What characterizes the type and condition of clay soils. The state of silty-clayey soils. Determination of the angle of repose

]: rocky (soils with rigid ties) and non-rocky (soils without rigid ties).

GOST 25100-95 Soils. Classification

In the class of rocky soils, igneous, metamorphic and sedimentary rocks are distinguished, which are divided by strength, softening and solubility in accordance with table. 1.4. Rocky soils, the strength of which in a water-saturated state is less than 5 MPa (semi-rocky), include shales, sandstones with clay cement, siltstones, mudstones, marls, chalk. With water saturation, the strength of these soils can decrease by a factor of 2-3. In addition, in the class of rocky soils, artificial ones are also distinguished - fractured rocky and non-rocky soils fixed in their natural bedding.

TABLE 1.4. CLASSIFICATION OF ROCK SOILS

Priming	Index
Uniaxial compressive strength in water-saturated state, MPa
Very durable	R c > 120
Lasting	120 ≥ R c > 50
Medium strength	50 ≥ R c > 15
Low-strength	15 ≥ R c > 5
Reduced strength	5 ≥ R c > 3
Low strength	3 ≥ R c ≥ 1
Extremely low strength	R c < 1
According to the coefficient of softening in water
Non-softened	K saf ≥ 0,75
Softened	K saf < 0,75
By the degree of solubility in water (sedimentary cemented), g / l
Insoluble	Solubility less than 0.01
Sparingly soluble	Solubility 0.01-1
Medium soluble	- || - 1—10
Readily soluble	- || - more than 10

These soils are subdivided according to the method of consolidation (cementation, silicatization, bitumization, resinization, firing, etc.) and according to the ultimate strength in uniaxial compression after consolidation, in the same way as rocky soils (see Table 1.4).

Non-rocky soils are subdivided into coarse, sandy, silty-clayey, biogenic and soils.

Coarse-grained soils include unconsolidated soils, in which the mass of debris larger than 2 mm is 50% or more. Sandy - these are soils containing less than 50% of particles larger than 2 mm and not possessing the property of plasticity (plasticity number I p < 1 %).

TABLE 1.5. CLASSIFICATION OF LARGE BLOCK AND SANDY SOILS BY GRANULOMETRIC COMPOSITION

Coarse-clastic and sandy soils are classified according to their particle size distribution (Table 1.5) and the degree of moisture content (Table 1.6).

TABLE 1.6. DIVISION OF LARGE BLOCK AND SANDY SOILS BY DEGREE OF MOISTURE S r

The properties of coarse soil with a sandy aggregate content of more than 40% and a silty-clayey more than 30% are determined by the properties of the aggregate and can be established by testing the aggregate. With a lower aggregate content, the properties of coarse soil are established by testing the soil as a whole. When determining the properties of a sandy aggregate, the following characteristics are taken into account - moisture, density, porosity coefficient, and of a silty-clay aggregate - an additional number of plasticity and consistency.

The main indicator of sandy soils, which determines their strength and deformation properties, is the bulk density. According to the density of addition, sands are subdivided according to the coefficient of porosity e, soil resistivity during static sounding q with and conditional soil resistance during dynamic sounding q d(Table 1.7).

With a relative organic matter content of 0.03< I from≤ 0.1 sandy soils are called soils with an admixture of organic matter. According to the degree of salinity, coarse and sandy soils are subdivided into non-saline and saline. Coarse-grained soils are classified as saline if the total content of easily and moderately soluble salts (% of the mass of absolutely dry soil) is equal or more than:

• - 2% - when the content of sand aggregate is less than 40% or dusty clay aggregate less than 30%;
• - 0.5% - with a sand aggregate content of 40% or more;
• - 5% - with a content of silty clay aggregate of 30% or more.

Sandy soils are classified as saline if the total content of these salts is 0.5% or more.

Dusty-clayey soils are subdivided according to the plasticity number I p(Table 1.8) and by consistency, characterized by the flow rate I L(Table 1.9).

