Investigation of the densification mechanisms and predictive methodologies for explosive compaction

The energy released by fully contained detonations of high explosive charges in a soil mass causes the soil particles to rearrange into a denser structure. This investigation has two primary objectives. The first objective is to achieve a better understanding of the densification process and the factors which affect the soil densification. The second objective is to utilize the available information from explosive compaction projects to assess existing guidelines and develop new methodologies for predicting the results achieved by this technique.; Densification mechanisms for explosive compaction include impact, vibration, shear, volumetric strain, and generation of excess porewater pressures. Blasting destroys the existing soil structure, then causes particles movement by the blast-induced shear and vibration. In addition, the generation of excess porewater pressures may induce liquefaction and subsequent resettlement into a denser configuration.; Available information from literature and consultants reports was collected, reviewed, and organized in a database. Based on the information in the database, new predictive methodologies are proposed and evaluated.; First, methodologies to estimate settlement resulting from explosive compaction were developed and evaluated. These predictive functions used energy attenuation descriptions that have been previously proposed by others, i.e., Hopkinson's Number, Normalized Weight, and Powder Factor. Functions which used Powder Factor and Normalized Weight had greater regression coefficients (R{dollar}sp2{dollar}) than the function using Hopkinson's Number, although the correlations are weak (R{dollar}sp2{dollar} = 0.45 to 0.46).; Then predictive methodologies for the final normalized cone penetration tip resistance {dollar}rm(qsb{lcub}1,f{rcub}){dollar} and the change in normalized tip resistance {dollar}rm (Deltasb{lcub}q1{rcub}){dollar} were developed and assessed. These methodologies include factors to account for the initial normalized cone penetration tip resistance {dollar}rm (qsb{lcub}1,o{rcub}){dollar} of the soil and the weight and spacing of the explosive charges. The functions that were developed show that {dollar}rm qsb{lcub}1,f{rcub}{dollar} and {dollar}rm Delta qsb1{dollar} increase with increasing magnitude of energy energy attenuation, and as {dollar}rm qsb{lcub}1,o{rcub}{dollar} increases {dollar}rmDeltasb1{dollar} decreases and {dollar}rm qsb{lcub}1,f{rcub}{dollar} increases. Correlations for predicting {dollar}rm qsb{lcub}1,f{rcub}{dollar} were fair, with the highest R{dollar}sp2{dollar} approximately equal to 0.6. Correlations for predicting {dollar}rmDelta qsb1{dollar} were poor, with the highest R{dollar}sp2{dollar} approximately equal to 0.2.; After the analyses, data used to develop the predictive methodology for {dollar}rm qsb{lcub}1,f{rcub}{dollar} was reviewed to develop insights into explosive compaction. This research indicates that densification of the soil by shear and vibration can be enhanced if the delay period between detonations is on the order of minutes, instead of milliseconds or seconds. When delay periods are adequate to allow the soil to resettle, but short enough that there is still significant excess porewater pressure, then shear and vibration may rearrange the soil particles into a denser structure than achieved by liquefaction and resettlement.; Further review of the data indicates that providing supplementary drainage with standpipes does not improve the results achieved. Also, benefits of using decked charges and detonating the decks in a specific sequence were not observed when the data were reviewed.