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笔者根据在全国各地进行的数十座水利工程的原位测试资料,概括归纳出一套较为系统的应用自然电场法检测土坝渗漏隐患的技术,该技术将集中渗流在自电电位曲线上的反映归结为窄幅异常、宽幅异常、宽幅双峰异常、多峰异常和塔式异常五种基本形态,并可正确地判断正常渗漏和异常渗漏,解释推断出集中渗漏带的宽度、埋深、走向以及渗流的时空动态,为工程除险加固提供可靠的技术资料. 相似文献
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地电场是重要的地震前兆物理场,其观测数据包含了自然电场、大地电场和干扰成分.自然电场源于地下介质的物理、化学过程,通常具有相对稳定性;大地电场则来源于空间电流和潮汐力,较稳定的日变形态主要表现出TGF-A、TGF-B两种波形.依据地电场的潮汐机理,邻近大水域的场地,潮汐力作用于岩石裂隙,易使裂隙水周期性渗流,产生周期性过滤电场,形成TGF-A波形地电场;空间Sq电流在地表的感应电场易引起裂隙水周期性渗流,进而产生大地电流场,使地表出现TGF-B波形地电场.以层状介质为例,设上层介质电阻率为p1,厚度为h1;水渗流层的电阻率为ρ2,厚度为h2;下层是不导电介质. 相似文献
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首先回顾了中国大陆地区震前自然电场前兆特征研究的发展历程.着重论述了震前自然电场的范围、形态、时间、与震级统计关系等前兆特征;指出震前自然电场产生的几种机理:过滤电场、扩散--吸附电位、电化学电位、机电转换效应以及压力作用下黄土层自然电位的变化;分析了自然电场是多种电信号叠加而成的一个综合电位,趋势性背景、季节性变化、地震信号和干扰因素都会引起岩石电阻率、土壤中溶液的溶解度和电离度、地下水的渗透条件、大地电场和自然电场的一系列变化.而面导电机制、体导电结构的变化造成宏观电阻率各向异性的增强并形成各测点间的电位异常,其形成机理和电磁响应特征的研究都能较好地认识地震前兆. 相似文献
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以中国大陆一百个地电场台站的数据为分析基础,将潮汐地电场分类为近正弦形的TGF-A型和近梯形的TGF-B型.TGF-A型地电场与固体潮汐密切关联,基本分布在大面积水域附近,并与附近水域面积和距离、岩性结构、构造活动等因素有关.TGF-B型地电场与气潮作用产生的空间Sq电流关系密切,并与岩石饱和度、渗透率等有关.TGF-A型波形畸变揭示了岩石所受应力可能出现变异,导致岩石裂隙水周期性渗流突变;TGF-B型背景值跃变可能是岩石微破裂加剧导致地下水向破裂区渗流.两类潮汐地电场变异的机理可能是地电场数据应用于强震短临分析的理论基础. 相似文献
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土石坝渗漏问题是制约水库大坝安全运行的重要隐患,准确查明大坝渗漏的病因以及靶区的空间展布是有的放矢实施加固的关键.针对土石坝隐患的空间位置信息多变、周围介质复杂等难点,单一探测手段在识别病灶方面存在误判、漏判等问题,考虑到电阻率对水敏感的特点,提出联合并行电法和瞬变电磁法优化诊断土石坝渗漏隐患的思路.为查明戴家坞水库渗漏的病灶,利用并行电法快速获得大坝坝体段不同高程下的二维视电阻率图像,分析比较了AMN、MNB以及AMN&MNB装置的反演结果,还采用瞬变电磁法对大坝两坝肩并行电法盲区部位进行补充探测,并依据成果进行防渗处理.试验结果表明,并行电法有效指示出大坝坝体段的渗流异常,综合多剖面异常信息能追踪到渗漏路径;AMN&MNB装置的反演结果有效吸收了AMN、MNB的局部高分辨的优势,对大坝边界以及隐患规模的细节刻画更清晰;结合二次场响应曲线和视电阻率图像,瞬变电磁法很好揭示出大坝坝肩K0-005～0+002 m段的渗漏通道,同时有效规避了硬化路面电极接触不良的难题.经对综合推断隐患区进行灌浆处理,大坝渗漏量明显降低,从而佐证了两种方法优化联合的可行性.研究成果可为水库大坝隐患的全面、精细探查提供技术支撑. 相似文献
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2007年西昌和天祝地电场观测台阵建立, 随后两年西昌台阵地电场的TGF-A波形明显, 天祝台阵则以TGF-B波形出现. 台阵内各台站间地电场相关性高, 这受地电场潮汐机理的支持; 不同台站或同一台站的不同方向地电场潮汐波峰谷值差异明显, 地电场潮汐机理和场地水文地质资料表明, 这主要与岩石、 裂隙度、 裂隙优势走向、 含水度、 透水率、 水矿化度和裂隙水压力差等因素相关. 潮汐电信号形成于裂隙水或水中电荷周期性移动, 电荷被岩壁吸附或脱离产生噪声, 该信噪比在同一台阵内基本相同, 信噪比值与潮汐电信号产生过程和场地电磁背景关系密切. 应用地电场潮汐谐波振幅计算裂隙水主体渗流方向, 结果与应用潮汐波峰谷值法基本一致, 这消除了峰谷值法取值的偶然误差. 2008年汶川MS8.0地震前, 两台阵内都存在场地裂隙水主体渗流方向的短临变异现象, 西昌台阵这种变异更明显. 相似文献
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无基坑振冲加密施工是一种比较先进的土石坝建筑方法。以海南省三亚市西部的宁远河中下游河段的大隆水利枢纽工程土石坝为研究对象,对其进行准确分区,以饱和-非饱和渗流理论为基础,通过三维有限元数值方法,模拟库水下降作用下的土石坝渗流场,并对各级水位下的孔压、流速及流向进行分析,评价大坝的渗流安全。研究结果表明：采用无基坑振冲加密施工方法后,坝体内填砂砾振冲层形成上游排水通道,在坝前水位骤降工况下,防渗土料内有效流速方向和渗透压力的方向由近水平的指向坝面变为竖直向下指向填砂砾振冲层,而且有效流速明显变大,利于渗透水通过填砂砾振冲层排到下游,有利于上游坝体稳定。 相似文献
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A hydrogeophysical survey is performed at small earthen dam that overlies a confined aquifer. The structure of the dam has not shown evidence of anomalous seepage internally or through the foundation prior to the survey. However, the surface topography is mounded in a localized zone 150 m downstream, and groundwater discharges from this zone periodically when the reservoir storage is maximum. We use self‐potential and electrical resistivity tomography surveys with seismic refraction tomography to (1) determine what underlying hydrogeologic factors, if any, have contributed to the successful long‐term operation of the dam without apparent