342.01 Description. The Contractor shall furnish all labor, materials, equipment, and incidentals required and perform all operations in connection with the construction of snow storage areas and infiltration basins in accordance with the lines, grades, design and dimensions shown on the Plans and as specified herein.
342.02 Submittals. The Contractor shall furnish the manufacturer's certificates of compliance for cellular concrete blocks/mats, revetment cable, and any revetment cable fittings and connectors. The Contractor shall also furnish the manufacturer's specifications, color samples, literature, shop plans for the layout of the mats, and any recommendations, if applicable, that are specifically related to the project.
Alternative materials may be considered. Alternative material packages must be submitted to the County for review and approval by the County and Engineer within eight (8) days following bid date. Submittal packages must include, as a minimum, the following:
1. Full-scale laboratory testing and associated engineered calculations quantifying the hydraulic capacity of the proposed cellular concrete mat system in similar conditions to the specific project.
2. A list of 5 comparable projects, in terms of size and applications, in the United States, where the results of the specific alternate revetment system use can be verified after a minimum of five (5) years of service life.
342.03 Materials.
342.03.01 Cellular Concrete Blocks. This specification covers erosion control mats used in revetments for soil stabilization. All cellular concrete mats shall be prefabricated as an assembly of concrete blocks laced with revetment cables. Cellular concrete mats may be assembled on-site by hand-placing the individual units with or subsequent insertion of cables. The color of the mats shall be dark chocolate brown as selected by the County from standard colors offered by manufacturer.
Individual units in the system shall be staggered and interlocked for enhanced stability. The mats shall be constructed of open and/or closed cell units as shown on the contract plans. The open cell units have two (2) vertical openings of rectangular cross section with sufficient wall thickness to resist breakage during shipping and installation. Parallel strands of cable shall extend through two (2) cable ducts in each block allowing for longitudinal binding of the units within a mat. Each row of units shall be laterally offset by one-half of a block width from the adjacent row so that any given block is cabled to four other blocks (two in the row above and two in the row below).
Each block shall incorporate interlocking surfaces that minimize lateral displacement of the blocks within the mats when they are lifted by the longitudinal revetment cables. The interlocking surfaces must not protrude beyond the perimeter of the blocks to such an extent that they reduce the flexibility or articulation capability of the cellular mats or become damaged or broken when the mats are lifted during shipment or placement. Once the mats are in place, the interlocking surfaces shall minimize the lateral displacement of the blocks even if the cables should become damaged or removed. The mats must be able to flex a minimum of 18° between any given row or column of blocks in the uplift direction and a minimum of 45° in the downward direction.
The cables inserted into the mats shall form lifting loops at one end of the mat with the corresponding cable ends spliced together to form a lifting loop at the other end of the mat. The cables shall be inserted after sufficient time has been allowed for the concrete to complete the curing process.
Concrete units may be fabricated from lightweight or normal weight aggregates, or both. The concrete units shall be produced by a dry cast method. The dry cast units obtain strength in a shorter duration as well as provide an increase in the durability and overall quality of product.
At the time of delivery to the work site, the units shall conform to the physical requirements prescribed in the following Table.
Physical Requirements Compressive Strength Net Area
Min. psi
Water Absorption Max. lb/ft3
Avg. of 3 units Individual Unit Avg. of 3 units Individual Unit
4,000 3,500 10 12
The manufacturer shall meet all requirements pertaining to a concrete unit’s durability pertaining to freeze-thaw environments.
Units shall be sampled and tested in accordance with ASTM D 6684-04, Standard Specification for Materials and Manufacture of Articulating Concrete Block (ACB) Revetment Systems.
All units shall be sound and free of defects that would interfere with either the proper placement of the unit or impair the performance of the system. Surface cracks incidental to the usual methods of manufacture, or surface chipping resulting from customary methods of handling in shipment and delivery, will not be deemed grounds for rejection.
Cracks exceeding 0.25 inches in width and/or 1.0 inch in depth shall be deemed grounds for rejection.
Chipping resulting in a weight loss exceeding 10% of the average weight of a concrete unit shall be deemed grounds for rejection. Blocks rejected at the job site shall be repaired with structural grout or replaced at the expense of the contractor.
Cellular concrete blocks shall be ARMORFLEX Class 50S, or equal, as sold and distributed by:
CONTECH Engineered Solutions, LLC 9025 Centre Pointe Drive, Suite 400 West Chester, OH 45069
(800) 338-1122 www.ContechES.com
The individual blocks comprising the mat shall have the nominal characteristics that are presented in the following Table.
