any advice is appreciated

Discussion in 'Hardscaping' started by qlcontractors, Mar 2, 2011.

  1. qlcontractors

    qlcontractors LawnSite Member
    Posts: 4

    Hello, i don't know much of anything about hardscaping, our company does not do any we do irrigation. However i would like learn the steps of constructing a retaining wall from you professionals. I am interested in building a wall in place of railroad ties that are currently at my house. Looking forward to any advice thank you
     
  2. Landrus2

    Landrus2 LawnSite Platinum Member
    Posts: 4,812

    what type of wall you want to build
     
  3. PatriotLandscape

    PatriotLandscape LawnSite Bronze Member
    from MA
    Posts: 1,209

    Really just go to the supplier and read the installation manual. Then come back here with a more specific question .
    Posted via Mobile Device
     
  4. qlcontractors

    qlcontractors LawnSite Member
    Posts: 4

    It's approximately 5 feet tall at its highest peak, 15 feet long with a 90 at each end and the wall extends for another 5 feet. I was going to build it out of uniblock or oaks.

    Was curious to know what steps you guys would take to do the base. What materials you would use, what you would backfill the drainage with.

    Thanks for any advice.
     
  5. castle555

    castle555 LawnSite Member
    Posts: 127

    Welcome to the world of building codes and standards
    I just completed a proposal for a concrete wall footing. The owner is doing his own wall block and I alreadyhave confidence in his ability. Also, I have built with CMU, Keystone, Pavestone, Boulders, natural Stone, and formed Concrete for wall materials.
    I do not fool around with wall construction, and draw out in detail what I plan to do, because of the possibility of later failure. This type of wall needs to be engineered, is usually permit required and/or should follow good wall construction guidelines. I also will usually design up the footing and wall on the computer to show my customer what it will look like and exactly what is in the bid.
    My brother is a senior engineer with CalTrans (Bridges and Highways division) and I've always followed his advice and wall construction plans, for any wall I've constructed. Yes, engineers tend to overbuild a project because their stamp is on a plan, and they have tremendous liability for public safety. However, they understand things like 'polar moment', 'live load', 'dead load', and 'torsion', etc :hammerhead:
    Experimenting on your own property is a great idea for starters. Do consider that if part of it is higher than 3' feet it may need a 42" high barrier to prevent someone falling off of it and suing you.
    Segmented Block (basalite) walls are fine, when built right and have different foundation requirements than CMU.
    When you go over 4' from the bottom of the foundation to the top of the wall, most cities want it permitted. Especially if it is backfilled, and/or there is a slope above it. (max. slope 2:1)
    A five foot wall like you are mentioning, with level backfill grade, will need to have approx. 2'6" wide by 12" deep footing, #4 rebar reinforcement, and if on a hillside a 6' key.
    Do not get into building structures if you do not have an understanding of the engineering and quality of construction involved, or you are asking for wall failure, especially when there is a segmented (one wall above and set back behind the other) or hydrostatic load. You even need to address drainage.

    Check a city or county government website for 'retaining wall' and it will show you
    the means of determining the engineering required.

    Should you decide to proceed, good luck, and read the manual. Hardscape is just that...hard.
     
