Creep improvement factors for vibro-replacement design

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.