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1.
通过电阻率原位测试和室内土工试验,研究黏性土电阻率特性及电阻率与岩土参数的相互关系。在武汉市轨道交通7号线勘察过程中,沿轨道走向,在长江一级阶地共布置完成电阻率测井22组,并于测井位置采取原状土样进行常规土工试验、无侧限抗压试验、直剪快剪试验及三轴UU试验。通过研究发现:黏性土电阻率随含水量及孔隙比的增加而增加,随无侧限抗压强度增加而减小。根据黏性土三轴UU试验结果,其电阻率随黏聚力、内摩擦角的增加而减小。通过拟合,给出了黏性土电阻率与岩土参数间的经验公式,其相关性显著。  相似文献   

2.
A combination of vertical electrical soundings (VES), 2D electrical resistivity imaging (ERI) surveys and borehole logs were conducted at Magodo, Government Reserve Area (GRA) Phase 1, Isheri, Southwestern Nigeria, with the aim of delineating the different aquifers present and assessing the groundwater safety in the area. The Schlumberger electrode array was adopted for the VES and dipole-dipole array was used for the 2D imaging. The maximum current electrode spread (AB) was 800 m and the 2D traverse range between 280 and 350 m in the east-west direction. The thickness of impermeable layer overlying the confined aquifer was used for the vulnerability ratings of the study area. Five lithological units were delineated: the topsoil, clayey sand, unconsolidated sand which is the first aquifer, a clay stratum and the sand layer that constitutes the confined aquifer horizon. The topsoil thickness varies from 0.6 to 2.6 m, while its resistivity values vary between 55.4 and 510.6 Ω/m. The clayey sand layers have resistivity values ranging from 104.2 to 143.9 Ω/m with thickness varying between 0.6 and 14.7 m. The resistivity values of the upper sandy layer range from 120.7 to 2195.2 Ω/m and thickness varies from 3.3 to 94.0 m. The resistivity of the clay layer varies from 11.3 to 96.1 Ω/m and the thickness ranges from 29.6 to 76.1 m. The resistivity value of the confined aquifer ranges between 223 and 1197.4 Ω/m. The longitudinal conductance (0.0017–0.02 mhos) assessment of the topsoil shows that the topsoil within the study area has poor overburden protective capacity, and the compacted impermeable clay layer shows that the underlying confined aquifer is well protected from contamination and can be utilized as a source of portable groundwater in the study area. This study therefore enabled the delineation of shallow aquifers, the variation of their thicknesses and presented a basis for safety assessment of groundwater potential zones in the study area.  相似文献   

3.
高精度测定渗透系数（K）的重要性不言自明,但是现阶段野外试验手段能够提供的关于K的信息不能满足高度非均质地层中污染物迁移预测模拟的需求。直接推进注入记录器(Direct Push Injection Logger, DPIL)和直接推进渗透仪(Direct Push Permeameter, DPP)是新发展的水文地质参数测量仪器,能够使K值的测定达到前所未有的分辨率和成本效益水平。工具向地下推进过程中,通过对注水量、注水压力和其它的水文地球物理参数的同步监测,直接推进技术(Direct Push, DP)能快捷准确地获得地层渗透系数的垂向分布。DP技术几乎适用于所有野外松散地层,并且对场地的干扰很小。因此,它克服了许多基于既有井的传统含水层测试方法的局限性。最近在美国MADE试验场的一个案例研究表明,使用DPIL/DPP可以获得空间分辨率达15cm的K值垂向分布。未来,高精度直接推进技术还可以与新一代的地球物理技术,例如高精度探地雷达相结合,以实现不同位置DP测定K值的互联以及整个试验场K值三维分布的确定。  相似文献   

