The Contractor shall complete all stability analyses in accordance with
either the NCMA TR127, or the Federal Highway Administration/AASHTO method
detailed in FHWA NHI-00-043. Only one method shall be followed for the
complete design, including reinforcement design strength, layout, stability
calculations, and seismic effects. The segmental retaining wall system
shall be designed under the direction of, and be signed by, a professional
engineer.[ The engineer shall visit the job at least once during the
construction.]
1.5.2
Design Parameters
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NOTE: The soil properties listed are given for the
purpose of establishing a common basis for bidding.
Verify that the contract documents provide
sufficient information for interpretation of soil
conditions below the wall, behind the wall, and at
Government furnished borrow locations. Listing soil
properties in the specification is optional. An
alternative is to provide testing results.
The soil properties listed commonly have a
significant influence on the reinforcement design,
but are not all inclusive. The parameters suggested
as defaults are limited to those commonly included
in standard design tables, since that will probably
be representative of a Contractors analysis during
bidding. More control over the product can be
obtained by specifying soil properties for retained
fill, soil properties for foundation soils, and
changes in water levels through the retained fill,
reinforced fill, and drains. Indicate surcharge
loads (live or dead) and location on drawings.
Government selected soil properties will give more
control in procuring a prudent design for
competitively bid projects. The Government usually
has access to all the geologic information that will
be available to the Contractor during construction,
and often has invested more time in consideration of
the data than the Contractor can afford during the
bidding process. However, there is a disadvantage
to listing the soil properties if the Contractor has
the option to change conditions and void the
assumptions. The soil properties should not be
listed if the borrow source is uncertain.
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Calculations shall include determination of long term design strength of
reinforcement specific to this project in accordance with the NCMA TR127 or
FHWA NHI-00-043. Calculations shall include analysis of all failure modes
listed in the NCMA TR127. Design calculations shall include a clear
outline of material properties and assumptions.[ The Contractor shall use
the following soil parameters and water elevation for stability analysis,
and shall select additional soil parameters as required to complete the
analysis.]
Moist Unit Weight of reinforced fill, [_____] kN/m3 pcf
Saturated Unit Weight of reinforced fill, [_____] kN/m3 pcf
SECTION 02832
Page 11
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