Spatial geostatistical interpolation of point measurements of streambed attributes in the hyporheic zone may be constrained by the streambed anisotropy, and data density and spatial distribution may ...significantly impact the results. Spatial clustering and low spatial data density can be caused by bedrock outcropping at the streambed limiting installation of in-stream piezometers. This study examines parameter error variability of the geostatistical interpolation using anisotropic interpolation methods and increasing the data density by adding left censored values (i.e., data below measurement limit) to locations where measurements were limited by exposed bedrock lining the streambed. The reduction in relative standard error of the interpolation was determined for the spatial distributions of streambed attributes including hydraulic conductivity, seepage flux, and mercury solute flux measured in two different years along a study reach in East Fork Poplar Creek, Tennessee, USA. Here, two methods to impute the left censored values were compared including the conventional half the detection limit substitution method, and the Stochastic Approximation of Expectation-Maximization (SAEM) algorithm, which both had comparable results. Imputing left censored data increased the data density to recommended ranges, reduced data clustering, increased the spatial dependence for some attributes, and reduced the standard error for each of the three attributes. For the reach considered herein, addition of the left censored values resulted in a larger error reduction than the consideration of anisotropy within the interpolation, which confirms the benefit of data addition to increase data density within data-limited river corridors.
One of the main modes of monitoring the geotechnical conditions of earth dams is piezometric measurement, which measures water levels in an open piezometer or water pressure in a closed piezometer. ...During piezometric measurements, various types of factors can cause disturbances in these measurements that take the form of systematic, accidental, or obvious mistakes. Before measurements from open or closed piezometers are analyzed, outliers due to coarse errors should be detected and rejected. Such observations may significantly influence the result of the analysis and cause erroneous assessment and interpretation of the phenomenon studied. To do this, statistical tests must be applied so that the doubtful measurement can be accepted or rejected at the assumed significance level. This paper uses five statistical tests for identifying and rejecting outliers: the Q-Dixon test, the Grubbs test, as well as the Hampel test, the Iglewicz and Hoaglin test, and the Rosner test. The aim of this article is to try to identify the most suitable test for periodic piezometric measurements. The scope of the study includes the analysis of piezometric measurements for the Czaniec Dam for the multi-year period 2017–2020.
•Geostatistical method and data evaluation is critical for hyporheic zone characterization.•Left censored methods SAEM and ½ detection limit were comparable for a streambed.•Left censored data ...addition increased data density and decreased interpolation error.•Decreasing data clustering can minimize geostatistical interpolation errors.•Anisotropic geostatistical interpolation decreased error even in a relatively straight stream.
Spatial geostatistical interpolation of point measurements of streambed attributes in the hyporheic zone may be constrained by the streambed anisotropy, and data density and spatial distribution may significantly impact the results. Spatial clustering and low spatial data density can be caused by bedrock outcropping at the streambed limiting installation of in-stream piezometers. This study examines parameter error variability of the geostatistical interpolation using anisotropic interpolation methods and increasing the data density by adding left censored values (i.e., data below measurement limit) to locations where measurements were limited by exposed bedrock lining the streambed. The reduction in relative standard error of the interpolation was determined for the spatial distributions of streambed attributes including hydraulic conductivity, seepage flux, and mercury solute flux measured in two different years along a study reach in East Fork Poplar Creek, Tennessee, USA. Two methods to impute the left censored values were compared including the conventional half the detection limit substitution method, and the Stochastic Approximation of Expectation-Maximization (SAEM) algorithm, which both had comparable results. Imputing left censored data increased the data density to recommended ranges, reduced data clustering, increased the spatial dependence for some attributes, and reduced the standard error for each of the three attributes. For the reach considered herein, addition of the left censored values resulted in a larger error reduction than the consideration of anisotropy within the interpolation, which confirms the benefit of data addition to increase data density within data-limited river corridors.
The variation of groundwater table is important information for Civil Engineering and related practices. The most appropriate datasets for the groundwater table mapping are the water level ...measurements in borehole piezometers. The methods for development of the groundwater table distribution on a continuous surface are affected by the hydrological factors and spatial variability of the soils. In this study, the piezometer data of the groundwater table in soils from four formations in Singapore were used to predict the continuous surface of the groundwater table. The interpolation of groundwater table elevation was performed using geostatistical analyses: inverse distance weighted (IDW) and Ordinary Kriging (OK) interpolations within residual soils from Bukit Timah Granite Formation, Old Alluvium Formation, Jurong Formation, and Kallang Formation. The interpolations were completed based on 80% of dataset (1,282 piezometers for wet season and 2,567 piezometers for dry season). The evaluation of the predicted groundwater table maps was carried out using cross-validation method (CVM) based on 20% of the datasets (256 piezometers for wet season and 512 piezometers for dry season). The results show that the IDW and OK interpolations generated quite similar predictions of the groundwater table distribution ranging between -3.7 m and 58 m elevation with respect to sea level, depending on hydrogeological conditions and soil formation characteristics. The validation method indicated a very good performance of IDW and OK in predicting the groundwater table distribution in Singapore (r2 > 0.8). The proposed procedures and methodologies covering the interpretation of data from piezometers , spatial analyses and evaluation of groundwater table map via geographical information system (GIS) approach presented in this paper will benefit Civil Engineers prior to building construction. The developed groundwater table map will be useful to determine the optimum number of piezometers still required for designs, to design the low cost and effective ground improvement, foundation and retaining wall in order to ensure the stability of the building during and after the completion of the project.
