Under the observational design and construction method, original tunnel design is immediately verified or modified based on the prediction results of geological conditions from in-situ data sequentially obtained during construction, such as seismic profiling, probe hole drilling and geological ratings at tunnel faces. Because data used and its processing method for geotechnical prediction change according to purposes, this study proposes the integrated prediction system for geological conditions ahead of tunnel faces, which is composed of long-interval, middle-interval, and short-interval prediction subsystems. The long-interval prediction subsystem is used for master planning, such as estimation of the total period and cost of a project. The middle-interval prediction subsystem is used for detailed planning, such as judgment of execution of preliminary reinforcement and selection of tunnel support pattern. The short-interval prediction subsystem is used for final decision making, such as confirmation or modification of the detailed plan and determination of tunnel excavation parameters. The applicability of those subsystems is verified with actual field data obtained in the motorway tunnel project, where Cretaceous granite occurs, involving a main tunnel excavated by the drill and blast method, and an accompanied evacuation tunnel excavated by a TBM in advance of the main tunnel.

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