| 摘要 |
<p>A rock bolt (15, 115, 215) able to withstand two levels of tension within its tendon (16) is disclosed. The rock bolt is used in a tunnel (1) where the rock is subject to squeezing. After an initial installation with initial tension, plates (4) carried by the rock bolts are permitted to be squeezed together. Then a higher tension is created in the tendons (16) and the plates used to construct a concrete lining (9). The rock bolt preferably has first and second anchors. The first anchor can be chemical (grout) or mechanical (50). The second anchor (30, 40) is able to be triggered (36) by a pull chord (23) after the initial squeezing has taken place. An electric circuit (92, 93) is located in a breather tube (91) to signal that no more grout should be inserted via a grout tube (21).</p> |