  6. Here is unilocks specs for retaining walls maybe this will help you
    DURA-HOLD2® CRIB RETAINING
    WALL INSTALLATION
    SPECIFICATIONS
    Prepared by Risi Stone Systems – Used by
    permission.
    1-800-UNILOCK www.unilock.com
    Dura-Hold2® Crib Retaining Wall
    Unilock Specifications Page 2
    FOREWORD
    This outline specification has been prepared for the general guidance of specifiers,
    engineers, contractors and superintendents associated with the construction of Dura-
    Hold2® Crib Retaining Wall. A qualified engineer must determine the suitability of the
    design, confirm site conditions and monitor the installation in critical applications.
    CROSS SECTION EXAMPLES
    A comprehensive compilation of specific retaining wall scenarios can be found at
    www.unilock.com. Also, under the Design Professional Resources section is the
    Risiwall software program, which can be used for site specific analysis for most
    Unilock® retaining wall systems.
    Call 1-800-UNILOCK for engineering assistance.
    Dura-Hold2® Crib Retaining Wall
    Unilock Specifications Page 3
    DURA-HOLD2® CRIB RETAINING WALL INSTALLATION
    SPECIFICATION
    SECTION 02832- CONCRETE SEGMENTAL RETAINING WALL
    PART 1 GENERAL
    1.1. Description
    A. The work covered by this section includes the furnishing of all labour, materials,
    equipment and incidentals for the design, inspection and construction of a modular
    concrete retaining wall including the drainage system as shown on the
    Construction Drawings and as described by the Contract Specifications. The work
    included in this section consists of, but is not limited, to the following:
    1. Design, inspection and certification by a registered professional engineer.
    2. Excavation and foundation soil preparation.
    3. Furnishing and placement of the levelling base.
    4. Furnishing and placement of the drainage system.
    5. Furnishing and placement of geotextiles.
    6. Furnishing and placement of segmental retaining wall facing units and
    tiebacks.
    7. Furnishing and compaction of infill, drainage and retained soils.
    1.2. Related Work
    A. Section 02100 - Site Preparation
    B. Section 02200 - Earthwork
    1.3. Reference Standards
    A. Engineering Design
    1. NCMA Design Manual for Segmental Retaining Walls, Second Edition.
    2. NCMA TEK 2-4 - Specifications for Segmental Retaining Wall Units.
    3. NCMA SRWU-2 - Determination of Shear Strength between Segmental
    Concrete Units.
    B. Segmental Retaining Wall Units
    1. ASTM C 140 - Sampling and Testing Concrete Masonry Units
    2. ASTM C 1262 - Evaluating the Freeze - Thaw Durability of Manufactured
    Concrete Masonry Units and Related Concrete Units.
    3. ASTM C 33 - Specification for Concrete Aggregates
    Dura-Hold2® Crib Retaining Wall
    Unilock Specifications Page 4
    4. ASTM C 90 - Standard Specification for Load-Bearing Concrete Masonry
    Units
    5. ASTM C 150- Specification for Portland Cement
    6. ASTM C 595 - Specification for Blended Hydraulic Cements
    C. Geotextile Filter
    1. ASTM D 4751 - Standard Test Method for Apparent Opening Size
    D. Soils
    1. ASTM D 698 - Moisture Density Relationship for Soils, Standard Method
    2. ASTM D 422 - Gradation of Soils
    3. ASTM D 424 - Atterberg Limits of Soils
    4. ASTM D G51 - Soil pH
    E. Drainage Pipe
    1. ASTM D 3034 - Specification for Polyvinyl Chloride (PVC) Plastic Pipe
    2. ASTM D 1248 - Specification for Corrugated Plastic Pipe
    F. Where specifications and reference documents conflict, the Owner's Engineer shall
    make the final determination of applicable document.
    1.4. Approved Products
    A. Dura-Hold2® Segmental Crib Retaining Wall System as supplied by Unilock®
    Unilock® Location (Address, Phone, Fax) ___________________________
    B. Color to be [_______].
    1.5. The Contractor
    A. The term Contractor shall refer to the individual or firm who will be installing the
    retaining wall.
    B. The Contractor must have the necessary experience for the project and have
    successfully completed projects of similar scope and size.
    1.6. Delivery, Material Handling and Storage
    A. The installing contractor shall check all materials delivered to the site to ensure
    that the correct materials have been received and are in good condition.
    B. The Contractor shall store and handle all materials in accordance with Unilock’s
    recommendations and in a manner to prevent deterioration or damage due to