4.
Seawater intrusion is a major problem in urbanized coastal regions of India which is due to over exploitation of groundwater for various purposes. This study was carried out with the objective of assessing the zone of mixing between seawater and groundwater in the coastal aquifer in south of Chennai, Tamil Nadu, India using high resolution electrical resistivity tomography. High resolution electrical resistivity tomography was carried out in five profiles perpendicular to the sea using IRIS make SYSCAL Pro-96 system with 2.5 m or 5 m inter-electrode separation. The maximum length of the profile was 170 m which resulted in a depth of investigation of 28.7 m. The apparent resistivity measured in this area varies from 0.3 ohm-m to 30,000 ohm-m. The apparent resistivity of saturated zone decreases towards the sea, indicating the influence of seawater. This was also confirmed by measuring the electrical conductivity of groundwater, which gradually increases from 156 μS/cm to 3430 μS/cm towards the sea. Further, the concentration profiles of electrical conductivity, sodium, chloride and chloride / bicarbonate ratio are compared with the high resolution electrical resistivity tomography profile. The distance of influence of seawater is comparatively high in northern part than in southern part of the area. The high resolution electrical resistivity tomography was effectively used to determine the effect of seawater mixing with groundwater.  相似文献   

5.
Vertical electrical soundings technique was used to evaluate the aquifer characteristics and distribution in the northern part of Paiko in Nigeria. A total of thirty vertical electrical soundings were carried out using ABEM SAS4000 Terrameter, and the data was analyzed both manually and with software (Resist software). The result revealed the aquifer resistivity and thickness to vary from 10.9 to 80,368 Ωm, and 1.06 to 72 m, respectively. Also, hydraulic conductivity ranges from 0.010267 to 41.61928 m/day while transmissivity values range from 0.035215 to 70.09302 m2. The hydrogeological maps (hydraulic conductivity and transmissivity image maps) showed the variations of these parameters in the study area and that the southwestern part of the area has prolific aquifer.  相似文献   

6.
Surface geophysics and a priori information were employed to delineate the subsurface geology at Idi-oro in Abijo, Ibeju Lekki area of Lagos, Nigeria for foundation investigation purpose. Resistivity measurement was conducted using 1-D and 2-D resistivity probing techniques. The resistivity measurements were made with ABEM tetrameter model SAS 1000 system. The 1-D vertical electrical resistivity sounding data were obtained using the Schlumberger electrode array while the 2-D resistivity data were obtained using the dipole–dipole array. The interpreted results revealed three to five subsurface geological layers. This is made up of the top soil with resistivity values that vary from 132.4 to over 2,313.5 Ω?m and thickness values that range from 0.3 to 4.8 m, the fine sand with resistivity values that vary from 221.0 to 3,032.7 Ω?m and thickness values that range from 0.4 to 5.5 m, the medium sand with resistivity values that vary from 202.8 to 1,247.7 Ω?m and thickness values that range from 4.9 to 58.4 m. On the other hand, the clayey sand has the resistivity values that vary from 146.1 to 1,744.0 Ω?m and thickness values that vary from 2.2 to 26.3 m, while the coarse sand has resistivity values that vary from 238.3 to 14,313.9 Ω?m but with no thickness value because the current terminated in this layer. The resistivity data correlate well with borehole logs. On the whole, it is concluded that the investigated area has competent sand layer that can support medium to giant engineering structures with resistivity values that vary from 202 to 14,314 Ω?m and thickness values that vary from 0.8 to 58.4 m.  相似文献   

7.
The Service National des Ressources en Eau (SNRE) of the Ministry of Agriculture of Haiti, in cooperation with the UNDTCD, carried out a geophysical investigation in the Northern Plain of Haiti. It included a reinterpretation of the available resistivity soundings and the realization of eight additional soundings and 11 electromagnetic profiles. The mathematical interpretation of the soundings permitted the determination of the true resistivity of different lithologies present in the area and the mapping of the thickness of the alluvial aquifer. The results of the five electromagnetic resistivity profiles in the Trou du Nord area are presented, with a total lenght of 17.4 km. They show distinctive resistivity anomalies, which are assumed to represent buried river channels filled with coarse sands and gravels. One of the anomaly zones was explored in more detail and shows clearly lateral resistivity differences at greater depths. The data interpretations have been checked through response calculations of geoelectrical layer models.  相似文献   

