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A new device for the direct measurement of soil suction over a wide range
Published in P.G. Fookes, R.H.G. Parry, Engineering Characteristics of Arid Soils, 2020
To date instruments for measuring soil moisture suction have suffered from a number of disadvantages. Devices which measure the suction directly do so by actually measuring the pore water pressure but they are restricted to measuring a suction lower than 100kPa (ie;tensiometer). Measurement techniques such as the Psychrometer, the gypsum block and the filter paper are calibrated against some other physical property such as humidity, electrical resistance or absorption which is also related to the soil suction. They all measure suction at atmospheric air pressure but many of them suffer from a “slow” response time (at best several hours and often weeks or even months). In addition the accuracy of many of them is not good, particularly in the range -100kPa to -1000kPa.
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Published in L.G. Wilson, Lorne G. Everett, Stephen J. Cullen, Handbook of Vadose Zone Characterization & Monitoring, 2018
Joseph P. Hayes, David C. Tight
Field data are presented in Figures 23.3 through 23.8. The instruments, which were installed in June 1987, were monitored periodically for approximately 5 months through the late summer and early fall. A single rainfall event, a storm that deposited approximately an inch of rain, occurred 129 days after the instruments were installed. Gypsum block readings were converted from resistance to soil tension using a calibration curve prepared by the gypsum block manufacturer. Soil tensions were read from the tensiometers in centibars. While a characteristic curve relating soil tension to soil moisture was not prepared for the site, standard curves for sandy loam and clay loam soils were used to compare soil tension readings to results of soil moisture analyses performed on soil samples taken during installation of the devices. Soil tensions agreed reasonable well with these soil moisture results except where noted below. Data from both tensiometers and gypsum blocks have been plotted together for each instrument station to allow comparison of results.
Robotics and Sensors: Environmental Applications
Published in John G. Webster, Halit Eren, Measurement, Instrumentation, and Sensors Handbook, 2017
Gypsum blocks use two electrodes placed into a small block of gypsum to measure soil water tension. Wires connected to the electrodes are connected to either a portable handheld reader or a data logger. The amount of water in the soil is determined by the electrical resistance between the two electrodes within the gypsum block. More water present in the soil will reduce the resistance, while less water will increase it.
Effect of Infills on Seismic Performance of Reinforced Concrete Frame structures—A Full-Scale Experimental Study
Published in Journal of Earthquake Engineering, 2019
For brittle infills such as MHB and PB blocks, in theory, the higher strength of infill will accelerate their damage at later stage of deformation. The result of cracking development indicates the damage of specimen Frame-PB concentred on the four corners of the wall, while the damage of the Frame-ALC focuses on mortar layer and compressive crush damage of ALC panels. Due to the compressive strength of gypsum block is small, the high compression in the corner zones of Frame-PB caused by lateral deformation of the beam and column leads to more corner crack and collapse in the wall. Figure 8 also proves that the damage development of the specimen Frame-ALC is more stable and lower significantly than the others. Before the end of testing, the collapse ratio of the Frame-ALC was controlled effectively fewer than 2.5% the total area of wall, which just is 1/10 of the one in Frame-PB. For MHB has higher strength and stiffness, the collapse damage of specimen Frame-MHB focused on the diagonal strut zones and the bottom zone of frame beam, which leads to the highest and fastest wall collapse ratio. This can be explained by the fact that the compressive behavior of bricks at corner zone of wall is transferred at diagonal direction as a result of high compressive strength of MHB and bond condition from mortar at early stage.
Design and fabrication of gypsum mold for injection molding
Published in Journal of the Chinese Institute of Engineers, 2018
C. C. Lin, G. H. Lee, Y. J. Wang
The development and fabrication of a gypsum insert for an injection mold is presented in this study. The influences of gypsum mixture and vibration with a compression process on the mechanical properties of gypsum molds were demonstrated. The vibration process reduces the voids inside the gypsum block during the gypsum solidification process. Vibration with a compression process can make the microstructures of gypsum more compact and dense, and thus, the gypsum mold can resist injection pressure. The compressive strength of the gypsum is increased by 63% after the gypsum material is processed by introducing vibration with a compression process. Hundreds of molding cycles can be achieved using the gypsum mold. The dimensional shrinkage of the molded part from the melted state back to the solid state can be compensated for the expansion characteristics of gypsum, and this creates high replication accuracy. The proposed method can significantly improve the porosity and the strength of a gypsum insert and make gypsum more useful for injection molding. This novel process provides an alternative approach to producing a mold rapidly, with low energy consumption and low environmental impact.