What is a Diaphragm Wall Pile?
Diaphragm wall is a continuous reinforced concrete wall cast in place constructed in the ground to support major construction activities like the construction of dams, tunnel approaches, deep basements and enclosures.
The construction includes the excavation of a trench under the protection of a support suspension (a thixotropic slurry such as bentonite mud) designed to temporarily stabilize the trench wall. After excavation with a mechanical or hydraulic grab, the support slurry is replaced by concrete and steel reinforcement is placed.
When to use Diaphragm Walls
Diaphragm walls tend to be used for retaining very deep excavations as they can be designed to take very high structural loads, also projects constructing tunnels and car parks in urban areas and quay walls.
How to Construct Diaphragm Walls
A diaphragm wall is generally constructed in a series of discrete panels typically ranging in length from 3m to 7m. Depths of diaphragm walls vary depending on the application and the specified requirements but typically they can range from a few meters to tens of meters. The width of the wall can vary from 600mm to 1800mm depending on the application. Once a panel is excavated and the support fluid cleaned the required stopends are installed. The stopend produces a defined profiled joint to the next panel and is also used to install a water bar if required. The number of stop ends used in each panel depends on the construction sequence.
The next stage of the process is to install a pre-fabricated reinforcement cage and concrete the panel. The concrete is poured in one continuous operation through one or more tremie pipes (depending on panel size) that initially extend to the bottom of the trench. As the concrete level rises within the panel the tremie pipes are progressively shortened however the discharge end of the tremie pipe always remains embedded in the fresh concrete.
Finally, after completion of a primary panel the adjacent running panel is excavated and the stopend removed to reveal the profiled joint and water bar. The reinforcement cage is then installed and the panel concreted in the usual manner. The construction sequence then continues with a combination of primary, running and closing panels. Closing panels are used to complete a series of panels and because they are constructed between two previously constructed panels they require no stopend.
Advantages of Diaphragm Walls
- The primary advantage of a diaphragm wall over a secant wall is the reduced number of joints in the wall which ultimately improves the walls water tightness.
- Water retaining function (impervious wall) and / or a soil retaining function. Eventually also a foundation function for heavy vertical loads (structural wall).
- Constructed as continuous walls or are designable as individual structural elements to carry vertical loads (barrettes).
- Designed to withstand very high vertical loads
- Support of deep excavation pits in the direct vicinity of existing structures
- Vibration-free installation
- Low noise pollution: engine noise only
- Removal of soil and disposal of bentonite
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