8.
Magnetotelluric soundings have been carried out across the archaean terrain of Singhbhum granite batholith from Bangriposhi to Keonjhar for a distance of about 100 km. One-dimensional inversion models reveal that the depth of the moho varied between 23 and 40 km. The depth of the lithosphere asthenosphere boundary varied from 58 to 76 km. A zone of higher electrical conductivity detected at the base of the lower crust just above the moho is present along the entire profile. Signals within the range of 0.25 to 600 seconds, which crossed the coherency threshold of 0.8 to 0.9, could be stacked. Resistivity ranges of the crust mantle silicates below Singhbhum granite batholith vary over a wide range. Resistivity ranges are (i) 30,000–80,000 ohm for Singhbhum granite phase II, (ii) 2,000 to 9,000 ohm-m for Singhbhum granite phase III, (iii) 250 to 2,200 ohm-m for lower crust (iv) 3,000 to 47,000 ohm for the upper mantle and (v) 200 to 2300 ohm-m for the asthenosphere. Sharp break in electrical resistivity at the (i) upper crust-lower crust (ii) lower crust upper mantle and (iii) lithosphere-asthenosphere boundary is obtained along the entire profile. Signals could see up to 100 km below the granite batholith. Singhbhum granite phase II and III could be demarcated on the basis of resistivity. Low resistive zones in the lower crust and upper mantle might have formed due to (i) water (ii) combined effect of water and carbon and (iii) high temperature and partial melt.  相似文献   

9.
A synthesis of previous work and new data on the stratigraphy of high terraces of the Ohio and Monongahela Rivers upstream from Parkersburg, West Virginia, indicates a correspondence between terrace histories in the ancient Teays and Pittsburgh drainage basins. Four terraces are identified in each. Sediments of the lower three alluvial and slackwater terraces, correlated with Illinoian, early Wisconsin, and late Wisconsin glacial deposits, have been traced along the modern Ohio River through the former divide between the Teays and Pittsburgh basins. Sediments in the fourth terrace, the highest well-defined terrace in each basin, were deposited in two ice-dammed lakes, separated by a divide near New Martinsville, West Virginia. Some deposits of the highest slackwater terrace in both the Teays and Pittsburgh basins have reversed remanent magnetic polarity. This, and the stratigraphic succession in the two basins, suggests that both were ponded during the same glaciation. Reversed polarity in these terrace sediments restricts the age of the first ice-damming event for which stratigraphic evidence is well-preserved to a pre-Illinoian, early Pleistocene glaciation prior to 788,000 yr ago. In contrast, slackwater sediments in the Monongahela River valley, upstream from an outwash gravel dam at the Allegheny-Monongahela confluence, have normal remanent magnetic polarity, corroborating correlation with an Illinoian ponding event.  相似文献   

10.
A large number of valleys and basin systems are present in the northwestern part of the Himalayas in Pakistan which form significant aquifers in the region. Hydrogeophysical investigations in the western part of Nowshera District, a part of the intermontane Peshawar basin, were undertaken to help to determine the availability of groundwater resources in the region. Thirty vertical electrical resistivity soundings (VES) were acquired using a Schlumberger expanding array configuration with a maximum current electrode spacing (AB/2) of 150 m in delineating the groundwater potential in the study area. The results of the interpreted VES data using a combination of curve matching technique and computer iterative modeling methods suggest that the area is underlain by 3 to 5 geo-electric layers. The interpretation results showed that the geo-electrical succession consists of alluvium comprising of alternating layers of clay, silty clay, fine to coarse sands, sand with gravels and gravels of variable thickness. High subsurface resistivity values are correlated with gravel–sand units and low resistivity values with the presence of clays and silts. The modeled VES results were correlated with the pumping tests results and lithological logs of the existing wells. The pumping test suggests the transmissivity of the aquifer sediments is variable corresponding to different sediments within the area. The gravel–sand intervals having high resistivity value show high transmissivity values, whereas clay–silt sediments show low transmissivities. It is concluded that majority of the high resistive gravel–sand sediments belong to an alluvial fan environment. These gravel–sand zones are promising zones for groundwater abstraction which are concentrated in the central part of the study area.  相似文献   

