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.
Support foundations, structural mats, slabs, embankments, tanks, MSE walls, and industrial equipment. The ideal applications for CSC/CAP:
Soft clay, silty clay, silty and sandy clay, and loose soil sites.
Compressible soil sites.
Undocumented fill sites.
Gain LEED® points at sites with local and recycled concrete.
Sites where drilled holes will stand open during construction.
Sites near occupied buildings and in dense urban areas.
RAP 4-Step Construction Process
Drill hole to remove soft clay or loose sand.
Load crushed rock to ram bottom bulb. Compact rock/soil to 1 dia. below bottom.
Load crushed rock in thin lifts & ram to install ground improvement at edge & form RAP.
Finished RAP and ground improvement with footing and/or slab above.
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®!
UC Davis Brewery/Winery and Food Pilot Facility
“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
Compacted Soil Column & Compacted Aggregate Pier
Geologic Hazard Application
18, 24, 30 in dia
6 – 32 ft deep
Silt (ML, MH)
Clay (CL, CH)
Clayey Sand (SC)
Silty Sand (SM)
Bearing Capacity Range
4,000 – 9,000 psf
Cost effective support
Readily available material - CAP
Re-use onsite soil - CSC
High bearing capacity
Requires confinement in liquefiable layers
Spoil haul-off - CAP
Moderate depth limit
Soil mix columns
Farrell Design-Build Inc. | Sacramento 530.621.4867 | Irvine 949.428.9596