13 Key Advantages and Disadvantages of Diaphragm Wall | Application & Uses of Diaphragm Wall
What Is the Diaphragm Wall? |Advantages and Disadvantages of Diaphragm Wall | Diaphragm Wall Construction Process |Uses of Diaphragm Wall | Types of Diaphragm Walls | Diaphragm Wall Vs Retaining
What Is the Diaphragm Wall?
Diaphragm walls are a type of rigid reinforced concrete wall that is made up of multiple panels that are linked together to form a single continuous wall.
The Diaphragm Wall can withstand bending moments and shear pressures caused by lateral soil loads, making it an excellent choice for deep excavations.
Diaphragm walls have a stabilizing and sealing function and can be used as cut-off walls for dams or excavation pits, foundations, or construction enclosures.
They are erected from the ground up as concrete or steel-reinforced concrete walls. They are thought to be highly deformable and virtually water-impermeable.
Diaphragm walls are often used in the construction of foundations for bridges, oil and gas tank farms, town halls, etc.
Diaphragm Wall Construction
The following is a summary of the diaphragm wall construction process:
- Construct a guide wall at the working platform level, often consisting of two parallel concrete beams to control panel alignment.
- Rectangular panels should be excavated using rope-suspended mechanical or hydraulic grabs. Hydraulically driven reverse circulation trench cutters can be used for penetration into tough rock hydro mills.
- Support trench excavation with bentonite or polymer slurry in all ground conditions to allow excavation below the groundwater table.
- Install temporary stop ends to construct the joints between neighboring panels, generally with a water stop incorporated.
- Set the panel reinforcing cages in place and tremie the concrete.
Applications and Uses of Diaphragm Wall
Common applications for diaphragm walls are:
1. Deep basements
Construction of foundations in deep basements, having very high loads applied to them. They are also used in the protection of foundation trenches from lateral abrasion produced by heavy vehicles.
2. Underground carparks and railway stations
Construction of underground carparks and railway stations. These must be built for the same depth underground as their buildings’ overground footprint.
3. Deep pump wells or below ground access tunnels
Construction of subsurface utility networks and access tunnels leading to buildings and other works such as ventilation shafts and manholes.
4. Tunnel approaches
Tunnel approaches are used to ensure cuts through soil and rock tunnels are properly constructed.
5. Pump stations
They are used to build complete pump stations or underground headworks and water reservoirs having large water storage capacity, such as irrigation dams.
6. Strong slopes
They are also used to prevent landslides and rockfalls.
7. Tunnel entries and exits
They are constructed to protect tunnel entrances from damage due to intense traffic flow or the threat of falling rocks.
8. Dam abutment protection works
They are used to protect abutments of dams from erosion and water seepage while regulating the effects of any failure within the dam structure itself.
9. Cut-off walls and retaining structures
They are also used in the construction of retaining structures constructed to a depth that would normally require the use of gravity or pressure-retaining wall systems.
10. Water reservoirs
The purpose of a water reservoir is to store water at a higher elevation than where it is diverted from, without allowing it to flow back down the original diversion works.
Types of Diaphragm Walls
- Load-bearing walls: They are applied in the foundation of towering structures, bridges, and piers in place of drilled piers.
- Structural Diaphragm walls: They are used to reinforce the perimeter walls of deep basements, subterranean parking garages, and subways.
- Cutoff walls: in hydraulic structures diaphragm walls are used as impermeable cutoffs to prevent seepage below earth dams and weirs.
Diaphragm Wall Variations
The main motivation for the development of this type is to provide a tougher wall than that required by the existing regulations and to guarantee walls protection from impact loads.
The types include:
- Diaphragm walls – traditional reinforced concrete construction
- Diaphragm walls – precast concrete construction
- Steel-reinforced diaphragm walls
- Concrete-filled steel tubes diaphragm walls
- Composite wall panels
- CFW (Composite Filled Walls)
Diaphragm Wall Vs Retaining Wall: Diaphragm Wall and Retaining Wall Difference
A retaining wall is a structure that holds back the ground. A diaphragm wall is an extra layer of the foundation with rebar reinforcement for additional support.
