In the global mineral resource development and transportation chain, ore terminals serve as critical hubs connecting land mining and maritime shipping. The construction of ore terminals often faces challenges such as complex coastal terrain, harsh climatic conditions, and the need for efficient heavy-duty transportation. Steel trestle bridges, with their unique structural advantages, have become an indispensable core component in ore terminal engineering, providing reliable solutions for access channels, equipment deployment, and temporary construction platforms. We take the Nouadhibou New Ore Terminal project in Mauritania as a typical case, elaborates on the definition and advantages of steel trestle bridges, analyzes the geographical, climatic, and mineral resource characteristics of Mauritania, and deeply explores the application scenarios and value of steel trestle bridges in the Nouadhibou New Ore Terminal project, providing reference for similar engineering projects in harsh environments.

I. What is Steel Trestle Bridge?

1.1 Definition and Structural Composition of Steel Trestle Bridge

A steel trestle bridge is a temporary or permanent load-bearing structure composed of standardized steel components, mainly used to span rivers, valleys, coastal shoals, or other complex terrains to form access channels or working platforms. Structurally, it typically consists of three core parts: supports, main girders, and deck systems. The supports, usually in the form of steel pipe piles or steel columns, are driven into the foundation to bear the overall weight of the bridge and external loads; the main girders, made of high-strength steel trusses or box girders, form the main load-bearing framework, ensuring the structural stability of the bridge; the deck system, composed of steel plates, anti-skid layers, and railings, provides a safe passage for vehicles, equipment, and personnel.

Unlike traditional cast-in-place concrete bridges, steel trestle bridges adopt a modular prefabrication production mode. All components are processed and manufactured in the factory with precise quality control, and then transported to the construction site for assembly. The assembly process mainly relies on bolt connection and simple welding, which greatly simplifies the on-site construction process.

1.2 Core Advantages of Steel Trestle Bridge Adapted to Ore Terminal Engineering

Ore terminal engineering has strict requirements for supporting structures, such as strong load-bearing capacity, rapid construction, and adaptability to harsh coastal environments. Steel trestle bridges perfectly meet these requirements with the following core advantages:

1. Excellent Load-Bearing Capacity: Steel materials have high tensile and compressive strength. The main girders of steel trestle bridges, usually designed as truss structures, can effectively disperse loads and bear heavy weights. They can be customized according to the weight of ore transport vehicles (such as 40-ton to 100-ton dump trucks) and loading and unloading equipment (such as gantry cranes and stackers), ensuring the stable operation of heavy-duty transportation in ore terminals.

2. Rapid Construction and Short Cycle: All components of steel trestle bridges are prefabricated in factories, and on-site assembly only requires simple mechanical cooperation. For a medium-span steel trestle bridge (span 20-50 meters), the on-site construction can be completed in 1-2 weeks, which is far shorter than the construction cycle of concrete bridges (usually 2-3 months). This rapid construction advantage is crucial for ore terminal projects that need to be put into operation as soon as possible to realize mineral export.

3. Strong Adaptability to Complex Terrains: Steel trestle bridges can be flexibly designed according to terrain conditions. Whether it is spanning coastal shoals, tidal flats, or connecting wharves and shore storage yards, they can be adjusted in terms of span, height, and structural form. Especially in coastal areas with soft soil foundations, steel pipe pile supports can be deeply driven into the stable soil layer to ensure the stability of the bridge.

4. Excellent Corrosion Resistance and Durability: Aiming at the harsh coastal environment of ore terminals (high salt spray, high humidity, and easy corrosion of steel structures), steel trestle bridges adopt professional anti-corrosion treatment processes, such as sandblasting derusting (Sa2.5 level) + epoxy zinc-rich primer + epoxy micaceous iron oxide intermediate paint + polyurethane topcoat. Some key components can also be treated with hot-dip galvanizing, which can effectively resist the erosion of salt spray and humidity, ensuring a service life of more than 20 years.

5. Convenient Maintenance and Reusability: The modular structure of steel trestle bridges makes maintenance simple. Damaged components can be replaced individually without overall demolition, reducing maintenance costs and downtime. In addition, after the completion of temporary projects (such as terminal expansion construction), steel trestle bridges can be disassembled and reused in other projects, realizing the recycling of resources and reducing the total cost of the project.

II. Mauritania: Geographical Climate, Mineral Resources and Infrastructure Background

2.1 Geographical and Climatic Characteristics

Mauritania is located in Northwest Africa, bordering the Atlantic Ocean to the west, Algeria to the northeast, Mali to the east and south, and Senegal to the southwest. Its territory covers an area of about 1.03 million square kilometers, most of which is covered by the Sahara Desert, accounting for about 75% of the total area. The country's terrain is dominated by plateaus and deserts, with a narrow coastal plain in the west, where the Nouadhibou region is located.

