Natural resources conservation service\
conservation construction sPECIFICATION

904 - gabions

1\. Scope

This work shall consist of furnishing, assembling, and installing rock
filled wire mesh gabion baskets for an installation as shown on the
drawings or as staked in the field.

II\. Materials

Gabions

Gabions shall be fabricated, assembled and installed in accordance with
the nominal wire sizes and dimensions found in Tables 1 and 2, using the
following materials.

[Woven Mesh]{.underline} Nonraveling, double twisted, hexagonal wire
mesh consisting of two wires twisted together in two 180-degree turns.
Wire for fabrication and assembly shall be hot-dipped galvanized. The
wire shall have a minimum tensile strength of 60,000 psi. Galvanized
steel wire shall conform to ASTM A 641, class 3 Coating, soft temper.

[Welded Mesh]{.underline} Welded-wire mesh with a uniform square or
rectangular pattern and a resistance weld at each intersection. The
welded wire connections shall conform to the requirements of ASTM A 185,
including wire smaller than W1.2 (0.124 in.), except that the welded
connections shall have a minimum average shear strength of 70 percent
and a minimum shear strength of 60 percent of the minimum ultimate
tensile strength of the wire

All gabion wire shall be Epoxy or Polyvinyl Chloride (PVC) coated. The
galvanized wire shall be coated by fusion bonded epoxy; or fusion
bonded, extruded, or extruded and bonded PVC material. The wire coating
shall be colored black, gray, green or silvery; and the initial
properties of the PVC coating shall meet the following requirements

\(a\) [Specific Gravity]{.underline}. In the range of 1.30 to 1.40, ASTM
D 792.

\(b\) [Brittleness Temperature]{.underline}. Not higher than 15^o^ F,
ASTM D 746.

\(c\) [Tensile Strength]{.underline}. Extruded Coating (not less than
2,980 psi. ASTM D 412). Fusion Bonded Coating (not less than 2,275 psi.
ASTM D 638).

\(d\) [Modulus of Elasticity]{.underline}. Extruded Coating (not less
than 2,700 psi. at 100 percent strain, ASTM D 412). Fusion Bonded
Coating (not less than 1980 psi. at 100 percent strain, ASTM D 638).

(e). [Ultraviolet light exposure]{.underline}. An exposure period of not
less than 3,000 hours at 63 degrees centigrade, ASTM G 152

\(f\) [Salt Spray Test]{.underline}. A test period of not less than 3000
hours, ASTM B 117.

After the exposure to ultraviolet light and the salt spray test as
specified above, the PVC coating shall not show cracks, blisters,
splits, nor noticeable change of coloring (surface chalk). In addition,
the specific gravity shall not change more than six (6) percent, tensile
strength shall not change more than 25 percent, and modulus of
elasticity shall not change more 25 percent from their initial values.

The wire sizes shown in Tables 1 and 2 are the size of the wire after
galvanizing and before coating with PVC.

Spiral binders are the standard fastener for welded-mesh gabion baskets
and mattresses, and shall be formed from wire meeting the same quality
and coating thickness requirements as specified for the gabion baskets
and mattresses.

Alternate fasteners for use with wire mesh gabions, such as ring
fasteners, shall be formed from wire meeting the same quality and
coating thickness requirements as specified for the gabions and, as a
minimum, shall conform to the manufacturer\'s recommendations. Hog rings
are not acceptable

Standard fasteners and alternate fasteners must provide a minimum
strength of 1,400 lb. per lineal foot for gabion baskets and 900 lb. per
lineal foot for gabion mattresses. When used to interconnect gabion
baskets or mattresses with PVC coating, ring fasteners shall be made of
stainless steel and spiral fasteners will be PVC coated. All fasteners
shall meet all of the closing requirements of the gabion manufacturer in
addition to any requirements specified the "Practice Requirements"
sheet.

