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SRW Design: Expert Level

Aaron Fisher | March 29, 2021

Are you an architect, engineer, or contractor looking for more technical information as you design and install a segmented retaining wall (SRW)?

Guidance Manual

NCMA Guides

One of the best places to look for more information on SRW construction is the National Concrete Masonry Association (NCMA)

Software Tools

Interested in designing an SRW, but don’t want to do the reading. There are several good software packages out there

Design Standards of SRW Block (ASTM C1372)

  • Dimensional tolerances: ±1/8 in. (except for architectural finished surfaces)
  • Minimum Compressive Strength = 3,000 psi
  • Maximum Absorption = 15 – 18 pcf

Freeze-Thaw Resistance of SRW Block (ASTM C1262)

SRW Exposure Map

Exposure Zone SRW Properties Freeze/Thaw  Testing (C1262)
Zone 1 and Non-Roadway Applications ASTM C1372 None
Zone 2 –

no/negligible de-icing salt exposure1

ASTM C1372 Proven field performance or test in water:

•≤1% wt. loss in 5 of 5 samples after 100 cycles; or

•≤1.5% wt. loss in 4 of 5 samples after 150 cycles.

Zone 2 –

de-icing salt exposure

ASTM C1372, plus

• Targeted compressive strength: 4000 psi

• Targeted absorption: 7 pcf

Test in 3% saline solution:

•≤1% wt. loss in 5 of 5 samples after 20 cycles; or

•≤1.5% wt. loss in 4 of 5 samples after 30 cycles.

Note: Only Zone 1 & 2 are shown because Ernest Maier does not service any regions that fall in Zone 3. Please see the Best Practices Guide for more information.

Minimum Design Standards

Appropriate design of an SRW should include a minimum safety factor. These are the minimum recommended safety factors.

SRW Design Requirements

Geosynthetic Reinforcement

Design Guidance

Use these design tables to understand how much reinforcement to place in your SRW

Wall Height ft (m) Reinforced Zone Material Design and Layout Criteria
Gradation Plasticity Reinf. Spacing, Max. L/H, min. Gravel Fill Thickness in. (mm)
H ≤10

(H ≤ 3)

Recommended See Table Below Moderate 24 in. 0.6 24 in. (610 mm) from face

12 in. (305 mm) behind unit

Alternate See Table Below

#200 waived

Moderate 16 in. 0.7 30 in. (762 mm) from face

18 in. (457 mm) behind unit

10 < H ≤ 20

(3 < H ≤ 6)

Recommended See Table Below Low 24 in. 0.6 Top 10 ft (3 m) same as

above, remainder 36 in.

(914 mm) from the face, 24

in. (610) behind unit

H > 20

(H > 6)

Recommended See Table Below Low 24 in. 0.6 Top 10 ft (3 m) and lower 10

ft (3 m) to 20 ft (6 m) same

as above, remainder 48 in.

(1219 mm) from the face,

36 in. (914 mm) behind unit

Sieve Size Percent Passing (Short/Medium Walls) Percent Passing (Tall Walls)
1 in. (25 mm) 100 100
No. 4 100 – 0 100 – 20
No. 40 0 – 60 0 – 60
No. 200 0-35 0-15 with PI<6

Material Choice

The proper use of geosynthetics, can compensate for many other imperfections, mistakes, or oversights in the design of an SRW. Be sure to select materials that provide the recommended material strength and are permeable to water.

An interesting application that showcases the power of geosynthetic reinforcement is: Geosynthetic Reinforced Soil- Integrated Bridge Systems (GRS-IBS). These are basically just SRW blocks with geotextiles every layer that are used for smaller bridges <140’ spans. These solutions are accepted by the FHWA and DOTs around the country.

Geosynthetic Reinforced Soil Integrated Bridge System Interim Implementation Guide, January 2011 - FHWA-HRT-11-026

Geosynthetic Reinforced Soil Integrated Bridge System

Drain Design

There are several drainage design options

  • Blanket Drain- runs underneath the reinforced soil zone- used to address the presence of migratory subsurface water
  • Toe Drain- located behind/below the SRW blocks- removes water from behind the blocks
  • Heel Drain- located at the base of the interface of the reinforced and retained soil zones- drainage structure to further reinforce the
  • Chimney Drain- located at the interface of the reinforced and retained soil zones- used to address high water tables or the presence of migratory subsurface water

Toe and Heel Drain Detail

Chimney and Blanket Drain Details

Ernest Maier, Gomoljak Parker Block, and Skyline Brick have professional sales representatives who in many cases have served as contractors and installers ourselves. Feel free to reach out with your questions.

VP of Business DevelopmentAaron Fisher

Phone
Location
MD: Bladensburg
Languages
English

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