GABION RETAINING WALLS

It may be determined, through an investigation and stability analysis, that additional stability of the gabion wall may be required to achieve acceptable factors of safety from sliding. One option to pursue prior to enlarging the wall cross section for additional stability is to place wall on a 5 to 6 degree batter towards the retained slope. This will require the founding soils to be graded and compacted to accommodate for the specified wall batter.

Gabions are flexible double twisted mesh gabions designed to settle without fracture and adhere to the ground as scour occurs. Graded fill material ranging from 4"-8" for standard gabions and 3"-6" for reno mattresses will ensure uniform flexibility of the apron and will create a new state of equilibrium of the structure once settlement has occurred providing continued stability. Gabion aprons are commonly used to protect the toe of a retaining wall structure from scour that could cause undermining in channel works applications. The gabion apron is typically  9"-12" in depth and the length of the gabion apron should extend beyond the toe of the structure a minimum of 2 times the anticipated depth of scour. This will ensure that the gabion apron reaches just beyond the outer limit of the anticipated scour hole that may form. 

The gabion apron will require minimal excavation and grade work. Generally the apron is placed directly on the ground utilizing a geotextile filter fabric between the gabion apron soil interface to prevent the leaching of soils from underneath the apron. If the gabion apron is placed in relatively deep water, and efficient method of large scale placement is prefabricating the apron on a barge and then launching it into the water. The size of the gabion apron that can be placed by this method is limited only by the deck area of the barge. Gabions or reno mattresses may also be connected together filled and then placed into the water with a sling arrangement. This method is frequently used for building scour-resisting mats around bridge piers etc. Gabion aprons may be fabricated using ... standard PVC gabion units or with PVC reno mattresses.

Backfill Material-Gabion gravity retaining walls, in comparison with reinforced soil walls, allows for a wider range of soil types to be utilized as backfill material. This is due to the gabion gravity walls configuration, typically low wall heights, and porous facing.   It is imperative to the overall long term performance of a gabion gravity retaining wall that the specified backfill material be properly placed and compacted. Poor compaction of backfill materials can lead to structural settlement, lateral wall movement, and result in insufficient shear strength to perform as designed. Specified backfill material shall be placed and compacted to minimum Standard Proctor 95% in lifts not to exceed 9” vertical and shall comply with local standards.

 Gabion walls design shall put special consideration on aspects related to water pressure and drainage. 

Gabion retaining walls can be designed and configured with a stepped front face or a smooth front face. When utilizing a gabion wall with a smooth front face, the gabion wall shall always be placed on a 6-10 degree batter and is not recommended for wall heights above 18’. Gabion walls with a stepped front face shall have a minimum 1’-1.5’ horizontal set back for each 3’ vertical lift.

Gabion gravity retaining walls can be designed and constructed up to 30’, however gabion gravity retaining walls their best suited for wall heights of 18’ or less. For wall heights of 18’- 36’ see the Steep Slope Section of this web site below 

 Geotextile filter fabric is a vital component of any gabion gravity retaining wall. The void ratio of the stone fill confined within the gabion baskets allows for free drainage of the retained soils and requires a filter fabric be placed between the wall and the specified backfill soil interface. The geotextile filter fabric will prevent loss of soil during drainage and drawdown. Gabion gravity retaining walls constructed without the placement of filter fabric will have a tendency to incur a loss of retained soils and grade elevation behind the gabion wall.  The type of backfill soil specified will determine the type, and placement of the geotextile filter fabric.

Contact us for recommendations on filter fabric.