What type of soil does loam belong to? Classification of soils, features and subtleties

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

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

• cohesion (adhesion) between soil particles;
• size, shape of particles and their physical properties;
• homogeneity of composition, the presence of impurities and their effect on the soil;
• coefficient of friction of one part of the soil against another (shear of soil layers);
• water permeability (water absorption) and changes in bearing capacity with changes in soil moisture;
• water holding capacity of the soil;
• solubility and solubility in water;
• plasticity, compressibility, loosening ability, etc.

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.
• Dispersive 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- peat sands, silts, sapropels, peat clays;
  • organic- peats, sapropels.
• Frozen soils- these are the same rocky and dispersive soils, additionally having cryogenic (ice) bonds. Soils in which only cryogenic bonds are present are called icy.

Based on their structure and composition, soils are divided into:

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

Mainly 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, soils are divided into:

• top layers;
• average depth;
• deep.

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

The top layers of soil are exposed to atmospheric influences (wetting and drying, weathering, freezing and thawing). This impact changes the condition 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 load-bearing characteristics of the soil.

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
Pebbles*, crushed stone	large	100-200
	medium size	60-100
	small	10-60
Gravel*, debris	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 fragments with rolled edges.

Measured soil characteristics

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

Specific gravity of soil

Specific gravity of soil γ is 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 of gravity, taken equal to 9.81 m/s².

Density of dry (skeletal) soil

Density of dry (skeletal) 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, respectively, the density of particles and the density of dry (skeleton) soil, g/cm³ (t/m³).

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

Porosity coefficient e, for sandy soils of different densities

Degrees of soil moisture

Degree of soil moisture S r- the ratio of the natural (natural) soil moisture W to the humidity 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 - soil porosity coefficient;
ρ w - density of water, taken equal to 1 g/cm³ (t/m³);
W is the natural soil moisture, expressed in fractions of a unit.

Soils by moisture level

Soil plasticity

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

To establish the ability of the soil to assume a plastic state, determine the humidity, 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 changes from a plastic state to a semi-liquid - fluid state. At this humidity, the connection between particles is disrupted due to the presence of free water, as a result of which soil particles are easily displaced and separated. As a result, the adhesion between particles becomes insignificant and the soil loses its stability.

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

Having determined the humidity at the border yield and rolling boundary, 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 defined as the difference between the yield limit and the rolling boundary of the soil:

I Р = 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 influence the plasticity limits and plasticity number.

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

Fluidity of clay soils

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

Determined by calculation from the formula:

I L =	W - Wp
	I r

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

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 connections, occurring in the form of a continuous massif or separated by cracks. These include igneous (granites, diorites, etc.), metamorphic (gneisses, quartzites, schists, etc.), cemented sedimentary (sandstones, conglomerates, etc.) and artificial.

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

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

Coarse soils

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Coarse - loose fragments of rocks with a predominance of fragments larger than 2 mm in size (over 50%).

Based on their granulometric composition, coarse 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 - wood). These include gravel, crushed stone, pebbles, and debris.

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

If coarse-grained soils contain sand filler of more than 40% or clay filler of more than 30% of the total mass of air-dry soil, the name of the type of filler is added to the name of the coarse-grained soil and the characteristics of its condition are indicated. The type of filler is determined after removing particles larger than 2 mm from coarse soil. If the fragmentary material is represented by shells in an amount of ≥ 50%, the soil is called shell-like; if from 30 to 50%, shells are added to the name of the soil.

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

Conglomerates

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

As a rule, the bearing capacity of such soils is quite high and can support the weight of a house of several floors.

Cartilaginous soils

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Cartilaginous soils are a mixture of clay, sand, broken stones, crushed stone and gravel. They are poorly washed out 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 a foundation with a depth of at least 0.5 meters.

Dispersive soils

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

Sandy soils

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

According to particle size, sandy soils can be:

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

Based on 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, allows water to pass through well;
• do not change in volume at different levels of water absorption;
• freeze slightly, not heaving;
• under load they tend to become very compact and sag, but in a fairly short time;
• not plastic;
• easy to compact.

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

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 larger 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 diluted with water, especially with admixtures of clay and silt, is unreliable as a base. Silty sands (particle size from 0.005 to 0.05 mm) weakly support the load, as the base requires strengthening.

Sandy loam

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

Quicksand are sandy loams whose properties are similar to silty sands, containing a large amount of dusty 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 liquid.

There are true quicksands and pseudo quicksands.

True quicksand characterized by the presence of silt-clay and colloidal particles, high porosity (> 40%), low water yield and filtration coefficient, a feature of thixotropic transformations, floating at a humidity of 6 - 9% and transition to a fluid state at 15 - 17%.

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

Quicksand are practically unsuitable for use as foundation bases.

Clay soils

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Clays are rocks consisting of extremely small particles (less than 0.005 mm), with a small admixture of small 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 water-permeability properties, therefore they always contain water (from 3 to 60%, usually 12-20%).
• increase in volume when wet and decrease when dry;
• depending on humidity, they have significant particle cohesion;
• Clay compressibility is high, compaction under load is low.
• plastic only within a certain humidity; at lower humidity they become semi-solid or solid, at higher humidity they turn from a plastic state into a fluid one;
• washed away by water;
• heaving.

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

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

Settlement of buildings on clay soils lasts longer than on sandy soil. Clay soils with sandy layers liquefy easily and therefore have low bearing capacity.

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

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

But such clay is rare, because... in its natural state it is almost never dry. The capillary effect present in fine-textured soils means that the clay is almost always wet. Moisture can also penetrate through sandy impurities in clay, so moisture absorption in clay occurs unevenly.

Heterogeneity of humidity when the soil freezes leads to uneven heaving at subzero temperatures, which can lead to deformation of the foundation.

All types of clay soils, as well as dusty and fine sands, can be heaving.

Clay soils are the most unpredictable for construction.

They can erode, swell, shrink, and 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 foundation.

Macroporous clays

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

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%.

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

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

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

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 highest and lowest standing.

Silt (silty soils)

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Silt - 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 peat mining areas, swampy 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 for 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;
• Organic (humic) acids in sludge act destructively on concrete structures and foundations.

