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Publication Number:  FHWA-HRT-12-051    Date:  August 2012
Publication Number: FHWA-HRT-12-051
Date: August 2012


Sample Guide Specifications for Construction of Geosynthetic Reinforced Soil-Integrated Bridge System (GRS-IBS)




Section 7.2 of the Geosynthetic Reinforced Soil Integrated Bridge System Interim Implementation Guide may be consulted for information regarding typical labor, tools, equipment requirements proven to efficiently construct the GRS-IBS, and suggestions on how to improve productivity.(1) However, it is the responsibility of the contractor to choose the construction method, labor, and equipment that is most efficient for the specific site.


Conduct a survey according to XXX Department of Transportation specifications.


  1. All excavation shall comply with the Occupational Safety and Health Administration as well as State and local requirements.

  2.  Excavation shall include provisions for drainage with a sloped cut to facilitate the movement of water downstream and away from the wall.

  3. Any over-excavation that forms a pit shall be backfilled with suitable free draining material and compacted.

3.4. RSF

In the absence of specific ground improvement requirements in the plans and special provisions, the following shall apply:

  1. Excavation for the RSF shall be in accordance with section 3.3 of this guide.

  2. The base of the RSF shall be cut smooth and excavated to uniform depth, and all loose, soft, wet, frozen, organic, and unsuitable material shall be removed from the base and sides of the excavation.

  3. The base of the RSF shall be graded level for the entire area of the base of such backfill plus additional 1 ft on all sides or to the limits shown in the plans.

  4. Excavation shall be backfilled as soon as possible to avoid adverse weather delays. If this cannot be achieved, the excavation shall be graded to one end to facilitate the removal of any water. If excavation is flooded, all water shall be removed along with soft saturated soils.

  5. The RSF shall be constructed with well-graded backfill material placed from the face to the back to roll folds or wrinkle to the free end of the reinforcement layer. It shall be compacted in 6-inch-thick lifts according to section 3.5 of this guide.

  6. The fill material shall be graded, leveled, and compacted before encapsulating the RSF.

  7. The RSF shall be encapsulated in the geotextile reinforcement and placed perpendicular to the abutment face to protect it from possible erosion. The geotextile shall be sized to fully enclose the RSF on the face and the wing walls sides.

  8. The first layer of the reinforcement shall be placed on the upstream side of the abutment with subsequent layers, if needed, overlapped a minimum of 3 ft on the top of the preceding layer.

  9. If the GRS abutment is adjacent to water, the reinforcement sheet shall overlap a minimum of 3 ft. All overlap sections in the area of the RSF shall be oriented to prevent running water from penetrating layers of reinforcement.

  10. The wrapped corners of the RSF need to be tight and without exposed soil within the RSF to complete the encapsulation.

  11. Reinforcement shall be in accordance to section 3.6 of this guide.


  1. For well-graded fills, the backfill material shall be compacted to at least 95 percent maximum dry density according to AASHTO T-99-10.(16)

  2. For well-graded fills, adjust the moisture content of the compacted backfill materials to within 2 percent of the optimum moisture content.

  3. The GRS mass shall be constructed using compacted lifts of 8 inches, which are equal to the facing block size.

  4. Compaction shall be performed using vibratory roller compaction equipment or other similar methods approved by XXX Department of Transportation.

  5. For open-graded fills, compact each layer using a suitable compactor capable of compacting 8 inches of fill until there is no visible evidence of further compression. A minimum of four passes shall be applied per lift.

  6. Hand-operated compaction equipment, such as lightweight mechanical tampers, plates, or rollers, approved by XXX Department of Transportation is required within 3 ft of the front of the wall face so as not to damage or dislocate the facing blocks.

  7. The top 5 ft of the abutment shall be compacted to 100 percent of the maximum dry density in accordance with AASHTO T-99-10.(16)

  8. Compaction equipment shall be selected to achieve the required fill material density.


  1. Geosynthetic reinforcement shall be installed in accordance with the manufacturer’s site-specific wall erection instruction.

  2. The geosynthetic reinforcement shall be placed so that the strongest direction (i.e., cross machine direction) is perpendicular to the abutment facing.