A retaining wall is a structure that holds back the ground to prevent erosion and landslides.
It can also be used as a form of decoration or landscaping design element if it has been built up high enough or in such a way that it blends into the surroundings when looked at from certain angles.
The material used varies depending on soil conditions, climate, and aesthetic preferences; however concrete masonry units are most common because they offer good resistance to moisture and provide stable footing for plants or retaining walls when the soil stabilizes.
A retaining wall is usually just a ground wall with some sort of construction on top, and it is an infamous source of problems in earthquake zones because they are easily damaged during an earthquake.
A diaphragm wall is a structure that holds back the ground especially in tight areas where there’s not enough space for a retaining wall.
A diaphragm wall is often used in the construction of tunnels and underground areas but may also be used in the construction of foundations and maintenance walls.
In most instances, they are designed to be self-supporting with an underlying foundation that stabilizes them from below.
They are often made up of concrete, stone, or metal rebar anchors to provide the necessary tensile force.
A diaphragm wall is often used in the construction of retaining walls but also offers additional support for buildings and other structures built above it.
A retaining wall is a type of wall that supports the ground or soil around it, typically at the edge of a hill.
A diaphragm wall is a reinforced concrete slab built in between two vertical walls to hold back pressure from the earth behind them.
They are designed this way because an outward force on one side only compresses the material on that side and not both sides as with a retaining wall.
Advantages and Disadvantages of Diaphragm Wall
Advantages of Diaphragm Wall Construction
1. Construction process has little or no vibrations:
Due to the fact that diaphragm walls are constructed with massive amounts of concrete, construction vibrations are reduced to a minimum.
2. Speed of erection
Because pre-camber panels can be prepared and placed in the trench very quickly, diaphragm wall construction is fast and economical. Diaphragm walls can be erected at a rate of 5 to 10 meters per day depending on ground conditions.
Concrete diaphragm wall construction is about 2 times faster than conventional retaining wall construction and much more economical.
3. Can be constructed to great depths
Diaphragm walls can be constructed to very deep depths, unlike retaining walls. As they are precast panels they can be fitted together in a shape that will fit the planned excavation depth.
4. Can handle very high loads
Because of the strength of concrete, diaphragm walls can support high loads and thus provide a greater load bearing capacity than other wall types (such as masonry or brick).
5. Can be constructed on various soil types and rocks
Diaphragm walls can be constructed on various soil types and rocks. Retaining walls are only suitable for light duty.
6. Flexibility of design
Because they are precast panels, diaphragm walls offer a high degree of flexibility in terms of design and match any site conditions, unlike retaining walls.
7. Diaphragm walls are watertight
The design of diaphragm wall allows for a considerable amount of water infiltration. As a result, diaphragm walls have zero dead load in relation to the load-bearing capacity of the soil.
8. Long life span
A typical life expectancy for tunnels and underground structures constructed with Diaphragm Wall is 50 years or more.
9. Outstanding seismic performance
Even if installed on soft soils, diaphragm walls still provide outstanding seismic protection (tighter than retaining walls).
10. Serves both as wall and foundation
Diaphragm walls serve both as an external wall for the basement and a foundation for the superstructure. Diaphragm walls can serve as foundation walls for concrete or steel structures.
Disadvantages of Diaphragm Wall Construction
1. Expensive
A diaphragm wall requires heavy and complicated precast elements which make it expensive. The need for excavating and pumping equipment makes diaphragm wall construction relatively costly, as compared to other types of excavation support systems.
2. Not economical for small & shallow basements
Because of the expense of installing them, diaphragm walls are not an economical option for small and shallow basements.
3. Very limited options in terms of design
Due to the weight of the structures and the equipment needed, diaphragm wall construction is limited in its design aspect.
