Settlement evaluation of explosive compaction in saturated sands

Explosive Compaction (EC) or Blast Densification (BD) has been commonly used as one of the deep soil improvement techniques to densify loose, saturated granular soils. Soil is compacted due to huge compression force of explosion in several depths and the corresponding liquefaction. Among soil characteristics, settlement is important since it is a fast and easy indicator of layer compaction degree. To measure settlement instrumentation can be used but they are expensive and susceptible to damage due to explosion. Predicting settlement using empirical equations is also another method, however, they cannot consider soil complex behavior and are consequently inaccurate. In this study, numerical approach has been used to evaluate settlement and excess pore water pressure (PWP) during and after explosion, using finite element software PLAXIS3D, in which the UBCSAND soil model has been employed to represent saturated sand. This model is capable of calculating PWP buildup due to dynamic loads such as earthquake and explosion. This method was calibrated and compared, using well-known case histories in the literature. Results of settlement from these cases, were compared with both empirical equations and measured site values. Pulses of PWP due to shock wave were also calculated by the model as well as PWP buildup until reaching liquefaction zone. Predictions from this approach were more accurate than empirical equations. Moreover, it was revealed that the rate of settlement and PWP dissipation is proportionate to soil's permeability. Thus, numerical approach can be confidently implemented to evaluate soil characteristics.