Author: Dr. Theo Notteboom
Ship and terminal demand characteristics determine the requirements for terminal construction in terms of nautical access conditions, quay walls, and terminal layout and equipment.
1. Greenfield and Brownfield Sites
Terminal construction techniques and procedures are influenced by the topological and technical characteristics of the site, such as its situation and geology and the intended use of the plot. It occurs under greenfield or brownfield conditions.
Terminal development on a brownfield site involves reconverting an existing (mostly industrial) site for terminal use.
Brownfield port construction usually involves large-scale clean-up operations of contaminated soil and renovating and deepening the quay walls. It results in the rehabilitation and reuse of existing port real estate, thereby avoiding lengthy and difficult port extension procedures. Redevelopment of port brownfields produces numerous environmental, social, and economic benefits. By cleaning up and returning these lands to use, communities can remove dangerous structures and stop or stabilize contamination near waterways. Port redevelopment presents valuable opportunities for waterfront redevelopment, and it may catalyze revitalization in the broader community. Brownfield redevelopment frees space for various uses and creates more available property for sale or lease, providing ports with additional sources of revenue. Besides, redevelopment of previously used sites can help alleviate pressure on undeveloped wetlands and coastal areas, thus protecting important coastal habitats.
Construction of a terminal on a greenfield site mostly involves extending a port on a vacant site along a river, estuary, or coastline.
Historically, the majority of port development projects were labeled greenfield, which often goes hand in hand with port migration. The vacant site might be located in a green zone, wetland, or agricultural area. Getting permission for a greenfield development usually takes a long time, given existing spatial planning and environmental rules and regulations, and the required extensive project evaluation. For example, the Bird and Habitat Directive and the Water Directive of the European Commission impose a complex regulatory condition on greenfield development for ports. Such developments can imply small or large-scale land reclamation works along a coastline or riverside or digging a dock on dry land connected to a river or existing dock system.
Land reclamation is based on hydraulic fill, a process whereby sediment or rock excavated by dredgers from the seabed or other borrow areas is transported and placed into the designated reclamation area.
Well-graded quartz sands are the preferred material for landfills. Before the hydraulic fill can commence, extensive preparatory engineering studies are conducted to collect bathymetrical (a measurement of the depth of bodies of water), topographical (physical features of the area), geological (soil and rock), and geotechnical data on the reclamation site and the borrow areas. This step also includes examining the hydraulic, meteorological, and environmental conditions. Based on these studies, a method and the right equipment are chosen to obtain the desired mix of soil/sand and water to facilitate the dredging, transport, and placement of fill material, and to meet the load-bearing and stability requirements of the reclaimed site. The quality of the landfill will be determined by its stiffness, strength, density (liquefaction resistance), and drainage capacity. The nature of the fill will influence the type of equipment, the means of transport, the reclamation method, and the possible need for ground improvement. Much-used ground improvement techniques include vertical drains and vibratory, dynamic, or explosive compaction with or without admixtures.
2. Nautical Access to Terminals
Terminal construction often involves adapting the nautical access to guarantee a minimum nautical draft for seagoing vessels. These adaptations can deepen the water depth near the quay wall and capital dredging work on the nautical route (river or sea) from the main shipping lane to the terminal site. Further improvements to the nautical access to the terminal might be needed, such as widening the fairway to allow two-way vessel traffic, widening the breakwater entrance to the port terminal, or widening the turning basin for vessels. The costs and efforts of dredging projects are closely related to the geographical, hydrological, and geological characteristics of the port site. Once the deepening or widening of the nautical access has been realized, regular maintenance dredging must ensure that nautical access conditions remain the same.
Capital dredging involves dredging to deepen and widen existing rivers or nautical access routes or create a new port or terminal.
Maintenance dredging is done to maintain an existing waterway or channel.
