Unstable behavior of segmental ring under various pressures and its discrete element simulation.

In February 2012, a serious accident which resulted in five fatalities happened during a TBM-tunnel construction under the seabed in Japan. The cause of the accident appeared to be due to the Key-segment slipping out of the segment ring by the thrusting tailskin (wire brushes) of the TBM into the segment ring. This resulted in the collapse of the rings, causing the seabed ground and seawater to flow into the tunnel. We investigated how thin and thick segments without any circumferential joints behave under isotropic and anisotropic pressures using small-scale physical model. In the model tests, pressures were applied to the surroundings of the segment rings and the strains at each segment were measured in order to evaluate the damage. In addition, cases where lubrication on the contact area between the K- and B-segments was present or not were investigated and their discrete element simulations were also conducted.

Analysis of labour accidents in tunnel construction and introduction of prevention measures.

At present, almost all mountain tunnels in Japan are excavated and constructed utilizing the New Austrian Tunneling Method (NATM), which was advocated by Prof. Rabcewicz of Austria in 1964. In Japan, this method has been applied to tunnel construction since around 1978, after which there has been a subsequent decrease in the number of casualties during tunnel construction. However, there is still a relatively high incidence of labour accidents during tunnel construction when compared to incidence rates in the construction industry in general. During tunnel construction, rock fall events at the cutting face are a particularly characteristic of the type of accident that occurs. In this study, we analysed labour accidents that possess the characteristics of a rock fall event at a work site. We also introduced accident prevention measures against rock fall events.