Rocky soils, dispersed, frozen and man-made.
Rocky soils are structures with rigid crystalline bonds (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 - magmatic outpouring and sedimentary rocks such as marl and gypsum. The division of this class into types is based on the characteristics 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 durable; In terms of solubility in water, quartzite is very water-resistant, limestone is not water-resistant.
Frozen soils have cryogenic structural connections, i.e. Ice is the cement of soils. 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. Varieties of frozen soils are assessed by icy (cryogenic) structures, salinity, temperature and strength properties, etc.
Technogenic soils are, on the one hand, natural rocks - rocky, dispersed, frozen, which have been subjected to physical or physico-chemical influence, and on the other hand, artificial mineral and organomineral formations formed in the process of everyday and industrial human activity. 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.
ENGINEERING - GEOLOGICAL CHARACTERISTICS OF ROCK SOILS.
Rocky soils are structures with rigid crystalline bonds (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 eruptive and sedimentary rocks such as marl and gypsum. The division of this class into types is based on features of mineral composition, for example, silicate type - gneisses, granites, carbonate - marble, chemogenic limestones. Further division of soils into varieties is carried out according to properties: in terms of strength- granite is very durable, volcanic tuff is less durable; by solubility in water – quartzite is very water-resistant, limestone is not water-resistant.
The class of rocky soils includes a group of rocky and semi-rocky soils and combines igneous, metamorphic and sedimentary rocks. On the plains, rocky soils are usually located at some depth under the thickness of sedimentary rocks; they rarely come to the surface of the earth. These soils are widely developed in mountainous regions, where they are located on the surface of the earth’s crust. Rocky soils are monolithic, are in a dense state and have high strength due to crystalline structural bonds. The upper part of the massifs, in contact with the atmosphere, is usually destroyed due to the effects of the weathering process. This destroyed zone is called the weathering crust and is characterized by the size k - degree of weathering, which is determined by comparing the density of weathered rocky soil with the “parent (unweathered) part of the rock mass.
Rocky soils, due to their deep location in the earth's crust, rarely serve as the foundation of structures. When this happens, it is better to rest the object on the parent rock, i.e. foundations must cut through the weathering crust. Foundations can also be rested on weathering crust, but to do this it must be strengthened by some method of technical soil reclamation.
When erecting a structure on rocky soils, one should take into account: a) rocky soils under small loads, for example from civil buildings, practically do not compress, but under the influence of very large loads and for a long time they can exhibit rheological properties;
b) for rocky soils capable of dissolving in water, it is necessary to establish the degree of solubility : sparingly soluble- limestones, dolomites, calcareous conglomerates and sandstones; medium soluble- gypsum, anhydrite ; easily soluble- rock salt.
c) the strength of rocky soils varies widely and depends on whether these rocks are in the form of a monolith or are fractured. Fractures reduce the strength of rocks. The presence of micas, especially biotite, leads to a decrease in the strength of all igneous rocks. Basalts are characterized by high density (up to 3-3.3 g/cm) and strength RWith up to 300-350 MPa. However, the strength drops sharply in basalts with a bubble texture, the porosity of which can be up to 50%.
PHYSICAL AND MECHANICAL PROPERTIES OF ROCK SOILS.
WATER - PHYSICAL PROPERTIES.
Rocks have low total porosity (less than 5%), semi-rocks have medium (5-20%) or even high (more than 20%) porosity.
Fracture can be characterized as additional porosity that occurs in rocks as a result of tectonic movements and exogenous processes (weathering)
From the size, density, direction, nature, genetic type of cracks in to a greater extent the strength, stability and water permeability of the foundation of the future structure depend.
Rocky rocks, as a rule, are not moisture-absorbing, and semi-rocky ones are weakly and moderately water-absorbing. Moisture-intensive rocks are more susceptible to frost weathering and softening.
Water absorption - for dense crystalline rocks less than 1%; for fractured, tuffaceous, porous rocks and semi-rocks it can be expressed in tens of percent.
Water saturation (forced) – the ability of rock to absorb water at an excess pressure of 15-20 MPa or in a vacuum. The higher the coefficient of water saturation, the greater the proportion of free pores in the rock and the easier the rock is saturated with water, filters, and is destroyed as a result of frost weathering.
For rocks, filtration, the movement of water through the rock, is possible only through cracks. For other hard rocks, filtration depends on the presence and size of all types of open voids: large pores, caverns, karst voids, suffusion passages.
Under water resistance one should understand the ability of solids rocks maintain mechanical strength, stability and integrity when interacting with water. The indicator of water resistance is softening coefficientKrz , taking into account the degree of reduction in the mechanical strength of the rock after its saturation with water.
Rocks that are softened include: Krz less than 0.75, they cannot withstand pressure on them, are capable of causing landslides, collapses on steep slopes, can be washed away by flowing water (agrellites, marls, limestones, shales, saline rocks)
MECHANICAL PROPERTIES OF ROCK SOILS.
Stresses arising under the influence of applied external loads lead to a violation of its strength and continuity. In rocks, deformations are elastic. As the stress increases, the deformation increases, which at maximum stress Pmax leads to the destruction of rock (see figure) In this case, the rock behaves like any solid body, obeying Hooke's law: relative deformation is directly proportional to stress.
When semi-rocky rocks (marl, chalk) are deformed, at first the deformation increases in proportion to the stress, but after reaching the limit of proportionality Rpr, it is not destruction that occurs, but crushing or the so-called plastic flow of the rock, which is expressed in the appearance of cracks and changes in the shape of the sample (see Fig. 2)
This stress corresponds to the yield strength Rt and in some cases the deformation can increase without increasing the stress, i.e. at Р=const (creep). The phenomenon of creep characterizes the strength of the rock over time because creep necessarily ends with resolution (see point Рз=Rz) thus tensile strength of hard rocks is estimated by the maximum load applied to a rock sample at the moment of its destruction (loss of continuity)
Rz= Pmax\ F
F– sample area, cm
Rz- temporary compressive strength or tensile strength, MPA
The strength of rocks is influenced by: mineral composition, the nature of internal bonds, fracturing, degree of weathering, degree of softening. Softened rocks have the least strength.
Indicators of deformability of solid rocks include:
Modulus of elasticity Еу and modulus of general deformation Ео determine the magnitude of the stresses that caused a single relative deformation of the rock as a result of the application of an external load.
Poisson's ratio (lateral strain) determines the extent to which the volume of soil changes during deformation and depends on the mineralogical composition of the soil, porosity and fracturing.
Lateral pressure coefficient(thrust coefficient) takes into account part of the vertical load transmitted to the sides.
ENGINEERING - GEOLOGICAL CHARACTERISTICS OF DISPERSE SOILS.
Dispersed soils. This class includes only sedimentary rocks. The class is divided into two groups - cohesive and non-cohesive soils. These soils are characterized by mechanical and water-colloidal structural bonds. Cohesive soils are divided into three types - mineral (clayey formations), organo-mineral (silts, sapropels) and organic (peat). Non-cohesive soils are represented by sands and coarse rocks (gravel, crushed stone). Soil varieties are based on density, salinity, particle size distribution and other indicators.
Silty and non-silty, clayey soils and loess rocks in most cases are the foundations of structures and are dispersed, i.e. crushed, consisting of small particles. In dispersed soils, there is close interaction between the solid, liquid and gaseous phases. Depending on the conditions of existence of the soil, the meaning of these phases changes and at the same time the physical and mechanical properties of soils change.