TABLE 1.7. DIVISION OF SANDY SOILS BY DENSITY OF FOLDING

Sand	Division by density of addition
	dense	medium density	loose
By the coefficient of porosity
Gravelly, large and medium-sized	e < 0,55	0,55 ≤ e ≤ 0,7	e > 0,7
Small	e < 0,6	0,6 ≤ e ≤ 0,75	e > 0,75
Dusty	e < 0,6	0,6 ≤ e ≤ 0,8	e > 0,8
Soil resistivity, MPa, under the tip (cone) of the probe during static sounding
	q c > 15	15 ≥ q c ≥ 5	q c < 5
Fine regardless of humidity	q c > 12	12 ≥ q c ≥ 4	q c < 4
Dusty: damp and wet water-saturated	q c > 10 q c > 7	10 ≥ q c ≥ 3 7 ≥ q c ≥ 2	q c < 3 q c < 2
According to the conditional dynamic soil resistance MPa, immersion of the probe during dynamic sounding
Coarse and medium size regardless of moisture	q d > 12,5	12,5 ≥ q d ≥ 3,5	q d < 3,5
Small: damp and wet water-saturated	q d > 11 q d > 8,5	11 ≥ q d ≥ 3 8,5 ≥ q d ≥ 2	q d < 3 q d < 2
Dusty, slightly moist and moist	q d > 8,8	8,5 ≥ q d ≥ 2	q d < 2

TABLE 1.8. DIVISION OF DUSTY-CLAYY SOILS BY THE NUMBER OF PLASTICITY

Among the silty-clayey soils, it is necessary to distinguish loess soils and silts. Loess soils are macroporous soils containing calcium carbonates and are capable of sagging under load when soaked with water, easily soaking and eroding. Sludge is a water-saturated modern sediment of water bodies, formed as a result of microbiological processes, having a moisture content exceeding the moisture content at the fluidity boundary, and a porosity coefficient, the values ​​of which are given in table. 1.10.

TABLE 1.9. DIVISION OF DUSTY-CLAYY SOILS BY FLOW RATE

TABLE 1.10. DIVISION OF SILT BY POROSITY RATIO

Dusty-clayey soils (sandy loam, loam and clay) are called soils with an admixture of organic substances with a relative content of these substances of 0.05< I from≤ 0.1. According to the degree of salinity, sandy loam, loam and clay are subdivided into unpopulated and saline. Saline soils include soils in which the total content of easily and moderately soluble salts is 5% or more.

Among silty-clayey soils, it is necessary to distinguish soils that exhibit specific unfavorable properties when soaked: subsidence and swelling. Subsidence soils include soils that, under the action of an external load or their own weight, when soaked with water, give a sediment (subsidence), and at the same time a relative subsidence ε sl≥ 0.01. Swelling soils include soils that, when soaked with water or chemical solutions, increase in volume, and at the same time, relative swelling without load ε sw ≥ 0,04.

In a special group in non-rocky soils, soils are distinguished, characterized by a significant content of organic matter: biogenic (lacustrine, boggy, alluvial-boggy). These soils include peat soils, peat and sapropels. Peaty soils include sandy and silty-clayey soils containing 10-50% (by weight) of organic matter. With an organic matter content of 50% or more, the soil is called peat. Sapropels (Table 1.11) are freshwater silts containing more than 10% organic matter and having a porosity coefficient, as a rule, more than 3, and a fluidity index of more than 1.

TABLE 1.11. DIVISION OF SAPROPELS BY RELATIVE CONTENT OF ORGANIC SUBSTANCE

Soils are natural formations that make up the surface layer of the earth's crust and are fertile. Soils are subdivided according to their granulometric composition in the same way as coarse-grained and sandy soils, and according to the number of plasticity, like silty-clayey soils.

Non-rocky artificial soils include soils compacted in natural bedding by various methods (tamping, rolling, vibration compaction, explosions, drainage, etc.), bulk and alluvial. These soils are subdivided according to the composition and characteristics of the state in the same way as natural non-rocky soils.

Rocky and non-rocky soils with a negative temperature and containing ice in their composition belong to frozen soils, and if they are in a frozen state for 3 years or more, then to permafrost.

The number of plasticity and the index of fluidity of silty clay soil.

For silty-clayey soils, it is not the overall grain size (granulometric) composition that is of primary importance, but the content of small and minute particles (flat-scaled or fine-needle-like monomineral particles with a size of at least 0.005 mm) and, most importantly, the moisture range in which the soil will be plastic.

This moisture range is characterized by the so-called plasticity number J P and is equal to the difference between two moisture contents corresponding to two states of the soil: at the fluidity boundary W L and at the border of rolling (plasticity) W P:

J Р = W L - W P.

Fluidity limit W L corresponds to the moisture content at which the soil turns into a fluid state, and the rolling boundary W P- humidity at which the soil loses its plasticity.

