| 摘要 |
<p>PURPOSE:To suppress the excavation cross-section of a cavity to the irreducible minimum as well as to enhance the economic efficiency of the device by a method wherein a structure with which the airtightness of a vacuum chamber can be confirmed from the inside only of the chamber. CONSTITUTION:A supporting member 4 is installed by a lock bolt 3 on the wall surface of a cavity 2 formed by excavation on a base rock 1. The edge of a pressure-resisting plate 5 is welded on the surface of the inner plate 4a of the support member 4, the edge of the inner plate 4a is welded on the outer surface of the pressure-resisting plate 5, and a ventilating path 10b to be used for inspection of airtightness is formed between the edge part of the pressure-resisting plate 5 and the surface of the inner plate 4a. Moreover, a small hole 11b is provided on the edge part of the pressure-resisting plate 5. He gas is sealed in the ventilation path 10b using the small hole 11b, and the jointed part on the inner surface of a vacuum chamber is inspected by detecting the leaking gas using an He detector along the junction line of the inner surface. As the leak test of helium is performed from the inner surface only of the vacuum chamber, the cross-section of excavation of the underground cavity can be suppressed to the irrducible minimum, thereby enabling to give high economical efficiency.</p> |
