Design of large-sized accelerator tunnel

There are several key points in designing the underground tunnel where large-sized accelerator is installed. The following two points are very important: (1) Transformation of the tunnel should be minimal, (2) Level of integrity and durability of the tunnel structure should be high. In order to accomplish minimal transformation of the tunnel and stable operation of the accelerator, we recommend not to provide the expansion joints in the tunnel concrete. As the result of structural analysis which we performed on temperature change inside the tunnel without expansion joints, we confirmed that there was few incidence of harmful cracks and transformation.