ABSTRACT:

Application of Tunnel Boring Machine (TBM) is considered as the rational and economical method of constructing road tunnel because rapid excavation by TBM leads to reduction of construction cost. The degree of reduction will be more high when the ground conditions are comprehended beforehand and auxiliary methods are adopted adequately. When the auxiliary method or countermeasure is not selected properly, rapid excavation by TBM cannot be expected and construction cost may increase. Countermeasures for TBM excavation were discussed, however, they targeted on each tunnel and less examination was done by analyzing the data transversely. In addition, load acting on TBM support and real phenomena was not discussed very much. In this study, the countermeasure for excavation trouble was analyzed by collecting the examples in bad ground condition in Japan and the relation between the kind of trouble and countermeasure was clarified. The design model for TBM tunnel support was also examined and load needed for support design was estimated.

INTRODUCTION

Rapid tunnel construction by mechanical excavation method is effective to reduce construction cost for long tunnel of road, railway and waterway because its advance tends to be faster and the reduction of tunnel support can be expected by restraining the looseness of ground without dividing section. Actual achievement up to now using hardrock Tunnel Boring Machine, especially for road tunnel excavation in Japan, was limited to that of evacuation tunnels or pilot tunnels which had small section area because geological condition in Japan is said to be complex and easy to change. Under such circumstances, the experience of TBM has been increasing recently, however, current support type of TBM tunnel is generally set on the basis of past experience of construction by TBM and mountain tunneling method such as NATM. However, more rational design method of support of TBM tunnel with numerical analysis should be established when the construction case by TBM increases for main tunnel, pilot tunnel, or evacuation tunnel of road tunnel.

Past previous research result for support design of TBM tunnel was limited. Scorali (1995) showed the concept of patterning support in accordance with characteristics of support and ground, and Isago (2004) showed the relationship between support type and machine data acquired from TBM excavation, and an example of the load acting on TBM tunnel support by limited numerical analysis. Little result of the model for designing analytically TBM tunnel support and the degree of load used for it has been shown up to now.

Investigation of trouble example in excavating by TBM in road tunnel construction was achieved and the model for support design of TBM was discussed on the basis of the phenomena of ground from the result above in this paper. The degree of load value and design model for the support excavated by TBM were shown on the basis of the result of field measurement and simple calculation for some expected type of loads.

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