•Inverse distance weighted for interpolation of groundwater table location.•Ordinary kriging for development of spatial distribution of groundwater table.•Inverse distance weighted has similar performance as ordinary kriging.•Cross Validation Method for evaluation of the accuracy of ordinary kriging.•Cross-validation method for evaluation of the accuracy of inversed distance weighted.
The measurement of the permeable water pressure, the flow rate of leakage and drainage from the beginning of the construction of the rockfill dam are the most important characteristics needed in ...analysis these dams. Failure to control the above parameters can cause the waste of water stored in the reservoir, threaten the safety of the dam, and also reduce the stability of the dam through piping or liquefaction. Rockfil1 dams are used to prevent seepage, store water, control floods and delay floods. The problem of leakage should be controlled and limited in such a way as to prevent the creation of adverse effects such as: loss of water stored behind the earthen structure, creation of pore pressure in the porous medium, reduction of the effective stress between soil particles and, as a result, reduction prevent its shear resistance. In many cases, rockfill dam meets the needs of the project, because gravel is far more stable than soil and its ability to be washed is less. The slopes of the gravel dam body are steeper than many other soils, which saves money. In the present research, gravel materials were first prepared from the river mines of Khuzestan province to conduct experiments. These materials were used in three sizes with an average diameter of 10, 20 and 30 mm respectively to make the model. In this research, it was tried to study the leakage parameters in the gravel dam by building a physical model. A physical model of a gravel dam was built in a laboratory flume with three gravel samples and three slopes with the aim of investigating and determining the amount of leakage from the dam body. Pore pressure was measured with piezometers installed in the flume body. The results of the research showed that in a constant slope, the flow-field angle increases as the flow depth increases. Also, with the increase of the flow rate and the increase of the diameter of the particles, the depth of the outlet flow is reduced and these changes are not clear at low flow rates, but are clearly visible at high flow rates. In constant diameter and flow rate, with the increase of the slope of the model, the depth of the outlet flow decreases, and in the constant flow rate, with the increase of the ratio (Bc/H), the value of the outlet height of the flow decreases. Based on the experiments, the following results are presented. In the ratio of Bc/H = 1, with the increase of upstream depth, the depth of outflow has increased. Considering that the depth of the outlet flow downstream can be determined using the concept of the flow-field angle, it can be said that the depth of the outlet flow increases with the increase of the flow-field angle. In the ratio Bc/H=2, with the increase in the width of the model, the depth of the outlet flow has decreased compared to Bc/H=1. In addition, it can be concluded that in a constant slope, with the increase in flow depth, flow-field angle increases. Also, with the increase in the diameter of the particles, the depth of the outflow decreases. These changes are not clear at low flow rates but are clearly visible at high flow rates.
Incipient groundwater salinization has been identified in many arid and semi-arid regions where groundwater is increasingly used for irrigation, but the dominant processes at stake in such context ...are yet uncertain. Groundwater solutes originates from various sources such as atmospheric inputs, rock dissolution and fertilizer residues, and their concentration is controlled by hydrological processes, in particular evapotranspiration. Here, we propose a deconvolution method to identify the sources and processes governing the groundwater Chloride concentration in agricultural catchments, using the relative variations of Sodium and Chloride and using a neighbouring pristine catchment as a reference for the release rate of Na by weathering. We applied the deconvolution method to the case of the Kabini Critical Zone Observatory, South India, where groundwater was sampled in 188 farm tubewells in the semi-arid catchment of Berambadi and in 5 piezometers in the pristine catchment of Mule Hole. In Berambadi, groundwater composition displayed a large spatial variability with Cl contents spanning 3 orders of magnitude. The results showed that the concentration factor due to evapotranspiration was on average about 3 times more than in the natural system, with higher values in the valley bottoms with deep Vertisols. Linked with this process, large concentration of Chloride originating from rain was found only in these areas. At the catchment scale, about 60 percent of the Chloride found in groundwater originates from fertilizer inputs. These results show that Potassium fertilization as KCl is an important source of groundwater salinization in semi-arid context, and stress that identifying dominant drivers is crucial for designing efficient mitigation policies.
