Types of soils and their characteristics. Clay soils Foundation type from soil

Dust-clay soils, depending on the amount of water they contain, can have a consistency (dough density) from solid to fluid. To determine the consistency, the characteristic moisture content of silty clay soils is found, which are called the rolling boundary and the yield boundary.

The rolling boundary is the moisture content of the soil, at which it loses its ability to roll into a cord with a diameter of 2..3 mm.

The yield point is the soil moisture at which the standard cone is immersed in the sample to a depth of 10 mm.

Rice. 1.4. Determining the border of soil rolling

The plasticity number of the soil is the difference between the yield boundary and the rolling boundary:

(1.18)

The consistency of silt-clay soil is estimated by the fluidity index:

(1.19)

Table 1.5. Condition of clays and loams

For sandy loam, due to the low accuracy of determining the values and, only three states are distinguished: solid, plastic, and fluid.

Table 1.6. Sandy loam condition

In the group of silt-clay soils, loess soils and silts are distinguished - they have specific unfavorable properties.

Loess soils contain more than 50% of silt particles with the presence of salts, mainly calcium carbonate, have a predominantly macroporous structure and belong to the category of structurally unstable subsidence soils. Subsidence is a rapidly developing settlement caused by a sharp change in the structure of the soil. Significant precipitation in violation of the structure of subsiding soils is due to the fact that under natural conditions they are undercompacted. In the process of their formation, there is no complete compaction due to the action of its own weight due to the formation of new structural bonds. Such soils become macroporous and, under certain external influences (soaking, vibration), which destroy the bonds that have arisen, they can be additionally compacted, which causes significant precipitation. The possibility of manifestation of subsidence properties of soils is preliminarily assessed by the degree of their moisture content and the subsidence index, which is determined by the formula:

where: e - coefficient of porosity of natural soil; - coefficient of porosity corresponding to moisture content at the yield point (1.16).

Clay soil is soil that is more than half composed of very fine particles less than 0.01 mm in size, which are in the form of flakes or plates. The distances between these particles are called pores, they are usually filled with water, which is well retained in the clay, because the clay particles themselves do not let water through. Clay soils have high porosity; high pore volume to soil volume ratio. This ratio ranges from 0.5 to 1.1 and is a characteristic of the degree. Each pore is a small capillary, so such soils are susceptible.

Clay soil retains moisture very well and never gives it all away, even when it dries, therefore it is. The moisture contained in the soil, when frozen, turns into ice and expands, thereby increasing the volume of the entire soil. All soils containing clay are susceptible to this negative phenomenon, and the greater the clay content, the stronger this property manifests itself.

The pores of the clay soil are so small that the capillary forces of attraction between the particles of water and clay are sufficient to bind them. Capillary forces of attraction, together with the plasticity of clay particles, provide the plasticity of clay soil. And the greater the clay content, the more plastic the soil will be. Depending on the content of clay particles, they are classified into sandy loam, loam and clay.

Clay soil classification

Sandy loam is a clay soil that contains no more than 10% of clay particles, the rest is sand. Sandy loam is the least plastic of all clay soils; when it is rubbed between the fingers, grains of sand are felt, it does not roll well into a cord. A ball rolled from sandy loam crumbles if you press a little on it. Due to the high sand content, the sandy loam has a relatively low porosity - from 0.5 to 0.7. Accordingly, it may contain less moisture and therefore be less prone to heaving. With a porosity of 0.5 (i.e. with good compaction), in a dry state, sandy loam is 3 kg/cm2, with a porosity of 0.7 - 2.5 kg/cm3.

Loam is a clay soil that contains 10 to 30 percent clay. This soil is quite plastic, when rubbing it between the fingers, individual grains of sand are not felt. A ball rolled from loam is crushed into a cake, along the edges of which cracks form. The porosity of loam is higher than sandy loam and ranges from 0.5 to 1. Loam can contain more water and is more prone to heaving than sandy loam. Dry loam with a porosity of 0.5 has a bearing capacity of 3 kg/cm2, with a porosity of 0.7 - 2.5 kg/cm2.

