True Intelligent Compaction

Article contributed by Ingersoll Rand.

There are so many variables on construction projects that logistics never seem to go according to plan. Earthmoving projects experience problems with material gradation and moisture content. Plant operations, hauling logistics and mix laydown are fraught with interruptions on paving projects. There are so many impediments to achieving success, it can be surprising when construction projects are completed in accordance with agency specifications.

"Intelligent Compaction" in Concept and Practice
Compaction is one of the most important stages in the construction process. Without proper compaction or densification, materials cannot provide the support needed for structures or traffic loads.

Many believe that the process of compaction involves science. Others believe compaction is simply the application of practical techniques, using relatively simple equipment.

Proponents of the "science of compaction" are encouraging the construction industry to require sophisticated equipment to achieve what is called "intelligent compaction." The problem with this concept is that materials in construction are not uniformly ideal for the applications for which they are being used. Soils on earthmoving projects vary in properties, especially in moisture content. Improper field moisture content is the main factor in failing to achieve soil density. Knowing this, how practical is a requirement to use "intelligent compaction" equipment on these materials? Can the compactor compare a low soil stiffness modulus resulting from high air void content with a low modulus level caused by high field moisture content?

On a hot mix asphalt (HMA) paving application, can any compactor distinguish between rises in pavement stiffness resulting from increasing density and increased stiffness caused by cooling of the mix?

The answer in both instances is that no compactor is intelligent enough to reliably make this distinction.

Practical Compaction in Operation
Agencies and contractors recognize the importance of compacting disturbed soils to remove voids and avoid structural damage once loads are applied. Rather than relying on technology to produce satisfactory results, a more practical approach to achieve proper compaction is to make certain the people employed on construction projects are properly trained.

A well-trained compactor operator is more valuable and versatile than the "intelligent compactor." An experienced operator reacts to jobsite variables and compensates for changes to materials that allow construction to continue on schedule, which is important on any high-volume project.

Experienced compactor operators on earthmoving projects visually recognize problems in the material and know how to improvise during changing conditions. For example, an experienced operator sees when soils are too dry or too wet and adjusts the operation of the compactor. The experienced operator can also alert other personnel onsite that material modifications are needed.

The compactor does not possess this ability. The computer on the machine can only react based on pre-programmed algorithms. If the measured dynamic stiffness modulus for the soil is too low, the "intelligent compactor" will adjust itself to generate more force and/or require additional passes over the material in an attempt to increase its stiffness modulus. If this soil is too wet, more compaction force and more passes only make the situation worse. The "intelligent compactor" does not distinguish between wet soil and soil with excessive air voids. Only an experienced compactor operator knows the difference.