    moisture, temperature changes, contaminants, breaking, chipping or other causes.
    1.7. Engineering Design and Certification
    A. The term Engineer shall refer to the individuals or firms who have been retained by
    the Contractor to provide design and inspection services for the retaining wall. The
    Design Engineer may be a different individual or firm from the Inspecting Engineer
    Dura-Hold2® Crib Retaining Wall
    Unilock Specifications Page 5
    as Unilock® may provide this service. The Engineer(s) must be qualified in the area
    of segmental retaining wall design and construction and must be licensed to
    practice engineering in the Province or State that the wall is to be constructed.
    B. The Engineer(s) will perform the following tasks:
    1. Produce sealed construction drawings and detailed design calculations,
    completed in accordance with the design requirements outlined in Part 3 of
    these specifications.
    2. Review the site soil and geometric conditions to ensure the designed wall is
    compatible with the site prior to construction.
    3. Inspect the site conditions, materials incorporated into the retaining wall, and
    the construction practices used during the construction.
    4. Provide the Contractor with a letter after completion, certifying the design
    meets the requirements of this specification, the design was compatible with
    the site and the wall was constructed according to design.
    1.8. Submittals
    A. The Contractor shall submit the following information for approval thirty (30) days
    prior to the construction of the segmental retaining wall.
    1. Design Submittal – Provide three (3) sets of stamped construction drawings
    and detailed design calculations, completed and sealed by the Engineer in
    accordance with the design requirements outlined in Part 3 of this
    specification.
    2. Materials Submittal – Manufacturer’s certifications, stating that the SRW units
    and imported aggregates and soils meet the requirements of this specification
    and the Engineer’s design.
    3. Installer Qualifications - The Contractor must be able to demonstrate that their
    field construction supervisor has the necessary experience for the project by
    providing documentation showing that they have successfully completed
    projects of similar scope and size.
    1.9. Measurement for Payment
    A. Payment for earthworks to prepare the site for the retaining wall construction will
    be based on the contract unit price per cubic meter (or cubic yard) for site cut and
    fill earthwork as detailed in the Site Plan. Additional earthwork as directed and
    approved in writing by the Owner, or Owner’s representative, shall be paid for
    under a separate pay item.
    B. Payment for the retaining wall system will be based on the contract price per
    square meter (or square foot) of vertical wall face area as shown on the
    construction drawings. The vertical wall face area shall be measured from the top
    of the base or footing to the top of the coping course multiplied by the length of the
    wall. The contract unit price shall include the cost of all engineering, labor,
    materials, and equipment used to install the leveling base or spread footing, wall
    modules, drainage materials, infill soil, retained soil and site clean up. Additional
    Dura-Hold2® Crib Retaining Wall
    Unilock Specifications Page 6
    items as directed and approved in writing by the Owner, or Owner’s representative,
    shall be paid for under a separate pay item.
    PART 2 MATERIALS
    2.1. Definitions
    A. Modular concrete retaining wall units are dry-cast solid concrete units that form the
    external fascia and semi-crib structure (including tie-backs and rear wall) of a
    modular unit crib retaining wall system.
    B. Coping units are the last course of concrete units used to finish the top of the wall.
    C. Infill soil is specified material that is placed within the semi-crib structure.
    D. Retained soil is an in-situ soil or a specified soil that is placed behind the back wall
    of the semi-crib structure.
    E. Foundation soil is the in-situ soil beneath the wall structure.
    F. Drainage aggregate is a free draining soil with natural soil filtering capabilities, or a
    free draining soil encapsulated in a suitable geotextile, or a combination of free
    draining soil and perforated pipe all wrapped in a geotextile, placed directly behind
    the back wall of the semi-crib structure.
    G. Drainage pipe is a perforated polyethylene pipe used to carry water, collected at