The most significant phenomenon that occurs in silty soils under the influence of external load, as mentioned above, is the destruction of their structural connections. Structural bonds in silt begin to collapse under relatively minor loads, but only at a certain external pressure value that is quite specific for a given silty soil does an avalanche (massive) disruption of structural bonds occur, and the strength of the silty soil sharply decreases. This amount of external pressure is called the “structural strength of the soil”. If the pressure on silty soil is less than the structural strength, then its properties are close to those of a low-strength solid, and, as relevant experiments show, neither the compressibility of silt nor its shear resistance are practically independent of natural moisture. 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 construction of foundations on silty soils:

• These soils are “excavated” and replaced layer by layer with sandy soil;
• A stone/crushed stone cushion is poured, its thickness is determined by calculation; it is necessary that the pressure exerted on the surface of the silty soil from the structure and the cushion is not dangerous for the silty soil;
• After this, the structure is erected.

Sapropel

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Sapropel is a freshwater sludge formed at the bottom of stagnant reservoirs from 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 the natural death and incomplete decomposition of marsh plants under conditions of high humidity and lack of oxygen and containing 50% (by weight) or more organic substances.

They contain a large amount of plant sediments. Based on the amount of their content, they are distinguished:

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

Peat bogs are usually very wet, have strong uneven compressibility and are practically unsuitable as a foundation. Most often they are replaced with more suitable bases, for example, sand.

Peaty 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 sand) are moist even when the groundwater level is low.

The water rise can reach:

• in loams 4 - 5 m;
• in sandy loams 1 - 1.5 m;
• in dusty sands 0.5 - 1 m.

Conditions for slightly heaving soil

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

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

Conditions for medium heaving soil

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

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

Conditions for highly heaving soil

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

Determining soil type 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 type of soil is loam or sandy loam? And what is the percentage of pure clay and silt in such soil?

First, inspect the neighboring residential areas. Neighbors' foundation foundation experience can provide useful information. Leaning fences, deformations of foundations when they are laid shallow, and cracks in the walls of such houses indicate heaving soils.

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

I propose 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, more can be) and width (at least 1 meter), which provides a lot 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.

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

Determining soil by appearance

Dry rock condition

Clay	It is hard in pieces and breaks into separate lumps when struck. Lumps are crushed with great difficulty. It is very difficult to grind into powder.
Loams	Lumps and pieces are relatively hard, and upon impact they crumble, 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 rubbing. Lumps are crushed easily.
Sandy loam	The adhesion between particles is weak. The lumps easily crumble under hand pressure and when rubbed, a heterogeneous powder is felt, in which the presence of sand is clearly felt. When rubbed, silty sandy loam resembles dry flour.
Sand	Sandy self-disintegrating mass. When rubbed in the palms, it feels like a sandy mass; large sand particles predominate.

Wet rock condition

Clay	Plastic, sticky and smearing	When squeezed, the ball does not form cracks at the edges. When rolled out, it produces a strong and long cord with a diameter of< 1 мм.
Loams	Plastic	When squeezed, the ball forms a cake with cracks along the edges. No long cord is formed.
Sandy loam	Weakly plastic	A ball is formed, which crumbles when pressed lightly. Does not roll into a cord or is difficult to roll and falls apart easily.
Sand	When over-moistened, it turns into a fluid state.	Does not roll into a ball or 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) into which a pinch of soil is placed.

Type of foundation from the ground

• Peat - pile foundation.
• Dusty sands, viscous clays - 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.

General information and classification of soils

G runts - these are any rocks (sedimentary, igneous, metamorphic) and solid industrial waste lying on the surface , the earth's crust and included in the sphereimpact onthem a person atconstruction of buildings, structures, roads and other objects.

When assessing the properties of soils acting as foundations, much attention is paid to their deformation and strength indicators. The indicators are largely dependent on many other characteristics of soils: chemical and mineral composition, structures and textures, the nature of the interaction of soils with water, the degree of their weathering and a number of others. Underestimation of certain features of the properties of “foundation soils” entails errors in the design and construction of buildings and structures, which ultimately leads to a loss of soil strength during operation.

Prediction of changes in the properties of pounds over time under the influence of various influences is possible only if we have complete information about how they were formed during the process of genesis and their entire subsequent “life.”

Soil condition

Recently, specialists in engineering geology have paid much attention to such an important category of soil assessment as their state. We have already discussed the concept of “soil condition” above; here we will try to somewhat streamline the previously presented information. It should be noted that there is no clearly defined definition of this category yet. The characteristics that determine the condition of pounds include degree of fracturing, weathering,humidity, water saturation, density etc. Characteristics such as cracking and weathering, determine the properties of rocks in the sample and in the massif; As is known, such a value as the compressive strength in a sample significantly exceeds its value in the massif, sometimes up to two orders of magnitude. The degree of weathering has a slightly different influence on the formation of soil properties in the sample and in the massif. Weathering cracks are usually filled with secondary mineral material, and this, naturally, sharply increases the heterogeneity of the massif, thereby reducing or, more precisely, changing the strength, deformation and filtration properties of the rocks in the massif.

Humidity level most often taken into account when assessing the properties of dispersed soils. It determines the occurrence, “revival” and development of such unfavorable phenomena and processes as landslides, solifluction, and in some cases contributes to mudflow formation and a number of other phenomena. The degree of humidity affects the deformation-strength characteristics of soil masses and the consolidation of soils at the base of structures when loads of engineering structures are applied to them. Very close to the humidity level degree of water saturation, which is currently more applicable to rocky, fractured soils. These two categories determine the ability of soils to deform under load and consolidate; significantly affect the strength characteristics of soil masses; in climatic zones subject to sharp temperature fluctuations, in areas where frozen soils are widespread, the degree of humidity and the degree of water saturation significantly influence the frost resistance of rocks in the massif.

For dispersed soils, the degree of their raftness For example, there are under-consolidated silty and sandy soils, such as fine-grained aeolian soils common in the southern part of the Kara-Kum, aeolian-marine (dune) sands of the Baltic coast, and loess soils of various origins.

The under-compacted state of these soils is one of the reasons for subsidence phenomena, partly liquefaction of sands, heterogeneous deformations at the base of structures, and disturbances in the stability of rocks in the slopes of natural and artificial excavations.

