April 12, 2019

Segmental Retaining Walls (SRW) or Cast-in Place - Which is Better?

Written by: Kyle Huerd
For decades, commercial site developments have commonly constructed cast-in-place reinforced concrete walls to retain soil. However, since the mid 1980’s, segmental retaining walls (SRW’s) have provided a better solution to these rigid walls. Some of the advantages SRW’s have over cast-in-place walls include the following:

  • Lower installation cost (30-70%)
  • Limited excavation for footing preparation since frost depth is not a factor
  • Faster installation
  • Easier to design
  • Better aesthetics
  • More reinforcement options (e.g. Geogrid, No-Fines concrete, wall anchors, etc.)
  • Flexible vs. rigid system

Aside from all the advantages listed above, what is often missed is the fact that SRW’s can also out-perform rigid walls, particularly in the most aggressive circumstances possible, such as during an earthquake. SRW’s ability to withstand seismic loading conditions has been proven in both the laboratory and the real world.
Allan Block’s full-scale seismic testing documented that SRW’s can withstand large seismic forces. The testing subjected the test walls to forces up to 0.8g and all experienced only minimal deflection and/or settlement. The tests showed the block facing, soil mass and geosynthetic reinforcement all moved together as a unit, in phase with the earthquake induced forces. It was suggested by Dr. Hoe Ling from the Columbia University that these structures, that are both flexible and coherent, are ideal for seismic conditions (ABSeismic Research Summary, Reference Document #R0505, August 2003).
In today's world, with Segmental Retaining Walls being tried and true for more than 30 years, there isn’t much of a market for traditional cast in place walls anymore.  The next time you think you have to use a cast in place wall on a project, just call Allan Block Engineering Department for a second set of eyes to see how we can find the most efficient design.

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