Allan Block Muros de Contención 

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Geogrid Reinforcement Systems

SECTION 2

  1. PART 1: GENERAL

    • 1.1    Scope
      Work includes furnishings and installing geogrid reinforcement, wall block, and backfill to the lines and grades designated on the construction drawings and as specified herein.

    • 1.2    Applicable Section of Related Work Section 1: Allan Block Modular Retaining Wall Systems. (See Section 1)

    • 1.3    Reference Standards
      See specific geogrid manufacturers reference standards.
      Additional Standards:
      1. ASTM D4595 - Tensile Properties of Geotextiles by the Wide-Width Strip Method
      2. ASTM D5262 - Test Method for Evaluating the Unconfined Creep Behavior of Geogrids
      3. ASTM D6638 Grid Connection Strength (SRW-U1)
      4. ASTM D6916 Grid Shear Strength (SRW-U2)
      5. GRI-664 - Grid Long Term Allowable Design Strength (LTDS)
      6. GRI-665 - Grid Pullout


    • 1.4    Delivery, Storage, and Handling
      1. Contractor shall check the geogrid upon delivery to assure that the proper material has been received.
      2. Geogrid shall be stored above -10° F (-23° C).
      3. Contractor shall prevent excessive mud, wet cement, or other foreign materials from coming in contact with the geogrid material


  2. PART 2: MATERIALS

    • 2.1    Definitions
      1. Geogrid products shall be of high density polyethylene or polyester yarns encapsulated in a protective coating specifically fabricated for use as a soil reinforcement material.
      2. Concrete retaining wall units are as detailed on the drawings and shall be Allan Block Retaining Wall Units.
      3. Drainage material is free draining granular material as defined in Section 1, 2.2 Wall Rock.
      4. Infill soil is the soil used as fill for the reinforced soil mass.
      5. Foundation soil is the in-situ soil.


    • 2.2    Products
      Geogrid shall be the type as shown on the drawings having the property requirements as described within the manufacturers specifications.

    • 2.3    Acceptable Manufacturer
      A manufacturer's product shall be approved by the wall design engineer.


  3. PART 3: WALL CONSTRUCTION

    • 3.1    Foundation Soil Preparation.
      1. Foundation soil shall be excavated to the lines and grades as shown on the construction drawings, or as directed by the on-site soils engineer.
      2. Foundation soil shall be examined by the on-site soils engineer to assure that the actual foundation soil strength meets or exceeds assumed design strength.
      3. Over-excavated areas shall be filled with compacted backfill material approved by on-site soils engineer.
      4. Contractor shall verify locations of existing structures and utilities prior to excavation. Contractor shall ensure all surrounding structures are protected from the effects of wall excavation.


    • 3.2    Wall Construction
      Wall construction shall be as specified under Section 1, Part 3, Wall Construction.

    • 3.3    Geogrid Installation
      1. Install Allan Block wall to designated height of first geogrid layer. Backfill and compact the wall rock and infill soil in layers not to exceed 8 in. (200 mm) lifts behind wall to depth equal to designed grid length before grid is installed.
      2. Cut geogrid to designed embedment length and place on top of Allan Block to back edge of lip. Extend away from wall approximately 3% above horizontal on compacted backfill.
      3. Lay geogrid at the proper elevation and orientations shown on the construction drawings or as directed by the wall design engineer.
      4. Correct orientation of the geogrid shall be verified by the contractor and on-site soils engineer. Strength direction is typically perpendicular to wall face.
      5. Follow manufacturers guidelines for overlap requirements. In curves and corners, layout shall be as specified in Design Details 9-12, see page 15 of the AB Spec Book.
      6. Place next course of Allan Block on top of grid and fill block cores with wall rock to lock in place. Remove slack and folds in grid and stake to hold in place.
      7. Adjacent sheets of geogrid shall be butted against each other at the wall face to achieve 100 percent coverage.
      8. Geogrid lengths shall be continuous. Splicing parallel to the wall face is not allowed.


