首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 15 毫秒
1.
A workflow is described to estimate specific storage (S s) and hydraulic conductivity (K) from a profile of vibrating wire piezometers embedded into a regional aquitard in Australia. The loading efficiency, compressibility and S s were estimated from pore pressure response to atmospheric pressure changes, and K was estimated from the earliest part of the measurement record following grouting. Results indicate that S s and K were, respectively, 8.8?×?10?6 to 1.2?×?10?5 m?1 and 2?×?10?12 m s?1 for a claystone/siltstone, and 4.3?×?10?6 to 9.6?×?10?6 m?1 and 1?×?10?12 to 5?×?10?12 m s?1 for a thick mudstone. K estimates from the pore pressure response are within one order of magnitude when compared to direct measurement in a laboratory and inverse modelled flux rates determined from natural tracer profiles. Further analysis of the evolution and longevity of the properties of borehole grout (e.g. thermal and chemical effects) may help refine the estimation of formation hydraulic properties using this workflow. However, the convergence of K values illustrates the benefit of multiple lines of evidence to support aquitard characterization. An additional benefit of in situ pore pressure measurement is the generation of long-term data to constrain groundwater flow models, which provides a link between laboratory scale data and the formation scale.  相似文献   

2.
Long-term changes in the physical and hydraulic properties of peat result from the decomposition and consolidation processes. The saturated hydraulic conductivity (K s) of peat is depth-dependent and could increase or decrease with depth; therefore, K s determination on a large number of samples is required to more accurately assess field variability. The cube method is a popular laboratory procedure to determine K s because it allows use of smaller sample dimensions, while minimizing edge effects. This article describes the design and use of an alternate split container to enclose undisturbed peat cubes during measurement of K s and the application of this method to a field site in Northwest Territories, Canada. The method allows for simpler and more controlled K s measurements while also permitting anisotropy measurements. Matched tests on identical samples (K s range 21–314 m/d), using the split-container and wax methods, showed a good agreement for intermediate K s values; however, significant deviations occurred for low and high K s values. Hydraulic-conductivity measurements taken on field samples showed a decrease with depth and exhibited anisotropic hydraulic conductivity as expected based on previous studies.  相似文献   

3.
Information on the anisotropy of streambed hydraulic conductivity (K) is a necessity for analyses of water exchange and solute transport in the hyporheic zone. An approach is proposed for the determination of K, developed from existing in-situ permeameter test methods. The approach is based on determination of vertical and horizontal hydraulic conductivity of streambed sediments on-site and eliminates the effects of vertical flow in the hyporheic zone and stream-stage fluctuation, which normally influence in situ permeameter tests. The approach was applied to seven study sites on four tributaries of the Platte River in east-central Nebraska, USA. On-site permeameter tests conducted on about 172 streambed cores for the determination of vertical hydraulic conductivity (K v) and horizontal hydraulic conductivity (K h) at the study sites indicate that the study sites have relatively small anisotropic ratios, ranging from 0.74 to 2.40. The ratios of K h to K v from individual locations within a study site show greater variation than the anisotropic ratios from the mean or median K at each of the study sites.  相似文献   

4.
The integration of geophysical data with direct hydrogeological measurements can provide a minimally invasive approach to characterize the subsurface at a variety of resolutions and over many spatial scales. The field of hydrogeophysics has attracted much attention during the last two decades. In this domain, the geophysical data inverted to geophysical models are interpreted in terms of the hydrogeology to serve as a basis for the definition of hydraulic models in the areas of interest. The hydraulic conductivity (K) value measured in a reference borehole has been combined with the electrical conductivity obtained from nearby geo-electromagnetic sounding data in the Cenomanian (Upper Cretaceous) aquifer, central Sinai, Egypt. The resulting relation was interpreted with Dar Zarrouk parameters to infer the transmissivity variations at other vertical electrical sounding locations, where K values are unknown. Coincident transient electromagnetic data have been adopted to increase accuracy while interpreting the aquifer geoelectrical properties. The results indicate that the transmissivity values in the aquifer of interest vary from 2,446 to 9,694 m2/day, and K varies from 12.9 to 57.0 m/day throughout the studied area.  相似文献   