For cohesive soils, due to their anisotropy, filtration coefficients in the horizontal and vertical directions can differ significantly. Especially in soils that are heterogeneous in their structure - loess loams, band clays, peats. When studying such soils, it is necessary to determine their water permeability in both horizontal and vertical directions.
Clay soils are characterized by water-colloidal bonds, which provide primary cohesion at the initial stages of the transformation of clay sediment into rock. At later stages, cement bonds and the corresponding hardening bond appear, which gradually transforms the rock from a number of highly dispersed systems into rocks such as shales and mudstones.
The density of clayey soils varies from 2.53 – 2.85 g/cm and depends on the mineral composition and organic impurities, as well as on humidity and the degree of compaction in the natural occurrence. Quaternary clays of marine, river and wind origin have a density of 1.6 – 1.85 g/cm; the skeleton density is 1.35 - 1.55 g/cm, and the porosity is 35-45%. In addition to air and water, the pores of clay soils may contain organic humus humus. In such cases, these soils are called soils and their moisture capacity, plasticity, and compression under loads increase.
Water and its quantity give soils a number of specific (characteristic) properties: plasticity, stickiness, swelling, shrinkage and soaking.
Angle of internal friction and adhesion WITH largely depend on the state of soil moisture and porosity. Thus, in a soft-plastic state, clays can have an angle of no more than 5-10, and in hard-plastic clays, 15-35.
Dusty clay soils in which there are more dusty particles than sandy ones and which have an under-compacted structure with very water-unstable bonds called loess. A feature of loess soils is their subsidence.
Silts, sapropels and peaty soils are classified as organomineral soils. All soils are highly porous and water-saturated. They contain: 1) sand-silt-clay particles 2) organic mineral 3) water - in large quantities . Il – water-saturated modern sediment of reservoirs, formed in the presence of microbiological processes, having moisture content at the fluidity limit, and a porosity coefficient of more than 0.9. Silts are characterized by structures with coagulation bonds, characterized by significant porosity (50-80%), high humidity, low strength, with well-defined thixotropy and creep of the mineral skeleton. The water permeability of silts is very low because in the pores of the soil there are gases of a biochemical nature, the so-called trapped gases. The mechanical properties of silts are characterized by their high compressibility. The total deformation modulus for them is less than 4 MPa, the compressibility coefficient a = 0.005-0.001 MPa. The shear resistance of silts is low, 0.0002-0.0007 MPa. Silts are weak soils on which construction is possible only with the use of technical reclamation methods.
Sapropel- freshwater silt formed during the self-decomposition of organic residues at the bottom of stagnant reservoirs - lakes. Sapropel, when pressure is transferred to it, can flow out from under the foundation or be pushed to the sides if the pressure is transmitted through a layer of peat. Under dynamic load it easily liquefies, when dry it shrinks and hardens.
Peat and peaty soils- These are soils formed in swamps as a result of the accumulation and decomposition of plant sediments and containing mineral impurities. The absolute humidity of peat can reach 800-1000%, which indicates its exceptionally high moisture capacity. Particle density is from 1.4-1.8 g/cm, soil density is 0.7 to 1.4 g/cm. In a dry state, peat can float on the surface of the water, since the density of dry soil is 0.2-0.4 g/cm. Peat has high compressibility, so the load-bearing capacity of peat is low. The water permeability of peat depends on the degree of its decomposition. Thus, undecomposed peat has a filtration coefficient measured in meters per day, and well-decomposed peat is practically waterproof and its Kf close to Kf clay From an engineering-geological point of view, peats are weak, highly and unevenly deformable soils with very variable properties that are unfavorable for construction.
Soils are called saline containing salt inclusions in quantity. Affecting their physical and mechanical properties. They are characterized by the degree of salinity, which, in accordance with GOST 25100-95, means the content of easily and moderately soluble salts as a percentage of the mass of absolutely dry soil. Easily soluble salts include chlorides, bicarbonates, sodium carbonate, sulfates; to moderately soluble gypsum and anhydrite. The presence of salts in soils leads to changes in their strength, compressibility, water permeability, soaking, swelling, angle of repose, and stickiness. When water is saturated and moistened, saline soils lose strength, exhibit additional suffusion deformations, swelling, subsidence, and increase the aggressiveness of groundwater. Dissolved components are carried out by water in case of filtration movement, and in case of obstructed outflow they pass into the pore solution. In addition, in loess rocks, suffusion processes, especially on slopes, can lead to the formation of voids and caves. This phenomenon is called loess karst, which can be expressed on the surface of the earth in the form of suffusion-sinkholes.
The main types of saline soils are salt marshes - are formed in low relief forms with groundwater levels close to the surface; Solontsy– are formed at higher elevations of the terrain and are located both in surface and in deeper horizons, takyrs represent significant areas of clay soils with low moisture, hard consistency, easily soak and have high stickiness.
SUDDENTION PHENOMENA IN LOESS SOILS
Loess rocks occupy large areas of Russian territory, lying on various geomorphological elements of the earth's surface. A continuous cover of loess rocks is located in the central and southern regions, in the West Siberian Lowland. Loess rocks are absent in the floodplains of river valleys and on young river terraces. Loess formations are widespread on foothill and mountain plains (Ceceucasus, slopes of the North Caucasus, Pre-Altai Plain, slopes of Altai, etc.).
The thickness of loess deposits ranges from several to tens of meters, and in some cases even more than 100 m (Eastern Ciscaucasia). The most common thickness of loess deposits is 10-25 m, the maximum is found both on watersheds and in relief depressions.
Loess rocks are represented by loams, less often sandy loams. Among them, a distinction is made between loess (primary formation) and loess-like loams (redeposited primary formations). Their granulometric composition is often similar, therefore in the construction industry it is advisable to use the single name “loess soils,” dividing them according to their granulometric composition into sandy loam, loam, and clay. Uniformity is typical for loess. Loess-like loams are usually layered and may contain fragments of various rocks.
Loess soils are pale-yellow, pale-yellow or yellow-brown in color. They are characterized by the following features: the ability to keep vertical slopes dry, quickly soak in water, high dust content (fraction content of 0.05-0.005 mm is more than 50% with a small amount of clay particles), low natural humidity (up to 15-17%); porous structure (more than 40 %) With network of large and small pores, high carbonate content, salinity with easily water-soluble salts.
The natural moisture of loess soils is mainly related to the climatic characteristics of the areas. In areas of insufficient moisture, the humidity is no more than 10-12 % (Eastern Ciscaucasia, etc.). In more humid areas it reaches 12-14% or more.
Loess strata are characterized by anisotropy of filtration properties. The vertical water permeability of loess rocks is often 5-10 times higher than the horizontal water permeability values. When water enters the loess strata, dome-shaped accumulations of perched water (or groundwater) are formed. This form of groundwater is currently characteristic of many areas where leaks of industrial domestic water constantly occur (Rostov-on-Don, Taganrog, etc.). Changes in the moisture content of loess soils seriously affect the compressibility, subsidence and shear resistance of soils.
