Given the success of DIAL PACK, the next test was a large scale HE shot on different soil types, over different subsurface geology, and over different terrain features. Large isolated areas meeting those criteria are not easily found. An area in the US about 15 miles west of Grand Junction, Colorado was identified, and dubbed the Colorado Test Site. It was a completely undeveloped site which would make the staging of an event there much more challenging than at DRES in Canada.
In July 1972, Park Service officials in Washington directed the Superintendent of the Curecanti Group, of which Colorado National Monument was a part, to reach an agreement with the Commander of the Defense Nuclear Agency (Department of Defense) regarding the use of 4.8 miles of Rim Rock Drive from the east entrance to the Glade Park turnoff. This stretch of road allowed the Department of Defense and its associate Mixed Company to access a the test site at Glade Park. Under the conditions of the agreement, the Park Service allowed the Department of Defense to use the road, provided personnel to conduct inspections of the road, kept records of road repair costs and billed the Department of Defense for those repairs. The Department of Defense agreed to plan its deliveries of high explosives so as to avoid extensive damage to the road, provided personnel to jointly inspect the road, notified the Park Service of oversized loads and agreed not to cross Monument property without a Park Service escort. They also agreed to reimburse the Park Service for repair costs. The terms of the agreement were to extend until January 1974 barring any unexpected changes.
The third 500-Ton event in the MIDDLE NORTH Series under the four nation TTCP was scheduled for that location in November 1972. It was called Event MIXED COMPANY. A group of environmentalists convincing a Federal Judge to put the detonation on hold until the Court could be convinced that a "balanced rock" located about 5.5 miles from GZ wouldn't be toppled by the explosion.
What explosive to use on MIXED COMPANY? NSWC, with the encouragement of Kelso, again submitted a proposal for using a spherical ANFO charge with a TNT equivalent yield of 500 tons. The reasoning was as follows: First, most of, the targets for MIXED COMPANY were to be blast targets; the superior merits of ANFO over TNT for blast had been demonstrated. with hemispherical charges weighing up to 100 tons, and. spherical charges weighing up to 25 tons; it could be expected that the same superiority would be maintained on a 500 ton shot; and so, airblast targets would be, subjected to a more predictable blast field than had been realized with TNT charges. (Remember DIAL PACK! Remember PRAIRIE FLAT! was the message:) And second, with the state of the ground motion and cratering art being what it was, predicting the ground effects of ANFO shots probably would be no worse than for TNT shots. Besides, by measuring the ground effect phenomena, e.g., acceleration, displacement, crater dimensions, the observed response of targets should be relatable to the effects inputs, and, so, the objectives of the underground structure studies would be realized.
Again, the ANFO arguments and proposal were not accepted. MIXED COMPANY, fired in November 1972, used a 500 ton spherical TNT charge; and again, the now familiar airblast refrain -- too many anomalies, too many airblast targets subjected to undesirably high (or low) pressures with distorted profiles. And the ground motion investigators again were finding that their predictions were not being realized adequately.
An experimental and theoretical examination was conducted for the static and dynamic mechanical behavior of a highly porous, dry sandstone from the MIXED COMPANY event site. The static behavior is obtained from data of hydrostatic loading, uniaxial strain loading, and uniaxial stress loading to failure for various confining pressures. The dynamic behavior is obtained from data of plane wave, plate-impact tests and spherical stress wave tests using 5.08-cm-dia explosive spheres. In-material measurements are made of the particle velocity and stress-time histories which characterize the dynamic response. The experimental results exhibit several complex features such as: irreversible compaction dependent upon both mean normal stress and shear stress; dilatancy; strain hardening and strain rate dependent response.
Pressure-volume, uniaxial strain loading, uniaxial stress loading to failure, and ultrasoric velocity determinations have been performed on samples of Kayenta sandstone from the site of the Mixed Company event. Hydrostatic pressure of 3 GPa produces about 23% volume compression, with 9% permanent compaction remaining upon unloading. The pressure-volume data indicate that crush-up of porosity begins between 200 and 300 MPa.In uniaxial strain loading, the sandstone loads directly to the vicinity of the failure envelope, then parallels that envelope to the highest confining pressure (480 MPa). At strain rates of about 10/sup -4//s, the loading path in uniaxial strain up to 200 MPa is coincident in pressure-volume space with the shock-loading path (at a strain rate of about 10/sup 5//s) observed on samples from the same block. The permanent compaction, after unloading under conditions of uniaxial strain from 625 MPa mean pressure, is about 3.8%.Uniaxial stress loading indicates a brittle-ductile transition between 400 and 500 MPa mean pressure. Between 100 and 500 MPa mean pressure, the slope of the failure envelope is decreased consideably with respect to that below 100 MPa and between 500 and 900 MPa. This plateau, which is not present in the failure envelope for material subjected to a 700-MPa confining pressure before the uniaxial stress test, is interpreted as being due to pore crush-up during hydrostatic loading. As confining pressure is increased from 0.1 MPa to 1 GPa, the measured compressional velocity increases from 3.0 km/s to 5.0 km/s and the shear velocity increases from 1.5 km/s to 2.4 km/s.Small decreases in compressional velocity ( approximates 5%1 between 10 and 40 MPa are attributed to local brittle failure resulting from highly localized stress concentrations within the sample under hydrostatic loading.
West of Glade Park, Colorado, there are still three large concrete 'quonset hut' type structures and concrete blocks that were built by the govt. in the 70s. The structures were constructed to test conventional explosives.
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