How to Compact Granular Soils

Alternatives When Compacting Granular Soils

compaction roller
••• compaction roller. Photo Flickr CNE CNA C6F

Granular soils refer to a category of soils where cohesion between particles of the soil is absent or minimal thus making agriculture projects or construction on such surfaces a challenge. There are ways to address these issues by compacting granular soil to make it more manageable for use.

Working and compacting on granular soils such as sands and gravels is difficult to perform. Due to their composition, water can enter or leave the voids with relative ease. If voids in the sand are completely filled with water or are completely dry there are no forces holding the sand particles.

Applying vibration to those particles will tend to create a dense configuration. The amount of water in the voids of the granular soils will affect the cohesion between the particles. Dumping sand or gravel from the bed of a truck or from a scraper places the granular material in a relatively loose condition, particularly if the sand contains only a small amount of surface moisture. This material must be compacted so it can provide the required strength. ​ If the material is not compacted, then it can lead to settlements in the future.

Vibratory Rollers

This type of equipment is designed to consolidate granular soils to a high density, compacting very efficiently to shallow depths. They come in different sizes and different tons capacity. This type of equipment will work effectively when the soil is placed in a confined space.

Flat Plate Vibrators

There are excellent flat plate vibrators with a gasoline engine mounted to a unit that causes a flat skid plate to vibrate. These will do an efficient job on sands and small gravels, compacting to a depth or lift thickness of about 6 inches. Commonly used on small tranches and for small diameters pipe installation. Because of their limited power and impact force, it is not recommended when lifts are thicker than 6 inches.

Vibratory Hammer

The vertical vibration in the pile disturbs or ‘liquefies’ the soil and causes the soil particles to lose their frictional grip on the pile. The pile moves downward under its own weight, plus the weight of the vibratory hammer. The amplitude of at least one inch is usually required to cause enough soil disturbances to achieve pile driving. Vibratory compaction works well as the soil disturbance due to vibration and causes the soil particles to move into a denser configuration. Large amplitude results in a high soil strain level, a greater influence radius and higher degree of compaction.

Vibroflotation

This is another very effective device for compacting clean, free-draining sands and gravels. It resembles a standard internal concrete vibrator but is much larger and more powerful. The probe provides large capacity water jets, which acts downward and sideways, flooding the soil and breaking the surface tension. This allows the sand particles more freedom to settle into a compact configuration as the granular particles are vibrated.

New Tools for Compacting Soils

Technology is also improving in the area of compacting granular soils. There is equipment available for compaction that uses a monitoring system through sensors. This will measure the soil stiffness and generate a value related to the compaction progress on how good or bad the process is going. This technique will provide real-time values by reducing the time wasted compacting an area that is already finished. The tool will let you know when the design value has been obtained preventing the excess use of resources in over-compacting granular soil.

Other Important Factors

When compacting soils, you must put safeguards in place for your employees' health. An illness called Raynaud's syndrome is very common among workers who operate or manage compacting equipment. The all-day-long vibration transmitted to the hands and arms cause this illness. This can cause your employees to feel a sort of numbness and tingling in the fingers. If that worsens it can lead to loss of sensation in hand and finger muscles. Some manufacturers have designed equipment with reduced vibration to deter this.

Certain jurisdictions have laws limiting the use vibration forces.