Dr. Villalobos-Jara, Felipe

The objective of the paper is to study the shear stiffness of Bío Bío sand. To this end, a system to measure the travel time of shear waves in Bío Bío sand samples using bender elements was designed and setup in an adapted oedometer device. Measurements were carried out for sand samples with different relative density, pressure/deformation, diameter/height, dry/saturated and varying the frequency, amplitude, and type of the triggered electric signals. The shear wave velocity and elastic shear modulus increased with relative density and effective vertical stress as previously found by other authors. In addition, Hardin type empirical formulas for estimating the elastic shear modulus are used to compare with the experimental results. Estimations proved to be good only in loading for effective vertical stresses around 100 kPa, since underestimation and overestimation of the shear modulus occurred for stresses below and above that value, respectively. Soil shear stiffness during unloading/reloading cycles was underestimated with the expressions used for loading.

Se presenta un análisis de respuesta sísmica de excavaciones usando un programa comercial de elementos finitos que considera la interacción suelo-muro y el efecto de las etapas constructivas en arena Bío Bío durante el evento sísmico del 27F/2010. Los resultados permiten concluir que puntos ubicados en el perímetro superior de la excavación pueden alcanzar valores de aceleración artificial máxima cercanos a 0.52g y factores de amplificación cercanos a 10, con desplazamientos horizontales relativos mayores a 20 mm. Los espectros de respuesta artificiales obtenidos muestran variaciones pequeñas en el periodo fundamental del sistema hasta una profundidad de 12 m. Finalmente, el uso del parámetro Ar recomendado por la normativa nacional NCh3206 (2010) resulta razonable para excavaciones no superiores a 5 m y para aquellas que superan los 10 m el efecto destructivo del sismo se ve incrementado por el contexto geotécnico local y perturbaciones del sistema analizado.