5.
Measurement of streambed hydraulic conductivity and its anisotropy   总被引：17，自引：0，他引：17  
 A method is described for the measurement of streambed hydraulic conductivity. Unlike permeameter methods, this method applies straight and l-shaped standpipes directly to streambeds for measurements of in-situ hydraulic conductivity in the vertical (K v ) and horizontal (K h ) directions, as well as in other oblique directions (K s ). This method has advantages in determination of K v values over grain-size analysis, permeameter tests, or slug test methods. Also unique to this method is that it provides K s values of a streambed. The measured results can be used to construct a hydraulic conductivity ellipse and to evaluate the anisotropy of streambed sediments. Field examples from the Republican River, Nebraska, demonstrated the usefulness of this method in the determination of streambed hydraulic conductivity and anisotropy along or across a river channel. Results indicate that the K h is about three to four times larger than K v , whereas K s values are larger than K v but smaller than K h . Received: 6 March 2000 · Accepted: 18 April 2000  相似文献   

6.
Soil saturated hydraulic conductivity (Ks) is considered as soil basic hydraulic property, and its precision estimation is a key element in modeling water flow and solute transport processes both in the saturated and vadose zones. Although some predictive methods (e.g., pedotransfer functions, PTFs) have been proposed to indirectly predict Ks, the accuracy of these methods still needs to be improved. In this study, some easily available soil properties (e.g., particle size distribution, organic carbon, calcium carbonate content, electrical conductivity, and soil bulk density) are employed as input variables to predict Ks using a fuzzy inference system (FIS) trained by two different optimization techniques: particle swarm optimization (PSO) and genetic algorithm (GA). To verify the derived FIS, 113 soil samples were taken, and their required physical properties were measured (113 sample points?×?7 factors?=?791 input data). The initial FIS is compared with two methods: FIS trained by PSO (PSO-FIS) and FIS trained by GA (GA-FIS). Based on experimental results, all three methods are compared according to some evaluation criteria including correlation coefficient (r), modeling efficiency (EF), coefficient of determination (CD), root mean square error (RMSE), and maximum error (ME) statistics. The results showed that the PSO-FIS model achieved a higher level of modeling efficiency and coefficient of determination (R2) in comparison with the initial FIS and the GA-FIS model. EF and R2 values obtained by the developed PSO-FIS model were 0.69 and 0.72, whereas they were 0.63 and 0.54 for the GA-FIS model. Moreover, the results of ME and RMSE indices showed that the PSO-FIS model can estimate soil saturated hydraulic conductivity more accurate than the GA-FIS model with ME?=?10.4 versus 11.5 and RMSE?=?5.2 versus 5.5 for PSO-FIS and GA-FIS, respectively.  相似文献   

7.
This study was conducted in six plots along an elevation gradient in the Qinghai spruce (Picea crassifolia Kom.) forest ecosystem of the Qilian Mountains, northwest China. Soil CO2 efflux over bare soil (R s) and moss covered soil (R s+m) were investigated from June to September in 2010 and 2011 by means of an automated soil CO2 flux system (LI-8100). The results showed that R s ranged from 1.51 to 3.96 (mean 2.64 ± 0.72) μmol m?2 s?1 for 2010, and from 1.41 to 4.09 (mean 2.55 ± 0.70) μmol m?2 s?1 for 2011. The daily change trend of R s resembled that of air temperature (T a), and there was a hysteresis between R s and soil temperature (T s). The seasonal variations of R s at lowlands (i.e., Plot 1, Plot 2 and Plot 3) were driven by soil moisture and temperature (T a and T s), while that at highlands (i.e., Plot 4, Plot 5 and Plot 6) were obviously affected by temperature. There were higher values at Plot 2 and Plot 6, which were caused by the interaction between soil moisture and temperature. In addition, soil CO2 efflux over moss covered soil (R s+m) was 8.83 % less than that over bare soil (R s), indicating that moss was another factor affecting R s. It was concluded that R s had temporal and spatial variations and was mainly controlled by temperature and soil moisture; the main determinants differed at different elevations; moss could reduce R s.  相似文献   

