Développement d'un nouveau dispositif piézoélectrique d'essai d'impulsion et caractérisation des sols avec les ondes de cisaillement
Autre titre : Development of a new piezoelectric pulse testing device and soil characterization using shear waves
Date de publication2007
Gamal El-Dean, Deyab
The shear-wave velocity (Vs ) is a fundamental parameter that correlates well to soil properties, and is important in many applications. Hence, there is an increasing interest in using shear-wave velocity to define soil state (void ratio, effective stresses, density, liquefaction potential, etc).The global idea of this research is to establish correlations between shear wave velocity and the basic soil parameters that can be used to evaluate soil properties and estimate its strength and deformation characteristics. These relationships will also allow the interpretation of in situ geophysical measurements in terms of the design parameters of soil.The needed reliable correlations should be based on accurate measurements. In this research, it has been proven that the bender-elements method, which is widely used to measure shear wave velocity of soil in laboratory setups, suffers from fundamental and interpretative problems. Consequently, its results are controversial and might give highly erroneous values. After thorough numerical and laboratory investigations, a new piezoelectric pulse testing device (Ring Actuators Setup) was invented and developed in this research. This setup is composed of two units (emitter and receiver) and is capable of measuring shear and compression wave velocities of soil specimens. It is a completely new, versatile, advanced and accurate setup. With this device, many problems of pulse tests, which make interpretation of results difficult and ambiguous, were solved.The ring actuators setup overcomes wave reflections at boundaries (end-caps and sides), sample disturbance, weak shear coupling between soil and device (interaction) as well as the fixation problems, low resonant frequency and limited input voltage of the existing device.The development stages of this device were also useful in reaching important findings for building robust setups. This device was implemented in the top cap and pedestal of a large oedometer cell. This setup was also used with Proctor mold as well as other fabricated molds. Many pulse tests were carried out on different soil types using this device. Shear and compression wave velocities could be accurately measured at dry and partially saturated conditions under very low to high pressures.The compaction curves, in terms of Vs and water content, were drawn for two soil types using the new device. In addition, some correlations between Vs and soil parameters were obtained. Numerical simulations and analytical studies were also carried out in this research in order to study the characteristics of elastic waves transmission through soil specimens in different laboratory setups.The bender-elements and the ring actuators models were studied.The interpretation problems of pulse tests were thoroughly investigated numerically and experimentally. In this research, the reason of 'near-field effect' in pulse tests, which causes significant errors in the interpretation process, could be discovered.The parameters that control this phenomenon could be stated and their effects on the test results were quantified. In light of these results, a new criterion for carrying out and interpreting pulse tests was established. Also, a simple interpretation method is introduced (Energy Rise-Time). Furthermore, the dispersive nature of pulse tests was proven numerically and experimentally. Moreover, it was concluded that the shear wave velocity from pulse tests should be interpreted in the frequency domain, which renders 'the simple methods of interpretation' inaccurate. Based on these findings, a new interpretation technique for pulse tests using Wigner-Ville transform was presented. It was successfully used to interpret the numerical and physical pulse test results in this study.The last part of this research concerns soil characterization using shear wave velocity. Establishing correlations between Vs and soil parameters that can be used for soil characterization may be achieved in laboratory using piezoelectric devices, as mentioned above, or by deriving relationships between Vs and in situ test indices. In this research, the second approach was also examined for gravelly sands. Results of the comprehensive field testing program for the natural soil and the embankment materials (fill) at Péribonka dam site were used to achieve this goal. Thorough interpretations and analyses were carried out for these tests in order to derive correlations between each of CPTu and SPT indices and the in-situ Vs -measurements. Several important relationships and conclusions for soil characterization using shear waves could be reached. These correlations are useful for soil characterization not only at this site, but at other sites of similar soil composition.
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