6-199 The Prefabricated Concrete Modular Gravity Wall design shall f ollow the general dimensions of the wall envel ope shown in the contract plans. T he top of the leveling pad shall be located at or below the theoretical leveling pad eleva tion. The minimum wall embedment shall be at or below the elevation shown on the plans . The top of the face panels shall be at or above the top of the panel elevation show n on the plans. The Contractor shall require the design-supplier to supply 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. The work done by this representative is incidental.
674.02 Materials Materials shall meet the requirements of the following subsections of
Division 700 — Materials:
G r a v e l B o r r o w 703.20 Preformed Expansion Joint Material 705.01 Reinforcing Steel 709.01 Structural Pre-cast Concrete Units 712.061 Drainage Geotextile 722.02 The Contractor is cautioned that all of the materials listed ar e not required for every Prefabricated Concrete Modular Gravity Wall. The Contractor sh all furnish the Resident a Certificate of Compliance certif ying that the applicable materi als comply with this section of the specifications. Modify requirements in 712.061 as follows: Concrete Units: Concrete shall be Class P. The concrete shall contain a minimu m of 5.5 gallons per cubic yard of calcium nitrite solution. The minimum permeability of the concrete as indicated by Surfac e Resistivity shall be 17 KOhm-cm. Defects Defects which may cause rejection of precast units in clude, but are not limited to, the following: Any discontinuity (crack, rock pocke t, etc.) of the concrete wh ich could allow moisture to reach the reinforcing steel. Rock pockets or honeycomb over 6 square inches in area or over 1 inch deep. Edge or corner breakage exceeding 12 inches in length or 1 inch in depth. Any other defect that clearly and substantially impacts the qua lity, durability, or maintainability of the structure, as determined by the Fabricat ion Engineer. Repair honeycombing, ragged or irregular edges and other non-st ructural or cosmetic defects using a patching material from the Department Qualified Products List (QPL). The repair, including preparation of the repair area, mixing and ap plication and curing of the patching material, shall be in accordance with the manufacturer 's product data sheet. 6-200 Corners that are not exposed in the final product may be ground smooth with no further repair necessary if the depth of the defect does not exceed 1/2 inch. Remove form ties and other hardware to a depth of not less than 1 inch from the face of the concrete and patch the holes using a patching material from the Department QPL. Repair structural defects only w ith the approval of the Fabrica tion Engineer. Submit a nonconformance report (NCR) to the Fabrication Engineer with a proposed repair procedure. Do not perform struct ural repairs without an NCR tha t has been reviewed by the Fabrication Engineer. Structural defects include, but are not b e limited to, exposed reinforcing steel or strand, cracks in bearing areas, through c racks and cracks 0.013 inch in width that extend more than 12 inches in length in any directio n. Give the QAI adequate notice prior to beginning any structural repairs. Tolerances In addition to meeting the requirements of 712.061 , all prefabricated units shall be manufactured with the following tolerances. All units not meeting the listed tolerances will be rejected. 1.All dimensions shall be within (edge to edge of concrete) ±3/ 16 in. 2.Squareness The length differences between the two diagonals shall not exceed 5/16 in. 3.Surface Tolerances For steel formed surfaces, and other for med surface, any surface defects in excess of 0.08 in. in 4 ft will be rejected. For textured surfaces, any surface defects in excess of 5/16 in. in 5 ft shall be reje cted. Joint Filler (where applicable) Joints shall be filled with material approved by the Resident and supplied by the approved Prefabricated Concrete Mo dular Gravity Wall supplier. 4 in. wide, by 0.5 in. preformed expansion joint fil ler shall be placed in all horizontal joints between faci ng units. In all vertical joints , a space of 0.25 in. shall be provided. All Preformed Expansion Joint Material shall meet th e requirements of subsection 502.03. Woven Drainage Geotextile Woven drainage geotextile 12 in. wi de shall be bonded with an approved adhesive compound to the back face, covering a ll joints between units, including joints abutting concrete structures. Geotextile seam laps shall be 6 in., minimum. The fabric shall be secured to the concrete with an adhesive sa tisfactory to the Resident. Dimensions may be modified per the wall supplier’s recommendati ons, with written approval of the Resident. Concrete Shear Keys (where applicable) Shear keys shall have a thickness at least equal to the pre-cast concrete stem. Concrete Leveling Pad Cast-in-place concrete shall be Fill Co ncrete conforming to the requirements of Section 502 Structural Concrete. Leveling pad shall have a minimum thickness of 4 inches. The horizontal tolerance on the surface of the pad shall be 0.25 in. in 10 ft. Dimensions may be modified per the wall supplier’s reco mmendations, with written approval of the Resident. 