Dredgers and hydromechanization

All About Suction Dredgers and Hydraulic Engineering Works

People are used to making the world around them comfortable, and this applies to literally every area of human activity. We have learned to build houses, to create fast, efficient and comfortable means of transport, and to reshape the landscape of the places where we live. Over time, we have also tamed all the elements:

- fire became a means of producing practically everything (from food to precious metals);

- land still provides up to 80% of all the world's food supplies;

- air became the medium for the safest and fastest transportation;

- water has served as a source of energy and valuable resources, and has provided the least costly mode of transport.

In the past, people limited themselves to what was available, using water in its natural state and simply adapting their technical arsenal to the opportunities offered by countless water bodies. In today's world, however, there is a need to improve virtually everything related to the use of water resources. Riverbeds began to be widened artificially, man-made canals were dug, the beds of water bodies were cleared and deepened, shorelines were reinforced, and much more. This is how hydromechanization emerged and began to develop rapidly, with a huge variety of hydraulic engineering works.

Carrying out hydraulic engineering works, even on a relatively modest scale, requires high-capacity specialized equipment – suction dredgers. It is this equipment that today performs enormous volumes of work involving soil excavation, bottom cleaning, channel widening, island reclamation and the removal of unwanted vegetation. In the end, the general public sees only the result: waterways suitable for modern navigation standards, comfortable sandy shores, islands that seem to have appeared out of nowhere, clear water surfaces free of algae, and much more.

Applications of Dredgers

Dredgers are used in hydraulic engineering works to open up new opportunities in a wide range of sectors: from recreation (beaches, leisure areas, nature reserves) and transport (deepening for large vessels, construction of new shipping canals) to energy (hydroelectric and thermal power plants, etc.), construction (shoreline protection, land reclamation) and resource extraction (sand mining, extraction of fertilizers, minerals and other resources).

In its standard configuration, a modern dredger is a specialized floating vessel designed to loosen and mix the soil with water (forming a slurry) and then pump it with high-capacity pumping equipment through a dedicated discharge pipeline over a specified distance to a collection point (the hold of a cargo vessel or barge, or an onshore fill).

Today, dredgers have become far more versatile machines and are fitted with a whole range of additional equipment, which allows them to be used for a broad spectrum of tasks:

- cleaning water bodies of algae and bottom sediments;

- deepening the beds of water bodies;

- widening riverbeds, canals and straits;

- creating artificial canals;

- creating artificial water bodies (lakes, ponds and other hydraulic structures);

- mining gravel, sand of various fractions, sapropel and various metals;

- cleaning settling ponds at agricultural and industrial enterprises;

- working slag and ash ponds for metallurgical, mining and processing, chemical and coal industry enterprises;

- digging subsea trenches for pipelines with subsequent backfilling;

- reinforcing shorelines for a variety of purposes;

- creating new land by hydraulic fill (expanding beaches, industrial or cargo-handling waterfront areas, building artificial islands, constructing dikes and dams).

Dredger-based equipment is also used effectively in disaster recovery operations (after waterlogging, floods, etc.).

Dredger Design, Classes and Types of Equipment

As already mentioned, the basic equipment of a dredger is a high-capacity dredge pump with the corresponding pipeline. However, the range of equipment fitted to dredgers today is so wide that it can be divided into several subgroups.

Equipment

1. Main equipment of suction dredgers:
2. 1. Dredge (slurry) pump;
   2. Discharge pipeline;
   3. Suction pipeline;
   4. Intake devices;
   5. Hydraulic and mechanical systems for moving and repositioning the intake devices.
2. Auxiliary dredger equipment:
3. 1. Floating platform (dredger hull);
   2. Engines, generators and other power units;
   3. Auxiliary mechanisms and systems (cranes, winches, buckets, grabs, special graders, weed cutters, etc.);
   4. Additional pumps for intake and supply of clean water;
3. Operational equipment:
4. 1. Control systems for the dredger and its complete set of technical equipment;
   2. Monitoring and measuring instruments (sensors, meters, signaling devices);
   3. Communication and alarm systems;
   4. Lighting equipment;
   5. Fire safety equipment;
   6. Heating, ventilation and air conditioning systems.

