The question is especially typical for tired lands, clearing a site for a foundation, and horticultural areas. The latter tended to distribute "good" officials in those territories where it makes no sense to use agricultural enterprises and because of the poverty of the soil. To understand all the features, you need to consider everything in order.

Replacing fertile soil for a lawn

It is not easy to create a beautiful and even lawn, you need to bring the foundation in perfect condition. First, the earth is cleared of all flowers, roots, weeds, flower beds. Vegetation is removed in two ways:

- herbicides, which cause severe damage to the earth;

- bayonet shovel or excavator.

Both methods have their pros and cons. The optimal, but hard way, with a shovel. The thinnest layer should be removed, while capturing everything growing from the roots. To turn the removed sod into, you need to leave it in the compost pit for three years. The next steps: adding a new clean fertile soil, leveling, recharge.

Removal of plant soil under the foundation

Before starting any construction, it is necessary to remove the sod for the following reasons:

- save on the purchase and delivery of soil;

- use the natural fertile layer;

- to prevent the process of decay of organic matter in the foundation and on the sides.

The boundaries and thickness of the removed layer are determined by the project, more precisely by preliminary analysis.

1. The minimum depth is 10 cm, the maximum 50 cm.

2. On a sandy basis, the vegetative soil lies at a depth of 5–10 cm.

3. In soddy areas - 12 cm.

4. On arable fields - 20 cm.

5. In forests up to 25 cm.

The process is carried out with heavy construction equipment: bulldozer or excavator, loader, dump truck or tractor for transportation. Bad soil often has a yellowish color, fertile soil can be gray-brown-black. The cut layers are placed in heaps of 1.5–3 meters.

Replacing tired land in agricultural areas

The earth tends to deplete. Therefore, it is necessary to carry out technical or biological reclamation. On large areas, land up to 10 cm is not removed. Special rules are established by GOST 17.4.3.02-85 "Requirements for the protection of the fertile soil layer during earthworks."

In the yard or in the garden, the owners try to constantly fertilize with organic matter, peat and minerals. If this process has not been carried out, then the soil has no fertile strength. In order not to raise the site, you will have to remove a part and refresh it with new high-quality soil. In built-up spaces, it is impossible to use heavy equipment, manual labor is used.

After the collapse of the Soviet Union, plots for summer cottages and vegetable gardens were distributed en masse. Most in unsuitable swampy areas or with a minimum amount of fertile layer. In these cases, it is necessary to clear the territory and buy new fertile layers. If the fertile soil was removed during construction and did not bother to return it, then you will again have to import a new one.

The Recommendations set out engineering-reclamation, construction-structural and thermochemical measures to combat the harmful effects of frost heaving of soils on the foundations of buildings and structures, and also provide the basic requirements for the production of construction work on a zero cycle.

The recommendations are intended for engineers and technicians of design and construction organizations who design and construct foundations of buildings and structures on heaving soils.

FOREWORD

The action of the forces of frost heaving of soils annually causes great material damage to the national economy, which consists in reducing the service life of buildings and structures, in deteriorating operating conditions and in high monetary costs for the annual repair of damaged buildings and structures, for correcting deformed structures.

In order to reduce deformations of foundations and frost buckling forces, the Scientific Research Institute of Foundations and Underground Structures of the USSR State Construction Committee, on the basis of theoretical and experimental studies, taking into account advanced construction experience, developed new and improved measures that currently exist against deformation of soils during freezing and thawing.

Ensuring the design conditions for the strength, stability and serviceability of buildings and structures on heaving soils is achieved by using engineering-reclamation, construction-structural and thermochemical measures in construction practice.

Engineering and reclamation measures are fundamental, since they are aimed at draining soils in the zone of the normative freezing depth and at reducing the degree of moisture in the soil layer at a depth of 2-3 m below the depth of seasonal freezing.

Construction and structural measures against the forces of frost heaving of foundations are aimed at adapting the structures of foundations and partly above the foundation structure to the acting forces of frost heaving of soils and to their deformations during freezing and thawing (for example, the choice of the type of foundations, their depth in the ground, the rigidity of structures, loads on foundations, their anchoring in soils below the freezing depth and many other constructive devices).

Some of the proposed constructive measures are given in the most general formulations without proper specification, such as, for example, the thickness of the layer of sand-gravel or crushed stone cushion under the foundations when replacing heaving soil with non-heaving soil, the thickness of the layer of heat-insulating coatings during construction and for the period of operation, etc.; Recommendations are given in more detail on the size of filling the sinuses with non-porous soil and on the size of heat-insulating cushions, depending on the depth of soil freezing according to the experience of construction.

To help designers and builders, examples of calculations of structural measures are given and, in addition, proposals are given for anchorage of prefabricated foundations (monolithic connection of the rack with an anchor plate, welded and bolted connection, as well as embedding of prefabricated reinforced concrete strip foundations).

The examples of calculations for constructive measures recommended for construction were compiled for the first time, and therefore they cannot claim to be an exhaustive and effective solution to all the issues raised in combating the harmful effects of frost heaving of soils.

Thermochemical measures envisage, mainly, a decrease in the forces of frost bulging and the values ​​of deformation of foundations during freezing of soils. This is achieved by using the recommended heat-insulating coatings of the soil surface around the foundations, heat carriers for heating the soil and chemicals that lower the freezing point of the soil and the adhesion forces of the frozen soil with the planes of the foundations.

When appointing anti-debris measures, it is recommended to be guided primarily by the importance of buildings and structures, the peculiarities of technological processes, the hydrogeological conditions of the construction site and the climatic characteristics of the area. When designing, preference should be given to such measures that exclude the possibility of deformation of buildings and structures by frost buckling forces both during the construction period and during the entire service life. The recommendations were drawn up by M.F. Kiselev, Doctor of Technical Sciences.