Among loess rocks, according to the nature of the influence of moisture on them, they are distinguished: swelling, non-subsidence, subsidence. Swelling Loess rocks are rare. Typically, these are the densest and most clayey varieties with a fraction containing less than 0.005 mm of hydrophilic minerals such as montmorillonite. The amount of swelling of structural formations reaches 1-3%, less often - 5-7%.
Non-subsidence Loess rocks do not exhibit subsidence properties when soaked and applied loads. Such rocks are characteristic of low-lying parts of the relief and the northernmost areas of loess deposits. The lower parts of loess strata and areas that previously underwent significant watering are also non-subsidence.
Subsidence- a phenomenon characteristic of many loess rocks. In Fig. 131 shows the most typical case of the geological structure of the loess strata, in the upper part of which there are soils with subsidence properties. Subsidence is associated with the effect of water on the structure of rocks, followed by its destruction and compaction under the weight of the rock itself or with the total pressure of its own weight and the weight of the object. Compaction of rocks causes the ground surface to sink in areas where water is soaked.
Rice. 131.
1- building; 2- subsidence rocks; 3 - the same non-subsidence; 4-ground water; 5 - area where the drawdown appeared.
The shape of the descent depends on the characteristics of the soaking source. With point sources (break of water supply network, sewerage system, etc.), saucer-shaped depressions are formed. Water infiltration through trenches and channels leads to longitudinal subsidence of the surface. Area sources of soaking, including when the groundwater level rises, lead to a decrease in the surface over large areas.
Due to the lowering of the earth's surface, buildings and structures undergo deformations, the nature and size of which are determined by the magnitude of the subsidence S, (Fig. 133). The amount of surface subsidence (the amount of subsidence) can be different and ranges from several to tens of centimeters, which depends on the characteristics of the soaking of the thickness. For example, in Rostov-on-Don the subsidence can be 15-20 cm, and in the area of the Terek-Kuma irrigation system in the North Caucasus - 100-150 cm.
Rice. 133. Deformation of a building (diagram) on loess soils as a result drawdowns: 1- building; 2 - loess soil; S - drawdown value
The structure of loess soils varies in strength (Fig. 134). In some cases, subsidence occurs mainly within the deformable zone of the base from foundation pressure or another type of external load, and subsidence due to the own weight of the soil is absent or does not exceed 5 cm. Such rocks are classified as type I in terms of subsidence. Soils of type II subsidence, when subsidence occurs from the own weight of the soil of the subsidence layer (mainly its lower part) and its value exceeds 5 cm.
Rice. 134. Ratio of subsidence power And non-subsidence soils in loess strata of types I and II: P - subsidence soils; N- Same. Non-subsidence
The structural strength of loess soils is of great importance in the manifestation of the subsidence process. With weak and easily water-soluble structural bonds, subsidence occurs after a few hours, which is typical for type I pounds. Type I pound structures are generally stronger. In addition to a long, over a number of days, exposure to water, their destruction requires a higher pressure (the dead weight of the soil and the weight of the building standing on it). From this it follows that the subsidence process occurs only at a certain pressure for a given soil. This pressure is called initial drawdownpressure (P SL ). For type I rocks it is 0.13-0.2 MPa, for type II -0.08-0.12 MPa. The value of the initial subsidence pressure determines the deformable zones in the loess subsidence. In these zones, subsidence compaction of rocks occurs. In Fig. 135 shows where deformable zones form in rocks of types I and II. In the first case, subsidence deformation occurs under the foundation in the zone I In the second case, except for the zone 1, drawdown occurs in the zone 3, where it manifests itself under the influence of the rock’s own weight. In some cases the zone 2 there is no zone at all 1 merges with the zone 3 .
Rice. 135. Deformation zones in subsidence rocks of type I and II: F - foundation; 1 - upper deformable zone; 2 - transition zone; 3 - lower deformable zone; P - subsidence rocks; N - the same, non-sagging
The quantitative characteristic of subsidence is taken to be the value relative soil subsidenceE sl , which is determined in the laboratory from individual samples taken from the loess layer. Samples are taken through 1 m or from different layers of rock while maintaining the structure and natural moisture. Quantities E sl obtained from the results of laboratory compression tests
Esl = h – h 1 \h 0
Where h- height of the sample with natural humidity at a given pressure; h 1 - height of the sample after subsidence as a result of soaking at the same pressure; hO-height of the soil sample at a pressure equal to natural.
Initial subsidence pressureRpr - the minimum pressure at which subsidence occurs under conditions of complete water saturation of the soil. In laboratory tests Rpr accept a pressure at which the relative subsidence is equal to 0.01
With values E S lmore 0.01 rock is classified as subsidence. By size E SL of individual samples determine the total amount of drawdown S etc of this loess sequence.
In field conditions the value S n.p. determined by the stamp method, which is placed at the depth of the base of the future foundation and the necessary pressure is transferred to it and the rock is soaked. This type of determination provides the most accurate results.
The type of soil conditions (I or II) is established on the basis of laboratory tests based on the calculated value Snp, but more accurate results can only be obtained in the field by soaking loess strata in experimental pits and monitoring subsidence using benchmarks
When determining the magnitude of subsidence deformation of the soil, one should not forget about settlement. Under the weight of the structure, the soil becomes somewhat compacted and the structure settles. The amount of precipitation largely depends on the natural moisture of the soil - the higher the soil moisture, the more it compresses and the greater the amount of precipitation. Subsidence manifests itself as compaction additional to settlement. Thus, soil deformation consists of “settlement - subsidence.” For specific conditions, this value is usually constant. The relationship between settlement and subsidence may vary. In drier soils, settlement will decrease and subsidence will increase, and vice versa.
Construction on loess subsidence soils. IN In a state of natural moisture and undisturbed structure, loess soils are a fairly stable foundation. However, the potential for subsidence to occur, which leads to deformation of structures, requires the implementation of various types of measures. All events are divided into three groups:
waterproof - drainage of surface water, waterproofing the surface of the earth, eliminating water leaks from the water supply system,
structural - adaptation of the object to various uneven settlements, increasing the rigidity of walls, reinforcing buildings with belts, using piles, as well as widened foundations that transmit pressure to the ground less than P. Thin subsidence soils N are cut through by deep foundations, including piles
eliminating the subsidence properties of rocks - surface compaction by ramming, soaking through wells, followed by explosion under water.
ENGINEERING - GEOLOGICAL CHARACTERISTICS OF COLLECTIVE SOILS.
Sandy soils composed of angular and rounded fragments of minerals, ranging in size from 2 to 0.05 mm. The bulk of the sands consists of quartz and feldspars. Other minerals are always present as impurities - silicates, clay, etc. Sands on the surface of the earth are widespread, both on land (river and lake sands) and in the seas (sea sands). Sea sands occupy large areas, are many meters thick, are most often well sorted by particle size, and are often monomineral, for example, purely quartz. River sands (alluvial) are always local in area of distribution, thin, poly-mineral, unsorted, and often have an admixture of clayey particles and humus. Even more diverse in their occurrence and composition proluvial(foothill) sands. They are typically characterized by interlayering of sands with different particle sizes. According to the form of occurrence, these are layers and lenses among coarse soils.
