**Minnesota Construction Specification 64---Wire Mesh Gabions and
Mattresses Twisted (Woven) or Welded Mesh**

**1. Scope**

The work consists of furnishing, assembling, and installing rock filled
wire mesh gabion baskets and mattresses.

**2. Types**

Gabions shall consist of rectangular wire mesh formed containers filled
with rock. Gabions will conform to one of the following types:

**Woven mesh---**Nonraveling, double twisted, hexagonal wire mesh
consisting of two wires twisted together in two 180-degree turns.

**Welded mesh---**Welded-wire mesh with a uniform square or rectangular
pattern and a resistance weld at each intersection. The welded wire
connections shall conform with 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.

**Gabions---**Gabions shall be furnished as baskets or mattresses as
specified in section 7. Baskets and mattresses shall be fabricated
within a dimension tolerance of plus or minus 5 percent.

**Baskets---**Baskets are at least 12 inches high.

**Mattresses---**Mattresses are no more than 12 inches thick.

**3. Material**

Gabions shall be fabricated, assembled, and installed in accordance with
the nominal wire sizes and dimensions shown in tables 64--1 and 64--2,
using the following materials unless otherwise specified in section 7.

Wire for fabrication and assembly shall be hot-dipped galvanized. The
wire shall have a minimum tensile strength of 60,000 pounds per square
inch. Galvanized steel wire shall conform to ASTM A 641, class 3, soft
temper.

When epoxy or polyvinyl chloride (PVC) coated wire is specified in
section 7, the galvanized wire shall be coated by fusion bonded epoxy;
fusion bonded, extruded; or extruded and bonded PVC material. The wire
coating shall be black, gray, green, or silvery, and the initial
properties of the PVC coating shall meet the following requirements:

a\. Specific gravity. In the range of 1.30 to 1.40, ASTM D 792.

b\. Abrasion resistance. The percentage of weight loss shall be less
than 12 percent when tested according to ASTM D 1242, method B, at 200
cycles, CSI-A abrader tape, 80 grit.

c\. Brittleness temperature. Not higher than 15°F, ASTM D 746.

d\. Tensile strength. Extruded coating (not less than 2,980 lb/in2, ASTM
D 412); fusion bonded coating (not less than 2,275 lb/in2, ASTM D 638).

e\. Modulus of elasticity. Extruded coating (not less than 2,700 lb/in2
at 100 percent strain, ASTM D 412); fusion bonded coating (not less than
1,980 lb/in2 at 100 percent strain, ASTM D 638).

f\. Ultraviolet light exposure. A test period of not less than 3,000
hours using apparatus type E at 63 C, ASTM G 23.

g\. Salt spray test. A test period of not less than 3,000 hours, ASTM B
117.

**[Table 64--1]{.underline} Minimum requirements\***

**Gabion baskets---height 12, 18, or 36 inches; length as specified**

Type of wire Mesh Wire PVC Total Galvanized\
size diameter coating diameter coating\
(in)    (in)    (in)    (in)  oz./ft2

Woven mesh 3.25 x 4.5 0.118 None 0.118 0.80

3.25 x 4.5 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 3 x 3 0.118 None 0.118 0.80

Mesh 3 x 3 0.105 0.02 0.145 0.80

Spiral binder 0.105 0.02 0.145 0.80

**[Table 64--2]{.underline} Minimum requirements\***

**Gabion mattresses---height 6, 9, or 12 inches; length as specified**

Type of wire Mesh Wire PVC Total Galvanized\
size diameter coating diameter coating\
(in)   (in)   (in)    (in)  oz./ft2

Woven mesh 2.5 x 3.25 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 1.5 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.

After the exposure to ultraviolet light and the salt spray test as
specified above, the PVC coating shall not show cracks, blisters,
splits, or noticeable change of coloring (surface chalk). In addition,
the specific gravity shall not change more than 6 percent, resistance to
abrasion shall not change more than 10 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 64--1 and 64--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.

Standard fasteners and alternate fasteners must provide a minimum
strength of 1,400 pounds per lineal foot for gabion baskets and 900
pounds 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 in section 7.

Rock shall conform to the quality requirements in Material Specification
MN-523, Rock for Riprap, unless otherwise specified in section 7. At
least 85 percent of the rock particles, by weight, shall be within the
predominant rock size range.

> Gabion basket Predominant Minimum rock Maximum rock\
> or mattress rock size dimension dimension\
> height (in) (in) (in)
>
> 12-, 18-, or 36-inch 4 to 8 4 8
>
> basket
>
> 6-, 9-, or 12-inch 3 to 6 3 6
>
> mattress

At least 30 days before delivery to the site, the contractor shall
inform the engineer in writing of the source from which the rock will be
obtained. The test data and other information by which the material was
determined by the contractor to meet the specification are included. The
contractor shall provide the engineer free access to the source for the
purpose of obtaining samples for testing and source approval.

Bedding or filter material, when specified, shall meet the gradation
shown on the plans, or as specified in section 7, and the requirements
of Material Specification 521, Aggregates for Drainfill and Filters.
Geotextile, when specified, shall conform to the requirements specified
in section 7 and those of Material Specification 592.

**4. 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 the foundation. When fill is required, it shall consist
of material 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 inspector.

Compaction of bedding or filter material is required as specified in
section 7. The surface of the finished material shall be to grade and
free of mounds, dips, or windrows. Geotextile shall be installed in
accordance with the requirements of Construction Specification MN-95.

**5. Assembly and placement**

Unless otherwise specified in section 7, the assembly and placement of
gabions shall be in accordance with the following procedures:

**Assembly---**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 are required where any inside dimension exceeds 3
feet. Diaphragms are installed to assure that no open intervals are
present that exceed 3 feet.

**Placement---**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 section 7, 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 half of a cell
length.

**6. Filling operation**

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 crosstie 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 crossties are placed evenly spaced
along the front face and connecting to the back face. All crosstie 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 crossties 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 by machine or hand
methods to ensure alignment, avoid bulges, and provide a compact mass
that minimizes voids. Machine placement requires supplementing with hand
work 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.

**7. Construction details**