Since dredging is an ad hoc activity linked to temporary projects, it is often contracted to specialized companies that position their equipment from one project to another. Dredging equipment operated solely by a port would likely remain idle for long periods of time. Therefore, land reclamation and dredging works are performed by dredging companies using specialized equipment such as trailing suction hopper dredgers and cutter-head and bucket-wheel dredgers. Each type of equipment has different characteristics that determine the suitability for a particular type of soil, rock, or sediment in a particular setting, accounting for the waves and swell, the currents, and the water temperature. Other elements that guide the selection of the right equipment include the location of the borrow area or dumping area (distance, vessel traffic intensity at location) and water depth.
Contaminated dredged material can be treated in situ or ex-situ. Many dredging companies have developed into comprehensive organizations specialized in offshore, marine, civil, environmental, and project development. Some of the largest companies in this field include the Belgian companies DEME and Jan De Nul Group, the Dutch companies Van Oord and Boskalis, National Marine Dredging Company (UAE), Great Lakes Dredging & Dock Company (US), and Penta Ocean (Japan). Other dredging companies, such as China Communications Construction Company (CCCC), are part of large construction conglomerates.
When designing or upgrading port approach channels and ship maneuvering and anchoring areas, engineers have to consider a multitude of factors associated with the channels and the expected and future generations of ship dimensions and maneuvering characteristics, such as:
- Draught-related factors include under-keel clearance (and related requirements), wave-induced motions, and squat (the hydrodynamic effect of a ship moving through shallow waters).
- Wind effects.
- Air draught for vertical clearance under bridges and overhead cables.
- Support craft requirements, such as towage.
- Existing and required aids to navigation onboard and as part of the Vessel Traffic Management System (VTMS) of the port or channel.
- Environmental factors.
- Safety risks.
The World Association for Waterborne Transport Infrastructure (PIANC) has developed design guidelines for harbor approach channels. They relate to vertical (channel depth, air draught) and horizontal (channel width) dimensions. Also, they contain guidelines on squat, under keel clearance in muddy channel beds, methods for predicting vertical ship motions due to waves, and tools for ship maneuvering simulation and capacity simulation modeling. Although there is a wide variety of port sites and physical constraints, construction, and engineering techniques have been standardized.
In some ports, terminals can only be reached when seagoing vessels pass through a lock or tide gate. The largest locks in seaports can be found in ports such as Antwerp (Belgium) and Amsterdam (the Netherlands). Some major canals, such as the Panama Canal, also feature lock systems that set ship size standards around which ships and port terminal characteristics are designed.
3. Quay Wall Construction
A quay wall is a soil retaining structure that provides a mooring place for ships, bearing capacity for crane loads, goods and storage, and sometimes a water-retaining function.
The basic role of a berthing structure is to accommodate a particular vessel or range of vessels as well as cargo handling operations. There is a wide variety of berth structures with different characteristics with a variety of engineering considerations. More specifically, the method and sequence of construction, the availability of construction materials, and the support of major construction plants such as cement-making can determine the type of structure finally selected. This structure and the availability of construction equipment can significantly influence the construction schedule in view of factors such as weather downtime and the availability of contractors.
General parameters that are considered when choosing an appropriate quay wall type include:
- Dredging and filling in order to minimize the environmental impact of those operations.
- Access and safety during all the stages of the construction and operation of the structure.
- Berth orientation, berth geometry, and berth length.
- Required depth alongside the berth.
- Seabed conditions.
- Local construction materials, method of construction, and construction difficulties.
- General site considerations such as drainage and filters, wave pressures on walls, scour protection, the risk of earthquakes, paving and surface water drainage, and the chance of ice formation.
Furthermore, the effects of marine propellers and bow thrusters, waves, and currents on the stability of the seabed and any underwater slopes near structures should also be considered. Where scour is considered likely, protection, such as a rubble anti-scour apron on the seabed, should be provided in front of the quay walls, particularly at berths where vessels will generally berth in the same position. The size of rock protection for the underwater slopes should not be less than that needed to resist the wash of propellers and bow thrusters.