Sands are a mass of particles with mechanical bonds. All dispersed soils consist of particles of one or, most often, several fractions. Under faction refers to a group of particles of a certain size that have some fairly constant general physical properties. Under granulometric composition refers to the quantitative ratio of various fractions in dispersed rocks, i.e. The granulometric composition shows what size particles and in what quantity are contained in a particular rock. Its determination is carried out using the sieve method or elutriation. The content of fractions is expressed in % relative to the mass of the dried sample. The granulometric composition is depicted in the form of a graph, from which one can judge the homogeneity of the rock by particle size. Based on particle size, sands are divided into gravelly, coarse-, medium- and fine-grained, and silty. The properties of sand are influenced not only by the size and mineral composition of the particles, but also by the uniformity of their granular composition, on which their density, compressibility, and water permeability depend.
Sand porosity in loose state is about 47%, and in a dense state - up to 37% - The finer the sand, the higher the porosity, the smaller the pores in size, hence the filtration capacity of sand decreases with a decrease in the size of its particles. A loose composition easily turns into a dense one under water saturation, vibration and dynamic influences. The density of sands is estimated by the value of the porosity coefficient e: dense build (e< 0,60), средней плотности и рыхлое (е >0.75). In table 22 and 23 show the standard characteristics of Quaternary sands.
Standard values C, kPa, f, deg andE, MPa,Quaternary sands
Is it possible to study soil characteristics without a laboratory?
1. Introduction
The most important stage of foundation design is engineering-geological surveys which make it possible to determine in detail what characteristics the soils underlying the future foundation have. These data will allow you to design the cheapest and most economical foundation while maintaining necessary indicators reliability.
[The lack of information about soils when designing a foundation can only be covered by large safety margins and, as a consequence, financial overruns, but this does not guarantee reliability]
Always, before abandoning geological surveys, evaluate the risks of making an incorrect decision on the foundation and compare them with the savings from abandoning surveys. In my region, drilling one well and laboratory testing of soil samples will cost 30-40 thousand rubles (with the issuance of an official report on geotechnical surveys).
Photo. Soil samples of undisturbed structure (monoliths) selected during geotechnical surveys
If there is no money to order surveys from a specialized organization, and you decide to design the foundations yourself, then you need to determine the characteristics of the soil, at least approximately, by visual signs. Read about this below in this article.
2. Classification of soils
To classify soils, it is useful to use the regulatory document “Soils. Classification" - it indicates everything a builder needs to know about the classification of soils.
The largest classes of soils:
- Rocky soils- soils with rigid structural bonds (crystallization and cementation)
- Dispersed soils- soils with physical, physico-chemical or mechanical structural bonds.
- Frozen soils- soils with cryogenic structural bonds.
- Technogenic soils- soils with various structural connections formed as a result of human activity.
| Groups and subgroups of non-rocky soils | Characteristic |
|---|---|
| Sedimentary uncemented: | |
| coarse-clastic | Uncemented soils containing more than 50% by weight of fragments of crystalline or sedimentary rocks with particle sizes greater than 2 mm |
| sandy | Loose soils in a dry state, containing less than 50% by weight of particles larger than 2 mm and not having the property of plasticity (the soil does not roll out into a cord with a diameter of 3 mm or its plasticity number Jp |
| silty-clayey | Cohesive soils for which the plasticity number Jp ≥1 |
| biogenic | Soils with a relative content of organic matter I from> > 0.1 (lake, marsh, lake-swamp, alluvial-swamp) |
| Soil-vegetable | Natural formations that make up the surface layer of the earth's crust and have fertility |
| Artificial | |
| Compacted in natural occurrence, bulk, alluvial | Transformed in various ways or transported soils of natural origin and waste from industrial and economic activity person |
Perhaps anyone, even a completely unprepared person, can distinguish rocky soils from all other types of soil. On rocky soils, due to their high strength, there are no problems with the foundation in terms of the bearing capacity of the foundation - they themselves can often serve as the foundation of a building or structure.
Photo. Rocky soil
Frozen soils are similar in strength to rocky soils and can be seasonally frozen or permafrost. Seasonally frozen soils turn into thawed soils in the spring and cannot be used as foundation foundations.
Permafrost soils (PMF) are specific soil conditions, the design of foundations for which is one of the most difficult tasks and it is not recommended to do this without the help of professionals. To some extent, the issues of designing foundations for permafrost are touched upon in relevant article.
Technogenic soils (construction or household waste landfills, soil dumps, industrial waste dumps, ash and slag embankments) are also very specific construction conditions. Designing foundations resting on such soils is a task for professionals and requires great care. Build a private house On such soils it is usually not necessary.
Photo. Technogenic soil
Biogenic soils and soil-vegetative layer should not be used as the basis for the foundation because In addition to their very low initial load-bearing capacity, the organic component decomposes over time, greatly decreasing in volume. This causes large uneven foundation settlements and increases the average foundation settlement. Biogenic soils are usually replaced with other more stable and durable imported soils.
A detailed classification of soils, if you are interested in it, will be discussed in separate article, and now let’s look in detail at dispersed soils, which in the vast majority of cases serve as the basis for the foundations of buildings and structures.
Dispersed soils are divided into two large types:
- Messengers– clayey soils: clay, loam, sandy loam (soil particles are connected by water-colloidal and mechanical structural bonds);
- Incoherent(loose) – sands and coarse soils.
Coarse soils consist mainly of very large stone particles (from 2 to 200 mm or more). If the space between the stone particles of coarse soil is filled with sand or clayey soil, and such filler is more than 30% by weight (for sand filler more than 40%), then the characteristics of the soil are determined only by the characteristics of the filler, without taking into account stone inclusions.
[Particles of coarse soil of the same size can be called differently: if their edges are rounded, then they are called boulders, pebbles, gravel; if not rounded (sharp chopped edges), then the particles are called blocks, crushed stone or gruss.]
According to their granulometric composition (see GOST 12536), coarse soils and sands are divided into varieties in accordance with the table:
| Variety of coarse soils and sands | Particle size d, mm | Particle content, % by weight |
|---|---|---|
| Coarse: | ||
| - boulder (with a predominance of unrounded particles - blocky) | > 200 | > 50 |
| - pebble (with unrounded edges - crushed stone) | > 10 | > 50 |
| - gravel (with unrounded edges - wood) | > 2 | > 50 |
| Sands: | ||
| - gravelly | > 2 | > 25 |
| - large | > 0,50 | > 50 |
| - medium size | > 0,25 | > 50 |
| - small | > 0,10 | ≥ 75 |
| - dusty | > 0,10 | |
According to the plasticity number Ip and the content of sand particles, clay soils are divided into varieties in accordance with the table:
| A variety of clayey soils | Plasticity number J p , % | Sand content particles (2 - 0.05 mm), % by weight |
|---|---|---|
| Sandy loam: | ||
| - sandy | 1 ≤ J p ≤ 7 | ≥ 50 |
| - dusty | 1 ≤ J p ≤ 7 | |
| Loam: | ||
| - light sandy | 7 | ≥ 40 |
| - light dusty | 7 | |
| - heavy sandy | 12 | ≥40 |
| - heavy dusty | 12 | |
| Clay: | ||
| - light sandy | 17 | ≥ 40 |
| - light dusty | 17 | |
| - heavy | J p >27 | Not regulated |
[Plasticity number I p– moisture difference corresponding to two soil states: at the yield boundary W L and at the border of rolling W p. In simple wordsI p this is the value of the humidity range in which the soil is plastic (can be rolled into a cord with a diameter of 3 mm). The higher the value I p the stronger the bonds between the particles, for non-cohesive soils (sands) I p <1%.]
