Abstract
Encased stone columns are vertical inclusions in soft soils formed by gravel wrapped usually with a geotextile. Their critical length is the one where further lengthening of the column provides a negligible improvement and it is therefore not effective to build columns longer than it. This paper aims to obtain common values of the critical length using simplified two-dimensional axisymmetric and full three-dimensional finite element analyses. A uniform soft soil layer with a linear elastic perfectly plastic behaviour is considered for the sake of simplicity. For the studied cases, the critical column length is around 1.3–2.5 times the footing diameter for encased stone columns, and slightly lower for ordinary stone columns, namely around 1.1–1.9. The critical length of the encasement is found to be slightly lower than the critical column length. The value of the critical column length is related to the extent of plastic deformation and that may be used to decide the column length in the design phase without the need of parametric analyses. As a first approximation, a general value of the critical column length of 2 and 2.5 times the footing diameter may be considered for ordinary and encased stone columns, respectively.
Highlights
Ground improvement using stone columns is a popular technique to improve soft soils for foundation of embankments or structures (e.g., Al Ammari and Clarke, 2018; Barksdale and Bachus, 1983; Bong et al, 2020; Etezad et al, 2018; Kirsch and Kirsch, 2010; Han, 2015; Hos seinpour et al, 2019; Lima et al, 2019; Ong et al, 2018; Siahaan et al, 2018)
The results show that an increase in the friction angle of the column reduces the settlement (Fig. 12), and this contribution is more notable in the case of Ordinary stone columns (OSC) (Fig. 12b) as they are not confined laterally
This paper presents, for the first time, a systematic analysis of the critical length of ESC and the critical length of their encasement
Summary
Ground improvement using stone columns is a popular technique to improve soft soils for foundation of embankments or structures (e.g., Al Ammari and Clarke, 2018; Barksdale and Bachus, 1983; Bong et al, 2020; Etezad et al, 2018; Kirsch and Kirsch, 2010; Han, 2015; Hos seinpour et al, 2019; Lima et al, 2019; Ong et al, 2018; Siahaan et al, 2018). Ordinary stone columns (OSC) and encased stone columns (ECS) may reach a rigid substratum (end-bearing columns) or may be embedded just on a soft soil layer (floating columns) For the latter case, the length of the columns is an important design parameter to be chosen. The length of the columns is an important design parameter to be chosen In some cases, it may be more cost-effective to add additional columns than increasing the length of the columns. It may be more cost-effective to add additional columns than increasing the length of the columns In this way, the concept of the critical length of stone columns appears. The load transfer mechanisms and the reasons for the critical length are different from piles, the meaning of the concept of critical length is equivalent (e.g., Fleming et al, 2009)
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