    the base of the retaining wall, to outlets in order to prevent pore water pressures
    from building up behind the wall facing modules.
    H. Non-woven geotextiles are permeable synthetic fabrics formed from a random
    arrangement of fibers in a planar structure. They allow the passage of water from
    one soil medium to another while preventing the migration of fine particles that
    might clog a drainage medium.
    I. All values stated in metric units shall be considered as accurate. Values in
    parenthesis stated in imperial units are the nominal equivalents.
    2.2. Products
    A. Concrete Segmental Retaining Wall Units
    1. The standard concrete wall modules shall be 305 x 1830 x 355 mm (12 x 72 x
    14 inches). The concrete tie-back wall modules shall be 305 x 355 x 1830
    mm (12 x 14 x 72 inches). The units have a maximum tolerance of plus or
    minus 3 mm (1/8 inch) for each dimension.
    2. The retaining wall modules shall be solid units and have a minimum weight of
    480 kg (1050 lbs.) per unit.
    3. The concrete wall modules shall have a integral shear key connection that
    shall be offset to permit a minimum wall batter of 1H : 8V.
    4. The concrete wall modules shall have a minimum 28-day compressive
    strength of 35 MPa (5000 psi) as tested in accordance with ASTM C 140. The
    Dura-Hold2® Crib Retaining Wall
    Unilock Specifications Page 7
    concrete shall have a maximum moisture absorption rate of 5 percent to
    ensure adequate freeze-thaw protection.
    5. The concrete tie-back wall modules shall be reinforced with two (2) 10M (3/8
    inch diameter), grade No.60 steel reinforcing bars with a minimum of 100mm
    (4 inches) of concrete cover. Placement of the bars shall be as per
    Manufacturer’s details
    B. Infill Soil
    1. The infill soil shall consist of free draining sands or gravels with less than 5%
    passing the #200 sieve size or as specified in the Construction Drawings.
    2. The Engineer shall review and determine the suitability of the wall infill soil at
    the time of construction.
    C. Retained Soil
    1. The retained soil shall be on site soils unless specified otherwise in the
    Construction Specifications or as directed by the Owner’s Representative. If
    imported fill is required, it shall be examined and approved by the Engineer.
    D. Foundation Soil
    1. The foundation soil shall be the native undisturbed on site soils. The
    foundation soil shall be examined and approval by the Engineer prior to the
    placement of the base material.
    E. Leveling Base Material
    1. The footing material shall be non-frost susceptible, well graded compacted
    crushed stone (GW-Unified Soil Classification System), or a concrete leveling
    base, or as shown on the Construction Drawings.
    F. Drainage Soil
    1. The drainage soil shall be a free draining angular granular material of uniform
    particle size smaller than 25 mm (1 inch) separated from the infill soil or
    retained soil by a geotextile filter. The drainage soil shall be installed directly
    behind the SRW units if the infill soil is unable to provide adequate drainage
    capacity.
    G. Drainage Pipe
    1. The drainage pipe shall be perforated corrugated HDPE or PVC pipe, with a
    minimum diameter of 100 mm (4 inches), protected by a geotextile filter to
    prevent the migration of soil particles into the pipe, or as specified on the
    construction drawings.
    H. Geotextile Filter
    1. The non-woven geotextile shall be installed as specified on the construction
    drawings. Although selection of the appropriate geotextile specifications is
    site soil specific, a commonly used geotextile for filtration will have an
    Apparent Opening Size ranging between 0.149 and 0.210 mm (U.S. Sieve
    Sizes 100 to 70) and a minimum unit weight of 135 grams per square meter
    Dura-Hold2® Crib Retaining Wall
    Unilock Specifications Page 8
    (4.0 oz /square yard). The coefficient of permeability will typically range
    between 0.1 and 0.3 cm/second.
    PART 3 WALL DESIGN
    3.1. Design Standard
    A. The Design Engineer is responsible for providing a design that shall consider the
    external stability, internal stability, and local stability of the SRW System. It is the
    responsibility of the Certifying Engineer or Site Geotechnical Engineer to determine
    if further design considerations must be implemented to ensure adequate
    global/overall slope stability, and/or, if the foundation soils will require special
