7 Common Compaction Testing Questions

As a Calgary based geotechnical engineering firm that also performs a significant amount of materials and soil testing, our scope of work commonly includes compaction testing.

At E2K Engineering, compaction testing is performed using industry-standard nuclear densometers by our team of qualified and professional technicians.

What is Compaction Testing?

In a nutshell, compaction testing is the comparison of the moisture and density of a specific soil being placed during construction to an optimum moisture and density for that soil, which was determined in a geotechnical lab.

Project documents usually specify what percentage of the maximum density is required during backfill and compaction.

Compaction Testing on Roadway

What is 98% Compaction?

98% compaction is simply the result of the comparison between field values and lab values for a specific soil. 98% compaction just means that the density of the material placed on site is 98% of the maximum density determined in the lab.

It’s important to note that each soil being used on-site needs its own maximum density test to be performed in the lab before compaction testing can begin. The lab test for determining the maximum density of soils is called a Proctor test.

How Do We Establish Compaction Requirements?

Depending on our role in a project, compaction requirements may be up to us, or they may be provided to us. Normally compaction requirements are determined based on what the backfill will be supporting, or what is nearby.

Generally, 98% is used for most projects and most applications. For road gravel and fill under slabs, the upper 6 – 12 inches (150 mm – 300 mm) is sometimes specified as 98% or 100%. Requirements are often relaxed in areas that do not require subgrade support, such as fields, gardens, and other open spaces. Called “landscape areas”, compaction requirements are sometimes relaxed to 95% here.

Why Are Compaction Specifications A Percentage?

In either of our geotechnical laboratories located in Calgary and Edmonton, optimum moisture and density levels are achieved in controlled conditions. There is not rapidly changing Alberta weather and the laboratory procedure is standardized to produce uniform and reliable results. This maximum density is called the Proctor density and is what would be referred to as 100% compaction.

Because we all understand that 100% is very difficult to achieve, design documents will request different compaction standards for the necessary structural integrity. You may see 95% compaction required in the sub-grade of a landscaped area, or 98% compaction required in the granular base course of a structural slab.

What Testing Methods Are Used For Compaction?

Traditionally, testing for compaction involved digging a hole and using balloon volumes to measure the displacement for density. A geotechnical engineer or technician would then take a sample and return to dry it inside a laboratory for moisture content. This process took a long time in determining compaction.

Technology has evolved. Geotechnical engineers and technicians are now able to utilize nuclear equipment to determine material density, moisture, and air void content.

At E2K we have a fleet of portable nuclear densometers capable of emitting radiation through compacted backfill. The densometer measures the amount of radiation that travels through the backfill, and provides density, air void content, and moisture contents to the operator. All within minutes.

Compaction Testing Near Footing

Where Do Compaction Testing Jurisdictions Apply?

Different specifications exist for projects in the areas where they are being built. City of Calgary and the City of Edmonton have their own technical specification manuals that apply to roads and utilities. Calgary and Edmonton also have the Alberta Building Code requirements to follow. These guidelines must be referenced in determining where moisture and density testing is required on each specific project.

Rural municipal jurisdictions often have their own specifications too. Rocky View County and Foothills County publish their construction technical specifications online for reference. Geotechnical professionals and architects review the guidelines as they are updated.

Alberta Infrastructure projects include roads and bridges. These projects have compaction testing requirements which are often a combination of general guidelines and special provisions. The combined specifications will stipulate frequencies and procedures for moisture and density testing during the construction phase.

Who Conducts Compaction Testing?

Projects usually require a Geotechnical Engineer of Record. The Geotechnical Engineer of Record, oversees testing, inspection, and construction practices that relate to soils and foundations. On projects that we are the Geotechnical Engineer of Record, we always use our own inhouse staff for all engineering inspections and materials testing.

Transportation and operation of a nuclear density gauge require training and certification. Geotechnical engineers and technicians must obtain their licensing through a registered engineering firm that employs a full-time Radiation Safety Officer (RSO). Geotechnical engineers must be registered with The Association of Professional Engineers and Geoscientists of Alberta (APEGA).

Many projects will require compaction testing to be the responsibility of the contractor. In this case, the contractor would hire us to monitor their work and provide them with compaction results and recommendations. In this scenario, E2K works alongside the contractor to get the job done as quickly as possible while being within project specifications.

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I hope we were able to help. If you have any questions please feel free to contact us, or request a quote!