Vertical Electrical Sounding of Water-Bearing Sub-Surface of Issele-Azagba in Southern Nigeria

An electrical resistivity survey involving vertical electrical sounding (VES) technique was carried out in Issele-Azagba, Aniocha North Local Government Area of Delta State, Nigeria. This was aimed at investigating the lithologic boundaries and classification of the various subsurface formations. The data obtained were subjected to a twofold interpretative procedure involving initial partial curve matching and computer iteration. Results showed that a maximum of five subsurface layers was delineated from the geoelectric sections. This is made up of loamy topsoil underlain by relatively continuous sandy units composed of different compaction, wetness and clay content. The result also showed that the fifth substratum of the geoelectric section was the aquiferous sand relevant in groundwater development within the study area. Analysis of the result had shown that the aquifers identified in this study were vulnerable contamination percolating from the surface due to the absence of a protective aquitards.

Electrical Resistivity Sounding for Groundwater Investigation around Enugu Metropolis and the Environs, Southeast Nigeria

This report evaluates the use of electrical method and borehole data to investigate the subsurface to delineate the groundwater potential in Enugu metropolis and the environs, south-eastern Nigeria other than rely only on resistivity method which could lead to interpretation error. Integrating these 2 data sets is key in this study. The study area is located in the Anambra Basin and is underlain by Nkporo/Enugu Shale which is overlain by the Mamu Formation. It is bounded by Latitudes 6°2 0'00"N to 6°30'00"N and Longitudes 7°25'00"E to 7°35'00"E and covers surface area of about 342 m2. Thirty-one vertical electrical soundings (VES) were carried out across the area using the Schlumberger electrode array with current electrode separation from 2 to 500 m to identify the depths and resistivity values of the identified geo-electric layers. Through data analysis using WinResist software, the apparent resistivity, thicknesses and depths and the thicknesses of the aquifers were generated. The resistivity and depths were modelled to generate resistivity map and depth map. The resistivity of the aquiferous zone within the study area varied from 20.55 - 427.8 ohm-m at depths of between 10.7 - 40.05 m. Depth to the water table appears to be shallow at the south western part of the map. The interpreted geo-electric layers show a sequence of lateritic top soil, shale, sand and shale. The frequency distribution of the VES curves generated shows the presence of 3 to 5 layers with HK type as the highest. Also, a 2D model was generated using the correlation of VES to VES data and borehole data to VES data to show the underlying stratigraphy beneath the study area as well as the direction of ground water flow. Result of the VES curve analysis reveals that the sub-surface is underlain by three lithological layers namely: lateritic top soil, shale, sand and shales with NW direction of groundwater flow from the 2D model. Groundwater prospective zones can be seen along NW, SW and central parts of the study area which have low resistivity values.

Determining the Basaltic Sequence Using Seismic Reflection and Resistivity Methods

This study was carried out in Harat Rahat (south of Almadinah Almonwarah) using seismic reflection and resistivity methods. The main objectives of this study are to determine the extent of the basaltic layer and to define the subsurface faults and fractures that could affect and control the groundwater movement in the study area. A 2D seismic profile was acquired and the result shows that the subsurface in the study area has a major fault. We obtained a well match when the seismic result was compared with drilled wells. As a complementary tool, the resistivity method was applied in order to detect the groundwater level. The results of the resistivity method showed that six distinct layers have been identified. The interpretation of these six layers show that the first three layers, the fourth layer, the fifth layer and the bottom of the section indicated various subsurface structures and lithologies;various basaltic layers, fractured basalt, weathered basement and fresh basaltic layers, respectively. It is obvious that the eventual success of geophysical surveys depend on the combination with other subsurface data sources in order to produce accurate maps.

基于边缘滤波法检测的光纤光栅声波传感研究

针对裸光纤光栅在声波作用下的应变灵敏度过低导致难以检测到有效反射波长变化的问题,文章提出以光纤光栅纵向传感为模型,并在光栅周围涂上一层厚度远超光纤内径的低杨氏模量圆柱状涂覆层,以增加光纤光栅的应变灵敏度,并用相移光栅反射谱的线性区作为边缘滤波法边缘来提高激光检测的灵敏度,利用传输矩阵法仿真分析光栅反射谱及激光反射率曲线。仿真结果表明,声波纵向传感模型的应变灵敏度要优于横向传感模型,且低杨氏模量的涂覆层可以显著提高光栅的应变灵敏度,在频率低于1.7 kHz的声波作用下,涂有聚氨酯涂覆层的光纤光栅纵向传感灵敏度达到了6.1 nm/MPa,是裸光纤光栅的381倍,结合相移光栅反射谱线性区综合灵敏度提升2203.6倍,有效地提升了光纤光栅在声波检测方面的灵敏度。

