SECTION 809 - RETAINING WALL SYSTEMS
809.01 Description. This work shall consist of designing and installing one of the
retaining wall systems described herein in accordance with th e lines, grades and dimensions shown in the plans and specifications.
809.01.1 General. Retaining wall systems shall comply with all material, fabrication and
construction requirements found in the Standard Specifications and the plans. The submitted retaining wall system shall be as sh own in the plans or consist of one of the following three types: Conventional Cantilevered Gravity Wall, Mechanically Stabilized Earth Wall (MSEW), or Precast Gravity Wall. All costs asso ciated with the design and construction of the wall system selected by the Contractor shall be included in the bid price for the wall. The Contractor may select different wall types for different sites, as provided for on the plans. In the event a MSEW System is chosen, the wall system supplier shall have submitted their system to the Highway Innovative Technology Evaluation Center (HITEC) for review and shall have had a formal evaluation completed for all components of the wall system. The wall system is considered to be the wall facing and the associated geosynthetic or steel soil reinforcement. Three copies of HITEC’s fi nal evaluation report for the chosen MSEW System shall be included with the initial design submittal. The time required for preparation and review of wall shop drawings shall be charged to the allowable contract time. No additional co mpensation will be made for any additional material, equipment, or other items foun d necessary to comply with the project specifications as a result of review by the De partment. All submittals shall be submitted to the Bridge Engineer for approval prior to construction. The retaining wall system shall follow the lines, grades, and location as shown in the plans. In the event that plan dimensions are revised due to field co nditions or other reasons, the Contractor shall be responsible for revisi ng the wall plans, design calculations, and summary of quantities.
809.01.2 Submittals.
809.01.2 1--Initial Design Submittal. The initial design submittal shall include three sets
of wall plans and three sets of design calculations and notes. The wall plans and design calculations and notes shall clearly state the wall type chosen. The wall plans and design calculations will be returned to the Contractor within thirty (30) calendar days of receipt. All final design calculations and plans shall be prepared, stamped and signed by a Professional Engineer licensed to practice in the State of Mississippi. The calculations shall include, but not be lim ited to, those items listed belo w. The designer/supplier furnishing the plans and calculations for the wall system proposed shall be responsible for the internal and external stability of the wall system. The drawings shall include all details, dimensions, quantities and cross-sections necessary to construct the wall. Prints of the original cross sections will be available to purchase with plans. The wall system plans shall include, but not be limited to, the following items: (a) A plan and elevation sheet(s) for each wall shall contain the following:
1.The elevation view of the wall that indi cates the elevation at the top of the wall, at all horizontal and vertical break points, and at least every 50 feet along the wall, elevations at the top of leveling pads and footings, and the original and final ground line. 2. The plan view of the wall that show s the offset from the construction centerline to the face of the wall at all changes in horizontal alignment. Also included should be the limits of the so il reinforcement, if required, and any drainage structures or pipes lying behind or extending through or under the wall. 3. General notes required for construction of the wall.
4.All horizontal and vertical curve data affecting the wall shall be included.
5.A list of all required materials and the required quantity of each shall be provided on the elevation sheet of each wall.
b.All bar bending details shall be included.
c.All details for foundations and leveling pads shall be shown including steps in the footings or leveling pads. Foundations and leveling pads shall have a minimum cover of two feet.
d.All panels, modular blocks, coping, and lagging shall be detailed. The details shall include all dimensions necessary to construct the element.
e.Details should be included for the walls around any existing drainage facilities.
f.All details concerning the appearance of the wall face shall be included. Three sets of wall plans shall be submitted w ith the initial submittal. The plans that are submitted with the initial design submittal shall be prepared on sta ndard 24-inch by 36- inch sheets. Each sh eet shall have a title block in the lower right hand corner. The title block shall include the sheet number of the drawing, type of wall designated, the project number, and the Contractor. The initial design submittal shall include a set of design calculations and notes for the wall(s). Three sets of design calculations and notes shall be submitted. The design calculations and notes shall contain the project number, type of wall designated, date of preparation, and the name of the designer. The package shall have a clear index outlining the design notes and shall include an explanation of the design procedure, explanation of any symbols, and technical documentation of any computer programs used. The design calculations shall clearly state the factors of safety for sliding, pullout, and overturning. In addition, the bearing pressures beneath the wall footing used in the calculations shall be noted.
