Difference between revisions of "807 - Guardrail, Guardrail Terminals, and Miscellaneous Posts"
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Latest revision as of 17:15, 12 May 2021
The Standard Plans R-56 through R-73 Series include details on guardrail layouts and dimensions. Review the proposal and plans for additional details, notes or special provisions. The designer should provide a completed Guardrail Worksheet, Form 265 for use as a reference. Attention should be given to subsection 807.03 of the Standard Specifications for Construction regarding completion of guardrail installations within specified time limits and treatment of incomplete guardrail endings.
Guardrail elements, end sections and posts may be accepted based on a supplier’s certification. Refer to the Materials Source Guide for approved certifiers and product marking requirements.
Contractors may submit requests to use salvaged re-galvanized guardrail panels. The use of these panels has been historically researched by the Barrier Advisory Committee (BAC) and the Traffic Recommendations Committee (TRC). These committees have determined there are several reasons that prohibit the use of salvaged re-galvanized guardrail panels. The research has determined the following:
- There is no available data on the results of long term use of salvaged re-galvanized guardrail.
- The lap areas of the re-galvanized guardrail are suspect for existing section loss.
- There is no efficient and practical way to create supporting documentation that ensures quality of the salvaged panels.
- MDOT cannot accommodate an inspection intensive procedure to allow different material.
- The Standard Specifications for Construction preclude the use of salvaged re-galvanized guardrail panels. Subsection 105.01.A states: A. Provide new materials and fabricated items that meet the requirements of the specifications and are certified by the supplier in writing or approved by the Engineer in writing before use in the work. Therefore, unless otherwise specified in the contract documents only new materials and fabricated items are to be incorporated in MDOT projects.
The use of salvaged re-galvanized guardrail panels is prohibited. The committees have stated that the Standard Specifications for Construction should be enforced as written.
Staking for line and grade is the responsibility of the Contractor. Staking of embankments is the responsibility of the Engineer. The Contractor will mark the locations of the guardrail endings, with verification by the Engineer. Any changes to the design plans, installation instructions or hardware should be discussed by the Contractor, Engineer and designer.
Posts may be driven or placed in augured holes. When augered holes are used, they are to be backfilled with sound earth and thoroughly tamped in 12 inches (300 mm) layers. Care should be taken in driving posts so that they are properly placed and plumb. Incorrect spacing may not be corrected by increasing the rail slot in the field.
The use of string line is recommended to establish proper line and grade. Vertical tolerances of 5.8 inch (15 mm) measured off a compacted surface or 1-1/4 inch (30 mm) measured off an earth surface are acceptable. Horizontal tolerances should not exceed 3/4 inch (20 mm) for a 100 foot (30 m) segment when measured using a string line held along the face of a rail section. Rail should be hung so that the rail elements overlap in the direction of traffic. For a guardrail with a radius of 165 to 1000 feet (50 to 300 m), all splice bolts must be tightened before attaching the rail to the posts to prevent buckling at the splice. After a run of guardrail is hung, a visual inspection and adjustments should be made to ensure that the top of the rail presents a smooth line.
Guardrail endings will be identified as Guardrail Approach Terminal, Type ___, Guardrail Departing Terminal, Type ___ or Guardrail Anchorage, Bridge, Detail. The pay items will be generic and based on usage (approach/departing, flared/non-flared, double sided, etc.). Several optional designs may be available for each of these types of terminal. The plans and proposal must be reviewed to identify all approved optional designs. Most of the guardrails in use are engineered and patented devices and must be installed according to the manufacturer’s instructions.
Guard posts and mailbox posts will be either driven or placed in augered holes. Existing mailboxes will be attached to the new posts. Existing newspaper boxes and supports that interfere with construction will be removed and stored for property owners’ future installation.
Base preparation is important for successful placement of concrete and HMA materials and long-term service life of the path. Complete removal of vegetative cover and root mat to a depth of at least 2 inches (50 mm) is necessary to avoid future vegetative growth up through the bike path. However, the use of herbicides to kill roots and vegetative cover is not recommended. Wind drift from herbicide spray could cause collateral damage to adjacent vegetation, shrubs and lawns.
Subgrade should be smoothed and trimmed to the tolerance specified and as directed by the Engineer. Compaction of the subgrade should be uniform and sufficient to support paving equipment and hauling units. Random checks should be made of the subgrade for smoothness, grading tolerances and compaction.
The profile should be checked during subbase preparation and adjustments made to provide surface drainage away from the path. Avoid trapping surface water on the bicycle path or the drainage of large quantities of water over the path.
After final rolling of a HMA path, or screeding of a concrete path, the surface will be checked using a 10 foot (3 m) straightedge. Variation of more than 1/4 inch in 10 feet (6 mm in 3 m) must be remedied.
The rise at the back of the gutter pan for curb drops must be a smooth, rounded transition, not a sharp rise or an abrupt curve. The bicycle path slope to the curb drop, driveway or street must meet slope requirements as specified for sidewalk ramps.
After backfilling along the path, the area will be restored using topsoil, roadside seeding and mulch.
The guardrail will be measured in feet (meters), in place, along its face. Guardrail terminals and miscellaneous posts are separate pay items and are measured and paid for individually. Refer to Section 807 of the Standard Specifications for Construction for more detail.