DISPLACEMENT MEASURING APPARATUS FOR GROUND OR BEDROCK

PROBLEM TO BE SOLVED: To provide a displacement measuring apparatus capable of accurately measuring displacement of ground or bedrock while improving waterproof performance.SOLUTION: A displacement measuring apparatus 1 for ground or bedrock according to the present invention measures a position of a measurement target 4 that is fixed to a measurement borehole of the ground or bedrock using magnetostriction generated on a first rod-like part 8, or a magnetostrictive line. No movable portion is present in a preamplifier 21, or information acquiring means for detecting the magnetostriction, so as to improve the waterproof performance of the preamplifier 21. Alternatively, the measurement target 4 has a fixed bag 6 expanded by a fluid pressure, so that the fixed bag 6 freely enhances a force pressing the measurement borehole by the fluid pressure to firmly fix the measurement target 4 to the inner wall of the measurement borehole. Furthermore, the fixed bag 6 comprises a nonmagnetic material so as not to disturb the magnetic field of a permanent magnet. This constitution can accurately measure the displacement of the ground or the bedrock.