All of the listed characteristics of the state of soils in their “limiting” values ​​sharply worsen the properties of massifs when vibration, dynamic, in particular, seismic loads are applied. Heavily cracked, weathered, water-saturated or wet, under-compacted soils in the massif significantly reduce the possibility of using them as the foundation of critical structures. When calculating the seismic stability of structures designed on soils that are in the above states, according to current regulatory documents, it is required to increase the design values ​​taking into account seismic impacts, in some cases by 1 point higher than the general seismic intensity established for the entire area.

Soil classification

Soil classification can be general, partial, regional and sectoral.

Task general classifications - if possible, cover all the most common types of rocks and characterize them as soils. Such classifications should be based exclusively on a genetic approach, in which it is possible to connect the engineering-geological properties of rocks with their genetic characteristics and trace changes in these properties from one group of soils to another. These classifications serve as the basis for the development of all other types of classifications.

Private classifications subdivide and subdivide soils in detail into separate groups according to one or more characteristics. These classifications include the following classifications:

Sedimentary, clastic, sandy-clayey soils by granulometric composition,

Clay rocks - according to the number of plasticity,

Loess rocks - according to the degree of subsidence, etc.

These classifications may be developments or components of general classifications.

Regional classifications consider soils in relation to a certain territory. They are based on the age and genetic division of breeds found in a given territory. The division of groups of pounds is carried out based on the formation-facies theory of rocks.

Industry Pound classifications are made in relation to the demands of a particular type of construction. Naturally, such classifications are based on the provisions of the classifications described above and are, as it were, a concrete result of general classifications for resolving issues in the engineering-geological assessment of territories and construction sites.

The classification of pounds reflects their properties. Currently, according to GOST 25100-95, pounds are divided into the following classes - natural: rock, dispersed, frozen and man-made formations. Each class has its own divisions. Thus, pounds of rock, dispersed and frozen classes are combined into groups, subgroups, types, types and varieties, and technogenic pounds are first divided into two subclasses, and then also into groups, subgroups, types, types and varieties. The classification of pounds according to GOST 25100-95 is shown in abbreviated form in the table:

Construction classification of soils

Classes	Groups	Subgroups	Types	Kinds	Varieties
Rocky soils (with rigid structural connections)	Rocky soils	Igneous rocks Metamorphic rocks Sedimentary	Silicate Silicate Carbonate Ferrous Silicate Carbonate	Granites, basalts, gabbro Gneisses, schists Marbles, etc. Iron ores Sandstones, conglomerates Limestones, dolomites	Are distinguished by: Strength Densities weathered Water solubility Softening in water 6. water permeability, etc.
	Semi-rocky soils	Magmat. Extrusive rocks Sedimentary	Silicate Silicate Siliceous Carbonate Sulfate Halide	Volcanic tuffs Mudstones, siltstones Opoki, tripoli Diatomites Chalk marls Gypsum, anhydrite Galita and others.
Dispersed soils (with mechanical and water-colloid bonds)	Cohesive soils Non-cohesive soils	Sedimentary rocks Sedimentary rocks	Mineral Organomineral Organic Silicate, carbonate, polymineral	Clay soils Silts, sapropels, peat lands sands, coarse soils	Are distinguished by: Granulometric and mineralogical composition Plasticity number Swelling Subsidence Water saturation Porosity coefficient Densities, etc.
Frozen soils (with cryogenic structural bonds)	Rocky soils Semi-rocky soils Cohesive soils Icy soils	Frozen igneous, metamorphic and sedimentary rocks Frozen igneous volcanic rocks Sedimentary rocks Frozen Sedimentary Rocks In-ground buried	Ice mineral Ice mineral Ice organomineral Ice organic	All types of igneous, metamorphic and sedimentary soils All types of dispersed cohesive and non-cohesive soils Glacial Ice, river, lake, etc.	Are distinguished by: Ice content Temperature-strength properties Salinity Cryogenic texture, etc.

Rocky soils. Their structures have rigid crystalline bonds, for example, granite, limestone. The class includes two groups of soils: 1) rocky, which includes three subgroups of rocks: igneous, metamorphic, sedimentary cemented and chemogenic; 2) semi-rocky in the form of two subgroups - igneous outpouring and sedimentary rocks such as marl and gypsum. The division of soils of this class into types is based on features of the mineral composition, for example, silicate type - gneisses, granites, carbonate type - marble, chemogenic limestones. Further division of soils into varieties is carried out according to properties: according to strength - granite is very strong, volcanic tuff is less strong; In terms of solubility in water, quartzite is very water-resistant, limestone is not water-resistant.

Dispersed soils. This class includes only sedimentary rocks. The class is divided into two groups - cohesive and non-cohesive soils. These pounds are characterized by mechanical and water-colloidal structural bonds. Cohesive pounds are divided into three types - mineral (clay formations), organo-mineral (silts, sapropels, etc.) and organic (peat). Non-cohesive pounds are represented by sands and coarse rocks (gravel, crushed stone, etc.). Pound varieties are based on density, salinity, particle size distribution and other indicators

Frozen soils. All soils have cryogenic structural bonds, i.e. the cement of the soil is ice. The class includes almost all rocky, semi-rocky and cohesive soils located in conditions of negative temperatures. To these three groups is added a group of icy soils in the form of above-ground and underground ice. The types of frozen soils are based on icy (cryogenic) structures, salinity, temperature and strength properties, etc.

Technogenic soils. These soils represent, on the one hand, natural rocks - rocky, dispersed, frozen, which for some purpose were subjected to physical or physico-chemical influence, and on the other hand, artificial mineral and organomineral formations formed in the process of domestic and human production activity. The latter are often called anthropogenic formation. Unlike other classes, this class is first divided into three subclasses, and after that each subclass, in turn, is divided into groups, subgroups, types, types and varieties of soils. Varieties of technogenic soils are distinguished on the basis of specific properties.

Many people are accustomed to perceiving the soil exactly in the form in which it is presented now. However, nature has been forming it for millions of years. Initially, the surface was rock. Over time, it was subject to erosion, rain and minerals. The remains of the first and subsequent plants enriched the soil with humus. Thanks to these metamorphoses, the top layer increased, becoming better in composition and structure. For geological reasons, mechanical and chemical characteristics vary throughout the surface. Soil - soil, all the variety of man-made formations. All this has been the subject of human engineering and economic activity for a long time.

