Segmental Retaining Wall Installation Guide

Segmental Retaining Wall Installation Guide

This guide covers the key steps, terminology, and engineering considerations for planning and installing segmental retaining walls (SRW). Always consult a qualified geotechnical or structural engineer for walls taller than 4 feet, walls situated in poor soils, walls supporting a driveway, or any application requiring a stamped design.

Safety Note: Always wear appropriate safety equipment including safety glasses and respirators when splitting, cutting, or hammering units.

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1. Stake Out the Wall

  • Have a surveyor stake out the wall placement and verify locations with the project supervisor
  • Verify the proposed height of the wall against approved plans

2. Excavation

  • Account for the leveling pad, lines, grades, and geosynthetic reinforcement material
  • The trench for the leveling pad should be at least 2 feet wide and a minimum of 1 foot deep — enough to bury the first course below grade, plus 6 inches for the leveling pad
  • Ensure a minimum of 8 inches (or 10% of finished wall height, whichever is greater) is below grade
  • If the planned grade changes along the wall front, the leveling pad may need to be stepped (typically 8-inch increments) — always start at the lowest level and work upward

3. Leveling Pad

  • Use a compactible base material of ¾-inch minus with fines
  • Compact the aggregate, making sure it is level from front to back and side to side — mist lightly with water before compaction if needed

4. Base Course

This is the most important step in the installation process.

  • Begin laying block at the lowest elevation of the wall, removing the rear lip of each block before placing
  • Place first block level front to back and side to side; lay subsequent blocks the same way
  • Place blocks side by side, flush against each other, ensuring full contact with the leveling pad
  • Place soil in front of the base course and compact — base course should be buried; fill and compact after each course

5. Constructing Subsequent Courses

  • Fill cores and voids between blocks with ¾-inch clean drainage aggregate before laying the next course — clear any debris off the top of the blocks
  • Place the second course on top of the base course maintaining running bond — pull each block forward as far as possible to ensure correct setback
  • Backfill with drainage aggregate directly behind the block, adding 6 to 8 inches at a time — add soil fill behind the aggregate
  • Compact before the next course is laid — do not drive heavy equipment near the wall; self-propelled compaction equipment should not be used within 3 feet of the back of the wall
  • You may need partial units to maintain running bond — use a masonry blade circular saw with safety glasses and protective equipment when cutting
  • If the wall is on an incline, do not slope the blocks — step them up so they remain consistently level
  • Use a string along the back edge of the block to check for proper alignment

6. Drainage Design

Good drainage is critical to the long-term performance of a segmental retaining wall. Water collected from behind the wall must be able to drain down and away — either at the end of the wall, via a carrier drain, or through drainage weep holes.

  • Each project is unique — grades on site determine the drainage pipe elevation; place 4-inch perforated pipe so water drains down and away from the wall into a storm drain or daylight just above grade
  • Fill in the area behind the blocks with clean drainage aggregate, at least 1 foot from the wall — you may need to place and backfill several courses to achieve proper drainage level
  • Drainage pipes should be spaced no more than every 50 feet and at low points of the wall — pipes must stay clear of regional fill soil
  • First Course (walls longer than 50 ft): Drainage weep holes must be installed through the wall face, no more than 50 feet apart — remove 2 inches off the front of two adjacent blocks to provide sufficient space for drainage to exit through the face
  • Build remaining courses using standard construction techniques

7. Compaction

  • Shovel the backfill soil behind the drainage aggregate and compact the backfill with a hand-operated compactor
  • Make sure the grade is level with or slightly below the top of the base course
  • Continue to fill and compact after each course is laid

8. Reinforcement (If Required)

Geosynthetic reinforcement is recommended for walls taller than 4 feet or walls situated in poor soils, supporting a driveway, etc. Consult an engineer for design assistance.

  • Check the wall construction plan to determine which courses will need reinforcement — clean any debris off the top layer of blocks; measure and cut reinforcement to the design length
  • The reinforcement has a design strength direction, which must be laid perpendicular to the wall
  • Place the front edge of the material on the top course, 1 inch from the face of the block
  • Apply the next course of blocks to secure in place — to keep from wrinkling, pull the reinforcement taut and pin the back edge in place with stakes or staples
  • Add drainage aggregate behind the blocks, then add the backfill soil and compact
  • Correct placement ensures you maximize the connection strength and keep the batter consistent — a minimum of 6 inches of backfill is required prior to operating vehicles on the reinforcement

9. Capping a Wall

  • Always start capping from the lowest elevation — if the wall elevation changes, caps can be stacked where the wall steps up
  • Lay caps at the elevation change and work back toward the previous step up — cut caps with a diamond-blade saw to fit as needed
  • Carefully glue caps in place with a high-strength concrete adhesive

