Clay soils. Modern problems of science and education Type of foundation from the ground
]: rocky (soils with rigid bonds) and non-rocky (soils without rigid bonds).
GOST 25100-95 Soils. Classification
In the class of rocky soils, igneous, metamorphic and sedimentary rocks, which are subdivided by strength, softening and solubility in accordance with the table. 1.4. Rocky soils, the strength of which in a water-saturated state is less than 5 MPa (semi-rocky), include clay shales, sandstones with clay cement, siltstones, mudstones, marls, and chalks. With water saturation, the strength of these soils can decrease by 2-3 times. In addition, in the class of rocky soils, artificial soils are also distinguished - fissured rocky and non-rocky soils fixed in their natural occurrence.
TABLE 1.4. CLASSIFICATION OF ROCK SOILS
| Priming | Index |
| According to the ultimate strength for uniaxial compression in a water-saturated state, MPa | |
| Very durable | Rc > 120 |
| Lasting | 120 ≥ Rc > 50 |
| Medium strength | 50 ≥ Rc > 15 |
| low-strength | 15 ≥ Rc > 5 |
| Reduced strength | 5 ≥ Rc > 3 |
| low strength | 3 ≥ Rc ≥ 1 |
| Very low strength | Rc < 1 |
| According to the coefficient of softening in water | |
| Non-softening | K saf ≥ 0,75 |
| softenable | K saf < 0,75 |
| By the degree of solubility in water (sedimentary cemented), g / l | |
| Insoluble | Solubility less than 0.01 |
| sparingly soluble | Solubility 0.01-1 |
| Medium soluble | - || - 1—10 |
| Easily soluble | - || - more than 10 |
These soils are subdivided according to the method of fixing (cementing, silicification, bitumization, resinization, firing, etc.) and according to the uniaxial compressive strength after fixing, just like rocky soils (see Table 1.4).
Non-rocky soils are divided into coarse-clastic, sandy, silty-argillaceous, biogenic and soils.
Coarse-clastic soils include non-consolidated soils in which the mass of fragments larger than 2 mm is 50% or more. Sandy soils are soils containing less than 50% of particles larger than 2 mm and not possessing the property of plasticity (plasticity number I p < 1 %).
TABLE 1.5. CLASSIFICATION OF LARGE-CLASTIC AND SANDY SOILS ACCORDING TO GRANULOMETRIC COMPOSITION
Coarse-clastic and sandy soils are classified according to their granulometric composition (Table 1.5) and the degree of moisture (Table 1.6).
TABLE 1.6. DIVISION OF LARGE CLASSIC AND SANDY SOILS BY THE DEGREE OF HUMIDITY S r
The properties of coarse-grained soil with a sand aggregate content of more than 40% and a silt-clay aggregate of more than 30% are determined by the properties of the aggregate and can be established by testing the aggregate. With a lower aggregate content, the properties of coarse soil are determined by testing the soil as a whole. When determining the properties of sand filler, the following characteristics are taken into account - moisture content, density, porosity coefficient, and dusty-clay filler - additionally the number of plasticity and consistency.
The main indicator of sandy soils, which determines their strength and deformation properties, is the bulk density. According to the density of addition, sands are subdivided according to the porosity coefficient e, soil resistivity during static sounding q with and conditional soil resistance during dynamic sounding q d(Table 1.7).
With a relative content of organic matter of 0.03< I from≤ 0.1 sandy soils are called soils with an admixture of organic matter. According to the degree of salinity, coarse-grained and sandy soils are divided into non-saline and saline. Coarse clastic soils are saline if the total content of easily and medium soluble salts (% of the mass of absolutely dry soil) is equal to or more than:
- - 2% - when the content of sand aggregate is less than 40% or dusty-clay aggregate is less than 30%;
- - 0.5% - with a sand aggregate content of 40% or more;
- - 5% - with a content of silt-clay filler of 30% or more.
Sandy soils are classified as saline if the total content of these salts is 0.5% or more.
