Soil mix - Triple pile wall

The triple pile wall (or mixed in place wall) consists of cylindrical overlapping columns, formed without casing where - when using the triple mixing tool - three intersecting piles are made simultaneously. The in situ soil is mechanically blended with a cement-based slurry. The result is a homogeneous mixed-in-place wall used for water cut-off and / or earth retention.

Construction chart

Construction sequence

Triple rod mixing installation process, in accordance with the requirements of standard prEN 14679: "Deep mixing” - Deep Soil Mixing or DSM (wet DMS method

1. In advance excavation of a guide trench approximately 0.5 m deep to accommodate the cement slurry during execution. Alignment of the triple mixing tool with the centreline of the wall. Commencement of the boring phase.

2. Throughout the descent, the auger-based triple mixing tool continues to rotate while self-hardening cement slurry is injected through the hollow stems of the central tubes, to the bottom of the augers.

3. The three mixing screws are driven by individual, however coupled rotary heads. Compared to the rotation direction of the inner auger, both outer augers rotate in opposite direction so as to mix the soil intensively with the binder grout.

4. After reaching depth specified by the design, standard up to 14 m, the triple mixing tool is withdrawn under rotation and simultaneous injection of grout. With a thickness of 0.40 m and a width of 1 m, several intersecting panels are installed in order to form a homogeneous and continuous wall in the soil.

5. Insertion of the reinforcing elements, e.g. profiles.

The installation process is under permanent quality control. The entire procedure it is electronically monitored, with registration of the parameters.

Fields of application

• Alternative solution to the ‘Berlin’ retaining wall or the secant pile wall

• Economical solution

• No decompression of soil

• Depending on the calculations and the desired function of the wall:

  • sheet piles could be vibrated in
  • profiles could be inserted (Berliner wall induced by the development of arching)
  • anchors could be made (for anchorage of MIP as a retaining wall)

Environmental impact

• Provision should be made to remove from the working platform the excess volume of cement slurry

• Vibration-free

• Limited noise pollution

Technical specifications

• Retaining function: depending on the geotechnical design

• Construction of a cutt-off wall with mixed in place columns (sealing): depending on the calculations, the properties of the slurry and the overlap between the secant columns. 

• Thickness: 0.40 m

• Depth: standard less than 20 m

• The soil is loosened and mixed with the suspension by means of a mixing unit consisting of slightly overlapping, multiple augers fixed on rods, all on the same line, attached on a rig.

• For structural purposes (withstanding bending moments), subsequent insertion of reinforcement elements or profiles in the freshly made columns is done.  

Related projects for this technique

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