Classification

There are several main types of soil. These include, in particular:

• Monolithic rock and semi-rock with rigid structural connections.
• Dispersed, separate-granular without strong structural connecting elements. Cohesive - clayey, non-cohesive - coarse-clastic.

Soil is used in the construction of building foundations, in engineering structures, as well as in road surfaces, embankments and dams. Well suited for creating underground channels: tunnels, storage facilities, etc. Soil science is a science whose field of study is soil.

Types of soils and their properties

To build a reliable foundation, it is necessary to take into account the physical qualities of the soil that is located at the base. The basic information is contained in the soil table. Before starting work, the earth resistance must be calculated. When assessing its technical suitability, aspects such as:

Types of soils are divided into two large categories, which differ in structure, physical properties and methods of development. Also included are intermediate groups of rocky eroded rocks. They consist of stones unrelated to each other or connected by foreign impurities. The latter are called conglomerates.

Loose structures

This group consists of sandy types of soil that do not lose their volume when dry. In their pure form they have almost negligible connections between particles. This also includes clay. It is capable of increasing its volume when wet and, depending on humidity, can have good cohesion. Sands do not have plasticity. After applying force, they instantly compress, but do not retain the shape given to them. But clay is very easy to modify. Under the influence of external force, it compresses quite slowly, but strongly.

Rock structures

These are rocks cemented and welded together. Externally, these structures appear as a solid mass or a fractured layer. Saturated with water, they show a high percentage of compressive strength. These structures are easily soluble and soften in water. They are well suited as a basis for a foundation due to their strength, resistance to compression and frost. The undoubted advantage of these structures is also that they do not require additional opening and deepening.

Conglomerates and non-rock structures

Most of them are made up of unconsolidated crystalline and sedimentary coarse-grained rocks. These structures are capable of supporting buildings of several floors. On these soils, a strip foundation is laid, the depth of which is at least half a meter. On the territory of the Russian Federation there are quite a lot of varieties of rock structures, which have a wide variety of

Loose structure

It should be said that sand-soil is considered a fairly common structure. What is this category? The composition of the soil includes a loose mixture of grain quartz, as well as other materials that appeared due to the weathering of very small rock particles. These structures are divided into several subgroups. These are, in particular, gravelly, medium and large, dusty rocks. All of these structures are easy to develop, have high water permeability, and are well compacted under pressure. By laying sand in an even layer of density and volume, you can lay a good foundation for subsequent construction. The use of its maximum characteristics will occur if the freezing level is located above groundwater. All this depends on the characteristics of the region in which construction takes place. Sand compression occurs in a short time, which means that settlement of such a structure will not take much time. Its size is directly proportional to its ability to withstand loads. The size of dust sand particles varies from 0.005 to 0.05 mm. It will not be a good foundation for construction, since it does not cope well with high loads. Sandy soil can sag under pressure. It also hardly freezes and allows water to pass through easily. If the foundation is based on such soil, then it should be laid at a depth not exceeding 70 cm, but not less than forty centimeters.

Plastic structures. Subcategories

The plastic characteristics of soils make it possible to divide them into several subgroups. Let's look at the main ones. Loose structures containing 5-10% clay are called sandy loam. Some of them, when diluted with water, become fluid, similar to liquid. Because of this, such soil is also called floating soil. Such structures are unsuitable for Loams containing from 10 to 30% clay. They are light, medium and heavy. These indicators ensure an intermediate position of such soils between clay and sand.

for foundation

The physical characteristics of soils are of great importance in the construction of structures. Not every rock can be used to build a building. Unlike the granular structure, clay has high compressibility. At the same time, under load, the compaction process is quite slow. Accordingly, settlement of buildings on such soil will take longer. Combined layers of soil - made of rock and granular structure - do not have resistance to liquefaction. Because of this, they have low load-bearing capacity. The soil contains tiny particles, the size of which does not exceed 0.005 mm. This structure also contains a small amount of loose particles. Clay is easily compressed and washed away. Having been compacted for many years, this structure will serve as an excellent basis for laying the foundation of a house. However, there are a number of reservations here, because in its natural state it is almost impossible to find dry clay.

The fine structure of the rock promotes the formation It leads to a constant wet state of the clay. But the disadvantage of this kind of structure is not its humidity, but its heterogeneity. It does not allow water to pass through well. Because of this, the liquid spreads through various soil impurities. At low temperatures, the clay begins to freeze to the building, which leads to its swelling. This helps raise the foundation. Clay moisture content is uneven. In turn, this means that it will rise differently in each place. All this leads to the destruction of the building. In some places it is stronger, in others it is insignificant, but over the entire surface the soil affects the foundation. Types of soil, depending on their properties, affect foundations in different ways.

Macroporous structures

This is a separate category, which is formed by clay soils. They got their name macroporous due to the presence of large spaces between the particles. Pores are visible even to the naked eye. Upon examination, you can see that they significantly exceed the soil skeleton. Loess rocks belong to this structure. They contain more than 50% dust particles. These structures are widespread in the south of Russia and the Far East. Under the influence of moisture, such rock becomes wet and loses its stability. If the initial stage of clayey soils was formed due to structural sediments in the water, in which microbiological processes were present, then it is called silt. They are most often found in swampy and marshy areas and in peat mining areas. If the foundation is being built in an area where there is a high probability of the presence of loess and silty soils, then the necessary measures should be taken to strengthen the structure.

Determining consistency on site

The structure of clayey soils is determined visually when excavating with a shovel. For example, a plastic mixture will stick to the tool. Hard soil will behave completely differently. The types of soils are determined by rolling them into a cord or rubbing them with your palms. This way you can evaluate their plasticity. Clay soils compress well, erode and swell when frozen. These structures are among the most finicky and unfavorable for foundation construction. In such areas, the foundation must be laid to the entire freezing depth. Assessment of the soil composition on the site is carried out using a watering can. Record the time of water absorption from the surface. If absorption occurs within a second, then the structure is rocky or sandy. Wet peaty rock also accepts water quite quickly. But on the surface of clay soil, liquid lingers.

After this, take a little of the soaked layer and squeeze it in your palm. If the structure has broken down into grains or has leaked through your fingers, then it is rocky or sandy. Clay is easy to compress and will be fixed in the form of a lump. It feels quite slippery. If the soil feels soapy, silky, and doesn't compress as much, it's likely silty or loamy. The peaty structure is similar to a sponge.

