Performance of manhole under severe condition in Japan

Japan is prone to natural disasters such as earthquakes and torrential rains. Since those disasters have become more severe, extending the life of infrastructure is an urgent issue. Modern sewer system in Japan have been constructed since 1884, and regular inspection, cleaning, and repair are essential to prolonging the life of sewage pipes. Manholes, which are entrances to sewage systems, can be regarded to be one of the important structures that support our safe, secure, and comfortable lives.

In this paper, two main parts composed of a manhole, a cover and its bottom, are introduced. The cover made of spheroidal graphite cast iron (cast iron cover) and the manhole bottom made of resin concrete have been developed to extend the life and performance of manholes. The cast iron cover has been made lighter by optimizing the material and structure, does not rattle even when automobiles pass through it at high speed, and automatically releases pressure when the pressure in pipe rises. In addition, the introduction of resin concrete compensates for the shortcomings of cement concrete, such as low curing speed, salt damage, and freezethaw characteristics. Finally, examples of implementations and achievements with the developed materials and structures are presented and discussed.