Diaphragm wall FAQs
1. What is the purpose of a diaphragm wall?
A diaphragm wall is a reinforced concrete wall built in a deep trench excavation using either in-situ cast concrete components or prefabricated concrete components.
Diaphragm walls are commonly implemented on cluttered sites, near existing structures, when headroom is limited, or if the excavation is of a depth that would otherwise necessitate the removal of much larger volumes of soil to provide stable shattered slopes.
2. What is a diaphragm wall used for?
Diaphragm walls are mostly utilized for retaining walls, heavy foundations, combined retaining wall and foundation, combined retaining wall and barrage, and deep basement top-down construction after wall execution.
3. What exactly is a diaphragm wall suited?
Diaphragm walls are suited for most soil types, and its construction creates just a modest amount of vibration and noise, making them ideal for work near existing structures.
Furthermore, floor slab connections and buried falsework can be built within the walls.
3. How does a diaphragm wall work?
A diaphragm wall is reinforced concrete structure built in between two external walls. The inner and outer walls are connected at multiple locations to form the shape of a cylinder that matches the excavation trench.
Reinforcing bars are installed within the concrete slab at regular intervals to provide tensile and flexural strength required by the soil pressure, respectively.
In addition, steel beams may be installed as required for foundation construction.
4. How far underground can a diaphragm wall extend?
In most cases, deeper excavations utilizing diaphragm walls involve the excavation of several feet of soil above the level of the top of wall and leveling off prior to pouring the concrete.
5. What are girders in diaphragm walls?
Girders are located in different positions depending on the type of construction.
In most cases, girders are located at the base of the wall to serve as support for foundation walls and combined retaining/basement walls.
In some cases, steel beams are installed over the top of the diaphragm wall to help establish a stronger base area for foundations.
However, they may also be used as columns to reinforce the sidewalls or basement floor.
6. What are the advantages of diaphragm walls?
Diaphragm walls are appropriate for unstable soil types beneath the water table, construction process is cut. It is capable of carrying vertical loads.
7. What are the disadvantages of diaphragm walls?
The design of the diaphragm wall is very complex and its cost is high.
8. What are the benefits of diaphragm walls?
The precast concrete panels are placed directly into the excavation trench. They do not require any formwork to support their placement, saving time and money.
They support the excavation weight and prevent collapse of unstable soils. Their extensive use in Japan makes them an ideal method for bridge or tunnel construction in soft ground conditions.
9. What is the difference between a diaphragm wall and a retaining wall?
A diaphragm wall is a reinforced concrete slab built in between two external walls. The inner and outer walls are connected at multiple locations to form the shape of a cylinder that matches the excavation trench.
Reinforcing bars are installed within the concrete slab at regular intervals to provide tensile and flexural strength required by the soil pressure, respectively.
In addition, steel beams may be installed as required for foundation construction.
Retaining wall on the other end is a wall built to retain soil outside of a construction site. The wall is constructed parallel to the contours of the ground and is made from precast concrete panels.
10. What are the main purpose of constructing diaphragm walls?
The excavated sections of diaphragm walls can be used for other purposes, such as creating separate foundation walls or additional space for basements and underground parking area.
Diaphragm wall is very suitable for the construction of bridges and tunnels in soft ground conditions.
11. What are the main benefits of using diaphragm walls?
Diaphragm walls are suitable for excavation sites with weak soil conditions and limited headroom. The towers can also be used as a foundation for concrete structures.
12. What prevents a lean to collapse when a diaphragm wall is built?
The use of wide diameter steel girders will act as additional reinforcement to help resist collapse.
13. What is a major disadvantage of the diaphragm wall?
Due to the high expense of diaphragm walls, they may be uneconomical unless they can be integrated into a construction process.
14. What is the difference between a diaphragm wall and secant wall?
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.
Diaphragm walls tend to be used for retaining very deep excavations as they can be designed to take very high structural loads