How to determine the structure at home?

A full tablespoon of soil is placed in a glass of clean water. It needs to be mixed and left. After a few hours you can see the result. If there is layered sediment at the bottom, and the water itself is relatively clean, then you have added Sand, stones at the bottom and clean liquid - this is a different structure. Most likely it is a rock. In particular, it may be sandy or rocky soil. Grayish water and whitish grains are characteristic of a limestone structure. Peaty soil will make the water cloudy. At the same time, thin and light fragments will float on the surface, and a small sediment will appear at the bottom. If the water contains clay and silty soil, it will become cloudy. In this case, a thin sediment forms at the bottom.

pH level

The soil can be divided depending on the degree of acidity. So, according to pH, structures are weakly acidic, neutral or slightly alkaline. In the latter, the soil acidity level varies from 6.5 to 7.0. It is great for garden plants, including vegetables, and promotes their faster growth and development. Acidic soil has values ​​from 4.0 to 6.5, but from 7.0 to 9.0 it is already an alkaline structure. In addition to those indicated, there are also extreme points of the scale - from 1 to 14, but in the practice of European gardening they are practically never found. Knowledge of this data is necessary for the correct selection of plants for planting. Soil acidity can be reduced by mixing the structure with lime. Organic conditioners will help raise the pH level. However, the latter process is quite expensive. In this regard, in areas with alkaline soil, acidophilus can be grown in containers and tubs that are filled with an acidic structure.

Growing plants

When choosing soil for plantings, it is necessary to focus on such points as:

• Scope of its application. There is soil for flowers, seedlings, as well as garden and universal soil. It is possible to purchase peat. It all depends on what the soil is needed for and what cultural or ornamental plants will be grown on it.
• Types of plants. If you are going to grow representatives of one category, then the best choice would be a special soil just for it. But if there are several, a universal one will do.
• Volume consumed.

To make the soil mixture looser, use vermiculite. To prevent the roots from rotting from stagnant water, a drainage layer is laid at the bottom when planting plants. For cacti and a number of other plants, the soil is mixed with a loose structure. If planting occurs in infertile places, then its quality will help improve the peat. The hydrogel helps improve moisture and air exchange processes. Charcoal is used to reduce the pH level. It is added to the soil for flowers (for example, orchids) and other plants.

Useful impurities

Plants are mainly used in landscape work. But the scope of application of structures with various “useful” impurities is much wider due to the inclusion of stones, clay and other components in the composition. What is the percentage of essential healthy ingredients? As a rule, fertile soil is a combination of 50% peat, 30% black soil and 20% sand. Thus, its composition includes a high content of minerals. Fertile soil is highly waterproof. This structure ensures complete nutrition of cultivated plants, regardless of the stage of their growth.

At agricultural enterprises, farms, as well as on private plots, fertile soil is used quite actively. It copes well with the tasks posed in the process of growing crops. Of particular importance is that it helps improve soil structure and increases productivity. In addition, this mixture does not require additional use of fertilizers.

How to improve soil structure?

For poor rocky and sandy soils, rotted manure mixed with straw is used. It is better to give preference to horse rather than cow. It promotes the retention of moisture and beneficial components in the root system of plants. But fresh manure cannot be added. Garden compost can be used for the same purposes. A mixture of rotted lime and peat is called mushroom compost. If it is necessary to create a slightly alkaline reaction in neutral soils, then this mixture is perfect. Leaf humus is suitable for plants that require acidic soil, that is, for moisture-loving acidophiles. Conditions, mulches and acidifies the soil. Wood shavings and sawdust can be used for the same purposes. Peat is used to oxidize the soil. It decomposes quickly, but contains virtually no nutrients. In winter, you can use bird feathers, which are rich in phosphorus. They are also added to areas where potatoes are supposed to be planted. To improve water permeability and structure of clay soils, crushed wood is used. The bark is also used for mulch due to its appearance and qualities. It is advisable to use a conditioner simultaneously or instead of applying organic fertilizers. Areas of soil that are only planned to be sown are dug up and mixed with them several months before planting begins. To fertilize already planted plants, the soil is enriched with a layer of mulch from conditioning organic materials with fertilizers at the very beginning and end of the season.

The purpose of geotechnical work during construction is to determine the characteristics and properties of the soils used for the foundation of the future building or structure. To simplify these works, a construction soil classification. What are the main types of soils and their construction properties?

Construction classification of soils and types of soils

Soils are varied in their composition, structure and nature of occurrence. Construction classification of soils and types of soils are determined in accordance with SNiP II-15-74 part 2.

Soils are divided into two classes: rocky- soils with rigid (crystallization or cementation) structural connections and non-rocky- soils without rigid structural connections.

1. Rocky soils

Rocky– soils with rigid structural connections occur in the form of a continuous massif or in the form of a cracked layer. These include igneous (granites, diorites, etc.), metamorphic (gneisses, quartzites, schists, etc.), cemented sedimentary (sandstones, conglomerates, etc.) and artificial.

They are waterproof, incompressible, have significant compressive strength and do not freeze, and in the absence of cracks and voids they are the most durable and reliable foundations. Fractured layers of rocky soils are less durable.

Rocky soils are divided according to their tensile strength, solubility, softness and salinity.

2. Non-rocky soils

Non-rocky soils are sedimentary rocks without rigid structural connections. Based on particle size and content, they are divided into coarse-clastic, sandy, silty-clayey, biogenic And soil. A characteristic feature of these soils is their fragmentation and dispersion, which distinguishes them from very durable rocks.

2.1. Coarse soils

Coarse clastic – loose fragments of rocks with a predominance of fragments larger than 2 mm (over 50%). Based on their granulometric composition, coarse soils are divided into: boulder d>200 mm (with a predominance of unrounded particles - blocky), pebble d>10 mm (with unrounded edges – crushed) And gravel d>2 mm (with unrounded edges – woody). These include gravel, crushed stone, pebbles, and debris.

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

If there is more than 40% sandy aggregate or more than 30% silty-clayey aggregate of the total mass, only the fine component of the soil is taken into account, since it is this that will determine the bearing capacity.

