6-230 Forty-five days prior to beginni ng construction of the wall, th e design computations shall be submitted to the Resident for review by the Geotechnic al Engineer. Any additional design or costs arising as a result of rejection of a wall desi gn 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 dem onstrating the design methodology used. Design calculations shall provide thorough d ocumentation of the sources of equations used and material properties. The design b y the wall system supplier shall consider the stability of the wall as outlined below and in the Contract Documents:
A.Failure Plane The theoretical failure plane within the rein forced soil mass shall be determined in accordance with LRFD Article 11 and be analyzed s o that the soil stabilizing components extend sufficiently beyond the failure plane within the reinforced soil mass to stabilize the material.
B.External Loads External loads which affect the internal an d external stability such as those applied through traffic loadings, impact on traffic barri er posts, slope surcharge, hydrostatic, and seismic loads shall be accounted for in the de sign. Traffic surcharge and traffic impact loads shall be calculated and applied in complia nce with LRFD Section 11.
C.External Stability Loads and load combinations selected fo r design shall be consistent with LRFD. Application of load factors shall be tak en 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.
D.Internal Stability Evaluation of reinforcement pullout, reinforcement rupture and reinforcement/block connection pullout or rupture shall be cons istent with LRFD Section 11, and checked at each level. Loads, load combinations and lo ad 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 us ing the Simplified Method approach. Calculations for factored stresses and resistances s hall be based upon assumed conditions at the end of the design life.
a.Geosynthetic Reinforcement Design Tensile Resistance The no minal long term reinforcement design strength (T al) shall be determined by reducing T ult by reduction factors (RF) in accordance with the documents referenced above. The designer shall procure and use the manufacturers tested and certified geosynth etic reinforcement reduction factors for creep (RF CR), durability (RF D), and installation damage (RF ID) to determine T al. In absence of manufacturers tested and certified reduction f actors, a combined default reduction factor RF = 7 shall be used in accor dance with the referenced documents. For RF ID, the installation damage reduction factor shall be checked in accordance with LRFD and FHWA-NHI—09-087.
b.Reinforcement/Facing Connection Design Strength The nominal long-term connection strength between the geosynthetic reinforcement and the concrete blocks 6-231 shall be checked in accordance with LRFD and FHWA-NHI-10-024 an d FHWA –NHI -10-025.
c.Reinforcement Pullout The pullout resistance factor, (F*) , and scale effect correction factor (α) used in pullout design, shall be determin ed from project specific pullout tests using the proposed geosynthetic in the specified project backfill material or equivalent soil. The pullout resistance factors shall be det ermined in accordance with LRFD and FHWA-NHI--10- 024 and FHWA –NHI -10-025. In the a bsence of test data, empirical relationships may be used to determine the pullout resistance factors, any empirical relati onships used in design shall be re ferenced in the design calculations.
E.Backfill and Foundation Soils Parameters The friction angl e of the backfill used in the 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 rand om backfill shall be assumed to be 30 degrees unless otherwise shown on the Plans.
F.Reinforcement Length The soil reinforcement shall be the s ame length from the bottom to the top of each wall section. The reinforcement leng th defining the width of the entire reinforced soil mass may vary with wall height. The minimum length of the soil reinforcement shall be 8 ft, but shall not be less tha n 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 differen ce between the top of the levelin g footing and the elevation at which the failure surface, as described above, int ercepts the ground surface supported by the wall.
G.Bearing Resistance The factored bearing pressures under th e Precast Aggregate- filled Concrete Block Gravity Wall shall be clearly indicated o n the Shop Drawings. Walls shall be dimensioned so that the factored bearing resista nce of the foundation soils, as noted on the Plans, is not exceeded.
H.Facing Stability Stability calculations for the concrete f acing blocks shall be in accordance with LRFD, and shall include an evaluation of the ma ximum vertical spacing between reinforcement layers.
I.Stability During Construction Walls shall be designed to resist failure by instability of temporary construction slope. P assive pressure in front of the wall mass shall be assumed to be zero for design purposes.
J.Design Life The wall design life shall be a minimum of 75 years.