8.
  相似文献   

9.
The Guarani aquifer system (GAS) represents one of the biggest aquifers in the world and is the most relevant groundwater resource in South America. For the first time, by combining field and laboratory measurements, a high-resolution aquifer analog model of fluvial–aeolian sediments of the GAS in São Paulo State (Brazil) is constructed. Three parallel sections of frontal outcrops, 28 m × 5.8 m, and two parallel sections of lateral outcrops, 7 m × 5.8 m, are recorded during open-pit mining of sandy sediments and describe in detail the three-dimensional distribution of the local lithofacies and hydrofacies. Variations of hydraulic conductivity, K, and porosity, n, are resolved on the centimeter scale, and the most permeable units of the fluvial–aeolian facies association are identified. The constructed aquifer analog model shows moderate hydraulic heterogeneity and a mean K value of 1.36 × 10?4 m/s, which is greater than the reported range of K values for the entire GAS in São Paulo State. The results suggest that the examined sedimentary unit constitutes a relevant portion of the GAS in São Paulo State in the context of groundwater extraction and pollution. Moreover, the constructed aquifer analog is considered an ideal basis for future numerical model experiments, aiming at in-depth understanding of the groundwater flow and contaminant transport patterns at this GAS portion or at comparable fluvial–aeolian facies associations.  相似文献   

10.
  相似文献   

11.
Water injection tests and electrical logging are particularly useful techniques in the characterization of geological media in engineering works. In this paper these techniques in conjunction with cracks measurements obtained from drilling cores, were used in the characterization of a singular location in a karst massif. The aim of our work is to determine the hydraulic characteristics of the investigated site, as well as to establish the relationship between the data obtained by the different techniques used. Thus, electrical resistivity records and fracture data were obtained from two boreholes of 100 and 120 m depth. Hydraulic conductivity was calculated from 25 low-pressure water injection tests (LPT) carried out at different depths in both boreholes. The relationship between hydraulic conductivity and fracture frequency was not very statististically significant (R2: 0.062–0.672; σest: 0.61–1.575). Conversely, electrical resistivity and hydraulic conductivity had a great relationship (R2: 0.725–0.935; σest: 0.159–0.738), so the electrical resistivity may be related to the functionality of the fractures. Finally, the LPT is shown as a very practical tool for determining the degree of the hydraulically interconnection with the surroundings, for establishing the hydraulic conductivity profile and for obtaining a measure of soil erosionability according to the significance of the fracture washing out processes recorded.  相似文献   

12.
In a small watershed underlain by relatively homogeneous (nonlayered), sandy, glacial outwash, hydraulic conductivity (K) and longitudinal dispersivity (α L) were systematically measured over a range in scale. Test methods employed in the investigation are conventional and/or based on accepted principles, measurement scales are those typically encountered in applied field problems, and the hydrogeologic setting is typical of large areas within the northern hemisphere and similar to many alluvial environments worldwide. The results show that K measured under radial flow is scale-dependent up to a radius of influence (r i) of approximately 15 m but reaches an asymptotic value above this threshold. This asymptotic value of K is consistent with results obtained at the regional scale (～104 m) for the same aquifer using non-radial three-dimensional techniques; the initial increase appears to reflect increasing dimensionality of the radial tests with larger r i. Although α L was evaluated over a much smaller interval relative to K, α L proved to be independent of scale over the full range tested, from 2 to 29 m, an unexpected result. The findings support the idea that there is, as yet, no predictable relationship between scale effects in K and α L at scales normally encountered in applied field hydrogeology.  相似文献   

13.
A numerical groundwater model of the weathered crystalline aquifer of Ursuya (a major water source for the north-western Pyrenees region, south-western France) has been computed based on monitoring of hydrological, hydrodynamic and meteorological parameters over 3 years. The equivalent porous media model was used to simulate groundwater flow in the different layers of the weathered profile: from surface to depth, the weathered layer (5?·?10?8?≤?K?≤?5?·? 10?7 m s?1), the transition layer (7?·?10?8?≤?K?≤?1?·? 10?5 m s?1, the highest values being along major discontinuities), two fissured layers (3.5?·?10?8?≤?K?≤?5?·?? 10?4 m s?1, depending on weathering profile conditions and on the existence of active fractures), and the hard-rock basement simulated with a negligible hydraulic conductivity (K = 1 10 ?9 ). Hydrodynamic properties of these five calculation layers demonstrate both the impact of the weathering degree and of the discontinuities on the groundwater flow. The great agreement between simulated and observed hydraulic conditions allowed for validation of the methodology and its proposed use for application on analogous aquifers. With the aim of long-term management of this strategic aquifer, the model was then used to evaluate the impact of climate change on the groundwater resource. The simulations performed according to the most pessimistic climatic scenario until 2050 show a low sensitivity of the aquifer. The decreasing trend of the natural discharge is estimated at about ?360 m3 y?1 for recharge decreasing at about ?5.6 mm y?1 (0.8 % of annual recharge).  相似文献   

