Quicksand is an unstable, water-saturated layer of soil, with a thickness varying from one to ten meters. Due to the pressure drop, it begins to move, which leads to collapse of the well shafts. But with proper drilling, you can safely go through a dangerous area.
Signs of Quicksand
Experts classify unstable layers as real and false.
The first are distinguished by the following features:
- They contain sand and dust particles of different sizes. Microscopic fragments act as lubricants, envelop and bind the entire earthen volume.
- They are rich in clay in the form of suspended matter, excessively hydrophobic. Clay constituents reliably retain moisture. They begin to move under the influence of hydroblow when opening a quicksand.
- They have low filtration properties and high moisture capacity, which exceeds three percent. Moreover, their moisture content is close to fluidity.
- Swell during freezing and acquire a monolithic hardness when completely dried.
Opinions differ on the formation of such layers, but there is a version that they appear as a result of the activity of microscopic living organisms.
Porous layers consisting of small particles of sand are called false. They are oversaturated with water. They lie at a depth of up to 50 m, as a result of which excess soil pressure acts on them. As a result, small grains of sand are washed into the well shaft.
Fake quicksand give water well enough, and with a natural or artificial decrease in hydraulic pressure go into a stable state. When drilling, they are not particularly dangerous.
The dangers of moving formations
Punching wells through quicksand without preparation can lead to problems:
- filling the annulus of the well with earth that literally floats;
- damage to pressure equipment that cannot cope with the increased load;
- loss of the drill string, which is drawn into the cavity that appeared after leaching of the rock.
Subsequently, the possible shift of the wellbore, its frequent drying out and regular ingress of mud particles into the water.
Features of arranging water intake in areas with quicksand
If there is a likelihood of a quicksand, you need to take into account certain nuances of arranging the intake. Prohibited:
- Install pipes made of plastic. The moving formation will eventually crush the polymer element, which will degrade the system or stop it after the complete destruction of the structure.
- Make a normal well. Even if you manage to achieve the required height of the water column in it, then quite quickly the water intake will stop working and supply water to its owners.
- Ignore the annual cleaning of the well, otherwise it will quickly become clogged.
Under natural conditions, the liquid layer is in a state of unstable rest. But at the beginning of any excavation, an excessively saturated with moisture layer of soil immediately begins to move, in physical properties it becomes like a liquid. All efforts to dig a well in such land can be compared with attempts to make a deepening in the surface of the water, since a liquefied layer will instantly fill the pit.
Finding out exactly whether there is a quicksand or not is quite difficult. To find out, before drilling a mine, it is necessary to conduct exploratory work.
If it is not possible to hire professionals, before punching the mine, take a soil sample using a hand drill. It is possible to determine the presence of an unstable formation when deepening by 1.5–2 m according to how the tool will be immersed: it will fail, as if into a void.
Additionally, you can chat with neighbors who have wells, or see the plans for the area, created on the basis of engineering and intelligence activities. They contain information about the specifics of the soil and the occurrence of aquifers.
Passing quicksand on shallow water intakes
If a sufficiently shallow well shaft is up to 20 m, an unstable layer can be passed through traditional percussion drilling. A similar method is used to equip Abyssinian water intakes. It’s easy to go through the quicksand during impact drilling of a well: all that is required is to hammer the pipe with a heavy metal “woman”.
You can use the shock-rope technique, which involves the use of a bobbin placed inside the casing. In this situation, the device will allow you to pull out floating soil. To facilitate the work, it is advisable to attach the cable to a special tripod, and lift using a gear motor with a clutch.
In order to prevent the drum from spinning due to inertia after the bump, a special device for braking can be installed.
If the shaft is shallow, and the mud layer itself is located close to the surface, another method can be applied. The quicksand passes here with the help of hand-crafted construction from the tongue-and-groove boards. Each element has a thickness of 5 cm and a length of 200 m, is pointed at the bottom.
To stop the mud flow, you must:
- Drive wooden workpieces to a depth of 0.4 m around the entire perimeter of the shaft.
- Carefully select the soil to the pointed bottom of the grooved boards and start drilling.
- Repeat the cycle - deepen the tongue by driving in and drill again. This must be done before the complete passage of the waterlogged layer.
The bottom of the well is strengthened with a simple wooden box with holes. It is placed on a sand and gravel pillow. This creates a homemade filter from dirt and grains of sand. You can also cover the bottom with a wooden board, in which, at the end of the drilling work, drill holes for water to enter.
However, such methods of protection against quicksand work only when the water stream with an admixture of dirt is not too powerful, flows without pressure.
Solution options for deep wells
The main task when punching a mine through a quicksand is to pass this non-solid, moving layer of soil, without losing the drill string. To solve the problem, three methods are actively used:
- Drilling by parallel casing method. The technique consists in the fact that the casing in the process of punching is lowered into the well with the drill. This significantly delays the entire course of work and makes them more expensive.
- The use of polymer adhesives or bentonite. They are needed for the formation of the walls of the mine, their strengthening and protection against destruction under the action of quicksand.
- The use of a special conductor. It is intended, as in the case of the casing, to protect the drill rod and the walls of the punched well shaft from the fluidized bed.
The latter option differs from the first in that the conductor is used to drill a layer of soil that is excessively saturated with moisture. Up to the boundary of this formation, drilling is carried out in the usual way. Well punching is also carried out by the traditional method, without the use of a jig, after the full passage of the quicksand.
Drilling through an unstable formation is a difficult task. It is better to choose a place with a more stable subsoil layer or to build an Abyssinian instead of a conventional well.
