DESCRIPTION
641.01.01 General. This work consists of furnishing and installing impact attenuator systems.
MATERIALS
641.02.01 General. Select approved impact attenuators from the manufacturers listed in the QPL. Use the
impact attenuator selected for the entire project and do not use a combination of types of impact attenuators. Impact Attenuator (Special) shall meet all the requirements of this Section except the type and configuration of the unit will be s pecified in the Special Provisions. Concrete used in the foundation slabs shall have a minimum compressive strength of 28 MPa (4,000 psi) and shall conform to Section 501. Reinforcing bars used in the concrete base slabs shall be Grade 420 (60) conforming to Section 505. Submit for approval the manufacturer’s shop drawings, foundation details, installation recommendations, and any other pertinent information for the impact attenuator. Receive approval for the exact model of impact attenuator proposed, pri or to installation. Furnish and install the units with all parts and materials necessary for them to perform as designed. CONSTRUCTION
641.03.01 General. Excavate any material encountered for the construction of base slabs according to
Section 206. Furnish and install aggregate base, reinforcing steel, concrete, backfill, asphalt pavement, anchor bolts, miscellaneous hardware, epoxy, reflectors on the nose sections, and any other incidentals required for construction of the attenuators. Construct concrete and metal reinforcement items according to Sections 502 and 505. Install impact attenuators according to the plans and the manufacturer’s recommendations. METHOD OF MEASUREMENT
641.04.01 Measurement. Impact attenuators will be measured by the eac h.
BASIS OF PAYMENT
641.05.01 Payment. The accepted quantities, measured as provided above, will be paid for at the contract
price per unit of measurement for the pay items listed below that are shown in the proposal. Payment will be full compensation for the work prescribed in this Section. Payment will be made under: Pay Item Pay Unit Impact Attenuator ................................ ................................ .............................................................................................................. Each Impact Attenuator (Special) ............................................................................................................................................................... Each SECTION 64 2 MECHANICALLY STABILIZED EARTH WALLS DESCRIPTION
642.01.01 General. This work consists of constructing mechanically stabilized earth (MSE) walls consisting of
precast concrete panel or segmental block s with metallic o r geogrid soil reinforcements.
642.01.02 Design Requirements . Design MSE retaining walls and ancillary elements associated with the
walls in accordance with the plans and as specified herein. Design MSE walls for a minimum service life of 100 years. Maximum reinforcement loads shall be calculated using the “Simplified Method” according to Subsection
11.10.6 2 of the AASHTO LRFD Bridge Design Specifications.
Design and detail base drains and back drains to collect and remove groundwater before it can enter the reinforced backfill of MSE retaining walls. Installation of the drainage system shall occur only during the placement of MSE backfil l. Provide a constant length of all reinforcement layers within a design section to form a uniform reinforced soi l mass, with the exception of the top two layers of reinforcement. Provide the top two layers of reinforcement with a length of reinforcement that is 1.5 m (5 ft) longer than all other layers below. For geogrid reinforcement layers, provide a reinforcement coverage ratio of 1.0 according to S ubsection
11.10.6 4 of the AASHTO LRFD Bridge Design Specifications.
Where concrete panel walls or wall sections intersect with an interior angle of 130 degrees or less, provide a special vertical corner element panel. The corner element panel shall cover the joint of the panels that abut the corner and allow for independent movement of the abutting panels. Geometry of the MSE walls shown on the plans is based on the external st ability of the wall system as determined by the Department. Be responsible for the internal design of the wall based on the design requirements . Design shall include verification of external stability , internal stability , design of concrete wall panel, and corrosion analysis for metallic soil reinforcements . Incorporate proposed highway surface drainage installations and other project specific requirements into the wall design. Top of wall elevation and alignment shall remain as shown on the plans regardles s of the wall system selected. Depth of wall embedment or length of reinforcement may be increased as required by internal design. Fully document all loading conditions and assumptions used for the wall design. Consider all load cases that may be anticipated to exist during construction and during the service life of the wall due to surcharges, hydraulic conditions, live loads, combinations of the preceding, and obstructions within the reinforced backfill. For each wall design section, provide a design summary that includes design section identification, location, wall geometry (height, backslope, etc.), loadings (traffic loading, hydrostatic, seismic, traffic barrier, etc.), governing design resistance fact ors and level where they occur, and other pertinent information.
642.01.03 Installer Qualifications. Provide a n on-site supervisor having experience in the construction of at
least five transportation related MSE walls within the last three years. Transportation related MSE walls are defined as walls that carry or are adjacent to vehicular traffic and are constructed with MSE reinfor cement in the reinforced structure backfill zone . The on-site supervisor shall have prior experience with the type of wall that will be constructed. The on-site supervisor shall be on the job site the entire time the wall is being constructed. Submit verification of the on-site supervisor’s qualifications containing a summary of the individual’s experience and the respective projects at least 30 days prior to beginning wall construction. Do not begin wall construction until the supervisor ’s qualifications have been approved.