Please send all suggestions and comments to the Research Institute of Foundations and Underground Structures of the USSR State Construction Committee at the address: Moscow, Zh-389, 2nd Institutskaya st., Bld. 6.

1. GENERAL PROVISIONS

1.2. The recommendations are developed in accordance with the main provisions of the chapters of SNiP II -B.1-62 "Foundations of buildings and structures. Design standards ", SNiP II -B.6-66 “Foundations and foundations of buildings and structures on permafrost soils. Design standards ", SNiP II -A.10-62 “Building structures and foundations. Basic principles of design "and SN 353-66" Guidelines for the design of settlements, enterprises, buildings and structures in the northern construction and climatic zone "and can be used for engineering-geological and hydrogeological surveys carried out in accordance with the general requirements for the study of soils for construction purposes. Engineering-geological survey materials must meet the requirements of these Recommendations.

1.3. Heavily (frost-hazardous) soils are soils that, when frozen, have the property of increasing in volume. The change in the volume of the soil is detected in the rise during freezing and lowering during the thawing of the day surface of the soil, as a result of which damage is caused to the foundations and foundations of buildings and structures.

Heaving soils include fine and silty sands, sandy loams, loams and clays, as well as coarse-grained soils with aggregate particles less than 0.1 mm in size in an amount of more than 30% by weight, freezing under humidification conditions. Non-rocky (non-frost-hazardous) soils include rocky, coarse-grained soils with a content of soil particles with a diameter of less than 0.1 mm, less than 30% by weight, Gravelly, large and medium-sized sands.

Table 1

Subdivision of soils according to the degree of frost heaving

The degree of heaving of soils at consistency V	Groundwater level position Z in m for soils
	fine sands	silty sands	sandy loam	loam	clay
I ... Heavily puffy at 0,5<V			Z≤0,5	Z≤1	Z≤ 1,5
II ... Medium porous at 0,25<V<0,5		Z<0,6	0,5<Z≤1	1<Z≤1,5	1,5< Z≤2
III ... Weakly bulging at 0<V<0,25	Z<0,5	0,6<Z≤1	1<Z≤1,5	1,5< Z≤2	2< Z≤3
IV ... Conditionally loose when V<0	Z≥ 1	Z>1	Z>1,5	Z>2	Z>3

Notes (edit) : 1. The name of the soil according to the degree of heaving is adopted when one of the two indicators is satisfied V orZ.

2. The consistency of clay soils V determined by soil moisture in the layer of seasonal freezing as a weighted average. The moisture content of the soil of the first layer to a depth of 0 to 0.5 m is not taken into account.

3. The quantity Zexceeding the calculated depth of soil freezing in m, i.e. the difference between the depth of the groundwater level and the estimated depth of soil freezing is determined by the formula:

where N 0 - distance from the planning mark to the occurrence of the groundwater level in m;

H- estimated depth of soil freezing in w according to chapter SNiP II-B.1-62.

1.4. Depending on the granulometric composition, natural moisture content, the depth of soil freezing and the level of standing groundwater, soils prone to deformations during freezing, according to the degree of frost heaving, are divided into: strongly heaving, medium heaving, slightly heaving and relatively non-heaving.

g n 1 -

standard load from the weight of the part of the foundation located above the design section, in kg.

4.15. The holding force of the anchor is determined by calculation according to the formula (6) at the time of the manifestation of the buckling force

		(6)
F a -	the area of ​​the anchor in cm 2 (the difference between the shoe area and the cross-sectional area of ​​the strut);
H 1 -	deepening of the anchor in cm (distance from the day surface to the upper plane of the anchor);
γ 0 -	volumetric weight of soil in kg / cm 3.

4.16. When erecting buildings in winter, in the event of inevitable freezing of soils under the foundations (to prevent the emergency state of buildings and take appropriate measures to eliminate possible unacceptable deformations of structural elements of buildings on highly heaving soils), it is recommended to check the foundations according to the condition of their stability against the action of tangential and normal forces of frost bulging according to the formula

		(7)
f -	basement foot area in cm 2;
h-	the thickness of the frozen soil layer under the base of the foundation in cm;
R-	the empirical coefficient in kg / cm 3 is determined as the quotient of dividing the specific normal buckling force by the thickness of the frozen soil layer under the basement base. For medium and heavily weathered soilsRit is recommended to take it equal to 0.06 kg / cm 3;
g n -	standard load from the weight of the foundation, including the weight of the soil lying on the ledges of the foundation, in kg;
n 1 ,N n, n, τ n, F-	the same as in the formula ().

The permissible amount of soil freezing under the base of the foundation can be determined by the formula

( 8)

4.17. Foundations for walls of light stone buildings and structures on highly heaving soils should be monolithic with anchors calculated for the action of tangential heaving forces. Prefabricated blocks and foundation shoes must be embedded in accordance with these Recommendations, according to II.

4.18. When constructing low-rise buildings on highly heaving soils, it is recommended to design a porch on a solid reinforced concrete slab on a gravel-sand cushion with a thickness of 30-50 cm (the top of the slab should be 10 cm below the floor in the vestibule with a gap between the porch and the building of 2-3 cm). For capital stone buildings, it is necessary to provide for the device of porches on prefabricated reinforced concrete consoles with a gap between the ground surface and the bottom of the console of at least 20 cm; with columnar or pile foundations, intermediate supports should be provided so that the location of the pillars or piles under the outer walls coincides with the installation site of the porch consoles.

