Research results

Research on application of permeable pavement on roads
- Pavement that reduces flood damage during torrential rains -

Figure 1: Short-term torrential rains of recent years

Figure 2: A general description of permeable road pavement

Source: Watkins Report
Figure 3: A road during rainfall in the 1950s
(Rainwater has seeped into the road and caused a quagmire.)

In recent years, the number of intensive, torrential rains influenced by global warming, the "heat island" phenomenon, and other trends have been increasing in urban areas (Figure 1). The ground surfaces of urban areas, in particular, are largely covered by structures such as buildings and roads that do not allow the passage of water. Consequently, when torrential rains occur, their waters flow directly into rivers and sewers and often result in flooding. Such flood frequently occurs in urban areas.
This situation led to the enactment of the "Act on Countermeasures against Flood Damage of Specified Rivers Running across Cities" in June of 2003. This law requires that run-off control measures be implemented in regions specified by the law when development (including roads) reaches or exceeds a certain level. "Permeable pavement" is garnering attention as one such measure due to its ability to control rainwater run-off.
"Permeable pavement" is comprised of materials that provide high permeability throughout the pavement. It has a structure that allows rainwater to pass not only through the surface and binder course but also down to below the base course (Figure 2). Consequently, it improves vehicle driving safety during rain and reduces road-surface noise just like drainage pavement, as it also provides new functions that help control rainwater run-off, recharge groundwater, and nurture roadside trees.
Until now, permeable pavement has been used primarily for sidewalks and parking lots for light vehicles. Its application in vehicle roads has been limited, and there are no established methods for calculating its durability and run-off control performance. Given this, the Pavement Research Team is currently engaged in studies toward making permeable pavement a practical option for vehicle roads.
What happens when water is allowed to easily penetrate a road? Figure 3 shows an unpaved road that is soaked with rain. Repeated traffic load on the road surface has caused it to lose strength and become a quagmire. Because of situations like this, the world’s pavement engineers have come to accept prevention of pavement permeation as a basic rule. Here, permeable road pavement stands contrary to international common sense because it allows water to penetrate its surface. A concept unique to Japan, permeable road pavement is a singular technology - seen nowhere else in the world - that is attempting to change conventional wisdom through Japanese technical prowess.

The Pavement Research Team In 2005, prepared a "Road Surface Rainwater Treatment Manual (Draft)" as a set of provisional technical standards that are based on results obtained from indoor tests and actual-size test pavements. Moreover, it is studying test pavements that are being used on heavily trafficked roads in 10 locations in Japan to quantitatively evaluate their durability on actual roads. The team has confirmed that these test pavements experienced no durability problems after five years in service, and it will continue to study them to verify their long-term durability.

(Contact: Pavement Research Team)

Development of Overtopping-Wave Prevention Fences Using Transparent Corrugated Plates
- Overtopping-wave countermeasures that take the landscape and the visibility into consideration -

Overtopping waves

Loading test

On-site adoption

Overtopping waves may occur on coastal roads due to the influence of weather, and the subsequent traffic restrictions may hinder community life and industrial activities. One measure to ensure smoother traffic conditions is the establishment of roadside fences to prevent the waves from overtopping. These fences are expected to be able to withstand large amounts of pressure from the wave action and impact of stones that are scattering along with the waves. At some sites the fences may also be required to not block out light and have a structure that takes the landscape into consideration. While ones combining steel posts and corrugated steel plates with holes (perforated steel plates) are usually used, they are not necessarily an agreeable addition to the landscape as they block the surrounding views. Therefore, development of overtopping-wave fences that are highly impact-resistant and do not block out light, take the landscape into consideration and cost less than conventional ones was considered.

In developing the new type of fences, focus was placed on polycarbonate, which is resistant to impact and temperature changes, transparent and unlikely to deform. With such features, this material is used in a variety of products around us, including helmets, shields and other safety appliances, domestic electrical appliances and construction materials. The impact- and weather-resistant polycarbonate plates used in the overtopping-wave fences are transparent and weatherproofed on both sides. More economical thickness, shape and dimensions of plates were determined depending on the magnitude of the loads applied. With a corrugated sheet structure, the fences can withstand large overtopping-wave loads. It is also possible to reduce material costs as the plates can be extremely thinner than those made of flat polycarbonate. However, since polycarbonate itself is a relatively soft resin material, it deforms under load application, and cracking and damage may occur around the fixed parts depending on the methods of fixing the edges of corrugated plates. To solve this problem, metallic material was placed on both sides of the corrugated polycarbonate plates, which secured with through-bolts at the center of the sloping section.

(Contact: Structures Research Team)