11.
Sinkhole collapse is one of the main limitations in the development of karst areas, especially where bedrock is covered by unconsolidated material. Studies of sinkhole formation have shown that sinkholes are likely to develop in cutter (enlarged joint) zones as a result of subterranean erosion by flowing groundwater. Ground-penetrating radar (GPR) and electrical resistivity imaging or tomography (RESTOM) are well suited to mapping sinkholes because of the ability of these two techniques for detecting voids and discriminating subtle resistivity variations. Nine GPR profiles and two-dimensional electrical resistivity tomography have been applied, with relative success, to locate paleo-collapses and cavities, and to detect and characterize karst at two sinkhole sites near Cheria City where limestone is covered by about 10 m of clayey soils. The survey results suggest that GPR and RESTOM are ideal geophysical tools to aid in the detection and monitoring of sinkholes and other subsurface cavities.  相似文献   

12.
The western sector of the Tagliamento River basin (Friuli Venezia-Giulia Region; northern Italy) is characterized by important water resources, both superficial and underground. In particular, in the Quaternary deposits of the plain, up to a depth of 500 m, six artesian aquifer systems exist. A large amount of lithological, geomorphological, and hydrogeological data is presented, allowing for definition of (a) the principal aquifer system of the area to a depth of about 500 m; (b) geometrical characteristics of the aquifers (thickness, lateral extension, etc); (c) the hydraulic parameters (hydraulic conductivity, transmissivity); (d) chemico-physical characteristics of the water; and (e) vulnerability to pollution of the aquifer systems. In a test area, where many boreholes were drilled for fresh water supply, the conceptual hydrogeological model was integrated by a detailed and repeated three-dimensional (3D) resistivity survey using combined electrical resistivity tomography (ERT) and time-domain electromagnetic (TDEM) soundings. ERT investigation was mainly used to get detailed information about geometry and porosity of the overburden and to calibrate the shallowest TDEM information.  相似文献   

13.
The objective of this study was to assess the subsurface strata and groundwater situation of Olomoro, Nigeria using borehole logging and electrical resistivity techniques. The borehole logging consisting of resistivity and spontaneous potential logs were conducted by using the Johnson Keck logger on a drilled well in the study area. The electrical resistivity survey involving 17 vertical electrical soundings (VES) with a maximum current electrode spacing of 100 to 150 m was conducted using the Schlumberger electrode configuration. Analysis of the well cuttings revealed that the lithology of the subsurface consist of topsoil, clay, very fine sand, medium grain sand, coarse sand and very coarse sand. Results of the downhole logging also revealed that the mean electrical conductivity and the total dissolved solid of the groundwater was obtained as 390 μS/cm and 245 mg/cm3 respectively. These values are within the acceptable limit set by the Standard Organization of Nigeria (SON) for drinking water. The result of the vertical electrical sounding interpreted using the computer iterative modeling revealed the presence of four to five geoelectric layers which showed a close correlation with result from the lithology and downhole logging. Results further showed that the resistivity of the subsurface aquifer ranged between 1584 and 5420 Ωm while the aquifer depths varied between 27.8 and 39.3 m. Groundwater development of the area is suggested using the depth and resistivity maps provided in this study.  相似文献   