4.19. It is recommended to give preference to such structures of foundations that allow mechanizing the process of performing foundation work and reducing the amount of earthwork for digging pits, as well as transportation, backfilling and compaction of soil. Columnar, pile and anchor pile foundations, which do not require large volumes of earthworks, are satisfied with this condition on highly heaving and medium-heaving soils.

4.20. In the presence of local cheap building materials (sand, gravel, crushed stone, ballast, etc.) or non-porous soils near the construction site, it is advisable to install continuous bedding under buildings or structures with a thickness of 2/3 of the standard freezing depth or sinus filling on the outside of foundations made of non-porous materials or soils (crushed stone, gravel, pebbles, large and medium sands; as well as slag, burnt rocks and other mining waste). Backfilling of sinuses, provided that water is drained from them and without drainage, is performed in accordance with clause 5.10 of these Recommendations.

Drainage of drainage backfills in the sinuses and cushions under the foundations in the presence of water-absorbing soils below the heaving layer should be carried out by discharging water through drainage wells or funnels (see I,). When designing foundations on backfills, one should be guided by the "Guidelines for the design and construction of foundations and basements of buildings and structures in clay soils by the method of drainage layers".

4.21. When constructing buildings and structures on heaving soils from prefabricated structures, the sinuses must be filled up with thorough compaction of the soil immediately after laying the basement; in other cases, the sinuses should be filled up with compaction of the soil as the masonry is erected or foundations are installed.

4.22. The design of the deepening of foundations in heaving soils to the calculated depth of freezing of soils, taking into account the thermal effect of buildings and structures, is adopted in accordance with the SNiP chapter II -B.1-62 in cases where they will not overwinter without protecting the soil from freezing during the construction period and after its completion until the building is put into permanent operation with normal heating or when they will not be in long-term conservation.

4.23. When designing the foundations of industrial buildings on heaving soils, the construction of which lasts for two to three years (for example, a thermal power plant), the projects should include measures to protect the soils of the foundation from moisture and freezing.

4.24. In the construction of low-rise buildings, decorative basement cladding should be provided with filling the space between the basement and the fence wall with low-heat-conducting and non-moisture-consuming materials (sawdust, slag, gravel, dry sand and various mining waste).

4.25. It is recommended to replace heaving soil with non-heaving soil at the foundations of heated buildings and structures only from the outside of the foundations. For unheated buildings and structures, it is recommended to replace heaving soil with non-heaving soil on both sides of the foundations for external walls and also on both sides of foundations for internal load-bearing walls.

The width of the cavity for backfilling with non-porous soil is determined depending on the depth of freezing of the soil and on the hydrogeological conditions of the soils of the foundations.

Provided that water is drained from the backfill of the sinuses and at a depth of soil freezing up to 1 m, the width of the sinus for filling non-porous soil (sand, gravel, pebbles, crushed stone) is sufficient at 0.2 m. sinuses for filling non-porous soil should be at least 0.3 m, and if the depth of soil freezing is from 1.5 to 2.5 m, it is advisable to fill the sinus to a width of at least 0.5 m.The depth of filling the sinuses in this case is taken at least 3 / 4 the depth of the foundation, counting from the planning mark.

If it is impossible to drain water from non-porous soil, filling the sinuses can be approximately recommended for a width equal to 0.25-0.5 m at the level of the base of the foundation and at the level of the daytime surface of the soil - not less than the estimated depth of freezing of soils with. compulsory overlapping of non-porous backfill material with a blind area with asphalt pavement in accordance with.

4.26. The device of slag cushions along the perimeter of buildings from the outside of the foundations should be used for residential and industrial heated buildings and structures. The slag pad is laid with a layer thickness of 0.2 to 0.4 m and a width of 1 to 2 m, depending on the depth of soil freezing and is covered with a blind area, as shown in.

With a freezing depth of 1 m - 0.2 m thick and 1 m wide; at a freezing depth of 1.5 m - a thickness of 0.3 m and a width of 1.5 m; and at a freezing depth of 2 m or more - a slag cushion layer thickness of 0.4 m and a width of 2 m.

In the absence of granulated slag, it is recommended, with an appropriate feasibility study, to use expanded clay with the same dimensions of the thickness and width of the cushion as for the slag cushions.

5. THERMOCHEMICAL MEASURES

5.1. In order to reduce the buckling forces for the construction period, it is recommended to apply soil salinization layer by layer after 10 cm around the foundations with technical table salt at the rate of 25-30 kg per 1 m 3 of loamy soil. After sprinkling salt on a soil layer 10 cm high and 40-50 cm across the width of the sinus, the soil is mixed with salt and thoroughly compacted, then the next layer of soil is laid with salinization and compaction. The soil of the sinus backfill is salted starting from the base of the foundation and not reaching 0.5 m to the planning mark.

The use of soil salinization is allowed if it does not affect the decrease in the strength of the materials of foundations or other underground structures.

5.2. To reduce the magnitude of the freezing forces between the soil and the foundation material for the construction period, it is recommended to lubricate the leveled side surfaces of the foundation with fragile freezing materials, for example, bitumen mastic (prepared from fly ash from CHPP - four parts, bitumen grade III - three parts and diesel oil - one part by volume).

The foundation should be coated from its sole to the planning mark in two layers: the first is thin with careful lapping, the second is 8-10 mm thick.

5.3. In order to reduce the tangential forces of frost heaving of soils when installing lightly loaded pile foundations for special technological equipment on highly heaving soils, the surface of the piles in the zone of seasonal freezing of soils with a polymer film can be applied. Experimental testing in the field has shown the effect of reducing the tangential forces of frost heaving of soils from the use of polymer films from 2.5 to 8 times. The composition of high-molecular compounds and the technology of preparation and application of films on the plane of reinforced concrete foundations are set out in "Recommendations for the use of high-molecular compounds in the fight against frost bulging of foundations."

