Diaphragm wall
A diaphragm wall is a structural concrete wall constructed in a deep trench excavation, either cast in situ or using precast concrete components. Diaphragms walls are often used on congested sites, close to existing structures, where there is restricted headroom, or where the excavation is of a depth that would otherwise require the removal of much greater volumes of soil to provide stable battered slopes.
Diaphragm walls are suitable for most subsoils and their installation generates only a small amount of vibration and noise, which increases their suitability for works carried out close to existing structures. In addition, floor slab connections and recessed formwork can be incorporated into the walls.
The walls generally range in thickness from 500 - 1,500 mm and can be excavated to depths of over 50 m. Excavation is typically carried out using rope-suspended mechanical or hydraulically-operated grabs. Specific ground conditions or greater depths may require the use of hydromills – hydraulically-operated reverse circulation trench cutters – to penetrate into hard rock by ‘cutting’ rather than ‘digging’. Hydromills can achieve depths of up to 80 m.
The excavation stability is maintained by the use of a drilling fluid, usually a bentonite slurry. This is a controlled mixture that has thixotropic properties, meaning that it exerts a pressure in excess of the earth and hydrostatic pressures on the sides of the excavation. The walls are constructed, using reinforced or unreinforced concrete, in discrete panel lengths generally ranging between 2.5 - 7 m. Purpose-made stop ends can be used to form the joints between adjacent panels, with a water bar incorporated across the joints. More complicated arrangements such as ‘L’ or ‘T’-shaped panels can be constructed where additional bending moment capacity or wall stiffness is required.
Precast concrete diaphragm walls have the same advantages but are less flexible in terms of design. The units are installed in a trench filled with a special mixture of bentonite and cement with a retarder added to control the setting time. Ground anchors are used to tie the panels or posts to the retained earth to provide stability.
The high cost of diaphragm walls can make them uneconomic unless they can be incorporated into part of a building structure. As such, they are suited for deep basements, underground car parks and rail stations, tunnel approaches, underpasses, deep shafts for tunnel ventilation, pumping stations, and so on.
[edit] Related articles on Designing Buildings Wiki
- Basement excavation.
- Building foundations.
- Crosswall construction.
- Curtain wall.
- Diaphragm.
- Excavating plant.
- Ground anchor.
- Groundworks.
- Metal profile cladding.
- Partition wall.
- Rainscreen.
- Retaining walls.
- Secant pile wall.
- Sheet piles.
- Substructure.
- Trench.
- Trombe wall.
- Wall ties.
- Wall types.
[edit] External references
- Bacsol - Diaphragm walls
- ‘Building Construction Handbook’ (6th ed.), CHUDLEY, R., GREENO, R., Butterworth-Heinemann (2007)
Featured articles and news
Classroom electrician courses a 'waste of money'
Say experts from the Electrical Contractors’ Association.
Wellbeing in Buildings TG 10/2025
BSRIA topic guide updates.
With brief background and WELL v2™.
From studies, to books to a new project, with founder Emma Walshaw.
Types of drawings for building design
Still one of the most popular articles the A-Z of drawings.
Who, or What Does the Building Safety Act Apply To?
From compliance to competence in brief.
The remarkable story of a Highland architect.
Commissioning Responsibilities Framework BG 88/2025
BSRIA guidance on establishing clear roles and responsibilities for commissioning tasks.
An architectural movement to love or hate.
Don’t take British stone for granted
It won’t survive on supplying the heritage sector alone.
The Constructing Excellence Value Toolkit
Driving value-based decision making in construction.
Meet CIOB event in Northern Ireland
Inspiring the next generation of construction talent.
Reasons for using MVHR systems
6 reasons for a whole-house approach to ventilation.
Supplementary Planning Documents, a reminder
As used by the City of London to introduce a Retrofit first policy.
The what, how, why and when of deposit return schemes
Circular economy steps for plastic bottles and cans in England and Northern Ireland draws.
Reporting on Payment Practices and Performance Regs
Approved amendment coming into effect 1 March 2025.
Comments
Understanding the advantages and disadvantages of ground water control in reference to this method would be interesting.