809.01.2 2--Final Plan Submittal. All final construction plans shall be submitted on 24-
inch by 36-inch reproducible mylar sheets. In addition, the plans shall be accompanied by either flash drive or compact disk containing the plans in Tagged Image File Format (TIFF) for archive purposes. The final construction plans shall reflect all changes made on the plans submitted for the design submittal.
809.01.3 Design Criteria. The design for any proposed wall shall consider the internal
and external stability of the wall including the bearing pressure, overturning and sliding. The design shall consider lateral earth pressures, including any applicable surcharge loads. In addition, the following general guidelines shall be followed.
a.The chosen wall system shall be designed in accordance with the current version of the AASHTO Standard Specifications for Highway Bridges.
b.Prior to the design of the wall system, the designer/supplier shall be required to perform an in-house geotechnical revi ew of the available geotechnical information with the Geotechnical Branch of Materials Division. The purpose of the geotechnical review will be to obtain the pertinent design information relating to global stability as well as answer questions concerning any of the geotechnical information provided in the plans. The final design shall take into account any global stability issues that are brought forth by the geotechnical review. A generic analysis for global stability will be conduc ted by the Department and the results provided to the Retaining Wall System Designer at the geotechnical review. Any allowed changes to the wall lines and grades or stabilized soil mass that affect the global stability calculations will require the wall supplier to include a global stability analysis with the final design . The Geotechnical Engineer may be contacted to schedule an appointment. (c) The minimum factors of safety to be used in design are as listed below.
1.External Stability Sliding ............................................ 1.5 Overturning .................................... 2.0 Eccentricity, e, at Base ................... <L/6 for MSEW, where L is the length of the reinforced soil mass Bearing Capacity ............................ 2.5 Temporary Slopes .......................... 1.2 Global Stability .............................. 1.4, as noted above
2.Internal Stability Pullout Resistance for MSEW ........ 1.5
d.The wall design shall take into account all appurtenances behind, in front of, under, mounted upon, or passing through the wall and supply the appropriate construction details. These items should be accounted for in the internal and external stability calculations.
e.Leveling pads, foundations, or footings shall have a minimum cover of two feet. For design purposes, passive pressure in front of the wall shall be assumed to be zero. (f) The front face of th e wall may be battered into the slope to improve stability as long as this does not interfere with other project appurtenances such as drainage features or right-of-way. (g) The wall design shall provide positive drainage behind the wall to assure that the backfill material remains in a drained condition.
h.Where geogrid is to be used for MSEW st ructures as the soil reinforcement, the following design criteria should be followed:
1.The allowable tensile load (T A) shall be calculated using the following equation and be based on a 100 year design life. The variables used in the equation shall be as allowed by AASHTO or as demonstrated with supporting data in the HITEC evaluation. Allowable Design Strength of Geogrid: TA ൌ TCR FSID x FSD x FSUN Where: T A = Maximum Design Strength T CR = Creep Limited Strength FS ID = Factor of Safety For Installation Damage FS D = Factor of Sa fety For Durability FS UN = Factor of Safety For Uncertainties
2.The maximum design tensile load of the geogrid shall not exceed the laboratory tested ultimate strength of the geogrid/facing unit connection divided by a factor of safety of 1. 5. The connection strength testing and computation procedures shall be in accordance with AASHTO and demonstrated in the HITEC evaluation.
809.02 Materials. Material requirements will vary depending on the type of wall system
chosen. Specific material requirements for each wall type are given below.
809.02.1 Conventional Cantilevered Gravity Wall. Concrete for conventional
cantilevered gravity walls shall meet the requirements for Class “AA” concrete as set forth in Section 804 of the Standard Specifications . Reinforcing steel shall conform to the requirements set forth in Subsection 711.02 of the Standard Specifications. Driven Piles shall meet the requirements set forth in Sections 803 and 804. Unless otherwise indicated on the plans, th e exposed concrete surfaces of the wall shall have a Class “2” finish as defined in Section 804.
809.02.2 Mechanically Stabilized Earth Walls (MSEW). Materials for Mechanically
Stabilized Earth Walls shall meet the following minimum standards.