5.4. Columnar foundations, until their full load during the construction period, should be wrapped with brizol or roofing felt in two layers 2/3 of the standard freezing depth of soils, counting from the planning mark, provided that the load on the foundation is less than the frost buckling forces.

5.5. During construction, around the foundations of buildings and structures, temporary heat-insulating coatings of sawdust, snow, slag and other materials should be arranged in accordance with the instructions for protecting soils and subgrade bases from freezing.

5.6. In order to avoid freezing of soils under the soles of the foundations of internal walls and columns in technical undergrounds and basements of unfinished or constructed buildings that overwinter without heating, temporary heating of these premises should be organized in the winter months in order to prevent damage to structural elements of buildings (in practice, air heaters, electric heaters , metal ovens, etc.).

5.7. During construction in winter, in some cases, it is necessary to provide for electric heating of soils by periodically passing (in the winter months) electric current through a 3-mm steel wire specially laid under the foundations; control over the heating of the soil under the foundations should be carried out according to the data of measurements of its temperature with mercury thermometers or according to the data of observations of the freezing of the soil near the foundations according to the Danilin permafrost meter.

5.8. Industrial buildings or structures for which, for technological reasons, deformation cannot be allowed due to freezing of soils around the foundations and below their soles (foundations for installations for producing liquid oxygen, for refrigerators, for automatic and other installations, in cold unheated workshops and for special installations and equipment) must be reliably protected from deformations of frost heaving of soils.

For these purposes, it is recommended to apply periodically (from November to March, and for the northern and northeastern regions from October to April) soil heating around the foundations by passing hot water through a pipeline from a central heating system or from waste industrial hot water. You can also use steam for this.

A steel pipeline covered with bitumen enamel with a cross section of at least 37 mm should be laid directly into the ground to a depth of 20-60 cm below the planning mark and 30 cm away from the foundation from the outside with a slope for draining water. Where production conditions permit, it is recommended to lay plant soil with a layer of 10-15 cm above the pipeline along the surface of the earth, with a slope away from the foundation. On the surface of the vegetation layer, for the purpose of thermal insulation, it is useful to sow sod-forming perennial grass mixtures.

5.9. The preparation of the soil layer, sowing of sod-forming grasses and the planting of shrubs should be carried out, as a rule, in spring, without violating the site layout adopted for the project.

5.10. It is recommended to use grass mixtures as grasses, consisting of seeds of wheatgrass, bent grass, fescue, bluegrass, timothy and other sod-forming herbaceous plants. It is advisable to use grass seeds of the local flora in relation to the natural and climatic conditions of the area. In the dry summer months, it is recommended to periodically water the areas that are turfed and planted with ornamental shrubs.

6. SPECIFICATIONS OF REQUIREMENTS FOR PRODUCTION OF WORKS ON ZERO CYCLE

6.1. The use of the hydromechanization method for the excavation of foundation pits for buildings and structures on construction sites with heaving soils, as a rule, is not allowed.

Refueling of heaving soils during the construction period on built-up sites can be allowed only if the alluvial soils lie no closer than 3 m from the foundations of the outer walls.

6.2. When constructing foundations in heaving soils, it is necessary to strive to reduce the width of the pits and to immediately fill the sinus with the same soil with careful compaction. When backfilling the sinuses, it is necessary to ensure surface water flow around the building, without waiting for the final planning and laying of the soil layer for turf or asphalt blind area.

6.3. Open pits and trenches should not be left for a long time before installing foundations in them. Ground or atmospheric water appearing in pits and trenches must be immediately discharged or pumped out.

The water-saturated soil layer from the accumulation of surface water must be replaced with non-porous soil or compacted with rubble or gravel tamped into it to a depth of at least 1/3 of the liquefied soil layer.

6.4. When developing in winter pits for foundations and trenches for underground utilities near foundations on heaving soils, the use of artificial thawing with water vapor is not allowed.

6.5. The sinuses should be backfilled in layers (if possible with the same thawed soil) with careful compaction. Filling the pits sinuses with a bulldozer without compaction of heaving soils should not be allowed.

6.6. Foundations installed in the summer and left unloaded for the winter must be covered with thermal insulation materials.

Concrete slabs with a thickness of more than 0.3 m on highly heaving soils should be covered with a soil freezing depth of more than 1.5 m with mineral wool slabs in one layer or expanded clay with a bulk density of 500 kg / m 3 with a thermal conductivity coefficient of 0.18, a layer thickness of 15-20 cm.

6.7. Temporary water supply lines may only be laid on the surface. During the construction period, it is necessary to ensure strict control over the condition of the temporary water supply networks. If water leakage from the temporary water supply pipes into the ground is detected, it is necessary to take emergency measures to eliminate soil moisture near the foundations.

APPENDIX I
Examples of calculating the foundations of buildings and structures for stability during freezing of highly heaving soils

For examples of calculating the stability of foundations, the following soil conditions of the construction site are taken:

1) vegetation layer 0.25 m;

2) yellow-brown loam from 0.25 to 4.8 m; the volumetric weight of the soil ranges from 1.8 to 2.1; natural humidity ranges from 22 to 27%, humidity at the fluidity boundary 30%; at the border of rolling 18%; plasticity number 12; groundwater level at a depth of 2-2.5 m from the day surface. Loam of soft-plastic consistency in terms of natural moisture and moisture conditions refers to highly loamy.

