Installation FAQs

Frequently Asked Questions

Got a question about the installation manual?  This should help answer some of your questions and help you define some of the terms we use in our install manual.

What is base material?

It is a ¾" aggregate with fine that is used to create a level base on which the first base course is installed. The exact type of material used will be dependent on the type of aggregate available in your area.

What is fine?

It is the smaller particles of aggregate that are ideal for a level base material.

What is backfill?

It is a "clean" ¾ inch aggregate fill that is used directly behind a wall. The amount of backfill required will be dependent on the type of wall system and drainage. The exact type of material used will be dependent on the type of aggregate available in specific region.

What is clay?

Clay is fine, flat shaped particles that are invisible to the naked eye and possess both plasticity and cohesiveness. It is considered a poor soil.

What is compaction?

Compaction is one of the most fundamental elements in wall construction. Each course of a wall should be backfilled and compacted to a 95% proctor. A plate compactor or hand tamper can be used for compaction.

Is a concrete footing necessary?

No. A compacted ¾" aggregate with fine is the best material to use for retaining walls. Its composition makes it cost effective and easy to compact.

What is geosynthetic reinforcement?

Typically known as geo grid, it is a high tensile polypropylene or polyester material that helps stabilize the soil mass behind a wall. The number of grid layers and lengths are determined by the wall system being used and what is being retained behind the wall. For example, the installation of geo grid should be considered for a parking lot in which surcharge loading is present or a wall with a slope behind it, as the pressure may negatively affect the wall. Depending on the application, engineering services may be required.

What is hydrostatic pressure?

Hydrostatic pressure is saturation of water in the soil mass directly behind a wall. This pressure can compromise the integrity of wall if adequate drainage is not provided.

What do you mean by grade?

The ground level.

What is a leveling pad?

It is the base on which the base course of wall is installed. This material needs to be level and compacted to ensure that subsequent courses of the wall are properly aligned.

What is surcharge loading?

It is a force that can be exerted at the top of a SRW. A roadway, parking lot or even a large construction vehicle can be considered a source of this type of pressure. Special consideration should be given to an application that may be exposed to this type of pressure.

What types of tools are needed to cut a block or cap?

A hammer and chisel or a saw with a masonry blade, can be used to cut the units. With any type of cutting or splitting, be sure to wear safety glasses and other protective gear to help prevent possible injury.

What is retained soil?

It is the soil behind a wall that is not directly affected during the installation of a Rockwood wall.

What is silt?

It is the fine, granular particles that are invisible to the naked eye and are nonplastic and noncohesive.

What does permeability mean?

Permeability is a word that is used to describe soils that allow water to pass unrestricted or at a reasonable rate.

What is a swale?

Formed directly behind the wall, it is a ditch or depression, which can help alleviate water collection and divert it to another location.

What is overturning?

An external lateral pressure that causes the entire reinforced soil mass to rotate at the base of the wall therefore creating an external stability failure.

What is filter fabric?

Placed between the drainage column and the reinforced soil, filter fabric can help prevent the migration of fine grained soils from contaminating the drainage column or the face of the wall. This can help prevent wall face staining. While it is not necessary in every retaining wall project, it is very effective in water applications, when drainage needs to be efficient.

What is a drain tile?

Installed directly behind the lowest course above grade, a 4" perforated drain tile with sock sleeve can help alleviate hydrostatic pressure from water. While it is not required, it should be considered in special applications where adequate drainage is of concern.


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