Date of Graduation
Several military attack scenarios involve the detonation of explosive in the soil backfill surrounding a target structure. In this study, experiments and numerical simulations were performed to determine if the enhanced mechanical properties of geogrid-reinforced soil backfills could mitigate blast effects from buried explosions. The dynamic response of an explosively-loaded, geogrid-reinforced sand was successfully characterized, identifying and quantifying certain blast mitigating effects. Six high explosive experiments were conducted, each involving a 0.91 kg nitromethane explosive charge placed at 76.2 cm depth within a test pit of compacted fill. Two experiments were unreinforced, serving as control tests. Three experiments were conducted with horizontal panels of geogrid reinforcement of varying type and tensile strength. One experiment was conducted with vertical panels of geogrid reinforcement. Geogrid panel spacing was 15.2 cm for all experiments. Three of the experiments were instrumented with soil stress and particle velocity gages to quantify blast mitigating effects. Results from the experiments indicated that sand backfills reinforced with horizontally-oriented geogrids were effective at mitigating crater formation, ejecta, and blast-induced soil motions from shallow-buried explosions. For the explosive weight and depth of burial tested, apparent crater volumes were reduced 90 to 100 percent. Measured soil particle velocities revealed a more rapid attenuation of blast-induced particle velocities in the reinforced soil, resulting in a mitigation of soil particle displacements associated with stress wave passage. Soil stresses were not mitigated, however, with peak stresses in the reinforced soil increased 80 to 120 percent, and soil impulses increased 25 to 40 percent. The SABER code, a finite element computer program previously developed for predicting ground shock from buried explosions, was used to numerically simulate the effects of the geogrid reinforcement. Hybrid elastic-plastic material models were developed for both the unreinforced and reinforced soil which output soil stress and particle motions similar to those measured. Stiffening the uniaxial compression and failure relations of the unreinforced soil model reproduced many of the observed effects of the geogrid reinforcement (e.g., mitigated particle motions, elevated soil stresses, etc.). This numerical approach permits extension of the experimental results to other explosive weights and depths of burial.
Ohrt, Alan Paul, "Mitigation of blast effects with geogrid-reinforced soil backfills." (1996). Graduate Theses, Dissertations, and Problem Reports. 9530.