Why is Compaction Necessary When Building a Retaining Wall?

Compaction is often overlooked in residential wall projects and sometimes under considered in commercial projects.  Whether you are building a small landscape wall or a large commercial or DOT project compaction is essential to the success of the project.

Wall rock is always placed in the cores of the segmental retaining wall (SRW) units and directly behind the facing to aid in the compaction in and around the facing.  Every Segmental Retaining Wall (SRW) manufacturer’s specification tell the installer to build and compact their wall project in no more than 8 inch lifts.  What does this mean?  It means that when you stack one course of 8 inch block you must place and compact the wall rock and the infill soils behind the facing fully before stacking the next course of block.

It is very simple, NO SRW manufacturer allows any installer to stack 2 or 3 courses of block and then place the wall rock and infill soils.  Doing this WILL NOT allow for proper compaction levels.  The most common compaction level for commercial projects is 95% of standard proctor which we will not define here.

Typically compaction is done using a walk behind vibratory plate compactor or in small landscape project a simple hand tamper.

The results of improper or poor compaction is most often unwanted settlements at the top of the wall over time.  This settlement can cause ponding of water that will eventually work its way into the wall structure and potentially cause stability problems down the road.  Settlement can also cause down-drag forces on the geogrid layers that over time can cause damage to the geogrid and in some cases cause the geogrid layers to rupture.  Improper compaction can also cause wall bulging due to settlements behind the wall that drags the upper portion of the wall backwards into the settled area and pushes out the lower portions causing the bulge.