Dewpoint Potential Meter Abstracts

American Society for Testing and Materials 2003, 'Standard test methods for determination of the soil water characteristic curve for desorption using a hanging column, pressure extractor, chilled mirror hygrometer, and/or centrifuge. Designation D 6836-02.', in 2003 Annual Book of ASTM Standards, ed^eds, American Society for Testing and Materials, Philadelphia, PA, pp.

1.1 This test method covers the determination of soil water characteristic curves (SWCCs) for desorption (drying). SWCCs describe the relationship between suction and volumetric water content, gravimetric water content, or degree of water saturation. SWCCs are also referred to as soil water retention curves, soil water release curves, or capillary pressure curves. 1.2 This standard describes five methods (A-E) for determining the soil water characteristic curve. Method A (hanging column) is suitable for making determinations for suctions in the range of 1 to 80 kPa. Method B (pressure chamber with volumetric measurement) and Method C (pressure chamber with gravimetric measurement) are suitable for suctions in the range of 0 to 1500 kPa. Method D (chilled mirror hygrometer) is suitable for making determinations for suctions in the range of 500 kPa to 100 MPa. Method E (centrifuge method) is suitable for making determinations in the range of 0 to 120 kPa. Method A typically is used for coarse soils with little fines that drain readily. Methods B and C typically are used for finer soils which retain water more tightly. Method D is used when suctions near saturation are not required and commonly is employed to define the dry end of the soil water characteristic curve (that is, water contents corresponding to suctions > 1000 kPa). Method E is typically used for coarser soils where an appreciable amount of water can be extracted with suctions up to 120 kPa. The methods may be combined to provide a detailed description of the soil water characteristic curve. In this application, Method A or E is used to define the soil water characteristic curve at lower suctions (1 to 80 kPa for A, 0 to 120 kPa for E) near saturation and to accurately identify the air entry suction, Method B or C is used to define the soil water characteristic curve for intermediate water contents and suctions (100 to 1000 kPa), and Method D is used to define the soil water characteristic curves at low water contents and higher suctions (>1000 kPa). 1.3 All observed and calculated values shall confirm to the guide for significant digits and rounding established in Practixe D 6026. The procedures in Practice D 6026 that are used to specify how data are collected, recorded, and calculated are regarded as the industry standard. In addition, they are representative of the significant digits that should generally be retained. The procedures do not consider material variation, purpose for obtaining the data, special purpose studies, or any considerations for the objectives of the user. Increasing or reducing the significant digits of reported data to be commensurate with these considerations is common practice. Consideration of the significant digits to be used in analysis methods for engineering design is beyond the scope of this standard. 1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responisibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to its use.

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Anderson, C.E. and Stormont, J.C. 2003, Laboratory Measurement of Soil Moisture at Capillary Potential Greater than 1500 kPa, Transportation Research Board Annual Meeting, Washington D.C.

Both the Brooks and Corey equation and van Genuchten equation for the soil moisture characteristic require the consideration of residual moisture. Testing of the soil moisture and capillary potential relationship using a hanging column or pressure plate may not be sufficient to accurately determine residual moisture. The Decagon WP4 Dewpoint PotentaMeter provides a relatively efficient method to measure total potential in dry soil. A testing procedure was developed to obtain small compacted samples for testing. Best results were obtained for total potential above 1500 kPa. Similar results were obtained by use of samples without control of bulk density. An air-dry procedure to obtain dry soil total potential without the use of special instrumentation is proposed. The results of testing on a silty sand soil are presented.

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Duniway, M.C., Herricka, J.E., et al. 2007, 'The High Water-Holding Capacity of Petrocalcic Horizons', Soil Science Society of America Journal, vol. 71, pp. 812-819.

Petrocalcic soil horizons occur in most arid and semiarid ecosystems around the world, often within the plant rooting zone. Little is known, however, about the water-holding characteristic of soils indurated with CaCO3. We conducted a replicated experiment to define the soil-water release curve (SWRC) for a range of petrocalcic horizon materials. Samples from both plugged and laminar zones of two Stage V petrocalcic horizons in southern New Mexico were characterized. Wetter soil-water potentials were measured using a pressure plate; more negative potentials (down to less than < –10 MPa) were measured using a chilled mirror water activity meter. Measured SWRC data were fitted to the van Genuchten equation. The SWRC methods used were found to be both reliable and repeatable. Plant-available water-holding capacity (AWHC) for desert species (with wilting point set at –4.0 MPa) ranged from 0.26 m3 m–3 in plugged zones to 0.06 m3 m–3 in some laminar zones in contrast to about 0.07 m3 m–3 in the loamy sand parent material. Correlation analyses across morphologies of AWHC and soil properties resulted in significant statistical relationships only with bulk density and porosity. The AWHC and CaCO3 content, however, were significantly negatively correlated within the laminar and positively correlated within the plugged petrocalcic horizon morphologies. Cementation by CaCO3 dramatically alters the water-holding characteristics of soils and understanding these horizons is crucial to understand patterns of soil water in desert systems throughout the world.

