672Precast Concrete Block Gravity Wall

672.01Description The work under this item shall consist of design, fabrication,

furnishing and construction of a Precast Concrete Block Gravity Wall in accordance with these specifications and in close conformance with the lines and grades shown on the Plans, or established by the Resident. The Precast Concrete Block Gravity Wall shall consist of facing blocks made of wet cast concrete made from Portland cement, water, chemical admixtures, and aggregates, supported on concrete leveling pads, and if required, geosynthetic-reinforced backfill. Included in the scope of the precast gravity wall construction are: geotechnical design of any wall with a exposed height greater than 4.5 feet or as specified on the Plans, all grading necessary for wall construction, compaction of the wall foundation soil, backfill, piped drainage, construction of leveling pads, and block wall installation. The top of the upper row of blocks shall be at or above the top of the face elevation shown on the Plans.

672.02Quality Assurance The wall system shall be one of the approved

combinations of facing block and soil reinforcement systems noted in the Plans or on the Department’s Qualified Products List (QPL). Alternate wall systems will not be considered for this Item. All design calculations and Shop Drawings shall be signed, che cked, and sealed by a Professional Engineer licensed in the State of Maine. The Contractor shall require the wall design-supplier to provi de an on-site, qualified experienced technical representative to advise the Contractor concerning proper installation procedures. The technical representative shall be on-site during initial stages of installation and thereafter shall remain available for consultation as necessary for the Contractor or as required by the Resident.

672.03Materials Materials for walls shall meet the requirements of the following

sections of Division 700: Gravel Borrow 703.20 Crushed Stone, ¾ -Inch 703.13 Underdrain Pipe 706.06 or 706.09 Reinforcing Steel 709.01 Reinforcement Geotextile 722.01 Drainage Geotextile 722.02 The Contractor is cautioned that all of the materials listed a re not required for every Precast Concrete Block Gravity Wall. The Contractor shall furnish the Resident a Materials Certification Letter certifying that the applicable materials comply with this section of the specifications. Materials shall meet the following additional requirements:

1 Concrete Units The Materials Certification Letter described above shall contain

the date of concrete casting, a lot identification number, compressive strength results, and entrained air results. All prefabricated concrete units shall conform to the requirements of Section 712.061 with the following exceptions: Materials. Materials are modified as follows: The maximum water cement ratio shall be 0.42, use of calcium nitrite is not required, and the minimum 28 day compressive strength shall be 4600 psi. Paragraph 3 of Materials is not applicable to this Section. Quality Control and Quality Assurance. Quality Control and Quality Assurance is modified as follows: delete the paragraph that begins with “The contractor shall provide a private office…” Curing. Curing requirements are modified as follows: Replace the first sentence in the paragraph which begins “Forms shall remain …” with the following: The forms shall remain in place until the concrete has gained sufficient strength such that removal of the forms and subsequent handling will not damage the units. Add the following paragraph at the end of the Curing section: Face texture of the units shall be a formed finish on all expo sed surfaces. Pigment shall be added during the casting process of the concrete unit to achieve a consistent shade of gray or other color as determined by the Resident. Concrete Testing. Concrete testing requirements are modified as follows: Replace the paragraph which begins “The Contractor shall cast a minimum of 8 ….” With the following: The Contractor shall make and test at least one set of cylinde rs for every 50 CY of production concrete used to cast the concrete units. Replace the paragraph which begins “At least once …” with the following: The Contractor shall make four cylinders for use by the Department to represent every 200 CY or fraction thereof. Tolerances. Maximum dimensional deviation of formed unit dimensions shall be ½ - inch or 2 percent or the manufacturer’s published tolerances, whichever is less. Units not meeting the specified tolerances will be rejected.

2 Geosynthetic Reinforcement Geosynthetic reinforcement shall be as required

by the proprietary wall system manufacturer or wall designer. Geosynthetic reinforcement shall consist of a geotextile or geogrid approved by the Geotechnical Engineer. Substitution of a geosynthetic other than that required by the proprietary wall system manufacturer shall not be allowed unless approved by the Geotechnical Engineer after submittal of shop drawings and pullout and interface friction test data.

chain polymeric filaments or yarns formed into a stable network such that the filaments or yarns retain their position relative to each other during handling, placement, and design life. At least 95 percent by weight of the long chain polymer shall be polyolefin or polyester. The material shall be free of defects and tears. Geotextiles used for reinforcement shall conform as a minimum to the properties indicated for 722.01, Stabilization/Reinforcement Geotextile and shall meet the requirements of part D and E below. Geotextiles shall have a minimum permeability greater or equal to that shown on the Shop Drawings and the reinforced soil permeability.

elements with aperture geometry sufficient to permit significant mechanical interlock with the surrounding soil or rock. The geogrid structure shall be dimensionally stable and able to retain its geometry under manufacture, transport and installation. Geogrids shall conform as a minimum to the criteria specified in part D and E below.

have the ultimate tensile strength (T ult) shown on the approved Shop Drawings for the geosynthetic specified and for the fill type shown. Tult shall be determined from wide width tests specified in ASTM D 4595 for geotextiles and ASTM D 6637 or GRI:GG1 for geogrids. The ultimate tensile strength value is based on the minimum average roll values

4355.

