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RETAINING WALLS

  
 
       

Gabion retaining wall systems are monolithic gravity mass structures that follow standard design methods for gravity retaining walls.

The following information is provided as a guide to assist contractors in the proper construction of gabion  retaining walls.


NOTE: THE PHOTOS AND SKETCHES SHOWN BELOW ARE EXAMPLES OF TYPICAL RETAINING WALLS

THIS  CONTENT IS PRESENTED FOR GENERAL INFORMATION PURPOSES ONLY AND SHOULD NOT BE TAKEN AS PROFESSIONAL ADVICE

 WE ALWAYS RECOMMEND THAT THE SOIL DATA FOR GABION WALL DESIGN BE BASED ON A CERTIFIED
GEO-TECHNICAL SOIL REPORT OF THE SITE LOCATION





EXAMPLES OF TYPICAL MULTI-COURSE  RETAINING WALLS



     

GENERAL DESIGN CONSIDERATIONS

Foundation Preparation
Gabion gravity retaining walls are typically placed directly on a graded soil foundation. To increase the bearing capacity, minimize differential settlement, and/or allow for additional drainage, a base layer of granular stone fill with consistent gradation ranging ½” – 11/2” may be placed and compacted to local standards 6” – 18” in depth.

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

Filter Fabric
Geotextile filter fabric is a vital component of any gabion retaining wall project. The rock voids within the gabion baskets allows for free drainage of the retained soils and requires a filter fabric be placed between the gabion wall and the 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.

Layout
To provide the maximum resistance to soil forces the gabion baskets should be placed with the length dimension of the gabion unit running from the back of the gabion wall to the front face of the gabion wall. This will result in the internal diaphragms being placed perpendicular to the wall face and parallel to soil thrust. When gabion units are placed with the length dimension of the gabion unit running parallel with the length dimension of the wall the vertical seams shall be offset.

Compression Loads
For gabion gravity retaining walls that are 15’ – 30’ in height the gabion basket foundation and bottom courses shall be placed in 1.5’ vertical lifts to better absorb the compression and shear stresses. 

Gabion Wall Face Configuration
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 should be placed on a 5-6 degree batter and is not recommended for walls above 18’ high. Gabion walls with a stepped front face shall have a minimum 1’-1.5’ horizontal set back for each 3’ vertical lift.

Gabion Wall Height

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

Gabion Wall base width relative to wall height
The base width of a gabion gravity retaining wall is related to height of wall. As the wall height increases the base of the wall becomes wider to ensure structural stability.  has provided the diagram below to illustrate a starting point for design analysis to determine the base width relative to wall height. A conservative value of base width = 2/3 wall height. A professional stability analysis may determine that the gabion gravity retaining wall base width be less than or greater than ½ - 2/3 wall height.

GABION ROCK FILL DATA


  Rock Fill Gradation for Gabion Baskets
Gabions 3" x 3" mesh
4 inches – 8 inches
                                                                 


Acceptable stone for gabion construction shall be hard, durable, equally graded, angular in shape, and shall not be less than 4” in any given dimension and no larger than 8” in any given dimension. The specific gravity shall be determined by the design and specified by the design engineer. Specific gravity for stone fill shall be no less than 2.5.


UNIT WEIGHT OF GABION ROCK FILL
TYPE OF ROCK
LBS/CUBIC FT
BASALT 180
GRANITE 160
LIMESTONE 138
SANDSTONE 140
 
 
NOTE: All the above examples are for information only and not to be considered design recommendations.

The information provided in the above examples including geo-technical data, dimensions and site conditions are assumptions made by  manufacturer and should be reviewed and certified by a Professional Engineer.

Please check Local, State and Federal requirements
 
 

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