LABORATORY STUDY OF EXTENSION FAILURE IN NEVADA TEST SITE TUFFS

CALCULATED GROUND MOTION FROM NUCLEAR EXPLOSIONS PREDICT THAT AT LOCATIONS NEAR THE CAVITY THE ROCK FAILURE SURFACE WILL BE ENCOUNTERED IN EXTENSION DURING LATER STAGES OF UNLOAD. THE RESULTING HOOP FRACTURES WILL PRODUCE A FAILED ROCK ZONE SURROUNDING THE CAVITY. HIGH PRESSURE CAVITY GASES COULD INITIATE A HYDRAULIC FRACTURE THROUGH THE FRACTURE ROCK WHICH, UNDER THE WORST CONDITION, WOULD LEAD TO VENTING. THE PURPOSE OF THE PROPOSED WORK IS TO EVALUATE EXTENSION STRENGTHS OF NEVADA TEST SITE TUFFS. ALTHOUGH SOME EXTENSION TESTS HAVE BEEN MADE, EXPERIMENTAL UNCERTAINTY EXISTS DUE TO LOCAL (SURFACE) FLAWS CAUSING PREMATURE SAMPLE FAILURE. IN PHASE I OF THE PROPOSED CONTRACT, TEST EQUIPMENT MODIFICATIONS NEEDED TO PERFORM THETESTS AND TEST SAMPLES WILL BE DESIGNED AND FABRICATED. EXTENSION TESTS WILL BE PERFORMED ON TUFFS AT CONFINED PRESSURES FROM ATMOSPHERIC TO 2 KILOBARS. PRELIMINARY TESTSWILL BE PERFORMED TO EXAMINE POTENTIAL EXPERIMENTAL PROBLEMSFOR THE WORK TO BE UNDERTAKEN IN PHASE II WHERE EXTENSION WILL FOLLOW PRELOADING ALONG THE COMPLETE STRAIN-PATH HISTORIES EXPERIENCED BY ROCK NEAR-IN THE CAVITY.