    treatment to control total and differential settlement. The design life of the
    structure shall be 75 years unless otherwise specified in the construction drawings.
    B. The segmental retaining wall shall be designed in accordance with
    recommendations of the NCMA Design Manual for Segmental Retaining Walls,
    Second Edition. The following is a summary of the minimum factors of safety for
    the various modes of failure evaluated in the proposed design.
    External Stability
    Base Sliding 1.5
    Overturning 1.5
    Bearing Capacity 2.0
    Global Stability 1.3
    Internal Stability
    Shear Capacity 1.5
    3.2. Soil
    A. Design parameters: The following soil parameters shall be assumed for the design
    unless otherwise shown on the plans or specified by the Engineer.
    Infill Soil:
    Unit Weight = [________] kN/m3 (lb/ft3)
    Friction Angle = [________] deg
    Cohesion = 0 kPa (lb/sq.ft)
    Retained Soil:
    Unit Weight = [________] kN/m3 (lb/ft3)
    Friction Angle = [________] deg
    Cohesion = 0 kPa (lb/sq.ft)
    Dura-Hold2® Crib Retaining Wall
    Unilock Specifications Page 9
    Foundation Soil:
    Unit Weight = [________] kN/m3 (lb/ft3)
    Friction Angle = [________] deg
    Cohesion = 0 kPa (lb/sq.ft)
    3.3. Design Geometry
    A. The length, height, and overall elevations of the retaining wall must comply with the
    requirements of the proposed elevation detail, station information and site grading
    plan.
    B. The structures' design height, H, shall be measured from the top of the leveling
    pad to the top of the wall where ground surface intercepts the wall facing.
    C. Slopes above and below all sections of the segmental retaining wall are detailed in
    the site grading plan.
    D. The minimum wall embedment shall be the greater of:
    1. The height of a SRW unit,
    2. 150 mm (0.5 ft) or,
    3. The minimum embedment required because of the slope below the wall:
    Slope Below Wall Minimum Embedment
    Level H/10
    3 : 1 (18.4 deg) H/10
    2 : 1 (26.5 deg) H/7
    E. The following surcharges shall be applied to the top of each design cross section
    based on the following proposed uses above the wall.
    Use Above Wall Minimum Surcharge
    No Traffic 0 kPa (0 lb/sq. ft)
    Light Traffic 4.8 kPa (100 lb/sq. ft)
    Heavy Traffic 12.0 kPa (250 lb/sq. ft)
    3.4. State of Stress
    A. The lateral earth pressure to be resisted by the composite weight of the semi-crib
    structure and infill soil shall be calculated using the Coulomb coefficient of earth
    pressure, Ka, times the vertical stress at the base of the wall. The coefficient of
    active earth pressure, Ka, shall be used from the top to the bottom of the wall. The
    coefficient of active earth pressure, Ka, shall be assumed independent of all
    external loads except sloping fills. For sloping fills, the coefficient of active earth
    Dura-Hold2® Crib Retaining Wall
    Unilock Specifications Page 10
    pressure, Ka, appropriate for the sloping condition, using Coulomb earth pressure
    shall be used in the analysis.
    3.5. Inclination of Failure Surface
    A. A Coulomb failure surface passing through the base of the wall behind the tie-back
    units up to the ground surface at or above the top of wall shall be assumed in
    design of walls.
    3.6. Settlement Control
    A. It is the responsibility of the Certifying Engineer or Site Geotechnical Engineer to
    determine if the foundation soils will require special treatment to control total and
    differential settlement.
    3.7. Global Stability
    A. It is the responsibility of the Certifying Engineer or Site Geotechnical Engineer to
    determine if further design considerations must be implemented to ensure
    adequate global/overall slope stability.
    PART 4 CONSTRUCTION
    4.1. Inspection
    A. The Engineer is responsible for verifying that the contractor meets all the
    requirements of the specification. This includes the use of approved materials and
    their proper installation.
    B. The Contractor's field construction supervisor shall have demonstrated experience
    and be qualified to direct all work related to the retaining wall construction.
    4.2. Construction Tolerances
    A. The following tolerances are the maximum allowable deviation from the planned
    construction
    Vertical Control: +/- 1.25 inches over a 10 ft distance, +/- 3 inches total
    Horizontal Control: +/- 1.25 inches over a 10 ft distance, +/- 3 inches total
    Rotation: +/- 2 deg from planned wall batter
    Bulging: 1.0 inch over a 10 ft distance
     
