GEOLOGIC AND ENGINEERING PROPERTIES INVESTIGATIONS.
ARMY ENGINEER WATERWAYS EXPERIMENT STATION VICKSBURG MISS
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The four Pre-Schooner high explosive cratering experiments were conducted in dry basalt on Bulkboard Mesa, Nevada Test Site. The preshot and postshot conditions were investigated by core boring, borehole photography, geophysical techniques, aerial photography, and exploratory excavations. Representative core samples were tested in the laboratory for strength properties and specific gravity. The rock consists of vesicular basalt over dense basalt, and each type is structurally modified by layering of vesicles resulting from viscous flow of the lava. Natural flow structure within the lava at the sites consists of flow-layered basalt types arranged as nested cylinders with gradational contacts. The axes of these cylinders parallel the flow direction inferred from topography. Cross folds are superimposed on the cylindrical structure. Joints and blast fractures tend to be parallel or perpendicular to flow layers, and as a result an anisotropy due to flow structure prevails at each site. This anistropy appears to explain the conspicuously elliptical form at two of the craters. In the two craters that were explored by trenching, the displaced ground surface was uplifted about 5 feet at the true crater. In the subsurface beyond the true crater at the Delta Site, zones of blast fracturing and bulking have been distinguished. These appear to be modified somewhat by the stratigraphy of the basalt. The limits of fracturing and bulking by the blast appear to lie at about 100 feet from the zero point. Author
- Geology, Geochemistry and Mineralogy