Firstly, when entering the water, it's important to understand that both hearing and vision will change due to the different propagation of light and sound in water compared to air. When light enters the water, refraction occurs. This causes the objects we see in water to appear 25% larger in volume than they actually are; visually, they seem closer. The distance at which we see objects will be shortened to 3/4 of the actual distance; the speed of sound transmission in water is 4.2 times faster than in air; and when sound arrives, it's almost simultaneous in both ears, making it difficult to determine the direction of the sound.
Next, during diving engineering operations, both descending and ascending should be done in a relaxed manner. This is because many people find it difficult to descend smoothly at first due to poor buoyancy control, and the descent speed is slightly faster. This can lead to excessive tension. For a relaxed descent, we can choose to descend along a slope at the bottom or use a descent line to control the speed. If your mask is being pinched, you can balance it by exhaling through your nose. If you experience pain due to ear pressure, stop descending and ascend to a shallower depth until the discomfort subsides. Then, pinch your nose and blow, or swallow saliva and move your chin from side to side before descending slowly. It's best not to dive when you have a cold or a flu. Similarly, a relaxed ascent during the ascent is also the same principle.
During diving operations, due to work or other reasons, one may sometimes forget to check the remaining air in their tank. It's too late when they run out of air. At that moment, fortunately, their dive buddy is nearby, so they must use their buddy's spare air supply to breathe and then ascend to the surface.
Construction process and key operational points
I. Situation Introduction
Silt in the cofferdam storage area is thick, about 80 cm. After the cofferdam is towed to the storage area, it sits on the silt. Due to the short storage time, the cofferdam has not settled properly. After two days, during a strong sea storm, the cofferdam slipped. It was quickly discovered and secured with ropes and steel cables to a more firmly seated and longer-stored cofferdam. However, half of the top surface of some cofferdams has submerged underwater.
Construction Process Flow
Template installation by divers underwater → Cofferdam stabilization → Water extraction and floating.
II. Key Operation Points
Receive high template production
Template production considers the immersion height of the caisson. In this typical case, half of the caisson is submerged underwater. With the local tidal construction in mind, it has been decided to raise the submerged portion of the caisson by 85cm in total. A set of top bolts is installed every 1.5 meters, and a stopper strip is applied along the bottom edge of the template.
Section 3: Underwater Template Installation by Divers
The submarine boat anchors, then the ship's long arm excavator (or crane) lifts the mold to the pre-installed position. The diver enters the water, adjusts the mold position, secures it onto the cofferdam, and tightens the top bolts. After the high mold installation is completed, connect the individual molds into a single unit using tie rods.