Standard Properties of ARMORFLEX Blocks
Class Type Lbs Lbs/Sq.
ft
Length Inches
Width Inches
Height Inches
Open Area %
50S Open 45-52 45-53 13.0 11.6 6.0 22 – 36
342.03.02 Revetment Cable and Fittings. Revetment cable shall be constructed of preformed galvanized aircraft cable. The cables shall be made from individual wires and strands that have been formed during the manufacture into the shape they have in finished cable.
Cable shall consist of a core construction comprised of six (6) or seven (7) wires wrapped within seven (7) or nineteen (19) wire strands. The revetment cable shall have the following physical properties:
Nominal Approx. Avg. Strength Weight - Lbs./100 ft
Cable Diam. Lbs. Min. Lbs. Max Lbs.
1/8" 1,700 2.8 2.9
3/16" 3,700 6.2 6.5
1/4" 6,100 10.6 11.0
3/8" 13,300 23.6 24.3
The revetment cable shall exhibit resistance to mild concentrations of acids, alkalis, and solvents. Fittings such as sleeves and stops shall be aluminum, and the washers shall be galvanized steel. Selection of cable and fittings shall be made in a manner that ensures a safe design factor for mats being lifted from both ends, thereby forming a catenary. Consideration shall be taken for the bending of the cables around hooks or pins during lifting. Revetment cable splicing fittings shall be selected so that the resultant splice shall provide a minimum of 75% of the minimum rated cable strength.
342.03.03 Filter Fabric. Non-woven geotextile filter fabric specified on the construction drawings shall meet or exceed the following minimum specifications.
Non-Woven Geotextile Filter Fabric Specifications
Grab Tensile Strength 120 lbs. ASTM D-4632
Grab Elongation 50% ASTM D-4632
Puncture Strength 310 lbs. ASTM D-6241
Trapezoidal Tear 50 lbs. ASTM D-4533
Apparent opening Size (AOS) 70 U.S. Sieve ASTM D-4751
Permittivity 1.7 sec-l ASTM D-4491
Water Flow Rate 135 gpm/sq.ft. ASTM D-4491
UV Resistance 70 % ASTM D-4355
342.03.04 Revegetation. Revegetation treatment shall be installed per Section 339 of these Special Provisions.
342.03.05 Drain Rock. The storage volume below the cellular concrete blocks at the bottom of the snow storage or infiltration basin shall be filled with washed Class D backfill per Section 200.03.05 of the Standard Specifications.
Where cellular concrete blocks are placed on the side slope of the basin, e.g. at the maintenance access points, the cellular concrete blocks shall be placed on a 6-inch layer of Class C backfill, per Section 200.03.04 of the Standard Specifications that is covered by a filter fabric as specified in paragraph 342.03.03.
342.03.06 Basin Outfall Standpipe. Corrugated metal pipe used for basin outfall standpipe shall be helical steel pipe (2 2/3" x 1/2" corrugation profile) as per Standard Specification Section 203.02. CMP sediment trap risers shall be perforated as shown on the Plans. The Standpipe shall have a one-foot stub of continuously welded corrugated metal pipe for the outfall pipe connection at the size and elevation indicated on the plans. Metal grate and appurtenances shall be hot dip galvanized after fabrication.
342.04 Construction.
342.04.01 Foundation Preparation. Areas on which filter fabric and cellular concrete blocks are to be placed shall be constructed to the lines and grades shown on the Plans and approved by the County.
The slope shall be graded to a smooth plane surface to ensure that direct contact is achieved between the slope face and the geotextile (filter fabric), and between the geotextile and the entire bottom surface of the cellular concrete blocks. All slope deformities, roots, grade stakes, and stones which project normal to the local slope face must be re-graded or removed. No grooves or depressions greater than 0.5 inches in depth normal to the local slope face with a dimension exceeding 1.0 foot in any direction shall be permitted.
Where such areas are evident, they shall be brought to grade by placing compacted homogeneous material.
Immediately prior to placing the filter fabric and cellular concrete blocks, the prepared subgrade shall be inspected by the County. No fabric or blocks shall be placed thereon until that area has been approved.
342.04.02 Drain Rock and Geotextile Filter Fabric. Class D backfill/drain rock, as specified in paragraph 342.03.05, shall be placed and wrapped in filter fabric. Filter Fabric shall be placed within the limits shown on the Plans. The filter fabric shall be placed directly on the prepared area, in direct contact with the subgrade, and free of folds or wrinkles. The geotextile shall not be walked on or disturbed when the result is a loss of direct contact between the cellular concrete block and the geotextile or between the geotextile and the subgrade. The geotextile filter fabric shall be placed so that the upstream strip of fabric overlaps the downstream strip. The longitudinal and transverse joints shall be overlapped at least two (2) feet. The geotextile shall extend at least one foot beyond the top and bottom revetment termination points.
