Advancements in human engineering technology have significantly heightened the demands and expectations for engineering projects.

Buildings are reaching greater heights, with what used to be landmark skyscrapers now considered ordinary residential structures.

While bridges in the past were admired for simply spanning a river, today's bridges not only cross mountains and valleys but also traverse seas, and straits with turbulent waters, withstand earthquakes, typhoons, and the corrosive effects of seawater over time.

Constructing bridges overseas involves significant expertise, with the pillars supporting these bridges being of utmost importance for safety. Today, let's discuss how these bridge pillars are constructed.

<b>1. "Turning the Sea into Land"</b>

Just like any structure on land, whether tall or short, a solid foundation deeply rooted in the soil is essential for any construction. If the structure fails to integrate tightly with the foundation, even the strongest upper structure can collapse.

The technology for constructing land-based foundations is well-established. Thus, when it comes to construction in marine environments, the first consideration is whether it can be transformed into a land-based structure for construction. Therefore, in areas with relatively shallow waters, engineers typically build cofferdams around the construction site.

In simple terms, this involves enclosing the area where the bridge pillars will be built using sheet piles, earth, and rock embankments to isolate the water inside from the outside.

Then, pumps are used to drain the water inside the cofferdam, effectively turning the enclosed area into solid ground similar to land. Afterward, excavation, piling, and construction of steel reinforcement cages for the pillars are carried out within the cofferdam.

Once the pillar construction is complete, the cofferdam is removed, allowing the water around the pillars to return to its original state. Cofferdam construction is relatively straightforward with low construction difficulty, but the extensive work required to build the cofferdam often leads to significant delays.

As water depth increases, the workload of cofferdam construction increases exponentially. Therefore, cofferdam construction is typically only suitable for shallow water areas.

<b>2. Caisson Method</b>

How do we deeply embed bridge pillars into the seabed?

One traditional method is using caissons. A caisson is essentially a bottomless box-like structure featuring a cutting edge at its lower end. It is internally partitioned and can float in water. The caisson's descent or ascent is controlled by adjusting the pressure inside it.

During construction, workers excavate soil from inside the caisson along the well wall while machinery or semi-machinery disposes of the excavated soil outside the well.

When encountering large rocks, blasting is performed. As excavation progresses inside, the caisson gradually sinks due to its own weight or external pressure.

Simultaneously, new concrete is poured into the upper part of the caisson above water. Once it reaches the intended depth, the bottom of the caisson is sealed, and the interior is filled with concrete to serve as the foundation for heavy structures such as bridge pillars or equipment.

However, working conditions inside a caisson involve extremely high pressure. Workers must operate under harsh conditions, experiencing the equivalent of an additional atmosphere of pressure on their bodies for every 10-meter increase in water depth. This has led to a decrease in the use of this method for bridge pillar construction in today's highly mechanized environment.

As engineering technology continues to advance and innovate, the choices for constructing projects like sea-crossing bridges are evolving. From cofferdam methods to caisson methods, each bridge construction technique addresses the challenges of marine construction to varying degrees.

With the ongoing pursuit of engineering safety and efficiency, we can anticipate more advanced technologies being applied in this field, creating even more magnificent and secure engineering wonders for humanity in the future.