Dusty clay soils are subdivided according to the number of plasticity Ip(Table 1.8) and according to the consistency, characterized by the fluidity index I L(Table 1.9).
TABLE 1.7. DIVISION OF SANDY SOILS BY BODY DENSITY
| Sand | Addition Density Subdivision | ||
| dense | medium density | loose | |
| According to the coefficient of porosity | |||
| Gravelly, large and medium size | e < 0,55 | 0,55 ≤ e ≤ 0,7 | e > 0,7 |
| Small | e < 0,6 | 0,6 ≤ e ≤ 0,75 | e > 0,75 |
| dusty | e < 0,6 | 0,6 ≤ e ≤ 0,8 | e > 0,8 |
| According to soil resistivity, MPa, under the tip (cone) of the probe during static sounding | |||
| qc > 15 | 15 ≥ qc ≥ 5 | qc < 5 | |
| Fine regardless of humidity | qc > 12 | 12 ≥ qc ≥ 4 | qc < 4 |
| Dusty: damp and wet water-saturated |
qc > 10 qc > 7 |
10 ≥ qc ≥ 3 7 ≥ qc ≥ 2 |
qc < 3 qc < 2 |
| According to the conditional dynamic soil resistance MPa, probe immersion during dynamic sounding | |||
| Large and medium size regardless of humidity | q d > 12,5 | 12,5 ≥ q d ≥ 3,5 | q d < 3,5 |
| Small: damp and wet water-saturated |
q d > 11 q d > 8,5 |
11 ≥ q d ≥ 3 8,5 ≥ q d ≥ 2 |
q d < 3 q d < 2 |
| Dusty low-moisture and damp | q d > 8,8 | 8,5 ≥ q d ≥ 2 | q d < 2 |
TABLE 1.8. DIVISION OF SILTY-CLAY SOILS BY THE NUMBER OF PLASTICITY
Among the silty-clay soils, it is necessary to distinguish loess soils and silts. Loess soils are macroporous soils containing calcium carbonates and capable of sagging under load when soaked in water, easy to soak and erode. Silt is a water-saturated modern sediment of reservoirs, formed as a result of microbiological processes, having a moisture content exceeding the moisture content at the yield line, and a porosity coefficient, the values of which are given in Table. 1.10.
TABLE 1.9. DIVISION OF SILTY-CLAY SOILS ACCORDING TO THE FLOW INDICATOR
TABLE 1.10. SILT DIVISION BY POROSITY COEFFICIENT
Silty clay soils (sandy loam, loam and clay) are called soils with an admixture of organic substances with a relative content of these substances of 0.05< I from≤ 0.1. According to the degree of salinity, sandy loam, loam and clay are divided into uninhabited and saline. Saline soils include soils in which the total content of easily and moderately soluble salts is 5% or more.
Among silty clay soils, it is necessary to single out soils that exhibit specific unfavorable properties during soaking: subsidence and swelling. Subsiding soils include soils that, under the action of an external load or their own weight, when soaked with water, give a sediment (subsidence), and at the same time, the relative subsidence εsl≥ 0.01. Swelling soils include soils that, when soaked with water or chemical solutions, increase in volume, and at the same time, relative swelling without load ε sw ≥ 0,04.
In a special group in non-rocky soils, soils are distinguished that are characterized by a significant content of organic matter: biogenic (lake, marsh, alluvial-marsh). The composition of these soils includes peaty soils, peat and sapropels. Peaty soils include sandy and silty clay soils containing 10–50% (by weight) of organic matter in their composition. When the content of organic matter is 50% or more, the soil is called peat. Sapropels (Table 1.11) are freshwater silts containing more than 10% organic matter and having a porosity coefficient, as a rule, more than 3, and a flow index more than 1.
TABLE 1.11. DIVISION OF SAPROELS BY RELATIVE CONTENT OF ORGANIC MATTER
Soils are natural formations that make up the surface layer of the earth's crust and are fertile. Soils are subdivided according to their granulometric composition in the same way as coarse and sandy soils, and according to the number of plasticity, like silty clay soils.
