. 2000. A portable data collection system for simultaneous cone penetrometer force and volumetric soil water content measurement. Can. J. Soil Sci. 80: 23-31. A new mechanism and sensors are described that can improve the quality of soil penetration resistance data. The electric-motor-driven mechanism pushes the cone into the soil at a constant rate. The force measurement is made with a miniature load cell sensor located adjacent to the cone head to reduce errors caused by friction between the soil and penetrometer shaft. A small water-content sensor is located on the shaft just above the load sensor, so that soil volumetric water content measurement is made on the hole walls just after the cone force is measured. The general nature of the electrical performance of the water content sensor was evaluated for different probe geometries by optimizing the portion of the electromagnetic energy passing into the soil compared to that remaining in the probe. Some early field and laboratory test results are shown, which were obtained using a complete prototype instrument. The resolution of each sensor is ±0.03 m 3 m -3 for water content, ±0.0007 MPa for cone penetration pressure (cone index) and ±0.003 m for depth. Le mécanisme activé par un moteur électrique pousse le cône dans le sol à une vitesse constante. La mesure de la force de résis-tance est faite par une cellule à pression miniature située juste au-dessus du cône, pour limiter l'erreur causée par la friction entre le sol et la tige du pénétromêtre. Une capteur d'humidité de taille réduite est situé sur la tige elle-même, immédiatement au-dessus de la cellule à pression, de façon que la mesure d'humidité soit faite sur les parois du trou juste après que la résistance ait été mesurée. Le comportement global de la performance éléctrique du capteur d'humidité a été évaluée pour différentes géométries, en optimisant la portion de l'énergie électromagnétique passant à l'extérieur du capteur et dans le sol, par rapport à la portion restant dans les limites physiques du capteur. Des résultats de tests initiaux réalisés sur le terrain et en laboratoire sont présentés. Ces résultats ont été obtenus avec un prototype de l'instrument. La résolution de chaque capteur est de ±0.03m 3 m -3 , de ±0.0007 MPa pour la résistance à la pénétration du cône, et de ±0.003 m pour la profondeur. Mots clés: Capteur d'humitidé, la résistance à la pénétration du coneCone penetrometer measurements are often used to quantify soil strength in arable soils. The measurement is performed by forcing a cone of standard geometry into the soil and measuring the force required to do the insertion as a function of depth of penetration. Some problems with existing instruments have been inconsistent driving velocity, friction forces on the drive shaft, absence of corresponding water content data, and lack of portability.Portable instruments are often hand-driven, requiring a practiced operator who has developed a technique for holding the insertion rate constant so that a depth estimate can be correlate...
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The critical-state theory can be applied profitably to analyse the mechanical behaviour of agricultural soil. Critical-state parameters and other soil properties are affected by the microstructure and unsaturated nature of agricultural soils. We determined the critical-state boundaries of an agricultural soil in both saturated and unsaturated triaxial tests and examined the effects of matric suction and initial structure on critical-state boundaries. On the compression plane, the presence of air and matric suction in the pores of unsaturated soil significantly affected critical-state boundaries by increasing compressibility, A.On the deviatoric stress-mean net stress plane, the strength increased with matric suction. On this plane, the critical-state lines for the unsaturated tests had non-zero intercepts. For a given soil structure, the frictional parameter M remained fairly constant with matric suction change. However, a change in the initial microstructure resulted in a change in M, causing the position of the critical-state line to 'pivot' in state space.
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