In these soil conditions, examples of calculating foundations for stability under the influence of tangential frost heaving forces are given for the following structural types of reinforced concrete foundations: example 1 - monolithic reinforced concrete columnar foundation with an anchor plate; example 2 - reinforced concrete pile foundation; example 3 - precast concrete columnar foundation with one-sided anchoring, strip and precast concrete foundation; example 4 - replacing heaving soil in the sinus with non-heaving soil and example 5 - calculating a heat-insulating cushion at the foundations. In other examples, the characteristics of soil conditions are given for each separately.

Example 1. It is required to calculate a monolithic reinforced concrete columnar foundation with an anchor plate for stability under the influence of frost buckling forces ().

H 1 = 3 m; h=2 m (depth of soil freezing);h 1 = 1 m (thickness of the thawed layer);N n = 15 T;g n = 5 T; γ 0 = 2 t / m 3;F a = 0.75 m 2; b= 1 m; With= 0.5 m (rack width);h 2 =0,5 m (thickness of the anchor plate);u=2 m; τ n = 1 kg / cm 2 = 10 t / m 2;km=0,9; n=1,1; n 1 =0,9; F= 4 m 2.

Find the value of the holding force of the anchor by the formula ().

Substituting the standard values ​​of various quantities into the formula (), we get:

0.9 9.0 + 0.9 (15 + 5)<1,1·10·4; 26,1<44.

As you can see, the condition of foundation stability during heaving of soils is not met, therefore it is necessary to apply anti-heaving measures.

Example 2. It is required to calculate the reinforced concrete pile foundation (pile with a square section of 30X30 cm) for stability when exposed to frost buckling forces ().

The initial data for the calculation are as follows:H 1 = 6 m; h= 1.4 m; g n = 1.3 T;Q n = 11.04 T;u= 1.2 m; With= 0.3 m; τ n = 1 kg / cm 2 = 10 g / m 2;N n = 10 T;km= 0,9; n=1,1; n 1 =0,9.

We check the stability of the pile foundation for frost bulging according to the formula () we get:

0.9 * 11.04 + 0.9 (10 + 1.3)> 1.1 * 10 * 1.68; 20.01> 18.48.

The check showed that under the influence of frost buckling forces, the foundation stability condition is met.

Anchor holding force value R we find by the formula ()

Substituting the values ​​of quantities into the formula (), we get:

0.9 * 21.9 + 0.9 (25 + 13.3)> 1.1 * 10 * 4.08; 54.18> 44.88.

The initial data are as follows; the soils are the same as in example 1; the estimated depth of freezing of soils and the depth of the foundations is 1.6 m; the width of the sinus, covered with gravel with crushed stone, is 1.6 m; the width of the asphalt blind area is 1.8 m, the width of the trench at the bottom, counting from the post, is taken equal to 0.6 m.

The volume of non-porous soil is obtained from the product of the cross-sectional area of ​​the backfill by the size of the perimeter of the building or structure.

To calculate the stability of the foundation on the action of tangential and normal forces of frost heaving, the following soil and hydrogeological conditions are taken:

In terms of composition, natural moisture and moisture conditions, this soil is classified as medium-porous.

The initial data for the calculation are as follows: N= 1.6 m;h 1 =1 m;h 2 =0,3 m;h=0,3 m; With= 0.4 m; With 1 = 2 m;F= 3,2 m;f=4 m;N n = 110 T;g n = 11.5 T;R= 0,06 kg / cm 3 = 60 t / m 3; τ n = 0.8 kg / cm 2 = 8 t / m 2;n 1 =0,9; n=1,1.

We check the stability of the foundation for frost bulging by the formula ().

Substituting the values ​​of the quantities into the formula, we get:

0.9 (110 + 11.5)> 1.1 * 8 * 4 + 4 * 0.3 * 60; 109.4> 107.2.

The check showed that the stability condition is met when the soil freezes below the base of the foundation by 30 cm.

Example 8. It is required to calculate a monolithic reinforced concrete foundation for a column for stability under the action of normal forces and tangential forces of frost heaving ().

Substituting the standard values ​​of the quantities into the formula, we get:

0,9(40+3)<1,1·10·3+1·0,3·60; 38,7<51.

The check showed that the condition of stability of this foundation structure on strongly heaving soil is not met when the soil freezes 30 cm below the base of the foundation.

The permissible amount of soil freezing under the base of the foundation can be determined by the formula ().

For this example, this valueh= 9,5 see. As you can see, depending on the structure of the foundation and soil conditions, i.e. the degree of heaving of the soil, it is possible to determine the permissible amount of freezing of the soil below the base of the foundation.

APPENDIX II
Proposals for structural adaptations of columnar and strip foundations to the conditions of construction on heaving soils.

Prefabricated reinforced concrete lightly loaded foundations, erected on medium and heavily weathered soils, are often subject to deformation under the influence of tangential forces of frost buckling. Consequently, prefabricated foundation elements must have a monolithic connection to each other and, in addition, must be designed to work with alternating forces, i.e. on loads from the weight of buildings and structures and on the forces of frosty buckling of foundations.

The smallest inner diameter of the hook bend is 2.5 diameters of the reinforcement; straight, hook section is equal to 3 reinforcement diameters.

The cross-sectional area of ​​the loop of the foundation block must be equal to the cross-sectional area of ​​the reinforcing bar. The height of the loop above the surface of the foundation pad should be 5 cm greater than the bendable part of the hook.

Concrete blocks are made with holes with a diameter equal to 8 reinforcement diameters. The smallest hole diameter must be at least 10 cm.

The bottom row of foundation blocks is installed on the foundation pads so that the loops of the pads enter approximately in the middle of the holes in the blocks. Following the installation of the lower row, reinforcing rods are installed in the holes of the blocks and hooked with the lower hooks on the loops of the foundation cushions. In the vertical position, the rods are held by the engagement of the upper hook on a metal rod with a diameter of 20 mm and a length of 50 cm, which is wedged by wooden wedges.