Clay is a soil in which the content of clay particles is more than 30%. Clay is very plastic, rolls well into a cord. A ball rolled from clay is compressed into a cake without cracking along the edges. The porosity of clay can reach 1.1, it is more susceptible than all other soils, because it can contain a very large amount of moisture. With a porosity of 0.5 clay has a bearing capacity of 6 kg/cm2, with 0.8 - 3 kg/cm2.

All clay soils under the action of the load from the foundation are subject to settlement, and it takes a very long time - several seasons. The sediment will be the greater and longer, the greater the porosity of the soil. To reduce the porosity of clay soil and thereby improve its characteristics, the soil can be compacted. The natural compaction of clay soil occurs under the pressure of the overlying layers: the deeper the layer is, the stronger it is compacted, the less its porosity and the greater its bearing capacity.

The minimum porosity of clay soil 0.3 will be in the most compacted layer, which lies below the freezing depth. The fact is that when the soil freezes, heaving occurs: soil particles move and new pores appear between them. In the soil layer, which is below the freezing depth, there are no such movements, it is maximally compacted and can be considered incompressible. depends on climatic conditions, in Russia it ranges from 80 to 240 cm. The closer to the surface of the earth, the less clay soil will be compacted.

In order to roughly estimate the bearing capacity of clay soil at a certain depth, we can take the maximum porosity of 1.1 on the surface of the earth, and the minimum of 0.3 at the freezing depth and assume that it changes evenly depending on the depth. Along with it, the bearing capacity will also change: from 2 kg / cm2 on the surface, to 6 kg / cm2 below the freezing depth.

Another important characteristic of clay soil is its: the more moisture it contains, the worse its bearing capacity. Clay soil saturated with moisture becomes too plastic, and it can become saturated with moisture when groundwater is close. If high and less than a meter from the depth of the foundation, then the above values \u200b\u200bof the bearing capacity of clay, loam and sandy loam should be divided by 1.5.

All clay soils will serve as a good foundation for the foundation of the house, if the groundwater occurs at a considerable depth, and the soil itself is homogeneous in composition.

Soils: types and properties

Soil classes

Soils are divided into three classes: rocky, dispersed and frozen (GOST 25100-2011).

Rocky soils- igneous, metamorphic, sedimentary, volcanogenic-sedimentary, eluvial and technogenic rocks with rigid crystallization and cementation structural bonds.
Dispersion soils- sedimentary, volcanogenic-sedimentary, eluvial and technogenic rocks with water-colloidal and mechanical structural bonds. These soils are divided into cohesive and non-cohesive (loose). The class of dispersion soils is divided into groups:
- mineral- coarse-clastic, fine-clastic, silty, clayey soils;
- organomineral- peaty sands, silts, sapropels, peaty clays;
- organic- peat, sapropel.
frozen ground- these are the same rocky and dispersed soils, additionally having cryogenic (ice) bonds. Soils in which only cryogenic bonds are present are called icy.

According to the structure and composition, soils are divided into:

rocky;
coarse-grained;
sandy;
clayey (including loess-like loams).

Basically, there are varieties of sandy and clay varieties, which are very diverse both in particle size and in physical and mechanical properties.

According to the degree of occurrence, soils are divided into:

top layers;
average depth;
deep seating.

Depending on the type of soil, the base can be located in different soil layers.

The upper layers of the soil are exposed to atmospheric action (wetting and drying, weathering, freezing and thawing). Such an impact changes the state of the soil, its physical properties and reduces the resistance to loads. The only exceptions are rocky soils and conglomerates.

Therefore, the foundation of the house must be located at a depth with sufficient bearing characteristics of the soil.

The classification of soils by particle size is determined by GOST 12536

Particles	Factions	Size, mm
Large debris
Boulders*, blocks	large	> 800
	medium size	400-800
	small	200-400
Pebble*, crushed stone	large	100-200
	medium size	60-100
	small	10-60
Gravel*, gruss	large	4-10
Gravel*, gruss	small	2-4
small debris
Sand	very large	1-2
	large	0,5-1
	medium size	0,25-0,5
	small	0,1-0,25
	very small	0,05-0,1
suspension
Dust (silt)	large	0,01-0,05
Dust (silt)	small	0,002-0,01
Colloids
Clay		< 0,002

* Names of large fragments with rolled edges.

