The construction case which adopts the ATM as a common tunneling technique has been increasing in difficult ground condition or in the shallow overburden. In these cases, the roof umbrella method such as the pipe roof method has been applied as an auxiliary method to minimize the surface settlement of ground. In this study, the relationship between general material properties such as the Young's modulus and Poisson's ratio, the cohesion and the internal friction angle of the ground and the micro-properties of the distinct element method has determined by the simple biaxial element test. By using this relationship, the numerical simulation by distinct element method in which the change of the interval between and the angle of each umbrella pipe was carried out. The correlation between the cohesion and the height of shape is obtained. Finally authors propose the rational design of the roof umbrella method using this relationship.
In recent years, the construction case which adopts the ATM as a common tunneling technique has been increasing in difficult ground condition or in the shallow overburden. In these cases, the roof umbrella method such as the TREV TUBE method or the pipe roof method has been adopted as an auxiliary method to minimize the surface settlement of ground, in cases of severe tunnel construction case close to the existing structures on the constraint of land use in urban area (see photo.1). However, an ordinary design method of roof umbrella method established based on an experiential study, so that it cannot estimate the effects of minimizing the settlement of the ground. Moreover, all the ground soil between each fore polling tubes along the tunnel cross section has intend to falling down by the roof umbrella method or the pipe roof method, as shown in a photo.2, so that the reinforcement of the ground by fore polling pipe cannot be expected. In this study, the relationship between general material properties such as the Young's modulus and Poisson's ratio, the cohesion and the internal friction angle of the ground and the micro-properties of PC which was one application program of distinct element method has determined by the simple biaxial element test. And the numerical simulation by using PC in which interval of fore polling pipes change was carried out. The relationship between the cohesion and the height of arching shape is obtained. Finally we propose the rational design of the roof umbrella method using this correlation.
Fig.1 shows the history of the diameter of fore polling pipe by using the pipe roof methods in JAPAN. It is clear from this figure, the diameter of a steel pipe was 200mm or less in 1960's, and recently it reaches the 1000mm. According to the construction records of the Japan pipe roof association1), one of the reasons of the large diameter of a steel pipe is the removal possibility by manpower in the soft ground including boulders.
