Robert Jansen
Technical Sales Manager
Combi-wall constructions are used for heavy quay walls, deep basements, harbour works, and tunnel reception shafts where the loads are too great for regular sheet piling. On this page, you can read how combi-walls work, when anchoring is necessary, and why strand anchors are an efficient solution for combi-wall anchoring.
A combi-wall is a composite earth and water-retaining structure consisting of steel pipe piles combined with intermediate sheet piles. The pipe piles provide the high bending stiffness and moment capacity of the structure; the sheet piles serve as the earth and water retention between the piles. This combination creates a wall that can withstand significantly higher loads than a regular sheet pile wall. Combi walls are used when a standard sheet pile can no longer withstand the occurring ground and water pressure. The pipe piles typically have a diameter of 900 to 3,400 mm and can be up to 48 metres long. The intermediate sheet piles are usually shorter than the piles and generally extend a few metres below the excavation level.
In cases of high retaining heights and heavy loads, even a combi-wall cannot always withstand the forces independently. In such situations, an anchored combi-wall construction is chosen, where an anchoring system transfers the forces to a more stable subsurface. Within this type of construction, strand anchors play an important role. These offer an efficient and technically strong solution for combi-wall anchoring, for both temporary and permanent applications.
Other solutions and applications
A combi-wall is used to safely retain soil and water in quay walls, deep excavations, harbour works and other infrastructure projects with large retaining heights. First, the tube piles are placed in the ground at the correct centre-to-centre distance using a leader rig; then, the sheet piles are installed in the grooves of the tube piles to seal the space between the piles.
Depending on the retained height, soil pressure, water pressure, and load from the surroundings, a freestanding combi-wall is not always sufficient. In that case, an anchored combi-wall is chosen. Strand anchors are an efficient solution here, particularly for large loads and significant counter heights. Compared to other solutions, such as bracing frames or traditional anchor systems, strand anchors offer several advantages:
As a result, a combi-wall solution with strand anchors is not only structurally strong but also practical and economically attractive.
When installing a combi-wall, several factors determine the construction's performance:
The choice of the right execution method has a major impact on the environment and the construction. Where vibrating and pile driving are not possible due to vibration nuisance, tube piles can also be installed using drilling and pressing methods.
The construction of a combi-wall begins with the precise positioning and insertion of the tube piles via a frame, ensuring their mutual distance and plumbness are maintained. After the tube piles are placed, the sheet piles are vibrated into place between the piles via the interlocks on the outer side of the tube piles. The sheet piles generally extend several metres below the excavation level, while the tube piles go significantly deeper to achieve the necessary embedment in the soil.
For large retaining heights, an anchored combi wall is almost always used to limit the bending moment in the piles and reduce horizontal deformations of the structure. An anchored combi-wall consists of:
In strand anchors, the load is transferred to the wall via the anchor head and the purlin. The anchored part of the anchor then transfers this force to the stable subsoil. When designing and installing a combi-wall, consideration must therefore be given not only to the wall itself, but also to:
Every situation is different. In a consultation, we will clearly outline your project and possibilities. You will immediately know where you stand.
Robert Jansen
Technical Sales Manager
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A combi-wall is an earth and water-retaining structure consisting of a combination of steel pipe piles and intermediate sheet piles. The pipe piles provide high bending stiffness and moment capacity; the sheet piles seal the space between the piles and provide earth and water retention.
Combi-walls are deployed when a standard sheet pile wall has insufficient capacity, for example in heavy quay walls, deep excavation pits and harbour works. Depending on the load and application, a combi-wall is implemented as a freestanding system or as a anchored construction in combination with an anchor system, such as a tie rod anchor.
A combi-wall construction absorbs ground and water pressure via the tube piles, which act as primary load-bearing elements. The sheet piles between the piles retain the soil and water, but do not carry the main load. The tube piles are installed in the ground by vibrating or driving; the sheet piles are subsequently installed in the grooves of the piles.
For heavy loads, the combi-wall is anchored with an anchor system. The forces are then transferred via the wall and a purlin to the anchor, which dissipates them into a more stable soil layer.
Combination walls are used in situations where the loads are too large for a regular sheet pile wall. Typical applications include:
The construction can be carried out from land as well as from a pontoon, which also makes it suitable for projects in and on the water.
An anchored combi-wall is used when a combi-wall cannot independently withstand the occurring loads. This is particularly relevant for:
By applying an anchoring system, such as strand anchors, the structure can be designed to be stiffer and more efficient.
Tendon anchors are widely used in combi wall anchoring due to their high capacity and efficient operation.
Key benefits include:
Additionally, Deepro strand anchors are supplied as a complete system, with all components matched to each other.
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