**TABLE 1 (Minimum Requirements)**

**GABION BASKETS\--Height 12, 18, or 36 Inches; Length as Specified**

> Type Mesh Wire PVC Total Galvanized
>
> of Wire Size Diameter Coating Diameter Coating

#  Inches Inches Inches Inches oz./SF 

### Woven Mesh 3-1/4 x 4-1/2 0.118 None 0.118 0.80

#####  3-1/4 x 4-1/2 0.105 0.02 0.145 0.80

## Selvage 0.153 None 0.153 0.80

> 0.132 0.02 0.172 0.80

## Lacing and Internal 0.086 0.02 0.126 0.70

#####  Connecting Wire

### Welded Mesh 3 x 3 0.118 None 0.118 0.80

> 3 x 3 0 105 0.02 0.145 0.80

## Spiral Binder 0.105 0.02 0.145 0.80

> NOTE: The wire sizes and PVC coating thickness shown are nominal
> sizes.
>
> The wire sizes include the galvanizing coating thickness.

**TABLE 2 (Minimum Requirements)**

###### GABION MATTRESSES\--Height 6, 9, or 12 Inches; Length as Specified

> Type Mesh Wire PVC Total Galvanized
>
> of Wire Size Diameter Coating Diameter Coating

########  Inches Inches Inches Inches oz./SF 

> Woven Mesh 2-1/2 x 3-1/4 0.086 0.02 0.126 0.70
>
> Selvage 0.105 0.02 0.145 0.80
>
> Lacing and Internal 0.086 0.02 0.126 0.70
>
> Connecting Wire

####### Welded Mesh 1-1/2 x 3 0.080 0.02 0.120 0.70

> Spiral Binder 0.105 0.02 0.145 0.80
>
> NOTE: The wire sizes and PVC coating thickness shown are nominal
> sizes.
>
> The wire sizes include the galvanizing coating thickness.

**Rock**

Rock shall be sound, dense and durable with a bulk specific gravity of
not less than 2.5. Rock gradation shall conform to that specified below:

Gabion Basket Predomi- Min. Rock Max. Rock or Mattress nant Rock
Dimension Dimension

[Height]{.underline} [Size Inches]{.underline} [Inches]{.underline}
[Inches]{.underline}

12, 18, or 36 4 to 8 4 8

Inch Basket

6, 9, or 12 3 to 6 3 6

Inch Mattress

The greatest dimension of the rock shall not be greater than 2 times the
least dimension. The engineer will inspect the rock gradation after it
has been placed in the gabion baskets. At least 85 percent of the rock
particles, by weight, shall be within the predominant rock size range.

III\. FOUNDATION Preparation

The foundation on which the gabions are to be placed shall be cut or
filled and graded to the lines and grades shown on the drawings. Surface
irregularities, loose material, vegetation, and all foreign matter shall
be removed from foundations. When fill is required, it shall consist of
materials conforming to the specified requirements. Gabions and bedding
or specified geotextiles shall not be placed until the foundation
preparation is completed, and the subgrade surfaces have been inspected
and approved by the Engineer.

IV\. Filter Layer or Bedding

When filter layers or bedding are specified in the "Practice
Requirements" sheet, the filter or bedding material shall be spread
uniformly on the prepared subgrade surfaces to the depth specified.
Compaction of filter layers or bedding will not be required, but the
surface of such layers shall be finished free of mounds, dips or
windrows.

**V. ASSEMBLY AND PLACEMENT**

The assembly and placement of gabions shall be in accordance with the
following procedures:

[Assembly]{.underline}. Rotate the gabion panels into position and join
the vertical edges with fasteners for gabion assembly. Where lacing wire
is used, wrap the wire with alternating single and double half-hitches
at 4- to 5-inch intervals. Where spiral fasteners are used for
welded-wire mesh, crimp the ends to secure the spirals in place. Where
ring type alternate fasteners are used for basket assembly, install the
fasteners at a maximum

spacing of 6 inches. Use the same fastening procedures to install
interior diaphragms where they are required.

Interior diaphragms will be required where any inside dimension exceeds
three (3) feet. Diaphragms will be installed to assure that no open
intervals are present that exceeds three (3) feet.

[Placement]{.underline}. Place the empty gabions on the foundation and
interconnect the adjacent gabions along the top, bottom, and vertical
edges using lacing wire. Wrap the wire with alternating single and
double half-hitches at 4- to 6-inch intervals. Unless otherwise
specified in***,*** the Practice Requirements sheet, lacing wire will be
the only fastener allowed for interconnecting woven mesh gabions. Spiral
fasteners are commonly used for the assembly and interconnection of
welded mesh gabions. Spirals are screwed down at the connecting edges
then each end of the spiral is crimped to secure it in place. Lacing may
be used as needed to supplement the interconnection of welded mesh
gabions, and the closing of lids.

