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Mystery of the Cargo Ships That Sink When Their Cargo Suddenly Liquefies (theconversation.com)
An anonymous reader writes (condensed for space): On average, ten "solid bulk cargo" carriers have been lost at sea each year for the last decade. Solid bulk cargoes -- defined as granular materials loaded directly into a ship's hold -- can suddenly turn from a solid state into a liquid state, a process known as liquefaction. And this can be disastrous for any ship carrying them -- and their crew. A lot is known about the physics of the liquefaction of granular materials from geotechnical and earthquake engineering. The vigorous shaking of the earth causes pressure in the ground water to increase to such a level that the soil "liquefies." Yet despite our understanding of this phenomenon, and the guidelines in place to prevent it occurring, it is still causing ships to sink and taking their crew with them.
Solid bulk cargoes are typically "two-phase" materials as they contain water between the solid particles. When the particles can touch, the friction between them makes the material act like a solid (even though there is liquid present). But when the water pressure rises, these inter-particle forces reduce and the strength of the material decreases. When the friction is reduced to zero, the material acts like a liquid (even though the solid particles are still present). A solid bulk cargo that is apparently stable on the quayside can liquefy because pressures in the water between the particles build up as it is loaded onto the ship. This is especially likely if, as is common practice, the cargo is loaded with a conveyor belt from the quayside into the hold, which can involve a fall of significant height. The vibration and motion of the ship from the engine and the sea during the voyage can also increase the water pressure and lead to liquefaction of the cargo. You can read more on this here.
Solid bulk cargoes are typically "two-phase" materials as they contain water between the solid particles. When the particles can touch, the friction between them makes the material act like a solid (even though there is liquid present). But when the water pressure rises, these inter-particle forces reduce and the strength of the material decreases. When the friction is reduced to zero, the material acts like a liquid (even though the solid particles are still present). A solid bulk cargo that is apparently stable on the quayside can liquefy because pressures in the water between the particles build up as it is loaded onto the ship. This is especially likely if, as is common practice, the cargo is loaded with a conveyor belt from the quayside into the hold, which can involve a fall of significant height. The vibration and motion of the ship from the engine and the sea during the voyage can also increase the water pressure and lead to liquefaction of the cargo. You can read more on this here.
As far as i understand they have a mixture of solid particles surrounded by liquid, the particles are more compressible, so under pressure the whole structure loses coherence as effectively the solid fraction is reduced, since the liquid is less compressible.
I wonder if this could be helped by injecting some gas from the bottom after loading, so there are pockets where the granular solid is surrounded by compressible gas instead of liquid. If the density of the liquid is less than that of the solid surplus liquid would be driven to the top where it could be extracted.
It might help if the gas pockets are well enough dispersed.
"By the way if anyone here is in advertising or marketing... kill yourself." -- Bill Hicks
For a fun example of liquefaction, check out Mark Rober's video on YouTube.
This is a common trope, but it's simply not true. The number of cargo ships lost at sea about equals the number of lives lost aboard those ships. That is, on average about 1 person dies for each ship that sinks.
The vast majority of people aboard a cargo ship which sinks are rescued. Life rafts are required by all shipping regulators. And satellite locator beacons have become so cheap that I suggest you get one if you do things like boating or hiking.. Their cost (a few hundred dollars, though a commercial model will run a few thousand) is much less than the liability and bad publicity of someone dying because your ship sank. When someone dies, it's usually because they were unable to reach the life raft in time (injured or blocked in due to the accident which sank the ship).
In fact, the fatality rate works out to (100 deaths) * (100,000) / (1.25 million) = 8 per 100,000. That makes it safer than a variety of jobs as mundane as taxi driver or landscaper. The fatality rate is right around the average for all jobs if you account for those people being aboard the ship 24/7, while people are at the other occupationss on average for less than 6 hours a day.