GATE 2022 MN – Question 38
A three-point borehole extensometer has anchors 1, 2, 3 from deepest to shallowest, as shown. Readings in mm on 2 May 2021 are (34.52, 29.04, 43.11); on 1 June they are (40.56, 34.67, 44.78). Where is the most likely single discontinuity?
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Correct answer: (B) Between anchors 2 and 3
Explanation
Reading changes are 6.04, 5.63 and 1.67 mm. The deepest two anchors show similar movement relative to the measuring head, whereas the shallowest has a much smaller change. The large change between the second and third anchor increments (3.96 mm) locates the principal separation between anchors 2 and 3, B.