Hydraulic,textural and geochemical characteristics of the Ajali Formation,Anambra Basin,Nigeria: implication for groundwater quality

This study highlights the distribution of hydraulic conductivity (K) in the regional aquiferous Ajali Formation of SE-Nigeria on one hand and assesses the possible influences of textural and geochemical characteristics on the hydraulic conductivity on the other hand. The investigation approach involved field sampling and collection of 12 sandstone samples from different outcrop locations, followed by laboratory studies such as grain-size analysis (GSA), constant head permeameter test and geochemical analysis of major and trace elements using X-ray fluorescence method. GSA and textural studies show that the sandstones range from fine to medium sands, constituting about <75–99% sand fraction, with graphic mean grain size of 0.23–0.53 mm. Other parameters such as coefficient of uniformity (C_u) range from 1.58 to 5.25 (av. 2.75), while standard deviation (sorting) values of 0.56Ø–1.24Ø imply moderately well sorted materials. In addition, the order of the estimated K values is K_permeameter>K_Beyer>K_Hazen>K_{Kozeny-Carmen}>K_Fair-Hatch with average values of 1.4×10^?3, 4.4×10^?4, 3.8×10^?4, 2.2×10^?4 and 8.1×10^?5m/s, respectively. These values fall within the range of 10^?5 and 10^?3m/s for fine to medium sands. However, multivariate factor analysis of the data revealed significant positive dependence of the empirically determined K values on graphic mean grain size and percentage sand content and much less dependence on sorting and total porosity. Geochemical profiles of the fresh samples are dominated by quartz with corresponding SiO₂ content of 76.1–98.2% (av. 89.7%) while other major oxides are generally below 1.0wt.% in the fresh samples. However, the ferruginized samples exhibited elevated concentrations of Al₂O₃ (3.50–11.60wt.%) and Fe₂O₃ (1.80–3.60wt.%), which are clear indications of weathering/ferruginization processes with attendant trace metal release/enrichment (2.5mg/l Cu, 7.5mg/l Pb, 6.5mg/l Zn, 3.9mg/l Ni and 19.6mg/l Cr) call for concern in respect of the chemical quality of the groundwater system. The associated groundwater is generally soft, slightly acidic, and with low dissolved solids (EC=14–134μs/cm) dominated by silica; implying water from clean sandy aquifer devoid of labile and weatherable minerals. Nonetheless, most of the metals (with exception of Si, Fe and Mn) exhibited higher degree of mobility (2–12 folds), which can be attributed to reduction of Fe-/Mn-oxyhydroxides as sinks/hosts for trace metals. Consequently, infiltration-induced geochemical reactions (redox, ferruginization and leaching processes) signify potential environmental impact in terms of groundwater quality as well as borehole/aquifer management, especially under humid tropical environment of the study area.     

Assessment of Some Hydraulic Properties of Slime Slurries from Sand Mining Pits Using a Modified Triaxial Cell

The generation of massive volume of slimes from sand mining industry ascertains the need for effective waste treatment. The application of slimes in landfill barrier construction works has been identified as one of the processes that can be used to reduce their volume, enabling in this way the rehabilitation of dangerous sites. This article presents a modified triaxial cell specially built to investigate high water content soils and discusses the results obtained from the investigation of the hydraulic properties of two slimes. The results of laboratory filter cake tests show that the slimes have reasonably good sealing capacities due to the formation of a cake layer on other porous materials upon draining. A relatively low hydraulic conductivity (1.5–3 × 10⁻⁹ m/s) was achieved, once the cake layer was formed. This is close to the prescribed 1 × 10⁻⁹ m/s required by the local environmental governmental authority for a landfill hydraulic barrier material, indicating their potential suitability as landfill barrier.     

Influence of Water Pressure on the Stress State in Stopes with Cohesionless Backfill

The rapid increase of backfill use in underground mines requires a better understanding of the interaction between the fill material and the surrounding rock mass. This is a fairly complex issue as backfill materials are weak compared to the rock mass. This difference in the mechanical behavior induces a stress transfer along the contact area. Previous work conducted on backfilled trenches and mining stopes has shown that basic arching theory can be used to estimate earth pressures in narrow, vertical openings. In this regard, most existing solutions have been developed for dry backfills. However, in many cases, water is present in mine stopes, so its effect should be assessed. In this paper, the authors present a solution to evaluate the stress state in submerged or partially submerged backfilled stopes. The proposed analytical solution is validated against numerical modeling results.     