Measured characteristics of soils

To calculate the bearing characteristics of the soil, we need the measured properties of the soil. Here are some of them.

Specific gravity of the soil

Soil specific gravity γ called the weight of a unit volume of soil, measured in kN / m³.

The specific gravity of the soil is calculated through its density:

ρ - soil density, t/m³;
g is the acceleration due to gravity, assumed to be 9.81 m/s².

Density of dry (skeleton) soil

Density of dry (skeleton) soil ρ d- natural density after subtracting the mass of water in the pores, g/cm³ or t/m³.

Set by calculation:

where ρ s and ρ d are the density of particles and the density of dry (skeleton) soil, respectively, g/cm³ (t/m³).

Accepted particle density ρ s (g/cm³) for soils

Porosity coefficient e, for sandy soils of different densities

Soil moisture levels

Degree of soil moisture S r- the ratio of the natural (natural) soil moisture W to the moisture corresponding to the complete filling of the pores with water (without air bubbles):

where ρ s is the density of soil particles (density of the soil skeleton), g/cm³ (t/m³);
e - coefficient of soil porosity;
ρ w is the density of water, taken equal to 1 g/cm³ (t/m³);
W - natural soil moisture, expressed in fractions of a unit.

Soils according to the degree of moisture

Soil plasticity

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Plastic soil- its ability to deform under the action of external pressure without breaking the continuity of the mass and retain the given shape after the cessation of the deforming force.

To establish the ability of the soil to take on a plastic state, the moisture content is determined, which characterizes the boundaries of the plastic state of the soil of fluidity and rolling.

Yield limit W L characterizes the humidity at which the soil from a plastic state passes into a semi-liquid - fluid. At this humidity, the connection between the particles is broken due to the presence of free water, as a result of which the soil particles are easily displaced and separated. As a result, the adhesion between the particles becomes insignificant and the soil loses its stability.

Rolling border W P corresponds to the humidity at which the soil is on the border of the transition from solid to plastic. With a further increase in moisture (W > W P), the soil becomes plastic and begins to lose its stability under load. The yield boundary and the rolling boundary are also called the upper and lower limits of plasticity.

Determining the humidity at the border yield and rolling limit, calculate the soil plasticity number I P. The plasticity number is the moisture interval within which the soil is in a plastic state, and is determined as the difference between the yield limit and the soil rolling limit:

I P \u003d W L - W P

The higher the plasticity number, the more plastic the soil. The mineral and grain composition of the soil, the shape of the particles and the content of clay minerals significantly affect the limits of plasticity and the plasticity number.

The division of soils according to the number of plasticity and the percentage of sand particles is given in the table.

Fluidity of clay soils

Show Yield I L expressed in fractions of a unit and is used to assess the state (consistency) of silty clay soils.

Determined by calculation from the formula:

I L =	W-Wp
	I p

where W - natural (natural) soil moisture;
W p - humidity at the boundary of plasticity, in fractions of a unit;
I p - number of plasticity.

Flow index for soils of different densities

Rocky soils

Rocky soils are monolithic rocks or in the form of a fractured layer with rigid structural bonds, lying in the form of a continuous massif or separated by cracks. These include igneous (granites, diorites, etc.), metamorphic (gneisses, quartzites, shales, etc.), sedimentary cemented (sandstones, conglomerates, etc.) and artificial.

They hold the compressive load well even in a water-saturated state and at low temperatures, and are also insoluble and do not soften in water.

They are a good base for foundations. The only difficulty is the development rocky ground. The foundation can be erected directly on the surface of such soil, without any opening or deepening.

Coarse clastic soils

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Coarse clastic - incoherent fragments of rock with a predominance of fragments larger than 2 mm (over 50%).

According to the granulometric composition, coarse-grained soils are divided into:

boulder d>200 mm (with a predominance of unrounded particles - blocky),
pebble d>10 mm (with unrounded edges - crushed stone)
gravel d>2 mm (with unrounded edges - grit). These include gravel, crushed stone, pebbles, gruss.