2, per ASTM D-5261.

7 may be used in design, provided the criteria of 2 through 6 are satisfied and 1 is adjusted to 70 percent after 500 hours is satisfied.

high degree of quality control. The Manufacturer is responsible for establishing and maintaining a quality control program to ensure compliance with the requirements of the specification. The purpose of the QC testing program is to verify that the reinforcement geosynthetic being supplied to the project is representative of the material used for performance testing and approval. Conformance testing shall be performed as part of the manufacturing process and may vary for each type of product. As a minimum the following index tests shall be considered as applicable for an acceptable QA/QC program: Property Test Procedure

with ASTM D-4354. Conformance testing procedures are established above. Geosynthetic product acceptance shall be based on ASTM D-4759. The quality control certificate shall include:

geosynthetics supplied meet the respective index criteria set when the geosynthetic was approved, measured in full accordance with all test methods and standards specified, or referenced, in this specification. The manufacturer’s certificate shall state that the furnished geosynthetic meets the requirements of these specifications as evaluated by the manufacturer’s quality control program. The values submitted shall be certified by a person having legal authority to bond the manufacturer. In case of dispute over validity of values, the Resident can require the Contractor to supply test data from an agency approved laboratory to support the values submitted, at the Contractor’s cost.

3 Geosynthetic Connection Reinforcing bar used in the geosynthetic connection

shall be a minimum ½-inch diameter corrosion resistant reinforcing bar, coated on the ends and meeting the requirements of Section 503, Reinforcing Steel. Installation shall be in accordance with manufacturer’s recommendations.

4 Concrete Leveling Pad Concrete for leveling pads shall be Fill Concrete

conforming to the requirements of Section 502 Structural Concrete. Leveling pad shall have a minimum thickness of 4 inches. Unless otherwise specified, concrete for leveling pads shall be accepted under Method “C” requirements. .

5 Backfill Material Backfill material placed behind the concrete units shall meet

the requirements of Section 703.20 Gravel Borrow, except that the backfill material shall only contain particles that will pass the 3-inch square mesh sieve. The contractor is required to submit a grain size distribution curve (ASTM D 422) and a moisture-density relationship curve (AASHTO T-180) for acceptance of the proposed backfill material and determination of the appropriate installation damage reduction factor (RFID). Walls with reinforced backfill require that the backfill material be subjected to pH testing to determine the appropriate durability reduction factor (RF D). Backfill materials shall meet the criteria in the following table: Base Polymer Property Criteria Test Method Polyester (PET) pH 3< pH < 9 AASHTO T-289 Polyolefin (PP & HDPE) pH pH > 3 AASHTO T-289 Material between blocks must be Gravel Borrow, or Crushed Stone, ¾ -Inch.

6 Materials Certification Letter The Contractor, or the supplier as his agent,

shall furnish the Resident a Materials Certification Letter for the above materials, including the backfill material, in accordance with Section 700 of the Standard Specifications. A copy of all test results performed by the Contractor or his supplier necessary to assure contract compliance shall also be furnished to the Resident. The Resident will base acceptance upon the materials Certificate Letter, accompanying test reports,, and visual inspection.

672.04Design Requirements The wall shall be designed with a service life of not

less than 75 years. The Precast Concrete Block Gravity Wall shall be designed and sealed by a Professional Engineer licensed in the State of Maine. The wall shall be designed in accordance with the following:

LRFD

and FHWA-NHI-10-025, Design and Construction of Mechanically Stabilized Earth Walls and Reinforced Soil Slopes, Volumes I and II, current edition.

Mechanically Stabilized Earth Walls and Reinforced Soil Slopes, current edition.