809.02.2 1--Precast Con crete Facing Panels. Precast concrete facing panels shall be
fabricated in accordance with Section 804 with the following exceptions and additions.
a.Concrete for the precast concrete facing panels shall conform to Class “AA” concrete.
b.In addition to the requirements of Section 804, the units shall be fully supported until the concrete reaches a minimum comp ressive strength of 1,000 psi. The units can be shipped after reaching a minimum compressive strength of 3,000 psi. At the option of the Contractor, the units may be installed after the concrete reaches a minimum compressive strength of 3,400 psi.
c.Unless otherwise indicated on the plans, the concrete surface for the front face shall have a Class “1” finish as defined in Section 804 of the Specifications and the rear face a uniformed surface finish. The rear face of the panel shall be screeded to eliminate open pockets of aggregate and surface distortions in excess of 1/4 inch. The panels shall be cast on a flat area. The soil reinforcing strips or other galvanized attachment devices used to attach the precast concrete facing panel to the soil reinforcement shall not contact or be attached to the face panel reinforcement steel.
d.The date of manufacture, the production lot number, and the piece mark shall be clearly scribed on an unexposed face of each panel.
e.All units shall be handled, stored, and shipped in such a manner as to eliminate the dangers of chipping, discoloration, cracks, fractures, and excessive bending stresses. Panels in storage shall be supported on firm blocking to protect the panel connection devices and the exposed exterior finish.
f.All units shall be manufactured within the following tolerances:
1.Panel Dimensions – Position of the panel connection devices shall be within one inch. All other dimensions shall be within 3/16 inches.
2.Panel Squareness – Squareness shall be determined by the difference between the two diagonals and shall not exceed 1/2 inches.
3.Panel Surface Finish – Surface defects on smooth formed surfaces measured over a length of five feet shall not exceed 1/8 inch. Surface defects on the textured-finish surfaces measured over a length of five feet shall not exceed 5/16 inch.
g.Section 804 of the Specifications will be modified as follows:
1.Acceptance of concrete panels with respect to compressive strength will be determined on the basis of production lots. A production lot is defined as a group of panels that will be represented by a single compressive strength sample and will consist of either 40 panels or a single day’s production, whichever is less.
2.During the production of the concrete panels, the manufacturer will randomly sample the concrete in accordance with AASHTO T 141. A single compressive strength sample, consisting of a minimum of four cylinders, will be randomly selected for every production lot.
3.Compression tests shall be made on standard 6-inch by 12-inch test specimen prepared in accordance with AASHTO T 23. Compressive strength testing shall be conducted in accordance with AASHTO T 22.
4.Air content will be performed in accordance with AASHTO T 152 or AASHTO T 196. Air content samples will be taken at the beginning of each day’s production and at the same time as compressive samples are taken to insure compliance with the specifications. The slump will be determined at the beginning of each day’s production and at the same time as the compressive samples are taken.
5.For every compressive strength sample, a minimum of two cylinders shall be cured in accordance with AASHTO T 23 and tested at 28 days. The average compressive strength of these cylinders, when tested in accordance with AASHTO T 22, will provide a compressive strength test result that will determine the compressive strength of the production lot.
6.If the Contractor wishes to remove forms or ship the panels prior to 28 days, a minimum of two additional cylinders shall be cured in the same manner as the panels. The average compressive strength of these cylinders when tested in accordance with AASHTO T 22 will determine whether the forms can be removed or the panels shipped.
7.Acceptance of a production lot will be made if the compressive strength test result is greater than or equal to 4,000 psi. If the compressive strength test result is less than 4,000 psi, then the acceptance of the production lot will be based on its meeting the following acceptance criteria in its entirety:
i.90% of the compressive strength test results for the overall production exceeds 4,150 psi (ii) The average of any six consecutive compressive strength test results exceeds 4,250 psi (iii) No individual compressive strength test result falls below 3,600 psi
8.Units shall be rejected because of failure to meet any or all of the requirements specified above. In addition, any or all of the following defects shall be sufficient cause for rejection.
i.Defects that indicate imperfect molding (ii) Defects indicating honeycombed or open texture concrete (iii) Cracked or severely chipped panels (iv) Color variation on from face of panel due to excess form oil or other reasons
809.02.2 2--Modular Block.
809.02.2 2.1--General and Architectural Requirements for Modular Block Units.