These soils are a good base if there is a dense layer under them. They shrink slightly and are reliable bases.

If there is more than 40% of sand aggregate in coarse-clastic soils or more than 30% of clay aggregate of the total mass of air-dry soil, the name of the type of aggregate is added to the name of the coarse-clastic soil, and the characteristics of its condition are indicated. The type of filler is established after removal of particles larger than 2 mm from the coarse-grained soil. If the detrital material is represented by a shell in an amount of ≥ 50%, the soil is called shelly, if from 30 to 50% - with a shell is added to the name of the soil.

Coarse-clastic soil can be heaving if the fine component is silty sand or clay.

conglomerates

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Conglomerates are large clastic rocks, a group of rocky destroyed rocks, consisting of individual stones of different fractions, containing more than 50% fragments of crystalline or sedimentary rocks that are not interconnected or cemented by foreign impurities.

As a rule, the bearing capacity of such soils is quite high and is able to withstand the weight of a house of several floors.

Cartilaginous soils

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Cartilaginous soils are a mixture of clay, sand, stone fragments, crushed stone and gravel. They are poorly eroded by water, are not subject to swelling and are quite reliable.

They don't shrink or blur. In this case, it is recommended to lay the foundation with a depth of at least 0.5 meters.

Dispersion soils

Mineral dispersion soil consists of geological elements of various origins and is determined by the physicochemical properties and geometric particle sizes of its constituents.

sandy soils

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Sandy soils - a product of the destruction of rocks, are a loose mixture of grains of quartz and other minerals formed as a result of weathering of rocks with particle sizes from 0.1 to 2 mm, containing no more than 3% clay.

Sandy soils by particle size can be:

gravelly (25% of particles larger than 2 mm);
large (50% of particles by weight larger than 0.5 mm);
medium size (50% of particles by weight larger than 0.25 mm);
fine (particle sizes - 0.1-0.25 mm)
dusty (particle size 0.005-0.05 mm). They are similar in their manifestations to clay soils.

By density they are divided into:

dense;
medium density;
loose.

The higher the density, the stronger the soil.

Physical properties:

high flowability, since there is no adhesion between individual grains.
easy to develop;
good water permeability, well pass water;
do not change in volume at different levels of water absorption;
freeze slightly, not heaving;
under loads, they tend to strongly compact and sag, but in a fairly short time;
not plastic;
easily compacted.

Dry clean (especially coarse) quartz sand can withstand heavy loads. The larger and cleaner the sands, the greater the load the base layer from it can withstand. Gravelly, coarse and medium-sized sands are significantly compacted under load, and slightly freeze.

If the sands lie evenly with sufficient density and thickness of the layer, then such soil is a good basis for the foundation and the coarser the sand, the greater the load it can take. It is recommended to lay the foundation at a depth of 40 to 70 cm.

Fine sand, liquefied by water, especially with impurities of clay and silt, is unreliable as a base. Silty sands (particle size from 0.005 to 0.05 mm) weakly hold the load, as the base requires strengthening.

sandy loam

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Sandy loam - soils in which clay particles smaller than 0.005 mm are contained in the range from 5 to 10%.

Quicksand is sandy loam in properties similar to silty sands, containing a large amount of silty and very fine clay particles. With sufficient water absorption, dusty particles begin to play the role of a lubricant between large particles, and some types of sandy loam become so mobile that they flow like a liquid.

There are true quicksands and pseudo quicksands.

True quicksand are characterized by the presence of dusty-clay and colloidal particles, high porosity (> 40%), low water loss and filtration coefficient, a feature for thixotropic transformations, slumping at a moisture content of 6–9% and a transition to a fluid state at 15–17%.

Pseudo quicksand- sands that do not contain fine clay particles, are completely saturated with water, easily give up water, are permeable, passing into a free-flowing state at a certain hydraulic gradient.

Quicksand is practically unsuitable for use as foundation foundations.

Clay soils

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Clays are rocks consisting of extremely fine particles (less than 0.005 mm), with a small admixture of fine sand particles. Clay soils were formed as a result of physical and chemical processes that occurred during the destruction of rocks. Their characteristic property is the adhesion of the smallest soil particles to each other.