As moisture content increases from dry to saturated, clay soils go through three states: solid, plastic and fluid.
In terms of fluidity I L (consistency index) clay soils are divided into varieties in accordance with the table:
| Types of clay soils | Yield index J L , f.u. |
|---|---|
| Sandy loam: | |
| - hard | J L |
| - plastic | 0 ≤ J L ≤ 1.00 |
| - fluid | J L > 1.00 |
| Loams and clays: | |
| - hard | J L |
| - semi-solid | 0 ≤ J L ≤ 0.25 |
| - hard-plastic | 0,25 |
| - soft plastic | 0,50 |
| - fluid plastic | 0,75 |
| - fluid | J L > 1.00 |
Based on deformability, dispersed soils are divided into varieties in accordance with the table:
3. Main characteristics of dispersed soils for foundation design
To say that the foundation can withstand the loads transferred to it, 3 conditions must be met:
- The pressure under the base of the foundation does not exceed the calculated soil resistance (checking the stability of the foundation) - the average pressure and maximum pressures at the edge and at the corners of the foundation are checked;
- The average settlement of the foundation under load does not exceed the permissible values (calculation based on deformations);
- Uneven foundation settlements are also within tolerances (calculation based on deformations).
To check the stability of the foundation it is necessary to calculate the design resistance R, and for this, in turn, the following characteristics are needed:
- soil type,
- sand size or flow index I L for clay soil
- angle of internal friction of soil φ ,
- specific adhesion With,
- volumetric weight of soil γ .
[It is possible for preliminary calculations of foundations to use tabular values of the calculated soil resistance R0, determined by the porosity coefficient and the type/consistency of clay soil or the type of sandy soil size]
For calculation by deformation(settlement calculations) additionally needed: soil deformation modulus E.
Let's try to determine all these characteristics without seeking the help of geologists and laboratories.
The sequence of calculations for columnar and strip foundations on a natural (not pile) foundation is described in detail Here. There you can also see the permissible settlements, tilts and uneven deformations of foundations according to regulatory documentation.
In addition, you will need to collect loads on the foundations - this will help you This article.
4. What soil characteristics can and should be determined without a laboratory?
So, if you are interested in how to determine the characteristics of soil without a laboratory, then we are most likely talking about building a summer house or a small private house. But there is still an opportunity to make more or less correct decisions on the foundation.
To do this, we need to determine for the soil under the base of the future foundation:
- Soil type (coarse, sand, sandy loam, loam or clay);
- If the soil turns out to be clayey (clay aggregate in coarse soils), then we will determine for it: soil subtype (clay, loam or sandy loam), porosity coefficient e and turnover rate I L;
- If the soil turns out to be sandy, then we will determine the size index for it (gravelly, coarse, medium, fine or dusty) and the porosity coefficient e.
Our plan is this: having determined the above soil indicators, we can use the “” tables to obtain tabulated physical and mechanical characteristics of the soil ( φ, s), including its deformation modulus E, and also preview the tabulated calculated resistance of the foundation soil R 0 . And this will allow us to perform all the necessary calculations for the foundations.
And although the result will be approximate, it is still better than building at random!
[Note! Soil characteristics related to moisture, such as flow rate I L or the degree of moisture Sr, are determined for the natural state of the soil, but these indicators change with changes in humidity - for example, when soaking. Clay soil, which is solid in its natural state, can turn into liquid mud ( I L> 1) in case of water saturation due to rising groundwater or breakthrough of communications]
If you have coarse-grained soils on your site (more than half the soil mass is pebbles ranging in size from 2 to 200 mm in diameter), then rejoice - you cannot find a better foundation for the foundation (unless it is better rocky soils, but they will create a lot of problems if you need to dig a pit). True, it is necessary to understand what kind of filler is between the coarse particles and how much of it:
- if the filler is clayey and its content is more than 30% (40% for sandy filler), then the soil should be considered as clayey (or sandy, respectively) and all characteristics should be determined based on the filler;
- if the filler is clay and its content is less than 30%, then it is necessary to determine the fluidity index for it I L;
5. Sampling of soil
To begin with, it is important to choose the right foundation depth - it will either be a foundation depth below the calculated depth of soil freezing, or a shallow foundation that is doomed in advance to distortions from heaving and is adapted to this. The issue of choosing the foundation depth is described in detail In this article.
After you have decided on the depth of the foundation, you need to make a pit or foundation pit (vertical mining excavation with a square, round or rectangular cross-section, of small depth)
Photo. Example of a pit/pit for taking soil samples
or, more simply put, dig a hole to a depth of 0.5-1.5 meters greater than the depth of the future foundation (you can dig using a cheap work force). The dimensions of the pit in plan can be made minimal, such that it is only possible to work with a shovel and the walls are vertical (this is safe only at a depth of no more than 2 m, then look at the circumstances) or stepped - stepwise reducing the pit with depth.
After digging a pit, layers of soil will be visible on its walls and it will be possible to determine their thickness. But most of all we are interested in the soil at a depth equal to the depth of the foundation and just below it - we take samples of the soil from there, if possible with an undisturbed structure (without loosening it).
Soil samples should be taken at a depth equal to the depth of the foundation and then take several more samples in increments of 20-50 cm in depth. Minimum number of samples – 3 pcs. Weight of samples of damaged structure (according to GOST 12071-2014):
- 1.5-2.0 kg - for clay soils;
- 2.0-3.0 kg - for sand;
- 3.0-5.0 kg - for coarse soils.
Monoliths (samples of undisturbed structure) of cohesive (clayey) soils are usually selected in the form of a cube with a side of 10-20 cm using a knife, shovel, etc. Monoliths from sandy soils are collected into thin-walled steel pipes with a diameter of 100-200 mm. The pipe is immersed by placing it, without much effort, on a column of soil, trimmed from the edges at the bottom of the pipe.
It is also very important to know whether there is groundwater at these depths. Groundwater does not appear immediately - you need to wait 30-60 minutes. If groundwater appears, it is necessary to accurately measure the depth from the surface of the earth to the water surface.
Photo. Groundwater in the pit
6. We determine the characteristics of dispersed soil independently without a laboratory
After taking soil samples (samples), you will have to tinker with them - you need to perform the following manipulations and experiments:
- Take a little soil from the sample and examine it visually (you can use a magnifying glass) and by touch (rubbing it in your palms) and first classify it as either sandy or clayey using the table below;
- Gradually moisten the sample to a plastic state (if the soil is saturated with water and looks like liquid mud, you need to dry it a little) and clarify the type of soil using the method of rolling into a cord (last column of the table):
| Type of soil | Rubbing on the palm | Visual cues | Plasticity (rolling into a cord) |
|---|---|---|---|
| Clay | When rubbed in a wet state, sand particles are not felt. Lumps are difficult to crush. Very sticky when wet | Homogeneous fine powder, almost no sand particles | It rolls into a tourniquet, the tourniquet easily rolls up into a ring. When squeezing the ball, a cake is formed without cracking at the edges |
| Loam | Sand particles are present when rubbed, but little is felt. Lumps are crushed more easily | Fine clay particles predominate fine sand particles 15 – 30% | When rolled out, a rope is obtained; when rolled into a ring, the rope breaks into pieces. When squeezing the ball, a cake is formed with cracks along the edges |
| Sandy loam | Small sandy particles predominate; for silty sandy loam, the appearance of dry flour may appear. Lumps crush easily | Fine sand particles predominate with a small admixture of clay particles | When you try to roll the tourniquet breaks into small pieces. It is impossible to roll the tourniquet into a ring. It rolls into a ball, but when squeezed, it crumbles |
| Sand | Separate grains of sand are distinctly felt. Almost no lumps are formed | Consists almost entirely of sand particles | Does not roll into a tourniquet and the ball - crumbles into small particles |
[Dust particles are particles with a size of 0.05...0.001 mm, clay particles with a size of less than 0.001 mm, sand particles with a size of more than 0.05 to 2 mm.]
