6-186 maximum laboratory dry densit y (AASHTO T-180 Method C or D). F rozen and unsuitable soil shall be removed and replaced with gravel borro w compacted to 95 percent of AASHTO T-180. A concrete leveling pad shall have a minimum thickness of 4 inc hes and shall be constructed as indicated on the plans. Dimensions may be modif ied per the wall supplier’s recommendations, with written approval of the Geotec hnical 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 repai red or replaced as directed by the Resident at no additional cost to the Departmen t. 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 p lacement of concrete block units after 12 hours at his own risk.
C.Method and Equipment. Prior t o erection of the prefabricate d concrete block wall, the Contractor shall furnish the Resident with detailed informa tion concerning the proposed construction method and equipment to be used. The ere ction procedure shall be in accordance with the manufacturer’s instructions. Any uni ts that are damaged due to handling will be replaced at the Contractor’s expense.
D.Installation of Wall Units. A field representative from the wall system being used 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 hor izontal joint shall be 1/4 in ch. 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.
E.Backfill Placement. Backfill pl acement shall closely follow the erection of each row of prefabricated wall units. The Contractor shall decrease the lift thickness if necessary to obtain the specified density. The maximum lift th ickness shall be 8 inches loose. Gravel borrow backfill shall be compacted in acc ordance with Section
203.12 except that the minimum required compaction shall be at least 92 percent of
maximum density as determined by AASHTO T-180 Method C or D. B ackfill compaction shall be accomplished without disturbance or displac ement of the wall blocks. Sheepsfoot rollers will not be allowed. Whenever a co mpaction test fails, no additional backfill shall be placed over the area until the lif t is recompacted and a passing test achieved. The moisture content of the backfill material prior to and duri ng compaction shall be uniform throughout each layer. Backfill material shall have a placement moisture content less than or equal to the optimum moisture content. Ba ckfill material with a placement moisture content in excess of the optimum moisture co ntent shall be 6-187 removed and reworked until the moisture content is uniform and acceptable throughout the entire lift. The optimum moisture content shall be determi ned in accordance with AASHTO T-180, Method C or D. At the end of the day’s operation s, the Contractor shall shape the last level of backfill so as to direct runoff o f 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 p revent loss of granular material between blocks. Compliance with the gradation require ments shall be the responsibility of the Contractor, who shall furnish a copy of t he backfill test results prior to construction. If crushed stone, 3/4-inch is used betw een blocks, no geotextile is required behind vertical joints.
672.07 Method of Measurement Precast Concrete Block Gravity Wall will be
measured by the square foot of fr ont surface not to exceed the dimensions shown on the Contract Plans unless authori zed by the Resident. Vertical and horizontal dimensions will be from the edges of the blocks. No field measurements for com putations will be made unless the Resident specifies, in writing, a change in the limi ts indicated on the Plans.
672.08 Basis of Payment The accepted quantity of Precast Conc rete Block Gravity
Wall will be paid for at the contract unit price per square foo t complete in place. Payment shall be full compensation for furnishing geotechnical design a s required, all labor, equipment and materials including all precast concrete units, h ardware, joint fillers, geosynthetics, reinforcing steel, drainage pipe, backfill mater ials and technical field representative. Excavation, foundation material and backfill ma terial 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 Gra vity Wall. There will be no allowance for excavating and backfilling for the Precast Concrete Block Gravity Wall beyond the limits shown on the approved subm itted plans, except for excavation required to remove unsuitable subsoil in preparation for the foundation. Payment for excavating unsuitable subsoil shall be full compens ation 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 20 3. Payment will be made under: P a y I t e m P a y U n i t
672.10 Precast Concrete Block Gravity Wall Square Foot
6-188 SECTION 673 - WET CAST SMALL LANDSCAPE BLOCK WALL
673.01 Description The work under this item shall consist of t he design, fabrication,
furnishing and construction of a Wet Cast Small Landscape Block Wall in accordance with these specifications and in conformance with the lines and grad es shown on the Plans, or established by the Resident. The Wet Cast Small Landscape Bloc k Wall shall consist of blocks made of Structural Precast concrete made from Portland c ement, water, chemical admixtures, and aggregates, supported on concrete leveling pads , and if required, geosynthetic reinforced backfill. The concrete blocks used in this system should have dimensions 18 inches or less wide and 6.125 inches high at the face, with a pattern to simulate small stones or cobbles. Included in the scope of the wall construction are ; geotechnical design of any wall with an exposed height greater than 2.5 feet or as specified on the Plans, all grading necessary for wall construction, compaction of the wall foundat ion soil, backfill, piped drainage, construction of leveling pads, and concrete wall unit installation. The top of the upper row of concrete wall units shall be at or above the top o f the face elevation shown on the Plans.
673.02 Quality Assurance The wall system shall be one of the approved
combinations of facing block and soil reinforcement systems not ed in the Plans or on the Department’s Qualified Products List (QPL). Alternate wall sys tems 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 c oncerning proper installation procedures. The technical representative shall be on-site duri ng initial stages of installation and thereafter shall remain available for consultation as neces sary for the Contractor or as required by the Resident.
673.03 Materials Materials for walls shall meet the requireme nts of the following
sections of Division 700: G r a v e l B o r r o w 703.20 C r u s h e d S t o n e , ¾ - I n c h 703.13 U n d e r d r a i n P i p e 706.06 or 706.09 Reinforcing Steel 709.01 Structural Precast Concrete Units 712.061 Reinforcement Geotextile 722.01 Drainage Geosynthetic 722.02 The Contractor is cautioned that all of the materials listed a re not required for every Wet Cast Small Landscape Block Wall. The Contractor shall furn ish the Resident a
Source: Maine Standard Specifications for Road and Bridge Construction, 2020 Edition. Pages 656–658 of 817.