液下泵内部非定常流动及噪声特性

为研究液下泵内部流动的非定常特性及噪声规律,通过采用计算流体动力学软件ANSYS CFX15.0与LMS Virtual.lab声学仿真软件相结合的一种间接混合计算方法,对液下泵内部流场及其声场进行求解.在该计算方法中,对流场进行求解得到监测点的非定常压力脉动,从而获得非稳态的压力脉动频域特性规律;基于声学边界元法,对液下泵蜗壳偶极子内场噪声和叶片偶极子内场噪声进行求解,获得了边界元表面的声压级分布以及典型场点的声压频率曲线.计算结果表明:叶片扫掠过程中与蜗壳隔舌的相互作用产生较大的压力脉动,隔舌附近的噪声是流动噪声的主要噪声源;声压级在叶片通过频率及其谐频时达到极大值,随频率的增大,声压级极大值都呈现衰减状态.研究结果可为液下泵的后续降噪分析提供一定的理论基础.

基于多普勒天气雷达的低空多普勒速度的切变识别算法研究

低空风切变是影响航空器起飞和着陆安全的重要因素,利用多普勒天气雷达径向速度数据,从风的空间和时间变化上对低空风切变的识别进行了研究,并利用一次飑线过程和一次低空急流过程的资料对识别算法进行了验证。识别算法的核心是分别计算二维合成风切变、垂直风切变和时间风切变。在计算二维合成风切变时,先利用风切变强度因子自适应地选择拟合"窗口"的大小,再利用最小二乘线性拟合方法,得到水平风切变。结果表明:自适应多尺度最小二乘法得到的合成风切变,在低空风切变识别效果、切变连续性和边缘数据处理等方面都优于我国多普勒天气雷达的PUP合成风切变;垂直风切变反映了雷达径向速度的高低空配置情况;时间风切变可提供径向速度随时间的变化情况。算法还可应用于民航机场低空风切变的识别和预警。

电离层高精度高频多普勒频移参量的时域探测方法

针对电离层数字测高仪垂直探测中频域探测方法的不足,利用电离层回波信号相位测量分析和运算处理算法,开发并实现了一种时域探测方法,用于实时获取高精度高频多普勒频移信息.实验观测表明:新发展的电离层时域探测方法可以实时获得高精度高频多普勒频移参量,能够满足电离层小尺度扰动观测研究需要.

垂直电测深二维反演中非均匀初始模型的给定

为了提高垂直电测深二维反演的收敛速度和反演精度,给出了利用直接反演公式确定初始模型的方法。在直接反演过程中,通过综合利用三次样条求导法、五点求导法和列维尔插值计算电测深曲线在每个极距处的梯度,并对直接反演结果进行深度校正,获得了更准确的反演结果,为二维反演提供了较好的初始模型。通过对模拟和实测电测深数据进行反演试算,验证了采用直接反演法给定非均匀初始模型的可行性和有效性。

预应力桥梁波纹管注浆质量检测

针对目前混凝土桥梁预应力波纹管注浆质量检测方法中的不足,提出采用低频声波沿波纹管纵向穿透法对波纹管注浆质量进行检测。通过室内测试试验,研究了波纹管注浆浆体的龄期(强度)、梁体混凝土龄期(强度)等因素对检测波速的综合影响。并基于声波在介质中的传播机理,构造波纹管注浆密实度与波的传播参数间的关系模型,经试验梁检测,表明模型与检测结果有较好的符合性。

综合物探解释在路面沉陷研究中的运用

采用多种地球物理勘探方法可以有效减少推断解释的多解性,提高解释准确性,借助高密度电法、垂向视电阻率测深和地震映像法对公路路面沉降的地质原因进行了综合分析和解释,基本查清了勘区内的地层结构、岩性接触带和异常分布空间特征,分析了构造的走向以及所影响的地层,并根据地震映像资料推测一处近地表塌陷区域,为公路路面沉降的治理提供了可参考的依据。

直流电测深法与中心回线瞬变电磁法联合反演

分析了直流电测深法(VES)与中心回线瞬变电磁法(TEM)对地层的响应特征,结果显示:TEM对低阻层反应灵敏,而VES对高阻层具有较高的分辨能力。基于TEM与VES对地层响应特征互补的特点,尝试将TEM与VES数据进行联合反演,模型试算结果表明,联合反演的效果明显比单一方法反演的效果好。

