Ground Densification due to Sand Compaction Piles (IWS-ATHENS 2003「地盤力学における予測とシュミレーション手法」特集号) GROUND DENSIFICATION DUE TO SAND COMPACTION PILES

The geotechnical properties of granular soils can be improved using compaction piles. However, the compaction effect and the extent of the densification are not yet clear. Well controlled in situ tests are necessary to investigate this problem. Further insight about the densification process can also be gained by performing numerical analysis using a constitutive model that takes into account the effect of density and confining pressure on the behavior of soils. This paper presents numerical analyses in which a recently proposed model, named subloading t_<ij>, is used to simulate these effects. The construction process of sand compaction piles involves two stages : the metal casing driving and the sand pile compaction. The process is simulated sequentially and the relative influence of each stage is quantified for different initial ground density conditions. The extent and effectiveness of the densification are also quantified. The results of these predictions are qualitatively compared with the results of field tests carried out before and after the execution of compaction piles in an artificial loose sand deposit. There is good overall agreement between the numerical predictions and the test results, showing that a combination of these two investigation approaches is a way forward to better understanding the densification process. However, this can only be achieved if the constitutive model can properly account for the change in soil behavior with densification.