Underwater exploration is commonly required for the structures which are constructed in/under water. The foundations of the structures like bridge piers, pipelines, port structures, and oil well platforms have to be constructed with great caution considering every bit of information as they remain exposed to water all the time. A proper underwater exploration helps in studying the condition of the soil and gaining other useful information required for the construction of sound structures.
Underwater sampling is not entirely different from dry sampling, but it requires special skill and proper equipment in order to obtain a high-quality soil sample. Sampling equipment is commonly installed on barges which are pulled to the construction site, anchored adequately, and castings are installed to a depth of around 2m.
Different tools and equipment are used based on the depth of water and waves. For instance, barge-mounted bridge rig is used for drilling in rivers and lake beds, drillship is used in deep water possibly greater than 1000m, and the platform may be constructed in very deep waters.
Types of Equipment for Underwater Sampling
1. Barge-mounted Drilling Rig
A drilling rig is installed on barges and drilling operation is conducted over the sides. Barge-mounted drilling is used for boring in lake bed and riverbed for bridge and port structure construction.
Fig. 1: Barge-mounted Drilling Rig
It is a small ship which is modified to a drilling platform by installing a center well of 460 to 610mm from the deck through the hull adding drilling rig. A drillship is used for deep water of more than 1000m.
Fig. 2: Drillship
3. Submarine-type Vessels
It is used for borings in water depths of 1000m and deeper.
For very deep waters, platforms are constructed and used for underwater sampling.
Fig. 3: Platform
5. Projectile Type Device
It is lowered to the ocean floor from drillship to recover soil specimens. A sample tube is driven into soil bed using the weight of surface vessel or reaction of devices placed on the seabed. Sometimes, gas or explosive devices are used to propel the sample tube into soil.