浅海环境中应答器法测量水下平台声目标强度的理论分析

应答器法是在浅海环境中测量水下运动平台声目标强度的常用方法。根据简正波理论分析浅海点源声场的空间特性,指出不同号简正波之间的相互干涉是导致声场空间起伏的主要原因。对基于应答器法的水平平均测量法(HAM法)进行了理论分析,并提出一种新的浅海环境中水下运动平台目标强度的测量方法,即垂直平均测量法(VAM法)。对比了HAM法和VAM法的有效性、物理意义、试验效率和技术难度,分析表明二者物理意义相同,VAM法比HAM法具有更高的有效性和试验效率,不过其技术难度更大。

直流电阻率法检测垂直铺膜深度问题研究

为了研究垂直铺塑防渗工程防渗膜检测中不同铺膜深度的电测深曲线特性,通过室内试验对若干组饱和砂土层垂直铺设不同深度防渗膜的简化模型运用直流电阻率法进行测量。结果表明,膜上土表处测点垂直膜走向测线的电测深曲线在每一层土的探测范围内表现出等梯度变化的特征,且各段的梯度与膜的铺设位置有密切的对应关系。

高频大地电磁法与电测深法结合在广东地区找热水的应用

为了提高应用地球物理方法指导地热资源开发的准确性,提出了将高频大地电磁法与电测深法结合,高频大地电磁法反映中深部地质为主(为主要方法),电测深法反映中浅部地质为主(为辅助方法)。将反映浅部和深部的物探方法相结合进行勘探,可以弥补不同方法各自的缺陷,减少多解性的风险,以达到更精确地指导孔位的效果。运用该组合方法在广东省清远市地热资源项目开展野外试验,利用野外实践成果直接指导钻孔的布置,通过实际钻孔验证表明该组合方法是有效可行的,在生产实践中值得推广。

基于MATLAB的直流电测深最优化反演法

在水平或近水平层状地层条件下,直流电测深的视电阻率可以近似表述为离散形式。为了便于电测深的解释工作,本文采用最优化反演法。根据实测数据,给出初始模型参数即层数、各层电阻率和厚度,推导出电阻率转换函数,计算理论视电阻率值,直接拟合实测视电阻率,计算拟合程度。在MATLAB开发环境下设计了可视化程序,操作简便,人机交互良好,可以很好地实现正演理论模拟,同时可以实现反演过程,拟合曲线效果可以实时显示。应用表明,该反演程序可以得到良好的结果,拟合精度达到要求。

五极纵轴激电测深法在划分岩性、含水层埋深中的应用

五极纵轴激电测深法常用来探测一些非层状地质体,并且具有较高的分辨率、设备简单、异常明显、分层详细、精度较高、曲线简单、解释简单等优点。通过对河南省南部某地区的土地整治项目机井工程的探测,进而了解五极纵轴激电测深法在岩性区分、含水层埋深的应用效果。

视电阻率垂向电测深在无锡市地质环境勘查中的应用

在城市中,存在着大量的多物理属性背景干扰,其中以地质发育,工业、民用电磁信号,城市噪声等为主要影响。视电阻率垂向电测深方法具有垂直方向分辨率高、装置简易、工作效率高的优点被广泛应用于城市地质环境勘查。本次在无锡市完成3条总长3160 m的测线E1、E2、E3,结合以往的勘查以及对异常区的钻探验证,结果显示在勘查区存在2条断层F1、F2,并且在垂向划分了岩层,确定了富水区域,取得了优良的应用效果,为无锡市地质环境评价提供了参考依据。

探测井下气层的VSP法方案

泥浆浸泡作用能提高井壁岩石的纵波声速,但只对含气岩石的作用明显。采用VSP 法对已受泥浆浸泡接近饱和的井壁岩石纵波声速和未受泥浆浸泡的深入井壁稍远的岩石纵波声速进行比较,从而得以明确气层在该井深处是否存在。

四极电阻率垂向测深法在评价土对钢结构腐蚀性中的应用分析

针对现行《岩土工程勘察规范(2009版):GB 50021-2001》未明确土对钢结构的腐蚀性评价指标中土壤视电阻率的具体测定方法,介绍了四极电阻率垂向测深法测定土壤视电阻率的原理,然后根据在珠三角地区两个地埋钢管工程中的实际应用情况,对案例的实测数据进行了比较和分析总结。实践表明,四极电阻率垂向测深法所测得的土壤视电阻率数据是基本可靠的,其在土对钢结构的腐蚀性评价中具有较高的应用价值,建议可作为土对钢结构腐蚀性评价指标中土壤视电阻率测定的主要方法。