Example of construction that temporarily restored a large-scale riverbank collapse in 8 days

日本では毎年のように台風や豪雨による水害が報告されています。岡山県倉敷市真備町も、2018年の「西日本豪雨」によって1級河川である末政川の両岸が崩壊し、大きな被害を受けました。

しかし、この大規模な被害に対する仮復旧工事は、『コンクリートキャンバス』でわずか8日間で完了しました。

末政川の迅速な仮復旧はいかにして実現したのか。本記事で詳しくご紹介させていただきます。行政の土木事業担当の方や、交通関係事業者の方のご参考になれば幸いです。

*西日本豪雨とは
2018年6月28日から7月8日にかけて、台風7号と梅雨前線等の影響によって発生した集中豪雨のことで、正式には『平成30年7月豪雨』と呼ばれています。全国で記録的な大雨となり、西日本を中心に広い範囲で被害をもたらしました。

Damage in Mabi-cho, Kurashiki City, Okayama Prefecture

In Okayama Prefecture, there was a series of floods and landslides caused by overflowing rivers and breaches in levees, making it the worst flooding in the prefecture in the postwar period.

 

Damage was especially severe in Mabi-cho, Kurashiki City, where a total of eight levees were confirmed to have failed: two in the Oda River, two in the Takama River, three in the Suemasa River, and one in the Mayagawa River.

Sue Masa River Restoration and Challenges

The Suemasa River, a first-class river in the Takahashi River system that flows through Mabi-cho, had breached both its right bank and left bank levees, flooding the area and causing extensive damage. To minimize the damage, temporary restoration had to be completed in about two weeks, but this required the following challenges.

• The entire neighborhood is in the disaster area, and there are no builders with the capacity to respond quickly.
• Fresh concrete mixer trucks cannot be arranged due to the disaster.
• Space for fixed installation of heavy equipment such as pump trucks is not available.
• The initial plan to construct the concrete surface using fabric formwork would take more than one month, so it would not be completed in time.
• Inability to secure workers capable of performing the special construction required for concrete placement.

The “Concrete Canvas,” a membrane that creates a concrete surface simply by pouring water on it, solved these problems and enabled temporary restoration in a short period of time.

What is "Concrete Canvas"?

コンクリートキャンバスは『コンクリートと布地と遮水材の複合材料』です。特殊配合のドライコンクリートを繊維マトリクス織編物（表面）とPVCシート（裏面）で挟んだ構造をしています。

厚さ5mm～13mmの薄い布地を地面に敷設して水をかけるだけで、コンクリート面をつくることができ、散水は海水/淡水を問わず、水中でも使用できます。

 

コンクリートキャンバスの概要を2分間にまとめた動画があります。

 

 

 

Four characteristics and uses of concrete canvas

Concrete canvas has four characteristics: high workability, durability, environmental friendliness, and fire resistance, and is used in a variety of applications.

 

Feature 1: High workability

All that is needed to create a concrete surface is concrete canvas and water. Since the fabric can be transported in a rolled form, there is no need for mixer trucks or other large heavy equipment, no need for measuring or mixing, and no need for workers with special expertise since there is no need to worry about excess water.

 

Feature 2: Durability

Concrete canvas materials are chemically and weather resistant and are not degraded by ultraviolet light. It also has approximately twice the abrasion resistance of ordinary concrete and has demonstrated a life expectancy of over 50 years in accelerated deterioration tests in the UK.

 

Feature 3: Environmental

Concrete canvas is characterized by its low abrasion rate, which contributes to CO2 reduction and provides a high degree of environmental friendliness.

 

Feature 4: Fire resistance

Concrete canvas has excellent heat resistance and can be used as a fireproof layer in some applications. Because flames do not spread to the surface, smoke generation is kept low and the release of toxic gases is minimized.

 

Main applications of concrete canvas

• Disaster recovery (sandbag covering)
• Erosion prevention (surface protection)
• Waterway maintenance and expansion
• irrigation channel construction
• weed prevention
• slope protection
• Concrete Repair
• Outlet/residual water discharge
• cage protection

Case Study on Emergency Restoration of Suemasa River Levee Failure

summary

Concrete canvas was used in the restoration of the Suemasa River in Kurashiki City, Okayama Prefecture, which was damaged in the 2018 “Torrential Rainstorm in Western Japan.

The Okayama Prefectural Government approached us for consultation on July 18, 2018. Due to the aforementioned issues, the decision to use “concrete canvas” instead of conventional concrete pouring was made immediately. All the staff of our division in charge of the project were mobilized to back up the local construction company, and construction began on July 26. The necessary temporary restoration work was completed in just eight days.

 

Why Concrete Canvas was an immediate hit.

For the following reasons, an immediate decision was made to use concrete canvas instead of conventional concrete repair work.

 

Partial construction is possible.

Large sandbags, the base for repairing and raising the embankment, were under construction at the time, and there was no time to wait for this work to be completed. Since the concrete canvas could be partially constructed, and could be covered and cured while the sandbags were being piled, we were able to proceed with the work in parallel with the sandbag installation.

 

Can be handled by general workers.

Concrete placement using fabric formwork requires special workers with specialized knowledge and experience. In the disaster area, where it was difficult to arrange human resources, concrete canvas was chosen because it could be constructed by ordinary workers.

 

Work can be done without the need for large heavy machinery.

Even at damaged sites where it was difficult to secure space to secure the large, heavy equipment needed to place concrete, concrete canvas could be transported and laid by hand, allowing for a flexible response.

 

Measurements and construction can be taken on site

Conventional fabric formwork used for concrete placement work required measurements in advance, but the concrete canvas could be cut to any size while being laid on site, allowing for quick installation.

 

After temporary restoration to full restoration

The year after the temporary restoration, we received an order for our fabric formwork method (TACOM) to reinforce the upstream and downstream ends of the temporarily restored construction section. Finally, the embankment was raised by 0.7 to 1m and widened by 6 to 10m in three sections: a 40m and 110m section on the left bank of the Suemasa River and a 150m section on the right bank, and on September 06, 2019, all improvement and restoration work was completed including other rivers under prefectural management. *The quality and speed of the temporary restoration work was highly appreciated and an additional order was placed for the main restoration work.

summary

In many cases, concrete repair is required for emergency restoration work after flooding and disasters caused by typhoons and torrential rains. However, the following issues exist in concrete placement

• Need a plant to supply ready-mixed concrete
• Materials and equipment for construction (including heavy equipment) are required
• Skilled workers such as formworkers and reinforcers are needed.

Please consider “Concrete Canvas”, which solves these problems and realizes flexible and prompt disaster recovery work. For more information about Concrete Canvas, please click the link below.

> “Concrete Canvas” by Taiyo Kogyo Co.

>> Click here to contact us.