Non-rocky artificial soils include soils compacted in natural occurrence. various methods(tamping, rolling, vibrocompaction, explosions, drainage, etc.), bulk and alluvial. These soils are subdivided according to the composition and characteristics of the state in the same way as natural non-rock soils.
Rocky and non-rocky soils with negative temperature and containing ice in their composition, refer to frozen soils, and if they are in a frozen state for 3 years or more, then to permafrost.
5. Sandy soils consist of particles of grains of quartz and other minerals with a particle size of 0.1 to 2 mm, containing no more than 3% clay and do not have the property of plasticity. Sands are divided according to the grain composition and the size of the prevailing 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 there are from 15 to 50% of such particles in the sand, then they are classified as dusty . When there are more dusty particles in the soil than sandy particles, the soil is called dusty .
The larger and cleaner the sands, the greater the load the base layer from it can withstand. The compressibility of dense sand is low, but the rate of compaction under load is significant, so the settlement of structures on such foundations quickly stops. Sands do not have the property of plasticity.
gravelly, large And medium size sands are significantly compacted under load, slightly freeze.
The type of coarse-grained and sandy soils is determined by the granulometric composition, the variety - by the degree of moisture.
clayey - cohesive soils, consisting of particles with a particle size of less than 0.005 mm, which are mainly scaly in shape, with a small admixture of fine sand particles. Unlike sands, clays have thin capillaries and a large specific surface area of contact between particles. Since the pores of clay soils are in most cases filled with water, when the clay freezes, it swells.
Clay soils are divided depending on the plasticity number into clay (with a content of clay particles over 30%), loams (10...30%) and sandy loam (Z...10%).
The bearing capacity of clay bases depends on moisture, which determines the consistency of clay soils. Dry clay can withstand a fairly large load.
The type of clay soil depends on the plasticity number, the variety depends on the fluidity index.
Classification of soils by particle size.
6. According to the size of the mineral particles of the soil, their mutual connection and mechanical strength, the soils are divided into five classes: rocky, semi-rocky, coarse-grained, sandy (non-cohesive) and clay (cohesive).
TO rocky ground include cemented waterproof and practically incompressible rocks (granites, sandstones, limestones, etc.), which usually occur in the form of continuous or fractured massifs.
TO semi-rocky soils include cemented rocks capable of compaction (marls, siltstones, mudstones, etc.) and non-water resistant (gypsum, gypsum-bearing conglomerates).
Coarse clastic soils consist of unconsolidated pieces of rock and semi-rock; usually contain more than 50% of rock fragments larger than 2 mm.
sandy soils consist of unconsolidated rock particles with a size of 0.05 ... 2 mm; are, as a rule, naturally destroyed and transformed to varying degrees of rocky soils; do not have plasticity.
Clay soils are also a product of natural destruction and transformation of primary rocks, constituting rocky soils, but with a predominant particle size of less than 0.005 mm.
Classification of sandy soils according to the degree of moisture.
7. LARGE CLASSIC AND SANDY SOILS ARE SEPARATED BY THE DEGREE OF HUMIDITY.
Plasticity number and fluidity index of silty clay soil.
For silty clay soils, it is not the general grain (granulometric) composition that is of paramount importance, but the content of fine and smallest particles (flat-scaly or fine needle-like monomineral particles with a size of at least 0.005 mm) and, most importantly, the range of humidity in which the soil will be plastic.
This humidity range is characterized by the so-called plasticity number J P and is equal to the difference between two moisture content corresponding to two states of the soil: at the yield boundary W L and at the border of rolling (plasticity) WP:
J P \u003d W L - W P.
Yield limit W L corresponds to the humidity at which the soil passes into a fluid state, and the rolling boundary W P- humidity at which the soil loses its plasticity.
Depending on the plasticity number, three types of silty clay soils are distinguished: sandy loam,loam And clay(Table 2 GOST 25100-82).
