METHOD FOR MAKING FACE SELF-SUSTAINABLE IN TUNNEL EXCAVATED IN COLLAPSIBLE MATURAL GROUND

PURPOSE:To prevent clogging in a circuit of pressure conveyance by a method wherein specific gravities of fibers and conveyance fluid are made equal when constructing a number of horizontal piles of fiber-reinforced soil mortar to the surface of a face, and separation and sink-and-float of the fibers are eliminated. CONSTITUTION:A number of horizontal pits 9 are drilled with a drilling machine 1 to the surface 10 of a face in a tunnel in collapsible natural ground, and fiber- reinforced soil mortar is injected into the pits. Then, horizontal piles are constructed therewith to make the face self-sustainable when tunnel excavation is executed. An admixture made of concrete milk, water glass and vinylon fibers with a mixer 3 for hardening material and a mixer 4 for principal material is discharged at a specified ratio by a proportional discharge pump 5 and is injected from the front end of bits 8 into the pits. Hoses in small diameter larger than three times of maximum fiber length are used so that the fibers are not separated sink in or float on the conveyance fluid when being conveyed, and clogging arising from interwinement of the fibers in a circuit of pressure conveyance can be eliminated. Thereby, efficiency in execution of work can be improved.