Cap Configurations

  • Straight Wall: Alternate short and long cap faces — caps have a recess on the bottom to accommodate the locator, always laid with recess facing downward
  • Outside Curves: Lay cap units side by side and cut at least every other cap to produce a uniform look — start with the long side of the cap facing out and adjust to the radius
  • Inside Curves: Lay caps side by side with the short side facing out — in most circumstances, making two cuts on one cap and not cutting the cap on either side produces the most pleasing look
  • Corners: On a 90° corner wall, corner caps need to be saw-cut to achieve a 45° mitered corner
  • Finishing: After layout is complete and caps are saw-cut to size, carefully glue caps in place using exterior-grade concrete adhesive

10. Running Bond

Proper installation requires that running bond be maintained — this occurs when blocks are centered over the vertical joints of the previous course, adding to wall stability and making the wall aesthetically beautiful.

  • Straight walls: Maintain running bond throughout
  • Outside curved walls: Any wall that is not perfectly straight will eventually run off bond — when this happens, skip a block position and place the next block into the next place where it is back on bond; measure the remaining gap and cut or split a block to fit
  • Partial units must not be less than 8 inches long and should not be placed directly on top of each other — if the gap is larger than the length of one block, divide the measurement by two and put two partial units in place
  • Tip: It may be possible to run the off-bond block into the soil bank to avoid cutting partial units

11. Corners

Inside 90° Corners

  • Base Course: To create an inside 90° corner, begin by placing a block at the corner, then lay a second block perpendicular to the first and continue laying the rest of the base course working from the corner out
  • Additional Courses: Place all blocks in a running bond along one side of the corner — once the second course of one wall is established, begin the second course of the adjacent wall; several blocks away from the corner, pull blocks in a running bond back toward the corner until the gap becomes less than a full unit; spot units may be required to maintain running bond
  • Subsequent Courses: Block placement in the corner must alternate in direction with each succeeding course — the locator of the block being overlaid within the corner should be removed using a hammer and chisel; these units should be glued in place using concrete adhesive

Outside 90° Corners

  • Base Course: Begin by placing a corner unit and working from the corner unit outward
  • Next Course: Lay a corner block perpendicular to the one below and give the block in place with concrete adhesive — two or three blocks away from the corner, lay full blocks maintaining running bond back toward the corner; corner blocks lay back toward the corner block, leaving space for the final split units to complete the course
  • Use split units immediately adjacent to the corner block to complete the course — continue to alternate the corner unit orientation with each course and always use concrete adhesive on all corner units and split units
  • Always maintain running bond

12. Curves

Calculating the Radius

Check the wall plan to determine the radius of the base course — this will be the smallest radius in the wall and must not be less than the minimum for the block system used.

Quick formula for base course radius:

  1. Add ¾ inch to the setback of the block used — multiply that by the number of courses in the finished wall
  2. Subtract the result from the radius of the top course — this equals the approximate radius of the base course
  3. To determine the radius for the front edge of the trench, subtract 6 inches from the approximate radius of the base course

Laying Out the Trench

  • Drive a stake into the ground at the desired radius point of the curve — attach a string and rotate it in an arc at the desired length to mark the curve in the soil; dig the trench

Inside Curves with Reinforcement

  • Most retaining walls are designed assuming 100% reinforcement coverage — when building an inside curve the reinforcement will fan out, producing slight gaps; additional lengths of reinforcement are used to fill those gaps on the next course of blocks
  • Cut reinforcement to the lengths specified in the wall plan — lay segments within 1 inch of the face of the wall, with the strength direction perpendicular to the wall face; avoid overlapping the reinforcement by separating each section
  • The minimum inside radius varies by product — check product specifications

Outside Curves with Reinforcement

  • When building an outside curve the reinforcement will have gaps, and the back edges don't overlap — to ensure 100% coverage, additional lengths of reinforcement are used to fill those gaps on the next course of blocks
  • Cut reinforcement to the lengths specified in the wall plan — lay sections within 1 inch of the face of the wall; avoid overlapping the reinforcement by separating each section
  • Each product has a unique minimum outside radius — check product specifications

13. Finish Grade & Surface Drainage

  • Protect the wall with a finished grade at the top and bottom — ensure proper water drainage away from the wall; use a mixture of soil with low permeability and seed or plant to stabilize the surface
  • Consult the wall design engineer if water may be draining toward the wall — it needs to be designed to divert water away from the wall; this will minimize water seeding into the soil and drainage aggregate behind the wall

14. Site Cleaning & Restoration

  • Brush off the wall and clean up any debris left from the construction process
  • Notify the job superintendent in writing of the completion and that it is ready for final inspection and acceptance
  • Planting vegetation in front and on top of the wall will help reduce the chance of erosion
  • Following these best practices for construction will ensure the success of your segmental retaining wall — these instructions are meant as general guidelines; site-specific conditions may require additional installation requirements
  • For walls over 4 feet high, have compaction tested by a qualified geotechnical engineer

Industry & Regulatory References