Characteristic humidity quite well determines the physical state of silt-clay soils, which, depending on the water content, varies significantly and can be solid, plastic, and fluid. The characteristic of the state is the consistency, which refers to the density and, to a certain extent, the viscosity of clay soils, which determine their ability to resist plastic shape change. The numerical characteristic of the consistency is the fluidity index - J L, which defines the expression
Where W- soil moisture in its natural state.
A variety of silty clay soils in terms of fluidity is determined according to table 2 of GOST 25100-82.
The yield index is used when choosing the depth of foundations, determining the conditional design pressure on the foundation soils according to the tables of SNiP and in other cases.
Necessary equipment and materials:
o soil (dry and wet);
o desiccator, spatula (knife);
o a flask with water, bottles - 2 pcs;
o balance cone;
o a standard metal cup with a stand;
o technical vaseline, cup;
o scales with weights.
The soil sample was dried to an air-dry state, crushed in a porcelain mortar with a pestle with a rubber tip and sifted through a sieve with holes. 1 mm. Part of the soil was moistened with water to the state of a thick dough while stirring with a spatula and kept in a desiccator for at least 2 hours for even distribution of moisture.
Determination of the yield point
The yield point is characterized by the moisture content (in fractions of a unit) of the soil test, at which the standard cone is immersed in it under its own weight to a depth 10 mm behind 5 second. The determination of the yield limit consists in the selection of such soil moisture.
Balance cone (Fig. 3) with apex angle 30 °С has at a distance 10 mm from the tip to a circular risk. A balancing device is attached to the base of the cone in the form of two metal weights at the ends of a steel bar. The total weight of the device is 76 g.
Figure 3 - Instruments for determining the yield point
Progress:
1. The ground dough is thoroughly mixed with a spatula and placed in small portions (without voids) in a metal cup; the surface of the soil is leveled with a spatula to a level with the edges of the cup, which is then placed on a stand.
2. The tip of the cone, lubricated with a thin layer of petroleum jelly, is brought to the surface of the soil and lowered, allowing it to sink into the soil for 5 s under its own weight.
3. Immersion of the cone for 5 sec to a depth of less 10 mm indicates that the soil moisture has not yet reached the yield point. In this case, the ground dough is transferred to a cup and after adding water and thoroughly mixing, the experiment is repeated. If the cone sank deeper than 10 mm, you should add dry soil, mix it and repeat the experiment.
Building a house on silty clay soil has its own characteristics and requirements. In this article, you will learn about the types of silty clay soil, their features and the types of foundations that can be laid on this type of soil.
Dusty clay soils are heaving soils and can accumulate moisture. At low temperatures, moisture freezes (crystallizes) and turns into ice, increasing in volume. This process is called heaving force, which lifts houses, puts stress on the lower and side walls of the building, destroys poor-quality brickwork and base blocks. During the hot period, the heaving soil settles.
Types of silty clay soils:
- coarse sandy and fine sandy sandy loam (loose rocks).
- loam (soil with a predominant clay content and a significant amount of sand).
| No. p / p | Soil types | Contains particles, % | Plasticity number, Jp | Diameter of the unrolled cord from the ground, mm |
| 1 | Clay | >30 | >0,17 | <1 |
| 2 | Loam | <10% | 0.07 to 0.17 | 1-3 |
| 3 | sandy loam | from 10-30 | 0.01 to 0.07 | >3 |
| 4 | Sand | <30 | Not plastic | Doesn't roll out |
Note: Jp (plasticity number) is determined in the laboratory.
Clay particles are active components that have a scaly shape. They give the soil cohesion, plasticity, swelling, stickiness, water resistance.
The main differences between cohesive and non-cohesive soils
| Soil properties | Cohesive silty clay soils | Sands (non-porous materials) |
| W (natural soil moisture) fluctuates | from 3 to 600% | from 0 to 40% |
| Ground conditions | Hard, soft, fluid | bulk |
| Soil with rising W | Change their properties gradually, there is time to prevent an accident | Instant degradation |
| As it dries | settles | Does not shrink or crack |
| Soil compaction | Settling slowly (up to 3 years) | Deform immediately after application of a load |
| Water permeability | Virtually impenetrable | Permeable to moisture in all conditions |
Erection of structures on silty clay soil
Silty-clay soil is moisture-containing, exposed to low temperatures, increases in volume and raises foundation structures. The unevenness of the rise accumulates. Then, the structures are deformed and destroyed. Light low-rise premises on such soil suffer the most.
