THE EFFECT OF PRESHOCK LOADING ON THE RESPONSE OF NTS TUFF

PRESHOCKED PRECONDITIONING OF TUFF MAY OCCUR IN TWO MANNERS AT THE NEVADA TEST SITE. FIRST, THE MATERIAL IS "PRESHOCKED" IN A LINEOF-SIGHT TYPE UNDERGROUND NUCLEAR TEST BY THE FIRST WAVE PASSAGE. THE SECOND MANNER MAY OCCUR AS A RESULT OF AREAL SPACE LIMITATIONS WHEN A SECOND EVENT IS SITED WITHIN A REGION OF PRESHOCKED MATERIAL. UNDER CERTAIN LOAD-UNLOADED CONDITIONS THE MATERIAL STRENGTH MAY BE VERY MUCH REDUCED FOR SUBSEQUENT LOADING. A LARGE LOSS OF STRENGTH DUE TO PRESHOCKING COULD SIGNIFICANTLY INFLUENCE THE EFFECTIVENESS OF STEMMING AND CONTAINMENT. A TEST PROGRAM IS PROPOSED ON PROVIDE FOR A BETTER UNDERSTANDING OF THE EFFECT OF PRELOADING (LOAD AND UNLOAD) ON THE MICROMECHANICS OF MATERIAL LOADING AND THE SUBSEQUENT MATERIAL RESPONSE.