One of the challenges in modern ports is upgrading existing quay walls. Dutch contractor Hakkers BV has developed a device to install underwater grout anchors as a support for sheet pile walls. This technology was successfully tested during a pilot project in the Seinehaven for the Port of Rotterdam. Now they are curious whether underwater grout anchors can also be applied on combi-walls.

“The objective of this thesis is the design of an underwater anchoring system for combi-walls to enable the deepening of existing quays.”

For the design, the case study of the Afrikahaven was chosen. This project has a common type of combi-wall and therefore the design is applicable in many situations. There is currently no specific customer for the quay. The underwater anchoring system can be part of an upgrade proposal in case a customer is interested in deepening the bed level.

Because underwater grout anchoring of combi-walls was only a conceptual idea, this thesis carried out a full design process starting with the very basics. This was done by creating multiple concepts which varied the way of load transfer to the combi-wall. A multi criteria analysis resulted in the selection of two optimal concepts. These two concepts are designs where the anchors go through the sheet piles and are connected to a support structure that transfers the anchor forces to the king piles. These concept designs scored very well on the criteria for hole weakening and spatial usage. Hole weakening of the king piles was a major concern due to the capacity reduction at the locations of the largest moment distribution. By not placing the anchor through the king pile, its capacity does not need to be reduced. Additionally both concepts have limited protrusion outside the combi-wall system. This prevents conflicts with the mooring vessels.

For the two concepts various connection designs have been explored, including rubber connections, clamping connections, extendable connections, and conventional methods such as welding. After evaluating the pros and cons of each design, clamping connections emerged as the optimal solution.

A detailed design of the overall stability of the combi-wall was calculated using D-Sheet. The current situation is used as the starting point. Various positions and angles of the anchors where tested. Eventually the anchor was placed at -11m NAP at the location of the maximum moment distribution. It was essential to place the anchor at a relatively shallow angle to meet vertical stability requirements.

A critical part in the design was underwater anchor failure. An important finding is that the applicability of the current design standards used for anchor design is rather limited for underwater anchoring systems. Without considering the extent of redistribution, it is possible to create a structurally questionable design that still meets the common used standards. Therefore, it is important to thoroughly understand these standards and adapt their implementation if necessary for the design.

Evaluating the extent of force redistribution is crucial for determining anchor forces and stresses in the waling beam and king piles. To evaluate force redistribution, the design was modeled in SCIA
and calibrated using D-Sheet calculations focusing on deformations and anchor forces. The analysis revealed that force distribution depends heavily on the stiffness of the support structure. An overly flexible structure channels excessive force to upper anchors and increasing soil mobilization, while an overly stiff fixed structure risks a chain reaction of failures in adjecent anchors could occur. For the design, a CHF350x500 profile was chosen between the king piles with a moment-free connection. This allows for a redistribution of 40% of the forces to adjacent anchors. The remaining 60% of the anchor forces are absorbed by the four anchors at the top of the two king piles.

To ensure feasibility, understanding construction tolerances is crucial. The design accounted for king pile and sheet pile deformations, with a deformation allowance of 100 mm for the sheet pile. Minor deviations due to ovalization were also considered. While it is unrealistic to address all uncertainties in a single design, using a multi-beam survey to measure the quay wall with 1 mm accuracy is recommended. This approach cannot eliminate construction tolerances but helps mitigate unexpected conditions during installation by incorporating them in the design phase.

The clamping design is based on a support structure where the anchor will be supported in the waling beam. The waling beam will transfer the horizontal forces to the king piles. To avoid underwater welding, a semi-clamp has been designed. These clamps can be connected using four bolts, which can be tightened underwater easily because the system is not yet under tension. Only after pre-stressing the anchor, the clamps will be drawn tightly around the king pile. Vertical stability will be provided by steel cables, which will be attached to the capping beam where the vertical forces will be transfered to the king piles.

To ensure constructability, various components are adjustable. For instance, the waling beam can be cut to size above water and welded between two end plates. An extendable HDPE tube is incorporated into the waling beam to accommodate deformations of the sheet pile wall. Additionally, the radius of the clamps has been slightly enlarged to account for ovalization deformation. This design aims to minimize operations underwater and be construction tolerance proof.

The design makes it possible to deepen the existing combi-wall in the Afrikahaven by 1.5 meters. This enables an upgrade without requiring drastic changes to the quay. The proposed design is applicable to all similar combi-wall configurations. However, for each project, specific construction tolerances must be reassessed, and the redistribution of forces during anchor failure must also be evaluated.