The possible failure or malfunction of a quay wall can be caused by the failure of the sheet pile wall, too much groundwater flow, insufficient soil stability, or failure of the supporting points.
Quay walls are typically equipped with quay wall fenders, ship mooring bollards, crane rails, cable gutters, and other technical features.
A. Embedded retaining walls
Embedded retaining walls include sheet-pile walls and in-situ concrete pile walls. The latter are embedded retaining walls of in-situ concrete bored piles usually built on the existing ground or an artificial embankment, using either a contiguous or a secant pile system. This type of wall is generally most suitable for cohesive soils and weak rock and where heavy vertical loads are accommodated. They may also be built-in granular soils when a casing or support fluid is used during excavation. However, environmental issues connected with the use of support fluids or pumping of concrete in water-bearing soils need to be considered. A common method is the diaphragm wall, which consists of an embedded retaining wall in the form of in-situ concrete diaphragm walling. Diaphragm walls are used for high walls or where heavy vertical loads are imposed on the wall.
Sheet pile walls are among the most commonly used types of quay walls used in port construction. They are widely used in the construction of container and bulk terminals, as well as for sea walls and reclamation projects where a fill is needed seaward of the existing shore and for marinas and other structures where deep water is needed directly to the shore. Different materials might be used for the sheep piles:
- Steel sheet piles are the most widely used embedded retaining wall elements in quays. They are relatively light and easy to handle, can be supplied in long lengths, and can be extended and cut without undue difficulty. This type of pile can be driven to a considerable depth with low displacement in a wide range of ground conditions and into the weathered rock. With various forms of pre-treatment, steel sheet piles may also be installed in solid rock in a trench backfilled with concrete, by pre‑splitting the rock. The principal disadvantage of steel sheet piles is corrosion, which should be allowed in the design. Some types of floating fenders can cause abrasion of steel sheet piles or their protective coatings, and this should be taken into account in selecting the form of fendering to be adopted.
- Concrete sheet piles may be used to construct moderate height walls and where driving is not too hard. The penetration required might have to be achieved by pre‑boring or jetting. In rock, the piles may be installed in a trench backfilled with concrete. The main advantage of properly designed concrete sheet piles is their durability. However, the weight of the sheet piles, the care required during handling, the difficulty of forming extensions, and the usually poor interlock at joints are all factors that, in many cases, will dictate against their use. If there is a danger of losing material, the joints may be sealed by providing a filter behind the wall or grouting after driving.
- Timber sheet piles can provide an economical wall for moderate heights of retained material and where driving conditions are not too severe. Examples of suitable applications are bulkhead walls behind suspended decks and quays for small craft. Most timbers require protective treatment against rot and marine borers. Rubbing strips should be provided where abrasion is expected.
Fill placed behind embedded retaining walls should be granular material capable of free drainage. Where necessary, loss of material through joints in the wall should be prevented by providing a suitable filter behind the wall.
Combi-walls are retaining walls composed of primary and secondary elements. The primary elements are normally steel tubular piles or built-up boxes, spaced uniformly along the length of the wall. The secondary elements are generally steel sheet piles of various types installed in the spaces between the primary elements and connected to them by interlocks.
B. Gravity walls
Gravity walls are built behind a cofferdam in the dry and are usually constructed in situ. Still, most walls are constructed in water by a method used only in maritime works, in which large precast units are lifted or floated into position and installed on a prepared bed underwater. It is common to use rubble or a free draining granular fill immediately behind a quay wall so that the effects of tidal lag are minimized, and earth pressures are reduced. Gravity structures are usually used where the seabed is of good quality. They may be used where the foundation near the dredged level is of rock, dense sand, or stiff clay. The main types of gravity quay walls are:
- Concrete block walls consisting of heavy precast mass concrete blocks. This type of construction is suitable where a rock foundation exists since differential settlement cannot easily be accommodated by this form of gravity wall. Blocks are placed vertically above each other.
