testing expenses can be on the order of ,000.
FHWA RD-89-199 included a 3/4" Enkamat fabric below
the blocks for the purpose of installing
instrumentation to research block behavior. The
Enkamat provided a very effective drainage layer
that is not integral to the test method. A drainage
layer provides a very significant improvement in the
ACB stability in the flume test. Regardless of the
flume test conditions, the designer should consider
including a granular drainage layer in areas with
high turbulence flow.
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2.1.1.1
Flume Test
The ACB product shall have been tested in a flume chamber in substantial
conformance with FHWA RD-89-199, except that a drainage layer is not
required. If the product was tested with a drainage layer, the installed
product shall incorporate a similar drainage layer with adequate filtration
design for the site soils. The flume test shall be based on conservative
assumptions for field placement of the blocks (such as block orientation,
and joint spacing within construction tolerances). The critical shear
stress (and critical velocity) shall be indicated in the test report.
2.1.1.2
Extrapolation of Hydraulic Stability
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NOTE: Preliminary research has indicated that
extrapolation is conservative when extrapolating to
thicker blocks, and unconservative when
extrapolating to thinner blocks.
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Extrapolation of critical shear stress for untested blocks within a similar
family of ACB shall be subject to limitations. Extrapolation shall only be
used for blocks having a similar footprint area and interlock mechanism,
but with variable thickness or net weight/area. Extrapolation shall only
be accepted if the following conditions are met:
a. The extrapolation is in strict accordance with hydraulic similitude
methods commonly accepted by the industry, and includes quantitative
treatment for a block overturning failure mode.
b. The tested block is the smaller product size in both thickness and
net weight/area, and extrapolation does not extend the critical
velocity more than 3 meters per second 10 feet per second from the
tested product size.
2.1.2
Matrix Assembly - Interlocking Blocks
Interlocking blocks are assumed to function without the use of cables or
similar restraints. Void filler shall be placed to inhibit lateral
movement and block pullout, cover the geotextile, and increase hydraulic
stability.
2.1.3
Matrix Assembly - Cabled Systems
Cable tied concrete block shall be interconnected by flexible cables
SECTION 02382
Page 11
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