Geotechnical Engineering 101 and more…

Building firm foundations

Modular Retaining Wall Components

Posted by Kshitija Nadgouda on July 26, 2006

Since my article on Retaining Walls, I received queries regarding the components of a modular block retaining wall. So I deceided to write this post to supplemnt my earlier article.

reinforced.gif
(Courtsey Versa-Lok)
A modular block (or segmental) retaining wall consists of the following components:

  1. Modular blocks (Facing Unit)
  2. Levelling pad
  3. Drainage Material
  4. Engineered Fill
  5. Geosynthetic Reinforcement
  6. Impervious Fill
  7. Retained Backfill

Modular blocks are the facing units – the aesthetic component of the wall that meets the eye. There are several companies like VERSA-LOK, KEYSTONE, ALLAN BLOCK, MESA BLOCK , etc that sell these inter-locking units.
Levelling Pad refers to the base of the “founding” element of the retaining wall. It provides a level base for the retaining blocks.
Drainage material is placed immediately behind the facing units to ensure that any moisture or groundwater is drained away and doesn’t exert excess pressure on the facing units.
Engineered Fill refers to the soil that replaces the material excavated from the natural slope. Typically a silty sand is used as engineered fill.
Geosynthetic Reinforcement are the sheets or grids of geosynthetic reinforcement that are used to strengthen the system. Tensar and Mirafi are two of the popular companies that manufacture geosynthetic reinforcement sheets and grids in the US, while Techfab India provides these materials in India,
Impervious fill is used to cap the backfill behind the facing units so that rain water or other surficial water doesn’t permeate into it.
Retained backfill is the part of the natural slope or natural terrain that is still undisturbed.

Geogrid Retaining Wall Systems, Incorported has an excellent series of photographs showing the step-by-step construction of a segmental retaining wall.

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Copyright Kshitija Nadgouda.

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5 Responses to “Modular Retaining Wall Components”

  1. Karl said

    Versa-Lok makes an installation DVD in English and Spanish that’s available from Versa-Lok at 1-800-770-4525.

  2. There is also some information about reinforcing the slope in bleow website blog.
    http://www.geosyntheticsworld.com

  3. A lot of the walls we build are smaller walls (e.g. 1-4 ft. tall), with no surcharge above them. They don’t require geotextile fabric. But one thing we usually do is install a landscape fabric behind the aggregate drainage rock and in front of the native soil. This just keeps the drainage area from getting clogged up with silt over time. What do you think? Good practice, or no?

    Retaining Walls Portland Oregon

  4. Shane said

    It is good practice to put non-woven filter fabric between your drainage stone and native soil to keep the silt out of the stone which would clog the drainage stone. It is important to use non-woven fabric because woven may still allow silt through and cause draining probelms.

    Also with larger walls that require engineered fill and grid it is typical to use soil which contains 0-10% fines (passing #200 sieve) to backfill the wall. This will keep the soil free draining and reduce the stress on the wall. But it’s more typical to use a well graded sand and gravel. Soils that contain sand and gravel will be easier to compact to the required density stated in the spec. (usually either 92% or 95% of the maximium dry density determined by a modified proctor test).

  5. Can you tell name some good modular blocks companies in San Diego. What are the materials that we use to build drainage material?

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