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

2.2. Sandy soils

Sandy– consist of particles of quartz grains and other minerals with a particle size of 0.1 to 2 mm, containing clay no more than 3% and do not have the property of plasticity. Sands are divided according to grain composition and the size of the predominant fractions into gravel lines d>2 mm, large d>0.5 mm, medium size d>0.25 mm, small d>0.1 mm and dusty d=0.05 - 0.005 mm.

Soil particles with a particle size of d=0.05 - 0.005 mm are called dusty. If the sand contains from 15 to 50% such particles, then they are classified as dusty. When there are more dust particles in the soil than sand particles, the soil is called dusty.

The larger and purer the sand, the greater the load the base layer can withstand. The compressibility of dense sand is low, but the rate of compaction under load is significant, so settlement of structures on such foundations quickly stops. Sands do not have the property of plasticity.

gravelly, large And medium size Sands become significantly compacted under load and freeze slightly.

The type of coarse-grained and sandy soils is determined by the granulometric composition, the variety - by the degree of moisture.

2.3. Silty-clayey soils

Silty-clayey soils contain dusty (0.05 - 0.005 mm in size) and clay (less than 0.005 mm in size) particles. Among silty clay soils, there are soils that exhibit specific unfavorable properties when soaked: subsidence And swelling. TO subsidence include soils that, under the influence of external factors and their own weight when soaked with water, give a significant sediment, called drawdown. Swelling soils They increase in volume when moistened and decrease in volume when dry.

2.3.1. Clay soils

Clayey– cohesive soils, consisting of particles with a particle size of less than 0.005 mm, having a mainly scaly shape, with a small admixture of small sand particles. Unlike sands, clays have thin capillaries and a large specific contact surface between particles. Since the pores of clay soils are in most cases filled with water, when the clay freezes, it heaves.

Clay soils are divided depending on the plasticity number into clay(with clay particles content more than 30%), loams(10...30%) and sandy loam(3...10%).

The bearing capacity of clayey foundations depends on humidity, which determines the consistency of clayey soils. Dry clay can withstand quite a lot of load.

The type of clay soil depends on the plasticity number, the variety - on the fluidity index.

2.3.2. Loess and loess-like soils

Loess and loess-like – clayey soils containing a large amount of dust particles (contain more than 50% dust particles with an insignificant content of clay and calcareous particles) and the presence of large pores (macropores) in the form of vertical tubes, visible to the naked eye. These soils in a dry state have significant porosity - up to 40% and have sufficient strength, but when moistened they can produce large precipitation under load. They refer to subsidence soils (under the influence of external factors and their own weight they give a significant subsidence) and when erecting buildings on them, they require proper protection of the foundations from moisture. With organic impurities (plant soil, silt, peat, bog peat) they are heterogeneous in composition, loose, and have significant compressibility.

They are not suitable as natural foundations for buildings (when moistened, they completely lose strength and large, often uneven, deformations - subsidence) occur. When using loess as a base, it is necessary to take measures to eliminate the possibility of its soaking.

2.3.3. Quicksands

Quicksands- these are soils that, when opened, begin to move like a viscous-flowing body; they are formed by fine-grained silty sands with silty and clayey impurities saturated with water. When liquefied, they become highly mobile, in fact, they turn into a liquid state.

Distinguish true quicksand And pseudoquicks. True quicksand characterized by the presence of silt-clay and colloidal particles, high porosity (> 40%), low water yield and filtration coefficient, a feature of thixotropic transformations, floating at a humidity of 6 - 9% and transition to a fluid state at 15 - 17%. Pseudo-swimmers– sands that do not contain fine clay particles, are completely saturated with water, easily release water, are permeable, turning into a quicksand state at a certain hydraulic gradient.

They are of little use as natural bases.

2.4. Biogenic soils

Biogenic soils characterized by a significant content of organic substances. These include peaty soils, peats and sapropels. Peaty soils include sandy and silty-clayey soils containing 10 - 50% (by weight) of organic matter. If there are more than 50%, then it is peat. Sapropels are freshwater silts.

2.5. Soils

Soils- these are natural formations that make up the surface layer of the earth’s crust and have fertility.

Soils And biogenic soils cannot serve as a foundation for a building or structure. The first ones are cut and used for farming purposes, the second ones require special measures to prepare the base.

2.6. Bulk soils

Bulk– formed artificially when filling ravines, ponds, landfill sites, etc. or soils of natural origin with a disturbed structure as a result of soil movement. The properties of such soils are very different and depend on many factors (type of source material, degree of compaction, homogeneity, etc.). They have the property of uneven compressibility, and in most cases they cannot be used as natural foundations for buildings. Bulk soils are very heterogeneous; in addition, various organic and inorganic materials significantly worsen its mechanical properties. Even in the absence of organic impurities, in some cases they remain weak for many decades.

As a foundation for buildings and structures, fill soil is considered in each individual case, depending on the nature of the soil and the age of the embankment. For example, sands that have compacted for more than three years, especially sands, can serve as the basis for the foundation of small buildings, provided that there are no plant remains and household waste in it.

In practice, there are also alluvial soils formed as a result of the cleaning of rivers and lakes. These soils are called refilled fill soils . They are a good foundation for buildings.

You watched: Construction classification of soils. Types of soils.

In the previous article “How to analyze the soil on a site before selecting and laying a foundation,” we told you what measures need to be taken to analyze the soil on your plot. Let us once again focus on the fact that Always Before building a foundation (no matter what you plan to build: a one-, two-, or three-story private house), you must determine the types of soil, its characteristics, and also make calculations for the possible loads that the foundation can withstand.

It is better if you order engineering and geological services, but if conditions or financial opportunity do not allow, then at least study the soil yourself and carry out minimal calculations.

In this article we will look at what soil is, what types of soil are determined by building codes, and what types of soil fall under the category " bad luck".

Soil composition and structure

Before analyzing the types of soils, you need to understand what soil is and its basic composition in order to better understand its structure and properties in the future. The wonderful manual by S. A. Pyankov “Soil Mechanics”, as well as GOST, will help us in explaining this.

