Welcome to the May 2013 issue of Ground Improvement for which it has been my pleasure to write the editorial. This issue comprises five papers which reflect the truly international and diverse nature of ground improvement and fulfils the aims of this journal, which is to publish papers that will disseminate the latest research being conducted across the full range of ground improvement techniques. Rogers (2012) recently defined ground improvement as covering any method by which the ground, whether natural or disturbed in some way by anthropogenic processes, has its performance for any specific (geotechnical) purpose enhanced.
In the first paper Chai et al. (2013) review the methods for modelling the effect of prefabricated vertical drains (PVDs) in a plane strain finite-element analysis. Methods are classified into four groupings employing: solid element; macro-element; one-dimensional drainage element; and equivalent vertical hydraulic conductivity (kve). For all methods, the average degree of consolidation in plane strain analysis matches that under an axisymmetric condition by modifying the hydraulic conductivity of the subsoil, and/or the spacing or the discharge capacity of plane strain drains. Effectiveness of the kve method has been demonstrated by large-scale model tests of PVD consolidation.
In the second paper Hamidi et al. (2013) discuss the reasons for the unreliability of the concept of relative density as an acceptance criterion for ground improvement. Relative density is considered to be a definition rather than an inherent soil property and with no real influence on the soil's performance, its range of application does not span across all soil types and is subject to large inherent errors that make its use a technical risk. It is indicated that there is no benefit in stipulating relative density as a criterion, a more rational approach being to ensure that design criteria have been satisfied by directly specifying them as the acceptance criteria.
In the third paper Rotte and Viswanadham (2013) examine the influence of soil nail inclination and facing material types on the stability and deformation behaviour of soil-nailed slopes subjected to seepage flow at 30g in a series of instrumented centrifuge model tests. Tests were carried out on 5V:1H slopes both with and without soil nails. Two different nail inclinations of 10° and 25° to the horizontal were adopted with two different material facing types. Results indicate that use of soil nails for stabilisation of earth slopes subject to seepage has a significant effect on the stability and deformation behaviour of the slope and is strongly influenced by soil nail inclination and facing material type. Good comparison between the centrifuge model tests and slope stability analysis was observed.
In the fourth paper Estabragh et al. (2013) present the results of a series of laboratory-based experiments to investigate the effect of resin and cement (agents) on the strength of clay soil. The resin was shown to have a significant effect on increasing strength when more than 10% was present. Whilst the effect of cement on soil strength is shown to be greater than that of resin, the resin is also shown to improve the ductility of the soil. The increase in strength was demonstrated to be a function of percentage of agents and curing time.
In the final paper Becker et al. (2013) investigate the stress–strain–time behaviour for medium dense sand treated by a new biologically-inspired silicification process using 20% sodium silicate, with the potential to achieve parity of performance with existing soil treatment methods, whilst employing lower concentrations of environmentally benign component materials. The results show that the creep behaviour is similar to the behaviour of traditionally treated sand. Data also show that incremental creep tests may be a more rapid means of determining parameters for creep modelling than the existing standardised single-increment test method. Parameters for modelling long-term behaviour are indicated as being consistent with published parameters for existing soil treatment methods.
I hope you will find these papers stimulating and informative. I would also encourage discussion or comment on the papers published in this issue and in future issues of the journal, as this can promote useful and constructive debate to further enhance the contribution of the published research paper(s) to the ground improvement community. Instructions for making a contribution to a discussion paper can be found at the end of each paper.