K.Depth of Embedment The dept h of embedment for frost protec tion and stability shall be at or below the elevation shown on the Plans and the a pproved Shop Drawings. 6-232
L.Drainage System Piped drainage shall be designed to collec t and dispose of water from the base of the reinforced soil zone and backfill soil. T his shall outlet into surrounding drainage systems or ditches.
681.05 Submittals The Contractor shall supply wall design com putations, wall
details, dimensions, quantities, and cross sections necessary t o 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 provi ded. Spreadsheet calculations alone are not acceptable. Forty-five (45) days prior t o beginning construction of the wal l, four (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 sub mitted at the same time, including aggregate source, current gradation, aggregate qualit y 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 si ze distribution curve, moisture- density relationship curve, and pH test results required for re inforced backfill only. If geotechnical design is required, the fully detailed Plans sh all be prepared in conformance with Section 105 and shall include, but not be limi ted to the following items:
A.A plan and elevation sheet or sheets for each wall, containi ng 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 location of the original and fi nal ground line.
B.All details for foundations and leveling pads, including det ails for steps in the leveling pads, as well as allowable and actual maximum bearing pressures shall be provided.
C.Details for the barriers, posts, curbs and facing as require d by the project conditions.
D.Design computations prepared and sealed by a licensed Profes sional Engineer.
E.Prior to the beginning of cons truction, the contractor shall supply the Resident with two copies of the design-supplier’s Installation Manual. In ad dition, the Contractor shall have two copies of the Installation Manual on the project site.
681.06 Construction Requirements The Precast Aggregate-Filled Concrete Block
Gravity Wall shall have the following construction requirements :
A.Excavation. The excavation and use as fill or disposal of a ll excavated material shall meet the requirements of Section 203 -- Excavation and Embankme nt, except as modified herein. 6-233
B.Foundation. The area upon which the prefabricated, aggregat e-filled concrete block gravity wall structure is to rest, and within the limits shown on the submitted Plans, shall be graded for a width e qual to, or exceeding, the length of the blocks. Prior to wall and leveling pad construction, this foundation material sh all be compacted to at least 95 percent of maximum la boratory dry density (AASHTO T-18 0 Method C or D). Frozen and unsuitable soil shall be removed and replaced w ith gravel borrow compacted to 95 percent of AASHTO T-180, or as shown on the Pla ns. A concrete leveling pad shall be constructed a minimum of 6 inc hes beyond the front and back of the concrete wall units, or as indicated on the Pla ns. 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 d esign elevations as shown on the Plans, or as required by the wall supplier upon wr itten approval of the Geotechnical Engineer. The allowable elevation tolerances from the design elevations a re +0.01 ft and -0.02 ft. Leveling pads which do not meet this requirement shall be repaired 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 their own risk.
C.Method and Equipment. Prior to e rection of the wall, the Co ntractor shall furnish the Resident with detailed information concerning the proposed cons truction method and equipment to be used. The erection procedure shall be in accor dance with the manufacturer’s instructions. Any units that are damaged due to handling will be replaced at the Contractor’s expense.
D.Installation of Concrete Wall Units. A field representative from the wall system being used shall be available, as needed, during the erection o f the wall. The services of the representative shall be at no additional cost to the pro ject. The contractor shall place the first course of wall units direc tly on the leveling pad and check for level and alignment. Adjacent units should be in contact. The prefabricated concrete wall units shall be installed to a toler ance of plus or minus 3/4 inch in 10 ft in vertical and horizontal alignment. Fill all voids between and within the wall units with drainage stone as described in this specification. The drainage stone fill shall extend a min imum of 6 in behind the tails of the wall units unless a geotextile filter is placed ov er the inside joint at the back of adjacent wall units. If used, the drainage geotextile shall conform to the requirements of Section 722.02.
E.Backfill Placement. Backfill pl acement shall closely follow the erection of each row of prefabricated wall units. The maximum lift thickness shall be 8 inches loose. The
Source: Maine Standard Specifications for Road and Bridge Construction, 2020 Edition. Pages 700–703 of 817.