Unless otherwise specified in the plans, general and architectural requirements of modular block units shall be as follows:
a.Face Color – Gray
b.Face Finish – sculptured rock face in angular multi-planer configuration
c.Bond Configuration – running with bonds nominally located at the midpoint of vertically adjacent units, in both straight and curved alignments Exposed surfaces of units shall be free of chips, cracks or other imperfections when viewed from a distance of 10 feet under diffused lighting. Modular block units shall be manufactured in accordance with ASTM C 90 and C 140.
809.02.2 2.2--Material Requirements for Modular Block Units. Material requirements
shall be as follows:
a.Cement: Materials shall conform to the following applicable specifications and requirements:
1.Hydraulic Cement: AASHTO M 85
2.Modified Hydraulic Cement: Hydraulic cement conforming to AASHTO M 85, modified as follows: Limestone: calcium carbonate, with a minimum 85% content, may be added to the cement, provided these requirements of AASHTO M 85 as modified are met:
i.Limitation on insoluble residue, percent ............................ 1.5 ii) Limitation on air content of mortar, maximum volume percent ................................................... 22 iii) Limitations of loss of ignition, percent .................................. 7
3.Blended Cements: AASHTO M 295
4.Pozzolans: AASHTO M 295
5.Blast Furnace Slag Cement: AASHTO M 302
b.Aggregates: Aggregates shall conform to the following specifications, as applicable.
1.Normal Mass Aggregates: ASTM C 33
2.Lightweight Aggregates: ASTM C 331
c.Other Constituents: Air entraining agents, coloring pigments, integral water repellents, finely ground silica, and other constituents shall be previously established as suitable for use in modular block retaining wall units and shall conform to applicable AASHTO or ASTM standards or shall be shown by test or experience to not be detrimental to the durability of the modular block units or any material customarily used in retaining wall construction.
809.02.2 2.3--Structural Requirements for Modular Block Units. Structural
requirements for modular block units shall be as follows:
a.28-day Compressive Strength: .............................................. 4,000 psi, minimum
b.Absorption:..................................................................... 6% maximum by weight
c.Maximum horizontal gap between erected units: ..................................... 0.5 inch
809.02.2 2.4--Base Leveling Pad Material. Base leveling pad material shall be
constructed using non-reinforced concrete and be a minimum of six inches thick by 12 inches wide. Class C concrete shall be used for the base leveling pad material unless otherwise noted in the plans.
809.02.2 2.5--Unit Infill or Drainage Fill. Unit Infill or Drainage Fill shall consist of
clean, free draining crushed stone or gravel with a one inch maximum particle size and shall meet the gradation listed below. Sieve Size Percent Passing 1” 100 3/4” 75 – 100 # 4 0 – 10 # 40 0 – 5 The Engineer shall approve the gradation of the Unit Infill or Drainage Fill. Pea gravel shall not be used. A minimum of 1.5 cubic foot of drainage fill shall be used for each square foot of wall face. Drainage fill may be placed between, behind, and within the cores of units to meet this requirement. In no case will a geotextile or geocomposite be used as a substitute for the drainage fill.
809.02.2 3--Reinforced Backfill for Mechanically Stabilized Earth Walls. Reinforced
backfill shall be free of debris and meet the following gradation requirements: Sieve Size Percent Passing 3/4” 75 – 100 # 4 20 – 100 # 40 0 – 60 # 200 0 – 15 The maximum aggregate size shall be limited to ¾-inch unless field tests have been performed to evaluate potential strength reductions to the geogrid design due to damage during construction. The plasticity index (P.I.) as determined by AASHTO T 90 shall not exceed 6. The backfill material, when compacted to 95% of Standard Proctor, AASHTO T 99, at optimum moisture content, shall exhibit an angle of internal friction of not less than 34° as determined by a standard direct shear test, AASHTO T 236, or triaxial test, AASHTO T 296. In addition, the in-place density shall be within 5% of the assumed density used in wall design calculations. When metallic reinforcing strips are used, all backfill material shall conform to the following electrochemical requirements: Electrochemical Test Method, Properties Requirements AASHTO pH 5 – 10 T-289 Resistivity >3,000 ohms/cm minimum T-288 Chlorides 100 ppm maximum T-291 Sulfates 200 ppm maximum T-290 Organic Content 1% T-267 Contractor shall submit reinforced backfill sample and laboratory test results to the Engineer for approval prior to the use of any of the proposed reinforced backfill material.
