Behaviour of CFA, Driven and Bored Piles in Residual Soil. International Prediction Event - Experimental Site - ISC'2

Abstract

The 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 deformation evaluation). Fully instrumented pile load test are very much informative for the elaboration of specific correlations between load-deformation behaviour and in situ tests results (and also fundamental soil mechanics parameters obtained from precise laboratory tests), for establishing well-based design criteria. A fundamental base to this is the execution of extensive site investigation campaigns, and laboratory characterization tests, over specific soil profiles, allowing a confident and flexible choice in input parameters for a pile prediction event (PPE), i.e., a Class A exercise. In the preparation of the 2nd International Conference on Site Characterization (ISC'2), held in Sept. 2004 at the Faculty of Engineering of the University of Porto (FEUP), Portugal, an experimental site, here situated, was launched for the purpose of organizing an international PPE, organized under the auspices of TC-16 and TC-18 of ISSMGE.. A very extensive site characterization including a large variety of in-situ tests and also pile load tests were prepared in this experimental site, under the sponsorship of 4 construction companies. Data compiled during the investigation and characterization of the site, identified a residual (saprolitic) granite soil of varying thickness, overlaying more or less weathered granite contacting high grade metamorphic rocks. These investigations comprised the application of several geophysical borehole and surface methods, namely: P and S-wave seismic refraction, reflection, cross-hole (CH), down-hole (DH), electrical resistivity imaging and ground probing radar (GPR), as well as mechanical tests, namely: SPT, CPT, PMT and DMT, among others. Undisturbed samples were retrieved and an extensive laboratory testing program was carried out, including oedometric consolidation tests, CK0D triaxial tests using local strain measuring devices and bender-extender elements, as well as resonant column tests.