Divine Strake Description

DIVINE STRAKE would detonate up to 700 tons (635 metric tons) of heavy ammonium nitrate fuel oil emulsion (also known as heavy ANFO), a blasting agent, emplaced in a charge hole about 32 feet (9.8 meters [m]) in diameter and 36 feet (11 m) deep, located at the surface above U16b tunnel. In addition to the ANFO, up to 300 pounds (136 kilograms) of C 4 explosive would be used to initiate detonation. The bottom of the charge hole would be about 99 feet (30 m) above the back of the tunnel.

Site preparation would include: 1) improvement of an existing dirt road leading to the hilltop above the tunnel, 2) excavation of the emplacement (or charge) hole above the tunnel complex and a three point turnaround area for bulk delivery trucks, and 3) drilling holes in the back, floor and ribs of the tunnel for installation of instruments and gages for recording the effect of the detonation. Instrumentation bunkers would be constructed and located in previously disturbed areas near the portal of the tunnel. Several accelerometers would be placed in and around the test bed to record ground motion. High speed cameras would be installed to record portal and underground damage.

DTRA would provide site characterization data defining in situ properties and 3 D variations within the test bed, and would provide test data defining charge source performance, free field ground motions and asymmetries, tunnel near field environment and response data. The geotechnical site characterization would fill an important targeting gap, not only for DIVINE STRAKE, but also for other HDBT testing programs. This test would support the evaluation and validation of attack planning tools and capabilities, including fast running ground shock and tunnel damage models along with first principles target response and damage calculations.

Additional experiments may be included to supplement data obtained from the detonation. The following are examples of potential experiments. A reinforced concrete structure simulating a stairwell This structure would be built on the lower pad at the U16b tunnel. It would have an 18.5 feet (5.6 m) by 18.5 feet (5.6 m) concrete foundation, and would be 26.5 feet (8.1 m) tall, with a 16 feet by 16 feet (4.9 m by 4.9 m) stairwell with a hatch installed at the base. The pressure and acceleration instrumentation would be included on and near the structure, and cameras would record structural response. Depending upon the amount of damage, the structure could be left in place after DIVINE STRAKE for later experiments. However, the current plan is to dismantle and dispose of the structure in an appropriate NTS landfill after the detonation.

Sensor collections with a generator in Portal 1 and small fans in the back room area. The intent is to be able to see pre detonation, detonation, and post detonation images. Computer fragility studies Computers would be placed in Portal 3 along with additional surface mounted accelerometers and cameras to observe the fragility of the computers. Protective shelters may be provided for one or more of the computers for comparison purposes.

Ejecta studies would be conducted to characterize how the ejecta is "shot out" by the detonation and how far it travels. The studies would evaluate both large debris (softball size) and fines. Collection panels (possibly of tarp) would be placed at various distances from the charge hole to collect debris. The large debris would be evaluated for distance traveled, size, condition, and other parameters. For the fines, powdered dyes (tracers) would be placed on the ground around the crater site, most likely on one quadrant on the northern side. The powder would be lofted with the dust cloud during detonation. The fines would be evaluated for travel distance, size distribution, and dispersion.

The DIVINE STRAKE test early-time airblast, crater formation, and ejecta environment were calculated by Philip Hookham of Titan Research using the two-dimensional CRALE code. This solution was then overlayed onto two- and three-dimensional MAZe code computational meshes. The MAZe calculations simulated the airblast environment as well as the propagation of the dusty environment produced by the ejecta and subsequent dust sweep-up. The airblast environment will be compared to test measurements when they become available, while the predicted dust environment will be used to aid in planning of the test.

The first approximation for an explosion is usually taken to be a point, spherically symmetric dilatational source. While this would be correct for an explosion in an infinite, uniform medium, the presence of the earth surface renders that description inadequate. The explosion source can be modeled more realistically using nonlinear finite difference calculations of explosions in a realistic earth model with gravity. This approach models all near source effects including spall, cracking, and nonlinear deformation.

Non-ideal airblast is produced from detonations over urban and natural terrain. Mechanical effects of a blast wave reflecting off non-ideal surfaces produces shielding and channeling effects that may be considerably different than those from a detonation over an ideal surface. Sandia National Laboratory (SNL) has sponsored a number of computational fluid dynamics (CFD) airblast calculations of the DIVINE STRAKE event. SNL contracted Applied Research Associates, Inc. (ARA) to perform two- and three-dimensional (2D and 3D) predictive airblast calculations for the test. The CFD calculations were run with SHAMRC and characterize the airblast environments induced by the non-ideal charge configuration and the surrounding terrain. They include 2D calculations with and without terrain and with a responding and non-responding ground model. A single 3D calculation with a non-responding ground model was also completed. Results of the calculations provide test planners with environments that can be expected at instrumentation and test structure locations. A single, 3D calculation with a realistic ground model is planned once the charge and detonation site details are finalized.