Construction of a building is a very detailed-oriented process. Though specifications and permits vary from project to project, the operations remain the same. As constructions are time-consuming, making good decisions in this process is vital. Therefore, enough time should be allocated to access and perform due diligence.
What is a diaphragm wall?
A diaphragm wall (D-wall) is durable concrete construction framed panel by panel. Diaphragm walls are used mainly in full sites near an existing structure where the ground and depth would be challenging for piled walls. D-walls provide a cost-effective solution for permanent retaining walls and shafts with fewer construction joints. Furthermore, these walls support prime constructions such as dams, tunnels, and basements. These support the foundation for deep dig. The walls are particularly favourably in reclaimed areas.
Features of a diaphragm wall
Diaphragm walls form a rectangular segment framed beneath the soil. The walls are framed in such a way that each panel is interlocked to ensure the stability of the structure and water-holding capacity. There are additional features that other construction methods replace:
- Large depth: The depth of the shaft wall that can be reached allows for the d-wall to be easily constructed.
- Small Ground Surface Settlement: The ground surface area can be controlled by a diaphragm wall which is essential in downtown areas.
- Strong Adaptability: D-walls can be applied to foundations, retaining walls, pile foundations, and so forth, and in different plane shapes.
- Convenient top-down method construction: D-walls can combine with top-down methods of construction to control the deformation of ground buildings and underground structures.
- Can be used as a deep foundation: D-walls help to meet the requirement of machine shafts being used as the structural foundation of a ventilation shaft.
Construction procedure of a diaphragm wall
The typical sequence for constructing a diaphragm wall works as follows:
- Constructing a Guide Wall:
Such walls provide a template for wall evacuation layout and stabilize the top trench. The structure of such walls helps sustain the horizontal arrangement and connection of the d-walls. A guide wall also helps mark the position of the panel, hold the steel cages, and avoid collapsing of soil.
- Evacuation to form a diaphragm wall trench:
This requires the removal of soil and stabilization. A rectangular apparatus is used for panel excavation. Special clamshells such as grab and buckets excavate the vertical panels. The digging mechanism may be either cable or hydraulic operated.
- Supporting trench cutting via a slurry:
Bentonite slurry is used for strengthening the sides. This slurry creates sufficient pressure to maintain the good soil.
- Inert reinforcement and placement to form a wall panel:
To the dug panel, concrete is added. A support cage is put inside; depending on the depth, up to two cages can be added. Once the cage is added, concrete gets added via tremie pipes into the trench. This added concrete removes the bentonite slurry. This slurry can be reused again.
Materials for diaphragm walls
Materials used for d-walls are
- cement,
- an aggregate of a certain size,
- sand,
- water,
- chemical admixtures,
- reinforcement via steel bars
- bentonite.
Diaphragm wall connections
There are two main ways to make connections between diaphragm walls:
- Stop End Pipes:
Before concreting, two steel pipes are attached to the channel. This allows for a semi-circle section panel after concreting.
- Disposable Pipes:
The second way is where two PVC pipes are placed at the split ends of steel fortification cage panels. Concreting is done on the main panel parting behind the slurry. While converting the other panel, indentation is also filled, thus connecting with the main panel.
Purpose and advantages of diaphragm walls
Diaphragm walls help with retaining excavations designed to take a high structural load. These d-walls also help with maintaining water tightness. A d-wall is significantly quicker and more economical to build. Additionally, this construction is available worldwide. Further advantages of D-walls are as follows:
- Diaphragm walls can also be used as a permanent wall structure.
- The walls can be installed at greater depths.
- Vibration and noise with the installation of a D-wall are less.
- A rigid structure, so that ground movement from the excavation is less.
Application of diaphragm walls
Diaphragm walls work well for the following situations:
- In areas of dense infrastructure
- In areas where a very rigid retention system is required
- In areas where vibration and noise are to be minimal
- In areas where dewatering is not possible
- In areas where the geology restricts a conventional retention system.
The most common applications are areas such as tunnels, deep basements, underpasses, underground car parks, and railway stations.
Conclusion
While many construction projects are pretty straightforward, others require more specialised approaches that can withstand more pressure and are safe. For example, certain structures require deep foundations, wherein diaphragm walls come into use. D-walls create a strong underground structural element that can bear immense amount of load and pressure. D-walls are central to many commercial projects offering a very reliable means of construction. Without d-walls, one would not be able to witness skyscrapers, long tunnels, and underground structures.
FAQs
What is the usual depth a diaphragm wall can reach?
A diaphragm wall can reach up to 50 meters in depth.
What are the general guidelines when constructing a diaphragm wall?
Vibration or noise during construction should not damage existing structures and the people around them. Consideration should be given to the equipment used while constructing a d-wall in a restricted place.
How is a diaphragm wall selected?
The selection of a particular wall depends on the following: Site conditions Previous surface data Geological features The depth of the features Anticipated stress and deformations due to upcoming constructions Availability of construction materials Techno-economic considerations
What is the difference between a retaining wall and a diaphragm wall?
A diaphragm wall is a deep structural unit that often acts as a supporting wall. These d-walls are essential in congested sites. Whereas retaining walls are rigid walls used for supporting soil laterally. These walls help restrain soil to a slope that is not in its natural form.
What is the structure element used in a diaphragm?
Diaphragms are usually plywood in timber construction, metal in steel construction, or concrete slab in concrete construction.
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