MOST ANALYTICAL METHODS USED TO PREDICT THE BEHAVIOR OF TUNNELS SUBJECTED TO GROUND SHOCK REQUIRE MAKING JUDGMENTS REGARDING ACCEPTABLE LEVELS OF TANGENTIAL STRAIN AROUND THE TUNNEL SURFACE.

MOST ANALYTICAL METHODS USED TO PREDICT THE BEHAVIOR OF TUNNELS SUBJECTED TO GROUND SHOCK REQUIRE MAKING JUDGMENTS REGARDING ACCEPTABLE LEVELS OF TANGENTIAL STRAIN AROUND THE TUNNEL SURFACE. THE CAPABILITY TO MEASURE DYNAMIC TANGENTIAL STRAINS ON THE SURFACES OF TUNNELS WOULD PROVIDE AN EXCELLENT MEANS OF DIRECTLY ASSESSING THE VALIDITY OF ANALYTICAL METHODS. THE OVERALL STUDY OBJECTIVE IS TO DEVELOP A ROCK STAIN GAGE CAPABLE OF RELIABILITY MEASURING STATIC AND DYNAMIC STRAIN ON THE SURFACE OF A TUNNEL OR OTHER CAVITY IN ROCK. THE PHASE I OBJECTIVE IS TO DEVELOP A PROTOTYPE ACTIVE GAGE AND ASSESS ITS CAPABILITY UNDER LABORATORY CONDITIONS. THE CONCEPT TO BE INVESTIGATED USES A LINEAR VARIABLE DIFFERENTIAL TRANSFORMER (LVDT) AS THE STRAIN SENSOR. EMPHASIS WILL BE PLACED ON ACHIEVING ACCURATE MEASURMENTS AT ONE-HALF TO TWO PERCENT STRAIN. GAGES WILL BE DESIGNED TO MINIMIZE OFF-AXIS SENSITIVITY TO DYNAMIC LOADS. ANCHORAGE DESIGNS WILL ENSURE THAT THE GAGE DEFORMS WITH THE ROCK SURFACE, EVEN IN THE PRESENCE OF A STRAIN GRADIENT WITH DEPTH. LABORATORY TESTING WILL CONSIST OF UNCONFINED COMPRESSION, BEAM FLEXURE, AND VIBRATION TESTS. IF SUPPORTED BY THE RESULTS, A PREFERRED GAGE DESIGN WILL BE SELECTED FOR FOLLOW-ON LABORATORY AND FIELD TESTING IN PHASE II.