EXCAVATION ADDITIVE IN SHIELD TYPE TUNNEL CONSTRUCTION AND SHIELD EXCAVATION METHOD

摘要

PURPOSE:To facilitate the safe excavation of the gravel ground by fluidifying earth and sand by changing them to a muddy slurry having a pH of a specified value or more by adding an additive in excavation of earth, etc., while by coagulating the earth and sand by lowering the pH to a specified value or less in the discharge of the earth and sand. CONSTITUTION:The fluidity of earth and sand is improved by adding the excavation additive, whose pH is adjusted to 7 or higher (e.g. 7.5-9.5) by adding a boron compounds to a water-soluble high polymer, the earth and sand for excavating earth, and taking-into a screw conveyor port is facilitated. When soil is discharged the pH is adjusted to at most 7 (e.g. 4.5-6.5) by adding an acidic substance into a conveyor, and the action for suppressing the swelling solubilizing action is eliminated, and earth and sand are coagulated. Accordingly, in the excavation, the fluidization of earth and sand is accelerated, and the earth and sand in a fluidic state are allowed to flow into the screw conveyor, while in the discharge of earth, the fluidic earth and sand are coagulated by adding the acidic substance, and can be discharged from a earth discharge port.