Buried Explosive-Induced Blast Characterization by Geotechnical Centrifuge Modeling

Hansen, Curt Benjamin

Graduate Thesis Or Dissertation

Buried Explosive-Induced Blast Characterization by Geotechnical Centrifuge Modeling Public Deposited

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Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/8g84mm48m

Abstract

A comprehensive experimental regime was conducted to advance the understanding of the mechanistic phenomena of buried, explosive-induced soil responses using geotechnical centrifuge modeling. To address experimental gaps in the current literature, this research documents the high-rate dynamic soil behavior under explosive loads with parametric variations of charge size, burial depth, and g-level in conjunction with post-detonation static measurement of blast-excavated craters. The novel integration of a high-speed imaging system into the centrifuge domain, placed in close-proximity to the blast, enabled a rigorous in-flight characterization of the transient, multiphasic soil blast mechanics including initial soil deformation, early soil disaggregation, gas-particle interactions, and soil dome evolution. The results indicate that initial soil surface motions appear progressively later, post-detonation, with elevated acceleration. Furthermore, the data demonstrates that gravity-induced confining stresses reduce the temporal and spatial soil disaggregation flow kinematics. Crater dimensions, measured by a laser profilometer, exhibit a gravity-dependent decrease and a new, dimensionless coupling function correlates the physical ejecta dynamics to the crater dimensional statics evident in the buried blast phenomena. Piezoelectric sensors, embedded coincident to the test-specified burial depth and recorded simultaneous to soil ejecta kinematics, measure ground shock transmissivity as a function of radial distance from the charge, with parametric variations in explosive mass and in-situ soil conditions. This research also developed a computational model of the buried, blast event in a dry soil medium within an advanced, 3-dimensional, multi-material, arbitrary Lagrangian-Eulerian (ALE) framework and implemented in an explicit finite element solver. The empirically-determined soil ejecta velocities and crater dimensions demonstrate reasonable correspondence to the numerical model. Significantly, the ground shock peak accelerations and stresses data exhibit close agreement to the numerical predictions. An in-depth analysis compares this study’s empirical scaling relationships, in both dimensional and dimensionless form to a compilation of past field and centrifuge results and demonstrates their favorable correlation to full-scale explosive events.The parametric study of soil ejecta kinematics and crater morphology progressed to an in-depth investigation of buried, explosive-induced kinetic energy transfer to an overlying target. To address experimental gaps in the current literature, this research documents the near-field resultant force impacts and rigid-body dynamics under explosive loads, instead of the conventional discrete measurement methods, with parametric variations of target height, explosive mass, burial depth, g-level, target geometries, and in-situ soil conditions. The design and fabrication of a novel, laboratory-scale blast impact device, the Blast Impact Response Gage (BIRG), integrated into the centrifuge domain, enabled a rigorous characterization of the aboveground blast environment. The results from over 150 experiments demonstrate the BIRG’s unique capability to directly measure the complex, non-uniform, temporal and spatial distribution of the blast loading mechanisms and subsequent impulse transferred to the target. The BIRG’s tri-symmetric sensor configuration, mounted on the rigid target plate, effectively resolves the applied blast stresses and consequent out-of-plane rotational motions under both centric and eccentric explosive loads. Significantly, the BIRG measurements delineate the arrival times and magnitudes of the extremely transient early shock impact phase in conjunction with the complex, interfacial gas-soil ejecta loading mechanisms in the primary shock impact phase of longer duration. The comparative data analyses of the arrival times and magnitudes quantify the constituti

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