Further if you determine that the soil is sand it is necessary to determine its grain composition. You can most likely identify gravelly sand or coarse soil immediately by appearance and the presence of large stones.
Photo. Sandy soil
Let's check the granular composition of the sand. Let's use GOST 8735-88 “Sand for construction work. Test methods". To do this, a soil sample weighing 2 kg is completely dried (according to GOST in a drying cabinet, but we dry it indoors at room temperature).
We will need standard sieves with holes size 0.5; 0.25 and 0.1 mm (sieve No. 063; 0315; 016) and as accurate a scale as possible (kitchen scales are possible, laboratory scales are preferable).
Laboratory sieves
Procedure:
- We weigh the original soil sample - it should be at least 2 kg. We record the readings.
- We first sift the soil through a sieve with a hole. 0.5 mm. We weigh the residue on the sieve and compare it with the initial weight of the sample - if the weight of the residue is more than half (> the sand is coarse
- If the result is less than 50%, we sift that part of the soil that passed through a sieve with 0.5 mm holes on a sieve with 0.25 mm holes. Weigh the residue and add the resulting mass with the mass of the residue on a 0.5 mm sieve. We obtain the total mass of the residue on a 0.25 mm sieve and compare it with the mass of the initial sample - if the mass of the residue is more than half (>50%) of the total initial mass of the sample, then the sand is average, the test need not be continued;
- If again it turns out to be less than 50%, we sift that part of the soil that passed through a sieve with 0.25 mm holes on a sieve with 0.1 mm holes. We weigh the residue and add the resulting mass with the mass of the residue on sieves 0.25 and 0.5 mm. We obtain the total mass of the residue on a 0.1 mm sieve and compare it with the mass of the initial sample - if the mass of the residue is more than 75% of the total initial mass of the sample, the sand is fine, if the result is less than 75% the sand is dusty. That's all for the grain composition.
Now consider the case when the soil turned out to be clayey(such cases will be the majority). In this case, we have already identified loam, clay or sandy loam in front of us using the table above:
Photo. Soil - clay
Photo. Soil - sandy loam
and now it is necessary to determine the soil fluidity index I L(consistency) in its natural state, that is, at the humidity it had before sampling (natural humidity).
Because It is quite difficult to accurately determine the fluidity index without laboratory equipment (it is necessary to accurately determine soil moisture in three states, in dry conditions - after calcining the soil at a temperature of 105 ° C), then you will have to determine this indicator approximately by indirect signs using the table:
| Clay consistency soil | Indirect signs of the condition | Flow rate J L |
|---|---|---|
| Sandy loam | ||
| Solid | Breaks into pieces on impact. When rubbed dusty, breaks into pieces | J L |
| Plastic | Easily kneads, retains its shape, feels wet, sometimes sticky | 0 ≤ J L ≤ 1.00 |
| fluid | Easy to deform and spread when you press | J L > 1.00 |
| Loam and clay | ||
| Solid | Breaks into pieces on impact crumbles when squeezed in the palm of your hand, dusty when rubbed, blunt end pencil is pressed in with difficulty | J L |
| Semi-solid | Breaks without noticeable bending, the surface fracture - rough, when kneading crumbles, the blunt end of the pencil leaves shallow mark and is pressed in when pressing hard | 0 ≤ J L ≤ 0.25 |
| Tight-plastic | The soil block bends noticeably, without breaking. A piece of soil is kneading with labor. Blunt end of pencil presses in without much effort | 0,25 |
| Soft-plastic | Moist to the touch, easy to knead, retains its given shape, but sometimes for a short time, finger pressed in a few centimeters | 0,50 |
| Fluid-plastic | Very wet to the touch, kneading with light pressure, when forming does not retain its shape, does not roll out into tourniquet because too fluid, too much sticks | 0,75 |
| fluid | Flows down an inclined plane thick layer (tongue), similar in behavior to very viscous liquid | J L > 1.00 |
For reliability, it is better to take from the table I L at the upper limit of the range in the last column, but the average value of the range can also be taken.
Porosity coefficient e, e. for both sandy and clayey soils is determined in the same way; determined by its formula:
e = P s / P d,
Where ps- density of soil particles, g/cm3;
p d- density of dry soil, g/cm3.
Particle Density P s practically does not change for all soils and is taken according to the table:
Dry soil density Pd(density of the soil skeleton) is determined in the following way:
- We take a soil sample of an undisturbed structure of a known volume of about 100 cm3. This can be done by carefully cutting out, for example, a 5x5x5 cm cube, or a rectangular parallelepiped - then the volume is calculated with a ruler and a calculator, or you can press a piece of pipe to a certain depth. Fixing the volume Vabout. We weigh the sample and record its mass m– from it we can determine the natural density of the soil P=m/ Vabout.;
- Then place the sample in an open plastic bag and dry it in air in a dry room, it is better to loosen it to speed up the process (In general, the soil needs to be calcined at a temperature of 105 degrees to an air-dry state to remove bound water);
- After drying the sample, weigh it on an electronic scale - we obtain the mass of the dry sample m s;
- We calculate the density of the soil skeleton using the formula: P d =m s / Vabout.
- Let's return to calculating the porosity coefficient e = P s / P d,.
Now, based on the data obtained, we can, using tables 26..28 and 45..50, determine all the physical and mechanical characteristics necessary for calculating the stability of the foundation base and its settlement:
s p, φ n, deg, and deformation modulus E, MPa (kgf/cm2), sandy soils of Quaternary deposits.
Standard values of specific adhesion s p, kPa (kgf/cm 2), angle of internal friction φ n , hail, silty-clayey non-loess soils of Quaternary deposits
Standard values of the deformation modulus of silty-clayey non-loess soils
Notes on tables:
- For soils with intermediate values e, against those indicated in the tables, it is allowed to determine the values with n, φn And E by interpolation.
- If the values e, I L, And S r soils exceed the limits specified in the tables, characteristics s p, φ n And E should be determined based on direct testing of these soils.
- It is allowed to take into account the characteristics as a safety margin c p, φ n And E according to the corresponding lower limits e, I L And S r tables, if soils matter e, I L And S r less than these lower limits.
You can also use for preliminary calculations tabular values of calculated soil resistance R 0 , then you don’t have to calculate it using the formula, but you can lose a lot in accuracy:
Preliminary dimensions of foundations should be assigned for structural reasons or based on tabulated values of the calculated resistance of foundation soils R 0 according to the tables. Values R 0 can also be used for the final determination of the dimensions of the foundations of buildings and structures of class III, if the base is composed of horizontal (slope no more than 0.1) layers of soil maintained in thickness, the compressibility of which does not increase within a depth equal to double width the largest foundation, counting from its base.