809.02.2 3.1--Metallic Reinforcing and Attachment Devices. All reinforcing and
attachment devices shall be inspected to ensure they are true to size and free from defects that may impair their strength and durability, and shall meet the following conditions.
a.Reinforcing Strips – Reinforcing strips shall be hot rolled from bars to the required shape and dimensions. Their physical and mechanical properties shall conform to ASTM A709 Grade 50/50W or A 572, Grade 65 or equal. Galvanization shall conform to the minimum requirements set forth in AASHTO M 111.
b.Reinforcing Mesh – Reinforcing mesh shall be shop fabricated of cold drawn steel wire conforming to the minimum requirements of AASHTO M 32M/M and shall be welded into the finish mesh fabric in accordance with AASHTO M 55M/M. Galvanization shall be applied after the mesh is fabricated and conform to the minimum requirements of AASHTO M 111.
c.Tie Strips – The tie strips shall be shop fabricated of a hot rolled steel conforming to the minimum requirements of ASTM A 572, Grade 50 or equivalent. Galvanization shall conform to AASHTO M 111.
d.Fasteners – Fasteners shall consist of 1/2-inch diameter, hexagonal cap screw bolts and nuts that are galvanized and conform to the requirements of AASHTO M 164 or equivalent.
e.Connector Pins – Connector pins and mat bars for the MSEW system shall be fabricated from A36 steel and welded to the soil reinforcement mats as shown on the plans. Galvanization shall conform to AASHTO M 111.
809.02.2 4--Geogrid Reinforcement for Mechanically Stabilized Earth Walls.
809.02.2 4.1--General. A geogrid is defined as a geosynthetic formed by a regular
network of integrally connected elements with apertures greater than 0.25 inch to allow interlocking with surrounding soil, rock, earth and other surrounding materials to function primarily as reinforcement. The geogrid(s) to be utilized in the Modular Block Retaining Wall System shall be creep tested in accordance with ASTM D 5262. The long term design strength (TCR – Creep Limited Strength) shall be obtained from tests run on representative samples for no less than 10,000 hours. The long term design strength shall be defined as the load at which no more than 10% strain occurs over a 100-year design life. The geogrid shall be mildew resistant and inert to biological degradation and naturally encountered chemicals, alkalis and acids. The geogrid shall contain stabilizers and/or inhibitors, or a resistance finish or covering to make it resistant to deterioration from direct sunlight, ultraviolet rays, and heat.
809.02.2 4.2--Marking, Shipment and Storage. Each roll or container of geogrid shall
be visibly labeled with the name of the manufacturer, trade name of the product, lot number, and quantity of material. In addition, each roll or container shall be clearly tagged to show the type designation that corresponds to that required by the plans. During shipment and storage the geogrid shall be protected from direct sunlight, and temperatures above 120°F or below 0°F. The geogrid shall either be wrapped and maintained in a heavy duty protective covering or stored in a safe enclosed area to protect from damage during prolonged storage.
809.02.2 4.3--Manufacturer’s Certification. The Contractor shall furnish the Engineer
three copies of the manufacturer’s certified test reports indicating that the geogrid furnished conforms to the requirements of the specifications and is of the same composition as that originally approved by the Department.
809.02.2 4.4--Acceptance Sampling and Testing. Final acceptance of each shipment will
be based upon results of tests performed by the Department on verification samples submitted from the project, as compared to the manufacturer’s certified test reports. The Engineer will select one roll or container at random from each shipment for sampling. A sample extending full width of the randomly selected roll or container and being at least five (5) square yards in area will be obtained and submitted by the Engineer. The sample from each shipment shall be provided at no cost to the State.
809.02.3 Precast Gravity Walls. Materials for precast gravity walls shall meet the
following minimum requirements.
809.02.3 1--Foundation Preparation and Base Leveling Pad. The foundation bed for
the structure shall be graded as required before erection is started. Prior to wall construction the foundation shall be compacted as specified in Section 203 of the Standard Specifications. The base leveling pad may be either precast or cast-in-place, as directed by the wall supplier. The base leveling pad shall be constructed of Class “C” concrete unless otherwise specified and shall be cured until a compressive strength of 2,000 psi is attained before placement of wall modules. The completed surface shall be constructed in accordance with the lines and grades shown on the final wall plans. The base leveling pad shall be plane to within 1/8 inch in 10 feet.
