Introduction to CSM construction method and equipment

The CSM construction method is also called the milling deep mixing method. Combining the hydraulic groove milling machine technology & deep mixing technology, an innovative underground continuous wall construction method is carried out; the main principle is to mill the original formation through a pair of hydraulic milling wheels at the lower end of the drill pipe. Stirring, mixing, and mixing cement slurry solidification liquid at the same time, after fully stirring and mixing with the broken original foundation soil, a cement-soil continuous wall with certain strength and good water-stop performance is formed; CSM construction method is mainly used to stabilize weak and loose soil layer, sandy and cohesive soil, gravel soil, gravel soil, strong weathered rock and other strata; it is suitable for foundation reinforcement, foundation pit water-stop curtain, foundation pit retaining wall, subway shield entrance and exit hole reinforcement, retaining soil + stop Water + permanent wall three walls in one and so on. 

一、 Features of construction method: 

1. Adapt to wide strata

It can carry out deep mixing construction in hard stratum, and can cut hard stratum (pebble and gravel stratum, strong weathered rock stratum), which overcomes the shortcomings of traditional multi-axis mixing system that cannot be constructed in hard stratum;

2. The verticality of the wall is good

The accuracy of the wall is ≤1/250. The equipment has a high-precision verticality sensor. During the construction, the verticality of the groove can be dynamically monitored by the computer, and the deviation correction system equipped with the equipment can be adjusted in time to ensure the accuracy of the wall;

3. Good wall quality

The injection amount of cement slurry is controlled by computer, and the cement slurry and soil are evenly mixed, so that the wall uniformity and quality are good, and the material utilization rate is high. Compared with other mixing processes, materials can be saved;

4. The depth of the wall is large

The guide rod type double-wheel mixing equipment can excavate and mix to a depth of 65 m; the rope-type two-wheel agitator can excavate and mix to a depth of 80 m;

5. The construction is more environmentally friendly

The undisturbed strata are directly used as building materials, and the total amount of spoil and slurry is small;

6. Low construction disturbance

There is almost no vibration during the construction stage, and in-situ mixing is adopted, which has little disturbance to the foundation of surrounding buildings and can be constructed close to the buildings.

二,、the principle of construction method

The construction process of the CSM construction method is very similar to the deep mixing technology, which is mainly divided into two main parts: drilling down to form a groove and uplifting to form a wall. During the process of drilling into slots, the two milling wheels rotate relative to each other to mill the formation. At the same time, a downward propulsion is applied through the guide rod to cut deeply downward. In this process, bentonite slurry or cement (or cement-bentonite) slurry is simultaneously injected into the tank through the grouting pipeline system. to the required depth. The process of troughing is now completed. In the process of lifting into the wall, the two milling wheels are still rotating, and the milling wheels are slowly lifted upwards through the guide rod. During the lifting process, cement (or cement-bentonite) slurry is injected into the tank through the grouting pipeline system and mixed with the muck in the tank. The CSM trough forming technology is different from the grab bucket in the trough forming process, and will not form the grabbed muck. Finally, the dregs will be mixed with the injected cement slurry in the groove to form the underground diaphragm wall.

三、Construction technology and process:

The CSM construction method can adopt jump-beating mixing construction and down-beating mixing construction. The length of a single sheet is 2.8m, the lap length is generally 0.3m, and the effective length of a single sheet is 2.5m.

Construction steps: 

1. CSM construction method wall positioning and setting out;

2. Excavate the guide trench (the guide trench is 1.0-1.5 meters wide and 0.8-1.0 meters deep);

3.The equipment is in place, and the milling head is aligned with the position of the groove 

4.The milling wheel sinks and injects water to cut and mill the in-situ soil to the design depth;

5.The milling wheel is lifted and the grouting slurry is stirred into the wall synchronously;

6.Move to the next slot position and repeat the above steps.

四 、CSM construction method equipment:

CSM construction method equipment double-wheel mixing drilling rig, there are two types of guide rod type and rope type, the maximum construction depth of the guide rod type can reach 65m, the maximum construction depth of the rope type can reach 80m, and the thickness of the wall is 700~1200mm.

At present, pure electric double-wheel stirring equipment has been developed in China, and the traditional hydraulic motor is replaced by the frequency conversion motor. On the premise of ensuring the construction efficiency, the equipment cost and construction cost are further reduced.

五、Scope of application

1. Foundation reinforcement;

2. Water-stop curtain for foundation pit;

3. Foundation pit retaining wall;

4. Reinforcement of subway shield entrance and exit holes;

5. The working conditions with large formation undulations and many corners.

In recent years, the CSM construction method has been more and more widely used in China because of its high construction efficiency and good wall-forming effect. The CSM construction method can greatly save concrete and steel, reduce the cost of the project, ensure the smooth implementation of major projects, and solve complex geological problems. Under the sensitive environment conditions of cities and cities, the deep groundwater control problem faced by the development of deep and large underground spaces effectively protects the safety of adjacent buildings, underground structures, subway tunnels and municipal pipelines, and has remarkable social and economic benefits.