Classification of Dredging Equipment

It is worth noting that the classification of dredgers depends precisely on their equipment, its capabilities and the technical implementation of a number of key processes. In general, however, the class of a suction dredger depends on a broader set of parameters:

1. Dredger classes by hourly capacity:
2. 1. Extra small – up to 50 cubic meters of slurry per hour;
   2. Small – up to 200 cubic meters per hour;
   3. Medium – up to 500 cubic meters of slurry per hour;
   4. Large – up to 1,000 cubic meters per hour;
   5. Extra large – 1,000 cubic meters per hour and more.
2. Dredger classes by design type – modular (demountable) or ready for operation as delivered;
3. Dredger classes by excavation method:
4. 1. Suction dredgers with preliminary soil loosening (cutter);
   2. Suction dredgers without preliminary soil loosening;
   3. Single-bucket dipper dredgers (excavators, graders);
   4. Single-bucket grab dredgers;
   5. Continuous multi-bucket (bucket ladder) dredgers.
4. Dredger classes by soil transport method:
5. 1. Pipeline dredgers – soil is transported through a floating discharge pipeline (this method is considered the most cost-effective);
   2. Pipeline dredgers with boosters – designed to transport slurry over long distances, with flow power maintained by additional booster stations installed along the pipeline;
   3. Barge-loading dredgers – soil is transported by special vessels (hopper barges) that receive the excavated material in their holds;
   4. Self-hopper dredgers – the excavated soil is loaded into the dredger's own hold;
   5. Dredgers with jet (rainbow) discharge – relevant only for work in offshore marine areas.

In addition, dredgers are often classified as self-propelled or non-self-propelled, and by control system: manual, automatic or remote.

Working with a Dredger – Procedure and Key Principles

Hydraulic engineering specialists know well that the key to efficient, high-quality and uninterrupted dredger operation is high-performance pumping equipment, above all the dredge pump. In most cases, this equipment is installed in the hold of a special vessel, which prevents the formation of cavitation bubbles accompanied by water hammer that is destructive to the machinery, thereby significantly extending its service life.

It is also notable that dredging work on a water body does not begin with delivering the equipment and setting up the installed dredge pump. It is often preceded by fairly thorough survey and engineering calculations, preparation of a plan and map, and logistics planning (soil removal, arrangement of temporary or permanent storage sites, preparation of areas for drying algae).

The set of operations included in hydraulic engineering works using suction dredgers can be illustrated by the most in-demand services today: bottom deepening and sapropel extraction.

Bottom Deepening

For example, deepening the bed of a water body requires serious preparation, both in terms of equipment and in terms of organizing the work site. This includes:

- building embankments around the slurry disposal area;

- laying the discharge pipeline, both the floating section and the onshore section;

- installing a stop-log weir that returns water back to the water body;

- building a return channel from asbestos-cement pipes or concrete flumes to return water from the disposal area back into the water body and prevent the flow from eroding the shoreline.

Only after these steps is the dredger itself delivered to the site, assembled (if necessary), and put through all the required commissioning and testing.

Sapropel Extraction

The extraction of sapropel, a highly valuable material today, differs fundamentally from dredging both at the preparatory stage and in terms of the equipment used. This type of work is becoming increasingly popular, largely due to the high value of sapropel: thanks to its rich set of unique properties, this raw material is widely used in the production of micronutrient fertilizers, and its price on the world market has long exceeded 200 dollars per ton.

In this case, the water body is surveyed for large deposits of silt. Production sites are set up in the immediate vicinity of the planned works (depending on the method used to dewater the collected material).

In addition, sapropel is extracted using special equipment – a suction dredger with an auger (screw) head that allows the operator to remove a specific thickness of the silt layer, feed it into the discharge pipeline and transport it directly to the production site.