Physical properties:

low culvert properties, therefore always contain water (from 3 to 60%, usually 12-20%).
increase in volume when wet and decrease when dry;
depending on the humidity, they have a significant cohesion of the particles;
clay compressibility is high, compaction under load is low.
plastic only within a certain humidity; at a lower humidity, they become semi-solid or solid, at a higher one, they pass from a plastic state to a fluid one;
eroded by water;
heaving.

According to the absorbed water, clays and loams are divided into:

hard,
semi-solid,
hard-plastic,
soft plastic,
fluid plastic,
fluid.

Settling of buildings on clay soils continues for more than long time than on sandy soil. Clay soils with sandy interlayers are easily liquefied and therefore have a low bearing capacity.

Dry, densely compacted clay soils with a large layer thickness can withstand significant loads from structures if there are stable underlying layers under them.

Clay that has been compacted for many years is considered a good base for the foundation of a house.

But this kind of clay is rare, because. in its natural state it is almost never dry. The capillary effect present in soils with a fine structure leads to the fact that the clay is almost always in a wet state. Also, moisture can penetrate through the sandy impurities in the clay, so the moisture absorption of the clay is uneven.

Moisture inhomogeneity during soil freezing leads to uneven heaving at low temperatures, which can lead to deformation of the foundation.

Heaving can be all types of clay soils, as well as dusty and fine sands.

Clay soils are the most unpredictable for construction.

They can erode, swell, shrink, swell when frozen. Foundations on such soils are built below the freezing mark.

In the presence of loess and silty soils, it is necessary to take measures to strengthen the base.

macroporous clays

Clay soils that naturally have pores visible to the naked eye that are much larger than the soil skeleton are called macroporous. Macroporous soils include loess soils (more than 50% of dust particles), the most common in the south of the Russian Federation and the Far East. In the presence of moisture, loess-like soils lose their stability and soak.

loams

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Loams are soils in which clay particles less than 0.005 mm in size are contained in the range from 10 to 30%.

By their properties, they occupy an intermediate position between clay and sand. Depending on the percentage of clay, loams can be light, medium and heavy.

Such soil as loess belongs to the group of loams, contains a significant amount of silt particles (0.005 - 0.05 mm) and water-soluble limestones, etc., is very porous and shrinks when wet. It swells when frozen.

In a dry state, such soils have considerable strength, but when moistened, their soil softens and sharply compacts. As a result, significant precipitation, severe distortions and even destruction of structures erected on it, especially those made of brick, occur.

Thus, in order for loess-like soils to serve as a reliable foundation for structures, it is necessary to completely eliminate the possibility of their soaking. To do this, it is necessary to carefully study the groundwater regime and the horizons of their higher and lower standing.

Silt (silty soils)

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Silt - formed in the initial stage of its formation in the form of structural sediments in water, in the presence of microbiological processes. For the most part, such soils are located in places of peat extraction, marshy and wetlands.

Silt - silty soils, water-saturated modern sediment of predominantly marine areas, containing organic matter in the form of plant residues and humus, the content of particles less than 0.01 mm is 30-50% by weight.

Properties of silty soils:

Strong deformability and high compressibility and as a result - negligible resistance to loads and unsuitability of their use as a natural base.
Significant influence of structural bonds on mechanical properties.
Insignificant resistance of friction forces, which makes it difficult to use pile foundations in them;
Organic (humic) acids in the sludge act destructively on the concrete of structures and foundations.

The most significant phenomenon that occurs in silty soils under the action of an external load, as mentioned above, is the destruction of their structural bonds. Structural bonds in silts begin to break down at relatively insignificant loads, however, only at a certain external pressure, which is quite certain for a given silty soil, an avalanche (mass) violation of structural bonds occurs, and the strength of the silty soil sharply decreases. This amount of external pressure is called " structural strength soil". If the pressure on the silty soil is less than the structural strength, then its properties are close to the properties of a solid body of low strength, and, as the corresponding experiments show, neither the compressibility of the silt nor its shear resistance practically depend on the natural humidity. At the same time, the angle of internal friction muddy soil is small, and the adhesion has a well-defined value.

