Abstract: A cover for underground structures has a large number of mutually independent projections of the same size and shape uniformly provided on its surface, while small protrusions of the same size and shape are formed on the upper surfaces of some or all of these projections. On top of these small protrusions are formed even smaller protrusions of the same size and shape as the topmost protrusions. Spacing between one large projection and another, between one small protrusion and another, or between one small protrusion and a projection having no small protrusion on its top is set at the optimum distance, and the size of the topmost protrusions is also designed in a shape to fit an optimum size to ensure good skid-prevention effect on tires of vehicles passing over the cover, especially in bad weather over a long period of time, no matter where the cover is installed.

Abstract: A cover for underground structures, its cover body, and its frame designed to quickly discharge accumulations of rainwater and dirt so as to prevent slipping and skidding from increasing due to these accumulations. The cover body has a multiplicity of patterns of projections and depressions on its surface, one projection independent of another, so that the upper surface of each projection is on about the same level as that of the frame with the depressions formed to surround each of these depressions. The depressions are constructed to become gradually deeper from the central part of the cover body toward the periphery, while the frame also has depressions set up on part or all of its upper surface in a circumferential direction with discharge guides sloping up toward the outer periphery of the frame. The cover for underground structures is made up of a set of the cover body and the frame.