Types of soil according to GOST 25100-2011

All soils can be classified according to their granulometric composition into:

1. Rocky
2. Dispersed
3. Frozen, we will not consider them in this article.

Let's simplify the complex and detailed classification given above:

1. The most durable and capable of bearing a high load - rocky (limestone - but not all, and only not at high water levels, as well as granite, shales), they are not often found, dispersed ones are more common. Rocky soils do not swell or sag.
2. Dispersed soils. We are interested in the following types of soils: coarse soils (for example, boulders, debris, pebbles), clay, loam, sandy loam, sand, silt, sand, peat, silty sand, loess soils.

According to the classification of particle size distribution given in the table below, it is easy to determine the particle size.

If for some reason you cannot take soil samples to the laboratory (for example, there is no laboratory in your city), then without a laboratory, so to speak “in the field,” the soil can be diagnosed according to the description in the following table:

Another popular way to determine the type of soil in the field is to “roll sausages” in a wet state. Of course, you can determine crushed stone or peat visually; this method is suitable for clay-containing types of soil. Wet the soil sample with water and try to roll the flagellum with your palms. You determine the type based on its characteristics.

To give you an idea of ​​what loam, sandy loam, clay soil, and sandy soil look like, here is the following image:

There are some ways by which you can determine the types of soil, their granulometric composition, as well as some of their characteristics, such as density, humidity, but for this you will have to conduct experiments (which, by the way, we would not advise you to carry out on your own; it’s easier to contact laboratory, and do what you are good at, providing laboratory experiments to specialists who can measure the physical properties of soils, their composition most accurately, without large errors).

Problematic, complex soils

If you are the unlucky owner of such soils on your site, be careful and vigilant, think many times before building, or better yet, consult with a specialist and be sure to do a soil analysis on your site, if you have not already done so.

Next, we’ll look at what certain types of soil look like and look at their main characteristics. We won’t talk about boulders, pebbles, or crushed stone; you can distinguish this type of soil; you’ve seen it many times.

Let's talk about other types, which are often problematic, losing their strength under external influences, for example, being saturated with water, or combining with other soils and their impurities.

Such soils - structurally unstable soils, that is, subsidence soils that change their structure under external influences.

• Frozen and permafrost
• Karst soils
• Loess soils
• Organomineral and organic soils
• Swelling
• Bulk
• Salted

Frozen and permafrost

Frozen soils have a temperature below zero and contain icy particles in one form or another. After being in a frozen state for 3 years or more, such soils already acquire the properties of permafrost soils.

In a frozen state, frozen and permafrost soils are very strong and are not subject to deformation, since the cryogenic structures connecting them increase the initial strength.

During the melting process, the structure and physical and mechanical properties completely change, and serious deformations occur. Some soils even become liquid after thawing.

The main feature of the entire class of frozen soils is subsidence during thawing, when a large-scale reduction in soil volume occurs. Permafrost soils are a rather problematic type of soil for design and construction.

Which foundation to choose? This can be determined only after determining all the necessary calculated deformation-strength characteristics during laboratory tests.

• The first option is to preserve the structure of cryogenic bonds - the frozen state both during construction and during further operation. The preservation of soil permafrost is maintained by organizing cold first floors, ventilated cold undergrounds with ventilated ducts. In this case, we determine the minimum depth of foundation according to SNiP 2.02.04-88:

• The second option is to prepare the structure for uneven settlement. You can replace unstable soil with non-planting sand or coarse soil. You can also about pierce the foundation onto a more durable layer, then you can use permafrost soils in a thawed or thawing state. This is possible only if the soil mass contains strong soils that do not easily deform during the thawing process.

In this case, the deepening of the foundation is carried out on the basis estimated depth of seasonal soil freezingd fand the level of groundwater that forms during the thawing process.

It is necessary to develop areas on permafrost ground using only one of the options, and not so that the neighbor chooses the cold first floor, and you choose piles.

It is worth noting that piles widely used in northern construction are also subject to negative effects: water pressure when the soil freezes; chem. aggressiveness of the water of the thawed layer; the appearance of cracks due to temperature deformations.

Limestones

Limestones, like other soils from the group of rocky sedimentary carbonate rocks, are strong when dry, but when wet with groundwater they lose their strength.

There are limestones initially with low density and wide “porosity” - shell rocks, there is another much denser variety with low porosity. The strength of the former is hundreds of times lower than that of the latter.

One of the varieties of limestone soil is marl, which is a mix of limestone and clay.

A limestone base (by the way, the same applies to dolomite and chalk) is quite dangerous for building a foundation, although it would seem to be rocky soil. Where a limestone layer is easily accessible to water, a huge sinkhole may form over time, as limestone is susceptible to erosion. Limestones belong to karst rocks(as well as gypsum, dolomite) are rocks that can dissolve when washed away by surface and groundwater. As a result, a karst failure may occur:

If there is a limestone layer on the site, it is necessary to determine its porosity and consider the drainage of surface water. In such an unfavorable case, many resort to using a pile foundation. We advise you not to improvise; the best option for you would be to consult with a good specialist geologist; engineering surveys are required in this case.

Loess soils, loess, loess loams

It is impossible to say with certainty how such soils appeared; scientists are still arguing about this. Loess rocks belong to structurally unstable soils (but not all of them are subsidence).

This type is very common over large territories in Russia, Ukraine, and Europe, and more than 80% of the territory of Ukraine is occupied by loess. The occurrence of this type of soil is usually located immediately under the soil cover, in the upper layers.

Loess soils are usually light yellow or light brown (also called fawn), or even brownish-yellow.

Loess soils contain more air than solid particles, contain many macropores, and porosity up to 60%. More than 60 percent of the particles are fine dusty particles; it also contains clay and, to a lesser extent, sand.

In the images below you can see the presence of vertical “grooves”, veins or tubules, characteristic of loess rocks. Such macropores in the form of tubes reach a diameter of up to 3 mm.

There are typical loess and loess loam. Loess loams contain more clay than typical loess and are darker in color, sometimes reddish-brown. Loess loams are less porous and, therefore, more dense and less prone to subsidence.

In their normal state, loess deposits are very strong and can withstand heavy loads, but when moistened, the strength is lost, and additional subsidence deformations arise from the load - both external and from its own weight.

To determine the degree of loess subsidence, it is compacted under pressure in the laboratory and then soaked.

Organomineral and organic soils - peats, peat, sapropels

Peat bogs are common in the Moscow region, in the east and northeast. They belong to weak soils, with inherent low strength.

