Improving drainage in schoolyards and farmland! How to choose the best culvert drainage pipe

校庭やグラウンド、公園や農地など一定の広さを持つ土砂の地表は降雨後の水はけが悪く、ぬかるみや水たまりが発生してしまう場合があります。このような状態が多発し、校庭などを利用できずに頭を抱えている方も多いのではないでしょうか。

この記事では、水はけ問題に関する基礎知識の解説を交えつつ、改善策として最適な暗渠排水管『マックスドレーン』をご紹介します。詳しい知識をお持ちでない方にも分かりやすくまとめていますので、ぜひ参考にしてみてください。

What causes poor drainage?

The following is a brief explanation of the reasons for poor drainage at the soil surface. The causes include the following points

• Poor or deteriorated drainage performance of the soil or sand used
• Irregular irregularities or unbalanced gradients on the ground surface
• Culvert drainage is absent or its performance has deteriorated

The majority of the causes are first and foremost the poor drainage performance of the soil and the condition of the ground surface. Land that experiences drainage deterioration problems has often been used for many years, and the problem is exacerbated by age and deterioration. A common measure to remedy this problem is to install culvert drainage in advance. The following is an explanation of culvert drainage, which is a relatively easy measure to take.

What is culvert drainage?

「暗渠（あんきょ）」とは、地下に埋設したりふたをしたりした水路のことを指します。これを活用して土地の水はけを改善する手法を「暗渠排水」といい、そもそもは水田を乾田化するために取り入れる方法のひとつでした。

そこから派生し、現在では地表の残留水の除去や地下水位の低下を図るために地下に連続した通水空間を設けて余分な水を効果的に排除するための設備として発展して、各所で導入されるようになりました。

 

暗渠排水は主にコンクリートの排水路と地表の水を浸透させる地中管を設置する仕組みになっています。地中管にはプラスチック系や素焼きの土管などが使用されます。

Cases of poor drainage even with culvert drainage

Unfortunately, it is not safe to say that installing a culvert drainage system is a good idea. In some cases, adequate drainage may not be achieved, mainly due to the following reasons

• Poor durability and aging of drainage pipes
• Low drainage of the drain pipe itself
• Clogged drainpipes

These problems stem from the performance of the drainage pipes installed. Of particular importance is the design of the “suction hole” in the drainpipe. The importance of these holes is explained next.

Trouble lurking in culvert drainage pipes

Culvert drainage pipes have numerous water absorption holes on the surface of the pipe to allow water from the ground surface to percolate through. The size of these “water absorption holes” is an important point that determines drainage performance, and culvert drainage pipes have many problems stemming from this point.

Water intake hole is too large (sediment accumulation in pipe)

一般的な塩ビ有孔管などの吸水孔は20mm～30mmとなっています。このように吸水孔が大きいと、孔より小さな土砂は管内に吸い込まれてしまいます。管内にとどまった土砂は排水管の底に堆積し、菅の通水断面を減少させ、最終的に暗渠排水の能力が著しく低下してしまいます。
そのようなトラブルをさけるため、有孔管を暗渠排水管として利用する場合は、一般的に管の周りに不織布（フィルター材）を巻いて設置します。ところが、不織布で巻いた場合また違ったトラブルも考えないといけません。

Water absorption holes are too small (clogged)

有孔管をフィルター材で巻くと、フィルターの目合いより大きな土砂は管内に侵入しなくなります。しかし、今度はシルトと呼ばれるごく小さな土の粒子が管の表面やフィルター内に付着滞留します。目詰まりの最大の原因と言われているこのシルト分が集まることで、吸水孔の周りに水を通さない層ができ、将来的には吸水性が著しく低下（目詰まり）してしまいます。

理想的な吸水孔径と開孔率を持つ排水管が求められる

 

吸水孔の径が大きすぎると、管内に土砂がたまってしまう。かといって小さすぎるとシルトが付着し目詰まりを起こしてしまう。長く機能する暗渠排水管には、適切な吸水孔径が重要であるとお判りいただけたかと思います。
このような観点から、理想的な吸水孔径と開孔率を実現した暗渠排水管が、太陽工業社製の『マックスドレーン』です。従来の暗渠排水管と比較して極めて高い効果をもたらすこの製品について特徴をご紹介します。

Mesh flexible culvert drainage pipe "Max Drain

Max Drain” manufactured by Taiyo Kogyo is a culvert drainage pipe designed with two layers of mesh-like special split fibers. The optimum size and opening ratio of water absorption holes prevent sand from flowing in, while silt, which can cause clogging, flows out without stopping at the pipe wall, thus maintaining high drainage performance for a long time.

 

The “Max Drain” has the following outstanding features

• Materials and design that produce ideal pore size
• High external pressure strength, cold resistance, and impact resistance
• Flexible and lightweight, very easy to transport and install

Materials and design that produce ideal pore size

Max Drain has achieved an ideal structure focusing on the importance of pore diameter. Comparisons between Max Drain and other culvert drainage pipes in terms of opening rate and water absorption pore diameter, respectively, are summarized in the table below.

Porosity: Significant effect on water absorption capacity

暗渠排水管の種類	開孔率
Vinyl chloride perforated pipe, corrugated perforated pipe	0.7 to 2
Netron and other reticulated short tubes	10% of
Non-woven filter tube	Around 20
Max Drain	Around 22

Water absorption pore size: Greatly affects clogging durability (*0.08 mm or more, 0.5 mm or less is ideal)

暗渠排水管の種類	吸水孔径
Vinyl chloride perforated pipe, corrugated perforated pipe	20 to 30 mm
Netron and other reticulated short tubes	5mm
Non-woven filter tube	Around 0.06mm
Max drain	Around 0.2mm

Fiber materials for ideal fabrication

The filter permeable portion of Max Drain is composed of proprietary split fibers (high-density polyethylene). The ideal pore diameter of around 0.2 mm, which could not be achieved by any other method, is realized by layering and thermally bonding two pieces of split fibers with irregularly arranged pores with a maximum pore diameter of 1 mm or less. This pore diameter of around 0.2 mm is close to that of coarse sand, which has long been used as a drainage measure, and is ideal for culvert drainage, as it does not move surrounding sediment and discharges only silt, which causes clogging.

High external pressure strength, cold resistance and impact resistance

Because Max Drain is a flexible “tawami pipe,” slight deformation causes the external pressure load to be immediately distributed almost evenly around the entire circumference of the pipe. Therefore, Max Drain is not subjected to concentrated loads in the soil, and the loads are equally distributed, demonstrating its strong resistance to external pressure. In addition, the use of high-density polyethylene resin allows the pipe to be used in environments down to -70°C, and there is no risk of cracking, as is the case with PVC pipes.

Flexible and lightweight, easy to transport and install

MaxDrain is extremely light, weighing only 9 kg per 20-meter length, making it easy to transport and lay, and reducing the labor required for installation compared to other drainage pipes. Another major feature of Max Drain is that it can be easily carried to sites with unfavorable conditions. The structure is a flexible, long infiltration pipe with a special split fiber tubular body and helical reinforcement fused to it, making it easy to install in curves and follow the ground movement. The joints are screwed together for easy connection and a high level of safety.

summary

We have introduced “Max Drain,” the best culvert drainage pipe to improve poor surface drainage in schoolyards, grounds, parks, and other areas. Many people may have thought that it is difficult to identify effective and optimal remedial measures for a problem because it is an area where knowledge is generally not widespread. Max Drain” is a product that we can confidently recommend to such people. Please feel free to contact us if you are considering replacing your existing culvert drainage pipes or if you are considering taking countermeasures in the future.