Impact Pier® System

On sites where there is a high water table or where the soils are comprised of loose sands, soft silts and clays that are susceptible to caving, this variation of the Rammed Aggregate Pier system is often used to achieve the sturdiness required for foundation support. 

How Impact Pier Works

The unique install process displaces soil during installation and utilizes vertical impact ramming energy to construct vertical displacement rammed aggregate piers, which exhibit unsurpassed strength and stiffness. The cavity is created to full depth by pushing a specially designed mandrel and tamper foot using a relatively large static force augmented by dynamic impact energy. Tamper foot diameters vary from 12 to 16 inches and depths normally range from about 10 to 50 feet, depending on design requirements. This method eliminates spoils as all penetrated soils are displaced laterally. A sacrificial cap prevents soil from entering the tamper foot and mandrel.

After driving to design depth, the hollow mandrel serves as a conduit for the placement of aggregate. The aggregate is placed inside the mandrel and the mandrel is lifted, leaving the sacrificial cap at the bottom of the pier. The tamper foot is lifted approximately three feet and then driven back down two feet, forming a one-foot thick compacted lift.

Compaction is achieved through static force and dynamic impact energy from the hammer. The Impact hammer densifies aggregate vertically and the beveled tamper foot forces aggregate laterally into cavity sidewalls. This results in excellent coupling with surrounding soils and reliable settlement control and superior strength and stiffness.

Construction Advantages

Construction Advantages of Impact Pier technology include:

• • Avoids casing and allows for construction of aggregate piers in caving soils and soils with high groundwater conditions.
• • Eliminates/Minimizes spoils for sites with Contaminated Soils
• • Provides Deep Treatment for Liquefaction Mitigation
• • Displacement Method densifies surrounding soils
• • Rapid installation
• • Low vibration relative to piles
• • Reliable and Cost Effective
• • Can be used with Grout or Concrete for environmentally sensitive sites or projects requiring higher capacity
• • Provides equivalent stiffness to Geopier elements