Where conflicting requirements occur, the more stringent requirements shall govern. Forty-five days prior to beginning construction of the wall, the design computations shall be submitted to the Resident for review by the Geotechnical Engineer. Any additional design or costs arising as a result of rejection of a wall design by the Geotechnical Engineer shall be borne by the Contractor. Design calculations that consist of computer program generated output shall be supplemented with at least one hand calculation and graphic demonstrating the design methodology used. Design calculations shall provide thorough documentation of the sources of equations used and material properties. The design by the wall system supplier shall consider the stability of the wall as outlined below and in the Contract Documents:

determined in accordance with LRFD Article 11 and be analyzed so that the soil stabilizing components extend sufficiently beyond the failure plane within the reinforced soil mass to stabilize the material.

those applied through traffic loadings, impact on traffic barrier posts, slope surcharge, hydrostatic, and seismic loads shall be accounted for in the design. Traffic surcharge and traffic impact loads shall be calculated and applied in compliance with LRFD Section 11. C External Stability Loads and load combinations selected for design shall be consistent with LRFD. Application of load factors shall be taken as specified in LRFD Section 11. Sliding resistance factors and bearing resistance factors shall be consistent with LRFD. Overturning and sliding provisions of LRFD shall apply.

reinforcement/block connection pullout or rupture shall be consistent with LRFD Section 11, and checked at each level. Loads, load combinations and load factors shall be as specified in LRFD Section 11. Resistance factors for internal design are specified in LRFD Section 11. Maximum reinforcement loads shall be calculated using the Simplified Method approach. Calculations for factored stresses and resistances shall be based upon assumed conditions at the end of the design life.

reinforcement design strength (Tal) shall be determined by reducing Tult by reduction factors (RF) in accordance with the documents referenced above. The designer shall procure and use the manufacturers tested and certified geosynthetic reinforcement reduction factors for creep (RFCR), durability (RFD), and installation damage (RFID) to determine Tal. In absence of manufacturers tested and certified reduction factors, a combined default reduction factor RF = 7 shall be used in accordance with the referenced documents. For RFID, the installation damage reduction factor shall be checked in accordance with LRFD and FHWA-NHI-09-087.

connection strength between the geosynthetic reinforcement and the concrete blocks shall be checked in accordance with LRFD and FHWA-NHI-10-024 and FHWA-NHI- 10-025.

correction factor (α) used in pullout design, shall be determined from project specific pullout tests using the proposed geosynthetic in the specified project backfill material or equivalent soil. The pullout resistance factors shall be determined in accordance with LRFD and FHWA-NHI-10-024 and FHWA-NHI-10-025. In the absence of test data, empirical relationships may be used to determine the pullout resistance factors, any empirical relationships used in design shall be referenced in the design calculations.

reinforced fill zone for internal stability design shall be assumed have a friction angle of 34 degrees unless specific project select backfill is tested for frictional strength. The friction angle of the foundation soils and random backfill shall be assumed to be 30 degrees unless otherwise shown on the plans.

the top of each wall section. The minimum length of the soil reinforcement shall be 8 ft, but shall not be less than 70 percent of the wall height, H, for walls with level surcharges, or 70 percent of H1 for walls with a sloped surcharge or walls supporting an abutment. The mechanical wall height, H or H1, shall be the vertical difference between the top of the leveling footing and the elevation at which the failure surface, as described above, intercepts the ground surface supported by the wall.

Gravity Wall shall be clearly indicated on the Shop Drawings. Walls shall be dimensioned so that the factored bearing resistance of the foundation soils, as noted on the Plans, is not exceeded.

with LRFD, and shall include an evaluation of the maximum vertical spacing between reinforcement layers.

temporary construction slope. Passive pressure in front of the wall mass shall be assumed to be zero for design purposes.

or below the elevation shown on the Plans and the approved Shop Drawings.

base of the reinforced soil zone and backfill soil. This shall outlet into surrounding drainage systems or ditches.

672.05Submittals The Contractor shall supply wall design com putations, wall

details, dimensions, quantities, and cross sections necessary to construct the wall. A sample hand calculation including all equations, parameter values used, units, theory, free-body diagram, comparison to design requirements, etc. shall be provided. Spread sheet calculations alone are not acceptable. Forty-five days prior to beginning construction of the wall, f our (4) sets of the wall design computations and Shop Drawings shall be submitted to the Resident for review by the Geotechnical Engineer. Mix design information shall be submitted at the same time, including aggregate source, current gradation, aggregate quality information and concrete unit weight. The contractor shall also submit backfill material test results as part of the wall submittal package. Backfill material test results shall include grain size distribution curve, moisture-density relationship curve, and pH test results required for reinforced backfill only. If geotechnical design is required, the fully detailed planss hall be prepared in conformance with Section 105 and shall include, but not be limited to the following items:

elevations at the top of leveling pads, the distance along the face of the wall to all steps in the leveling pads, the location of the original and final ground line.

leveling pads, as well as allowable and actual maximum bearing pressures shall be provided.

two copies of the design-supplier’s Installation Manual. In addition, the Contractor shall have two copies of the Installation Manual on the project site.

