MODULAR BLOCK GRAVITY WALL
PART 1 GENERAL
1.1SECTION INCLUDES
A.Modular Block Gravity Walls without soil reinforcement
1.Limited to walls with a maximum exposed wall height less than 3 ft.
1.2RELATED SECTIONS
A.Section 02056: Embankment, Borrow and Backfill
B.Section 02317: Structural Excavation and Backfill
C.Section 03055: Portland Cement Concrete
1.3REFERENCES
A.AASHTO LRFD Bridge Design Specifications.
B.ASTM C 1372: Standard Specification for Dry-Cast Segmental Retaining
Wall Units
C.UDOT Quality Management Plan
1.4DEFINITIONS Not Used
1.5SUBMITTALS
A.Manufacturer’s product data sheets and recommended installation
instructions, construction manual, and installation guide for each manufactured product specified including concrete modular block and fill materials, for information
B.Retaining wall drawings for review
1.Include at least the following:
a.Wall geometry including plans, profiles, elevations, cross
sections, quantities, and project specific details.
b.Wall installation details.
Modular Block Gravity Wall
2.Design the wall as a gravity wall according to the AASHTO LRFD
Bridge Design Specifications.
3.Include supporting engineering calculations.
4.Provide the seal of a Professional Engineer (PE) or Professional
Structural Engineer (SE) licensed in the State of Utah on the drawings and calculations.
C.Certificate of Compliance for modular blocks and cap blocks for
information.
1.Include certified test reports for compressive strength, freeze-thaw
durability, absorption, density, and dimensional tolerances.
D.Sample for selection
1.One modular block that meets the face pattern, texture, and color
requirements shown
a.Propose a block that matches local features if face pattern,
texture, or color are not shown, unless directed otherwise by the Engineer.
1.6DELIVERY, STORAGE, AND HANDLING
A.Deliver, store, and handle materials according to the manufacturer's
recommendations, and in a manner to prevent damage.
1.Remove damaged or otherwise unsuitable material from the site.
B.Protect blocks from materials such as mud, debris, wet concrete,
adhesives and similar materials.
PART 2 PRODUCTS
2.1MATERIALS
A.Dry Cast Concrete
1.Meet specified 28 day minimum compressive strength.
B.Modular Block Fill
1.Free-draining crushed stone, 3/8 to 3/4-inch, with no more than 5
percent passing the No 200 sieve.
Modular Block Gravity Wall
C.Leveling Pad
1.Use one of the following:
a.Granular backfill borrow according to Section 02056.
b.Free draining granular backfill according to Section 02056.
c.Class B concrete according to Section 03055.
D.Alignment Pins
1.Use ½-inch diameter fiberglass pins having a minimum flexural
strength of 128 ksi and short beam shear of 6.5 ksi, if required.
E.Filter Fabric
1.Use type and grade recommended by the modular block
manufacturer.
F.Cap Block Adhesive
1.Use a medium-viscosity synthetic elastomeric polymer adhesive as
recommended by the modular block manufacturer.
G.Backfill
1.Granular borrow according to Section 02056.
2.2MODULAR 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.Meet the following requirements for modular blocks and cap blocks:
1.Have a 28 day compressive strength of 4,000 psi.
2.Conform to ASTM C 1372, except as follows:
a.Comply with the freeze-thaw durability requirements.
b.Comply with the following for each lot of blocks not tested for
freeze-thaw durability. 1) Have a water absorption no greater than one percent above the water absorption content of the blocks successfully tested for freeze-thaw durability.
C.Provide blocks having angled sides capable of producing concave and
convex alignment curves with a minimum radius of 4 ft.
D.Finish and Appearance
1.Refer to ASTM C 1372.
Modular Block Gravity Wall
PART 3 EXECUTION
3.1GENERAL
A.Construct the retaining wall according to the authorized retaining wall
drawings, and the modular block manufacturer’s construction manual and recommendations.
1.Apply the stricter of the two requirements where the Department’s
and the manufacturer’s requirements differ.
3.2EXCAVATION AND FOUNDATION PREPARATION
A.Excavate and prepare foundation to the lines and grades shown, or as
directed by the Engineer.
1.Refer to Section 02317.
2.Over-excavate unsuitable foundation soils and replace with backfill
or with other suitable material as directed 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.
B.Place modular blocks at least 12 hours after leveling pad placement when
concrete leveling pad is used.
3.4WALL CONSTRUCTION
A.Construct the wall as follows:
1.Place the first course of modular blocks in full contact with the
leveling pad.
a.Check the modular blocks for levelness and alignment.
2.Use alignment or connection devices if required by the modular
block manufacturer.
a.Extend connecting pins into adjoining courses at least 1 inch
where used.
3.Pull each block forward (away from the embankment) against the
connecting pins in the previous course.
4.Fill modular block voids with modular block fill when required.
a.Tamp the modular block fill in each course before
proceeding to the next course.
Modular Block Gravity Wall
5.Backfill each course of blocks and compact the entire lift before
placing the next course of blocks.
a.Compact with lightweight hand-held or hand-guided
equipment.
b.Exercise care in the compaction process to avoid
misalignment of the modular blocks.
6.Repeat the procedure for each additional course.
B.Construct wall facing to the following tolerances:
1.Joints
a.Limit the horizontal offset in any block joint during
construction to no more than 0.25 inch.
b.Limit the width of vertical joints to no more than 0.50 inch.
3.5CAP BLOCK INSTALLATION
A.Set cap blocks over top row of modular blocks with proper alignment and
uniform set-back orientation.
B.Provide a permanent connection between the cap blocks and the top
course of the modular blocks using cap block adhesive.
END OF SECTION
Modular Block Gravity Wall
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Source: Utah Standard Specifications for Road and Bridge Construction, 2026 Edition. Pages 756–760 of 1,331.
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