Deep Soil Mixing (DSM)

Deep Soil Mixing (DSM)

- The Deep Mixing (DM) method mixes in-situ soil with a hardening agent (cement, lime, slag, or other binders) at depths by augers. Deep mixing can be accomplished by a wet or dry method. The equipment for the wet method may have one to eight rotary hollow shafts with cutting tools and mixing blades above the tip. The binder slurry is introduced into the ground through each hollow shaft and exits from the nozzle while the shaft penetrates into the soil or is withdrawn. Some equipment has mixing blades rotating in opposite directions (i.e., double mixing) to improve the uniformity of the soil–binder mixture. The equipment for the dry method may have single or dual rotary shafts with cutting tools and mixing blades above the tip. The binder powder is introduced into the ground through each hollow shaft and the nozzle by air pressure.

History

The Deep Soil Mixing (DSM) method originated in Japan during the 1960s, primarily aimed at improving soft and sedimentary soils to enhance ground stability for construction projects. This innovative technique quickly gained traction due to its effectiveness in stabilizing weak soils, leading to its adoption in various countries, including those in Europe and the United States.

-1970s: The DSM method saw significant technological advancements, including the development of specialized machinery that facilitated its application in large-scale civil and industrial projects. The introduction of new additives further improved the method's effectiveness.

- 1980s and 1990s: Extensive research was conducted to optimize mixing processes and develop more effective additives, resulting in enhanced performance and reduced execution costs. These advancements solidified DSM's reputation as a reliable soil improvement technique globally.

By the late 1980s, DSM had expanded beyond Japan and Scandinavia, gaining popularity in the United States and Europe. The method became recognized as a standard practice for stabilizing weak soils, particularly in seismic regions where soil reinforcement is critical.

DSM Advantages

1. Ability to improve soil at great depths             

2. In-situ soil improvement, integrating the ground into the soil-structure system

3. Capability for quality control and verification of work

4. Very high execution speed

5. Cost-effective for deep soil improvement            

6. Low vibration and noise production

7. Applicable to various soil types

Design principles of DSM columns

The design procedure for deep soil mixing is similar to jet grouting columns design and also depends on the type of application. For foundation support, the following design procedure may be followed:

1. Based on the geotechnical conditions, select the type of method (dry or wet method) and type of binder for deep mixing.

2. Based on the geometry of the superstructure and the distribution and magnitude of loads, select the pattern of deep mixing (individual columns, blocks, walls, and grids).

3. Based on the required ultimate bearing capacity of the foundation and the soil strength, determine the required column capacity if the area replacement ratio is assumed or the area replacement ratio if the column strength is assumed.

4. Based on the column capacity requirement, determine the required minimum laboratory unconfined compressive strength of the stabilized soil considering the field to laboratory conversion factor and the scale factor.

5. Determine the minimum column length.

6. Determine the settlement of the column-reinforced foundation using the stress reduction method, the piled-raft method, or the column penetration method.

7. Determine the degree of consolidation of the column-reinforced foundation.

8. If columns are used to support embankments, stability analysis should be conducted. A numerical method is preferred, but a simplified limit equilibrium method may be used by limiting the column strength.

9. Iterations may be needed if at least one of the calculations does not meet the project requirement.