Interconnect each layer of gabions to the underlying layer of gabions
along the front, back, and sides.

Stagger the vertical joints between the gabions of adjacent rows and
layers by at least one-half of a cell length.

**VI. [FILLING OPERATION]{.underline}**

After adjacent empty woven wire gabion units are set to line and grade
and common sides properly connected, they shall be placed in
straight-line tension and stretched to remove any kinks from the mesh
and to gain a uniform alignment. Welded-mesh gabions do not require
stretching. The gabions may be staked to maintain the established proper
alignment before the rock is placed. No stakes shall be placed through
geotextile material. Connecting lacing wire and other fasteners (as
allowed) shall be attached during the filling operation to preserve the
strength and shape of the structure.

Internal connecting cross-tie wires shall be placed in each unrestrained
gabion cell of more than 18 inches in height, including gabion cells
left temporarily unrestrained. Two internal connecting wires shall be
placed concurrently with rock placement, at each 12-inch interval of
depth. In woven mesh gabions these cross-ties will be placed evenly
spaced along the front face and connecting to the back face. All
cross-tie wires shall be looped around two mesh openings and each wire
end shall be secured by a minimum of five 180-degree twists around
itself after looping.

In welded mesh gabions these cross-ties or stiffeners are placed across
the corners of the gabions (at 12 inches from the corners) providing
diagonal bracing. Lacing wire or preformed hooked wire stiffeners may be
used.

The gabions shall be carefully filled with rock, either by machine or
hand methods, ensuring alignment, avoiding bulges, and providing a
compact mass that minimizes voids. Machine placement will require
supplementing with handwork to ensure the desired results. The cells in
any row shall be filled in stages so that the depth of rock placed in
any one cell does not exceed the depth of rock in any adjoining cell by
more than 12 inches. Along the exposed faces, the outer layer of stone
shall be carefully placed and arranged by hand to ensure a neat, compact
placement with a uniform appearance

The last layer of rock shall be uniformly leveled to the top edges of
the gabions. Lids shall be stretched tight over the rock filling using
only approved lid closing tools as necessary. The use of crowbars or
other single point leverage bars for lid closing is prohibited as they
may damage the baskets. The lid shall be stretched until it meets the
perimeter edges of the front and end panels. The gabion lid shall then
be secured to the sides, ends, and diaphragms with spiral binders,
approved alternate fasteners, or lacing wire wrapped with alternating
single and double half-hitches in the mesh openings.

Any damage to the wire or coatings during assembly, placement and
filling shall be repaired promptly in accordance with the
manufacturer\'s recommendations or replaced with undamaged gabion
baskets.

VII\. Vegetative Cover

Unless otherwise specified in the "Practice Requirements" sheet, a
protective cover of vegetation shall be established on the disturbed
area. The planting of vegetative materials shall conform to the
requirements of Practice Specification 342, Critical Area Planting.

VIII\. Special Measures

Measures and construction methods shall be incorporated as needed and
practical that enhances fish and wildlife values. Special attention
shall be given to protecting visual and maintaining key shade food and
den trees.

IX\. Construction Operations

Construction operations shall be done in such a manner that erosion and
air and water pollution are minimized and held within legal limits. The
owner, operator, Contractor or other persons will conduct all work and
operations in accordance with proper safety codes for the type of
construction being performed with due regards to the safety of all
persons and property.

The completed job shall be workmanlike and present a good appearance.

OPERATION AND MAINTENANCE ITEMS

A properly maintained gabion structure is an asset to your farm. The
life of this installation can be assured and usually increased by
developing and carrying out a good maintenance program.

This will require you to perform periodic maintenance inspections. Here
are some recommendations to help you develop a checklist of items to
observe and to perform necessary maintenance:

Re-tie any breaks in baskets.

Replace any rocks that may have been removed.

Repair any locations due to settlement as differential settlement.

Removal any debris that may accumulate.

Repair any damage due to vandalism, vehicular, or livestock.

Other items specific to your project are listed on the \"Practice
Requirement\" sheet.