PREFABRICATED MODULAR GRAVITY (PMG) WALL
PART 1 GENERAL
1.1SECTION INCLUDES
A.Prefabricated Modular Gravity (PMG) wall using large modular block units.
1.2RELATED SECTIONS
A.Section 02056: Embankment, Borrow, and Backfill
B.Section 02075: Geotextiles
C.Section 02317: Structural Excavation and Backfill
D.Section 03055: Portland Cement Concrete
1.3REFERENCES
A.AASHTO M 111: Zinc (Hot-Dip Galvanized) Coatings on Iron and Steel
Products
B.AASHTO T 27: Sieve Analysis of Fine and Coarse Aggregates
C.AASHTO T 99: Moisture–Density Relations of Soils Using a 2.5-kg
(5.5-lb) Rammer and a 305-mm (12-in.) Drop
D.AASHTO T 267: Determination of Organic Content in Soils by Loss on
Ignition
E.AASHTO LRFD Bridge Design Specifications
F.UDOT Geotechnical Manual of Instruction (GMOI)
G.UDOT Quality Management Plan
1.4DEFINITIONS Not Used
Prefabricated Modular Gravity (PMG) Wall
1.5SUBMITTALS
A.Contractor-selected retaining wall system for information before the
preconstruction meeting
B.Qualifications for review
1.PMG Wall Quality Coordinator
a.Include the name and PMG wall construction experience.
2.PMG Wall On-Site Supervisor(s)
a.Include the name and PMG wall construction experience for
each person that provides direct supervision over each PMG wall construction crew.
C.Quality Control Plan for review
1.Include at least the following:
a.Methods and procedures that will be used to verify quality,
and to meet tolerances and other specification requirements specific to the wall system being used.
b.Methods to verify proper PMG backfill is being used and
compaction requirements are being met.
c.Procedures to correct out of-tolerance alignments and joints
d.Measurements, checklists, and daily documentation that will
be maintained during construction to verify consistency in meeting specification requirements. 1) Include control points where measurements are taken to verify compliance with facing tolerances. 2) Include checklists that document compliance with the quality control plan, the Wall Company’s construction manual and specification requirements.
a.Use the UDOT MSE Wall Construction
Checklist available on the Department’s website as a baseline. Refer to http://www.udot.utah.gov/go/standardsreferenc es
e.Wall Company’s construction manual for the selected wall
system
2.Coordinate with the PMG Wall Company’s technical representative.
D.Samples for verification.
1.PMG block face pattern, texture, and color that meet the
requirements shown before casting of the block
Prefabricated Modular Gravity (PMG) Wall
E.PMG Retaining Wall Drawings for review.
1.Include at least the following:
a.Plan, profiles, cross sections, quantities, and details for each
retaining wall
b.Provisions for facilities that penetrate the wall face such as
drainage catch basins, piping, foundation elements, guard- rail posts, and other buried facilities
c.Surface and subsurface drainage details
d.Architectural treatment details and concrete color for PMG
blocks and cap blocks
e.Structure number details
2.Include supporting calculations sufficient to demonstrate that the
retaining walls have been designed according to the required criteria.
3.Provide the seal of a Professional Engineer (PE) or Professional
Structural Engineer (SE) licensed in the State of Utah on the drawings and calculations.
F.Certificate of compliance for incorporated materials with test results of
tests performed for information.
G.Test results for source material of PMG Backfill for review. Include at least
the following:
1.Organic content
2.Sodium sulfate soundness
3.Gradation
4.Plasticity Index
H.Construction Documentation for information.
1.A letter at wall completion signed by the on-site supervisor and wall
quality coordinator certifying that the wall construction complies with the specified requirements and the authorized quality control plan.
a.Include the completed checklists.
I.Final Field Observations Report from the Wall Company for information.
1.Include the field observations.
2.Include a signed letter stating that the wall meets Department and
Wall Company requirements based upon the Wall Company’s technical representative’s onsite observations.
Prefabricated Modular Gravity (PMG) Wall
1.6QUALITY CONTROL
A.Wall Company’s Technical Representative
1.Provide a qualified technical representative from the selected Wall
Company. The Wall Company’s technical representative must:
a.Have PMG retaining wall design and construction
experience on at least three walls of similar size and type within the previous three years.
b.Provide technical and constructability support and training to
the Contractor’s wall construction crew(s) and Department inspectors regarding proper quality control for construction of the walls.
c.Be available and provide technical assistance during all
phases of wall construction.
d.Be present during wall construction at least as follows:
1) The first two working days of the construction of each wall and until all aspects of wall construction have been satisfactorily demonstrated to the Wall Company’s technical representative and the Engineer. 2) The Department reserves the right to require the Wall Company’s technical representative to be onsite at no additional cost to the Department if at any time the Engineer is concerned with the construction quality.
e.Meet with the Engineer near the conclusion of each site visit
to report on the observed wall construction procedures.