809.02.3 2--Prefabricated Modular Units. Prefabricated modular units shall be designed
for developed earth pressures behind the wall and from pressures developed inside the modules. Prefabricated modular units shall be constructed in accordance with AASHTO Standard Specifications for Highway Bridges, Section 5. Concrete for prefabricated modular units shall have a minimum 28-day compressive strength of 5,000 psi. The prefabricated modular units shall not be shipped before attaining the required 5,000 psi compressive strength. Unless otherwise indicated on the plans, the concrete surface for the front face shall have a Class “1” finish as defined in Section 804. The manufacturing process shall be such that it produces uniform modular units and shall be subject to inspection by the Engineer prior to shipment. Precast units will be subject to rejection if they fail to conform to any of the specification requirements or fail to meet the following tolerances.
a.Dimensions not conforming to the following tolerances: Face of Panes, length or width ....................................................... ±3/16 inch Deviation From Square, diagonals across front face ........................ 5/16 inch
b.Honeycombed or open texture
c.Any damage which would prevent making a satisfactory joint.
d.The date of manufacture, lot number, and type of unit in accordance with the approved erection drawings shall be clearly marked on the inside face of each unit.
809.02.3 3--Backfill Material for Modular Units. Backfill material and the embankment
behind the wall shall be placed and compacted in accordance with Section 203 of the Standard Specifications. In the event the select backfill recommended by the wall supplier consists of open-graded rock with insufficient fines for conventional compaction controls, the material shall be compacted to a maximum practical density as determined by the Engineer. Otherwise, the select backfill material shall be placed and compacted to at least 95% density as determined by AASHTO T 99. When the modular backfill material consists of open-graded rock containing insufficient fines to fill the voids between particles in a compacted state, any exposed modular backfill material shall be covered by a layer of Type V nonwoven geotextile to prevent migration of fines into the modular backfill material. The geotextile shall overlap the module a minimum of six inches, except for the front cell.
809.03 Construction Requirements.
809.03.1 General Construction Requirements for All Wall Types.
809.03.1 1--Excavation. The Contractor shall excavate to the lines and grades shown on
the final wall plans. The Contractor shall be careful not to disturb the embankment and foundation materials beyond the lines shown. The Engineer will inspect the excavation and give approval prior to placement of the base leveling pad. Soils that the Engineer deems to be unstable or unsuitable shall be excavated and replaced with select borrow material. Excavation for the wall system shall be as directed by the plans or as directed by the Engineer. Where excavation is required in the immediate vicinity of adjacent structures and/or properties, extreme caution should be exercised. It shall be the Contractor’s responsibility to place what bracing, shoring, or ground support system deemed necessary to prevent a failure and protect the persons working near the excavation. The soil supporting the wall system shall be inspected and approved by the Engineer to confirm that the actual foundation soil conditions meet or exceed the assumed design conditions. Over- excavated areas shall be backfilled with select borrow material.
809.03.1 2--Backfill Material. All backfill material shall be compacted in accordance
with Section 203 of the Standard Specifications unless otherwise noted on the wall plans. Unless otherwise noted all backfill material shall be placed in non-compacted lifts not to exceed eight inches and be compacted to at least 95% density as determined by AASHTO T 99. Compaction of the backfill within three feet of the back face of the wall shall be accomplished by making at least three passes with a lightweight mechanical tamper, roller, or vibratory system. At the end of each day’s operation, the Contractor shall slope the last level of backfill away from the wall facing to rapidly direct runoff away from the wall face. In addition, the Contractor shall not allow surface runoff from adjacent areas to enter the wall construction site.
809.03.2 Conventional Cantilevered Gravity Wall. The Contractor shall be responsible
for all temporary shoring required to construct the conventional cantilevered gravity wall in accordance with the wall design.
809.03.3 Mechanically Stabilized Earth Walls. All components of the MSEW wall
system shall be installed in strict accordance with the plans and the manufacturer’s recommendations. A representative of the wall manufacturer shall be present at the start of construction of the wall to train the Contractor in the proper installation procedures for the chosen wall system.
809.03.3 1--Foundation Preparation. The foundation for the structure shall be graded
level for a width equal to the length of the reinforcement elements plus one foot or as directed by the wall plans. Prior to wall construction, the foundation shall be compacted with a smooth wheel vibratory roller. Any foundation soils found to be unsuitable shall be removed and replaced as outlined in Subsection 809.03.1.1.