Expensive foundations (deep monolithic structures) are not cost-effective for the construction of low-rise buildings. It is possible to solve the issue of building a foundation on heaving soil using shallow foundations (immersion in the ground is 0.2-0.5 m) or shallow foundations (on the surface).
Unlike a deep foundation laid in heaving soil, shallow foundations are less susceptible to touching the ground. Non-buried foundations are completely protected from swelling.
Construction of shallow foundations
- Strip foundations of load-bearing walls and partitions are combined into a continuous horizontal frame that distributes loads.
- Columnar structures involve the formation of a frame of concrete beams, rigidly interconnected on supports.
If the silt-clay soil does not imply a high degree of swelling, then the foundation parts are installed freely, without connecting to each other.
Having cheap building materials (sand, gravel, crushed stone, ballast) or rocky soils near the construction of the foundation, it is advisable to make a sealing layer under the base with a thickness of 2/3 of the standard freezing height.
On soil with a freezing depth of up to 1.7 on easily erected foundations, small buildings can be built from the following building materials:
- tree;
- brick and stone;
- monolithic panels;
- reinforced concrete blocks.
The use of shallow structures reduces the consumption of concrete by 50-80%, labor costs - by 40-70%.
1. Mainland soil
2. Concrete pavement
3. Waterproofing layer (roofing material)
4. Capillary waterproofing (PE film)
5. Humus layer
6. Backfill
7. Backfill from ASG (sand gravel mixture)
8. Reinforced concrete foundation tape
9. Fittings
Drainage structure
- Point or linear drainage directed to the sewer. During the period of rains or thaw from the surface surrounding the building, water will not accumulate on the site.
- Deep drainage. The installation of an underground deep structure includes a water intake, a drainage well. Then they dig a trench under a closed collector that transfers water from pipes to a water intake.
- Along the perimeter of the object, concrete or asphalt pavements are installed, with a thickness of 1 m and a slope of 0.03.
In the process of waterproofing the foundation, installation of the water supply system input from the upland side of the room should not be carried out. During the operation of structures, do not change the conditions for the design of prefabricated foundations.
External vertical and horizontal insulation of a shallow foundation
- Tangent (lateral) insulation
The blind area (a strip around the perimeter of the structure, which has a durable waterproof surface) with insulation improves the temperature regime in the foundation area, protecting the building from temperature changes.
Thermal insulation is provided by sheets of extruded polystyrene foam (EPP) or sprayed with polyurethane foam.
- Horizontal insulation
Under the foundations, cushions compacting the soil with a thickness of 20-30 cm from coarse gravel sand, gravel or slag are organized. They replace clay soil with non-fluffy one. The latter option affects the reduction of uneven deformations of the building. The depth and height of the layer is calculated using formulas known to experienced technologists.
Dusty clay soils are heaving soils. Therefore, during seasonal changes, they affect the foundation of the building - raise the foundation or settle, destroying the structure. To build on this type of soil, slightly ruined strip and column foundations are used.
If the soil contains a sufficiently large amount of clay particles, then it is called clayey.
Clay soils
have the property of cohesion, which is expressed in the ability of the soil to maintain its shape due to the presence of clay particles.
If there are few clay particles (less than 10% by weight), the soil is called sandy loam
. sandy loam
has little cohesion and is often virtually indistinguishable from sand. Sandy loam is difficult to roll into a tourniquet or ball. If sandy loam
rub on a damp palm, then you can see sand particles, after shaking off the soil, traces of clay particles are visible on the palm. Lumps sandy loam when dry, they easily crumble and crumble on impact. sandy loam
non-plastic, sand particles predominate in it, almost do not roll into a bundle. A ball rolled from moistened soil crumbles under light pressure.
