| 摘要 |
PROBLEM TO BE SOLVED: To improve the construction property by widening widths of front and rear parts of one timbering corresponding to an insertion position when a steel pipe for pouring chemical is inserted into the natural ground from between timberings in the vicinity of a facing. SOLUTION: For example, timberings 1 in nine sections are arranged at substantially equal interval in one shift length of 9 meters. Next, when one shift length is digged, a distance from the first timbering 1 to the fifth timbering 1 when viewed from the direction of digging advance and a distance from the seventh timbering 1 to a facing 3 are digged along a designed digging line 2 on an inner peripheral face of a tunnel. At this time, a width of a tunnel cross section is widened for the line 2 over the front and rear of an arrangement position of the sixth timbering 1, its width expansion amount is made the maximum at the arrangement position of the sixth timbering 1, and its width expansion amount is such amount that a drill jumbo for drilling a lower hole for inserting a steel pipe for pouring chemical 4 between the sixth and the seventh timberings 1 and guide cell for supporting the steel pipe do not interfere with the timbering 1. Consequently, it is possible to reduce a width expansion digging area greatly more than in a conventional case and reduce an amount of mortar to be sprayed.
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