Over time, piles driven in cohesive soils usually experience a large increase in resistance, known as setup or freeze. Dynamic load tests (DLT) and static load tests (SLT) are usually performed to ...verify the axial resistances of piles at specific times after end of driving (EOD) and to quantify these resistances. An extensive field testing program was performed on full-scale instrumented precast prestressed concrete piles driven in cohesive soils at the Bayou Lacassine Bridge in Louisiana, to evaluate the pile setup phenomenon. The testing program included instrumenting two full-scale test piles with a network of vibrating wire strain gauges, pressure cells, and piezometers and instrumenting the surrounding soils with multilevel piezometers. Five SLTs and three DLTs were conducted on each test pile at different times after EOD to quantify the magnitude of setup. Measurements from the load tests on both piles confirmed that the pile setup after EOD followed a logarithmic rate with time. An increase in piles’ total resistances (or setup) of 1.60 to 1.77 times the EOD resistances was observed after the final restrikes. Piezometer data demonstrated a close relationship between the dissipation of excess pore water pressures that were generated during pile driving, following EOD, and pile setup. The load transfer curves derived from the strain gauge measurements were used to separate the side and tip resistance profiles from the total resistance. Piezometers installed in the ground showed that the influence zone, caused by pile driving, extends beyond the 3B distance (B = pile width).
•High-pressure and high-temperature PVT relationship of the dilute n-hexane+ methyl octanoate mixture.•Krichevskii parameter of the n-hexane+ methyl octanoate mixture.•The critical parameters of the ...n-hexane+ methyl octanoate mixture.•Bubble and dew-point curves of the n-hexane+ methyl octanoate mixture.
PρT and phase transition properties (PS,ρS,TS) of the dilute binary mixture of n-hexane + methyl octanoate have been studied near the critical point of pure n-hexane (solvent). The measurements were performed along 11 liquid, vapor and near-critical isochores between (39.3 and 621.1) kg·m-3 over a temperature range from (293 to 622) K at pressures up to 17.7 MPa for the fixed concentration of x = 0.088 mole fraction (or 0.05 mass fraction) of methyl octanoate. The measurements were made using a constant-volume piezometer technique. The study was concentrated in the single - and two- phase regions near the critical point of pure n-hexane to precisely determine the phase boundary properties (PS,ρS,TS) and the critical property (PC,ρC,TC) data of the mixture. The measured critical property data for the mixture were used to study of the isomorphic critical behavior of strongly singular properties such as isothermal compressibility KTX and isobaric heat capacity CPX along the critical isochore and the critical isotherm, i.e., Fisher renormalization (mixture-like behavior) of the critical exponent, -γ⇒γ/(1−α), for strongly singular properties of mixture under study. The measured PρT data were also used to estimate the values of physical meaningful (theoretically important) parameters such as characteristic reduced temperature τ1and density differencesΔρ1 of the mixture. We found that KTX and CPX of the studied mixture exhibit pure-like behavior along the critical isochore at temperature above 508.52 K (slightly above the critical temperature of pure n-hexane, 507.44 K) and along the critical isotherm at densities above 279.82 kg⋅m-3 (above the critical density of pure n-hexane, 232.8 kg⋅m-3). The measured data were used to estimate the Krichevskii parameter Kkr,structural (Nexc)and volumetric (V¯2∞) properties of the dilute mixture near the critical point of pure solvent (n-hexane).
A high-precision large-range fiber-optic interferometric piezometer is designed, packaged, and demonstrated for pore water pressure measurement. The piezometer is an optical fiber extrinsic ...Fabry-Perot interferometer (EFPI), which comprises a fiber ferrule connector/flat contact (FC/FC) connector and an aluminum foil pasted on a thin metal plate. The EFPI forms a sealed chamber with only the outer plane of the aluminum alloy plate being subjected to the water pressure through another hydraulic chamber with a standard filter stone. The deformation of the metal plate is analyzed and simulated for parameter optimization by using the small deflection theory. By adopting the conventional wavelength tracking method, the theoretical simulation and experimental results show a high measurement accuracy of the cm level but a limited measurement range. To resolve the problem, several wideband interferometry (WBI) methods, including free spectral range (FSR)-based, spatial frequency, interference order, and fitted FSR, are employed to analyze the spectrum of the EFPI for comparison. The fitted FSR method has demonstrated its superiority in applications that require simultaneous high resolution and large measurement range. A gas pressure test verifies that the proposed piezometer can work in a wide range of up to 0.5 MPa that is equivalent to a water depth of 50 m. In addition, the proposed piezometer offers several advantages, such as cost-effectiveness, robustness, repeatability, and stability, which further benefits its practical application.
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