Depending on the plasticity number, three types of silty-clayey soils are distinguished: sandy loam,loam and clay(table 2 GOST 25100-82).

The characteristic moisture content quite well determines the physical state of silty-clayey soils, which, depending on the water content, varies within significant limits and can be solid, plastic and fluid. The characteristic of the state is consistency, which is understood as the density and, to a certain extent, the viscosity of clay soils, which determine their ability to resist plastic change in shape. The numerical characteristic of the consistency is the flow rate - J L which is defined by the expression

where W- soil moisture in its natural state.

The variety of silty clay soils in terms of fluidity is determined according to table 2 GOST 25100-82.

The yield indicator is used when choosing the depth of the foundations, determining the nominal design pressure on the soils of the foundations according to the SNiP tables and in other cases.

Necessary equipment and materials:

o soil (dry and wet);

o desiccator, spatula (knife);

o flask with water, weighing bottles - 2 pcs;

o balancing cone;

o standard metal cup with a stand;

o technical petroleum jelly, a cup;

o scales with weights.

Preparatory work

The soil sample was dried to an air-dry state, ground in a porcelain mortar with a rubber-tipped pestle and sieved through a sieve with holes 1 mm... Part of the soil was moistened with water to a thick dough with stirring with a spatula and kept in a desiccator for at least 2 hours for an even distribution of moisture.

Determination of the yield point

The yield point is characterized by the moisture content (in fractions of a unit) of the soil dough, at which a standard cone is immersed into it under its own weight to a depth 10 mm per 5 seconds... Determination of the yield point consists in the selection of such soil moisture.

Balance cone (fig. 3) with apex angle 30 ° C has a distance 10 mm from the edge to a circular risk. A balancing device in the form of two metal weights at the ends of a steel bar is attached to the base of the cone. The total weight of the device is 76 g.

Figure 3 - Devices for determining the yield point

Progress:

1. The ground dough is thoroughly mixed with a spatula and placed in small portions (without the formation of voids) in a metal cup; the surface of the soil is leveled with a spatula level with the edges of the glass, which is then placed on a stand.

2. The tip of the cone, smeared with a thin layer of petroleum jelly, is brought to the surface of the soil and lowered, allowing it to plunge into the ground for 5 sec under its own weight.

3. Immersion of the cone behind 5 sec to a depth of less 10 mm shows that soil moisture has not yet reached the yield point. In this case, the soil dough is transferred to a cup and, after adding water and thorough mixing, the experiment is repeated. If the cone plunged deeper than 10 mm, you should add dry soil, mix it and repeat the experiment.

The physical properties of the soils underlying the foundation are investigated in terms of their ability to carry the load of the house through its foundation.

The physical properties of the soil change depending on the external environment. They are influenced by: humidity, temperature, density, heterogeneity and much more, therefore, to assess the technical suitability of soils, we will study their properties, which are unchanged and which can change when the external environment changes:

• connectivity (adhesion) between soil particles;
• size, shape of particles and their physical properties;
• uniformity of composition, the presence of impurities and their effect on the soil;
• coefficient of friction of one part of the soil against another (shift of soil layers);
• water permeability (water absorption) and change in bearing capacity when soil moisture changes;
• water retention capacity of soil;
• erosion and solubility in water;
• plasticity, compressibility, looseness, etc.

Soils: types and properties

Soil classes

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

• Rocky soils- magmatic, metamorphic, sedimentary, volcanic-sedimentary, eluvial and technogenic rocks with rigid crystallization and cementation structural bonds.
• Dispersive soils- sedimentary, volcanic-sedimentary, eluvial and technogenic rocks with water-colloidal and mechanical structural bonds. These soils are divided into cohesive and incoherent (loose). The class of dispersive soils is divided into groups:
  • mineral- coarse, fine, silty, clayey soils;
  • organomineral- peaty sands, silts, sapropels, peaty clays;
  • organic- peats, sapropels.
• Frozen ground- these are the same rocky and dispersive soils, additionally possessing cryogenic (ice) bonds. Soils in which only cryogenic bonds are present are called ice.

In terms of structure and composition, soils are divided into:

• rocky;
• coarse;
• sandy;
• clayey (including loess-like loam).

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

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

• upper layers;
• average burial depth;
• deep bedding.

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 influences (wetting and drying, weathering, freezing and thawing). This effect changes the state of the soil, its physical properties and reduces the resistance to stress. The only exceptions are rocky soils and conglomerates.

