Consolidation parameters – alternative to Casagrande and Taylor methods

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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EFFECTS OF PILE LATERAL MOVEMENT, PILE SPACING AND PILE NUMBERS ON LATERALLY LOADED GROUP PILES

ABSTRACT: Based on 3D finite element numerical analysis on 3×3 pile group Gouw and Hidayat (2015) suggested that that when base friction of the pile cap and the passive pressure acting against the pile cap are neglected, the effects of the pile cap thickness against group lateral efficiency is marginal and can be safely neglected. They also briefly mentioned that the center to center pile spacing and the lateral movement of the piles also affect the capacity of the laterally loaded group piles. To investigate the effect of the magnitude of pile lateral movement and pile spacing to larger pile groups, the study was continued by carrying further analysis on 5×5 and 9×9 pile groups, taking the same modelling assumption where base friction and passive resistance induced by pile cap were neglected. The study revealed that pile group lateral efficiencies were found to be larger when the center to center pile spacing were wider. It was also found the greater the number of piles in the group the lower the pile lateral efficiency. However, pile head lateral (horizontal) movement only have marginal effect on the lateral efficiency of group piles.

Full paper download: 170926s-PILE2017-GTL-Efffect of Lateral Movement

The Important Role of Execution and CQA/CQC Plans in Building with Geosynthetics

Matteo Lelli¹, Gouw Tjie-Liong², Riccardo Laneri³, Marco Cerro

Abstract: The use of geosynthetics for the construction of mechanically stabilized earth retaining structures is constantly growing in Indonesia. These structures have shown economic advantages if compared to traditional mass gravity retaining structures. However, the importance of their execution is sometimes underrated. Construction Quality Control and Quality Assurance plans are often meagre and sometimes even missing. Mechanically stabilized earth structures rely on the collaboration between the compacted soil and the geosynthetic reinforcement. If one of these two components is not properly installed or other factors such as drainage system do not comply with the project specifications, unsuitable structure deformations or even failures may occur. This paper aims to share some good construction practices in order to build reinforced earth structures using geosynthetics. Furthermore, the Authors propose some simple but effective testing procedures which can be included in CQC and CQA plans. The scope of this paper is therefore to give guidance to project Owners, Designers and Construction Companies to deliver cost effective, safe and durable geotechnical structures built with geosynthetics.

Full paper download: 171003s-GeonsintetikIndonesia2017