  7. Part 2
    4.3. Site Preparation
    A. The foundation soil shall be excavated or filled as required to the grades and
    dimensions shown on the Construction Drawings or as directed by the Owner or
    Owner’s Representative.
    B. The foundation soil shall be proof rolled and examined by the Engineer to ensure
    that it meets the minimum strength requirements according to the design
    assumptions. If unacceptable foundation soil is encountered, the contractor shall
    Dura-Hold2® Crib Retaining Wall
    Unilock Specifications Page 11
    excavate the affected areas and replace with suitable quality material under the
    direction of the Engineer.
    C. In cut situations, the native soil shall be excavated to the lines and grades shown
    on the Construction Drawings and removed from the site or stockpiled for reuse as
    retained soil.
    4.4. Installing Drainage System
    A. The approved non-woven geotextile shall be set against the back of the first
    retaining wall unit at the back of the semi-crib structure and extended towards the
    back of the excavation, up the excavation face and back over the top of the semicrib
    structure / infill soil to the retaining wall fascia, or as shown in the Construction
    Drawings.
    B. The drainage pipe shall be placed behind the leveling base, or lower course of
    facing units as shown in the Construction Drawings or as directed by the Engineer.
    The pipe shall be laid at a minimum gradient of 2% to ensure adequate drainage to
    free outlets.
    C. T - Sections and outlet pipes shall be installed on the drainage pipe at 15 m (50 ft.)
    centers or as shown on the Construction Drawings.
    D. The remaining length of geotextile shall be pulled taut and pinned over the face of
    the retained soil. Geotextile overlaps shall be a minimum of 300 mm (1 ft.) and
    shall be shingled down the face of the excavation in order to prevent the infiltration
    of retained soil into the wall infill.
    4.5. Leveling Base or Spread Footing Placement
    A. The leveling base material shall be crushed stone compacted to 98% Standard
    Proctor Density, or vibrated concrete along the grades and dimensions shown on
    the Construction Drawings or as directed by the Engineer. The minimum thickness
    of the leveling base shall be 305 mm (12 inches).
    4.6. Installation of Modular Concrete Retaining Wall Units
    A. The bottom row of retaining wall modules shall be placed on the prepared leveling
    base as shown on the Construction Drawings. Care shall be taken to ensure that
    the wall modules are aligned properly, leveled from side to side and front to back
    and are in complete contact with the base material.
    B. The tie-back wall modules shall be installed perpendicular to the base course on
    2440 mm (96 inches) centers, separated by standard wall modules to form the
    front and rear wall of the semi-crib structure. The tie-back modules are aligned
    vertically on every other course up to the gravity portion of the wall, as determined
    by the design. Standard and tie-back modules above the bottom course shall be
    placed such that the tongue and grove arrangement provides the design batter (i.e.
    setback) of the wall face. Successive courses shall be placed to create a running
    bond pattern with the edge of all units being approximately aligned with the middle
    of the unit in the course below it. Infill material underlying tie-back units shall be
    Dura-Hold2® Crib Retaining Wall
    Unilock Specifications Page 12
    compacted with hand operated compaction equipment ensuring that the tie-back
    modules are in full contact with the infill material.
    C. The wall modules shall be swept clean before placing additional levels to ensure
    that no dirt, concrete or other foreign materials become lodged between
    successive lifts of the wall modules.
    D. A maximum of 3 courses of wall units can be placed above the level of the infill soil
    at any time.
    E. The contractor shall check the level of wall modules with each lift to ensure that no
    gaps are formed between successive lifts.
    F. Care shall be taken to ensure that the wall modules are not broken or damaged
    during handling and placement.
    4.7. Drainage Soil
    A. The drainage soil will be placed behind the back wall with a minimum width of 300
    mm (1 ft.) and separated from other soils using the approved non-woven
    geotextile.
    B. Drainage soil shall be placed behind the wall facing in maximum lifts of 6 inches
    and compacted to a minimum density of 95% Standard Proctor.
    C. No heavy compaction equipment shall be allowed within 1 meter (3 ft.) of the back
    of the crib system.
    4.8. Infill Soil
    A. Wall infill soil shall be placed within the semi-crib structure in maximum lifts of 150
    mm (6 inches) and compacted to a minimum density of 95% Standard Proctor.
    B. Wall infill soil shall be compacted in and around the tieback modules with hand
    operated compaction equipment ensuring that the tie-back modules are in full
    contact with the underlying infill soil.
    C. No construction equipment shall be allowed to operate directly on top of the tieback
    units. No heavy equipment shall be allowed within 1 meter (3 ft.) of the back
    of the crib system.
    4.9. Retained Soil
    A. Retained soils shall be placed and compacted behind the semi-crib structure and
    drainage layer in maximum lift thickness of 150 mm (6 inches). The retained soils
    shall be undisturbed native material or engineered fill compacted to a minimum
    density of 95% Standard Proctor.
    B. No heavy compaction equipment shall be allowed within 1 m (3 ft.) of the back of
    the wall modules.
    4.10. Finishing Wall
    A. Items 4.5 to 4.9 shall be repeated until the grades indicated on the Construction
    Drawings are achieved.
    Dura-Hold2® Crib Retaining Wall
    Unilock Specifications Page 13
    B. Coping units shall be secured to the top of the wall with two 10 mm (3/8 inch)
    beads of the approved flexible concrete adhesive positioned 50mm (2 inches) in
    front and behind the tongue of the last course of retaining wall units.
    C. Finish grading above the wall to direct surface run off water away from the
    segmental retaining wall. Use a soil with a low permeability to restrict the rate of
    water infiltration into the retaining wall structure.
    END OF SECTION
     

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