Rice. 10. Precast concrete strip foundation

a - strip foundation; b - section of the strip foundation; в - concrete block with holes for reinforcement installation; d - connection of reinforcing bars to each other and to the foundation cushion; d - foundation pad with loops for connecting reinforcing bars:
1 - reinforcing bars with a length equal to the height of the concrete block; 2 - loop of the foundation pad

After installing the reinforcement, the hole is filled with a mortar with a seal. For this purpose, the same mortar is used as for laying concrete blocks. After the start of the mortar setting, the wedges and the rod are removed.

The next row of blocks is installed in such a way that the hooks of the reinforcement of the lower row would be approximately in the center of the holes in the blocks.

When installing foundations with an anchor plate, special attention should be paid to the density of the soil backfilling of the pit sinuses. It is recommended to fill the sinuses with only thawed soil in layers of no more than 20 cm with careful ramming with manual pneumatic or electric rammers.

Before starting the construction of the foundation of the house, an operation such as checking the bearing capacity of the soil must be carried out without fail. Research is carried out in a special laboratory. In the event that the existence of a risk of collapse of a building during its construction at a given specific location is identified, measures can be taken to strengthen or replace soils.

Classification

All soils are subdivided into several basic types:

• Rocky. They are a solid rock mass. They do not absorb moisture, do not sag and are considered non-porous. The foundation on such bases is practically not deepened. Coarse-grained soils, consisting of large ones, are also classified as rocky.
• Bulk. Soils with a disturbed natural layering structure. Simply put, artificially poured. Buildings on such a foundation can be built, but first you should perform a procedure such as soil compaction.
• Clay. They consist of very small particles (no more than 0.01 mm), absorb water very well and are considered heaving. Houses on such soils sag much more than on rocky and sandy ones. All are classified into loam, sandy loam and clay. These include, among other things, loess.
• Sandy. Consist of large sand particles (up to 5 mm). Such soils are compressed very weakly, but quickly. Therefore, the houses built on them are upset at a shallow depth. Sandy soils are classified by particle size. The best substrates are gravelly sands (particles from 0.25 to 5 mm).
• Quicksands. Silty soils saturated with water. Most often found in wetlands. They are considered unsuitable for the construction of buildings.

Such a classification by type is carried out in accordance with GOST. The soils are examined in laboratory conditions with the determination of physical and mechanical characteristics. These surveys are the basis for calculating the power of foundations for buildings. According to GOST 25100-95, all soils are divided into rocky and non-rocky, subsiding and non-subsiding, saline and non-saline.

Basic physical characteristics

When conducting laboratory studies, the following soil parameters are determined:

• Humidity.
• Porosity.
• Plastic.
• Density.
• Particle density.
• Deformation modulus.
• Shear resistance.
• Particle friction angle.

Knowing the density of particles, it is possible to determine such an indicator as the specific gravity of the soil. It is calculated primarily to determine the mineralogical composition of the earth. The fact is that the more organic particles there are in the soil, the lower its bearing capacity.

What soils can be classified as weak

The procedure for conducting laboratory tests is also determined by GOST. Soils are examined using special equipment. The work is carried out only by trained specialists.

If, as a result of tests, it is revealed that the mechanical and physical characteristics of the soil do not allow constructing structures and buildings on it without the risk of their collapse or violation of the integrity of the structure, the soil is considered weak. For the most part, these include quicksands and bulk soil. Loose sandy, peaty and clayey soils with a high percentage of organic residues are also recognized as weak.

If the soil on the site is weak, construction is usually transferred to another place with a better foundation. But sometimes it is not possible to do this. For example, on a small private plot. In this case, a decision can be made to erect a pile foundation with a depth of up to dense layers. But sometimes the procedure for replacing or strengthening the soil seems to be more expedient. Both of these operations are quite costly in terms of both financial and time costs.

Substitution of soils: principle

The process can be done in two ways. The choice of method depends on the depth of the dense layers. If it is small, weak soil with insufficient bearing capacity is simply removed. Further, a poorly compressible pillow made of a mixture of sand and other similar materials is poured onto the dense base of the underlying layer. This method can be used only if the thickness of the layer of soft soil in the area does not exceed two meters.

Sometimes it happens that dense soil is located very deep. In this case, the pillow can be laid on a weak one. However, in this case, accurate calculations of its dimensions in the horizontal and vertical planes should be performed. The wider it is, the lower the load on soft soil due to pressure distribution will be. Such pillows can be used for the construction of foundations of all types.

When using such an artificial base, there is a risk of crushing the pillow under the weight of the building. In this case, it will simply begin to bulge into the thickness of the weak soil from all sides. The house itself will sag, and unevenly, which can lead to the destruction of its structural elements. In order to avoid this, sheet piles are installed around the perimeter of the pillow. Among other things, they prevent waterlogging of the sand and gravel mixture.

Is it possible to change the soil on the site yourself

Substitution of soils for the foundation should be carried out only with the preliminary conduct of appropriate studies and calculations. Of course, you won't be able to do this kind of work yourself. Therefore, most likely, you will have to invite specialists. However, when erecting not too expensive buildings, for example, household buildings, this operation can be performed "by eye". Although we would not recommend taking risks, for general development, let's take a closer look at this procedure. So, the stages of work in this case are as follows:

• Excavation is carried out to a solid base.
• Sand of medium size is poured into the trench to the level of the sole of the future foundation. Backfilling is carried out in layers of small thickness with each tamping. The sand must be moistened with water before compaction. Tamping should be done as carefully as possible. The sand itself should not contain any inclusions, especially large ones. Sometimes soil-concrete mixtures and slags are used instead.

