Net-bag layered method using filled bags for foundation consolidation (emergency restoration)

Needs Address

• The need for emergency restoration of collapsed river bank revetment
• The need for emergency restoration of collapsed embankment

Adaptation effects

• Emergency restoration of revetments in river catchments that have collapsed due to intensified flooding from climate change.
• Temporary road installation on dikes that have collapse due to storm surge, in coastal areas. 

Overview and Features

• The foundation reinforcement method using fillable bags involves using rocks to fill net bags made of synthetic fibers and compacting them evenly. The method was traditionally used for river bank protection (this method for consolidation of foundations is described below). This bag-type foundation consolidation method can be used for emergency restoration of river dikes that have collapsed in disasters from heavy rain due to extreme events, or for building a temporary road on a dike that has collapsed due to a storm surge. Because specialty construction methods are not needed for filling or placing the bags, this technology could be considered suitable for emergency temporary restoration. 
  
  Figure Emergency restoration of collapsed embankment
  (Source: Leaflet on utilization of "foundation reinforcement method using fillable bags " for emergency restoration)
• Another use is coastal areas, for emergency restoration by building a temporary road on an embankment that was destroyed by storm surge. It could be used to secure a route to access a disaster area that was isolated by the disaster, then when reconstruction work has reached a certain point, to remove the temporary road while withdrawing back. Later, the permanent restoration work can be done for road construction. 
  
  Photos: Examples of temporary road construction in coastal area
  (Source: Leaflet on utilization of "foundation reinforcement method using fillable bags " for emergency restoration)
• Because the material used for this method is stable, it is excellent in terms of durability, reusability (versatility), and workability, and it is cost-effective.
• The foundation reinforcement methods for river embankments described consist of the following structural components, as shown in the illustrations below: slope protection work, foundation work, and foot protection work.  Among these, the foot protection work pertains to the foundation portion that supports the structure, and mitigates rapid riverbed scouring action from the current flow, and plays the role of preventing the subsidence of foundation work, and the scouring of soil.
  
  Figure: Names of components of river revetments (from draft riverbank protection and maintenance manual)

Cost

Pricing (for reference)

• 2-ton size: 18,500 yen per bag (14,800 yen/m3)
• 4-ton size: 30,500 yen per bag (12,200 yen/m3)

Ease of maintenance

If the work is performed with the aim of emergency restoration at the time of a disaster, then monitoring, construction, and maintenance will be relatively easy, as the intention would be to replace the work soon thereafter.

Technology performance

If the "net-bag layered method" is being used as an embankment fill structure, the height of the embankment should be limited to 12 meters, including the top surface cover. If it is used to structurally secure the base the maximum gradient should be gentle, at 1 to 0.3.

Considerations

None in particular

Co-benefit, suitability for developing countries

The bag filler can be sourced from concrete arising locally during a disaster, which leads to effective use of disaster rubble.

Information Resources

• Bagged Materials Utilization Study Group: Leaflet on utilization of "foundation reinforcement method using fillable bags " for emergency restoration
• Riverbank Protection Maintenance Manual, by Japan Civil Engineering Consultants Association, Kinki Branch, Study Group on Maintenance of Public Works Facilities, Rivers Subcommittee, Bank Reinforcement Working Group (in Japanese)
  https://www.kk.jcca.or.jp/upload/oteire/03/file01.pdf