672.06Construction Requirements The Precast Concrete Block Gravity Wall shall have

the following construction requirements:

meet the requirements of Section 203 -- Excavation and Embankment, except as modified herein.

rest, and within the limits shown on the submitted plans, shall be graded for a width equal to, or exceeding, the length of the blocks. Prior to wall and leveling pad construction, this foundation material shall be compacted to at least 95 percent of maximum laboratory dry density (AASHTO T-180 Method C or D). Frozen and unsuitable soil shall be removed and replaced with gravel borrow compacted to 95 percent of AASHTO T-180. A concrete leveling pad shall have a minimum thickness of 4 inches and shall be constructed as indicated on the plans. Dimensions may be modified per the wall supplier’s recommendations, with written approval of the Geotechnical Engineer. The leveling pad shall be cast to the design elevations as shown on the plans, or as required by the wall supplier upon written approval of the Geotechnical Engineer. The allowable elevation tolerances from the design elevations are +0.01 feet and -0.02 feet. Leveling pads which do not meet this requirement shall be repaired or replaced as directed by the Resident at no additional cost to the Department. Placement of wall units may begin after the strength of the concrete leveling pad reaches 1000 psi or is adequate to support the proposed loads. Contractor may begin placement of concrete block units after 12 hours at his own risk.

the Contractor shall furnish the Resident with detailed information concerning the proposed construction method and equipment to be used. The erection procedure shall be in accordance with the manufacturer’s instructions. Any units that are damaged due to handling will be replaced at the Contractor’s expense.

shall be available, as needed, during the erection of the wall. The services of the representative shall be at no additional cost to the project. Horizontal joint fillers shall be installed as needed. The maximum offset in any unit horizontal joint shall be 1/4 inch. The prefabricated wall blocks shall be installed to a tolerance of plus or minus 3/4 inch in 10 feet in vertical alignment and horizontal alignment.

of prefabricated wall units. The Contractor shall decrease the lift thickness if necessary to obtain the specified density. The maximum lift thickness shall be 8 inches loose. Gravel borrow backfill shall be compacted in accordance with Section

203.12except that the minimum required compaction shall be at least 92 percent of

maximum density as determined by AASHTO T-180 Method C or D. Backfill compaction shall be accomplished without disturbance or displacement of the wall blocks. Sheepsfoot rollers will not be allowed. Whenever a compaction test fails, no additional backfill shall be placed over the area until the lift is recompacted and a passing test achieved. The moisture content of the backfill material prior to and during compaction shall be uniform throughout each layer. Backfill material shall have a placement moisture content less than or equal to the optimum moisture content. Backfill material with a placement moisture content in excess of the optimum moisture content shall be removed and reworked until the moisture content is uniform and acceptable throughout the entire lift. The optimum moisture content shall be determined in accordance with AASHTO T-180, Method C or D. At the end of the day’s operations, the Contractor shall shape the last level of backfill so as to direct runoff of rain water away from the wall face. Material between blocks must be Gravel Borrow or Crushed Stone, ¾ -Inch, meeting the requirements of Section 703.13. If Gravel Borrow is used between blocks, 722.02 drainage geotextile shall be placed behind vertical joints to prevent loss of granular material between blocks. Compliance with the gradation requirements shall be the responsibility of the Contractor, who shall furnish a copy of the backfill test results prior to construction. If crushed stone, 3/4-inch is used between blocks, no geotextile is required behind vertical joints.

672.07Method of Measurement Precast Concrete Block Gravity Wall will be

measured by the square foot of front surface not to exceed the dimensions shown on the Contract Plans unless authorized by the Resident. Vertical and horizontal dimensions will be from the edges of the blocks. No field measurements for computations will be made unless the Resident specifies, in writing, a change in the limits indicated on the Plans.

672.08Basis of Payment The accepted quantity of Precast Conc rete Block Gravity

Wall will be paid for at the contract unit price per square foot complete in place. Payment shall be full compensation for furnishing geotechnical design as required, all labor, equipment and materials including all precast concrete units, hardware, joint fillers, geosynthetics, reinforcing steel, drainage pipe, backfill materials and technical field representative. Excavation, foundation material and backfill material will all be incidental to the Precast Concrete Block Gravity Wall. Cost of cast-in-place concrete for leveling pad will not be pa id for separately, but will be considered incidental to the Precast Concrete Block Gravity Wall. There will be no allowance for excavating and backfilling for the Precast Concrete Block Gravity Wall beyond the limits shown on the approved submitted plans, except for excavation required to remove unsuitable subsoil in preparation for the foundation. Payment for excavating unsuitable subsoil shall be full compensation for all costs of pumping, drainage, sheeting, bracing and incidentals for proper execution of the work, and will be paid as Common Excavation in accordance with Section 203. Payment will be made under: P a y I t e m P a y U n i t

672.10Precast Concrete Block Gravity Wall Square Foot