If cellular concrete blocks are assembled and placed as large mattresses, the top lap edge of the geotextile shall not occur in the same location as a space between cellular concrete mats unless the space is concrete filled.
Class C backfill shall be placed on graded and compacted subgrade, compacted to 95% relative compaction, and covered with filter fabric to receive the cellular concrete blocks.
342.04.03 Cellular Concrete Blocks/Mats. Cellular concrete blocks/mats shall be installed within the specified lines and grades shown on the Plans. The cellular concrete blocks shall be placed on the filter fabric in such a manner as to produce a smooth plane surface in direct contact with the filter fabric. No individual block within the plane of placed cellular concrete blocks shall protrude more than one-half inch.
To ensure that the cellular concrete blocks are flush and develop direct contact with the subgrade, the blocks shall be "seated" with a roller or other means as approved by the County.
If assembled and placed as large mattresses, the cellular concrete mats shall be attached to a spreader bar or other approved device to aid in the lifting and placing of the mats in their proper position by the use of a crane or other approved equipment. The equipment used shall have adequate capacity to place the mats without bumping, dragging, tearing or otherwise damaging the underlying fabric. The mats shall be placed side-by-side and/or end-to-end, so that the mats abut each other. Mat seams or openings between mats greater than two (2) inches shall be filled with 4000 psi concrete or grout. Whether placed by hand or in large mattresses, distinct changes in grade that results in a discontinuous revetment surface in the direction of flow shall require a concrete/grout seam at the grade change location so as to produce a continuous surface.
The cells or openings in the cellular concrete blocks shall be backfilled with open graded aggregate. The Contractor shall revegetate the disturbed area outside of the snow storage area and infiltration basins.
342.04.04 Loose Riprap. Loose riprap for the slope protection where the rock lined channel meets the infiltration basin shall be Class 150/Class 300/400 Bedding with a D50 of 6 inches according to Table 200.07.03-I of the Standard Specifications.
342.05 Measurement and Payment.
342.05.01 SOUTHWOOD BOULEVARD SNOW STORAGE AREA. Payment for SOUTHWOOD BOULEVARD SNOW STORAGE AREA will be made at the contract LUMP SUM price and shall be full compensation for furnishing all materials, labor, equipment, tools, and appurtenances necessary to complete the work. This item includes, but is not limited to, excavation, soil disposal, grading and compacting native and imported materials, installation of cellular concrete blocks, connecting cables, concrete anchoring, erosion control mat, drain rock, filter fabric, infiltration bed, concrete curb, and revegetation treatment.
Sawcut, removal of existing asphalt and aggregate base and construction of patch paving is included in a separate bid item.
342.05.02 MAYS BOULEVARD SNOW STORAGE AREA. Payment for MAYS BOULEVARD SNOW STORAGE AREA will be made at the contract LUMP SUM price and shall be full compensation for furnishing all materials, labor, equipment, tools, and appurtenances necessary to complete the work.
This item includes, but is not limited to, excavation, soil disposal, grading and compacting native and imported materials, installation of cellular concrete blocks, connecting cables, concrete anchoring, erosion control mat, drain rock, filter fabric, infiltration bed, concrete curb, and revegetation treatment. Sawcut, removal of existing asphalt and aggregate base and construction of patch paving is included in a separate bid item.
342.05.03 INFILTRATION BASINS. Payment for NORTH INFILTRATION BASIN will be made at the contract LUMP SUM price and shall be full compensation for furnishing all materials, labor, equipment, tools, and appurtenances necessary to complete the work as shown on the plans and details. This item includes, but is not limited to, excavation, soil disposal, grading and compacting native and imported materials, installation of cellular concrete blocks, connecting cables, concrete anchoring, erosion control mat, drain rock, filter fabric, infiltration bed, CMP outfall standpipe and connection to the storm drain, staff gauges, and revegetation treatment.
Payment for SOUTH INFILTRATION BASIN will be made at the contract LUMP SUM price and shall be full compensation for furnishing all materials, labor, equipment, tools, and appurtenances necessary to complete the work as shown on the plans and details. This item includes, but is not limited to, excavation, soil disposal, grading and compacting native and imported materials, installation of cellular concrete blocks, connecting cables, concrete anchoring, erosion control mat, drain rock, filter fabric, infiltration bed, rock slope protection, staff gauges, and revegetation treatment.