When using values R 0 for the final assignment of foundation dimensions pp. design soil resistance of the foundation R, kPa (kgf/cm2), determined by the formulas:
at d ≤ 2 m (200 cm)
R = R0 · · ( d+d 0) / 2d 0 ;
at d> 2 m (200 cm)
R = R0 · +k 2g ‘ II ( d - d 0),
Where b And d- respectively the width and depth of the designed foundation, m (cm); g ‘ II - calculated value specific gravity soil located above the base of the foundation, kN/m 3 (kgf/cm 3); k 1 - coefficient accepted for foundations composed of coarse and sandy soils, except for silty sands, k 1 = 0.125, silty sands, sandy loams, loams and clays k 1 = 0,05; k 2 - coefficient accepted for foundations composed of coarse and sandy soils, k 2 = 0.25, sandy loam and loam k 2 = 0.2 and clays k 2 = 0,15.
Note. For buildings with a basement width IN≤ 20 m and depth d b³ 2 m, the depth of external and internal foundations taken into account in the calculation is taken equal to: d = d 1 + 2 m (here d 1 - reduced depth of foundation, determined by formula (34 (8)) of these standards). At B> 20 m accepted d = d 1 .
Calculated resistances R0 coarse soils
Calculated resistances R 0 sandy soils
Calculated resistances R 0 silt-clay (non-subsidence) soils
Calculated resistances R 0 bulk soils
Notes: 1. Values R 0 in this table refer to bulk soils containing organic matter I from ≤ 0,1.
- 2. For unpacked dumps and landfills of soil and industrial waste, the values R 0 are accepted with a coefficient of 0.8.
The degree of soil heaving can be determined from the table in the article
7. Conclusion
In conclusion, I note once again that in order to design the most correct, reliable and at the same time economical foundation, accurate information about the soils at the base of the future building is necessary.
If you decide to build without geotechnical surveys, then using the materials in this article you can at least approximately determine the characteristics of the soil by visual and indirect signs using tables of normative literature.
[without laboratory research it will not be possible to determine such important soil properties as: subsidence, swelling, aggressiveness to concrete and steel, etc.]
The article discusses the sequence of actions that allows you to obtain the soil characteristics required for foundation calculations, starting from sampling and ending with extracting data from the tables yourself.
It would also be useful to study, for example, tutorial" " - a lot of useful information on this topic.
8. Related Articles
- Expanded soil classification
- Special ground conditions - permafrost
- Special ground conditions – rocky soils
- Collection of loads on foundations, floors, columns and other structures
- Calculations of columnar and strip foundations for vertical compressive load
Ground (German Grund - base, soil)- rocks, soils, technogenic formations, which represent a multicomponent and diverse geological system and are the object of human engineering and economic activity.
V - category- Strong clay shale. Weak sandstone and limestone. Soft conglomerate. Permafrost seasonally freezing soils: sandy loams, loams and clays with an admixture of gravel, pebbles, crushed stone and boulders up to 10% by volume, as well as moraine soils and river sediments containing large pebbles and boulders up to 30% by volume.
VI - category- Shales are strong. Clay sandstone and weak marly limestone. Soft dolomite and medium serpentine. Permafrost seasonally freezing soils: sandy loams, loams and clays with an admixture of gravel, pebbles, crushed stone and boulders up to 10% by volume, as well as moraine soils and river sediments containing large pebbles and boulders up to 50% by volume
VII - category- Silicified and mica shales. Sandstone is a dense and hard marly limestone. Dense dolomite and strong coil. Marble. Permafrost seasonally freezing soils: moraine soils and river sediments containing large pebbles and boulders up to 70% by volume.
Types of soil
Quicksands- contain small clay or sand particles diluted with water. The degree of buoyancy is determined by the amount of water in the soil.
Loose soils (sand, gravel, crushed stone, pebbles) consist of loosely interconnected particles of different sizes.
Peat bogs- a biological object, an ecosystem, including a complex of plants and their remains that form an interdependent community under conditions of high humidity. The highest type of existence of living organisms, similar coral reefs, forested areas and urban cities.
Soft soils- contain loosely interconnected particles of earthen rocks (clayey or sandy-clayey)
Weak soils (gypsum, shales, etc.) consist of loosely interconnected particles of porous rocks.
Medium soils- (dense limestones, dense shales, sandstones, calcareous spar) consist of interconnected particles of rocks of medium hardness.
Hard soils- (dense limestones, quartz rocks, feldspars, etc.) contain interconnected rock particles of great hardness.
It is easy to mine quicksand, loose, soft and weak soils, but they require constant strengthening of the shaft walls with wooden panels with spacers. Medium and hard soils are more difficult to develop, but they do not crumble and do not require additional support.
Asphalt(from Greek άσφαλτος - mountain resin) - a mixture of bitumen (60-75% in natural asphalt, 13-60% in artificial asphalt) with mineral materials: gravel and sand (crushed stone or gravel, sand and mineral powder in artificial asphalt). They are used for coatings on roads, as a roofing, hydro and electrical insulating material, for the preparation of putties, adhesives, varnishes, etc. Asphalt can be of natural and artificial origin. Often the word asphalt refers to asphalt concrete - an artificial stone material, which is obtained as a result of compaction of asphalt concrete mixtures. Classical asphalt concrete consists of crushed stone, sand, mineral powder (filler) and bituminous binder (bitumen, polymer-bitumen binder; tar was previously used, but it is not currently used). For the destruction (cutting) of asphalt pavements, there is such equipment for rent as
Table 1
|
Name of soils (rocks) and minerals |
Soil group |
Strength coefficient according to the professional scale. M. M. Protodyakonova |
|
Fine-grained, unweathered igneous rocks of exceptional strength (diabase, gabbro, diorites, jaspilites, porphyrites, etc.) and fine-grained, unweathered metamorphic rocks of exceptional strength (quartzites, etc.), confluent quartz, titanium-magnetite ores | ||
|
Igneous rocks, fine-grained, unweathered, very strong (diabases, diorites, basalts, granites, andesites, etc.) and metamorphic rocks, fine-grained, unweathered, very strong (quartzites, hornfelses, etc.) |
19 > f ³ 17 |
|
|
Flint, quartzite sandstones, unweathered limestones of exceptional strength, fine-grained magnetite and magnetite-hematite iron ores |
17 > f ³ 15 |
|
|
Igneous rocks, medium-grained, unweathered and weakly weathered, strong (granites, diabases, syenites, porphyrites, trachytes, etc.) and metamorphic rocks, medium-grained, unweathered, strong (quartzites, gneisses, amphibolites, etc.) |
15 > f ³ 12 |
|
|
Fine-grained silicified sandstones, limestones and dolomites are very strong, marbles are very strong, siliceous shales, quartzites with noticeable schistosity, silicified brown ironstones, fine-grained lead-zinc and antimony ores with quartz, strong copper-nickel, magnetite and hermatite ores |
12 > f ³ 10 |
|
|
Conglomerates and breccias strong on lime cement, dolomites and limestones strong, sandstones strong on quartz cement, pyrites, martite-magnetite ores, coarse-grained magnetite-hematite ferruginous ores, brown ironstones, chromite ores, porphyry copper ores |
10 > f ³ 8 |
|
|
Igneous rocks, coarse-grained, unweathered and slightly weathered (granites, syenites, serpentines, etc.) and metamorphic rocks, coarse-grained, unweathered (quartz-chlorite schists, etc.) |
8 > f ³ 7 |
|
|
Strong mudstones and siltstones, weathered igneous rocks (granites, syenites, diorites, serpentines, etc.) and weathered metamorphic rocks (shales, etc.), unweathered limestones of medium strength, siderites, magnesites, martite ores, copper pyrites, mercury ores, quartz polymetallic ores (pyrites, galenas, chalcopyrites, pyroxenes), chromite ores in serpentinites, apatite-nipheline ores, durable bauxites |
