No abstract

Ultrasonic and bender element tests in the laboratory are typically used to measure elastic modulus and damping ratio. However, interpretation of the results is challenging for a variety of reasons, including the influence of experimental details, geometrical effects and the analytical techniques used for data processing. It is therefore convenient to cross-check results by performing several independent measurements. Three different types of measurements were performed on cementedsand specimens. Longitudinal waves or constrained compressional waves in a cylindrical specimen were generated in a high-frequency range (20-70 kHz) using a newly designed transducer interface. Full dynamic characterisation was made possible by independent measurement of the transducer response. Pure unconstrained compressional waves or simply compression waves were measured in the same specimens with high-frequency transducers. The shear modulus was computed and used to predict the arrival of shear waves on independent bender element measurements. The predicted arrival was close to first-break estimates, and bender measurements were therefore confidently employed to track cement curing effects on a different set of specimens. The specimen frequency response function obtained from the longitudinal wave measurements was examined in detail and damping ratios were estimated for the compression vibration modes in a rod.

This paper summarizes the results of an experimental site investigation and characterization survey, on a residual (saprolitic) soil from granite, in the framework of a research project led by the Faculty of Engineering of the University of Porto (FEUP). This project aims at characterizing these unusual soils in the context of the development of an International Prediction Event (Class A) on the behaviour of different types of piles. A very extensive site characterization campaign, including a large variety of in-situ tests and field methods, has been held. These investigations comprised the application of several geophysical borehole and surface methods, namely P-and S-wave seismic refraction, reflection, cross-hole (CH), downhole (DH), electrical resistivity imaging and ground probing radar (GPR), as well as mechanical tests, namely SPT, CPT and DMT, among others. The site is geologically formed by an upper layer of heterogeneous residual granitic soil, overlaying rather weathered granite contacting a gneissic migmatite. Direct and indirect results from some of the referred surveys were compared between them and with some of the available geological and geotechnical information, namely those obtained from seismic, electrical and GPR profiles, conducted adjacent to three boreholes in which undisturbed soil samples were collected previously to geophysical data acquisition. In addition, a comprehensive laboratory testing program was carried out using the collected undisturbed samples. A discussion of the obtained results is hereby presented, giving emphasis to the correlations encountered between the different tests, specific of saprolitic soils with weak relic structures.

No abstract

Este artigo apresenta um resumo dos trabalhos realizados e os resultados obtidos, numa extensa campanha de caracterização dum maciço predominantemente de solo residual granítico (saprolítico), localiza do nos terrenos da Faculdade de Engenharia da Universidade do Porto (CEFEUP), no âmbito do ISC’2. Este projecto teve como finalidade a caracterização destes solos pouco comuns, no contexto dum programa inter nacional de previsão do comportamento de diferentes tipos de estacas (classe A). Foram utilizados, na referida campanha, vários ensaios mecânicos, nomeadamente, SPT, CPT, DMT e diferentes métodos geofísicos de su perfície e em furos de sondagem, designadamente, sísmica de refracção, reflexão, cross-hole (CH) e down hole (DH), de ondas S e P; resistividade eléctrica; radar de solos (GPR), etc. O maciço é geologicamente for mado por uma camada superficial de solo residual granítico heterogéneo, sobrejacente a um substrato granítico muito alterado em contacto com um migmatito gnaissico. Resultados directos e indirectos de alguns dos mé todos e ensaios utilizados são comparados entre si e com a informação geológica e geotécnica disponível sobre o local, nomeadamente os resultantes de perfis sísmicos, eléctricos e electromagnéticos realizados na proxi midade de três furos de sondagem, nos quais foram recolhidas amostras indeformadas, previamente à realiza ção de ensaios sísmicos CH e DH. Foi também realizado um extenso programa de ensaios laboratoriais com as amostras indeformadas recolhidas. Neste trabalho discutem-se os resultados, com ênfase para as correlações encontradas, específicas de solos saprolíticos com estrutura relicar frágil, conducente a um modelo geológico geotécnico do local estudado.