Soil, in which the content of clay particles reaches 30% by weight, is called loam
. Loam
has greater cohesion than sandy loam and is able to be preserved in large pieces without breaking up into small pieces. pieces sandy loam
when dry, they are less hard than clay. On impact, they break into small pieces. When wet, they have little plasticity. When grinding, sand particles are felt, lumps are crushed more easily, there are larger grains of sand against the background of finer sand. A tourniquet rolled out of damp soil turns out to be short. A ball rolled from moistened soil, when pressed, forms a cake with cracks along the edges.
When the content of clay particles in the soil is more than 30%, the soil is called clay
. Clay
has a lot of connectivity. Clay
in a dry state - hard, in a wet state - plastic, viscous, sticks to the fingers. When rubbing with fingers, sand particles are not felt, it is very difficult to crush lumps. If the piece is raw clay
cut with a knife, the cut has a smooth surface on which grains of sand are not visible. When squeezing a ball rolled from raw clay
, it turns out a cake, the edges of which do not have cracks.
Greatest impact on properties clay soils has the presence of clay particles; therefore, it is customary to classify soils according to the content of clay particles and the plasticity number. Plasticity number Ip
- moisture difference corresponding to two soil conditions: at the yield boundary W L and at the border of rolling W p , W L and W p is determined according to GOST 5180.
Table 1. Classification of clay soils according to the content of clay particles.
Most clay soils in natural conditions, depending on the water content in them, can be in a different state. The building standard (GOST 25100-95 Classification of soils) defines the classification of clay soils depending on their density and moisture content. The state of clay soils characterizes turnover rate I L
- the ratio of the difference in humidity corresponding to two states of the soil: natural W and at the border of rolling Wp, to the number of plasticity Ip. Table 2 shows the classification of clay soils in terms of fluidity.
Table 2. Classification of clay soils in terms of fluidity.
By granulometric composition and plasticity number Ip clay groups are subdivided according to table 3.
Table 3
| A variety of clay soils | Plasticity number Ip |
Content of sandy Particles (2-0.5mm), % by weight |
| Sandy loam: | ||
| - sandy | 1 — 7 | 50 |
| - dusty | 1 — 7 | < 50 |
| Loam: | ||
| - light sandy | 7 -12 | 40 |
| - light dusty | 7 – 12 | < 40 |
| - heavy sandy | 12 – 17 | 40 |
| - heavy dusty | 12 – 17 | < 40 |
| Clay: | ||
| - light sandy | 17 – 27 | 40 |
| - light dusty | 17 — 27 | < 40 |
| - heavy | > 27 | Not regulated |
According to the presence of solid inclusions, clay soils are subdivided according to table 4.
Table 4. The content of solid particles in clay soils.
Table 5 shows the methods by which the characteristics of clay soils can be visually determined.
Table 5. Determination of the mechanical composition of clay soils.
Clay soils should include:
peaty soil;
subsiding soils;
swelling (heaving) soils.
Peaty soil - sand and clayey soil containing in its composition in a dry sample from 10 to 50% (by weight) of peat.
According to the relative content of organic matter Ir, clay soils and sands are subdivided according to table 6.
Table 6
Swelling soil is a soil that, when soaked with water or another liquid, increases in volume and has a relative swelling strain (under conditions of free swelling) greater than 0.04.
Subsiding soil is a soil that, under the action of an external load and its own weight or only from its own weight, when soaked with water or another liquid, undergoes vertical deformation (settlement) and has a relative deformation of subsidence e sl ³ 0.01.
Heaving soil is a dispersed soil, which, upon transition from a thawed to a frozen state, increases in volume due to the formation of ice crystals and has a relative deformation of frost heaving e fn ³ 0.01.
According to the relative deformation of swelling without load e sw, clay soils are subdivided according to table 7.
Table 7
According to the relative deformation of subsidence e sl, clay soils are subdivided according to table 8.
Table 8
