Go Vertical with Confidence®

Compacted Soil Column &
Compacted Aggregate Pier

Slide 1

BART station parking garage in Pleasant Hill, CA. RAP - 30" diameter by 20' to 26' deep for foundation support and uplift RAP for seismic overturning of new 8 story garage.

Slide 2

Cavallo Point at Fort Baker in Golden Gate National Park, CA. RAP – 30" diameter by 15' deep to provide foundation support of new resort lodges at Cavallo Point Resort.

Slide 3

Rice Growers processing expansion West Sacramento, CA. RAP - 30" diameter by 14' deep for foundation support of new building inside operating plant.

Slide 4

Caltrans Highway 880 and Highway 92 interchange in Hayward, CA. RAP - 30" diameter by 18' deep for Caltrans East bound and West bound H92 MSE wall support.

Slide 5

Engineering IV at Cal Poly, San Luis Obispo, CA. RAP - 30" diameter by 16' deep for foundation support and uplift RAP for seismic overturning of new 3 story building.

Slide 6

Carmel Lofts in Sunnyvale, CA. RAP - 30" diameter by 18' deep for foundation support of mixed use residential building.

Slide 7

West Entry Parking Garage at UC Davis. RAP – 30" diameter by 15' deep for foundation support of new 6 story parking garage.

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Compacted Soil Column and Compacted Aggregate Pier (CSC and CAP) are soil-replacement, ground improvement methods. CSC/CAP are like rammed piers, aggregate piers, sand piers, and compacted soil/soil-cement columns. CSC/CAP improve soft clays and silts, loose sands, undocumented fills, and compressible soil. The CSC/CAP process constructs strong, engineered, “composite ground” for the support of foundations and slabs. CSC/CAP improve the ground by vertical and horizontal compaction of lifts of select material like crushed rock, sand, recycled material, and soil-cement mixes. Compressible soil is drilled out and replaced with the select material that is rammed into dense compacted lifts that expand the drilled cavity. The ramming of the select material creates a cavity expansion effect that increases soil strength and stiffness, resulting in higher bearing capacity and reduced soil compressibility. CSC/CAP provide strong, composite ground to support conventional foundations, slabs, and mats with reduced settlement.

CSC/CAP Applications

Support foundations, structural mats, slabs, embankments, tanks, MSE walls, and industrial equipment. The ideal applications for CSC/CAP:

  1. Soft clay, silty clay, silty and sandy clay, and loose soil sites.
  2. Compressible soil sites.
  3. Undocumented fill sites.
  4. Gain LEED® points at sites with local and recycled concrete.
  5. Sites where drilled holes will stand open during construction.
  6. Sites near occupied buildings and in dense urban areas.


4-Step Construction Process

Slide 1


Drill hole to remove soft clay, loose sand, or undocumented fill.

Slide 2


Load select material to ram and compact bottom bulb to 1 diameter below drilled hole.

Slide 3

Step 3

Load select material in lifts & ram and compact to install ground improvement at edge & form CSC/CAP.

Slide 4

Step 4

Finished CSC/CAP and ground improvement with footing and/or slab above.

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Technical Details

Compacted Soil Column and Compacted Aggregate Pier (CSC and CAP) provide excellent ground improvement support of foundations and slabs. The CSC/CAP process uses rammed and compacted select material in a drilled hole to form strong, engineered, “composite ground.” Select materials include crushed rock, sand, recycled material, and engineered soil-cement mixes. The CSC/CAP compaction process is applied to each lift of select material. The compaction force causes the select material to compact and to press laterally into a drilled hole; resulting in a coarse-sided CSC/CAP with a finish diameter greater than the drill diameter. CSC/CAP produces cavity expansion effects on the adjacent soil that 1) increase lateral confining pressure, 2) increase shear strength, 3) increase over-consolidation ratio, 4) reduce void ratio, and 5) increase soil stiffness. As CSC/CAP composite ground is loaded, high friction forces at the edges resist load and transfer the footing stress out and lower into the soil profile. A CSC/CAP is akin to a stiff spring that is confined in a soft spring medium (the native soil), where the stiff spring will attract more load and resist compression by virtue of the very dense lifts of compacted select material.

Most CSC/CAP are 5 to 25 feet deep and occupy between 5% to 25% of the footing bottom. CSC/CAP installed with local and recycled materials qualify for sustainability and LEED® points. CSC/CAP can be equipped with steel anchors to resist net tension forces. Full-scale load tests to 200% confirm the design bearing capacity on all projects.

Farrell uses excavators with hydraulic hammer attachments to install CSC/CAP. The hamming tool is designed to compact an 18 to 24-inch thick lift of select material.

CSC/CAP diameters are 18, 24, and 30-inches. CSC/CAP are cost effective, settlement control, ground improvement systems that support your project to Go Vertical with Confidence®!


Testimonial Image

UC Davis Brewery/Winery and Food Pilot Facility

Davis, CA

“The recycled concrete content in the system really made this a double win as we saved money for the project instead of using concrete drilled piers and we enhanced sustainability for the project.”

John Westphal, SE

KPW Structural

Compacted Soil Column & Compacted Aggregate Pier

Geologic Hazard Application

Soft/Loose Soil

Slope Stability


  • 18, 24, 30 in dia
  • 6 – 32 ft deep

Compatible Soils

  • Silt (ML, MH)
  • Clay (CL, CH)
  • Clayey Sand (SC)
  • Silty Sand (SM)
  • Undocumented Fill

Bearing Capacity Range

4,000 – 9,000 psf

Key Advantages

  • Cost effective support
  • Readily available material - CAP
  • LEED opportunity
  • Re-use onsite soil - CSC
  • High bearing capacity
  • Uplift-tension hold-down

Key Considerations

  • Vibration system
  • Requires confinement in liquefiable layers
  • Spoil haul-off - CAP
  • Semi-rigid inclusion
  • Casing
  • Moderate depth limit

Comparable To

  • Overex/replace
  • Concrete piers
  • Driven piles
  • Geopier®
  • Soil mix columns

Farrell Design-Build Inc.  |   Sacramento  530.621.4867   |   Irvine  949.428.9596

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