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.
The paper analyzes the data of groundwater level (GWL), groundwater temperature (TW), and electrical conductivity (EC) measurements in three deep piezometers (B1, B2, B3) in the Jadro spring basin, ...taken from October 2010 to December 2021. The variation of these parameters is analyzed at different time scales: annually, monthly, daily (24 hours), and hourly. They are compared with the data of the same parameters measured at the Jadro Spring. The analysis of the maximum observed rise and fall rates of the GWL showed that the piezometers were drilled in very different karst environments. Piezometer B1 is located in a karst matrix where the water flows predominantly in a diffuse laminar (slow-flow) regime. Piezometers B2 and B3 are located in a fault line where numerous large karst underground formations occur and rapid turbulent water flow takes place. The mean annual flows of the Jadro Spring strongly depend on the mean annual GWL-s in each of the piezometers. For much of the year (about 99%), the GWL in all three piezometers is more than 210 m below the ground surface. As the measuring sensors are located near the bottom of the piezometers, the groundwater temperature is almost stagnant. It is always at 12.5 ºC in piezometer B1 and behaves almost identically in piezometer B3. Water temperature is the highest in piezometer B2 and hovers around the average value of 13.5 ºC. At the Jadro Spring, the average water temperature is 12.95 ºC. The electrical conductivity values are the highest in piezometers B2 and B3, with an average of around 0.5 mS/cm. They are lower in piezometer B1, where they range around an average value of 0.465 mS/cm, while at the Jadro Spring, they vary from 0.40 mS/cm to 0.48 mS/cm, with an average value of 0.44 mS/cm. A distinct seasonal pattern in groundwater level behavior is evident across all piezometers. However, no discernible upward or downward trend is observed.
•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.
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).
We calibrate a subgrain‐size piezometer using electron backscatter diffraction (EBSD) data collected from experimentally deformed samples of olivine and quartz. Systematic analyses of angular and ...spatial resolution test the suitability of each data set for inclusion in calibration of the subgrain‐size piezometer. To identify subgrain boundaries, we consider a range of critical misorientation angles and conclude that a 1° threshold provides the optimal piezometric calibration. The mean line‐intercept length, equivalent to the subgrain‐size, is found to be inversely proportional to the von Mises equivalent stress for data sets both with and without the correction of Holyoke and Kronenberg (2010, https://doi.org/10.1016/j.tecto.2010.08.001). These new piezometers provide stress estimates from EBSD analyses of polymineralic rocks without the need to discriminate between relict and recrystallized grains and therefore greatly increase the range of rocks that may be used to constrain geodynamic models.
Plain Language Summary
Understanding the tectonic stress in lithospheric plates is key to evaluating a breadth of geological phenomena, such as the evolution of major ductile shear zones. One method of estimating past stress magnitudes is to measure microstructural features that vary systematically with the applied stress, a technique known as “piezometry.” Several piezometers have been calibrated based on the size of recrystallized grains in a rock, but they are limited to domains consisting of only a single mineral, as the presence of multiple minerals inhibits grain growth. Subgrains, however, are features inside individual grains and are unaffected by the presence of other minerals. We use electron backscatter diffraction (EBSD), a scanning electron microscopy technique, to quantify the relationship between subgrain size and stress in rocks that have been deformed in a laboratory under controlled conditions, providing the first subgrain‐size piezometer calibrated for EBSD. In addition, unlike many piezometers that are calibrated for a single mineral, our piezometer can be applied to each mineral in a rock. This piezometer offers the potential to investigate the macroscopic stress and microscopic stress distributions in a wide range of rock types.
Key Points
We present a new subgrain‐size piezometer calibrated for EBSD, with a 1° critical misorientation angle
This subgrain‐size piezometer can be applied to multiple minerals and appears to be independent of the deformation geometry
This subgrain‐size piezometer should be unaffected by the presence of secondary minerals and thus applicable to polymineralic rocks
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