Therefore, the base 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	Fractions	Size, mm
Large debris
Boulders *, blocks	large	> 800
	medium size	400-800
	small	200-400
Pebbles *, crushed stone	large	100-200
	medium size	60-100
	small	10-60
Gravel *, grit	large	4-10
	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
	small	0,002-0,01
Colloids
Clay		< 0,002

* Names of large debris with rolled edges.

Measured soil characteristics

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

Specific gravity of soil

Specific gravity of soil 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 - acceleration due to gravity, taken equal to 9.81 m / s².

Density of dry (skeleton) soil

Density of dry (skeleton) soil ρ d- natural density minus 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, g / cm³ (t / m³), ​​respectively.

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

Porosity coefficient e, for sandy soils of different density

Soil moisture levels

Soil moisture level 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 - 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

class = "h3_fon">

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

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

Fluidity limit W L characterizes the moisture content at which the soil from the plastic state turns into a semi-liquid - fluid. At this humidity, the bond 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 negligible and the soil loses its stability.

Rolling border W P corresponds to the moisture content at which the soil is at 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 point and the rolling edge are also called the upper and lower plasticity limits.

Having determined the humidity at the border 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 point and the soil rolling boundary:

I Р = W L - W P

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

The fluidity of clay soils

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

Determined by calculation from the formula:

I L =	W - W p
	I p

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

Indicator of fluidity for soils of different density

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 solid mass or separated by cracks. These include magmatic (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 negative temperatures, and are also insoluble and do not soften in water.

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

Coarse soils

class = "h3_fon">

Large-detrital - incoherent fragments of rocks with a predominance of fragments larger than 2 mm (over 50%).

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

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

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

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

Coarse soil can be heaving if the fine component is dusty sand or clay.

Conglomerates

class = "h3_fon">

Conglomerates are coarse-clastic rocks, a group of rocky destroyed, consisting of separate stones of different fractions, containing more than 50% fragments of crystalline or sedimentary rocks that are not connected with each other 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

class = "h3_fon">

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

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

Dispersive soils

Mineral dispersed soil consists of geological elements of various origins and is determined by the physicochemical properties and geometric dimensions of the particles of its constituents.

Sandy soils

class = "h3_fon">

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 a particle size of 0.1 to 2 mm, containing clay no more than 3%.

In terms of particle size, sandy soils 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);
• small (particle size - 0.1-0.25 mm)
• dusty (particle size 0.005-0.05 mm). They are similar in their manifestations to clayey 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 cohesion between individual grains.
• easy to develop;
• good water permeability, good water permeability;
• do not change in volume at different levels of water absorption;
• freeze slightly, not heaving;
• under loads they tend to thicken and sag strongly, but in a rather short time;
• not plastic;
• easy to tamp.

Dry clean (especially coarse) quartz sand can withstand heavy loads. The coarser and cleaner the sands, the greater the load the base layer from it can withstand. Gravelly, large and medium-sized sands are significantly compacted under load, 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 admixtures of clay and silt, is unreliable as a base. Dusty sands (particle size from 0.005 to 0.05 mm) weakly hold the load, as the base requires strengthening.

Sandy loam

class = "h3_fon">

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

Quicksands are sandy loams in properties close to silty sands, containing a large amount of silty and very small 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.

Distinguish between true and pseudo-quicksands.

True quicksands are characterized by the presence of silty-clayey and colloidal particles, high porosity (> 40%), low fluid loss and filtration coefficient, peculiarity to thixotropic transformations, sagging at a moisture content of 6 - 9% and a transition to a fluid state at 15 - 17%.

Pseudo-sluggers- sands that do not contain fine clay particles, completely water-saturated, easily releasing water, permeable, turning into a quicksand state at a certain hydraulic gradient.

Quicksands are practically unsuitable for use as foundations.

Clay soils

class = "h3_fon">

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

Physical properties:

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

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

• solid,
• semi-solid,
• tough plastic,
• soft-plastic,
• flowable,
• fluid.

Settlement of buildings on clayey soils lasts longer than on sandy soil. Clay soils with sandy interlayers are easily liquefied and therefore have a low bearing capacity.

Dry, densely packed clayey soils with a high layer thickness can withstand significant loads from structures if there are stable underlying layers under them.

Clay that has built up over the years is considered a good foundation for a house.

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

Inhomogeneity of moisture when the soil freezes leads to uneven heaving at negative temperatures, which can lead to deformation of the foundation.

