Taiyo Kogyo Column
Issues and Solutions for Temporary Protective Fences │ What is the new low-cost and short construction period construction method that does not make holes in the road surface?
Temporary protective fences protect the safety of passing vehicles during road slope construction while the road is in service. The danger of road slopes collapsing due to typhoons, guerrilla rains, and other extreme weather events in recent years has increased, and the importance of countermeasures against rockfall accidents during slope construction is becoming increasingly important. However, the installation of temporary protection fences using conventional methods poses many problems, is expensive, and the construction period tends to be long due to incidental work. This article introduces the basics of temporary barriers, the challenges of conventional construction methods, and the solutions. We hope that local governments, construction companies, construction consultants, and other related parties managing roads will take a look at this article.
What is a temporary protective fence?
Temporary protective fences are mainly used to protect vehicles and pedestrians from falling rocks and collapses during construction work on road slopes in mountainous areas. In the conventional method, a concrete foundation is constructed or H-shaped steel is cast into the ground to make the support columns stand on their own to set up the fence.
Situations requiring temporary protective fences
It is required for safety in construction projects involving cut slope work. For example, it is used at the following sites
- Road widening in mountainous areas
- Slope protection work for waterways, dams, etc.
- Disaster prevention work
Issues in Conventional Methods of Temporary Protective Fence
The “Oyaki-Sheet Pile” method, in which H-shaped steel is driven into the road surface, is commonly used for the installation of temporary protective fences. However, this conventional method has the following problems.
- Large heavy machinery will be needed for delivery of materials and installation work.
- Noise and vibration cause environmental impact on the surrounding and neighboring areas.
- Large footprint required, and narrow roads require two-sided roadblocks
- Heavy burden of ancillary works such as underground investigation, overhead line relocation, road surface restoration, etc.
What are the characteristics required for the installation method of temporary protective fences?
A new construction method is required to solve the points listed as challenges. In other words, a construction method with the following characteristics would be ideal.
- No need for large heavy equipment for delivery and installation
- Low installation noise and vibration
- Can be installed in the smallest of spaces
- No need to drill holes in the road surface
In addition, construction costs tend to be high in Japan, a country with many mountainous areas and snow-covered and cold regions, and it is desirable to keep costs and construction periods low for the installation of temporary protective fences, which are becoming increasingly important.
MWG construction method," an ideal new construction method for temporary protective fences
We introduce the “MWG construction method” as an ideal new construction method that solves the problems of conventional construction methods, while at the same time realizing low cost and short construction period.
What is MWG construction method?
The MWG method is a method of temporary protection fence construction in which posts (H-shaped steel) are erected on a continuous box-shaped steel frame (meshwall). The meshwall is a continuous box-shaped steel frame, in which the posts are fixed to a base plate, and the frame is filled with locally generated soil or other materials to make the posts self-supporting. Since no holes are made in the road surface, there is no need for large heavy machinery or special work. Since there is no need for any ancillary work such as road surface restoration, the construction period and cost can be greatly reduced.
The MWG method takes into account not only the impact load of falling rocks, but also wind load. The MWG method can be applied to a wide range of sites, with fence heights ranging from 2m to 5m.
Eight Strengths of the MWG Construction Method
The MWG method has the following eight advantages over conventional temporary barrier construction
- Construction period is about 75% shorter
- Cost reduction of approx. 30
- Suitable for narrow roads
- Low noise and vibration
- Can use locally generated soil
- Easy removal
- No prior research required
- No need to relocate overhead lines
Construction period is about 75% shorter
Since H-beams do not need to be driven into the road ground (i.e., no holes are made in the road surface), incidental work such as underground investigation and road surface restoration are not required. As a result, the installation of temporary protective fences using the MWG construction method significantly shortens the construction period. Compared to conventional construction methods, the MWG method can reduce the construction period by up to 75%.
Cost reduction of approx. 30
The MWG method does not require steel to be cast into the roadbed or L-shaped supports. Therefore, the amount of steel used is extremely small. Also, the overall cost of construction is greatly reduced because large heavy machinery and large vehicles are not required and incidental work is also reduced. Compared to conventional construction methods, costs can be reduced by up to 30%.
Suitable for narrow roads
The construction work is possible even on narrow roads such as mountainous or forest roads because large heavy machinery and large vehicles are not required for construction and the maximum width of the foundation is only 1.6 m. Even when the road width is narrow, one lane can be sufficiently secured on each side, eliminating the need for full road closures and minimizing the burden on traffic.
Construction with low noise and vibration
Since there is no need to drive H-shaped steel into the ground, construction can be done without using a pile-driving machine. Therefore, noise and vibration are reduced compared to conventional construction methods, and the environmental impact on the surrounding area is reduced and neighborhood residents are taken into consideration.
Can use locally generated soil
The special structure of the “Meshwall,” a continuous box-shaped steel frame that supports the support columns, allows the use of locally generated soil for filling material. This reduces the need to move purchased materials and locally generated soil, and facilitates construction work.
Easy removal
Since it is installed without damaging the road, there is no need to restore the road surface when it is removed.
No prior research required
No prior investigation of underground burial is required, as no steel piles are driven into the ground.
No need to relocate overhead lines
Since no pile-driving machine is used, there is no need to relocate overhead lines. This also contributes to shorter construction period and lower cost.
Method of constructing temporary protective fences using the MWG method
Temporary barrier construction using the MWG method is simple and quick. The following is a description of the construction procedure that does not require large heavy equipment or special skills.
1. Carry-in
Mesh walls can be folded for transport and delivery, saving space for storage.
2. Installation of base plate
Base plates are installed to set the support columns. Base plates are connected to each other by connecting plates to ensure stability.
3. Installation of mesh wall
The continuous box-shaped steel frame “Meshwall” is deployed. Deployment can be smoothly performed by only 3 to 4 ordinary workers. No special skills are required.
4. Filling of earth and sand
The posts are installed on the base plate and the inside of the mesh wall is filled with soil and sand. At this time, locally generated soil can be used, thus reducing the cost of delivery and purchase. Filling work can be performed without being in close proximity to heavy equipment.
5. Sheet pile insertion
After the transverse joints are secured and the wooden sheet piles are installed, the temporary protection fence is complete. After the work is complete, the mesh wall guard is dismantled and the earth and sand are removed.
MWG Method Application Examples
The MWG method has already been adopted in many places as an excellent installation method for temporary protective fences. Some of the examples are shown below with photos.
Utilization in slope repair work for disaster prevention dam facilities
| Location | Iwate Prefecture |
| Specifications | Protective wall height 3.0m, T-1.0 |
| Applications | Temporary protective fences |
| Scale | 45m |
summary
Conventional methods of installing temporary barriers have many problems and require long construction periods and high costs. The MWG method, which does not make holes in the road surface, solves the problems of conventional methods without sacrificing safety, while at the same time realizing low cost and short construction period.
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