Modular Block MSE Retaining Wall MODULAR BLOCK MSE RETAINING WALL
Part 1 — General
1.1 Section Includes
A.Modular block M echanically Stabilized Earth (MSE) retaining wall using metal or geogrid soil reinforc ement .
1.2 Related Sections
A.Section 02317: Structural Excavation and Backfill
B.Section 02832: MSE Backfill
C.Section 03055: Portland Cement Concrete
1.3 References
A.AASHTO M 111: Zinc (Hot -Dip Galvanized) Coatings on Iron and Steel Products
B.ASTM A 641: Zinc -Coated (Galvanized) Carbon Steel Wire
C.ASTM A 1064: Carbon -Steel Wire and Welded Wire Reinforcement, Plain and Deformed, for Concrete
D.ASTM C 1372: Dry -Cast Segmental Retaining Wall Units
E.ASTM D 5262 : Evaluating the Unconfined Tension Creep and Creep Rupture Behavior of Geosynthetics
F.ASTM D 6637: Determining Tensile Properties of Geogrids by the Single or Multi -rib Tensile Method
G.UDOT Quality Management Plan
1.4 DEFINITIONS Not Used
1.5 SUBMITTALS Not Used
Modular Block MSE Retaining Wall
Part 2 — Products
2.1 Materials
A.Concrete
1.Dry Cast Concrete
a.Meet specified 28- day minimum compressive strength
2.Leveling Pad
a.Class B according to Section 03055.
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.
2.Meet electrochemical properties according to Section 02832.
C.Soil Reinforc ement
1.Metal reinforcing elements
a.Welded Wire and Grid 1) Refer to ASTM A 1064 .
b.Galvanize according to AASHTO M 111 or ASTM A 641 with a coating thickness of at least 3.4 mils.
2.Geogrid reinforcing elements
a.Use geogrid consisting of a regular grid network of integrally connected, discontinuous, select high- density polyethylene or polypropylene resin polymer or polyester tensile elements 1) Aperture geometry sufficient to permit significant mechanical interlock with the surrounding soil and rock. 2) Geogrid structure to be dimensionally stable and be able to retain its geometry under manufacture, transport, and installation.
b.Meet c reep rupture test for 75- year service life according to ASTM D 5262.
c.Meet the ultimate tensile strength from wide -width tests based on minimum average roll values, according to ASTM D 6637. 1) Utilize geogrid reinforcement reduction factors as appropriate for the p roject.
D.Loop Embeds
1.As provided by the Wall Company.
2.Galvanize according to AASHTO M 111 with a coating thickness of at least 3.4 mils. Modular Block MSE Retaining Wall
E.Connecting Pins
1.Fiberglass Connecting Pins
a.½ inch diameter having a minimum flexural strength of 128 ksi and short beam shear of 6.5 ksi.
2.Steel Connecting Pins
a.Meet Wall Company’s requirements
b.Galvanized with a coating thickness of at least 3.4 mils.
F.Fasteners
1.Fasteners to wingwalls and abutment wall, if required, to be provided by the selected Wall Company.
G.Filter Fabric
1.Use type and grade recommended by the Wall Company. H Cap Block Adhesive
1.Use a medium -viscosity synthetic elastomeric polymer adhesive as recommended by the Wall Company .
I.MSE Backfill
1.Refer to Section 02832.
J.MSE Free Draining Backfill 1. Refer to Section 02832.
2.2 Modular Blocks and Cap Blocks
A.Use a Department pre qualified supplier of precast concrete products according to the UDOT Quality Management Plan 505: Precast/ Prestressed Concrete Structures.
B.Meet the following requirements for drycast concrete modular block s and cap block s:
1.Have a 28- day minimum 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 radius no less than 4 ft. Modular Block MSE Retaining Wall
D.Finish and Appearance
1.Refer to ASTM C 1372.
Part 3 — Execution
3.1 General
A.Haul, store , and ship wall materials in a manner that minimize s the potential of producing defects.
1.Store soil reinforcement products as recommended by the Wall Company.
2.Inspect soil reinforcement and attachment devices to verify they are true to size and free from defects that may impair their strength and durability.
3.Keep the soil reinforcement and connections free of contaminants .
B.Construct the retaining wall system 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.
3.2 Excavation 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.Make the width of excavation equal to or greater than the length of soil reinforc ement .
3.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.
4.Over -excavate unsuitable foundation soils and replace with MSE Backfill, or with other suitable material as directed by the Engineer.
3.3 Leveling Pad
A.Place the cast-in-place concrete leveling pad upon the 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.
B.Do not place modular blocks until leveling pad has been placed for at least 12 hours. Modular Block MSE Retaining Wall
3.4 Wall Construction
A.Construct the wall as follows:
1.Place the first course of modular blocks on the leveling pad.
a.Check the modular block s for level ness and alignment .
b.The first course is the most important to verify accurate and acceptable results.
c.Verify modular blocks are in full contact with the leveling pad.
2.Install connecting devices in modular blocks as required by the Wall Company.
a.Extend connecting pins into adjoining courses at least 1 inch where used.
3.Pull each block forward ( away from the backfill) 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.
5.Backfill each course of blocks and compact the entire lift before placing the next course of blocks .
6.Repeat the procedure for each additional course.
B.Construct wall facing to the following t olerances .
1.Horizontal alignment
a.Not to exceed 0.7 percent (for example , 0.75 inch in 10 ft).
2.Vertical alignment (measured from the points of maximum and minimum offset at a bulge or depression)
a.Not to exceed 0. 7 percent ( measurements taken at the bottom, center and top of bulge or depression )
3.Plumbness from top of wall to bottom of wall (measured from the design batter)
a.Positive (into the retained mass) 1) Not to exceed 0. 7 percent (for example , 1.7 inch in 20 ft of wall height).
b.Negative (away from the retained mass) 1) Not to exceed 0.4 percent (for example, 0.96 inch in 20 ft of wall height).
4.Facing Block Levelness
a.Not to exceed 0.5 percent (for example , 1.2 inch in 20 ft)
5.Joints
a.Limit t he horizontal offset in any block joint during construction to no more than 0.25 inch.
b.Limit the width of vertical j oints to no more than 0.50 inch. Modular Block MSE Retaining Wall
C.Metal Soil Reinforcement Installation
1.Place the soil reinforcement on compacted backfill.
2.Connect soil reinforcement to the blocks as required by Wall Company.
3.Place soil reinforcement normal to the face of the wall in plan view.
a.Provide at least 2 inch clear distance between soil reinforcement and piles or other metallic obstructions.
4.Provide at least 3 inch vertical separation between soil reinforcement when overlapping.
D.Geogrid Soil Reinforcement Installation
1.Verify the correct orientation (roll direction) of the geogrid.
2.Place the geogrid on compacted backfill.
3.Connect geogrid to the concrete wall block s as required by Wall Company.
4.Pull the geogrid taut to eliminate loose folds and remov e slack in the geogrid at the block connections, pretension the geogrid, and then stake or otherwise secure the back edge of the geogrid before and during backfill and compaction.
5.Follow the Wall Company's overlap requirements for uniaxial and biaxial geogrids.
6.Provide at least 3 inch vertical separation between soil reinforcement when overlapping.
3.5 Cap 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 block s using cap block adhesive.
Source: Utah Standard Specifications for Road and Bridge Construction, 2026 Edition. Pages 698–703 of 1,331.