14.
The objective of this study is to evaluate the effectiveness of DC resistivity surveys for imaging the wastewater percolation around the stabilization ponds in the Tenth of Ramadan City, the desert fringes of East Nile Delta, Egypt. Detailed resistivity surveys, including DC soundings and electrical resistivity tomography (ERT), were carried out along several profiles. Furthermore, synthetic modeling of ERT was designed to optimize the survey configurations and interpretation of the results. A 2D modeling of smoothness-constrained least-squares inversion scheme was applied to delineate the possible wastewater infiltration zones from oxidation ponds. Because the geoelectrical interpretation has a degree of non-uniqueness, the resistivity inversion was constrained using borehole lithological information and soil sample laboratory measurements. The DC inversion results indicate decreasing resistivity down to a depth of 15 m around waste disposal sites. The inferred soil zone close to the oxidation ponds was a mixture of sand, silt and clay. Moreover, the clay minerals were characterized by moderate swelling that could have reduced the vertical infiltration speed, causing wastewater seepage, especially around unlined disposal sites and open surface drains. Accordingly, the medium-to-low resistivity values can be attributed to wastewater leakage in clayey sand soil. Because the area slopes generally toward the northeast, the surface seepage was dominant in the shallow impermeable sandy clay subsoil. Therefore, measuring soil parameters is a complementary method to optimize resistivity interpretation, with potential for mitigating environmental hazards from wastewater leakage around disposal ponds.  相似文献   

15.
Hydrogeophysical investigations of the Pleistocene aquifer at the Kom Hamada area, Egypt, have been conducted to determine the characteristics of groundwater. The main water-bearing formations in the study area are composed of Quaternary deposits. Water samples were taken and chemically analyzed at 29 sites. The constructed iso-salinity contour map of the study area showed an increase in salinity from 451.75 mg/l at eastern parts to 1,091.85 mg/l at western parts. The groundwater of the study area showed a hydrochemical evolution from Ca–HCO3 at the eastern side to Na–Cl at the western side. Some of groundwater constituents have high concentration values exceeding the safe limit for drinking. Eighteen vertical electrical soundings (VES) were conducted in the study area. These soundings were conducted near existing wells to obtain layer parameters of the various penetrated layers and to calculate the petrophysical characteristics of the aquifers. The resistivity of the first water-bearing layer ranges between 34 and 47 Ω m. The thickness of this layer ranges between 26 and 79 m. This layer represents the first aquifer, where it is followed by another water-bearing layer with resistivity ranges between 29 and 62 Ω m and extends downward. The two aquifers are hydraulically connected. Variation of the resistivities of these two water-bearing layers is mainly due to the lithological variation. The resistivity values along with the TDS values of the two water-bearing layers indicate fresh to brackish water types.  相似文献   

16.
With a view towards understanding the evolutionary history of the complex South Indian shield, several geological and geophysical studies have been carried out. Recent geophysical studies include magnetotelluric (MT), deep seismic sounding (DSS), gravity, magnetic and deep resistivity soundings (DRS). In the present study, MT results along 140 km Andiyur-Turaiyur east-west profile is presented. The data are subjected to Groom-Bailey decomposition and static shift correction before deriving a 2-D model. The 2-D modeling results have shown that the upper crust (up to about 15 km) towards western part of the profile have exhibited high resistive character of about 40, 000 ohm-m as compared to the eastern part (less than 5, 000 ohm-m). The mid-lower crust has shown a decrease in resistivity in western part of the profile, the order of resistivity being 2, 000 ohm-m. An anomalous steep conductive feature (less than 100 ohm-m) is observed near Sankari at mid-lower crustal depths (>20 km) towards middle part of the profile. This feature is spatially correlatable with the well-known Moyar-Bhavani Shear Zone (MBSZ). The features obtained in the present study are consistent with earlier MT studies in this region and correlatable with other geophysical studies. DSS studies near the study region gave an evidence for differing crustal structure on either side of MBSZ. Variation in geoelectric character along the profile both in the upper crust and mid-lower crust indicate a block structure in the SGT with shear zones acting as boundaries. The new evidence in the form of distinct geoelectric structure and also variation in seismic structure indicate a continent-continent collision zone in this region and plays an important role for the Gondwana reconstruction models of South Indian shield.  相似文献   

