Influência do comprimento de bucha nos métodos de previsão da resistência estática do ensaio SPT

Abstract

The present research deals with a study realized from CPT and SPT tests performed close to each other and forming a selected database organized by the author. The main objective of the research has been the comparison of two calculation models for predicting static resistance mobilized during the 45 cm sampler penetration proposed by Schmertmann (1979) and Aoki (2013). The first proposal was developed from the premise of open -ended sampler penetration, while the second proposal considered the possibility of closed ended sampler penetration. Aoki (2013) considered the possibility of better interpretation of the SPT test when the length of the soil sample is measured after the sample penetration of 45 cm. The author adapted Schmertmann's equations (1979) to the dimensions of the sampler used in Brazil, and to different soil sample lengths, in order to allow their direct comparison with Aoki's (2013) equations results. Through the application of the two calculation models, the unit tip resistance and the unit lateral friction during soil sampler penetration was estimated and compared to qc and fs results from CPT, using different approaches. The author detailed the interpretation for a chosen tests set, indicating the other tests results in attached documents. The author observed that from Schmertmann (1979) and Aoki's (2013) proposals, it was possible to predict values close to the experimental ones. The results indicated the great possibility of qc predictions in clay soils when applying Aoki (2013) model, but not in sandy soils, better reproduced by Schmertmann's (1979) and Aoki (2013). Aoki (2013) expectations were confirmed: the possibility of measurement of the soil length at the end of penetration brings new possibilities for interpretation of the SPT test, allowing it to be an even more useful tool for the foundation designer. The interpretation reveals that the careful test procedure, by more qualified teams and reaching more accurate results, together with the instrumentation of the energy arriving at the sampler top are fundamental to a better interpretation of the test, allowing the continuous evolution of its interpretation.