What causes quicksand?

The causes of quicksand formation are as follows: Quicksand refers to thick layers of loose, fine sand piles; since there is no cohesion between the sand particles, and water fills the pores between them, swamps or ponds that, for some reason, contain sand particles, along with a compacted mud layer at the bottom, are also prone to forming quicksand. Dr. Smith, a renowned geology professor, was determined to unravel the mystery of quicksand. He went to an area where quicksand was present, and at first glance, it looked no different from ordinary sand. He casually picked up a stone and threw it; the stone landed on the shifting sand, and in the blink of an eye, it was swallowed by the sand. Smith carefully collected some sand from the shifting sand area, put it in a bucket, and kept the sand at its original moisture level. Then he placed a small stone on top of the sand, but the stone did not sink. Dr. Smith therefore believes that the formation of quicksand traps has nothing to do with the humidity of the sand. Dr. Smith returned to the area where quicksand was present to learn about it from the local residents. The local people told the doctor that quicksand doesn’t always trap people; in August each year, people can even dance on it without any risk. Dr. Smith was greatly inspired. Dr. Smith thought to himself that August is the dry season, so it seems water is to blame after all. Smith filled a large barrel with sand, and installed several pipes at the top and bottom of the barrel so that water could flow in from the top and out from the bottom, as well as flow in from the bottom and out from the top. Then he created a toy figure with a density similar to that of human flesh and placed it on top of the sand in the barrel. Smith conducted several different experiments: when the sand in the sandbucket fairy’s container dried out, the toy figure could stand or lie on the sand ； When the sand is wet, the toy figure does not sink ； When water is poured in from above, the toy figure doesn’t sink either ； When water is poured in from below and flows upward through the sand layer, the toy figure sinks up and down ； The larger the toy figure, the finer the sand grains, and the stronger the water flow, the faster the toy figure will sink. Dr. Smith concluded from this that the water surged upward, forming quicksand. The upward force of the water flow causes the sand particles to separate from one another; they no longer overlap but are held up by the water, remaining in a semi-floating state. This results in objects with a density greater than that of water sinking. The mystery of the flowing sand has finally been solved. What to do if you encounter quicksand? First, get rid of the heavy objects on you right away and lie down quickly, because human density is less than that of water, so one won’t sink immediately ； Second, stay calm and don’t move around chaotically ； Third, if no one is nearby to help, roll or crawl slowly and carefully to get out of the quicksand area as soon as possible.

When the dynamic water pressure is greater than or equal to the effective unit weight of the soil, the soil particles remain in a suspended state and can move along with the seepage flow, entering the foundation pit along with groundwater; this phenomenon is known as fluidization.

The packing density is too low, resulting in reduced load-bearing capacity and the formation of quicksand~

Quicksand is often seen as a giant monster that can suck people into an bottomless pit. Quicksand is the most ingenious mechanism devised by nature; it can be hidden along riverbanks or even in one’s own backyard, waiting quietly for people to approach, leaving them in a difficult situation. In 1692, in Port Royal, Jamaica, an earthquake caused soil liquefaction, resulting in quakeslides that led to the destruction of one-third of the city and the death of two thousand people. Places such as the seemingly calm seas of northern England and the beautiful yet dangerous Alaska fjords have also seen incidents of people being trapped by quicksand. However, most people have never seen quicksand, let alone witnessed someone fall into it or experienced it themselves. People's impression of quicksand is mainly based on various movies, in which it is depicted as a giant monster that can suck people into an bottomless pit. Once people are trapped in it, they often cannot escape, and their companions can only watch helplessly as the trapped individuals are swallowed up by the sand in an instant. The surface of quicksand will \"liquefy\" once disturbed. Barn from the University of Amsterdam in the Netherlands met a local shepherd during a vacation trip to Iran. He pointed at the quicksand and told Byrne that camels in the village had once gotten stuck there and then disappeared immediately. Bairn was skeptical about this and began researching it immediately upon returning to his home country. He carefully watched and analyzed dozens of movies depicting scenes of quicksand consuming people, and found that the descriptions of quicksand in these movies were full of errors. Later, Byrne mixed fine sand, clay, and saltwater in the laboratory to recreate a miniature indoor shifting sand model for research. Through repeated experiments, the researchers led by Byrne discovered that it takes several days to make sand as sticky as toffee, but it is easy to remove its stickiness – all that is needed is to apply appropriate pressure to its surface. Once the surface of shifting sand is disturbed by movement, it quickly \"liquids,\" the sand on the surface becomes loose and soft, and the sand in shallower layers also flows downward rapidly. This migratory movement causes objects moving on the shifting sand to sink. However, as the sinking depth increases, the sand and clay that fall from the upper layers to the lower layers due to this migratory movement gradually accumulate, forming thick sediment layers that increase the viscosity of the sand and prevent further sinking of the objects. Objects with a density lower than that of quicksand will float on top of it. The study also found that when an object gets stuck in quicksand, its rate of sinking depends on the object’s own density. The density of quicksand is generally 2 grams per milliliter, while the density of humans is 1 gram per milliliter. At such a density, a human body sinking into quicksand will not face catastrophic consequences; it usually stops at the waist level. Researchers also found that even objects with a density much higher than that of quicksand can float on it. In the experiment, the researchers placed an aluminum basin with a density of 2.7 grams per milliliter on top of the flowing sand. Although its density was greater than that of the flowing sand, it was able to remain stationary on its surface due to the buoyancy exerted by the sand and the surface tension of the sand. When the scientists began to shake this aluminum container gently, something changed: the container sank slightly. As they increased the force of shaking, it gradually settled to the bottom of the sand. It takes the strength to lift a car in order to pull one’s foot out of quicksand. Research suggests that people trapped in quicksand generally cannot move; the denser sand sticks to the lower part of the body, applying significant pressure that makes it difficult to exert force. Even strong men find it difficult to pull the trapped person out of the quicksand at once. According to the calculations of researchers, pulling one of the trapped person’s feet at a speed of one centimeter per second would require a force of about 100,000 newtons, which is roughly equivalent to the force needed to lift a medium-sized car. So unless a crane is available to help, it’s difficult to pull someone out of quicksand all at once. The study also indicates that, based on the calculations of such forces, if one tries to pull forcefully, a person’s body would be torn apart by those intense forces before the quicksand releases its grip. The danger posed by this action is far greater than letting him stay temporarily in the quicksand.