6-201 Backfill and Bedding Material Bedding and backfill material p laced behind and within the reinforced concrete modules shall be gravel borrow c onforming to the requirements of Subsection 703.20. The backfill materials shal l conform to the following additional requirements: backfill and bedding material shall o nly contain particles that will pass the 3-inch square mesh sieve and the plasticity index (PI) as determined by AASHTO T90 shall not exceed 6. Compliance with the gradation and plas ticity requirements shall be the responsibility of the Contractor, who shall furnish a copy of the backfill test results prior to construction. Materials Certificate Letter The Contractor, or the supplier as his agent, shall furnish the Resident a Materials Certificate Letter for the above mater ials, including the backfill material, in accordance with Section 700 of the Standard Specif ications. A copy of all test results performed by the Contractor or his supplier necessary t o assure contract compliance shall also be furnished to the Resident. Acceptance will be ba sed upon the materials Certificate Letter, accompanying test reports, and visual inspe ction by the Resident.
674.03 Design Requirements The Pre fabricated Concrete Modular Gravity Wall shall be
designed and sealed by a Professional Engineer licensed in the State of Maine. The design to be performed by the wall system supplier shall be in accorda nce with AASHTO LRFD Bridge Design Specifications, current edition, except as requir ed herein. Design calculations that consist of computer generated output shall be supplemented with at least one hand calculation and graphic demonstrating the design methodology us ed. Design calculations shall provide thorough documentation of the sources of equation s used and material properties. The design by the wall system supplier shall cons ider the stability of the wall as outlined below:
A.Stability Analyses Wall systems shall be investigated for be aring resistance failure, lateral sliding and overturning failure in accordance with LRFD Pullout resistance shall be investigated at every module level using nominal resistances and forces in accordance with Paragraph C., below. The ratio of the sum of the nominal resistances to the sum of the nominal forces sha ll be greater than, or equal to, 1.5. Traffic impact loads transmitted to the wall through guardrail posts shall be calculated and applied in compliance with LRFD with the except ion that Article
11.10.10 2 is modified such that the upper 3.5 ft of concrete m odular units shall be
designed for an additional horizontal load of γP H1, where γP H1=300 lbs per linear ft of wall.
B.Backfill and Wall Unit Soil Parameters For overturning and sliding stability calculations, earth pressure shall be assumed acting on a verti cal plane rising from the back of the lowest wall stem. For overturning, the unit we ight of the backfill within the wall units shall be limited to 96 pcf. For sliding analyses, the unit weight 6-202 of the backfill within the wall units can be assumed to be 120 pcf. Both analyses may assume a friction angle of 34 degrees for backfill within t he wall units. These unit weights and friction angles are based on a wall unit backfill meeting the requirements for select backfill in this specification. Backfi ll behind the wall units shall be assumed to have a unit weight of 120 pcf and a frictio n angle of 30 degrees. The friction angle of the foundation soils shall be assumed to be 30 degrees unless otherwise noted on the plans. Internal Stability Internal stability of the wall shall be dem onstrated using accepted methods, such as Elias’ Method, 1991. Shear keys shall not con tribute to pullout resistance. Soil-to-soil frictional component along stem shall not contribute to pullout resistance. The failure plane used to determine pullou t resistance shall be found by the Rankine theory only for vertical walls with level backfills. When walls are battered or with backslopes greater than 0 degrees are cons idered, the angle of the failure plane shall be per Jumikus Method. For computation of pullout force, the width of the backface of each unit shall be no greater than 4.5 ft. A unit weight of the soil inside the units shall be assumed no greater than 120 pcf when computing pullout. Coulomb theory may be used.