B.PMG Wall Quality Coordinator
1.Designate a qualified PMG wall quality coordinator. The PMG wall
quality coordinator must:
a.Have PMG wall construction experience on at least three
PMG retaining walls of similar size and type within the previous three years.
b.Coordinate closely with the Wall Company’s technical
representative and the Engineer to verify issues and potential issues are properly addressed in a timely manner.
c.Be responsible for ensuring that the quality control
procedures and documentation are implemented according to the PMG wall quality plan.
d.Have sufficient authority to carry out wall quality coordinator
responsibilities
e.Be in the field during PMG wall construction
Prefabricated Modular Gravity (PMG) Wall
f.Maintain required checklists and other documentation
according to the PMG wall quality plan.
g.Verify that wall construction personnel attend the PMG wall
construction training.
C.PMG Wall On-Site Supervisor
1.Provide a PMG wall on-site supervisor at each wall construction
site. PMG wall onsite supervisor(s) must:
a.Have PMG wall construction experience on at least three
PMG retaining walls of similar size and type within the previous three years, at least two of which were in a supervisory role.
b.Provide continual supervision during all phases of wall
construction.
D.PMG Wall Construction Training
1.Provide training for Contractor and Department personnel before
wall construction begins. Include at least the following:
a.Correct PMG wall construction procedures
b.Important aspects for the selected wall system from the Wall
Company’s construction manual.
c.Procedures, methods, and documentation according to the
PMG wall quality plan.
2.The PMG wall quality coordinator and the Wall Company’s
technical representative conduct the training.
3.Attendance is mandatory for the following:
a.PMG wall quality coordinator
b.On-site supervisors
c.All personnel who participate in the wall construction
d.Wall Company’s technical representative
4.The PMG wall quality coordinator trains new personnel who did not
attend the initial training.
5.Document training attendance.
E.Complete documentation according to the PMG wall quality plan
1.Maintain quality records onsite and make available to the
Department upon request.
2.Checklists for each PMG wall are signed by the PMG wall on-site
supervisor and PMG wall quality coordinator.
Prefabricated Modular Gravity (PMG) Wall
PART 2 PRODUCTS
2.1PMG RETAINING WALL SYSTEMS
A.Use a Department approved PMG retaining wall system.
1.A list of approved retaining wall systems is maintained by the
Department.
a.Refer to: http://www.udot.utah.gov/go/standardsreferences.
2.Provide a complete retaining wall system from the Wall Company.
a.Obtain wall system components from the Wall Company or
the Wall Company’s authorized supplier.
3.Wall system and system components must meet the Wall
Company’s published requirements.
B.Use only one PMG retaining wall system on the project.
1.Do not change the wall system after the preconstruction meeting
without the Engineer’s approval.
C.Design Requirements
1.Design PMG retaining wall system according to the AASHTO LRFD
Bridge Design Specifications, as modified by the following:
a.Provide seismic design according to the UDOT GMOI.
1) Use the factored site acceleration, as shown.
b.Provide stability calculations, except global stability and
foundation bearing capacity.
c.Provide a service life of at least 75 years.
d.Verify that drainage features do not negatively impact the
wall system.
e.Design the retaining wall to accommodate drainage features
to function properly through and beneath the wall without negatively impacting the wall system. 1) Check the drainage system details, and develop appropriate details in the vicinity of the drainage features (for example, pipes, catch basins) within the compacted backfill and for the outlet point at the wall face.
f.Provide horizontal benches with at least a 4 ft width at the
base of walls founded on earth slopes as shown.
2.Structure Number Details
a.Locate the structure number on the exposed face of the
retaining wall as shown using one of the following methods. 1) Cast the structure number into the PMG block unit face as shown.
Prefabricated Modular Gravity (PMG) Wall
2) Cut the structure number into a steel plate and attach the steel plate to the wall face as shown.
a.Completely remove excess material from the
outline of each character.
b.Hot-dip galvanize the plate after cutting the
numbers into the plate. Refer to AASHTO M 111.
b.Locate the structure number at the beginning of each
retaining wall and at 500 ft intervals.
2.2PMG BLOCKS AND CAP BLOCKS
A.Use a Department prequalified supplier of precast concrete products
according to the UDOT Quality Management Plan 505: Precast/ Prestressed Concrete Structures.
B.Concrete.
1.Class AA(AE). Refer to Section 03055.
2.Verify the compatibility of components and the environment that the
block will be used, including high-sulfate soils, groundwater, or both.
C.Provide blocks having angled sides capable of producing concave and
convex alignment curves with the radii shown in the authorized retaining wall drawings.
D.Dimensional Tolerances:
1.Height: +/- 3/16 inch
2.Width: +/- 1/2 inch unless field cut for fitting purposes
3.Depth: +1 inch/-0 inch from the unit design depth of the blocks
E.Finish and Appearance:
1.Blocks to be sound, free from visual defects, and free from cracks
and other defects that interfere with the proper placement of the unit or impair the strength or durability of the construction.
a.Unacceptable defects include imperfect molding,
honeycombing, and open-texture concrete
2.Verify the exposed face or faces of blocks are free of chips, cracks,
color variation, and other imperfections when viewed from a distance of 30 ft under diffused lighting.
3.Up to 5 percent of a shipment may contain slight cracks or small
chips not longer than 1 inch.
