What Is the Dry Soil Mixing (DSM) Process and Its Purpose?

Dry Soil Mixing (DSM) is a widely used in-situ mechanical soil mixing technique, where a dry binder (commonly referred to as cementitious binder) is introduced into the soil and distributed using compressed air. The mixing action can be performed vertically or horizontally using paddle propellers (as shown in Figure 1), or using cylindrical tools with cutting blades (see Figure 10-2).

Purpose of Dry Soil Mixing

The goal of DSM is to evenly distribute the binder throughout the soil to trigger a chemical reaction that improves strength and stability. This process is commonly applied for:

  • Cement-lime columns

  • Deep soil stabilization

  • Jet-dry mixing

  • Mass soil treatment

  • Retaining wall support

Using compressed air as a carrier for the dry binder offers key advantages, such as reduced binder consumption while achieving the required strength. This is especially effective in wet or soft soils, where wet slurry methods would require more binder due to high water content.

Execution of the DSM Process

DSM is commonly used to form vertical soil-cement columns, typically 0.5 to 1 meter in diameter and 3 to 25 meters deep. In some projects, inclined columns are installed at slopes of 4:1 to 10:1.

For shallow depths, mass mixing is more suitable. This can be executed:

  • As interlocking columns forming a block

  • Or as a mass of blended soil using a rotating horizontal drum fitted with cutting heads (Figure 2).

Mass mixing typically reaches depths of 0.5 to 6 meters, though deeper applications (up to 15 meters) have been achieved with interlocking columns.

Three Phases of DSM Execution

The DSM process can be divided into the following core stages:

  1. Tool Penetration – Insert mixing tool to the target depth.

  2. Binder Injection & Initial Mixing – Inject the dry binder while starting the mixing process.

  3. Molecular Dispersion – Achieve a homogenous mix for optimal soil improvement.

Figures 3 and 4 illustrate the column formation and mass mixing process, respectively.

European Standard (EN 14679:2005) – Five-Stage Method

  1. Accurate positioning of mixing equipment.

  2. Tool penetration with simultaneous soil disaggregation.

  3. Binder injection (powder or granules) after reaching depth.

  4. Horizontal mixing of binder with native soil.

  5. Completion of soil-cement column.