14.
Recognizing the heterogeneity of hydraulic conductivity and hyporheic flow is critical for understanding contaminant transfer and biogeochemical and hydrological processes involving streams and aquifers. In this study, the heterogeneity of hydraulic conductivity and Darcian flux in a submerged streambed and its adjacent exposed stream banks were investigated in the Beiluo River, northwest China. In the submerged streambed, Darcian flux was estimated by measurement of vertical hydraulic conductivity (K v) and vertical head gradient (VHG) using in-situ permeameter tests. On exposed stream banks, both horizontal hydraulic conductivity (K h) and K v were measured by on-site permeameter tests. In the submerged streambed, K v values gradually decreased with depth and the higher values were concentrated in the center and close to the erosional bank. Compared to the exposed stream banks, the K v values were higher in the streambed. From stream stage to the topmost layer of tested sediment, through increasing elevation, the K h values increased on the erosional bank, while they decreased on the depositional bank. The values of VHG along the thalweg illustrate that downwelling flux occurred in the deepest area while upwelling flux appeared in the other areas, which might result from the change of streambed elevation. The higher value of the Darcian flux in the submerged streambed existed near the erosional bank.  相似文献   

15.
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 (Cu) 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 Kpermeameter>KBeyer>KHazen>KKozeny-Carmen>KFair-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.  相似文献   

16.
The hydraulic conductivity represents an important indicator parameter in the generation and redistribution of excess pore pressure of sand–silt mixture soil deposits during earthquakes. This paper aims to determine the relationship between the undrained shear strength (liquefaction resistance) and the saturated hydraulic conductivity of the sand–silt mixtures and how much they are affected by the percentage of low plastic fines (finer than 0.074 mm) and void ratio of the soil. The results of flexible wall permeameter and undrained monotonic triaxial tests carried out on samples reconstituted from Chlef river sand with 0, 10, 20, 30, 40, and 50 % non-plastic silt at an effective confining pressure of 100 kPa and two initial relative densities (D r = 20, 91 %) are presented and discussed. It was found that the undrained shear strength (liquefaction resistance) can be correlated to the fines content, intergranular void ratio and saturated hydraulic conductivity. The results obtained from this study reveal that the saturated hydraulic conductivity (k sat) of the sand mixed with 50 % low plastic fines can be, in average, four orders of magnitude smaller than that of the clean sand. The results show also that the global void ratio could not be used as a pertinent parameter to explain the undrained shear strength and saturated hydraulic conductivity response of the sand–silt mixtures.  相似文献   

17.
Various approaches exist to relate saturated hydraulic conductivity (K s) to grain-size data. Most methods use a single grain-size parameter and hence omit the information encompassed by the entire grain-size distribution. This study compares two data-driven modelling methods??multiple linear regression and artificial neural networks??that use the entire grain-size distribution data as input for K s prediction. Besides the predictive capacity of the methods, the uncertainty associated with the model predictions is also evaluated, since such information is important for stochastic groundwater flow and contaminant transport modelling. Artificial neural networks (ANNs) are combined with a generalised likelihood uncertainty estimation (GLUE) approach to predict K s from grain-size data. The resulting GLUE-ANN hydraulic conductivity predictions and associated uncertainty estimates are compared with those obtained from the multiple linear regression models by a leave-one-out cross-validation. The GLUE-ANN ensemble prediction proved to be slightly better than multiple linear regression. The prediction uncertainty, however, was reduced by half an order of magnitude on average, and decreased at most by an order of magnitude. This demonstrates that the proposed method outperforms classical data-driven modelling techniques. Moreover, a comparison with methods from the literature demonstrates the importance of site-specific calibration. The data set used for this purpose originates mainly from unconsolidated sandy sediments of the Neogene aquifer, northern Belgium. The proposed predictive models are developed for 173 grain-size K s-pairs. Finally, an application with the optimised models is presented for a borehole lacking K s data.  相似文献   