All types of clay soils, as well as silty and fine sands, can be heapy.

Clay soils are the most unpredictable for construction.

They can erode, swell, shrink, swell when freezing. 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, which in their natural constitution have pores visible to the naked eye, significantly exceeding the skeleton of the soil, are called macroporous. Macroporous soils include loess soils (more than 50% of dust particles), which are most common in the south of the Russian Federation and the Far East. In the presence of moisture, loesslike soils lose their stability and become soaked.

Loam

class = "h3_fon">

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

According to 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 dusty particles (0.005 - 0.05 mm) and water-soluble limestone, etc., is very porous and shrinks when wet. It swells when frozen.

In a dry state, such soils have significant strength, but when moistened, the soil softens and sharply compresses. As a result, significant precipitation, severe distortions and even destruction of structures erected on it, especially 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 soaking them. For this, it is necessary to carefully study the regime of groundwater and the horizons of their highest and lowest standing.

Silt (silty soils)

class = "h3_fon">

Sludge - formed at 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, swampy and wetlands.

Silt - silty soils, water-saturated modern sediment mainly of 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 consequence, negligible resistance to loads and unsuitability of their use as a natural base.
• Significant influence of structural bonds on mechanical properties.
• Insignificant resistance to friction forces, which makes it difficult to use pile foundations in them;
• Organic (humic) acids in the sludge have a destructive effect 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 collapse under relatively insignificant loads, however, only at a certain value of external pressure, which is quite definite for a given silty soil, does an avalanche (mass) disruption of structural bonds occur, and the strength of the silty soil decreases sharply. This value of external pressure is called the "structural strength of the soil". If the pressure on the silty soil is less than the structural strength, then its properties are close to the properties of a low-strength solid, and, as the corresponding experiments show, neither the compressibility of the silt, nor its shear resistance practically do not depend on the natural moisture content. In this case, the angle of internal friction of the silty soil is small, and the adhesion has a well-defined value.

The sequence of erecting foundations on silty soils:

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

Sapropel

class = "h3_fon">

Sapropel is freshwater silt formed at the bottom of stagnant water bodies 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

class = "h3_fon">

Peat is an organic soil formed as a result of natural withering away and incomplete decomposition of marsh plants in conditions of high humidity with a lack of oxygen and containing 50% (by weight) or more of organic matter.

They include a large amount of plant sediments. By the amount of their content, they are distinguished:

• lightly peat soils (the relative content of plant sediments is less than 0.25);
• medium peat (from 0.25 to 0.4);
• heavily peat (from 0.4 to 0.6) and peat (over 0.6).

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

Peeled soil

Peat soil - sand and clay soil containing from 10 to 50% (by weight) peat.

Soil moisture

Due to the capillary effect, soils with a fine structure (clay, silty sands) are wet 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 loose soil

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

• in silty sands by 0.5 m;
• in sandy loam per 1 m;
• in loams by 1.5 m;
• in clays by 2 m.

Conditions for medium-loamy soil

The soil can be classified as medium-porous, when the groundwater is located below the calculated freezing depth:

• in sandy loam by 0.5 m;
• in loams per 1 m;
• in clays by 1.5 m.

Conditions for highly heaving soil

The soil will be highly porous if the water table is higher than for medium porous soils.

Determination of the type of soil by eye

Even a person far from geology will be able to distinguish clay from sand. But not everyone will be able to 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 a soil?

First, examine neighboring residential areas. The experience of building the foundations of your neighbors can provide useful information. Sloping fences, deformations of foundations when they are shallow, 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 cannot dig a deep narrow hole, and what to do with it then?

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

You will end up with a well with sufficient depth (at least 3 meters, more is possible) and width (at least 1 meter), which gives 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 bury the hole back.

Just install concrete rings in the well in the near future so that the well does not crumble from the rains.

Determination of soil by appearance

Dry rock condition

Clay	Solid in pieces, when struck, it pricks into separate lumps. The lumps are crushed with great difficulty. Very difficult to grind into powder.
Loam	Lumps and pieces are relatively hard, crumbling on impact, forming fines. The mass rubbed on the palm does not give the feeling of a homogeneous powder. There is little sand to the touch when rubbed. The lumps are easily crushed.
Sandy loam	The adhesion between the particles is weak. Lumps easily crumble from pressure by hand and when rubbed, an inhomogeneous powder is felt, in which the presence of sand is clearly felt. Silty sandy loam when rubbed resembles dry flour.
Sand	Sandy self-crumbling mass. When rubbed in the palms, the feeling of a sandy mass, large sandy particles prevail.

