无论裂隙如何变化,均是最小主轴方向电阻率的变化幅度大于其他方向;对于含水孔隙介质,沿孔隙主要变化方向的主轴电阻率变化幅度大于其他方向.对于各向异性变化,视电阻率和介质电阻率存在π/2的方向差异.相较于含水岩石,无水岩石介质电阻率的各向异性变化不显著.本文提出的电阻率表达式可以对实验室和野外实际观测的许多结果做出合理的解释.
相似文献7.
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本文先研究了矿井中岩体(或矿体)和混凝土胶结充填试件受力作用下地电阻率(s)年变化的方向性.结果表明,平行压力方向的地电阻率年变化幅度最小,垂直压力方向则最大,与压力方向成45夹角的则介于二者之间.根据此结果,我们统计了全国98个地电台的地电阻率资料,并将中国大陆按应力场方向划分为三大应力场区:1.中国西部应力场区,其方向为近南北向;2.中国北部应力场区,其方向为近北东向;3.中国东南部应力场区,其方向为近东西向.因此,可以利用同点三向等极距地电阻率年变化法来测量当时当地不同方向的应力场作用. 相似文献
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用实验模拟动态岩石的破裂和摩擦滑动过程 ,观测其电阻率变化形态 ,研究电阻率变化与岩石受力的关系 ,国内外的学者曾做过大量实验研究工作 (北京大学地球物理教研室地电组 ,兰州地震大队报室 ,1 978;张同俊 ,1 981 ;陈大元等 ,1 983;赵玉林等 ,1 983;张金铸 ,陆阳泉 ,1 983;张天中等 ,1 985;Brace,Orange,1 968;Kurite,1 986;Teisseyre,1 989) .在实验中 ,学者们发现岩石在受力破裂过程中 ,不光其电阻率形态变化显著 ,而且其方向变化也很明显 .不少学者对电阻率变化的方向性产生了浓厚的兴趣 ,开展了一些这方面的研究工作 . 80年代初 ,陈… 相似文献
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M. N. French R. L. Bras W. F. Krajewski 《Stochastic Environmental Research and Risk Assessment (SERRA)》1992,6(1):27-45
A procedure for short-term rainfall forecasting in real-time is developed and a study of the role of sampling on forecast ability is conducted. Ground level rainfall fields are forecasted using a stochastic space-time rainfall model in state-space form. Updating of the rainfall field in real-time is accomplished using a distributed parameter Kalman filter to optimally combine measurement information and forecast model estimates. The influence of sampling density on forecast accuracy is evaluated using a series of a simulated rainfall events generated with the same stochastic rainfall model. Sampling was conducted at five different network spatial densities. The results quantify the influence of sampling network density on real-time rainfall field forecasting. Statistical analyses of the rainfall field residuals illustrate improvement in one hour lead time forecasts at higher measurement densities. 相似文献
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《地震工程与工程振动(英文版)》2014,(4)
正This journal is established by the Institute of Engineering Mechanics(IEM),China Earthquake Administration,to promote scientific exchange between Chinese and foreign scientists and engineers so as to improve the theory and practice of earthquake hazards mitigation,preparedness,and recovery.To accomplish this purpose,the journal aims to attract a balanced number of papers between Chinese and 相似文献
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George W. Housner 《地震工程与工程振动(英文版)》2008,7(2):I0001-I0001
Destructive earthquakes have caused great damage in China and the United States and collapsing buildings havecaused many deaths and injuries. The field of earthquake engineering studies earthquake hazards, the occurrence ofearthquakes of various magnitudes, the nature of the ground shaking during an earthquake, the vibration of structuresduring earthquakes, the strengthening of existing structures and the design of new structures to be earthquake resistant,and finally, how to cope with earthquake damage and restore a city to normal functioning. Such efforts are in progressin both countries, but unfortunately, the language barrier interferes with the free flow of information between China andthe Untied States. It would be mutually beneficial if some means could be developed to promote the exchangeof information across the Pacific Ocean. This new journal has been established for this purpose and its success willbe an important step in promoting earthquake engineering in China and the United States. 相似文献
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《国际泥沙研究》2014,(4)
正President:Giampaolo Di Silvio,Italy Vice Presidents:Ulrich C.E.Zanke,Germany Zhao-yin Wang,China The World Association for Sedimentation and Erosion Research(WASER),inaugurated on Oct.19,2004,is an independent non-governmental,non-profit organization.The mission of WASER is to promote international co-operation on the study 相似文献
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JianCheng Shi 《中国科学:地球科学(英文版)》2014,57(10):2281-2282
正Global Change includes climate change and other environmental changes caused by the joint interaction among various layers of Earth. From the positive side, global change provides new opportunities to human and other living forms on Earth. In the meantime, it creates tremendous challenges and negative impact. At present, the negative impacts have reached all primary processes of the global ecosystem and every aspect of human society, especially causing degradation of the ecosystem. For instance, intensive deforestation causes decline of biodiversity; global warming causes sea level rise and increases 相似文献
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O. Martins 《水文研究》1988,2(1):19-29
Water quality analyses for the Niger River for the 1980/81 hydrological year are presented. The samples were collected from the main river at Lokoja, and from two main tributaries, the Kaduna and the Benue Rivers. Different water types were distinguished by the concentrations of major ions. The type Ca > Na > Mg > K - HCO3 > SO4 > Cl was represented at all stations during at least part of the year. Chloride was found to dominate the sulphate ion in the Kaduna and Niger, while the Benue maintained a higher concentration of sulphate relative to chloride all year round. Distinct patterns of seasonal variation in the ion concentrations were observed, particularly for the samples collected at Lokoja. Low ion concentrations were prominent during periods of high discharge, while low flow periods coincided with high dissolved ion concentrations. The contribution of rainwater to the total dissolved solids in the river waters was assessed indirectly using rainwater chemistry data from the Gulf of Guinea. The estimated rainwater contribution to the Lower Niger amounts to 5.15 mg 1?1. Geochemical weathering calculations involving reactions of the four major minerals of granitic rocks - anorthite, biotite, albite, and K-feldspar - with carbon dioxide and water, can account for the average water composition of the Lower Niger. The proportion of the ionic components was also related to the occurrence of the respective element in the minerals. 相似文献