Thermal Effect of Water Flowing through Fractures on the Cooling of Kurobe Jobu Railway Tunnel (Hot Tunnel), Central Japan

Abstract

Kurobe Jobu railway tunnel was accomplished in 1940, and the maximum wall temperature between Asobaradani and Sennindani was 165 °C. Since then, the tunnel has been considerably cooled by natural ventilation, but the present maximum wall temperature near small fumaroles or hot springs exceeds 90°C in places, and such a high temperature is supposed to be caused by thermal fluid flowing through fractures. Meteoric water which flows through fractures from the ground surface is assumed to extract and transport heat from the rock matrix above the tunnel to the wall of the tunnel and cause a high temperature near small fumaroles or hot springs. The assumption was evaluated by a simple mathematical model. The model consists of the cylindrical rock mass having a fracture through which water flows downward at the center. The differential equations govering the rock temperature were numerically solved by the finite difference method. Consequently in case many small fractures in the upper part of the rock mass join a single large fracture in the lower part, the temperature near fumaroles or hot springs can exceed 90 °C.