Soils are any rocks that occur mainly within the zone of weathering of the Earth and are objects of engineering and human construction activities. Soils are used as a base, medium or material for the construction of buildings and structures.
In accordance with GOST 25100-82, all soils are classified depending on the origin and conditions of education, the nature of the structural bonds between the particles, the composition and construction properties of the soils.
Soils are divided into two main classes: rock and non-rock.
Rocky soils are soils with hard structural bonds, which include igneous (granites, diorites, etc.), metamorphic (gneiss, quartzite, shale, etc.), sedimentary cemented (sandstones, conglomerates, etc.) and artificial.
Rocky soils are subdivided into varieties depending on the ultimate strength for uniaxial compression in a water-saturated state, according to the degree of softening in water, solubility, etc.
Non-rocky soils are soils without rigid structural bonds. The non-rock soils include loose rocks, including incoherent (loose) and cohesive rocks, the strength of which is many times less than the bond strength of minerals that make up these rocks. A characteristic feature of these soils is their fragmentation, dispersion, which fundamentally distinguishes them from rocky, very strong rocks.
The composition of the soil includes solid mineral particles, water in various types and states, and gaseous inclusions. Some soils contain organic compounds.
Solid mineral particles of the soil are a system of various in shape, composition and grain size. Grain sizes range from tens of centimeters for boulders to the smallest colloidal particles.
Non-rocky soils by the size of mineral particles are divided into the following types:
coarse-grained (boulder, pebble, gravel and rubble) with a particle content larger than 2 mm more than 50% by weight;
sandy (gravel, large, medium size, small and dusty);
silty clay (sandy loam, loam and clay).
According to the density of addition, sandy soils are divided into types depending on the value of the porosity coefficient.
Among the silty-clay soils, it is necessary to isolate the soils that exhibit specific adverse properties during soaking — pro-transfer and swelling. The subsidence includes soils that, under the action of an external load or its own weight, when soaking with water, give a draft called a subsidence.
Sagging soils are characterized by relative subsidence ese, initial subsidence pressure pse and initial subsidence humidity wse. Loess and other macroporous soils have drawdown properties.
Loess soils are macroporous soils containing calcium carbonates and exhibiting subsidence properties when soaked with water under load.
The swelling includes soils that, when soaked with water or chemical solutions, increase in volume, and the relative swelling without load is esme0.04.
Special types of soil should also include biogenic soils, quicksand, vegetable and frozen soils.
Soils containing a significant amount of organic matter are called biogenic. These include peaty ground, peat and sapronela (freshwater mud).
Sludge is a water-saturated modern sediment of water bodies, formed as a result of microbiological processes, with moisture exceeding the moisture content at the yield line, and a porosity coefficient of more than 0.9.
Sinks are soils which, when opened, start to move like a viscous body, occur among water-saturated, fine-grained, silty sands. There are true swims and pseudo-swims. True fluids are characterized by the presence of silty-clay and colloidal particles, high porosity (> 40%), low water loss and filtration coefficient, a characteristic of thixotropic transformations, melting at a humidity of 6-9% and a transition to a fluid state at 15-17%.
Psevdoplyvuny - sands that do not contain thin clay particles, fully water-saturated, easily giving away water, permeable, interleaved in a flowing state at a certain hydraulic gradient.
Soil or vegetable soil -
these are natural formations that compose the surface layer of the earth's crust and are fertile. Non-rocky artificial soils include soils compacted by various methods (tamping, rolling, vibration compaction, explosions, drainage, etc.), bulk and all-up.
In construction practice, it is customary to call the top layer of rocks composing the weathering crust, which are used as the basis or material for engineering structures to be called soils. Soils can also be used as a medium for some engineering structures, in particular, tunnels, subways, mines, etc.
Depending on the degree of destruction of the rock and some other properties that are important in construction, the soil lying at the base or used as a building material can be classified into:
- rock - igneous, metamorphic and sedimentary rocks with a rigid connection between minerals or aggregates, in the form of a solid or fractured massif;
- loose - not cemented soils that do not have cohesion in the dry state and do not possess plasticity;
- clay - coherent in a dry state, fine-grained soils,
having the properties of plasticity;
- special soils with low bearing capacity and structurally unstable.
The rocks are characterized by high strength characteristics. Thus, the temporal resistance to uniaxial compression is from 300.0 to 2.0 MPa. Rocks with temporary resistance to compression in a saturated state of less than 5.0 MPa are referred to as semi-rock.
Most of the rocks are inherently fractured. The presence of cracks leads to a weakening of the array and creates conditions for filtering. From the surface to a depth of 25 ... 50 m, the rocks can be more or less weathered, which also leads to a decrease in the strength of the massif.
Some of the rocks due to their layered structure have anisatropy - different properties in different directions. In general, rocky soils are reliable bases and require detailed study only when erection of water-holding and other important structures on them.
For rocky soils in the survey determine the following main characteristics:
- density;
- temporary resistance to uniaxial compression;
- shear resistance;
- tear resistance;
- indicators of fracturing (modulus of fracture, characteristics of cracks);
- degree of weathering;
- specific water absorption.
Bulk rocks can be divided into two groups, which differ only in the content of particles of a particular size. These are coarse-grained with a content of more than 50% by weight of particles with sizes greater than 2 mm and sandy with a content of less than 50% by weight of particles larger than 2 mm and not having plasticity.
Bulk rocks are characterized by the absence of strong bonds between individual grains, porosity, high water permeability, and instability under dynamic loads. Their compactibility under static loads is negligible. In general, loose rocks are sufficiently reliable bases for structures with relatively small vertical loads and minor horizontal ones. They are not suitable for the construction of water retention facilities.
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