Wet rock condition

Clay	Plastic, sticky and smearing	The ball does not crack at the edges when squeezed. When rolled, it gives a strong and long cord with a diameter< 1 мм.
Loam	Plastic	The ball, when squeezed, forms a cake with cracks along the edges. No long cord will form.
Sandy loam	Weakly plastic	A ball is formed, which crumbles with light pressure. Does not roll into the cord or roll hard and breaks easily into pieces.
Sand	When waterlogged, it turns into a fluid state	Does not roll into a ball and cord.

Water clarification method

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

Type of foundation from the ground

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

Clay soils are one of the most common types of rocks. The composition of clayey soils includes very fine clay particles, the size of which is less than 0.01 mm, and sandy particles. Clay particles are in the form of plates or flakes. Clay soils have a large number of pores. The ratio of pore volume to soil volume is called porosity and can range from 0.5 to 1.1. Porosity characterizes the degree of compaction of the soil. Clay soil very well absorbs and retains water, which, when frozen, turns into ice and increases in volume, increasing the volume of the entire soil. This phenomenon is called heaving. The more clay particles are contained in soils, the more they are susceptible to heaving.

Clay soils have the property of cohesion, which is expressed in the ability of the soil to maintain its shape due to the presence of clay particles. Depending on the content of clay particles, soils are classified into clay, loam and sandy loam.

The ability of the soil to deform under the action of external loads without rupture and maintain its shape after the termination of the load is called plasticity.

The plasticity number Ip is the difference in moisture content corresponding to two states of the soil: at the fluidity boundary WL and at the rolling boundary W p, W L and W p are determined according to GOST 5180.

Table 1. Classification of clay soils by the content of clay particles.

Priming	particles by mass, %	Plasticity number Ip
Loam

The number of plasticity of clay soils determines their construction properties: density, moisture, compression resistance. With decreasing humidity, the density increases and the compression resistance increases. With increasing humidity, the density decreases and the resistance to compression also decreases.

Sandy loam.

Sandy loam contains no more than 10% clay particles, the rest of this soil is sand particles. Sandy loam practically does not differ from sand. There are two types of sandy loam: heavy and light. Heavy sandy loam contains from 6 to 10% clay particles, light sandy particles contain from 3 to 6% .. When rubbing sandy loam on a wet palm, you can see sand particles, after shaking off the soil, traces of clay particles are visible on the palm. Lumps of sandy loam in a dry state easily crumble and crumble from impact. Sandy loam almost does not roll into a bundle. A ball rolled from a moistened soil crumbles under light pressure.

Due to the high sand content, sandy loam has a relatively low porosity - from 0.5 to 0.7 (porosity is the ratio of pore volume to soil volume), so it can contain less moisture and, therefore, be less prone to heaving. The lower the porosity of dry sandy loam, the greater its bearing capacity: with a porosity of 0.5 it is equal to 3 kg / cm 2, with a porosity of 0.7 - 2.5 kg / cm 2. The bearing capacity of sandy loam does not depend on moisture, therefore this soil can be considered non-porous.

Loam.

Soil, in which the content of clay particles reaches 30% by weight, is called loam. In loam, as in sandy loam, the content of sandy particles is greater than that of clay particles. Loam is more cohesive than sandy loam and can be stored in large pieces without breaking up into small pieces. Loams are heavy (20% -30% clay particles) and light (10% - 20% clay particles).

Chunks of soil in a dry state are less hard than clay. On impact, they crumble into small pieces. When wet, they are not very plastic. When rubbing, sand particles are felt, lumps are crushed more easily, there are larger grains of sand against the background of finer sand. A tourniquet rolled out of damp soil turns out to be short. A ball rolled from a moistened soil, when pressed, forms a cake with cracks along the edges.

The porosity of loam is higher than that of sandy loam and ranges from 0.5 to 1. Loam can contain more water and, therefore, is more prone to heaving than sandy loam.

Loams are characterized by a fairly high strength, although they are prone to slight subsidence and cracking. The bearing capacity of the loam is 3 kg / cm 2, in the humid one - 2.5 kg / cm 2. Loams in a dry state are non-porous soils. When moistened, clay particles absorb water, which turns into ice in winter, increasing in volume, which leads to heaving of the soil.

Clay.