The climate of Mauritania is typically arid and semi-arid. The coastal area (including Nouadhibou) has a tropical desert climate, with hot and dry weather throughout the year, annual average temperature of 25-30℃, and extremely low annual precipitation (less than 100 mm). The coastal area is often affected by the Harmattan wind (a dry and hot wind blowing from the Sahara Desert), which brings a lot of sand and dust, causing serious sand erosion to structures. In addition, the coastal waters of Nouadhibou have strong tides, with a tidal range of up to 2-3 meters, and the coastal shoals are exposed during low tides and submerged during high tides, which brings great challenges to the construction of coastal infrastructure.

2.2 Rich Mineral Resources and the Importance of Ore Terminals

Mauritania is rich in mineral resources, which are the pillar of its national economy. The main mineral resources include iron ore, copper, gold, silver, and phosphate, among which iron ore is the most important export product, accounting for more than 60% of the country's total exports. The iron ore reserves of Mauritania are estimated to be about 1.5 billion tons, with high grade (iron content of 65-70%), mainly distributed in the Zouérat region in the northeast of the country.

The transportation of iron ore from the mining area to the export terminal is the key link of Mauritania's mineral resource development. The existing transportation system mainly relies on the railway from Zouérat to Nouadhibou, with a total length of about 670 kilometers, which is the longest railway in Mauritania. The Nouadhibou Ore Terminal, located in the Nouadhibou region, is the only large-scale ore export terminal in Mauritania, responsible for loading and shipping most of the country's iron ore. However, with the continuous increase of iron ore mining output, the existing terminal capacity has been unable to meet the export demand. Therefore, the Mauritanian government decided to build a new ore terminal in Nouadhibou to expand the loading and shipping capacity and promote the development of the mineral resource industry.

2.3 Application Scenarios of Bridges in Mauritania's Infrastructure Construction

Due to Mauritania's complex geographical environment (deserts, plateaus, and coastal shoals) and the needs of mineral resource transportation, bridges play an important role in its infrastructure construction. The main application scenarios include:

1. Mineral Transportation Routes: Bridges are needed to span rivers and gullies along the railway and highway from the Zouérat iron ore mining area to the Nouadhibou terminal, ensuring the smooth transportation of iron ore.

2. Coastal Terminal Construction: In the construction and operation of ore terminals, steel trestle bridges are needed to connect the wharf and the shore storage yard, as well as to provide working platforms for loading and unloading equipment and construction personnel.

3. Rural and Urban Infrastructure: In urban and rural areas, bridges are used to span rivers (such as the Senegal River on the border with Senegal) to improve local transportation conditions.

4. Emergency Disaster Relief: In the event of sandstorms, floods, or other natural disasters that damage transportation routes, temporary steel trestle bridges can be quickly deployed to restore traffic.

Among these scenarios, the application of steel trestle bridges in coastal ore terminals is the most representative, as they can effectively adapt to the harsh coastal environment and the heavy-duty transportation needs of ore terminals.

III. Case Study: Application of Steel Trestle Bridge in Nouadhibou New Ore Terminal Project

3.1 Project Overview of Nouadhibou New Ore Terminal

The Nouadhibou New Ore Terminal project is a key national infrastructure project in Mauritania, invested and constructed by the Mauritanian National Mining Corporation (SNIM) in cooperation with international investors. The project is located in the coastal area of Nouadhibou, about 10 kilometers north of the existing ore terminal. The main construction content includes a new 1.2-kilometer-long wharf, a 500,000-square-meter ore storage yard, a loading system, and supporting transportation facilities. The designed annual loading capacity of the new terminal is 30 million tons, which will double the existing terminal's capacity after completion, greatly promoting the export of Mauritania's iron ore.

The construction of the project faces many challenges: first, the coastal terrain is complex, with a large area of shoals and soft soil foundations, which requires high stability of the supporting structures; second, the coastal environment has high salt spray and strong tides, which requires the structures to have excellent corrosion resistance; third, the project schedule is tight, and the supporting transportation channels need to be put into use as soon as possible to ensure the transportation of construction materials and subsequent ore loading. After in-depth demonstration, the project team decided to adopt steel trestle bridges as the core supporting structure for connecting the wharf and the shore storage yard, as well as the temporary construction platform.

3.2 Design and Selection of Steel Trestle Bridge in the Project

According to the actual needs of the Nouadhibou New Ore Terminal project, the project team customized two types of steel trestle bridges: the permanent steel trestle bridge for ore transportation and the temporary steel trestle bridge for construction.

