Deep soil mixing

Deep soil mixing or DSM is one of the practical methods of soil improvement in the world, which produces cemented columns and modified soil characteristics by injecting stabilizing materials such as cement or lime using a mechanically hollow shaft drill in the soil. In this method, by successively executing the DSM columns and creating an overlap between them, sealing walls can be created or any arrangement can be performed under the foundation of the building, and after obtaining sufficient resistance, the foundation of the structure can be built on the executed DSM columns.

DSM execution method

As shown in the figure below, drilling is first done by auger to the desired depth. Then the drilling is stopped and the auger moves slowly upwards and during the movement, the slurry from the nozzles installed in the tips of the arms is injected into the soil with high pressure. This movement and injection is in stages and after 1 meter upwards, it rotates in that level for 1 minute and injects the slurry and this work continues until it reaches the level of natural ground. Of course, the distances and times mentioned vary according to the type of device and the type of soil. In addition, the top-down injection method can be performed depending on the project conditions and the location of the injection nozzles.

Additives for Deep Soil Mixing (DSM)

Cement slurry or dry cement is the most common additive in the deep soil mixing method. The volume of slurry used, depending on the case and soil conditions, is about 20 to 30% of unmodified soil volume. Lime is also a suitable additive that is sometimes mixed with cement and used simultaneously. In this case, the weight ratio of cement to lime is about 1 to 4 and their total is added to the amount of about 100 to 200 kg per cubic meter of unmodified soil. Other additives such as volcanic ash, kiln slag and other chemicals can also be used if possible.

Applications of Deep Soil Mixing (DSM) Method

the deep mixing method is used to improve a wide range of inorganic soft soils and soils in which other methods of improvement are not suitable, but in the case of organic soils can be considered Adding sand to the mixture improved the properties of the soil.

Deep soil mixing method is one of the most economical methods for improving soft soils. Economic, temporal, or environmental constraints sometimes make other improvement methods, such as preloading, or dynamic methods, uneconomical. On the other hand, these two methods are not very useful in urban areas due to vibrations and noise. The deep mixing method has proven its capabilities as a suitable alternative to these two methods as well as the deep foundation method (pile execution).

About 50 years after the invention of this method, due to the lack of technology needed to implement it, in a few cases this method has been used in Iran. Due to the existence of coastal areas in the north and south of Iran, the importance of using this method becomes clearer. Especially in our country, due to high seismicity and the possibility of liquefaction in coastal areas, the use of this method reduces the potential for liquefaction and prevents problems. Also, the possibility of improving the soil from the barge in the construction of ports and marine structures is another advantage of this method for use in coastal areas.

Soil remediation in deep soil mixing method depending on:

• Type of additives
• Mixing energy level

is different. In this method, by mixing the slurry with the soil, materials are made that harden over time and its strength increases and can be used as engineering materials with better geotechnical characteristics than the local soil in the designs.

Some applications of deep soil mixing method in bed improvement:

• Strengthen the foundations of various structures
• Decreased liquefaction potential
• Strengthen the foundation
• Strengthen foundations in road construction
• Oil tank foundations
• Sealing wall
• Execution of vertical retaining wall
• Excavation slope protection
• Port development
• Tunnel stabilization

Advantages of Deep Soil Mixing (DSM)

• The economics of this method compared to similar methods of improvement
• The cost of equipping the workshop is very low compared to similar methods such as dynamic compaction or pile execution
• Reduce soil permeability
• Increase soil resistance
• Reduction of settlement due to overhead
• Avoid liquefaction
• Correction of the ground
• Land becoming part of the soil-structure system
• Ability to control and approve the quality of work
• Very high execution speed
• Very low vibration and noise pollution compared to other common urban remediation methods
• Environmentally ideal