Research Outputs
Experimental study of the fine particles effect on the shear strength of tuff zeolites
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.
Geotechnical properties of a natural zeolite
The work presented by Georgiannou et al. (2017) on geotechnical properties of a natural zeolite is an important contribution because there are not many published works on this subject. The authors mention some of the several studies with natural zeolites in other research areas, mainly in environmental applications such as waste-water treatments, soil–bentonite mixtures and in the improvement of cement and concrete properties. They also mention the existence of numerous engineering and industrial applications of natural zeolites in farming, fisheries, textiles and construction materials. This discussion will complement and comment on some of the results obtained by the authors and suggest that extra information would be useful in order to make a more comprehensive analysis.
Study of the static and seismic performance of a geogrid reinforced soil wall as bridge abutment in Concepción
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.
Design, construction, and operation of a monitored district heating pipeline system
The need for understanding the performance of district heating pipeline systems has led to the development of a monitoring program. This program includes the design of the connection of an instrumented section of piping within an in-use district heating network. The design complies with the current European district heating recommendations and standards. Monitoring consists of the measurement of earth pressures against the pipes, axial pipe displacements, and temperature of the fluid and soil around the pipes. There are different conditions being tested such as thickness of insulation materials, temperature ranges, and bedding soil type. In particular, there is interest in testing the corner positions. Details of the piping and instrumentation arrangements as well as soil geotechnical characteristics are presented. It was found that when the fluid temperature increased from ambient conditions up to 90°C, pipes were moving all along their length. Moreover, after a fluid temperature drop from 90°C to 20°C over 20 days and subsequent increase to 90°C again, pipe axial displacements did not return to the same values as before
Observations from a parametric study of the seismic design of soil nailing
A parametric study of the seismic design of soil-nailed walls is performed. Values of a set of geometrical and mechanical parameters for the nail and soil of a slope have been varied to assess their effects on the global factor of safety FSG. Equations of limit equilibrium of forces based on the Coulomb criterion for a two-block-failure mechanism are adopted. Pseudo-static force analyses with a horizontal seismic coefficient of 0·15 are carried out, which is normally used in engineering practice for temporary soil-nailing projects. It was found that FSG clearly increases with soil cohesion and friction as well as nail length, diameter and inclination, although nail inclinations higher than 15° can become detrimental. It was found that there is a combination of nail spacing and wall inclination for which the trend of FSG changes from decreasing to increasing. This situation is caused by a software mathematical optimisation routine, which does not take into account whether it is possible for the failure surface shape to occur or not. Additionally, perforation diameters larger than 100 mm are necessary for FSG ≥ 1·1 and soil–nail shear stress rs values of more than 200 kPa are not significantly beneficial.
Study of the elastic shear modulus of Bío Bío sand using bender elements in an oedometer
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.
Análisis numérico de la respuesta sísmica de excavaciones sostenidas con muro Berlinés en arena
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.