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  Behavior of lining concrete under high temperature condition

  Permanent lining has various functions for tunnel and naturally the fire proof resistance is included, and it is expected to confirm the safety for users. The road tunnels in Japan constructed by conventional method uses plain concrete as permanent lining in general conditions. The thickness is 30 cm and its compressive strength is 18 MPa mainly [1]. Installation of emergency facilities against tunnel accidents such as fire etc. is also regulated by technical standard [2]. When the reduction of construction cost and the improvement of the long-term durability of structure are discussed, high strength concrete or fiber reinforced concrete is applied for mountain tunnel to boost the load-bearing capacity even in normal condition. Steel bar for reinforcement in permanent lining is also used in special condition, in addition to portal area. As for shield tunnelling method, secondary lining for slurry or EPB tends to be omitted recently in Japan due to cost reduction. Meanwhile, the concept for tunnel safety was shown and some regulation has published [3]. Some countermeasures are applied on the basis of some fire accidents in tunnels. The securement of evacuation environment during tunnel fire and risk against fire in terms of facilities' design has been discussed recently [4]. Thus, the concept for permanent lining may be various recently. The study about the characteristics of lining under high temperature when tunnel fire occurs was mainly shown for the segmental lining for EPB or slurry, which used high strength concrete and the results of the performance of fire-proof members were accumulated in Japan [5]. Experiment for temporary lining was reported and some time-temperature curve for the consideration of tunnel fire was proposed when the tunnel locates in special condition. However, basic characteristics about permanent lining with plain concrete are limited. To secure the further safety of tunnel user and structure under high temperature condition such as during tunnel fire, the fundamental characteristics of tunnel concrete lining with a strength of 18 to 30 MPa, which is generally used in mountain tunnel in Japan, should be accurately grasped, as well as the examination in special condition. The basic behavior of permanent lining concrete which is applied for road tunnel in Japan is mainly examined when it receives high heat under various conditions in this study. Firstly, the element experiment using the cored concrete specimen with similar mixture material of permanent lining concrete is conducted and the reduction of compressive strength and Young’s modulus are grasped. Next, the element experiment supposing the permanent lining by giving the heat simulating tunnel fire is done and the change of the temperature inside the specimen and the phenomena of concrete explosion and structural instability are observed, in addition to grasp

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