电导率法在海水入侵监测中的应用

海水入侵是人类不合理开采地下淡水而导致的一种环境恶化的地质灾害，其发生过程是一个可监测和可预报的过程。目前海水入侵的监测方法主要为物探和水化学方法，本文讨论了电导率法在海水入侵实际监测中的原理及应用。     

Hydraulic anisotropy characterization of pneumatic-fractured sediments using azimuthal self potential gradient

The pneumatic fracturing technique is used to enhance the permeability and porosity of tight unconsolidated soils (e.g. clays), thereby improving the effectiveness of remediation treatments. Azimuthal self potential gradient (ASPG) surveys were performed on a compacted, unconsolidated clay block in order to evaluate their potential to delineate contaminant migration pathways in a mechanically-induced fracture network. Azimuthal resistivity (ARS) measurements were also made for comparative purposes. Following similar procedures to those used in the field, compressed kaolinite sediments were pneumatically fractured and the resulting fracture geometry characterized from strike analysis of visible fractures combined with strike data from optical borehole televiewer (BHTV) imaging. We subsequently injected a simulated treatment (electrolyte/dye) into the fractures. Both ASPG and ARS data exhibit anisotropic geoelectric signatures resulting from the fracturing. Self potentials observed during injection of electrolyte are consistent with electrokinetic theory and previous laboratory results on a fracture block model. Visual (polar plot) analysis and linear regression of cross plots show ASPG lobes are correlated with azimuths of high fracture strike density, evidence that the ASPG anisotropy is a proxy measure of hydraulic anisotropy created by the pneumatic fracturing. However, ARS data are uncorrelated with fracture strike maxima and resistivity anisotropy is probably dominated by enhanced surface conduction along azimuths of weak ‘starter paths’ formed from pulverization of the clay and increases in interfacial surface area. We find the magnitude of electrokinetic SP scales with the applied N₂ gas pressure gradient (ΔPN₂) for any particular hydraulically-active fracture set and that the positive lobe of the ASPG anomaly indicates the flow direction within the fracture network. These findings demonstrate the use of ASPG in characterizing the effectiveness of (1) pneumatic fracturing and (2) defining likely flow directions of remedial treatments in unconsolidated sediments and rock.     

Aquifer Transmissivity and Basement Structure Determination Using Resistivity Sounding at Jos Plateau State Nigeria

A geoelectric investigation involving twenty-six vertical electrical soundings was carried out at Jos, Plateau State, North Central Nigeria. The survey was aimed at determining the structure of the underlying bedrock, as well as computing the transmissivity for the aquifer in the area. The basement geometrymapproduced from the results of the survey indicates that the bedrock is undulating lying at depths between 30 m to 6.5 m. There is evidence of faulting and fracturing within the area. Computation of aquifer transmissivity values based on the results obtained made it possible to demarcate regions with good ground water potential in the area.     

海滨垃圾填埋场渗滤液污染土壤的复电阻率特性

为了解渗滤液污染土壤的复电阻率特性及其与海水入侵所造成的电特性差异,指导海滨场地的污染探测,设计了黏土和砂土两种土壤,在水饱和情况下通入不同浓度的渗滤液,测量复电阻率的幅值和相位响应;在砂土中通入与渗滤液电阻率相同的模拟海水,对比海水入侵与渗滤液污染所造成的相位差异.结果表明:受渗滤液污染土壤的复电阻率变化明显,0.1 Hz下被2%渗滤液（渗滤液体积占溶液总体积比例为2%）污染的土壤中,与背景值相比,黏土的幅值和相位分别降低了78%和70%,砂土的幅值和相位分别降低了66%和33%,且渗滤液浓度越高,幅值和相位的值就越小;而对于电阻率背景值较低的土壤（如海水入侵场地或地下水-海水交错带区域）,通入渗滤液后,其复电阻率参数没有明显变化.对比海水入侵与渗滤液污染,受渗滤液污染较轻的土壤的相位略高于海水入侵污染土壤,而当渗滤液浓度较高时,二者几乎没有区别.研究显示,正常条件下,复电阻率法对渗滤液污染的反映灵敏,有较好的指示意义,其参数变化主要与孔隙水中金属离子的含量和双电层极化有关;而在天然低电阻率背景条件下,渗滤液污染引起的电阻率变化很小,但相位变化较为明显,这种相位的变化有可能被识别出来.      

