HOW TO BUILD A GABION RETAINING WALL

INTRODUCTION

Gabion gravity retaining walls are constructed of rock filled wire mesh baskets creating monolithic gravity mass structures and follow standard ASTM design methods for gravity retaining walls.

The following information is provided by GABION PROS as a design guide only to assist Contractors and DIY's in the suggested construction of gabion gravity retaining walls.

Note ... GABION PROS recommends that soil data utilized for gabion retaining walls should be based on a certified geotechnical soils report on the site location and certified by a Professional Engineer.

Gabion walls are constructed with natural stone. As drainage occurs soil particles are deposited into the small voids of the natural stone fill within the wall allowing for pockets of vegetation to take root.

PRESSURE AT THE BASE

The total pressure of the gabion wall must be less than the anticipated bearing capacity of the soil under the base of the wall. The contact pressure on a flexible gabion footing is not distributed in a planar fashion, but decreases from a maximum at the point of application of the resultant to lesser values at the edges of the footing. The pressure at the toe of a gabion wall is, therefore, generally less than for a rigid wall.

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 as a founding course for wall placement.

FOUNDATION GRADE & WALL BATTER

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 for sliding. One option to pursue prior to enlarging the wall cross section for additional stability is to place wall on a 6 – 10 degree batter towards the retained slope. This will require the founding soils to graded and compacted to accommodate for the specified wall batter.

FOUNDATION BELOW GRADE

Gabion gravity retaining walls may be placed or keyed in below sub grade to prevent 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.

Backfill and Compaction

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.

SCOUR APRON

Gabion baskets and mattresses are 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. It is recommended that the gabion apron be a minimum of 9"-12" in depth. The length of the gabion apron shall 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 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 Gabion Pros standard PVC gabion units or with PVC reno mattresses.

Clean sand, stone and gravel GW, GP, SW, SP
Dirty sand and gravel of restricted permeability GM, GM-GP, SM, SM-SP
Stiff residual silt and clays, silty fine sands, clays, sands and gravels CL, ML, CH, MH,SM SC, GC.
Very soft to soft clay, silty clay, organic silt and clay: CL, ML, OL, CH, MH,OM.
Medium to stiff clay deposited in chunks and protected from infiltration: CL, CH

For type 5 material H is reduced by 4 ft resultant Acts at a height of (H-4)/3 above base. adapted from Terzaghi and Peck

GEO-TEXTILE FILTER FABRIC

Non-woven Geo-textile 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.

Call Gabion Pros for recommendations on filter fabric.

LAYOUT

To provide the maximum resistance to soil forces, the gabion baskets shall be placed with the length dimension of the 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 shall be placed with the length dimension of the gabion unit running parallel with the length dimension of the wall the vertical seams shall be offset.

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 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 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 Steep Slope Section of this web site.

GABION WALL SIZES & DIMENSIONS

Gabion 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. The adjacent diagram illustrates 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. The stability analysis may determine that the gabion gravity retaining wall base would vary more than 1/2 - 2/3 wall height.

GABION ROCK FILL

Acceptable rock 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 required for the stone fill shall be determined by the design and specified by the design engineer. Specific gravity for stone fill shall be no less than 2.5.ht.

hog ring tools

Model C1511

Our Model C1511 commercial grade gabion pneumatic hog ring tool is designed to dispense and firmly close hi-tensile steel and stainless steel gabion hog rings. It will save over 50% in labor cost vs hand tying of twisted wire gabion panels. The tool is designed for long service life and easy maintenance. Made in USA

See our Use and Buy Back Program below

PRICE ... $ 2,399.00 ea RECON ... $1,899.00

FREE SHIPPING & NO SALES TAX

"USE and BUY-BACK" PROGRAM

For projects requiring a one time use, we offer a BUY-BACK program that allows you to use the C1511 pneumatic hog ring tool for your project and after returning the gun in good working condition, we will buy the tool back at a reduced rate.

Model KC1511

Our Model KC1511 is a heavy duty commercial grade tool designed to firmly close hi-tensile steel and stainless steel hog rings.

This is a manually operated tool and commonly used to dispense and firmly close hog rings in remote locations not accessible to an air compressor.

The tool is designed for long service life and easy maintenance.

PRICE ... $ 1,399.00 ea

FREE SHIPPING & NO SALES TAX

MADE IN USA

Disclaimer

As shown above... 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. The gabion retaining wall designs we show above are provided for information only and not intended to be the correct design for your wall. We recommend you contact a engineer to do a soil analysis that will determine the correct wall design.

HOW TO BUILD A GABION RETAINING WALL

INTRODUCTION

PRESSURE AT THE BASE

FOUNDATION PREPARATION

FOUNDATION GRADE & WALL BATTER

FOUNDATION BELOW GRADE

Backfill and Compaction

SCOUR APRON

GEO-TEXTILE FILTER FABRIC

LAYOUT

GABION WALL FACE CONFIGURATION

Gabion Wall Height

GABION WALL SIZES & DIMENSIONS

GABION ROCK FILL

typical DESIGNS OF GABION RETAINING WALLS

6 ft

7.5 ft

6 ft

6 ft

7.5 ft

6 ft

6 ft

7.5 ft

7.5 ft

7.5 ft

7.5 ft

7.5 ft

9 ft

9 ft

9 ft

9 ft

9 ft

9 ft

9 ft

9 ft

9 ft

9 ft

9 ft

9 ft

9 ft

12 ft

9 ft

9 ft

12 ft

9 ft

12 ft

12 ft

12 ft

15 ft

12 ft

12 ft

Steep Slope™ Gabion Walls

EXAMPLES OF STEEP SLOPE™ GABION WALLS

DIY Gabion Accessories & Tools

hog ring tools

Model C1511

"USE and BUY-BACK" PROGRAM

Model KC1511

HELICAL SPIRALS

HELICAL SPIRALS - 50 ct bundles

CORNER STIFFENER braces

13.5 ga GALVANIZED STEEL GABION TIE WIRE

Disclaimer