18.
This paper applies and validates a method for generating spatially distributed hydraulic conductivity (k) based on the specific capacity (Q s) for data-scarce regions. This method has been applied to the Araripe sedimentary basin, Brazil, and consists of four steps: (1) selection of (32) wells for which both k and Q s data are available; (2) estimation of k as a function of Q s for the (128) wells for which only specific capacity data are available; (3) spatial distribution of k using the kriging geostatistical tool; (4) validation of the method, using (17) representative wells with k measured data. The equation relating k and Q s showed a statistically significant linear relationship (R = 0.93), from which a database has been generated using kriging with the spherical model. The results showed a calibration coefficient of Nash and Sutcliffe (NS) of 0.54 and moderate spatial dependence ratio of 69 %. The validation process provided only a moderate efficiency (NS = 0.22), possibly due to the geological complexity of the focus system. Despite its limitations, the method indicates the possibility of application of ordinary kriging to generate reliable data from auxiliary variables, especially for the water management of data-scarce areas.  相似文献   

19.
Compacted soil–bentonite liners, consisting of a sandy soil mixed with bentonite as backfill, are used extensively as engineered barriers for contaminant containment. This paper studies the valorization of local materials containing calcareous sand, tuff obtained from Laghouat region (in the South Algeria), to associate with bentonite in order to improve their hydraulic characteristics for use as landfill liner material. Firstly, a geotechnical characterization of mixtures chooses from a fixed percentage to 10% bentonite and different percentages of calcareous sand and tuff so that they are complementary to 90% by not 10%. Thereafter, the determination of saturated hydraulic conductivity at falling-head permeability (Kv) and oedometer (Kid, indirect Measure) tests of all compacted mixtures at Optimum Normal Proctor have been carried out using both permeates by tap water and a landfill leachate in order to simulate long-term conditions. The results showed that the saturated hydraulic conductivity of tap water is relatively lower than the one saturated by leachate in the falling-head test, unlike the oedometer test. The B10CS20T70 mixture has satisfied the hydraulic conductivity criterion of bottom barriers (i.e. water permeated: kv20° = 1.97 × 10?9 and kid from 7 × 10?9 to 1.83 × 10?10 < 10?9m/s; leachate permeated: kv20° = 2.91 × 10?9 and kid from 7 × 10?9 at 1.44 × 10?10 < 10?9 m/s). Finally, a comparison between direct measurements of the saturated hydraulic conductivity by triaxial (Kd) test and oedometer test (Kid) in the range of effective stress applied 100–800 kPa led to propose equations of correlations between these two methods. In conclusion, adopted formulation B10CS20T70 perfectly meets the regulatory requirements in force and constitutes an economic product based on available local materials for engineers barriers.  相似文献   

20.
The purpose of this study is to quantify the magnitudes of surface conduction and pore water conduction from the measured electrical conductivity of kaolinite, with the ultimate goal of estimating the electrical conductivity of kaolinite with a wide range of pore water conductivities (σ w = 0.013–3.356 S/m) and porosities (n = 0.368–1.0). Therefore, the theoretical background of the electrical conductivity in soils was reviewed, and electrical conductivity measurements on kaolinite were performed using both slurry and consolidation tests in this study. The results of this study demonstrate that the variations of measured electrical conductivity (σ mix) with n are debatable according to the values of σ w, because a decrease in n results in both an increase in surface conduction (K s) and a decrease in pore water conduction (K w); this causes the relative magnitude of K s compared to that of K w to vary with σ w and n. Consequently, this study develops the relation between the porosity-normalized K s/K w and 1/σ w. Additionally, the surface conductivity of the tested kaolinite is back-calculated and compared with the previous relationship between K s and zeta potential of kaolinite. The measured and estimated σ mix values are compared with the varying pore water conductivity and porosity values.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号