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Many problems are inherent in measuring stresses in granular materials such as soils. The presence of an inclusion such as a gage disrupts the stress field, causing either stress concentration or stress relief depending on whether the inclusion is more or less stiff than the medium. This phenomenon can seriously affect gage registration. Inertial effects must also be taken into consideration in designing a gage for dynamic measurements. This paper describes the work of the Waterways Experiment Station during the past 2 1/2 years in developing a free-field soil stress gage to minimize these problems. Two different gage sizes were developed. Both sizes use piezoresistive strain gages bonded to stiff diaphragms as sensing elements. Fluid calibrations for the gages are linear to at least 500 psi. Dynamic rise times are approximately 6 μsec. Results of laboratory calibrations in dry sand, and of field measurements during a 500-ton TNT test are presented.
soil stress gages, strain gages, soils (types), piezoresistive crystals, sand, static tests, dynamic tests, measurement, stresses
Ingram, J. K.
Physicist, U. S. Army Engineer Waterways Experiment Station, Vicksburg, Miss.