1. Permanent Steel Trestle Bridge for Ore Transportation: This trestle bridge is 850 meters long, with a span of 30 meters per section, and a total of 28 sections. The deck width is 12 meters, which can meet the two-way passage of 80-ton ore dump trucks and the operation of loading equipment. The main girders adopt steel truss structures made of Q355B high-strength steel, which have strong load-bearing capacity and wind resistance. The supports adopt φ800mm steel pipe piles, which are driven 15 meters deep into the soil layer to ensure stability in the soft coastal foundation. The anti-corrosion treatment adopts the "sandblasting derusting (Sa2.5 level) + epoxy zinc-rich primer (80μm) + epoxy micaceous iron oxide intermediate paint (100μm) + polyurethane topcoat (60μm)" process, and the key components are treated with hot-dip galvanizing to enhance corrosion resistance in the high-salt-spray environment.

2. Temporary Steel Trestle Bridge for Construction: This trestle bridge is 420 meters long, with a span of 20 meters per section and a deck width of 8 meters, mainly used for the transportation of construction materials (such as steel, cement, and equipment) and the passage of construction personnel. The main girders adopt prefabricated steel box girders, which are lightweight and easy to assemble. The supports adopt φ600mm steel pipe piles, which can be disassembled and reused after the completion of the main project. The anti-corrosion treatment adopts a simplified process (sandblasting derusting + epoxy zinc-rich primer + polyurethane topcoat) to balance cost and durability.

In addition, the design of the steel trestle bridge fully considers the local climatic conditions. The wind load is calculated according to the maximum wind speed of 50 m/s (Harmattan wind), and the deck is equipped with sand-proof railings to reduce the impact of sand and dust on the operation of vehicles and equipment. The bridge deck is also designed with a drainage slope to avoid the accumulation of rainwater (though rare) and seawater splashes, protecting the deck structure.

3.3 Construction Process of Steel Trestle Bridge in the Project

The construction of the steel trestle bridge in the Nouadhibou New Ore Terminal project adopts a modular assembly method, which is divided into four stages: prefabrication of components, transportation of components, on-site installation, and quality inspection. The whole construction process fully embodies the advantage of rapid construction of steel trestle bridges.

1. Prefabrication of Components: All steel components (main girders, supports, deck plates, etc.) of the trestle bridge were prefabricated in the factory of Evercross Bridge Technology (Shanghai) Co., Ltd., a professional modular steel bridge manufacturer. During the prefabrication process, strict quality control was implemented, including the inspection of raw materials (chemical composition and mechanical properties of steel), welding quality (non-destructive testing such as UT and MT), and anti-corrosion treatment (coating thickness and adhesion testing). Before delivery, SGS, an authoritative third-party inspection institution, conducted a comprehensive inspection of the components and issued an inspection report, ensuring that the quality of the components met the BS5400 bridge design standard and the project requirements.

2. Transportation of Components: The prefabricated components were transported from Shanghai Port to Nouadhibou Port by sea. Considering the limited transportation capacity of Nouadhibou Port and the complex coastal road conditions, the components were packaged in a modular way, with each package weight controlled within 20 tons to facilitate on-site unloading and transportation. The transportation process was supervised by a professional logistics team to ensure that the components arrived at the construction site intact and on time.

3. On-Site Installation: The on-site installation was carried out by a professional construction team with rich experience in coastal trestle bridge construction. First, the steel pipe pile supports were driven into the foundation using a pile driver. The driving depth and verticality were monitored in real time to ensure the stability of the supports. Then, the prefabricated main girders were hoisted to the supports by cranes and fixed with bolts. Finally, the deck plates, railings, and anti-skid layers were installed. The installation of the permanent steel trestle bridge (850 meters) was completed in 22 days, and the temporary steel trestle bridge (420 meters) was completed in 10 days, which was 40% faster than the original construction plan.

4. Quality Inspection and Acceptance: After the completion of the installation, the project team and SGS inspectors conducted a comprehensive quality inspection of the steel trestle bridge, including load-bearing performance testing (simulating the passage of 80-ton dump trucks), structural stability testing, and anti-corrosion performance testing. The test results showed that all indicators met the design requirements and international standards. The trestle bridge was officially put into use after passing the acceptance.

3.4 Specific Application Scenarios and Operational Effects of Steel Trestle Bridge

Since its commissioning, the steel trestle bridges in the Nouadhibou New Ore Terminal project have played an important role in the construction and operation stages, with the following specific application scenarios and excellent operational effects:

1. Connection between Wharf and Storage Yard: The permanent steel trestle bridge connects the new wharf and the shore ore storage yard, forming a continuous transportation channel. 80-ton ore dump trucks can directly transport iron ore from the storage yard to the wharf loading point through the trestle bridge, with a daily transportation capacity of 8,000 tons. The smooth operation of the trestle bridge ensures the efficiency of ore loading and shipping, laying a foundation for the new terminal to reach its designed annual capacity.

