Abstract Understanding the dynamic behavior of soils is essential to the study of the influence of seismic loads on the instability of submarine slopes, an important issue in Brazil and other countries. The shear modulus and the damping ratio are two fundamental parameters for the study of this behavior. Determining these parameters for Speswhite kaolin clay is the object of the present study using resonant column tests and dynamic centrifuge tests with accelerometers and pairs of bender elements. The curves obtained in the laboratory are compared with empirical curves and comparable data in the literature. Good agreement was observed between experimental data and the empirical prediction for the degradation curve of the normalized shear modulus. The damping curve for very low strains, obtained with resonant column tests, was consistent with the empirical curve. However, consistent with a trend observed in the literature, the centrifuge test results presented considerable scatter (dispersion), attributable to the difficulty in modelling damping dissipation mechanisms in the centrifuge.

Abstract Dynamic soil parameters such as the shear modulus suffer degradation while damping in soil increases under dynamic loading. These can be determined from various tests such as element tests, field tests and centrifuge experiments. Most of the studies about dynamic soil characterization have focused on evaluating these parameters assuming horizontal ground conditions without considering the effect of static shear stresses induced by ground inclination. This paper presents a dynamic centrifuge test conducted on a layered gentle slope comprising clay and sand, to obtain experimental data in terms of shear modulus and damping for various shear strains. Particle Image Velocimetry (PIV) was employed to measure the displacements and to calculate accelerations due to seismic loading at various depths throughout the slope model. The results suggest that the static shear stress caused by the profile inclination causes a more pronounced degradation of the shear modulus when compared to flat ground conditions. Moreover, the damping during the centrifuge test exhibited larger values than expected, following a similar behavior observed in other experimental programs. The strain rate analysis revealed the mobilization of shear stresses higher than the monotonic shear strength for the clay layers during the seismic shaking. experiments sand strains PIV (PIV model Moreover expected programs shaking

Resumen Brasil se encuentra en una región intra-placa de baja a moderada sismicidad, esto quiere decir que hay una limitada disponibilidad de registros de acelerogramas representativos de la región. Parte de un estudio de respuesta local o del diseño sísmico de estructuras requiere del uso de registros aceleración-tiempo que sean compatibles con un espectro de diseño. El presente trabajo tiene como objetivo la aplicación de metodologías para obtener acelerogramas representativos de la región sudeste brasilera, en particular en la región offshore de la cuenca de Campos. Se utilizó la información del análisis probabilístico del riesgo sísmico desarrollado para la región de interés en este estudio para obtener el espectro de respuesta de diseño y para definir los escenarios sísmicos que generan mayor influencia. Adicionalmente, se utilizó la información de acelerogramas registrados a partir de dos sismos relativamente recientes ocurridos en la región sudeste brasilera, para la aplicación de una de las metodologías de obtención de acelerogramas sintéticos.

Abstract Brazil is in an intraplate area of low to moderate seismicity, this means that few or no records of strong ground motions are available. Part of the site response analysis and seismic design of structures require the use of acceleration time-histories compatible with a specified target response spectrum. This study aims to utilize methodologies based on the use of existing earthquake records from a well-known database and synthetic accelerograms to obtain ground motions representative of the Brazilian Southeast Region, particularly in the offshore Campos Basin. Information from a probabilistic seismic hazard assessment performed in the interest area was employed as input to the methodologies applied in terms of target response spectrum and the dominant earthquake scenarios. Besides, the acceleration time-histories of two relatively recent earthquakes that occurred in the Brazilian Southeast were used to apply one of the approaches to obtain a synthetic spectrum compatible accelerogram.

Resumen Las arenas carbonatadas son caracterizadas por la presencia de granos frágiles que pueden influenciar su respuesta mecánica, especialmente por cargas cíclicas. La velocidad de la onda de corte (VS) proporciona información relevante para el diseño de una cimentación inserida en este tipo de suelo y puede ser obtenida a partir de ensayos de laboratorio con el uso de bender elements (BE). Este artículo tiene como objetivo evaluar el valor de VS de una arena carbonatada a partir de ensayos triaxiales con BE utilizando tres métodos en el dominio del tiempo. También se evalúa la influencia de la carga, descarga y ciclado sobre la rigidez al corte. Los resultados mostraron que la presión de confinamiento influencia los parámetros dinámicos. Para niveles de presión más altos, las señales son más susceptibles a los efectos de campo próximo y los parámetros dinámicos son menos influenciados por el ciclado.

Abstract Carbonate sand is characterized by the presence of fragile grains, which may influence their mechanical response due to the imposed loading; especially cyclic loading. The shear wave velocity (VS) provides relevant information for the design of foundation inserted in this type of soil, which can be obtained from laboratory tests with the use of bender elements (BE). This paper aims to evaluate the VS value of a carbonate sand from triaxial tests with BE using three methods in the time domain. The influence of loading, unloading and cycling on VS is also evaluated. The results confirmed that the confining stress affects the dynamic parameters. At higher stress levels, the signals are more susceptible to the near field effects and the dynamic parameters are less influenced by cycling.