During construction and mining, soil development is traditionally carried out in one of three ways: cutting, hydromechanical fracture, and the explosive method.
An engineer makes a choice in favor of a specific method based on the forthcoming volumes of work, the nature of soil soils at the disposal of technical development tools, etc.
If a small excavator can easily cope with digging a pit for the construction of a country house, then when extracting minerals it is necessary to use a whole complex of machines and mechanisms. Moreover, most of these means of production will not be directly involved in the development of soil. Their purpose is to service the production process and ensure the continuity of work.
Soil is the top layer of the earth's crust formed by weathered rocks. Depending on the density and origin, soils can be classified into:
- Rocky (such soil is resistant to moisture, tensile strength of more than 5 MPa). This category includes granite, limestone, sandstone.
- Half-strength (tensile strength up to 5 MPa). For example: clay, gypsum, marl.
- Large-detrital - non-cemented fragments of semi-rock and rock.
- Sand (they are dispersed (up to 2 millimeters in diameter) rock particles).
- Clay (finely dispersed (0.005 millimeters in diameter) rock particles).
Manually digging in trenches is a rather labor-intensive process. In principle, it cannot be carried out when developing rock formations.
The composition of the soil includes solid parts, water, as well as various gases (accumulate in the pores). Soil moisture is a value that characterizes the ratio of the mass of liquid to the mass of solids in a unit volume. It can vary over a wide range and can range from one (sand) to two hundred percent (silt at the bottom of water bodies).
Soil in the development process increases in volume. This is due to the formation of pores and cavities. The magnitude of the change in volume is characterized by the coefficient of loosening (the ratio of the volume occupied by the soil before work, to the volume that the soil occupies after development). Over time, the density of loosened soil decreases (natural compaction). It is also possible the implementation of forced soil compaction using heavy construction equipment. The density of such soil is approaching the original, although somewhat less. This difference can be neglected, especially since over time it will disappear, and the soil itself will completely restore its properties (grow old).
The mechanical properties of soils (first of all, it is strength and the ability to deform) depend on the composition and nature of the bond between the particles. In the process of development, communications are destroyed, during compaction, they are restored.
To develop the soil in this way, earth moving and earth moving machines are used.
In the process, the cutting tool experiences very significant frictional and mechanical loads. In such conditions, the usual structural hoist will not stand for a long time. Therefore, the cutting edge of the working body is reinforced by elements made of cermets or special steels. Composite ceramic-metal plates are most effective in work. But their cost is quite high. Therefore, most often, buckets are strengthened by soldered electrodes made of wear-resistant alloys. Among other things, such a bucket has the effect of self-sharpening during operation due to more accelerated wear of part of the bucket of ordinary steel.
Such machines cut a certain layer of soil. The cut off mass is delivered to a dump via a special conveyor or is immediately poured into the dump truck body for export to a quarry or to other construction sites. Excavation of soil development falls into this category.
Types of Excavators
Depending on the design and parameters of the bucket, excavators are divided into the following types:
- single bucket;
- rotor and chain (bucket);
The most common is the bucket type excavator. This type of machine is universal, has very good maneuverability. The optimal usable volume of the bucket is from 0.15 to 2 meters cubic. Excavation of the soil by an excavator (single-bucket) with a more massive and capacious bucket is not economically feasible, since the hydraulics and the mechanical part of the equipment often fail due to heavy loads.
Also, depending on the drive mechanism, earthmoving machines are divided into tracked and automobile. There are so-called walking excavators, as well as pneumatic wheeled excavators. However, in practice, such machines are extremely rare, if at all, caught the eye. Even experienced builders, and even not everyone can boast that they have ever worked at the same facility with this type of machine.
This type of excavator can conduct soil development both lateral and straight through. In the first case, the excavator performs work along the axis of movement. The soil at the same time falls into the back of a truck, which drives up on the other side.
In the second case, work is carried out in front of the excavator, and vehicles for loading are fed from the rear.
If it is necessary to obtain significant excavation to a greater depth, then there is no alternative to mechanized excavation. All work is carried out by development in several stages (tiers). The tier does not exceed the technological capabilities of a particular model of excavator in depth of excavation.
Work bucket excavator
This type of machine is a prime example of a continuous mechanism. Therefore, of course, the performance of such an excavator is an order of magnitude higher than that of conventional single bucket machines. But it should be said that such equipment is used only in the construction of large-scale facilities. For the development of soil in a small trench, this type of equipment is absolutely unsuitable: very expensive maintenance, very high fuel consumption.
Work buckets can be fixed on a chain or on a rotor. From here comes the name of excavators: chain and rotary.
This type of excavator can be used in the development of soil of group 2. Although in practice there are cases when such machines easily coped with soils of 1 ... 3 groups. The soil should be relatively clean, without large stones and powerful stumps.
Development by earthmoving machinery
One machine in one working cycle carries out the extraction of the rock, its movement over small distances. Scrapers, graders, and also bulldozers belong to such cars.
