Abstract
Centrifuge model tests were conducted to clarify the mechanism of the passive state at failure around ECL tunnels. The model ground movements were observed with controlling the pressure of the rubber balloon filled with de-aired water. The passive earth pressure derived from some calculation models were compared to the results of the centrifuge model tests. Following conclusions may be drawn by these studies. (1) The pressure when the ground surface started uplifting was higher than the initial vertical earth pressure, but the pressure became lower according to the shear resistance reduces. (2) The failure surface observed in the tests resembled the logarithmic spiral in appearance. (3) The calculation model that the shear plane was considered as a straight line could simulate the passive earth pressure and the shear plane observed in the centrifuge model tests as well as the logarithmic spiral.