Peaty soil differs from peat in the percentage of organic matter content - a content of more than 50% of organic matter indicates peat, and a content of 10 to 50% of organic residues indicates that this is peaty soil, based on sandy or clay soil.

What characteristics are inherent in peat and peaty soils?

• High water saturation
• Strong compressibility
• Sedimentation, slowly flowing
• Variability of characteristics under loads
• Groundwater is a very aggressive environment in relation to building structures.

In addition to gradation according to the quantitative content of peat, organomineral and organic soils are divided into:

• Open, located near the surface;
• Buried, located in the form of layers or lenses deep in the thickness;
• Artificially buried

Also important is the degree of decomposition of peat soils - the degree of decomposition of its constituent plant residues - humus.

It is very important to evaluate the nature of the occurrence of peat-containing rocks:

Bedding, which contains peat and peaty soils, is one of the worst foundations, as it leads to further deformations and subsidence.

Sapropel- silt-containing and at the same time peat-containing rock, with a percentage of organic substances greater than 10%. The porosity coefficient of sapropel is in the region of e> 3; it is characterized by a fluid-plastic or fluid consistency.

It is impossible to build a foundation directly resting it on heavily peaty soils, peats, sapropels and silt.

Measures to strengthen unstable organic and organic-mineral soils are described in SP 22.13330.2011 section 6.4 “Organomineral and organic soils”.

Activities include replacing unstable soil with medium- or coarse-grained sand and gravel (which can be very expensive, for example, due to the high thickness of the peat layer), and you can also resort to the construction of a pile foundation with piles resting on a layer of soil with high strength characteristics.

We must not forget that in organic soils there is very aggressive environment for concrete and metal, therefore it is undesirable to use steel piles; care must be taken to insulate the piles to extend the life of the structure.

Swelling

Such soils include some types of clay-containing soils. Swelling soils tend to increase in volume when in contact with water, and they also tend to shrink when dry. The moisture content at the yield point, as well as the plasticity number of such soils, are very high; natural moisture< влажности на границе раскатывания. Пески и супеси не подвержены набуханию практически, зато суглинки и глины подвержены этому свойству пропорционально содержанию в них частиц глины.

The danger of such soils is that any change in the groundwater level will provoke swelling and subsequent subsidence of the soil due to a decrease in the volume of the soil after drying.

The degree of possible swelling is determined during laboratory compression tests.

Read more about swelling soils, design characteristics, and base deformations due to shrinkage and swelling in section 6.2 “Swelling soils” in SP 22.13330.2011. There is also a formula for calculating the rise of the base as a result of swelling.

What measures are taken to prevent soil shrinkage under the foundation?

• good drainage and drainage;
• pre-soaking;
• installation of sand cushions;
• replacement of swelling soil in whole or in part;
• cutting through swelling soil, resting the foundation on a more reliable layer of soil (if the layer of swelling soil is no more than 12 m).

Weak water-saturated clayey

This group is represented by silt, sapropel, as well as clayey soils in a fluid or fluid-plastic state. The characteristic properties of this type of complex soil are:

• high water saturation: humidity from 0.8, more than 80% of pores filled with water;
  
• internal friction angle 3°-14°, adhesion 0-0.02 MPa
  
• frequent high thickness of the water-saturated layer - up to 20 m;
• high soil compressibility and low strength;
• The calculated settlements of structures sometimes differ significantly from the real, actual settlements.
• uneven and very large settlement of the foundation built on water-saturated soil.

We described and showed sapropel a little higher; we will give only its physical properties:

IL- organomineral soil, containing >3% organic matter and >30% fine particles less than 0.01 mm, with a fluid consistency IL> 1, porosity coefficient e ≥ 0.9.

What types of foundations are used in construction?

• pile foundations made of reinforced concrete piles,
• sand pillows,
• drains (sand piles),
• lime piles,
• drainage slots

It is worth noting that there is sand clogging process (natural ingress of small particles, especially clay and dusty particles, into the pores and cracks of the foundations) when constructing sand cushions and piles, which over time reduces the stability and strength of foundations.

Bulk

Bulk soils belong to the so-called technogenic soils; their peculiarity is that they have a disturbed structure.

Their main characteristics include:

• uneven compressibility, and as a consequence further deformations, especially due to vibration loads and soaking;
• gradual self-compaction

Bulk soils can self-compact; the duration of this process varies, depending on the type of embankment. The approximate self-sealing period is given in the joint venture:

Approximate values ​​of physical and mechanical properties of bulk soils (NIIOSP)

	specific gravity, kN/m3	beat weight of soil particles, kN/m3	deformation modulus, MPa	angle of internal friction	adhesion, kPa
caked over 100 years old	16,5	26,5	from 8 to 12	18-20	4-8
systematically constructed embankments from sandy soils	16,5	26,5	from 10 to 15	22	1
unplanned, non-compacted embankments	16	26,5	from 6 to 8	17-18	0-2

The strength level of bulk soils is increased by compacting them in various ways:

• tamping, rolling, hydraulic vibration compaction
• installation of ground cushions
• cutting through pile foundation
• chemically, for example, silicatization

Salted

Saline soils in Russia are distributed over approximately 10 percent of the entire territory, mainlyin Crimea, the Caucasus, as well as the West Siberian Lowland.

Quote from SP 22.13330.2011: "The degree of soil salinity Dsal, % - the ratio of the mass of water-soluble compounds lei in the soil to a mass of absolutely dry soil."

Saline soils undergo leaching during water filtration. Water dissolves salts, increasing porosity. Soil bases are ultimately subject to suffusion sedimentation. When saline soils are moistened, their physical and mechanical properties change: density, strength, deformability and water permeability. In addition, another danger of saline soils is the aggressiveness of water with salts dissolved in itto building materials, concrete.

Saline soils in a soaked state can be swelling or subsiding. Entrust all calculations for saline soils to specialists.

No matter how difficult the soil may be on your site, modern construction technologies can provide you with a durable building on any foundation. But only under the condition of a full engineering-geological survey and carrying out all the necessary calculations based on this study. Having knowledge of the future structure, you can make an economically feasible choice of a foundation suitable in all respects, which will not cause cracks and deformations, which so often abound in photographs of incorrectly designed buildings on forums.