indicators of anomalous seepage through its core and foundation; and (2) investigate the hydraulic connection between the reservoir and the seepage zone to determine whether there exists a potential for this success to be undermined. Geophysical data are informed by hydraulic and geotechnical borehole data. Seismic refraction tomography is performed to determine the geometry of the phreatic surface. The hydro‐stratigraphy is mapped with the resistivity data and groundwater flow patterns are determined with self‐potential data. A self‐potential model is constructed to represent a perpendicular profile extending out from the maximum cross‐section of the dam, and self‐potential data are inverted to recover the groundwater velocity field. The groundwater flow pattern through the aquifer is controlled by the bedrock topography and a preferential flow pathway exists beneath the dam. It corresponds to a sandy‐gravel layer connecting the reservoir to the downstream seepage zone. 相似文献
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引起大地电场变化的一些因素 总被引：3，自引：0，他引：3
对河北省4个电场台站3年多的大地电场资料进行了全面的分析、整理,总结出引起大地电场变化的一些因素,这对我们认识资料有所帮助。对分析和利用大地电场资料有一定意义。 相似文献
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针对地震(或静力)液化作用对尾矿坝渗流场和孔压分布的影响进行研究,基于多孔介质渗流理论,考虑到尾矿坝渗流特性,编写分析程序SAFTD。根据程序假设的初始浸润面,通过调整浸润面处网格迭代求解最终浸润面的位置,选取一个经典算例验证程序的可靠性。针对典型的上游法尾矿库,采用SAFTD程序分析液化前后尾矿坝的渗流场与孔压分布特征。数值模拟结果表明,液化后尾矿坝的浸润面中间部分发生明显抬升,而在入渗点处和出渗点附近变化不大;液化后尾矿坝的孔压明显增加,坝体内部孔压增大约18%~280%,最大的孔压增量发生在初期坝的右下部,数值模拟结果与Ishihara对Mochikoshi 2号坝的分析结果相似。 相似文献
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Seepage driving effect on deformations of San Fernando dams 总被引：2，自引：0，他引：2
In the process of flow deformation of an earth dam, the seepage force inside the dam plays a role as a driving force. The seepage force acts just like the gravitational force in terms of pushing soils away from their original locations after liquefaction is triggered. This paper draws attention to this seepage driving effect by presenting a set of fully coupled finite element analyses on the well-known San Fernando dams, with the objective of evaluating the impact of this seepage effect. The results indicate that while this effect is always there, its practical significance depends on a number of factors. In the case of the upper San Fernando dam, which experienced a significant, but restricted, downstream movement during the 1971 earthquake, the seepage driving effect was indeed significant. On the contrary, for the lower dam, which failed and slid into the upstream reservoir during the same earthquake, this seepage effect was relatively less pronounced. The detailed results of the analyses reveal the likely mechanisms of failure and deformation of the two dams and the likely cause behind the difference between their responses during the earthquake. 相似文献
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《Journal of Applied Geophysics》2011,75(4):277-286
