Simulation of the articulated shield behavior in very soft clay
This research aims to verify the performance of the shield kinematic model in very soft clay by comparing the shield behavior calculated by the shield kinematic model with the measured shield behavior in very soft clay.
The in-situ data at Nihon-tsutsumi shield tunnel is used for the simulation, where the tunnel is located in the border between the Lower Yuraku-chou clayey layer upper with N Value = 0 (Ylcu layer) and the Lower Yuraku-chou clayey layer lower with N Value = 0 to 6 (Ylcl layer).
The following special shield behaviors were observed at this site:
1) the shield looks upward while the jack vertical moment acts on the shield downward
2) the jack horizontal moment acts on the shield rightward while the tunnel alignment is straight.
To represent the above shield behaviors, the following modeling was made:
1) the adhesive parameter is used for calculating the dynamic friction force around the skin plate in axial direction instead of the coefficient of friction
2) the effective rate of the over excavation is adjusted to represent the effect of inclined ground layer.
Irrespective of the above characteristics of this analysis, the applicability of the shield kinematic model to very soft clay can be confirmed, since the simulation results on the tunnel alignment, yawing angle, and pitching angle has a good agreement with those measured data.