Dr. Villalobos-Jara, Felipe

The effect of fine particles on the zeolite shear strength is assessed for possible construction applications. A brief geological description of the zeolite is presented. Three groups of zeolite samples were prepared, namely a coarse material with no fines, a finer material with 3% of silt and a silty material with 15% of clay. Results from standard classification, compaction and compressibility tests are shown and explained. It was found that due to the low specific gravity, low values of density were obtained in compaction tests. Additionally, shear strength tests were performed, resulting in different response in terms of shear stress and horizontal and vertical displacements. The coarse zeolite followed a similar friction-dilation response as in feldspathic and quartz sands. However, addition of 3% of fines reduced significantly the zeolite shear strength. Furthermore, the finest material was tested under two different displacement rates, reflecting also marked differences in shear strength and stiffness.

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.

The 27th February 2010 earthquake in central and south of Chile was a very strong test for recently constructed geosynthetics reinforced soil wall solutions as bridge abutments. This 8.8 moment magnitude subduction earthquake caused severe damage to several traditional reinforced concrete walls for bridge abutments. However, no significant damage was found in relatively new geosynthetics reinforced solutions. For that reason, it is important to review the design and construction employed in these projects. To this end, a representative case located close to the epicentre is described and studied. Moreover, information is provided regarding the foundation soils, design and construction sequence of the geosynthetics reinforcement used for bridge abutments. The foundation soils were poor, corresponding mainly to marine and fluvial deposits close to the stream and mouth of the Andalién River. The analysis covers the verification of static and seismic external and internal stability. In addition, global static and seismic analyses are carried out. The methods used for the analyses are limit equilibrium and pseudo-static following recommendations of the FHWA. Results show that the design was adequate to cope with such a strong seismic event in terms of external and internal stability. Nevertheless, it was found that the inclusion of piles prevented a global seismic failure of the geogrid reinforced soil walls as bridge abutment. Final comments and remarks are presented related to design and construction which may explain the favourable performance of geosynthetics reinforced structures under this strong subduction earthquake.