| Full flow penetrometers (the Ball and T-bar) have seen increased use as an alternative tool for estimating initial and remolded undrained shear strength of soft clay in situ. Conventional methods used to estimate undrained shear strength, such as correlations with piezocone data, field vane shear, and sampling and laboratory testing produce varied results and can be particularly costly for offshore site investigations. Full flow penetration profiles were performed at five international well characterized soft clay sites to construct a high quality database from which conclusions and recommendations for the use of full flow penetrometers could be reliably made.;Results of this study have enabled development of standardized methods for penetrometer design, testing procedures, data analysis, and data reduction. Variable rate full flow penetration testing was used to assess strain rate effects and consolidation parameters. Appropriate dimensions of full flow penetrometers were identified through in situ testing with multiple sized penetrometers. A Ball penetrometer that can measure pore pressures at its tip, equator or mid-face was developed to further evaluate the failure mechanism of soil flow around the penetrometer.;Initial penetration resistance is used to estimate undrained shear strength while the remolded shear strength is evaluated with the remolded penetration resistance obtained by cycling the probe vertically about a desired depth. Strength factors are used to compute intact and remolded undrained shear strength in the same manner as with the piezocone. Strength factors for remolded conditions are markedly different from intact strength factors due to changes in the soil flow mechanism. During cycling, soil strength degrades with each penetrometer pass, stabilizing once remolded conditions have been attained. An analytical degradation model was adapted for practical application reducing the number of cycles required to estimate the remolded shear strength to one. Relationships were developed using full flow penetrometer penetration and extraction resistance allowing for direct estimation of strength factors and sensitivity without the use of other strength references. Examples of the cyclic degradation model and regressions for estimating sensitivity, undrained shear strength, and remolded shear strength are presented with data from two additional soft clay test sites.;The findings of this project provide a sound experimental basis for the use and continued development of full flow penetrometer testing in practice. For offshore geotechnical engineering, where full flow penetrometers are most commonly used, the data, recommendations, analyses, and correlations developed, both verify and expand the current knowledgebase. Additionally this project provides a basis for further use of full flow penetrometers for onshore geotechnical investigations, where they have not commonly been used. |