The clay contains more than 30% clay particles. Clay has a lot of cohesion. Clay in a dry state is hard, in a wet state it is plastic, viscous, sticks to fingers. When rubbing the sand particles with your fingers, it is very difficult to crush the lumps. If a piece of raw clay is cut with a knife, then the cut has a smooth surface, on which no grains of sand are visible. When squeezing a ball rolled from raw clay, a cake is obtained, the edges of which do not have cracks.

The porosity of clay can reach 1.1, it is more prone to frost heaving than all other soils. Clay in a dry state has a bearing capacity of 6 kg / cm 2, Clay saturated with water can increase in volume by 15% in winter, losing its bearing capacity up to 3 kg / cm 2. When saturated with water, clay can go from a solid state to a fluid one.

Table 2 shows the methods by which you can visually determine the type and characteristics of clay soils.

Table 2. Determination of the mechanical composition of clayey soils.

Name of soil	Magnifying glass	Plastic
	Homogeneous fine powder, almost no sand particles	Rolls into a bundle and curled up into a ring
Loam	Dominated by sand, particles clay 20 - 30%	When rolling, it turns out tourniquet, when coagulating in a ring falls apart
	Sand particles with a small admixture of clay particles predominate	When trying to roll the tourniquet breaks down into small

Classification of clayey soils.

Most clay soils in natural conditions, depending on the water content in them, can be in a different state. The building standard (GOST 25100-95 Soil classification) defines the classification of clay soils depending on their density and moisture content. The state of clay soils is characterized by the fluidity index IL - the ratio of the difference in moisture content corresponding to two states of the soil: natural W and at the rolling boundary Wp to the plasticity number Ip. Table 3 shows the classification of clay soils in terms of fluidity.

Table 3. Classification of clay soils in terms of fluidity.

A kind of clay soil	Indicator of fluidity
Sandy loam:
plastic
Loams and clays:
semi-solid
rigid plastic
soft-plastic
fluid-plastic

According to the granulometric composition and plasticity number Ip, clay groups are subdivided according to Table 4.

Table 4. Classification of clay soils by particle size distribution and plasticity number

	Plasticity number	particles (2-0.5mm),% by weight
Sandy loam:
sandy
silty
Loam:
light sandy
light dusty
heavy sandy
heavy dusty
Clay:
light sandy
light dusty
		Not regulated

According to the presence of solid inclusions, clay soils are subdivided according to table 5.

Table 5. Content of solid particles in clay soils .

A variety of clay soils
Sandy loam, loam, clay with pebbles (crushed stone)
Sandy loam, loam, pebble clay (gravelly) or gravelly (gritty)

Among clay soils, the following should be distinguished:

Peat soil;

Subsidence soils;

Swelling (heaving) soils.

Peat soil - sand and clay soil containing in its composition in a dry sample from 10 to 50% (by weight) of peat.

According to the relative content of organic matter Ir, clay soils and sands are subdivided according to Table 6.

Table 6 Classification of clay soils by organic matter content

Variety of soils	The relative content of organic matter Ir, unit fraction
Heavily peeled
Medium peat
Lightly peeled
With an admixture of organic substances

Swelling soil - soil that, when soaked with water or other liquid, increases in volume and has a relative swelling deformation (under conditions of free swelling) greater than 0.04.

Subsidence soil - soil that, under the action of an external load and its own weight, or only from its own weight, when soaked with water or other liquid, undergoes vertical deformation (subsidence) and has a relative subsidence deformation e sl ³ 0.01.

Subsidence soils are divided into two types depending on the subsidence and their own weight during soaking:

• type 1 - when the subsidence of the soil from its own weight does not exceed 5 cm;
• type 2 - when the subsidence of the soil from its own weight is more than 5 cm.

According to the relative deformation of subsidence e sl, clay soils are subdivided according to Table 7.

Table 7. Relative deformation of subsidence of clay soils.

A variety of clay soils	Relative deformation of subsidence e sl, e.
Non-collapsing
Drawdown

Heaving soil - dispersed soil, which, during the transition from thawed to frozen state, increases in volume due to the formation of ice crystals and has a relative deformation of frost heaving e fn ³ 0.01. These soils are not suitable for construction, they must be removed and replaced with soil with good bearing capacity.

According to the relative swelling deformation without load e sw, clay soils are subdivided according to table 8.

Table 8. Relative swelling deformation of clay soils.

