Explaining the Basics of Temporary Protective Fences│New “MWG Construction Method” with Superior Merits

A temporary rockfall protection fence is installed to protect vehicles and pedestrians from falling rocks and flying rocks when they occur due to soil cuttings, mainly during road slope construction. General contractors, construction consultants, and local government officials may have heard of these fences, but some of them may not know much about them. This article explains the basics of temporary protective fences for those who deal with them or are considering using them in the future. We also introduce the “MWG method,” a new method of temporary barriers that has many advantages over conventional methods, so please take a look at it.

 

Click here formore information about the MWG construction method

What is a temporary protective fence?

そもそも仮設防護柵とはどういったものなのでしょうか。多くは工事期間中の落石事故を未然に防止する、文字通り仮設の落石防護柵を指します。供用中の道路の安全確保のために用いられる設備です。

現在では様々なメーカーより仮設防護柵は販売されており、用途はどれも同じながらも素材やコスト、細かな工法などに違いが見られます。

Construction requiring temporary protective fences

工事において仮設防護柵を必要とするケースは、その多くが道路沿いの法面工事で切土を伴う工事です。特に山間部などは道幅が狭く、道路工事を行う際、道路沿いの斜面を一部掘削することも要求されます。このような工事では、交通車両や歩行者の安全確保を目的として仮設の落石防護柵が用いられます。

仮設防護柵が無いと落石が発生した際、通行車両や歩行者に思わぬ事故や被害を招く恐れがあるため、仮設防護柵は切土などを伴う道路工事では、とても重要な設備です。

Issues in Conventional Temporary Protective Fence Methods

Temporary rockfall protection fences are available from a variety of manufacturers, but despite differences in construction and installation methods, there are inevitable challenges associated with conventional construction methods. It is important to understand these challenges when installing temporary rockfall barriers. The main challenges are as follows

• Incidental work such as excavation of pavement surface and pouring of support columns is required
• Requires large heavy equipment for delivery and installation work
• High burden of ancillary work such as road surface restoration
• Site environment may require road closures
• Noise and vibration are generated

Incidental work such as excavation of pavement surface and pouring of support columns is required

In the conventional method, it is necessary to cast H-beams or other steel into the road ground in order to install the support columns. In some cases, concrete is used as the base in areas where the ground is hard. Thus, the conventional construction method inevitably involves a large amount of incidental work.

Requires large heavy equipment for delivery and installation work

Conventional temporary fences often require large vehicles and heavy equipment for delivery and installation. In addition, it is sometimes difficult to transport large heavy equipment to the site on narrow roads in mountainous areas.

High burden of ancillary work such as road surface restoration

In order to make the fence posts self-supporting, piles will be driven into the road base (or concrete base), and the ground and road surface will need to be restored after the work is completed. Since ancillary work is required before and after the main construction work, the construction period will be long.

Site environment may require road closures

Many of the sites that require temporary protective fences are roads in mountainous areas. Some of these roads are very narrow. In some cases, the space may have to be filled with materials and heavy equipment, and the road may have to be closed off completely.

Noise and vibration are generated

Conventional construction methods require pile driving, which involves excavation of underground deposits and the ground. This process inevitably generates loud noise and vibration. Since this is a temporary protection fence construction that is incidental to the main construction work, the environmental impact should be minimized as much as possible.

What is required for an ideal temporary protective fence

We have explained that there are unavoidable challenges associated with the conventional method of temporary protective fences. By sorting out these disadvantages, we can see what the ideal temporary barrier should be like. Compared to conventional construction methods, the characteristics required for an ideal temporary barrier include the following.

• Less labor and workload for installation and removal work
• Shorten the construction period
• Friendly to the surrounding environment

New construction method "MWG construction method" with abundant merits

We have organized the elements required for temporary protective barriers. The MWG method has many advantages over conventional methods.

Here are some of its features and advantages.

What is MWG construction method?

MWG is an abbreviation for Mesh Wall Gard. And MWG method refers to a construction method using continuous box-shaped steel frames (mesh wall). The most distinctive feature of the MWG method is that it differs from conventional methods in that it does not require excavation of the ground for the foundation work, since the support columns are fixed to the base plate installed in the mesh wall and are made self-supporting by placing soil and sand inside the frame.