In the event that an artificial foundation is used for the foundation, it is also worth arranging this will slightly increase the density of the soil surrounding the pillow and prevent it from being squeezed out to the sides.

Drainage system works

• A moat is being dug a meter away from the building. In this case, the excavation is carried out below the depth of the foundation. Width - not less than 30 cm. The slope of the trench bottom should be at least 1 cm per 1 m of length.
• The bottom of the trench is tamped and covered with a five-centimeter layer of sand.
• Geotextiles are spread on the sand with the edges fixed on the ditch stacks.
• A ten-centimeter layer of gravel is poured.
• Lay a perforated drainage pipe.
• Fill it with gravel with a layer of 10 cm.
• Cover the "cake" with the ends of the geotextile and sew them together.
• They fill everything up with soil, leaving viewing wells in the corners of the building.
• At the end of the pipe, a receiver well is arranged. It is necessary to divert the drain at least five meters from the wall of the building.
• Gravel is poured at the bottom of the well and a plastic container with holes drilled in the bottom is installed there.
• Take the pipe into the container.
• From above, the well is covered with boards and sprinkled with earth.

Of course, a drainage system should be installed on the building itself.

How soil reinforcement is done

Since soil replacement is a rather laborious and costly operation, it is often replaced by a procedure for strengthening the base for the foundation. In this case, several different methods can be applied. One of the most common is soil compaction, which can be shallow or deep. In the first case, a tamper in the form of a cone is used. It is lifted off the ground and dropped down from a certain height. This method is usually used for preparation for construction of bulk soils.

Deep soil compaction is carried out using special piles. They are driven into the ground and pulled out. The resulting pits are covered with dry sand or filled with soil concrete.

Thermal method

The choice of the soil reinforcement option depends, first of all, on its composition, the procedure for determining which is regulated by GOST. which was presented above, usually require amplification only if they belong to a non-rocky group.

Thermal amplification is one of the most common methods of amplification. It is used for loess soils and allows for strengthening to a depth of about 15 m. In this case, very hot air (600-800 degrees Celsius) is injected into the ground through pipes. Sometimes the heat treatment of the soil is carried out in a different way. Wells are dug into the ground. Then, flammable products are burned in them under pressure. The wells are previously hermetically closed. After such treatment, the fired soil acquires the properties of a ceramic body and loses its ability to absorb water and swell.

Cementation

Sandy soil (a photo of this variety is presented below) is strengthened in a slightly different way - cementation. In this case, pipes are hammered into it, through which cement-clay mortars or cement suspensions are pumped. Sometimes this method is used to seal cracks and cavities in rocky soils.

Soil silicification

On quicksand, silty sandy and macroporous soils, the silicatization method is more often used. For reinforcement, a solution of liquid glass is pumped into the pipes and the injection can be done to a depth of more than 20 m. The radius of spread of liquid glass often reaches one square meter. This is the most effective, but also the most expensive, method of amplification. The low specific gravity of the soil, as already mentioned, indicates the content of organic particles in it. In some cases, such a composition can also be enhanced by silicatization.

Comparison of the cost of soil replacement and strengthening

Of course, the amplification operation will cost less than complete soil replacement. For comparison, let's first calculate how much it will cost to create artificial gravel soil per 1 m 3. Selecting land from one cubic meter of area will cost about $ 7. The cost of crushed stone is $ 10. for 1 m 3. Thus, replacing a weak soil will cost $ 7. for the notch plus $ 7 for moving gravel, plus $ 10 for the gravel itself. Total $ 24 Strengthening the soil costs $ 10-12, which is half the price.

A simple conclusion can be drawn from all this. In the event that the soil on the site is weak, you should choose another place for building a house. In the absence of such an opportunity, it is necessary to consider the option of erecting a building on piles. Reinforcement and replacement of soil are performed only as a last resort. When determining the need for such a procedure, one should be guided by SNiP and GOST. Soils, the classification of which is also determined by the standards, are strengthened by methods suitable for their specific composition.

All over Russia soils with a high clay content are very widespread. In winter, when the temperature drops to below zero, the volume of liquid in the ground increases and the soil "swells". Swelling damage and the rate at which a home collapses is dependent on the foundation and weather conditions. In the best case, when you arrive at a new summer cottage next year, you will not be able to open the door due to the fact that the structure is seriously deformed; in the worst case, you will find serious structural violations. The only way to avoid the effect of swelling is the correct laying of the foundation, which will be able to resist increased loads for a long time.

Why and how swelling occurs

With the wrong foundation or the wrong type of foundation, swelling begins to destroy the building quite quickly. The milder the weather conditions, the slower the force of compression and expansion of the soil will act; in highly heaving soil, the foundation will have to withstand vertical changes in soil level up to 35 cm and a horizontal load of up to 5 tons per 1 m2. Several factors directly affect the soil's susceptibility to swelling:

• soil composition Clay soils (clay, loam, sandy loam) are most susceptible to swelling, and sandy soils to a lesser extent. The higher the clay content in the soil, the greater the frost swelling. There are many closed pores in clay, which retain moisture well; sand, on the contrary, practically does not retain moisture;
• the saturation of the soil with water is also important. For this reason, clayey but dry soils are less prone to swelling than mixed, but moist soils. The moisture content in the soil is determined by the level of groundwater during the period of freezing of the earth;
• the temperature regime affects the depth and duration of the period of soil freezing.