Scrapers are used to carry out large-scale work. These machines are very productive, can be used in conditions of type 1 ... 4 soils. However, despite the incredible power, the scraper can not afford dense soils. Therefore, such soils must first be loosened. In one pass, this machine can remove a layer of soil up to 320 millimeters thick. The specific value depends on the power, bucket shape and model of the scraper.
The bottom of the scraper bucket is equipped with a knife. This is not the knife with which most people cut food in the kitchen. In this case, a strip of abrasion-resistant and self-hardening Hadfield steel is welded .
Bulldozers are used for work at shallow depths and over long distances. Also, this type of machine is used for cleaning and leveling the bottom of pits, the excavation of which was carried out by large-sized excavators.
To the depth, the bulldozer moves in tiers. The depth of the tier is equal to the size of the layer that the machine can remove in one pass. It is very important that the working movement of the bulldozer is carried out under a slope. This will allow several to unload the power units and minimize the likelihood of equipment failure.
Graders have low power and potential capabilities. They are used to a greater extent for decorative work: the installation of embankments and slopes, the implementation of planning works.
Description and scope of hydromechanical development
In this case, the development of soils manually is out of the question. However, as with the use of earthmoving machines. The scope is very extensive: from the creation of artificial reservoirs to the construction of roads. The technology also allows you to reclaim areas for residential and industrial development in swampy and coastal areas subject to floods. All processes are mechanized. This method of soil development requires the creation of a special infrastructure, which makes it advisable to use it only with very large amounts of work ahead.
Hydromechanical development using hydromonitors
The essence of this development method is as follows: the soil is washed with a stream of water under high pressure (about 15 MPa). The resulting mud mass (on the slang of professionals - pulp), initially accumulates in the intermediate tanks, and from there it is pumped to the right place through the pipeline.
Over time, the moisture completely evaporates, and a dense layer of soil is formed. If it is compacted with a roller, then such soil becomes quite suitable for the construction of communication lines (roads and railways).
The great technological advantage of this method is the ability to conduct the development of soils of almost any category of complexity.
Hydromechanical design using dredger shells
When carrying out work at the bottom of water bodies, the development of soil manually, as well as using traditional earth-moving machinery, is excluded. Special vessels are needed.
A suction dredger is a swimming facility equipped with special equipment. A powerful pump pumps the eroded soil from the bottom of the reservoir and transports it through the pipeline either to the hold of the vessel, or to the auxiliary transport vessel, or throws it with a powerful jet far from the place of excavation.
Such suction dredges have found application in the deepening and clearing of ship fairways in shallow water, in deepening rivers to ensure uninterrupted shipping, as well as in the extraction of diamonds from the shelf of the oceans.
Ground mass is sucked through the pipe. For suction of sludge and soft soil, the pipe is not equipped with an additional cultivator. The presence of the latter is necessary when developing dense soils. According to the difficulty of development, this method leads. The operation and maintenance of special transport, its parking in port waters is very expensive. High demands are placed on the qualifications of staff.
Development of frozen soils
For development in permafrost conditions, as well as for the development of rocky rocks, powerful directional explosions are used. Trotyl, ammonite and toll can be used as explosives.
Explosive shells can be placed both on the surface and laid deep into pre-drilled holes or in natural cavities.
The so-called borehole charges are used in the development of a large basin, as well as for dumping soils. Explosive shells are installed in pre-drilled wells. The minimum well diameter is 200 millimeters. To increase the destructive power of charges, openings on the outside are covered with sand or fine rock (formed when drilling wells).
Spur charges are used when it is necessary to excavate a small amount of soil. It is possible to carry out both in open-cast mining and in underground mining. Spurs are a kind of sleeve. They have a diameter of 25 to 75 millimeters. They are filled with explosives by a maximum of two-thirds. The remaining space is filled with rock (in order to receive a directed blast wave and achieve the greatest beneficial effect).
Chamber charges. This type of charge is used when it is necessary to excavate significant volumes of soil by means of directional ejection. The essence of the method is as follows. In the development zone, vertical wells or horizontal tunnels are arranged, in the walls of which blind holes are drilled for laying charges. After laying explosives, adits and wells are filled with soil (this allows you to increase the power of the explosion). The direction of release is provided by the uneven filling of the explosive. So, on one side there can be several times more drill holes for charges. Also, mismatch of explosions may be used for this purpose.
The so-called slotted charge is used mainly in the development of soil in permafrost. It is unlikely that it will be possible to carry out directed emission of such a rock. But loosening it, so that in the future it can be removed with a bulldozer or excavator, is quite realistic. To do this, a tool is used that, in principle and in appearance, resembles a metal disk mill. Only, of course, such a tool is much larger. Such a mill cuts out peculiar grooves in the ground at a distance of up to 2.5 meters from each other. Explosive is not placed in every groove, but after one - a hollow empty space acts as a compensator. The blast wave crushes the soil, and it moves towards the cavity. Such work requires careful preparation and detailed study of the project.