The sequence of building foundations on silty soils:

These soils are "excavated" and replaced layer by layer with sandy soil;
A stone / crushed stone pillow is poured, its power is determined by calculation, it is necessary that pressure on the surface of the silty soil from the structure and the pillow is not dangerous for the silty soil;
After that, the building is erected.

Sapropel

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Sapropel is a freshwater sludge formed at the bottom of stagnant reservoirs from the decay products of plant and animal organisms and containing more than 10% (by weight) of organic matter in the form of humus and plant residues.

Sapropel has a porous structure and, as a rule, a fluid consistency, high dispersion - the content of particles larger than 0.25 mm usually does not exceed 5% by weight.

Peat

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Peat is an organic soil formed as a result of natural death and incomplete decomposition of marsh plants under conditions high humidity with a lack of oxygen and containing 50% (by mass) or more organic substances.

They include a large amount of plant sediments. According to the amount of their content, they distinguish:

slightly peaty soils (relative content of plant sediments - less than 0.25);
medium peat (from 0.25 to 0.4);
heavily peaty (from 0.4 to 0.6) and peat (over 0.6).

Peat bogs are usually highly moistened, are characterized by strong uneven compressibility and are practically unsuitable as a base. Most often they are replaced with more suitable bases, for example, sandy.

Peaty soil

Peated soil - sand and clayey soil containing from 10 to 50% (by weight) of peat.

Soil moisture

Due to the capillary effect, soils with a fine structure (clay, silty sands) are in a wet state even at low groundwater levels.

The rise in water can reach:

in loams 4 - 5 m;
in sandy loam 1 - 1.5 m;
in silty sands 0.5 - 1 m.

Conditions for weakly heaving soil

Relatively safe conditions for the soil to be considered weakly heaving when groundwater is located below the estimated freezing depth:

in silty sands by 0.5 m;
in sandy loam per 1 m;
in loam at 1.5 m;
in clay at 2 m.

Conditions for medium heaving soil

The soil can be classified as medium-heaving when groundwater is located below the estimated freezing depth:

in sandy loam at 0.5 m;
in loam per 1 m;
in clays at 1.5 m.

Conditions for strongly heaving soil

The soil will be strongly heaving if the groundwater level is higher than for medium heaving soils.

Determining the type of soil by eye

Even a person far from geology will be able to distinguish clay from sand. But not everyone can determine by eye the proportion of clay and sand in the soil. What kind of soil is loam or sandy loam in front of you? And what is the percentage of pure clay and silt in such soil?

To get started, examine the neighboring residential areas. The experience of creating the foundation of neighbors can give useful information. Crooked fences, deformations of foundations when they are not deep, and cracks in the walls of such houses speak of heaving soils.

Then you need to take a soil sample from your site, preferably closer to the place of the future home. Some advise to make a hole, but you can’t dig a deep narrow hole, and then what to do with it?

I offer a simple and obvious option. Start your construction by digging a hole for a septic tank.

You will get a well with sufficient depth (at least 3 meters, if possible more) and width (at least 1 meter), which provides a bunch of advantages:

space for taking soil samples from different depths;
visual inspection of the soil section;
the ability to test the soil for strength without removing the soil, including the side walls;
You don't need to dig the hole back in.

Only set in the well soon concrete rings so that the well does not crumble from the rains.

Determination of soil by appearance

Dry rock condition

Clay	Hard in pieces, on impact it is pricked into separate clods. Lumps are crushed with great difficulty. Very difficult to grind into powder.
loams	Lumps and pieces are comparatively hard, crumble upon impact, forming a trifle. The mass pounded in the palm of your hand does not give the feeling of a homogeneous powder. There is little sand to the touch when rubbing. Lumps are crushed easily.
sandy loam	Cohesion between particles is weak. The clods easily crumble from hand pressure, and when rubbed, an inhomogeneous powder is felt, in which the presence of sand is clearly felt. Dusty sandy loam resembles dry flour when rubbed.
Sand	Sandy self-disintegrating mass. When rubbed in the palms, there is a feeling of a sandy mass, large sandy particles predominate.