高密度电法在采空区勘测中的应用

通过一工程勘测实例,分析了高密度电法中常用的Wennerα装置和四极测深装置(Wenner-Schlumberger)的适应特征.认为,勘测浅层(如15m内)的采空区或地质灾害异常体时,以四极测深装置为好,对深层(如50m以上)则用Wenner装置为好.地层性质和饱水状态不同地区所测的视电阻率,即使在同一深度(或层位)上,其所表达的意义是不同的,不能用这种资料来作平面等值线图并以此图件来寻找采空区或其它地质灾害异常体.     

高电阻率收尘极板的实验研究

用电阻率较高的非金属材料制作电收尘器的收尘极板收尘,对于比电阻低于10~4Ω·cm的烟尘,能有效地克服积尘的跳跃式二次飞扬。对于比电阻为10~8Ω·cm左右的氧化铝粉尘,在工业现场实验,收尘效率达98.5％;对于比电阻为10~(13)Ω·cm左右的莹石粉尘,采用比电阻为10~(10)Ω·cm左右的混凝土极板,实验室实验,电晕电流正常,未观察到反电晕现象,推断存在“受抑制”的尘层间隙放电。     

大地介质极化率和二次场衰减特性时序观测与研究

大地介质极化率和二次场衰减特性时序观测是探索介质新的电性参数作为前兆观测项目的研究课题。经两年的观测研究发现,极化率存在年变化形态;主要研究的放电时段应放在１０～１００ｍｓ范围;在观测时段（１９９４ ０３～１９９５ １１）内台站３００ｋｍ范围发生的唯一一次大于５．０级的苍山５．２级地震（△３０４ｋｍ）前,极化率参数异常不明显,而极化率衰减度在该次地震前出现异常,衰减曲线极大值位移、曲线畸变、半衰时亦出现高值。对比地电阻率与极化率衰减度和半衰时的观测数据,在苍山５．２级地震前异常时间同步,呈低电阻率、高衰减度、高半衰时变化。研究结果表明应用介质新电性参数极化率作为前兆观测项目是可行的。     

土桥3.4级地震与榆树台地电阻率异常回顾

回顾了1994年11月24日榆树市土桥镇东发生3.4级地震的情况;简要介绍了榆树台的基本情况;分析了土桥地震的宏观异常以及波及的范围;本文同时还解析了此次地震前榆树台地电阻率异常表现及其方法.     

低品位硫铁矿烧渣制备导电掺合料

采用川南低品位硫铁矿烧渣为主要原料,利用其中的高铁含量及大量活性烧粘土组分,通过在还原气氛下将硫铁矿烧渣与少量还原剂混合粉磨均匀后成型焙烧这一最优工艺,制备电阻率较低的具有胶结性质的导电掺合料,研究了温度、保温时间、配合比、粉磨细度等关键参数对电阻率的影响。结果表明:还原剂为混合料质量分数的9.1%(还原剂与烧渣比值=0.1),5～30 MPa成型后在800℃高温中焙烧60 min,可制备出电阻率为2.02Ω.m的导电掺合料。该方法不仅能解决川南硫铁矿烧渣的综合利用问题,而且工艺流程简单,产品附加值高。     

Geomorphological and geophysical approach for locating favorable groundwater zones in granitic terrain, Andhra Pradesh, India

The increasing demand for fresh water has necessitated the exploration for new sources of groundwater, particularly in hard rock terrain, where groundwater is a vital source of fresh water. A fast, cost effective and economical way of exploration is to study and analyze remote sensing data. Interpreted remote sensing data was used to select sites for carrying out surface geophysical investigations. Various geomorphologic units were demarcated and the lineaments were identified by interpretation of remote sensing satellite images. The potential for occurrence of groundwater in the watershed areas was classified as very good, good, moderate and poor by interpreting the images. Sub-surface geophysical investigations, namely vertical electrical soundings, were carried out to delineate potential water-bearing zones. Integrated studies of interpretation of geomorphologic and geophysical data were used to prepare a groundwater potential map. The studies reveal that the groundwater potential of shallow aquifers is due to geomorphologic features and the potential of deeper aquifers is determined by lineaments such as faults and joints.