17.
黄河上游全新世特大洪水及其沉积特征   总被引：43，自引：7，他引：36       下载免费PDF全文
黄河上游官亭盆地的黄河二级阶地面上沉积了厚约2m左右的平流沉积物,每次洪水形成1个由红色粘 土水平层和黑灰色粘土水平层组成的洪水单元。对研究剖面洪水沉积层的磁化率测量区分出了14个洪水单元, 代表了14次特大洪水的发生;利用盆地内的考古资料,将古洪水频繁发生的时期定为3700～2800aB.P.。粒度分 析表明官亭盆地平流沉积的沉积物几乎全部由粒径小于4φ的悬移物质组成,其分选系数>2,偏度<0,峰态中等。 与黄河中游进行比较,官亭盆地的平流沉积粒级更小,偏度更小且呈负偏。  相似文献   

18.
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19.
Vertical electrical sounding (VES), employing a Schlumberger electrode configuration, was used to investigate the sediments and aquifer repositories in Itu Local Government Area of Akwa Ibom state, southern Nigeria. This was done in sixteen (16) locations/communities with the maximum current electrode spread ranging between 800–1000m. The field data were interpreted using forward and iterative least square inversion modeling, which gives a resolution with 3–5 geoelectric layers. The observed frequencies in curve types include 31.25% of AKH, 18.8% of AAK and HK and 6.25% of K, QHK, AKH, KA and KHQ, respectively. These sets of curves show a wide range of variabilities in resistivities between and within the layers penetrated by current. The presence of K and H curve types in the study area indicates the alteration of the geomaterials with limited hydrologic significance to the prolific groundwater repository. A correlation of the constrained nearby borehole lithology logs with the VES results shows that the layers were all sandy formations (fine and well sorted sands to gravelly sands or medium to coarse-grained sands as described by nearby lithology logs) with some wide ranges of electrical resistivity values and thicknesses caused by electrostratigraphic inhomogeneity. The geologic topsoil (motley topsoil) is generally porous and permeable and as such the longitudinal conductance (S) values for the covering/protective layer is generally less than unity of Siemens (S < 1Ω?1), the value considered for efficient protection of the underlying aquifers by the topmost and overlying layer. The spatial orientations and the leveling patterns of the most economically viable potential groundwater repository within the maximum current electrode separations has been delineated in 2-D and 3-D contoured maps. The estimated depth range for the desired groundwater repository is 32.6–113.1m and its average depth value is 74.30m. The thickness of this layer ranges from 27.9–103m while its average depth has been evaluated to be 63.02m. Also, its resistivity range and average value have been estimated to be 507–5612m and 3365.125Ωm  相似文献   

20.
The large-scale (i.e. bar-scale) structure of channel deposits of the braided, low-sinuosity Calamus River, Nebraska, is described using ground-penetrating radar (GPR) profiles combined with vibracores. Basal erosion surfaces are generally overlain by medium-scale, trough-cross-stratified (sets 3–25 cm thick), very coarse to medium sands, that are associated with relatively high amplitude, discontinuous GPR reflectors. Overlying deposits are bioturbated, small-scale cross-stratified (sets <3 cm thick) and vegetation-rich, fine to very-fine sands, that are associated with low-amplitude discontinuous reflectors. Near-surface peat and turf have no associated GPR reflectors. In along-stream profiles through braid and point bars, most GPR reflectors dip downstream at up to 2° relative to the basal erosion surface, but some reflectors in the upstream parts of bars are parallel to the basal erosion surface or dip upstream. In cross-stream profiles through bars, GPR reflectors are either approximately parallel to bar surfaces or have low-angle inclinations (up to 6°) towards cut banks of adjacent curved channels. Basal erosion surfaces become deeper towards cut banks of curved channels. These structures can be explained by lateral and downstream growth of bars combined with vertical accretion. Convex upwards forms up to 0·5 m high, several metres across and tens of metres long represent episodic accretion of unit bars (scroll bars and bar heads). Stratal patterns in channel fills record a complicated history of erosion and deposition during filling, including migration of relatively small bars. A revised facies model for this type of sandy, braided river has been constructed based on this new information on large-scale bedding structure.  相似文献   

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