. (2014). Appraising stone column settlement prediction methods using finite element analyses. Acta Geotechnica, 9(6), 993-1011. doi: 10.1007/s11440-013-0260-5
PublisherSpringer Verlag
AbstractNumerous approaches exist for the prediction of the settlement improvement offered by the vibro-replacement technique in weak or marginal soil deposits. The majority of the settlement prediction methods are based on the unit cell assumption, with a small number based on plane strain or homogenization techniques. In this paper, a comprehensive review and assessment of the more popular settlement prediction methods is carried out with a view to establishing which method(s) is/are in best agreement with finite element predictions from a series of PLAXIS 2D axisymmetric analyses on an end-bearing column. The Hardening Soil Model in PLAXIS 2D has been used to model the behaviour of both the granular column material and the treated soft clay soil. This study has shown that purely elastic settlement prediction methods overestimate the settlement improvement for large modular ratios while the methods based on elastic-plastic theory are in better agreement with finite element predictions at higher modular ratios. In addition, a parameter sensitivity study has been carried out to establish the influence of a range of different design parameters on predictions obtained using a selection of elastic-plastic methods.3
The majority of numerical studies investigating stone column performance have used 'wished-in-place' columns (no installation effects) in conjunction with elasto-plastic soil models (no viscous effects). In this first half of this paper, Cylindrical Cavity Expansion is used in conjunction with the PLAXIS 2D elasto-viscoplastic Soft Soil Creep model to evaluate the effect of creep on column installation. Creep leads to lower post-installation lateral earth pressure coefficients (K) than if primary consolidation was considered alone, although the values of K/K 0 , which decay with distance from the column centre, are nevertheless greater than 1.0. In the second half of this paper, two sets of unit cell analyses have been carried out to investigate the effect of accounting for column installation on subsequent settlement performance. The results indicate that 'primary' settlement improvement factors are larger than 'total' settlement improvement factors and that the relative differences between them increase when installation is taken into account.
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General rightsCopyright for the publications made accessible via the Queen's University Belfast Research Portal is retained by the author(s) and / or other copyright owners and it is a condition of accessing these publications that users recognise and abide by the legal requirements associated with these rights. Although the vibro-replacement stone column technique is being deployed increasingly in soft cohesive soil deposits in which creep settlements may be significant/dominant, the majority of existing stone column settlement design methods are either non-specific or pertain to primary settlement only. Consequently, in the absence of further guidance, designers sometimes apply the same settlement improvement factor to creep settlements that they have estimated for primary settlements. In this paper, Plaxis 2D finite-element analyses carried out in conjunction with the elasto-viscoplastic soft soil creep model have indicated that settlement improvement factors are lower when creep is considered and therefore the design of stone columns ignoring creep is unconservative. These analyses were used to establish the impact of a range of relevant variables on 'primary', 'total' and 'creep' settlement improvement factors, leading to the development of a simplified empirical approach for predicting creep settlement improvement factors for use in conjunction with an existing primary settlement design method.
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