Collapse of a Model Strip Footing on Dense Sand Under Vertical Eccentric Loads

The paper focuses on the behaviour of a model strip footing, resting on a saturated dense sandy soil, subjected to centred or eccentric vertical loading. Experimental tests, carried out on a small-scale physical model, are able to reproduce effective stress levels equivalent to those prevailing in prototype problems, thanks to the maintenance of a downward steady-state seepage in the soil. The test program consists of three series of tests, each corresponding to an imposed value of hydraulic gradient, and each involving five load eccentricities; one series, in particular, is carried out with still water. Relevant points of load–settlement curves are related to the evolution of soil-footing collapse mechanism, evidenced by the distortion of some vertical coloured sand strips. The collapse mechanism is formed either by one or two sliding surfaces, depending on both load eccentricities and hydraulic gradient values. Significant differences are shown to occur between centred and eccentric loading footing response. Shear strength parameters obtained from back-analyses carried out on load values recorded at the appearance of each sliding surface on the free soil surface, in both hypotheses of associated and non-associated flow rule validity, are adopted to draw, for each test, a theoretical collapse mechanism consisting, in plane strain, of a log-spiral line with adjacent-end tangents; the obtained theoretical sliding surfaces, in turn, are compared to the experimental ones, showing that these latter are either stress characteristic or zero-extension lines depending mainly on cumulative footing displacements and current effective stress level in the soil.     

广州市夏季高温特点及其危害

对广州市1951年1月~2004年10月的逐日最高气温资料统计发现:7、8月是广州市高温天气的频发期;广州市高温频数有明显的年际变化,其中20世纪80年代以后长时间持续高温发生概率显著增大。持续高温会影响城市居民正常的生产生活状况,高温会使人体发病率、死亡率增加,使城市水电供应紧张,加剧干旱,严重影响工农业生产的正常进行。     

用离心模型试验研究花岗岩残积土边坡的破坏特性

推导了边坡坡体及锚固体的离心相似模型,得出了相关参数的相似比尺。通过试验得出了花岗岩风化残积土边坡可能以平面形式失稳也可能产生圆弧滑动,分析了含水量对破坏形式的影响。通过试验得出无控制性结构面的边坡的极限稳定高度与坡角的关系大致满足马斯洛夫方程。     

Google Earth在水利水电测绘中的应用

分析了Google Earth软件的强大功能,并详细介绍了Google Earth软件在水利水电测绘中的各种实际应用,包括水利工程断面测绘、地形图测绘、控制网优化设计、非涉密控制点成果资料管理及其他应用等,供广大水利水电测绘工作者参考。     

Inversion of multi-frequency electromagnetic induction data for 3D characterization of hydraulic conductivity

Electromagnetic induction (EMI) instruments provide rapid, noninvasive, and spatially dense data for characterization of soil and groundwater properties. Data from multi-frequency EMI tools can be inverted to provide quantitative electrical conductivity estimates as a function of depth. In this study, multi-frequency EMI data collected across an abandoned uranium mill site near Naturita, Colorado, USA, are inverted to produce vertical distribution of electrical conductivity (EC) across the site. The relation between measured apparent electrical conductivity (EC_a) and hydraulic conductivity (K) is weak (correlation coefficient of 0.20), whereas the correlation between the depth dependent EC obtained from the inversions, and K is sufficiently strong to be used for hydrologic estimation (correlation coefficient of ? 0.62). Depth-specific EC values were correlated with co-located K measurements to develop a site-specific ln(EC)–ln(K) relation. This petrophysical relation was applied to produce a spatially detailed map of K across the study area. A synthetic example based on EC_a values at the site was used to assess model resolution and correlation loss given variations in depth and/or measurement error. Results from synthetic modeling indicate that optimum correlation with K occurs at ~ 0.5 m followed by a gradual correlation loss of 90% at 2.3 m. These results are consistent with an analysis of depth of investigation (DOI) given the range of frequencies, transmitter–receiver separation, and measurement errors for the field data. DOIs were estimated at 2.0 ± 0.5 m depending on the soil conductivities. A 4-layer model, with varying thicknesses, was used to invert the EC_a to maximize available information within the aquifer region for improved correlations with K. Results show improved correlation between K and the corresponding inverted EC at similar depths, underscoring the importance of inversion in using multi-frequency EMI data for hydrologic estimation.     

兰坪金顶跑马坪矿段水文地质特征

对跑马坪矿段地质、水文地质条件的调查,划分水文地质单元,对比矿段开采前后水文地质条件的变化、矿段涌水量与大气降水的关系等,分析矿段地下水水文地质特征。     

北京地区新5孔晚新生代沉积物中的地球化学特征及古环境意义

通过对新5钻孔晚新生代地层中的主要氧化物、微量元素和主要元素比值的变化特点进行研究分析。表明该地区自新近纪以来该地区气候总体趋势是由温暖湿润向温和干旱气候方向发展。其中经历了3个较大的氧化阶段。本文综合分析磁化率、古地磁和孢粉等资料。分析了主要氧化物、微量元素在不同地层中的分布特征。从地球化学角度把新5钻孔的沉积环境分为6个变化波动区间。揭示该地区晚新生代以来的气候经历了温暖湿润-温和湿润—温和偏干—温暖湿润—温凉湿润—温和偏干的气候波动。