A variety of clay soils	Relative swelling deformation without load e sw, e.
Non-swelling
Weak swelling
Medium swelling
Highly swellable

If the soil contains a sufficiently large amount of clay particles, then it is called clayey. Clay soils have the property of cohesion, which is expressed in the ability of the soil to maintain its shape due to the presence of clay particles.
If there are few clay particles (less than 10% by weight), the soil is called sandy loam . Sandy loam has little cohesion and is often virtually indistinguishable from sand. It is difficult to roll the sandy loam into a rope or ball. If sandy loam rub on a damp palm, then you can see particles of sand, after shaking off the soil, traces of clay particles are visible in the palm of your hand. Lumps sandy loam dry easily crumble and crumble from impact. Sandy loam non-plastic, it is dominated by sand particles, almost do not roll into a rope. A ball rolled from a moistened soil crumbles under light pressure.
The soil in which the content of clay particles reaches 30% by weight is called loam . Loam has greater cohesion than sandy loam and is able to persist in large pieces without falling apart into small pieces. Pieces sandy loam less solid than clay when dry. On impact, they crumble into small pieces. When wet, they are not very plastic. When rubbing, sand particles are felt, the lumps are crushed more easily, there are larger grains of sand against the background of finer sand. A tourniquet rolled out of damp soil turns out to be short. A ball rolled from a moistened soil, when pressed, forms a cake with cracks along the edges.
When the content of clay particles in the soil is more than 30%, the soil is called clay . Clay has great connectivity. Clay dry - solid, wet - plastic, viscous, sticks to fingers. When rubbing the sand particles with your fingers, it is very difficult to crush the lumps. If the piece is raw clays cut with a knife, then the cut has a smooth surface on which no grains of sand are visible. When squeezing a ball rolled from raw clays , you get a cake, the edges of which do not have cracks.
Greatest effect on properties clay soils has the presence of clay particles, so soils are usually classified according to the content of clay particles and the number of plasticity. Plasticity number I p - the difference in humidity corresponding to two states of the soil: at the boundary of fluidity W L and at the border of rolling W p, W L and W p is determined according to GOST 5180.
Table 1. Classification of clay soils by the content of clay particles.

Most clay soils in natural conditions, depending on the water content in them, can be in a different state. The building standard (GOST 25100-95 Soil classification) defines the classification of clay soils depending on their density and moisture content. The state of clay soils characterizes flow rate I L - the ratio of the difference in moisture content corresponding to two states of the soil: natural W and at the border of rolling W p, to the number of plasticity I p... Table 2 shows the classification of clay soils in terms of fluidity.
Table 2. Classification of clay soils in terms of fluidity.

Granulometric composition and plasticity number I p clayey groups are subdivided according to table 3.
Table 3.

A variety of clay soils	Plasticity number I p	Content of sand Particles (2-0.5mm),% by weight
Sandy loam:
- sandy	1 — 7	50
- dusty	1 — 7	< 50
Loam:
- light sandy	7 -12	40
- light dusty	7 – 12	< 40
- heavy sandy	12 – 17	40
- heavy dusty	12 – 17	< 40
Clay:
- light sandy	17 – 27	40
- light dusty	17 — 27	< 40
- heavy	> 27	Not regulated

According to the presence of solid inclusions, clay soils are subdivided according to table 4.

Table 4. The content of solid particles in clay soils.

Table 5 shows the methods by which you can visually determine the characteristics of clay soils.
Table 5. Determination of the mechanical composition of clay soils.

Among clay soils, the following should be distinguished:
peat soil;
subsiding soils;
swelling (heaving) soils.
Peat soil - sand and clay soil containing in its composition in a dry sample from 10 to 50% (by weight) of peat.
According to the relative content of organic matter Ir, clay soils and sands are subdivided according to Table 6.
Table 6.

Swelling soil - soil that, when soaked with water or other liquid, increases in volume and has a relative swelling deformation (under conditions of free swelling) greater than 0.04.
Subsidence soil - soil that, under the action of an external load and its own weight, or only from its own weight, when soaked with water or other liquid, undergoes vertical deformation (subsidence) and has a relative subsidence deformation e sl ³ 0.01.
Heaving soil - dispersed soil, which, during the transition from thawed to frozen state, increases in volume due to the formation of ice crystals and has a relative deformation of frost heaving e fn ³ 0.01.
According to the relative swelling deformation without load e sw, clay soils are subdivided according to table 7.
Table 7.

According to the relative deformation of subsidence e sl, clay soils are subdivided according to Table 8.
Table 8.