F.Cure blocks for at least 7 days and meet 28-day minimum compressive
strength before placing the block in the wall.
Prefabricated Modular Gravity (PMG) Wall
2.3CAP BLOCK ADHESIVE
A.Use an adhesive that is specifically described as forming a bond with
concrete and masonry materials, consisting of one of the following adhesives as recommended by the Wall Company:
1.Urethane or polyurethane.
2.Medium viscosity synthetic elastomeric polymer.
2.4LEVELING PAD
A.Use one of the following:
1.PMG Backfill.
2.Free Draining Granular Backfill. Refer to Section 02056.
3.Class B concrete. Refer to Section 03055.
2.5PMG BACKFILL
A.Use material that meets the following:
1.Free from frozen, organic and otherwise deleterious materials.
2.Free of shale and other soft, low durability particles.
3.An organic content less than 1 percent as determined by AASHTO
T 267 on the portion of the material finer than the No. 10 sieve.
4.Conforms to the gradation limits in Table 2 as determined by
AASHTO T 27.
Table 2 PMG Backfill Gradation Sieve Size Percent passing 2 inch 100 ¾ inch 75-100 No. 4 0-60 No. 40 0-30 No. 200 0-5
2.6GEOTEXTILE
A.Use Drainage Geotextile where shown.
1.Refer to Section 02075.
Prefabricated Modular Gravity (PMG) Wall
PART 3 EXECUTION
3.1GENERAL
A.Haul, store, and ship wall materials in a manner that minimizes the
potential of producing defects.
B.Construct the retaining wall according to the authorized retaining wall
drawings and the Wall Company’s construction manual and recommendations.
1.Apply the stricter of the two requirements where the Department’s
and the Wall Company’s requirements differ.
3.2EXCAVATION AND FOUNDATION PREPARATION
A.Excavate and prepare foundation to the lines and grades shown, or as
determined by the Engineer.
1.Refer to Section 02317.
2.Compact the foundation before the wall construction using at least
three passes of a lightweight, steel, smooth-drum vibratory roller, or as determined by the Engineer.
3.Over-excavate unsuitable foundation soils and replace with PMG
Backfill or other suitable material as determined by the Engineer.
3.3LEVELING PAD
A.Place the leveling pad upon a properly placed and compacted foundation.
1.Place leveling pad to a thickness of at least 6 inch.
2.Provide a level surface so that the modular blocks are in complete
contact with the leveling pad.
3.4WALL CONSTRUCTION
A.Place the first course of PMG blocks on the leveling pad.
1.Check the blocks for level and alignment.
2.Verify blocks are in full contact with the leveling pad.
B.Follow the erection of each course of PMG blocks with the backfill
placement.
1.Complete backfilling in front of the wall before backfilling behind the
wall more than 4 ft above the bottom of the wall.
a.Locate the bottom of the first course of PMG blocks as
shown, but not less than 1 ft below finished grade.
Prefabricated Modular Gravity (PMG) Wall
2.Do not damage, disturb or misalign block units during backfill
placement.
3.Place backfill in lifts not to exceed 12-inch thickness before
compaction.
a.Decrease the lift thickness as necessary to obtain the
specified density.
b.Place backfill in uniformly thick layers.
4.Place and compact each layer of backfill in a level manner before
placing subsequent backfill layers.
a.Meet at least 95 percent of the maximum laboratory density
according to AASHTO T 99, Method C or D (with oversized correction, outlined in Note 7 of T 99).
C.Lay each successive course of PMG blocks making sure that the bottom
recess is in full contact with the block unit locators of the course below.
1.Clean the top of the course below before setting the successive
course.
2.Check and maintain level and wall batter.
a.Do not use shims.
D.Construct the wall facing to the following tolerances:
1.Horizontal alignment (including curves and corners)
a.Not to exceed 0.7 percent (for example, 2.5 inch in 30 ft, or
0.5 inch in 6 ft).
2.Vertical alignment (measured from the design batter)
a.Not to exceed 1 percent (for example, 0.8 inch in 6 ft of wall
height).
3.Levelness
a.Not to exceed 0.5 percent (for example, 1.2 inch in 20 ft).
4.Joints
a.Limit the horizontal offset between blocks during
construction to no more than 0.5 inch.
b.Limit the width to no more than 0.5 inch and no less than
0.125 inch.
E.Slope the backfill away from the wall at the end of each day's operation to
direct rainwater runoff away from the wall face.
1.Do not allow the surface runoff from adjacent areas to enter the
wall construction site.
Prefabricated Modular Gravity (PMG) Wall
F.Place wall cap blocks
1.Provide a permanent connection between the cap block and the top
course of the PMG blocks using cap block adhesive.
2.Trim sides of interior cap blocks to provide proper fit of cap blocks.
a.Do not leave cut surfaces exposed to view in the finished
wall.
G.Complete the placement and compaction of backfill to finished grade.
END OF SECTION
Prefabricated Modular Gravity (PMG) Wall
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Source: Utah Standard Specifications for Road and Bridge Construction, 2026 Edition. Pages 710–720 of 1,331.
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