Advantages of the MWG Method

The MWG construction method has the following superior advantages over conventional methods. Each of them is explained in detail.

• Shortened construction period through simplification and reduction of work
• Lower cost than conventional methods
• Space-saving, even on narrow roads
• Low noise and vibration
• Can use locally generated soil

Shortened construction period through simplification and reduction of work

MWG工法では、資材搬入や防護柵の設置に際して大型重機や車両、特殊作業を必要としません。また、事前の地下埋設物調査や架空線移設も不要です。さらに、地盤の掘削もしないため工事後の路面復旧も不要であり、従来に比べて多くの作業を削減・簡略化することができます。

そのため、総合的に工期を大幅に短縮することが可能です。従来比で、およそ最大75％ほどの短縮を見込めます。

Lower cost than conventional methods

The MWG method uses a very small amount of steel, which is the key component of a temporary barrier. This is due to the fact that there is no need to cast into the road ground or to attach supports to make the fence self-supporting. In addition, because there is no ground excavation or pouring, as mentioned above, large heavy machinery and vehicles are not used, and no ancillary construction work is required, making it possible to significantly reduce the overall cost of construction. This can reduce overall construction costs by up to 50% compared to conventional methods.

Space-saving, even on narrow roads

メッシュウォールは折り畳めるため、搬入や保管時にも場所を取りません。そして、拡げた際にも、防護柵の高さによりますが基礎部の幅が1.0〜1.6mであることから、山間部などの狭小な道路においてもスムーズかつ省スペースで工事を行えます。大型車両や重機なども不要なので、車両などで道を塞いでしまうこともありません。

そのため、狭小な現場でも片側1車線を十分に確保可能で、完全通行止め対応もほとんど必要ありません。交通への負荷を最小限に抑えられることで、周辺への影響も少なく、理想的なメリットと言えるでしょう。

Low noise and vibration

The fence can be laid without the use of pile-driving machines, thus reducing noise and vibration caused by heavy machinery. This method is also suitable for sites where there are residences and other structures in the vicinity.

Can use locally generated soil

One unique feature of the MWG method that distinguishes it from conventional methods is the use of locally generated soil to support the support columns. This is due to the special structure of the mesh wall, which is the frame of the posts, which allows the use of locally generated soil for the filling material. This specification reduces the purchase of materials for the installation of protective fences and leads to the effective use of locally generated soil.

Temporary protective fence construction method using the MWG method

The following is a brief explanation of the method and procedure for constructing temporary protective fences using the MWG method.

1. 搬入
   メッシュウォールは折り畳んで輸送・搬入可能、保管も省スペース。

2. ベースプレートの設置
   支柱をセットするためのベースプレートを設置。ベースプレート同士を連結プレートにより接続することで、安定性を確保。

3. メッシュウォールの設置
   連続箱型鋼製枠であるメッシュウォールを展開。展開作業は3,4人でスムーズに行うことが可能。

4. 土砂の充填
   ベースプレートに支柱を設置し、メッシュウォール内に土砂を充填。メッシュウォールが自立し、重機に近接せずに充填作業が可能。

5. 矢板の差込
   横継材を固定し木矢板を設置し、仮設防護柵の完成。作業後はメッシュウォールガードを解体し、土砂を撤去で完了。

MWG Method Application Examples

The MWG construction method is actually utilized at various sites due to its convenience and high functionality. The following are some examples of actual use of the MWG construction method.

Utilization in slope repair work for disaster prevention dam facilities

所在地	岩手県
Specifications	Protective wall height 3.0m, T-1.0
Applications	Temporary protective fences
Scale	45m

Utilization in slope repair work on general national highways

所在地	岩手県
Specifications	Protective wall height 4.0m, T-1.3
Applications	Temporary protective fences
Scale	90m

Use in disaster prevention construction

所在地	長野県
Specifications	Protective wall height 4.0m, T-1.3
Applications	Temporary protective fences
Scale	100m

summary

Temporary protective fences required for road widening and repair work in mountainous areas inevitably involve burdens other than the original purpose of the work using conventional construction methods. Many people want to minimize the cost and construction period for such incidental work and proceed efficiently. The MWG construction method introduced here solves many of the problems of conventional construction methods, and is a new construction method that could become a standard in the future.

For those who are considering or researching temporary protective fences, more detailed information is available on the official MWG construction method page.