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The stiffness and Young modulus of a geotechnical structure like an embankment, a pavement layer or even the "in situ" ground mass, can be obtained with this light and user friendly equipment. It is a reliable equipment, providing results on time, allowing the immediate verification of the properties of the terrain, increasing the efficiency of the construction control and the reduction of costs.
The technology of the GeoGauge was originally developed by the defense industry of the United States of America for the detection of land mines, and was further developed towards the conception of light equipment for use in the industry of construction. The stiffness of the ground is obtained provoking small vibrations, in 25 different frequencies between 100 and 196 Hz, and measuring the resulting deformations (less than 1.27x10-6 m at 125 Hz). The ring base or foot, it put in contact with the ground and the connection between the base and GeoGauge body is done using a rubber insulating. The equipment records the value of the stiffness for each one of the 25 frequencies and displays the average value. The depth of measurement ranges from the surface up to 31 cm. The interval of functionality is between 3 and 70 MN/m for the stiffness and between 26.2 and 610 MPa for the Young module. The Poisson ratio can vary between 0.20 and 0.70 in increments of 0.05. For a Poisson ratio of 0.35 the deformability module it is obtained multiplying the rigidity (K) for 8.67. While the Young module refers to a property of the material and doesn't present any physical limit, the stiffness is a property of the structure, being influenced by its physical dimensions, by its limit conditions and by the module of the constituent materials.
The results of the GeoGauge showed correlation with several other geotechnical procedures like the dry unit weight, the plate load test, the impact deflectometer or the dynamic penetrometer. Our results are in accordance with the bibliography data.
A comparative analysis of the results obtained with the GeoGauge and the Falling Weight Deflectometer (FWD) on the sub-base and base layers was also done. The results showed that, in spite of the different test methodologies and data analysis procedures, the results presented agreement. However it is considered necessary to develop further studies to define a reliable methodology to use the GeoGauge in the control of the pavement layers deformability. The technical standards used for the evaluation of the deformability using the falling weight deflectometer, could be a good start for the preparation o similar procedures to use the GeoGauge in the control of pavement layers.
The reliability, the reduced operation costs, requiring only one operator and the user friendly interface will certainly provide a large use for the GeoGauge in the geotechnical practice.
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