Author(s): M. Hanzawa; A. Matsumoto; N. Hirose; M. Tanaka; J. Mitsui; S. Maruyama
Linked Author(s):
Keywords: Coastal Structures; Design Wave; Tsunami; Long-Period Wave; Eco-Friendliness
Abstract: Concrete blocks have been widely used in Japan since the 1950’s, as economic growth in Japan has been mostly based on the coastal areas. In addition, a historically devastating Typhoon attacked and heavily damaged the Isewan bay areas in1959, and the need for shore protection was clearly recognized. Since then various wave-dissipating blocks and flat type blocks have been applied and the technology behind such concrete blocks has advanced. In this paper, this advancement of concrete block technology is described with a focus mainly on the following four aspects. The first point is coping with a continued increase in design wave heights, due to deeper construction sites and larger waves, the size of wavedissipating concrete blocks has increased gradually resulting in the development of a fully reinforced 80t Dollos to cover a wave height over 10m up to 13m (Hanzawa, et al., 2006). The second is tsunami disaster mitigation. One of the causes of failure of composite breakwaters at the time of the Tohoku earthquake on March, 11 th, 2011 was scouring of the rubble foundation and subsoil on the harbor-side of breakwaters due to tsunami overflow. This was formerly an inconceivable type of failure. A very practical method which can simply and accurately estimate the stability of armor units by using the overflow depth has just been proposed (Mitsui, et al., 2014). The third is to long-period wave dissipation inside a harbor area to mitigate serious problems in cargo handling in many Japanese ports. As a countermeasure, a slightly submerged mound type long-period wave absorbing structure with high performance on the harbor side of composite breakwaters has been proposed with an accurate harbor side stability formula for Tetrapods covering this structure against wave overtopping (Tanaka, et al., 2013). The fourth is an environmental aspect. In recent years, the importance of maintaining a good natural environment in harbors and coastal areas is also widely recognized. Innovative concrete blocks designed for “eco-friendliness” have recently been developed and their effectiveness is being verified in underwater surveys (Hirose, et al., 2014). A detailed explanation and discussion on the contents above from various points of view including future assignments will be described in this paper.
Year: 2014