Stratigraphic profiling by cluster analysis and fuzzy soil classification from mechanical cone penetration tests J. Facciorusso & M. Uzielli Department of Civil Engineering, University of Florence, Italy Keywords: geologic uncertainty, stratigraphy, cone penetration testing, clustering, fuzzy ABSTRACT: Cone penetration testing has gained increasing popularity in geotechnical site characterization due to its speed and economy, and to the good quality of its data in terms of precision, accuracy, repeatability and continuity of measurement when compared to other in-situ tests. In the present paper, cluster analysis and fuzzy soil classification from mechanical cone penetration tests are applied for stratigraphic delineation in the harbor area of the southern Italian town of Gioia Tauro. The main features of the clustering and fuzzy algo- rithms adopted are described. The results of stratigraphic profiling by cluster analysis and fuzzy classification for a number of soundings are shown and compared; the applicability of the adopted site characterization techniques is assessed through comparison with adjacent borehole logs and standard penetration tests. 1 INTRODUCTION Cone penetration testing is increasingly employed in geotechnical site characterization due to the preci- sion, accuracy, and repeatability of its output data. Data deriving from mechanical cone penetration testing, however, are affected by larger uncertainties than those from electrical cone penetration and pie- zocone testing; furthermore, the data sampling inter- val is greater and the distance between cone-tip re- sistance and sleeve friction measures is larger. Nonetheless, in Italy, at present, a considerable number of databases used for important geotechnical analyses - such as liquefaction susceptibility evalua- tion - consists of data from mechanical cone tests. Thus, it appears advisable to apply different tech- niques and compare their results to obtain reliable stratigraphic profiling from such data. In the geotechnical literature, results of cone penetration tests have been interpreted to delineate stratigraphic profiles in one or more of the following ways: 1) visual examination of raw data; 2) empiri- cal soil classification charts; 3) statistical methods; 4) fuzzy soil classification techniques; and 5) neural networks. Here, the applicability of cluster analysis and fuzzy soil classification to mechanical cone penetration test data for stratigraphic profiling is evaluated for the harbor area of the town of Gioia Tauro, in southern Italy; this study also assisted with liqufaction risk analysis in this area.. A description of the basic features of the algorithms employed is provided, as well as an overview and an assessment of the main results. 2 GEOLOGICAL FEATURES AND SOURCE DATA The harbour area of Gioia Tauro, in the southern Italian region of Calabria, is located in a flat plain, originating from a depression, spreading along its length in a N-S direction and filled by continental sediments of Quaternary Age. The plain primariliy comprises granular saturated soils in its surficial lay- ers (up to a depth ranging from 50 m to 70 m from ground level), overlying a layer of compacted clays and silty clays of considerable thickness (500m or more). The bedrock is located at variable depths of 500-600 m (Facciorusso and Vannucchi, 2003). Figure 1 shows a representative cross-section from borehole log data and the locations of CPT and SPT tests. As may be observed, the first 20 meters (represented by a dashed area) of the cohesionless deposit - the maximum depth commonly investi- gated for liquefaction risk analyses - include a thick layer of made ground, overlying, with increasing depth: − Soil A: coarse to medium loose aeolian sands, with a thickness varying between 3 and 5 m; 905 Proceedings ISC-2 on Geotechnical and Geophysical Site Characterization, Viana da Fonseca & Mayne (eds.) © 2004 Millpress, Rotterdam, ISBN 90 5966 009 9