Self-potential (SP) and electrical resistivity measurements are used to investigate seepage at a remote moraine dam in the Sierra Nevada of California. The site is a small terminal moraine impounding roughly 300,000 m3 of water at ~ 3400 m a.s.l. Suspicious fine sediment in a small lake at the dam's downstream toe prompted initial concerns that anomalous seepage may be eroding matrix material from the moraine. 235 individual SP measurements covering the surface of the dam were collected in order to investigate electrokinetic current sources resulting from seepage, while resistivity soundings probed moraine stratigraphy and suggest that the till contains interstitial ice. Contoured SP data reveal a non-uniform voltage distribution over the moraine dam and two distinct negative SP anomalies. The first, located in the central area of the moraine, shows a broad negative SP zone around the crest and increasingly positive SP moving downhill towards both the upstream and downstream toes. This anomaly can be explained by shallow gravitational groundwater flow in the near subsurface combined with upward groundwater flux through evapotranspiration; numerical simulation of the combined effect matches field data well. The second SP anomaly has a tightly localized distribution and can be explained by vertically descending flow into a bedrock fault conduit. Our conceptual seepage model suggests that flow travels from Dana Lake first at the boundary of ice-filled moraine and bedrock before converging on a concentrated channel in the subvertical fault zone. Positive SP near the dam abutments results from groundwater inflow from adjacent hillslopes. Combined analyses suggest that seepage erosion is not currently affecting the moraine dam, and that the sediment observed on the bed of the downstream toe lake is likely a remnant of past outflow events. 相似文献
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Takeshi Hashimoto 《Island Arc》2001,10(3-4):306-317
Abstract A resistivity survey method using artificial telluric noise was examined and applied to a field of a fault zone. The electric earth current was measured at 50 sites in the Nojima Fault zone, which is in the northwestern part of Awaji Island, southwestern Japan. The dominant component of the observed electric field is supposed to be leakage currents from DC electric railways running outside the island. Amplitude and polarization of the stray current were systematically investigated and were revealed to represent the subsurface electrical structure of the study area. Some features on the fault zone's electrical structure have been pointed out, including: (i) an electrical boundary that corresponds to a geological one between granite (resistive) and sediments (conductive); and (ii) a low resistivity spot on the surface rupture of the earthquake fault. The structure estimated in the present study is both qualitatively and quantitatively consistent with previous resistivity surveys done using other methods pursued in the same area. It shows the validity of the 'stray current method' as one that is easy and uses low-cost resistivity exploration tools in a region where the effect of artificial noise caused mainly by leakage currents from electrical railways cannot be ignored. 相似文献
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基于渗流-应力耦合分析的野鸡尾尾矿坝稳定性研究 总被引：1，自引：0，他引：1
基于渗流场与应力场耦合机理,对柿竹园野鸡尾尾矿坝进行稳定性研究。研究渗流-应力的耦合效应,提出了渗流-应力耦合以及渗流体积力计算的实施方案;建立二维的有限元渗流-应力耦合计算模型,分析了考虑耦合效应时的尾矿坝渗流场、位移场、应力场;最终分析了不同耦合关系对于渗流量、位移场、等效渗透集中力以及应力场的影响。研究结果表明：当前水力条件下,尾矿坝稳定性良好;尾矿坝主要受水平渗透力作用,初期坝坝顶、坝脚以及坝底等处应力集中;尾矿坝的渗流-应力作用不容忽视,不同的耦合关系对于x方向位移、渗透力的预测影响巨大;考虑渗流-应力耦合关系得到的主应力、剪应力以及竖向位移,比不考虑耦合效应时大。 相似文献