809.03.3 2--Wall Erection.
809.03.3 2.1--Precast Concrete Facings. Precast concrete panels shall be placed so that
their final position is vertical or battered as shown on the wall plans. For erection, panels shall be handled by means of lifting devices connected to the upper edge of the panel. Panels should be placed in successive horizontal lifts in the sequence shown on the wall plans as backfill placement proceeds. As backfill material is placed behind the panels, the panels shall be maintained in position by means of temporary wedges or bracing according to the wall supplier’s recommendations. Concrete facing vertical tolerances and horizontal alignment tolerances shall not exceed 3/4 inch when measured with a 10-foot straightedge. During construction, the maximum allowable offset in any panel joint shall be 3/4 inch. The overall vertical tolerance of the wall from top to bottom shall not exceed 1/2 inch per 10 feet of wall height. Reinforcement elements shall be placed normal to the face of the wall, unless otherwise shown on the plans.
809.03.3 2.2--Modular Block Facings. The first course of modular block units shall be
carefully placed on the base leveling pad and each unit checked for level and alignment. The following sequence of operations shall then be followed:
a.The modular block units shall be placed so that they are in full contact at the base and properly seated. The modular block units are to be placed side by side for full length of wall alignment. Alignment may be done by means of a string line or offset from a base line.
b.The voids in and around the modular block units shall be filled with unit drainage fill material. Tamp or rod unit drainage fill to insure that all voids are completely filled.
c.The maximum stacked vertical height of wall units, prior to wall drain fill and backfill placement, shall not exceed two courses.
d.Excess material shall be swept from the top of the modular blocks prior to installation of the next course. Ensure that each course of modular block units is completely filled with unit drainage fill before proceeding to next course.
e.Position vertically adjacent units as recommended by the wall manufacturer.
f.Whole or cut units on curves and corners shall be erected with running bond approximately centered on units above and below.
g.Reinforcing shall be laid at the proper elevations and oriented such that the strong direction is normal to the wall alignment. Correct orientation of the reinforcing shall be verified by the Engineer.
h.Splicing of geogrid pieces shall not be allowed unless approved by the Engineer.
809.03.3 2.3--Precast Gravity Walls. At each foundation level, the base leveling pad
shall be given a wood float finish and shall be cured a minimum of 72 hours or reach a compressive strength of 2,000 psi before placement of any modular units. The completed surface of the base leveling pad shall not vary more than 1/8 inch in 10 feet. All precast modular units above the first course shall interlock with lower courses. Vertical joints shall be staggered with each successive course. The vertical joint opening on the front face of the wall shall not exceed ¾ inch. Joint filler and neoprene pads shall be installed in the horizontal joints of both faces. All vertical joints between modules shall be covered on the back side of the front face of the wall by a Type V nonwoven geotextile that is a minimum of 18 inches wide. Joints at the corners or angle points shall be closed in accordance with the recommendations of the wall manufacturer. When the modular backfill material is a rock backfill containing insufficient fines to fill the voids between particles in a compacted state, any exposed modular backfill material shall be covered by a layer of Type V nonwoven geotextile to prevent migration of soil fines into the modular backfill material. The overall vertical tolerance of the wall, plumbness from top to bottom, shall not exceed 1/2 inch per 10 feet of wall height.
809.04 Method of Measurement. The retaining wall system of the type specified will
be measured by the square foot of accepted vertical face area of the completed structure, constructed as directed by these specifications. The area measured for payment will be computed from the horizontal length of the wall segments and the average wall height between the bottom of the wall or top of the base leveling pad and the top of the wall. In the case of a battered wall, either specified in the plans or battered at the Contractor’s option, the vertical distance will be used in the area calculation and not the slope distance along the face of the wall.
809.05 Basis of Payment. The retaining wall system shall be paid for at the contract unit
price per square foot, which price shall be full compensation for the design and construction of the retaining wall system, all excavation, select backfill material, leveling pads, undercut, all the materials for the wall drainage system, facing materials, soil reinforcement, equipment, labor, and incidentals necessary to complete the work as directed by the Engineer. Payment will be made under: 809-A: Retaining Wall System * - per square foot * Type of wall may be specified
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Source: Standard Specifications for Road and Bridge Construction, 2017 Edition. Pages 1024–1035 of 1,113. View official source ↗