14
Oct

Consolidation parameters – alternative to Casagrande and Taylor methods

Written by Gouw Tjie Liong, Ir., M.Eng, ChFC, PhD. Posted in GTL Paper, Publication

ABSTRACT: For decades, consolidation parameters are derived graphically. Pre-consolidation pressure is derived by Casagrande method where technician has to pick the point of smallest curvature from e-log s’ curve. Coefficient of consolidations is derived by Taylor’s method where technician has to draw a linear line from deformation vs square root of time curve. Both graphical methods can lead to different results depending on the technician’s judgment. Given the same e-log s’ curve, pre-consolidation pressure determined by different interpreters easily varies by three folds. Great variations also obtained in determining coefficient of consolidation through Taylor’s method. As soil compresses, void ratio reduces and so does permeability, hence the higher consolidation pressure the lower coefficient of consolidation should be. However, it is often found that plot of coefficient of consolidation vs consolidation pressures goes up and down irregularly. The author tries to derive pre-consolidation pressure by ‘Parallel Rebound Method’, that is: first line is drawn through unloading part of e-log s’ plot, second line is drawn tangent through initial part of e-log s’ curve parallel to the first line, third line is the normal consolidation line. The intersection of the third line with the second line is the pre-consolidation pressure. With regard to coefficient of consolidation, Asaoka’s method is employed to determine 100% consolidation under constant load, certain degree of consolidation time is then decided to derive coefficient of consolidation. It was found that the resulted coefficient of consolidation curve reduces consistently with higher consolidation pressures. With the help of computer spreadsheet program and mathematical formulation, both methods appear to give consistent results. It was concluded ‘Parallel Rebound Method’ and Asaoka’s method lead to better results in deriving pre-consolidation pressure and coefficient of consolidation, respectively

Full paper download: 170921s-19ICSMGE-GTL-ConsolidationParameters

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Gouw Tjie Liong, Ir., M.Eng, ChFC, PhD

Mr. Gouw is a certified Professional Geotechnical Engineer. He has been working in the field of Geotechnical Engineering since 1984. His expertise covering geotechnical investigation, soil intrumentation, deep foundation and excavation for high rise buildings, pile load testing (Static and PDA), pile integrity testing (PIT), sonic logging test, vibration monitoring, slope stability, ground anchors, pumping test, dewatering, micropiles, tunnelling and ground improvement works, e.g. dynamic compaction, vertical drain, vibro-compaction, geosynthetic and grouting. The jobs cover more than 180 projects in Indonesia, Singapore and Srilanka. He has a great passion in the teaching and disseminating of geotechnical engineering knowledge. He serves as lecturer since late 1984. Currently, he serves as a senior lecturer at Bina Nusantara University, Jakarta, Indonesia. He also conduct regular geotechnical training for engineers. He also chaired the Indonesian Chapter of International Geosynthetics Society since 2006. He has published 80 papers and 22 technical notes.

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