2. Operation Platform for Loading Equipment: The deck of the permanent steel trestle bridge is equipped with railings and fixing devices for gantry cranes. The gantry cranes can move along the trestle bridge to complete the loading of iron ore onto ships. The high load-bearing capacity of the trestle bridge ensures the stable operation of the gantry cranes (weight 150 tons), avoiding equipment failure caused by structural instability.

3. Transportation of Construction Materials: During the construction stage, the temporary steel trestle bridge was responsible for the transportation of construction materials such as steel, cement, and mechanical equipment. It solved the problem of difficult transportation in coastal shoals, ensuring that the main project was completed on schedule. After the completion of the main project, the temporary trestle bridge was disassembled and reused in the expansion project of the existing terminal, realizing resource recycling.

4. Adaptation to Harsh Coastal Environment: After 18 months of operation, the steel trestle bridges have shown excellent corrosion resistance. The anti-corrosion coating on the surface of the components is intact, with no obvious rust or peeling. The steel pipe pile supports have no signs of settlement or deformation, even under the impact of strong tides and sandstorms. The daily maintenance work is simple, only requiring regular cleaning of sand and dust on the deck and inspection of bolt connections, with a monthly maintenance cost of only $2,000, which is much lower than the maintenance cost of concrete structures in the same environment.

IV. Key Success Factors and Experience Enlightenment of Steel Trestle Bridge Application in Mauritania

4.1 Key Success Factors

The successful application of steel trestle bridges in the Nouadhibou New Ore Terminal project is due to the following key factors:

1. Scientific Design Adapted to Local Conditions: The design of the steel trestle bridge fully considers Mauritania's harsh climatic conditions (high salt spray, strong wind, and sandstorms) and complex terrain (soft coastal foundation), and adopts targeted structural forms and anti-corrosion measures, ensuring the adaptability and durability of the bridge.

2. Strict Quality Control of Components: The prefabrication of steel components was completed in a professional factory, with strict quality control from raw materials to finished products. The third-party inspection by SGS ensured that the quality of the components met international standards, laying a solid foundation for the stable operation of the trestle bridge.

3. Efficient Modular Construction: The modular assembly method greatly shortened the on-site construction cycle, ensuring that the trestle bridge was put into use on time. This not only met the project schedule requirements but also reduced the impact of construction on the local environment and fishery activities.

4. Professional Construction and Maintenance Team: The construction team had rich experience in coastal trestle bridge construction, and the maintenance team was familiar with the characteristics of steel structures and the local environment, ensuring the smooth progress of construction and the long-term stable operation of the trestle bridge.

4.2 Experience Enlightenment for Similar Projects

The application experience of steel trestle bridges in the Nouadhibou New Ore Terminal project provides important enlightenment for similar ore terminal projects in harsh environments (deserts, coastal areas, etc.):

1. Prioritize the Selection of Modular Steel Trestle Bridges: For projects with tight schedules, complex terrains, and high load-bearing requirements, modular steel trestle bridges should be prioritized, as they have obvious advantages in construction speed, adaptability, and load-bearing capacity compared to traditional concrete bridges.

2. Strengthen Anti-Corrosion Design and Quality Control: In coastal or high-salt-spray environments, the anti-corrosion design of steel trestle bridges should be strengthened, and professional anti-corrosion processes and high-quality coatings should be adopted. At the same time, strict quality control should be implemented in the anti-corrosion treatment process to ensure the durability of the bridge.

3. Conduct In-Depth Site Investigation: Before the design and construction of the trestle bridge, in-depth site investigation should be conducted to master the local geographical, climatic, and geological conditions, so as to formulate a scientific and reasonable design scheme and construction plan.

4. Cooperate with Professional Manufacturers and Inspection Institutions: Choosing professional modular steel bridge manufacturers ensures the quality of components and the rationality of the design. Cooperating with authoritative third-party inspection institutions (such as SGS) ensures the objectivity and authority of quality inspection, avoiding quality risks.

Steel trestle bridges, with their excellent load-bearing capacity, rapid construction speed, strong adaptability, and good durability, have become an ideal choice for ore terminal engineering in harsh environments. The application of steel trestle bridges in the Nouadhibou New Ore Terminal project in Mauritania fully proves their important value in connecting transportation channels, ensuring construction progress, and adapting to harsh coastal environments. Under the background of the continuous development of global mineral resource trade, the demand for ore terminal construction in harsh environments will continue to grow. Steel trestle bridges will play a more important role in future ore terminal engineering with continuous technological innovation and optimization of design and construction schemes.

For countries with rich mineral resources and harsh natural environments like Mauritania, the promotion and application of steel trestle bridges will help improve the efficiency of mineral resource transportation, promote the development of the national economy, and accelerate the process of infrastructure construction. At the same time, the successful experience of this project also provides a useful reference for the global application of steel trestle bridges in similar engineering projects, contributing to the sustainable development of the global infrastructure construction industry.