All negative phenomena associated with temperature fluctuations affect a limited layer of soil to the level of freezing. It is easy to determine this level (GPG - the depth of soil freezing) using a special map, you can see one of them. You can also refer to SNiP, which contains a table of standard soil freezing depths, which determines the minimum depth of foundation laying. It should be borne in mind that in the maps and the table is given very approximately and with a margin of 20-40%, for soil not covered with snow and at the lowest average temperatures. The actual depth of freezing is much less, especially if the house will be heated during the cold season. Therefore, there is no particular danger in deepening the foundation to a slightly shallower depth.

Types of foundations for heaving soil

Therefore, there are several basic solutions to the swelling problem:

1. Deepening the foundation below the GPG gives the structure additional strength. But it should be borne in mind that a buried pile-type foundation resists vertical loads well, but with significant horizontal loads it can show itself much worse. Recessed foundations are suitable for the construction of both small and heavy permanent structures. For the foundation, either screw piles or reinforced concrete poured in place (the latter is a more effective solution) are used; a layer of roofing material serves as waterproofing for a reinforced concrete pile, which is laid before pouring into a well drilled for the pile. For small buildings (gazebos, wooden outbuildings), a simple foundation based on brick pillars is suitable - this is the most economical option;

   

2. You can replace the required amount of soil with non-swelling coarse sand or similar material. To replace the soil, a pit is dug to a depth below the GPG, its bottom is covered with compacted sand or sand gravel, then a layer of waterproofing, on top of which is already filled with soil convenient for the foundation. Replacing the soil is more expensive than laying a deepened foundation, requires a large amount of earthwork, but allows you to finally solve the problem of swelling;

   

3. Lightweight structures on heaving soil are often built on a reinforced slab or shallow strip foundation (a more complex and expensive structure in which reinforced concrete is laid along the contour of the building and surrounded by sand and a waterproof coating). This type of shallow foundation has a significant plus - the load is very efficiently distributed over the entire structure of the building, minus - a shallow foundation is suitable only for a lightweight wooden house;

   

4. Another option is not to let the foundation freeze with the soil. To do this, it can be insulated by creating a sufficient layer of thermal insulation: a layer of polyurethane foam, expanded polystyrene or expanded clay is laid along the perimeter of the building. The cake of the insulating layer consists of compacted sand used as a substrate, in fact, a heater and a waterproofing layer. The thickness of the insulation must be equal to the GPG;
5. If we supplement the measures for warming the foundation with the creation of a drainage system, it is possible to significantly reduce the level of groundwater and freezing of the soil. A drainage ditch, laid along the perimeter of the foundation at the depth of its laying, will collect moisture from the soil and remove it below. The second variant of the drainage system is drainage wells drilled around the perimeter of the house at a distance of 2-3 meters.

   

Of the above solutions, the most economical is the insulation of the foundation and the device of the drainage system, the most expensive and effective is the replacement of soil under the foundation. It is possible to carry out the drainage system and insulate the foundation on your own, but in this case it is necessary to carefully study the thermal insulation properties of the selected material and place the waterproofing layer correctly.

It is very difficult to resist soil swelling in some areas of the country; deepening and reinforcing the foundation is indispensable. There is no universal and inexpensive solution, but modern technologies offer many solutions to the problem of deformation of buildings due to swelling: from effective insulation materials to a complex strip foundation design. The optimal solution in each case will have to be chosen independently, comparing the material and time costs in specific conditions.

03.07.2014

In a number of cases, it is economically feasible to remove these soils and put a cushion of sand, gravel, stone in their place instead of deepening the foundation through a small thickness of weak (silty, peaty, bulk, etc.) soils or strengthening weak soils located under the foundation. , cement-soil, lime-soil mixture or other low-compressible material.

Rice. 5.3. Pillow device diagram
on the left - with a small thickness of the layer of soft soil; on the right - with a large thickness of a layer of soft soil; 1 - foundation; 2 - a pillow made of low-compressible material; 3 - a layer of solid soil; 4 - soft ground

With a layer of soft soil 1.5-2 m thick, it is advisable to lay the pillow directly on the underlying layer of more durable soil (on the left in Fig.5.3). If the soft soil extends to a considerable depth, the dimensions of the pillow are assigned from the condition of reducing the pressure under it to a value that does not exceed the design resistance of this soil. In this case, the thickness of the pillow and its lower width are taken based on the pressure distribution at an angle a to the vertical from 20 to 40 °. The value of the angle a depends on the physical and mechanical properties of the pillow material.

It is advisable to use pillows for single and strip foundations with a base width of 1-1.5 m in clay, loamy and sandy soils with a design resistance of 0.10-0.15 MPa above the level. For the device of the pillow, a material with a design resistance under the base of the foundation of 0.20-0.25 MPa is used. In sandy and sandy loam soils, non-cohesive soils are used for making pillows. In loamy and clayey soils, in order to avoid the accumulation of water in the pit, the pillows are made of compacted cohesive soils or a mixture of soils with cement or lime is used for their construction.

To eliminate the possibility of lateral expansion of the soil under the foundation, to prevent bulging of soft soil, as well as to protect the base from undermining, sheet pile fences are used, which in some cases are left in the ground for the entire period of operation of the structure. Sheet piling can also be used when installing soil cushions to reduce the volume of work on removing soft soil from the pit and filling the cushion.

Depending on the design of the fence, the depth of driving the sheet pile into the soil below the base of the foundation, as well as the physical and mechanical properties of the base soils, its bearing capacity as a result of the use of sheet piling can be increased by up to 2 times, and the subsidence of the base is reduced by 2-3 times. The best design of the fence, which absorbs the forces of expansion of the soil of the base, is a round-shaped fence made of flat steel sheet piling.
4. In what cases is the replacement of weak soils used?

5. What is the role of sheet piling in soil strengthening?

6. What is cementation, bitumization, silicatization, resinization of soils?