Wet rock condition

Clay	Plastic, sticky and smearing	The ball, when squeezed, does not form cracks along the edges. When rolled out, it gives a strong and long cord with a diameter of< 1 мм.
loams	Plastic	The ball, when squeezed, forms a cake with cracks along the edges. There is no long cord.
sandy loam	Weakly ductile	A ball is formed, which crumbles with light pressure. Does not roll into a cord or is difficult to roll and breaks into pieces easily.
Sand	When waterlogged, it turns into a fluid state	Does not roll into a ball and cord.

Water clarification method

A method for determining the type of soil by the rate of water clarification in 1 minute in a test tube (or glass) in which a pinch of soil is placed.

Type of foundation from the ground

Peat - pile foundation.
Dusty sands, viscous clays - a deep foundation with waterproofing.
Fine and medium sands, hard clays - a shallow foundation.
In wet soils (clay, loam, sandy loam or silty sand), the depth of the foundation is greater than the calculated freezing depth.

1.4.2. Physical properties of soils

Soil properties should be characterized by quantitative indicators that depend on the composition, structure and condition of the soil. They are determined from experiments, most often with soil samples taken in field conditions with the preservation of the natural structure and moisture. The correspondence of the characteristics of the state of the soil underlying the structure obtained in this way is one of the most important conditions for the accuracy of engineering forecasts.

Let us consider only those characteristics of soils that determine their physical properties. The physical state of soils is determined mainly by three characteristics: soil density, mineral particle density and soil moisture. The remaining characteristics are calculated using these three.

Imagine some unit volume of soil V, consisting of solid, liquid and gaseous components, each of which has the corresponding volume and mass (Fig. 1.5).

Ground density- the ratio of the mass of soil to its volume, has the dimension g / cm 3, t / m 3:

. (1.1)

Soil density depends on its mineralogical composition, porosity and humidity and varies within 1.5 ÷ 2.4 g/cm 3 . It is determined by the method of a cutting ring with a known volume or waxing of a sample of arbitrary shape. Density is an important characteristic of the soil and is used in calculating the bearing capacity of the foundation, the natural pressure of the soil, the pressure of the soil on retaining walls, stability of landslide slopes and slopes.

Soil particle density- the ratio of the mass of solid particles to their volume

= , (1.2)

depends only on their mineralogical composition. For soils, it varies from 2.4 to 3.2 g / cm 3, including for sands - from 2.55 to 2.66 g / cm 3, for sandy loams - from 2.66 to 2.68 g / cm 3, for loams - from 2.68 to 2.72 g / cm 3, for clays - from 2.71 to 2.76 g / cm 3. The particle density is determined using a pycnometer.

Soil moisture- the ratio of the mass of water to the mass of solid particles, expressed as a percentage or in fractions of a unit

W= (1.3)

and is determined by drying the soil sample in a thermostat at a temperature of 105 ºC until a stable mass of dried soil is reached. The natural moisture content of soils varies over a wide range from units to hundreds of percent. High humidity values are characteristic of low-compacted water-saturated clay soils, low values are characteristic of low-moisture coarse-grained, sandy and loess soils.

The above basic physical characteristics of the soil , , are always determined experimentally. They are used to calculate the other characteristics listed below.

Dry ground density or the density of the soil skeleton is defined as the ratio of the mass of soil particles to the entire volume of soil:

Using expressions (1.1) and (1.3), we can write

Rock composition		breeds
content of dioxide SiO 2 (%)	minerals	deep	poured out (analogues of deep)
Acid Rocks (75-65)	Quartz, feldspars (usually orthoclase), micas	Granites	Quartz porphyry, liparite
Medium breeds (65-52)	Feldspars (usually orthoclase, hornblende, biotite)	syenites	orthoclase porphyry, trachyte
Medium breeds (65-52)	Plagioclase, hornblende, biotite	Diorites	Porphyrite, andesite
Main breeds (52-40)	Plagioclases (more often labradorite), augite, sometimes olivine	Gabbro	Diabase, basalt
Ultramafic rocks (less than 40)	Augite	Pyroxenites	-
	augite, olivine, ore minerals	Peridotites	-
	Olivine, ore minerals	Dunites	-