  3. Reinforcement coverage shall be 100 percent of the embedment area unless otherwise shown in the working drawings.

  4. Adjacent sections of the geosynthetic reinforcement do not need to be overlapped except when exposed in the wrap-around face system, at which time, the reinforcements rolls shall be overlapped or mechanically connected per the manufacturer’s requirements.

  5. Geosynthetic reinforcement shall be laid so that it is taut and free of wrinkles prior to backfilling.

  6. Geosynthetic reinforcement shall be placed directly on the compacted horizontal fill surface. The reinforcement shall bear uniformly on the compacted reinforced soil from the connection to the wall to the free end of the reinforcing elements.

  7. The geosynthetic reinforcement shall extend between the layers of the CMU block.

  8. The geosynthetic reinforcement shall cover a minimum of 85 percent of the top surface of the CMU block. Any excess reinforcement material showing through the face shall be removed in accordance with the manufacturer’s directions.

  9. A minimum backfill layer of 6 inches shall be placed on the geosynthetic prior to operating any vehicle over it.

  10. Bearing reinforcement beds shall be placed behind the CMU block at 4-inch spacings in the top five layers of the GRS abutment or as determined by the design.

  11. In the superelevation case, the reinforcement layers become stair-stepped in the upper wall layers as the superelevation of the abutment is constructed. In such situations, the reinforcement shall terminate along the angle surface of the superelevation. The GRS wall reinforcement schedule shall show the termination of each layer of the reinforcement across the abutment wall from low to high elevations.


  1. CMU, as specified in section 2.1, shall be used for the GRS wall facing.

  2. The CMU block construction shall begin at the lowest portion of the excavation with each layer placed horizontally.

  3. Each CMU block shall be placed tightly against the adjoining block without any gaps.

  4. Each CMU layer shall be completely constructed and cleaned of any debris and fill material prior to placing the next layer of geosynthetic reinforcement and CMU.

  5. A stretcher or running bond shall be maintained between courses of blocks to ensure that the joints between the blocks are offset with each row.

  6. If a scour countermeasure, such as riprap, is used, a geotextile filter fabric shall be placed under the countermeasure and anchored between the first and second course of the CMU block.

  7. CMU blocks displaced out of required alignment during construction shall be carefully moved back into position by methods that will not cause damage to the CMU blocks or other work.

  8.  Any damaged CMU blocks shall be replaced to retain the new wall integrity.

  9. Battered wall alignment shall be maintained following the same procedures as for vertical walls.

  10.  Detail facing to account for wall batter and corners.

  11. All cuts shall be performed to maintain the standard running or stretcher bond between the rows of the dry-stacked blocks, with the vertical joints of each course midway between those of adjoining courses.

  12. In superelevations, the top course of CMU beneath the superstructure shall be trimmed to match the elevation difference and clear space across the abutment.

  13. Facing wall and wing wall courses shall be staggered to form a tight interlocking stable corner.

  14. Corner details shall be submitted to accommodate corners other than right angles.

  15. The top three courses of CMU blocks shall be filled with concrete wall fill, pinned with No. 4 steel bar, and embedded with a minimum of 2-inch cover (see specifications in section 2.4).


  1. The first course of the facing block shall be set level and to grade.

  2. A thin leveling layer of fine aggregate, which shall not exceed 0.5 inches, may be used on the top of the RSF to facilitate construction of the first course of the facing block. If the leveling layer required exceeds 0.5 inches, a mortar or grout shall be placed in the gap between the RSF and the first CMU block course.


Refer to section 7.8 of FHWA-HRT-11-026 at https://www.fhwa.dot.gov/publications/research/infrastructure/structures/11026/007.cfm#beam.(1)

3.10. Placement of Superstructure

Refer to section 7.9 of FHWA-HRT-11-026 at https://www.fhwa.dot.gov/publications/research/infrastructure/structures/11026/007.cfm#placement2.(1)

3.11. Approach Integration

Refer to section 7.10 of FHWA-HRT-11-026 at https://www.fhwa.dot.gov/publications/research/infrastructure/structures/11026/007.cfm#approach.(1)


Refer to section 7.11 of FHWA-HRT-11-026 at https://www.fhwa.dot.gov/publications/research/infrastructure/structures/11026/007.cfm#drainage.(1)


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