Estimate of earth media shear strength at the Nevada Test Site

A method is presented of estimating the effective shear strength of the fractured rock that surrounds a nuclear detonation. To do this, we measure the cavity radii from previous detonations. We also use numerical computer codes to model the explosion phenomenology and develop the functional relationship between the normalized cavity displacement and the normalized shear strength of the rock. In this sense, the computer codes serve as replica models that are dimensionally analyzed to interpret the field experience. We separate the effects of gravity and overburden pressure from the effects of the material properties and give scaling laws for each. We have analyzed approximately 300 nuclear detonations at the Nevada Test Site (NTS) and have found that the most frequent shear strengths are between 0.020 and 0.060 kbars. They are also essentially independent of the depth-of-burial ranges considered. We obtained good agreement between predicted shear strengths and those measured from core samples for different areas at the Nevada Test Site