When building on soft clay — a large warehouse floor or a road embankment, for example — many people think of "driving piles" first. But for work where the load is spread over a wide area and settlement is a bigger concern than point loads, engineers often consider cement columns, one of the most popular "Ground Improvement" methods. This article explains the principles and how to choose them from a geotechnical engineering perspective.
What are cement columns (deep soil mixing)?
Cement columns (Cement Column / Deep Soil Mixing, DSM) improve soft soil by mixing a cementitious binder into the existing soil in place (in-situ) with a mixing tool, producing soil-cement columns with higher strength and stiffness than the original soil. The method is also known as the Deep Mixing Method (DMM) or Soil Cement Column.
The key point is that it is not a "pile" in the sense of a structural element carrying point loads like a concrete pile; rather, it "turns the existing soil into a better material". Soil-cement columns therefore work as a system with the surrounding soil to raise the average bearing capacity of the soil layer and reduce settlement, rather than carrying the entire load themselves like piles.
Legally, the Ministerial Regulation on Building Foundations and Ground Supporting Buildings B.E. 2566 (2023) defines "foundation soil" to include other materials provided to improve the soil supporting a building's foundation. Ground improved with soil-cement columns must therefore be designed and checked for bearing capacity in line with the Ministerial Regulation, just like ordinary foundation soil (see Summary of the 2023 foundation Ministerial Regulation)
How do cement columns work?
The working principle is to blend a binder — mostly Portland cement (other materials may be added per the design) — into the soft soil at the required depths. Reactions between the cement, water and soil minerals cause hardening (cementation), so the previously soft soil gains shear strength and stiffness. The typical steps are:
- Drill and mix: The mixing tool rotates down into the soft soil to the design level while breaking up the soil.
- Inject binder: Cement slurry (wet method) or cement powder (dry method) is injected and mixed with the soil as the tool rotates.
- Withdraw with re-mixing: The tool is slowly withdrawn while rotating to make the mix uniform over the full depth.
- Cure and harden: The soil-cement column hardens over time before carrying the design load.
These columns can be arranged in several patterns depending on the purpose — for example as single columns on a grid across the area to support floors and reduce settlement, or overlapping in walls/blocks to resist lateral movement in excavations or embankments.
What projects are cement columns suited to?
Cement columns suit work that carries loads spread over a wide area on soft soil, where settlement control is the main concern. Common applications include:
- Warehouse and factory floors: Reduce settlement of floor areas carrying goods and machinery on soft soil.
- Embankments and roads on soft soil: Improve embankment stability and reduce differential settlement at bridge approaches or transitions.
- Ground improvement under shallow foundations: Allow spread footings to sit on improved soil instead of deep piles, where appropriate.
- Deep excavation and earth retention: Columns arranged as walls resist lateral movement and reduce water seepage.
Conversely, work carrying high point loads, such as high-rise columns, usually still needs concrete piles that transfer loads directly to stiff soil, because the strength of soil-cement columns is much lower than that of concrete. For wide areas on soft soil, engineers often compare cement columns with other ground improvement methods such as PVD with preloading, which takes longer to wait out settlement but has a different cost (see the overview in Ground improvement methods)
The 3D view below shows the most common application — a warehouse floor on soil-cement columns laid out on a grid — together with column layout patterns and quality control steps.
What are the advantages and limitations of cement columns?
Advantages
- Effectively reduce settlement of floors and embankments on soft soil over wide areas
- Use the in-situ soil as part of the material, reducing soil import and export
- Lower vibration and noise than pile driving, suitable for sites with adjacent buildings
- Fast to install on large ground improvement areas
Limitations
- Unit strength far lower than concrete piles; not suited to high point loads
- Quality depends on mixing uniformity; construction must be strictly controlled
- Soils high in organic matter or certain chemicals may interfere with cement reactions; mix trials are needed first
- Requires soil investigation and project-specific design; no one-size-fits-all formula
Binder content, column size and spacing, and design strength depend on soil type, applied loads and laboratory mix test results. This article explains principles only and does not give design values; the design engineer should set them based on each project's actual soil investigation results.
How do cement columns differ from concrete piles?
Both make it possible to build on soft soil, but they work on different principles. Concrete piles are structural elements carrying point loads and transferring them to stiff soil, while cement columns improve the soil to make it stiffer and work together with the surrounding soil. The table below summarizes the main differences.
← Scroll to see the full table →
| Issue | Cement columns (DSM) | Concrete piles |
|---|---|---|
| Principle | Improve the existing soil to make it stiffer | Structural element carrying point loads |
| Material | Existing soil mixed with cementitious binder | Reinforced concrete |
| Load carrying | Works with surrounding soil; low unit strength | Carries high point loads |
| Best for | Warehouse floors, embankments, wide-area settlement reduction | Building columns, high point loads |
| Vibration/noise | Low | Higher (if driven) |
| Verification | Sample strength tests · coring · parameter control | PDA · Static Load · Seismic Integrity |
No method is always better; it depends on the type of load, soil type and budget. Many projects use both together — for example concrete piles under building columns and cement columns to improve the soil beneath floors and embankments. The right approach is to have an engineer compare options based on actual soil investigation results.