| 摘要 |
PROBLEM TO BE SOLVED: To provide a tunnel construction method which is implemented by employing a simple structure at a low cost, and allows the substantial monitoring of a tunnel, and to provide the tunnel where the method is implemented. SOLUTION: An ultrasonic axial force measuring rock bolt 10 of a steel pipe expanding type is driven into a tunnel internal wall, and tunnel excavation is carried out while an axial force generated at a rock bolt by the displacement of the tunnel internal wall is monitored. The rock bolt is formed of an expandable steel pipe 20 and a measuring rod 50 having a plurality of gauge marks 55 for measuring the axial force. Then the rock bolt is driven into the tunnel internal wall as part of timbering, and expanded to make intimate contact with the natural ground. Further, axial force distribution generated at the rock bolt is reflected to the designing of the timbering. Specifically, after driving/expansion, the monitoring of the axial force generated at the rock bolt is started, ultrasonic waves are made to fall on the measuring rod via an entrance portion 11 as an exposed section of the measuring rod, and receiving time differences of reflected waves are obtained from the gauge marks 55, to thereby calculate the axial force distribution. COPYRIGHT: (C)2008,JPO&INPIT
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