Jaime Santos

Comparison of Simultaneous Bender Elements and Resonant Column Tests on Porto Residual Soil

Bender elements are a powerful and increasingly common laboratory tool for determining the shear wave velocity hence the small strain shear stiffness (G0) in soil samples. There are several advantages of the bender element technique, namely its simplicity and ease of use; however, there is no standard developed for this technique as the interpretation of the results involves some uncertainty and subjectivity. Different approaches have been proposed to deal with these issues, especially in terms of the interpretation techniques, based on the time and on the frequency domain. In the present work, a modified resonant column, equipped with bender elements, has been used, where shear wave velocities can be measured independently and different interpretation methodologies of the bender element results can be applied. For this study, natural samples of Porto granitic residual soil were tested, since this geomaterial has been object of research and interest for many years in the University of Porto. The paper will focus on the comparison of simultaneous results of shear wave velocities by the resonant column and the bender elements. It is intended to provide some contribution to the routine laboratory practice using bender elements, with further insight in the interpretation of the results.

Use of surface waves for geotechnical characterization of soft alluvial deposits - the Póvoa de Santa Iria case study

The surface-wave method using a multistation approach is a powerful field test as it is fast, robust and cost-effective for geotechnical zonation of large areas. A case study is presented to illustrate the application of the method for the geotechnical characterization of an area located at Povoa de Santa Iria, where Miocene bedrock is covered by thick Quaternary terraces and soft alluvial deposits. The results are analysed along with other relevant data: boreholes with standard penetration test data, resonant-column tests on undisturbed samples and other available geological and geotechnical data.

DESIGN SPECTRUM-COMPATIBLE TIME HISTORIES FOR NUMERICAL ANALYSIS: GENERATION, CORRECTION AND SELECTION

In nonlinear seismic analysis the ground motion has to be represented through time histories. In this paper, a high number of spectrum-compatible time histories were generated, based on random vibration theory. In order to correct non-physical shifts in velocity and displacement, the generated time histories were corrected using the procedure described by Pinto and Pegon [1991]. The characteristics of the resulting time histories display a significant scatter. Additional conditions were introduced to improve the time histories taking into account the recent recommendations of Eurocode 8 [CEN, 2003], some recent developments in displacement spectra, and also the procedure developed by Seed et at. [1975] to evaluate the equivalent number of uniform cycles. The proposed approach was applied to the Portuguese code to illustrate its advantages and limitations.

Insight Learning from the Results of ISC2 Pile Prediction Event in Residual Soil

In the north-western region of Portugal residual soils from granite are dominant, with specific and complex characteristics, typical of non-textbooks materials. Current design practice of bored and driven piles in residual weathered formations is merely semi-empirical and based on bearing capacity analyses (in general, without settlement evaluation). Fully instrumented pile load tests are very much informative for the elaboration of correlations between load-deformation behaviour and in situ tests results, for establishing well-based design criteria. A thorough study was held in 2004 at the University of Porto, with the execution of an extensive site investigation and laboratory characterization tests, allowing good input parameters for a pile prediction event. This project, supported by 4 construction companies, made use of pile load tests, aiming to launch a class A prediction event, i.e., all the predictions were submitted before the conduction of static pile load tests. Three different kinds of piles were executed: bored piles with temporary casing, continuous flight augered, CFA, piles with circular section — nominal diameter phi600mm, and driven piles (square section, B=350mm). The piles were loaded axially to failure. The submitted predictions is resumed, revealing surprising overestimations in the bored piles capacities, while for the driven piles there was an underestimation of the gains due to pile installation effects (densification, etc.). In this paper a simple approach to quantify the locked-in toe residual loads will be addressed.

Site Characterization of São Sebastião Volcanic Crater Using Geophysical Tests

The Azores archipelago is located at the North America, Eurasia and Africa triple junction showing high seismicity and volcanism typical of an active plate boundary. Terceira Island has been affected by several damaging earthquakes and the 1980 January 1st earthquake (M=7,2) was the strongest in Azores during the last century. The Sao Sebastiao volcanic crater, located at SE of Terceira Island, is characterized by an amplification of ground movements inside the crater with respect to the surroundings. Inside this volcanic crater, is located the village of Sao Sebastiao that has shown an anomalous seismic behaviour in a more local expression during the past earthquakes. The local geology and geotechnical characteristics of the soil deposit play a strong role in the seismic ground shaking at the site. Some previous geophysical studies with information merely qualitative were not able to perform a rigorous and well-defined model of the crater. A recent survey added new information that allows a better comprehension of the damage distribution, since it indicates inside the crater a basaltic lava layer controls the seismic behaviour of that area, serving as a protection to the buildings in the SW region of the crater.