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As shown below... The typical designs for gabion walls are pyramid shaped structures. A general rule of thumb is for every 3 ft increase in wall height, the bottom row basket depth should be increased by half a 1.5 ft . For a 6 ft high wall the bottom row should be 4.5 ft deep and the top row should be 3 ft deep.
DISCLAIMER
THE INFORMATION AND PHOTOS OF TYPICAL RETAINING WALLS IS PRESENTED FOR GENERAL INFORMATION ONLY AND SHOULD NOT BE CONSIDERED A SUGGESTED DESIGN OR PROFESSIONAL ADVICE FOR BUILDING YOUR RETAINING WALL.
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GABION PROS ALWAYS RECOMMENDS THAT BEFORE STARTING A RETAINING WALL PROJECT, FIRST SEEK OUT ANY LOCAL RESTRICTIONS OR BUILDING CODE REQUIREMENTS AND CONTACT A PROFESSIONAL ENGINEER TO EVALUATE SOIL FOR GABION WALL DESIGN.
RULE OF THUMB ... When constructing a gabion retaining wall, be sure to conform to at least a 2:1 height to width ratio. Gabion retaining walls that are narrower than this ratio are not suitable for retaining wall applications.
Gabion retaining walls are typically placed directly on a graded soil foundation with a layer of non-woven geotextile fabric. To increase the bearing capacity and keep the wall from sliding forward, minimize settlement and allow for additional drainage, excavate a base toe of 6" to 18" deep with a layer of 1/2" to 1- 1/2" gravel fill may be placed and compacted as a base course for wall placement.
FOUNDATIONS BELOW GRADE
Gabion gravity retaining walls may be placed or keyed in below sub grade to prevent the wall from sliding forward or scour and wave action from undermining the toe of the structure. The rule of thumb for depth of placement below sub grade is approximately 2 times anticipated depth of scour. 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 and 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 baskets or with PVC reno mattresses.
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.
Shown here is an example drawing of a typical 9 ft high gabion retaining wall
Gabion retaining walls are soil retaining structures comprised of wire mesh gabion baskets filled with natural rocks and mechanically connected to create a monolithic structure. .
A layer of geotextile filter fabric is typically placed between the gabion structure and the retained soil interface to prevent small soil particles from leaching through the stone fill.
Once the gabion structure is in place, soils naturally deposit into the stone fill of the gabion structure resulting from surface drainage or draw down of the retained soils.
Over time, the voids in the rocks become filled with soil that allows vegetation to take root and further reinforce the overall strength of the wall.
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
The base width of a gabion gravity retaining wall is related to height of wall so as the wall height increases the base of the wall becomes wider to ensure structural stability. Above are diagrams to illustrate typical starting points for determining the base width relative to wall height.
A conservative value of base width = 2/3 wall height.
Note... A stability analysis should be performed to determine the correct base widths for a specific wall height
Shown here is a 6 ft high x 2 course retaining wall with a 6 degree
.Shown here is a 6 ft high x 2 course stacked retaining wall with backfill
Shown here is a 6 ft high x 2 course retaining wall with double stacked base
Shown here is a 7.5 ft high retaining wall with base footer
Shown here is a 9 ft high retaining wall
.Shown here is a 9 ft high retaining wall with geo-grid reinforcement
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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.
The Steep Slope™ System is a mechanically reinforced soil gabion wall fabricated from a continuous double twisted PVC coated wire mesh that makes up the gabion basket facing and the mesh reinforcement panel.