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Milczarek, M., van Zyl, D., et al. 2006, Saturated and Unsaturated Hydraulic Properties Characterization at Mine Facilities: Are We Doing It Right?, 7th International Conference on Acid Rock Drainage, St Louis, MO, USA,, American Society of Mining and Reclamation (AMSR). pp. 1273-1286.

The accurate determination of saturated and unsaturated hydraulic properties of mine waste and cover material is critical for predicting long-term drainage behavior and closure performance. The rock fragments typically found in mine waste and borrow materials complicate laboratory hydraulic property measurements. Many hydraulic testing laboratories address this issue by removing all material greater than 4.75 mm in diameter, repacking the remaining fine-earth sample in small diameter cores, and “correcting” the resulting measurements for the gravel content using published correction factors. In order to evaluate several of the aforementioned gravel correction and hydraulic property prediction methods, a laboratory experiment was designed to test various well-graded gravelly materials. An alluvial material sample was used to fabricate eight soils with various particle size distributions. The primary sample matrix for all testing was chosen to be the fine-earth fraction, less than 4.75 mm in diameter. Additional soil materials were then fabricated in which either part of the fine-earth fraction was removed, or gravel material ranging from 4.75 mm to 19 mm diameter was added. Test results show that saturated hydraulic conductivity (Ksat) decreased with up to 30% gravel content but increased by orders of magnitude at higher gravel contents. Moisture retention characteristic (MRC) data showed that the air entry value decreased with increasing gravel contents, although the amount of retained water only slightly decreased as gravel content increased. Depending on how the MRC data is interpreted, the predicted unsaturated hydraulic conductivities either showed increasing hydraulic conductivity as gravel contents increased, or the values converge. The measured hydraulic property data could not be accurately predicted using published correction factors, or by other prediction methods that use particle size distribution data. Consequently, removing the gravel fraction could result in significant error in the prediction of mine waste drainage behavior and the performance of cover systems. It is recommended that published correction factors not be used unless the sample is similar in gradation and bulk density to the soils tested by the published method.

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Petry, T.M. and Jiang, C.-P., 2004, Final Project Report: Evaluation and Utilization of the WP4 Dewpoint Potentiameter Phase I & II Decagon Devices pp

The potential use of the WP4 dewpoint potentiamenter to determine total suction of expansive clay soils has been substantiated by initial testing by the Principal Investigator, as shown in the paper in the Appendix. This project provided further evaluation using a process of Round-Robin testing of prepared specimens of three expansive clay soils at three water content-dry unit weight configurations. One soil came from Texas, one was sampled in New Mexico and the third one came from Missouri. Seven geotechnical laboratories evaluated the suction characteristics of the nine specimens provided and returned their results to the UMR Geotechnical laboratory. There were involved three geotechnical companies from Texas, one geotechnical company from each of Colorado and New Mexico, the geotechnical engineering laboratory at BYU and the UMR Geotechnical laboratory. The results indicate that the relationships of total suction to soil moisture as defined by the WP4 device had significantly less variance and provided slightly more conservative values of suction, when compared to the filter paper method. Research to separate the osmotic and matric suction components of total suction using the WP4 is ongoing. The Round-Robin test results clearly support a revision of the most current ASTM testing standard for use of the WP4 device.

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Sreedeep, S. and Singh, D.N. 2006, 'Nonlinear curve-fitting procedures for developing soil-water characteristic curves', Geotechnical Testing Journal, vol. 29, no. 5, pp.

Measurement of soil suction for developing soil-water characteristic curve, SWCC, is a laborious and time-consuming task. On the other hand, commercially available databases that employ empirical fitting functions or the estimation algorithms for establishing the SWCC are quite costly and hence, beyond the reach of many. In such a situation, application of two simple nonlinear curve-fitting procedures (viz., a spreadsheet based program, SBP, and Levenberg-Marquardt Algorithm, LMA) for developing the drying SWCC was investigated. The utility and efficiency of these fitting procedures have been demonstrated by comparing the results vis-à-vis those obtained from a dewpoint potentiameter, WP4, and a knowledge-based database, KBD. In addition to this, efforts were made to develop correlations between the parameters used in the SWCC fitting functions and the physical properties of the soil, which can be determined quite easily by conducting routine laboratory tests. It has been demonstrated that these correlations can be used very efficiently for indirect estimation of the SWCC of the fine-grained soil.

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Thakur, V.K.S., Sreedeep, S., et al. 2006, 'Laboratory investigations on extremely high suction measurements for fine-grained soils', Geotechnical and Geological Engineering, vol. 24, no. 3, pp. 565–578.

A Dewpoint Potential Meter (WP4) was used to measure suction of two fine-grained soils: a locally available silty soil and commercially available white clay, rapidly. Using these results, efforts were made to check the suitability and efficiency of various fitting functions, for defining the soil–water characteristic curve, SWCC, for high suction ranges (0–80 MPa). In addition to this, a knowledge-based database SoilVision 3.34 was used to estimate the SWCC using Pedo-transfer functions, PTFs. The study brings out that the Fredlund et al. [1997, Proceedings of the 3rd Symposium on Unsaturated Soil, Rio de Janeiro, Brazil, pp. 13–23] PTF yields the best estimate of SWCC for fine-grained soils. The influence of the soil type and dry unit weight, on suction and the SWCC fitting parameters, have also been studied.

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