MIGHTY NORTH 1 Precision Test
Technical rept. 13 Apr 93-31 Oct 96
SRI INTERNATIONAL MENLO PARK CA
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MIGHTY NORTH 1 was a precision test performed on a 0.4-m-diameter lined tunnel in a 2-m-cube of jointed limestone made from over 4000 50-mm-square x 0.6- to 1.2-m-long limestone bricks. The test article was embedded in a concrete testbed and loaded with an explosively produced, 100 MPa, cylindrical, stress wave. The velocity around the boundary of the jointed limestone test article was measured with 22 accelerometers and these data were used to generate a continuous velocity boundary condition for computational simulations. Additional internal instrumentation measured brick stress, brick slip, and tunnel closure. All gages provided clear and credible measurements, except the closure gages, which were inoperable at the time of the test. Stress at the tunnel depth was about 75 MPa. Very little horizontal slip occurred at the locations of the slip gages at the interface tangent to the crown. The mechanism of response was vertical cleavage fractures emanating upward from the springlines, with the bricks between the cleavage planes moving downward about 10 mm relative to the brick outside. The cleavage planes also extended below the springlines, but the relative displacement was only about 2 mm, with the bricks outside the cleavage planes moving downward relative to those between the planes. posttest liner deformation was -2.5 closure at the crown-invert diameter and 1.3 opening at the springlines.
- Test Facilities, Equipment and Methods