    • 3.4    Fill Placement
      1. Infill material shall be placed in lifts and compacted as specified under Section 1, Part 3.4, Unit Installation.
      2. Infill soil shall be placed, spread and compacted in such a manner that minimizes the development of slack or movement of the geogrid.
      3. Only hand-operated compaction equipment shall be allowed within 3 ft (0.9 m) behind the wall. This area shall be defined as the consolidation zone. Compaction in this zone shall begin by running the plate compactor directly on the block and then compacting in parallel paths to the wall face until the entire consolidation zone has been compacted. A minimum of two passes of the plate compactor are required with maximum lifts of 8 in. (200 mm).
      4. When fill is placed and compaction cannot be defined in terms of Standard Proctor Density, then compaction shall be performed using ordinary compaction process and compacted so that no deformation is observed from the compaction equipment or to the satisfaction of the engineer of record or the site soils engineer.
      5. Tracked construction equipment shall not be operated directly on the geogrid. A minimum fill thickness of 6 in. (150 mm) is required prior to operation of tracked vehicles over the geogrid. Turning of tracked vehicles should be kept to a minimum to prevent tracks from displacing the fill and damaging the geogrid.
      6. Rubber-tired equipment may pass over the geogrid reinforcement at slow speeds, less than 10 mph (16 Km/h). Sudden braking and sharp turning shall be avoided.
      7. The infill soil shall be compacted to achieve 95% Standard Proctor (ASTM D698). Compaction tests shall be taken at 3 ft (0.9 m) behind the block and at the back of the reinforced zone. The frequency shall be as determined by the on-site soils engineer or as specified on the plan. Soil tests of the infill soil shall be submitted to the on-site soils engineer for review and approval prior to the placement of any material. The contractor is responsible for achieving the specified compaction requirements. The on-site soils engineer may direct the contractor to remove, correct or amend any soil found not in compliance with these written specifications.
      8. Una compañía de ensayos independiente debe ser contratada por el dueño para proveer los servicios necesarios.
      9. La compañía de ensayos independiente debe mantener una bitácora de inspección y reportes escritos a un intervalo de tiempo determinado por el dueño
      10. Establecer una frecuencia de ensayos para garantizar un protocolo de compactación apropiada para lograr consistentemente el requerimiento mínimo de compactación asociado con los parámetros de diseño. Si no es posible una inspección a tiempo completo y ensayos a cada capa de 20cm (8 pulg), entonces se debe seguir la frecuencia de ensayos siguiente:
        1. Una prueba por cada 20 cm (8 pulg) de relleno vertical colocado y compactado, por cada 7.60ml (25 pies lineales) de la longitud del muro de contención, comenzando en el primer bloque de la hilera.
        2. Variar la ubicación de los ensayos de compactación para cubrir el área completa de la zona de reforzada, incluyendo el área compactada por el equipo de compactación manual.
        3. Una vez aceptado el protocolo de la frecuencia y rangos, los ensayos pueden ser realizados al azar en ubicaciones y frecuencias determinadas por el ingeniero geotécnico.
      11. Las pendientes encima de la corona del muro deben ser compactadas y chequeadas en forma similar de la descrita anteriormente.


SPECIAL CONSIDERATIONS
  1. Geogrid can be interrupted by periodic penetration of a column, pier or footing structure.
  2. Allan Block walls will accept vertical and horizontal reinforcing with rebar and grout.
  3. If site conditions will not allow geogrid embedment length, consider the following alternatives:
    • Masonry Reinforced Walls
    • Earth Anchors
    • No Fines Concrete
    • Increased Wall Batter
    • Double Allan Block Wall
    • Rock Bolts
    • Soil Naling
  4. Allan Block can be used in a wide variety of water applications. See the AB Spec Book, Section 3, Part 1.8, page 8.
  5. See the AB Spec Book, Design Details pages 17 and 18.
Consult the Allan Block Engineering Department for details 800-899-5309. Specifications subject to change without notice, this document was last updated on 09/01/2007.

Section 1


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