Options for Building A Better Base

Any time you dig a trench or excavate an area for a driveway, foundation, floor, etc., compacting the soil is an essential part of that task. And since getting a good base is critical to any finished project, it's important to select the right compaction tool for the job.

Trench rollers and carrier-mounted attachments (such as those for excavators or backhoe-loaders) are popular choices for these particular compaction jobs. Both options offer the ability to keep workers out of harm's way by keeping them out of the trench or any area where there is the potential for cave-ins.

Remote and radio control of trench rollers enables workers to operate the machine from a safe distance. "The mobility and wireless remote allow for operators to compact [the soil] while following safety regulations and staying outside of trenches," says Fabian Salinas, Dynapac.

In the case of an attachment mounted on the end of a boom, no one has to enter the trench, minimizing the risk of accidents, adds Carsten Soltau, Stehr Baumaschinen GmBh.

Beyond that similarity, each option offers advantages for a particular application. When evaluating which is right for your job, assess soil conditions, the size of the job and your existing fleet.

Assess soil conditions
Obtaining optimum compaction is critical to any finished project. "The effects of inadequate soil preparation may take weeks or even years to become apparent," says Jay Baudhuin, Wacker Corp. "However, once the results begin to show, the costs of repairs far outweigh the time and costs of proper soil compaction the first time around."

To assess how to complete any compaction project, it's important to understand soil compaction and its characteristics. As it relates to construction, soil compaction is the process of mechanically increasing the density of the soil by packing the soil particles closer together to force out air, explains Al Springer, Allied Construction Products.

"The result is a denser soil that has the ability to hold greater weight," adds Baudhuin.

Mechanically compacting the soil is required because the density of the soil changes during excavation, and some soils become exposed. As a result, their natural ability to support a structure is altered. Mechanical compaction also accelerates the natural process of soil settling and, in some cases, enables construction even on marginal building sites.

Soil is generally classified into two main categories: granular and cohesive. A third category - organic soil - is typically not addressed because it is not compactable and would need to be removed and replaced with imported material.

Granular soils (sand and gravel) are coarse and large enough to see with the naked eye. When they are wet, they may be molded, but will crumble easily. The forces that hold them together are frictional due to their jagged, rough surface texture.

Conversely, cohesive soils (clay and silt) are very small and feel smooth when rubbed between your fingers. When wet, they are sticky and can be molded or rolled into almost any shape. When dry, they tend to be very hard and difficult to crumble. The forces that hold the particles together are molecular in nature.

Properly identifying the soil type you will be compacting is crucial for determining which type of compaction equipment is best for the job.

To optimally compact granular soils, you will need a tool that compacts via vibration. That can mean a trench roller with a smooth vibrating drum or, more commonly, a vibratory plate mounted on a carrier such as an excavator or even a wheel loader or skid steer.

"The vibration action reduces the frictional forces at the contact surfaces, allowing the particles to fall freely under their own weight," says Baudhuin. "At the same time, as the soil particles are vibrating, they become momentarily separated from each other, allowing them to turn and twist until they can find a position that limits their movement."