Water resources such as oceans, rivers and lakes are a major part of the landscape, but they are not ideal places to build structures. Most of our tools and construction materials work dry. However, many of the infrastructure, warps, bridges and dams on which we depend on a daily basis are installed under water.
How do they do it underwater?
We are talking about different types of underwater structure. One of the major costs of large construction projects on or near water bodies is the way that water is managed. The first thing you should consider after you consider an under-water structure is divers. Humans can survive and even work under-water with the help of diving equipment, which allows he to breathe and stay warm. Professional divers can perform good tasks such as welding, cutting and building formwork and other structures.
However, professional diving is dangerous, and the types of tools and equipment that operate under-water and are used safely by the diver are limited. Remote vehicles and submersibles can eliminate some risk, but they are also limited in the tasks they can achieve. Therefore, most of the under-water construction will get rid of water, so you will not build under it.
In industry, this is often referred to as dewatering and it involves good construction equipment and technologies that have one goal for everyone: to create water in areas where it is impossible or impractical to allow construction to take place safely and soundly.
Building underwater structures involves specialized construction techniques and equipment to overcome the challenges posed by working in a submerged environment. Here is a general overview of how underwater structures are built:
1. Site Preparation: The first step is to select a suitable location for the underwater structure. The site is surveyed to assess the conditions, including water depth, currents, and seabed stability. Any necessary clearance or excavation work may be carried out to prepare the area.
2. Temporary Enclosures: To create a dry working environment, temporary enclosures called cofferdams or caissons are constructed around the work area. These structures are typically made of steel or concrete and are sealed to prevent water ingress. The water inside the enclosure is then pumped out, creating a dry space for construction.
3. Foundation Construction: The foundation for the underwater structure is built, which may involve driving piles into the seabed or placing a concrete base. The foundation provides stability and support for the structure.
4. Structural Elements: The main structural elements of the underwater structure are constructed using various methods. These may include:
– Pre-casting: In this method, concrete or steel sections are fabricated onshore and then transported to the site for installation. These sections are typically lowered into place using cranes or specialized lifting equipment.
– Floating Construction: Some structures, such as floating platforms or pontoons, can be built in a dry dock or shipyard and then floated to the final location. Once in position, they are ballasted to sink to the desired depth.
– In-situ Construction: For smaller structures or those that require precise positioning, in-situ construction methods are used. This involves placing and securing each component underwater using divers or remotely operated vehicles (ROVs). Techniques such as underwater welding or concrete pouring are utilized to join the elements together.
5. Protection and Maintenance: To ensure the longevity of the underwater structure, protective coatings or linings may be applied to resist corrosion or prevent marine growth. Regular inspections and maintenance are conducted to monitor and repair any damage caused by the marine environment.
It’s important to note that the specific techniques and equipment used for underwater construction can vary depending on the project requirements and site conditions. Experienced engineers, divers, and specialized construction teams are typically involved in planning and executing underwater construction projects to ensure safety and successful completion.
The heart of the many site-dewatering plans is that the cofferdam, usually a temporary structure, built to separate the construction site from the body of water. Naturally, the cofferdam needs a structure that you can build in the wet; Otherwise, you will need another cofferdam to build it. In many cases, it is just a clay berm. You can soak the clay in water until the embankment creates a bundle long enough to work. Once your construction area is surrounded, you pump out the water. Of course, the soil is somewhat permeable, so you want to constantly pump out water. In addition, compacted and saturated soil is not very strong.
Fall is very dangerous for any workers below the cofferdam, so these types of structures require careful design by the engineer to ensure that they are safe. In addition to the mounds, there are a large variety of cofferdam designs on construction sites.
Some sheet piles and thick steel plates interlock together are driven into surface soils that use a heavy hammer to make a water-filled barrier. If the soils to run sheet piles are too rocky, or the depth is too great, sheet piles are sometimes used to create small individual enclosures filled with soil called cellular cofferdam. There are also cofferdams lined with steel frames and rubber bags filled with water. No matter what they are made of, cofferdams are usually built to be demolished and removed after construction.
An important use of cofferdams is to create original dams. In this case, two cofferdams are often required to dam the river at the upstream and lower ends. However, when constructing across the river, it is clear that the impoundment is not the only action required for diverting. You also need to know how to divert traditional river flows around the construction site. That is why many dams are being built in phases. You can build a lot of structure away from the very channel, and then divert the river through a recently built takeover or spillway and eventually build a closure section of the dam.
For some types of structures, the structure is often built off-site and transported by barge, commonly called a caisson. A hollow box or cylinder is lowered into its proper position, then the soil is excavated and far away from within until a sound layer of rock or strong soil is reached. Finally, the caisson is filled with concrete. Of course, that part about excavating down to a sound rock layer is not as easy as it sounds. In the past, this was often done by workers, which meant that the within of the caisson needed to be dewatered.
In addition, when you dewater a caisson, you create difference in pressure between outside and inside, with only soil in between. This means that a continuing battle of seepage flowing in from rock bottom of the caisson, or much worse, unstable soils which will rapidly erode and permit the caisson to flood.
These problems are what led to the pneumatic caisson, a variation on the original design where compressed air is injected into the structure to balance pressure from the water below. In a pneumatic caisson, the air pressure is maintained equal to or higher than the water pressure at the bottom of the structure so that seepage and soil instability can be avoided. It works a bit like once you turn a cup upside-down before putting it under water, except during this case the cup is far bigger and therefore the pressures inside can be much higher than normal atmospheric air pressure. This is why workers on underwater foundations often got “Caisson Disease” that divers get if they surface too quickly.
The use of pneumatic caissons is very rare today due to all security issues. In fact, most advances in water-related construction technology are not toward better diversion methods, but how to prevent diversion. The use of such an advance drilled shaft. With special tools and construction methods, you do not need to dig a hole, install steel reinforcements and fill with concrete. Concrete is much denser than water, so if you can dilute the cement paste and do this without further turbulence weakening the final product, the submerged concrete will heal and harden if not better than conventional.
The main way we do this is by sending the concrete down the form by shaking, hose or gravity. The end of the pipe fills the excavation from the top of the concrete, preventing water from completely washing away and diluting the cement. Whether the construction site is below a lake or river, or in a floodplain and is only at risk in extreme weather conditions, engineers and construction contractors give considerable thought and consideration to the feasibility and cost of maintaining this water.
Hope, it helps you understand a bit more about how we build basic infrastructure around water.