7 > f ³ 5 |
|
|
Lightly weathered limestones and dolomites of medium strength, sandstones on clay cement, medium-grained weathered metamorphic rocks (mica shales, etc.), brown ironstones, clay-grained ores, anhydrites, coarse-grained sulfide lead-zinc ores |
5 > f ³ 4 |
|
|
Weathered limestones and dolomites of medium strength, marl of medium strength, coarse-grained metamorphic rocks of medium strength (clayey, carbonaceous, sandy and talc shales), pumice, tuff, limonites, conglomerates and breccias with pebbles from sedimentary rocks on limestone-clay cement |
4 > f ³ 3 |
|
|
Anthracites, strong hard coals, conglomerates and sandstones of medium strength, siltstones and mudstones of medium strength, unweathered opokas of medium strength, malachites, azurites, calcites, weathered tuffs, strong rock salt |
3 > f ³ 2 |
|
|
Low-strength mudstones and siltstones, medium-strength weathered opoka, low-strength weathered limestones and dolomites, boulder soils, medium-strength hard coal, strong brown coal |
2 > f ³ 1.5 |
|
|
Hard carbonate clays, dense chalk, gypsum, low-strength chalk-like rocks, weakly cemented shell rock, gravel, pebble, gruss and crushed stone soils with boulders. Coal soft, hardened loess, brown coal, tripoli, soft rock salt, hard and semi-solid clays and loams, content up to 10% pebbles, gravel or crushed stone |
1.5 > f ³ 1 |
|
|
Clays and loams without admixtures of pebbles, gravel or crushed stone, hard- and soft-plastic, pebbly, gravel, dense crushed soils, gravelly sands, soils with roots and with impurities, compacted slag |
1 > f ³ 9 |
|
|
Sands, plant layer soils without roots and impurities, peat without roots, dolomite flour, loose slag, loose gravel, pebble, gruss and crushed stone soils, compacted construction waste |
0.9 > f ³ 0.5 |
|
|
Loose limestone tuffs, loess, loess-like loams, sandy loams and sand without impurities or with an admixture of crushed stone, gravel or construction waste. Quicksand sands |
0.5 > f ³ 0.4 |
Notes:
1. Soils (rocks) should be classified into one group or another according to the value of the rock strength coefficient on the professional scale. M. M. Protodyakonova.
2. This classification does not apply to frozen soils.
9. The prices assume the duration of work shifts given in table. 2 this technical part.
10. The prices in this collection include the cost of operating machines and mechanisms that consume electricity and compressed air from stationary installations. When receiving electricity and compressed air from mobile units (before putting stationary units into operation), the number of machine-hours of PES and compressors is determined by the POS.
11. The costs of transport over the surface of developed soils, including unloading them on a dump and maintaining the dump, are not taken into account in the prices of this collection; these costs should be determined additionally.
The mass and volume of developed soil are determined by technical parts relevant sections of the collection.
12. In the prices of the collection tables, in which the consumption of reinforcement is indicated with the letter “P” (according to the project), the consumption and cost of reinforcement are not taken into account.
When drawing up estimates, the consumption of reinforcement and the class of steel should be taken according to design data based on the total mass of all types of reinforcement (frames, meshes, individual rods) without adjusting the labor costs of construction workers and machines and mechanisms for its installation.
13. The “up to” size indicated in this collection includes this size.
Soils play an important role in the process of calculations and design of foundation construction for various construction projects. This is due to natural reasons: different kinds soils behave differently in certain weather conditions and with seasonal temperature changes, and have special characteristics.
The durability and reliability of the foundation depends on the physical characteristics of the soil.
The stability and reliability of the foundation depends on the physical characteristics of the soil, which must be taken into account during the construction of the foundation.
Particular attention is paid to cohesion, homogeneity, moisture holding capacity, water resistance, and solubility of the soil mass. The coefficients of friction, loosening, plasticity and compressibility are considered separately. There are main types of soil:
- clay;
- dusty;
- sandy;
- rocky;
- clastic.
The density indicators and loosening coefficients necessary to carry out the appropriate calculations for each type of soil are given in the table.
Clay soils
Clay soil is the result of physical decomposition and mechanical breakdown of rocks.
Clay soils are one of the most problematic for construction. They have all the negative properties that complicate the construction process: they freeze, erode, swell, and have high subsidence. When building on such a foundation, it is necessary to carry out scrupulous and accurate calculations during the construction of the foundation.
Clay soil is a product of chemical decomposition and mechanical breakdown of rocks. It has scaly and fine-grained fractions, which makes it viscous and capable of deforming when wet without cracking under the influence of load. As humidity decreases, the cohesion of such soils also decreases. Based on consistency, they are divided into the following types:
- hard;
- fluid;
- plastic.
When constructing a foundation, it is necessary to take into account the magnitude of the load of the structure on the ground. It must be laid to the maximum freezing depth. The exception is dry clay soils.
Clayey types of soil are subject to settlement resulting from the weight of the foundation, and this process occurs over a long period of time - over several years. The stronger its porosity, the longer and more sediment there will be.
Return to contents
Dusty soils
Silty soil has the disadvantage that it turns into slurry when it becomes saturated with water.
Construction on this type of soil is not recommended. This type soil has a bad feature: it turns into slurry when it is saturated with water, and accordingly, its behavior is difficult to predict. It is silty sand, which is flooded by groundwater.
Silty soil has different origins. It can be sedimentary, which formed at the site of weathering, or transported and deposited elsewhere. This type also includes silts, which are water-saturated modern sediments of reservoirs formed as a result of microbiological processes.
But despite this, there are certain technologies that make it possible to build a foundation in such terrain. Such a process is quite expensive, and no one can give exact guarantees that a foundation made in accordance with all the rules will not settle in 5-10 years. The construction of structures on floating floats is only possible with the work of experienced builders. Still, you should think carefully and evaluate all the advantages and disadvantages before starting to build a building.
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Sandy soils
Sandy soil is waterproof, which makes it more durable and of higher quality.
Sands, which are stable large fractions, are the most convenient types of soil for successful construction. They are easy to develop, they are well compacted due to the load, and with a uniform and dense layer, they are an ideal basis for constructing a foundation. During the construction process, it is necessary to take into account that large sand particles can bear a large load. freezes little, and this fact has a slight effect on its properties.
This type of soil consists of particles whose sizes do not exceed 2 mm, but not less than 0.1 mm. Sandy soil has good water resistance, which makes it more durable and reliable. Therefore, even in winter, it will not bulge outward from the depths. Before you start laying the foundation, you need to take into account that groundwater is at a lower level in winter than in the warm season. The depth of laying the foundation depends on this factor, which is recommended to be done at a depth of 50 to 70 cm.
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