D.Safety against Structural Failure Prefabricated units sha ll be designed for all strength and reinforcement requirements in accordance with LRFD .
E.External loads which affect the internal stability such as t hose applied through piling, bridge footings, traffic, slope surcharge, hydrostatic and seis mic loads shall be accounted for in the design.
F.Stability During Construction Stability during construction shall be considered during design, and shall meet the re quirements of the AASHTO LR FD Bridge Design Specifications, Extreme Limit State.
G.Hydrostatic forces Unless specified otherwise, when a desig n high water surface is shown on the plans at the face of t he wall, the design stresses calculated from that elevation to the bottom of wall must include a 3 ft minimum dif ferential head of saturated backfill. In addition, the buoyant weight of saturat ed soil shall be used in the calculation of pullout resistance.
H.Not more than two vertically consecutive units shall have th e same stem length, or the same unit depth. Walls with units with extended height cur bs shall be designed for the added earth pressure. A separate computation for pullo ut of each unit with extended height curbs, or exte nded height coping, shall be prep ared and submitted in the design package described above.
674.04 Submittals. The Contractor shall supply wall design com putations, wall details,
dimensions, quantities, and cross sections necessary to constru ct the wall. Thirty (30) days prior to beginning construction of the wall, the design computa tions and wall details shall be 6-203 submitted to the Resident for review by the Department. The fu lly detailed plans shall be prepared in conformance with Subsection 105.7 of the Standard S pecifications and shall include, but not be limited to the following items:
A.A plan and elevation sheet or sheets for each wall, contain ing the following: elevations at the top of leveling pads, the distance along the face of the wall to all steps in the leveling pads, the designa tion as to the type of prefabr icated module, the distance along the face of the wall to whe re changes in length of the un its occur, the location of the original and final ground line. B. All details, including reinforcing bar bending details, sha ll be provided. Bar bending details shall be in accordance with Department standard s.
C.All details for foundations and leveling pads, including de tails for steps in the leveling pads shall be provided. The maximum calculated factor ed bearing pressure under the Prefabricated Concrete Modular Gravity wall shall be indicated on the wall plans. D. All prefabricated modules shall be detailed. The details s hall show all dimensions necessary to construct the element, and all reinforc ing steel in the element.
E.The wall plans shall be prepared and stamped by a Professio nal Engineer.
F.Four weeks prior to the beginning of construction, the cont ractor shall supply the Resident with two copies of the design-supplier’s Installation Manual. In addition, the Contractor shall have two copi es of the Installation Manual on the project site.
674.05 Construction Requirements Excavation The excavation and use as fill or disposal of all excavated material shall
meet the requirements of Section 203 -- Excavation and Embankme nt, except as modified herein. Foundation The area upon which the modular gravity wall struc ture is to rest, and within the limits shown on the submitted plans, shall be graded for a width equal to, or exceeding, the length of the module. Prior to wall and levelin g pad construction, this foundation material shall be compacted to at least 95 percent o f maximum laboratory dry density, determined using AASHTO T180, Method C or D. Frozen s oils and soils unsuitable or incapable of sustaining the required compaction, shall be removed and replaced. A concrete leveling pad shall Leveling pad shall have a minimu m thickness of 4 inches and shall be constructed as indicated on the plans. 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 Resident. Allowable elevation tolerances are + 0.01 ft and -0.02 ft from the design elevations. Leveling pads which do not meet this requir ement shall be repaired or
Source: Maine Standard Specifications for Road and Bridge Construction, 2020 Edition. Pages 669–673 of 817.