224GEOSYNTHETIC STABILIZED BRIDGE APPROACH (GSBA)

(GSBA)

224.1DESCRIPTION—This work is the construction of Geosynthetic Stabilized Bridge Approach (GSBA). to

the lines and grades indicated, and as directed. Construct GSBA as shown on the Standard Drawings, as indicated in the Plans, and as directed.

224.2MATERIAL—

identified by the manufacturer with the product model designation, manufacturing plant, and lot number. Stabilization geosynthetic must meet one of the following material requirements:

224.3CONSTRUCTION—

material information that includes identification samples of all geosynthetics, and all data necessary to indicate the geosynthetic(s) meet the specified requirements. Submit required information for approval by the Representative as specified in Section 106.02(a)2.b at least 30 days before the beginning of GSBA construction. For stabilization geosynthetic not listed in Bulletin 15, submit acceptance sample, sized and packaged according to Publication 2, Part B, Section 6, to the Representative.

as specified in Section 206.3, and as follows:

• Excavation for equipment access beyond the line and grade as indicated at no additional cost to the Department.

• Prepare foundation free of deleterious or unsuitable soils.

• Proof roll the foundation to provide a uniform and firm surface as specified in Section 206.3 (a).1.

• Repair any areas identified as unstable as specified in Section 206.3(a).1.

• If the top of bedrock elevation is encountered during the planned excavation, field adjustments may be made to the bottom of the GSBA elevation as directed, if approved by the District Geotechnical Engineer.

• The GSBA foundation will be inspected and approved by the Representative before placing fill or geosynthetics.

bridge structure plan, and do not construct a separate GSBA foundation drain. When retrofitting an existing bridge with a GSBA, construct the GSBA foundation drain as shown on the Standard Drawings.

greater than 140F, from direct exposure to sunlight, and from debris that may damage the material. Store geosynthetics elevated from the ground surface. Reject all geosynthetics with defects, tears, punctures, flaws, deterioration, or damage incurred during manufacture, transportation, storage, or installation. Replace any damaged geosynthetic materials at no additional cost to the Department.

on the Standard Drawings, and as follows:

• Grade the emba nkment subgrade and layback slope to the required profile and proof roll. When subgrade consists of AASHTO No. 1 or No. 3 coarse aggregate, R-rock or shot rock fill, choke the fill by placing and compacting a sufficient thickness of No. 2A aggregate on the proof rolled surface to cap and fill any surface voids or irregularities, as identified by the Representative.

• Place a layer of Class 4, Type A, separation geosynthetic to cover the entire prepared subgrade and excavated layback slope.

• Maintain required vertical spacing between geosynthetic layers.

• Splicing of any geosynthetic, including seams or connections, is prohibited. With a given layer, overlap any adjacent sections of geosynthetic along parallel roll edges a minimum of 12 inches . When wrapping geosynthetic at the edge of a layer provide only continuous material with no overlapping within 4 feet of the wrapped edge.

• Extend a ll layers of stabilization geosynthetic in continuous lengths perpendicular to the roadway direction whenever possible. When placed in lengths perpendicular to the roadway direction, partial rolls of stabilization geosynthetic must extend a minimum of 4 feet from the wrapped face before a n overlap is allowed. Alternately, t he stabilization geosynthetic may be placed in continuous strips parallel to the roadway direction, overlapping adjacent roll edges a minimum of 12 inches.

• Place geosynthetic to lay flat, pulled tight and anchored in place until backfill is placed. Place geosynthetic within ±1/2-inch of the elevations required and indicated in the Plans.

• Do not dump the aggregate directly from a haul truck onto the exposed geosynthetic. Place the required lift thickness of aggregate in a non -destructive manner such as hand placement, lightly raining from an excavator bucket, or blading out gradually from adjacent areas.

• Grade the surface of the aggregate without wrinkling the geosynthetic. No vehicles are allowed on the geosynthetic until a minimum of 6 inches of loose backfill has been placed. Sudden braking and sharp turning of any vehicle, including tracked equipment, on stabilized backfill is prohibited. Correct any disturbance or distortion of geosynthetics due to operation of vehicles or equipment, at no additional cost to the Department.

• When using Class 2, Type A biaxial geogrid as the stabilization geosynthetic , use Class 4, Type A, geotextile to back the geogrid wrap at the slope face. Place the full width of geogrid before placement of the Class 4, Type A geotextile face wrap backing. The Class 4, Type A, geotextile backing at the

face wrap must extend a minimum length of 4 feet (top) and 2 feet (bottom) from the front edge of the stabilization geosynthetic, as shown.

• When using Class 4, Type C, geotextile as stabilization geosynthetic, a supplemental face wrap is not required.

• In all cases, o verlap adjacent strips of stabilization geosynthetic and Class 4, Type A , geotextile a minimum of 12 inches along parallel roll edges.

• Place and compact two 6-inch compacted layers of the required coarse aggregate backfill up to the elevation of the next layer of stabilization geosynthetic. Repeat the placement process for all stabilization layers up to subgrade elevation to establish a roughly stepped appearance of the slope ratio and dimensions shown on the Standard Drawings . The top layer of stabilization geosynthetic is backfilled with two 6-inch compacted layers of PennDOT No. 2A coarse aggregate. Place GRS slope caution tape as shown on the Standard Drawing. GRS slope caution tape is to be customized detectable underground warning tape as shown on the Standard Drawing.

slope, repair damaged sections by placing a patch over the damaged portion of the geosynthetic, unless otherwise indicated. The patch is to consist of the same geosynthetic material as the damaged material and is to be placed in the same manner and orientation as the undamaged geosynthetic. The patch for the geosynthetic is to extend a minimum of 3 feet beyond the damaged area on all sides. Geosynthetics with damaged areas greater than 3 square feet are required to be completely removed and replaced.

as shown on the Standard Drawing.

224.4MEASUREMENT AND PAYMENT—

The measured plan view area of each constructed geogrid stabilization layer. Geogrid overlapping at roll edges and seams is incidental. Includes all excavation except for excavation of unsuitable foundation materials. Includes all proof rolling, preformed cellular polystyrene panels, and caution tape.

The measured plan view area of each constructed geotextile stabilization layer. Geotextile overlapping at roll edges and seams is incidental. Includes all excavation except for excavation of unsuitable foundation materials. Includes all proof rolling, preformed cellular polystyrene panels, and caution tape.

The measured area of the constructed geotextile needed for the required separation layers and end wrapping. Geotextile overlapping at roll edges and seams is incidental.

For new bridge structures, foundation drain at abutment is included in the Lump Sum for the bridge. For a GSBA existing structure retrofit, both foundation drains are measured and paid from pipe outlet to pipe outlet. Includes all excavation, drainage pipe, coarse aggregate backfill, and geotextile.

BASE COURSES