Creep improvement factors for vibro-replacement design

Abstract

This work is made available online in accordance with the publisher's policies. Please refer to any applicable terms of use of the publisher. 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.

The Impact of Using Different Types of Soft Soils Treated by Stone Columns on Creep Behavior

“…The creep effect on the settlement performance of stone column in a soft one layer, soil profile was investigated numerically using an isotache-based soil model in combination with the Plaxis 2D FE program. They concluded that stone columns significantly reduced the creep settlement in the long term, but not to the limit of the primary settlement; similarly, conclusions were reached by Sexton and McCabe for a multi-layer soil profile [5,6]. Fattah and Majeed (2012) study the performance of usual and encased floating stone columns under a variety of conditions and discovered that the increase of bearing improvement ratio linked to the increase of length/diameter (L/D) ratio; to the extent when the L/D ratio exceeding the 8 for all the area replacement ratio, also in the case with encasing stone column, there is no practical limit to the L/D ratio.…”

“…The effect of creep on the settlement performance of stone columns is investigated using two groups of analyses: the first group with standard soil criteria from Table 3 and the second group with very low creep coefficients, µ*≤1% of the standard value, effectively reduce the majority of the creep effects. Using of µ*= 0 cannot be used because it results in division by zero [5].…”

Analytical Solution for Plane Strain Consolidation of Soft Soil Stabilised by Stone Columns

“…Similar to the consolidation of soil with the inclusion of vertical drains, stone columns are commonly installed into soft ground in a square or triangular pattern in real practice [8,9]. To develop an equivalent plane strain model, several models from available studies [10][11][12][13] can be applied in which the equivalent geometries or material properties (e.g.…”

Award-winning paper in 2017

“…The Telford Premium Prize, awarded for the best paper on ground improvement, was awarded to Sexton et al (2017).…”