- L-walls obtain their stability through their structural weight and soil weight that rests on the horizontal part of the L-shaped structure. L-walls can be built in-situ in dry conditions (i.e. an excavated building pit, as was the case for the Deurganckdock in the port of Antwerp) or prefabricated ex-situ and then brought to the waterside.
- Concrete caissons are based on the caisson method. A pressurized chamber underneath the structure is created to keep the water out of this chamber. From this chamber, the soil under the structure can be removed. By carefully and evenly removing the soil from under the structure, it will submerge gradually until its final depth. During this process, verticality is monitored continuously, and the place where the soil is removed from under the structure is adjusted accordingly to maintain verticality. Concrete caissons consist of open‑topped cells prefabricated in the dry (on land, in a dry dock, or a floating dock), usually floated to their final location and then sunk into position on the seabed. Concrete caissons may be built in a wide variety of shapes, such as rectangular, circular, or cloverleaf. Caissons are usually limited to about 30 meters in width in the greatest plan dimension. They are usually designed so that, after sinking, the top is just above low water level with due allowance for waves. The cells are filled, usually with sand and sometimes with concrete or gravel. The superstructure may consist of a solid in-situ concrete capping or a reinforced concrete edge retaining wall, which is backfilled, and the top surfaced with concrete paving. Caissons, after filling, form self‑stable structures that can be used to support heavy construction equipment. Large caissons will generally need to be strengthened with internal walls.
C. Suspended deck structures (piles)
Suspended deck structures may be of steel, concrete or timber, or of a combination of more than one of these materials:
- Timber piles are easy to handle and cut to length; they require only simple driving equipment, and their flexibility can be useful in energy‑absorbing structures. The length of timber piles is generally restricted, varying from 12 to 18 meters. Lengths up to 24 meters are sometimes available. Timber should generally be treated or cased with concrete muffs to prevent attack by marine borers.
- Precast reinforced concrete piles may be driven in many ground types and may also be placed in pre‑bored holes in the seabed. If the piles are to be cast at a yard remote from the site, their maximum length might be restricted to about 20 meters. If necessary, provision may be made for extending the piles using an interlocking joint.
- Steel piles are relatively light and easy to handle and can be driven in most ground types, including many types of rock. External corrosion may be minimized through protective coatings or cathodic protection or may be allowed for in the design.
Suspended deck structures will usually be the most suitable type in the following circumstances:
- Ground consisting of weak upper materials.
- Ground immediately below the seabed consisting of suitable material for bearing piles.
- Non-availability of suitable backfill for use in a retaining wall type of quay.
- Great water depth.
With the rapid growth of port activities worldwide, including the emergence of global terminal operators, a wave of construction projects has taken place. The standardization of terminal design, particularly in the container sector, has been associated with standard construction techniques and equipment along with well-designed guidelines.
- Chapter 3.1 Terminals and Terminal Operators
- Chapter 3.2 Terminal Concessions and Land Leases
- Chapter 7.3 Port planning and development
- Center for Civil Engineering Research and Codes (CUR), 2002. Handbook Quay Walls, CUR-publication 211E, September 2005, Gouda, the Netherlands.
- Gordijn, R., 2017. Amsterdam port: building the largest sea-lock, Port Technology International, issue 75, p. 36-38.
- McBride, M., Boll, M. and Briggs, M., 2014. Harbour approach channels—Design guidelines. PIANC Report No. 121.
- Van der Plas, R., 2013. Maasvlakte 2, providing ample space for the future, Port Technology International, issue 58, p. 20-22.
- van’t Hoff, J. and van der Kolff, A.N. eds., 2012. Hydraulic fill manual: for dredging and reclamation works (Vol. 244). CRC press.
- Vandamme, M., Bernaers, G., Aerts, F., Construction of the Deurganckdok in the Port of Antwerp, Belgium.