a. Technical Research Institute of Mitsui Construction Co., Ltd., Nagareyama. Chiba 270-0132, Japan
b. Graduate School of Engineering, Hokkaido University, Kita-ku, Sapporo 060-8628, Japan
c. Central Research Institute of Electric Power Industry., Abiko, Chiba 270-1166, Japan
d. Kamioka Mining and Smelting Co., Ltd., Kamioka, Fifu 506-1114. Japan

In Karnioka-mine, the conical-shaped steel reinforced concrete plug, whose length is only one thirds of the Japanese conventional standard, was designed and constructed, according to the principles proposed by the authors (see 1-st report). Pressure up to 4.5 MPa was applied in the pressurized cavern adjacent to the plug and the mechanical behaviors of the plug as well as the rock mass around the neighboring roadway were monitored.
It has been observed that both the plug and the rock mass around it, that is, the plug-rock mass structure behaves elastically without inducing the relative movement of the fissures in the rock mass beneath the plug, and that the pressure applied to the plug was resisted by the rock mass by inducing the compressive stresses. Since no symptoms indicating the unstableness of the plug-rock mass structure were observed, the plug has been proved to resist the pressure up to 4.5 MPa