Bender elements are used to measure the low-strain shear-wave velocity of soils in many geotechnical laboratories worldwide. Despite their popularity, the method remains without a standard, mainly owing to the difficulties in controlling the actual behaviour of the bender element inside the specimen. Previous experimental and analytical studies on the behaviour of bender elements have found evidence that the actual transmitter movement is not equal in shape or frequency content of the electrical signal used as the input excitation. Furthermore, the size and geometry of the specimen influence the response of these piezoelectric transducers. In this study, miniature accelerometers are used to measure the particle vibration inside specimens during bender elements tests, which were performed in a resonant column device. The comparison between shear wave velocities obtained by resonant column and miniature accelerometers tests allow a better interpretation of bender element testing. The sine pulse bender element test results showed good agreement with the resonant column measurements. The results show the importance of the resonant frequencies of the bender element and their influence on frequency domain analysis of bender element testing.
Objective: This research work addressed the comparison of the stiffness of a granular base under optimum water content and total saturation conditions. Methodology: The methodology focused in the development of an experimental program and the computation of a function, which permits to assess the elastic moduli of the material. A triaxial cell equipped by local LVDT transducers, capable of managing different stress paths, was used to measure the smallstrain stiffness of a granular base under two different conditions of moisture. The material was compacted with optimum water content and subjected to a series of loading-unloading cycles under isotropic conditions. In addition, identical specimens were prepared to be saturated and the experimental procedure was repeated to obtain the moduli in these new circumstances. The moduli were assessed by a hyperbolic model, and its relationship with the confining pressure was computed.
Results:The results indicated that numerical model was adjusted to the experimental results. In addition, it was found that the elastic moduli decrease 3% to 8% in conditions of total saturation versus the condition of optimum water contents.
Conclusions:The small-strain stiffness in the granular base depends on the water content, and the moisture can affect the deformation in the pavement structures.
Se utilizaron tres aditivos (cal, cenizas volantes y aceite sulfonado) para disminuir las propiedades de una arcilla altamente expansiva (bentonita), con el fin de determinar las ventajas técnicas de cada alternativa bajo las mismas condiciones y ensayo. Para tal fin la bentonita se mezcló con diferentes concentraciones de aditivo y se realizaron ensayos de caracterización física y mecánica que permitieron analizar el comportamiento de cada uno. Se encontró que las cenizas volantes requieren ser adicionadas en cantidades excesivas para lograr disminución del potencial de expansión a valores admisibles. Con la cal se encontró un valor óptimo del 10% ya que logró una reducción considerable en las propiedades expansivas de la bentonita. Los resultados obtenidos con el aceite sulfonado evidenciaron que la estabilización electroquímica que lleva a cabo, requiere de factores ambientales favorables para desarrollar su efecto.
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