The Recommendations outline 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 basic requirements for zero-cycle construction work.

The recommendations are intended for engineering and technical workers of design and construction organizations that carry out the design and construction of foundations of buildings and structures on heaving soils.

PREFACE

The action of the forces of frost heaving of soils annually causes great material damage to the national economy, consisting in a decrease in the service life of buildings and structures, deterioration of operating conditions and large monetary costs for the annual repair of damaged buildings and structures, for the correction of deformed structures.

In order to reduce foundation deformations and frost heaving forces, the Research Institute of Foundations and Underground Structures of the USSR State Construction Committee, based on theoretical and experimental studies, taking into account advanced construction experience, has developed new and improved currently existing measures against soil deformation during freezing and thawing.

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

Engineering and reclamation measures are fundamental, since they are aimed at draining soils in the zone of standard freezing depth and 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 foundation structures and partially above-foundation structures 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, the depth of their placement in the soil, the rigidity of structures, loads on foundations, anchoring them in soils below the freezing depth and many other structural 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.; More detailed recommendations are given on the size of filling the sinuses with non-heaving soil and on the size of thermal insulation pads depending on the depth of soil freezing based on construction experience.

To help designers and builders, examples of calculations of structural measures are given and, in addition, proposals are given for anchoring prefabricated foundations (monolithic connection of a rack with an anchor plate, connection by welding and bolts, as well as anchoring of prefabricated reinforced concrete strip foundations).

The examples of calculations for structural 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 primarily involve reducing the forces of frost heaving and the magnitude of deformation of foundations when soils freeze. This is achieved by using the recommended thermal insulation coatings on the soil surface around the foundations, coolants for heating the soil and chemical reagents that lower the freezing temperature of the soil and the adhesion forces of the frozen soil to the foundation planes.

When prescribing anti-heaving measures, it is recommended to be guided primarily by the significance of buildings and structures, the characteristics 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 heaving forces both during the construction period and throughout their entire service life. The recommendations were compiled by Doctor of Technical Sciences M. F. Kiselev.

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., building. 6.

1. GENERAL PROVISIONS

1.2. 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 populated areas, enterprises, buildings and structures in the northern construction-climatic zone" and can be used for engineering-geological and hydrogeological surveys carried out in accordance with the general requirements for soil research for construction purposes. Materials of engineering-geological surveys must meet the requirements of these Recommendations.

1.3. Heaving (frost-hazardous) soils are those soils that, when freezing, tend to increase in volume. A change in soil volume is detected in the rising during freezing and lowering during thawing of the daytime soil surface, resulting in damage to the bases and foundations of buildings and structures.

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

Table 1

Subdivision of soils according to the degree of frost heaving

Notes : 1. The name of the soil according to the degree of heaving is accepted if one of two indicators is satisfied IN orZ.

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

3. Magnitude Z, exceeding the calculated depth of soil freezing in m, i.e. the difference between the depth of the groundwater level and the calculated depth of soil freezing is determined by the formula:

Where N 0 - distance from the planning mark to the groundwater level in m;

H- calculated depth of soil freezing in the well according to the chapter of SNiP II -B.1-62.

1.4. Depending on the granulometric composition, natural humidity, depth of soil freezing and groundwater level, soils prone to deformation during freezing are divided according to the degree of frost heaving into: highly heaving, medium heaving, slightly heaving and conditionally non-heaving.

g n 1 -

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

(6)

F a -

anchor area in cm 2 (the difference between the area of ​​the shoe and the cross-sectional area of ​​the post);

H 1 -

anchor depth in cm (distance from the ground surface to the upper plane of the anchor);

γ 0 -

volumetric weight of soil in kg/cm3.

(7)

f -

area of ​​the foundation base in cm 2;

h-

thickness of the frozen soil layer under the base of the foundation in cm;

R-

empirical coefficient in kg/cm 3, defined as the quotient of the specific normal buckling force divided by the thickness of the frozen soil layer under the base of the foundation. For medium and highly heaving soilsRit is recommended to take 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 foundation ledges, in kg;

n 1 ,N n, n, τ n , F-

the same as in formula ().

( 8)

The degree of soil heaving at consistency IN

Groundwater level position Z in m for soils

fine sands

dusty sands

sandy loam

loams

clay

I . Highly heaving at
0,5<IN

Z≤0,5

Z≤1

Z≤ 1,5

II . Medium heaving at
0,25<IN<0,5

Z<0,6

0,5<Z≤1

1<Z≤1,5

1,5< Z≤2

III . Slightly heaving at
0<IN<0,25

Z<0,5

0,6<Z≤1

1<Z≤1,5

1,5< Z≤2

2< Z≤3

IV . Conditionally non-heaving at
IN<0

Z≥ 1

Z>1

Z>1,5

Z>2

Z>3

(6)

F a -

anchor area in cm 2 (the difference between the area of ​​the shoe and the cross-sectional area of ​​the post);

H 1 -

anchor depth in cm (distance from the ground surface to the upper plane of the anchor);

γ 0 -

volumetric weight of soil in kg/cm3.

(7)

f -

area of ​​the foundation base in cm 2;

h-

thickness of the frozen soil layer under the base of the foundation in cm;

R-

empirical coefficient in kg/cm 3, defined as the quotient of the specific normal buckling force divided by the thickness of the frozen soil layer under the base of the foundation. For medium and highly heaving soilsRit is recommended to take 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 foundation ledges, in kg;

n 1 ,N n, n, τ n , F-

the same as in formula ().

( 8)

Intended for engineering and technical workers of design and construction organizations.

PREFACE

The action of forces of frost heaving of soils and heaving of foundations worsens operating conditions and shortens the service life of buildings and structures, causes their damage and deformation of structural elements, which leads to large annual costs for repairing damage and causes significant damage to the national economy.

This Guide contains engineering and reclamation, construction and structural, thermal and thermochemical measures proven in construction practice to combat the harmful effects of frost heaving of soils on the foundations of buildings and structures, and also provides a brief summary of instructions for carrying out construction work on the zero cycle and measures to prevent heaving of non-buried and shallow-depth foundations for low-rise stone buildings for various purposes and one-story prefabricated wooden houses in rural areas.

The most common damage to foundations and destruction of structures above the foundation structure of buildings and structures from frost heaving is caused by the following factors: a) the composition of soils in the zone of seasonal freezing and thawing; b) the state of natural soil moisture and the conditions of their moistening; c) the depth and speed of seasonal soil freezing; d) design features of foundations and superstructures; e) the degree of thermal influence of heated buildings on the depth of seasonal soil freezing; f) the effectiveness of measures taken against the effects of frost heaving forces of foundations; g) methods and conditions for carrying out zero-cycle construction work; h) conditions of operational maintenance of buildings and structures. Most often, these factors affect foundations collectively in various combinations, and it can be difficult to establish the actual cause of damage in buildings.

How As a rule, the results of studies of the interaction of freezing soil with foundations, obtained using the modeling method in laboratory conditions, still do not bring a positive effect when transferring these results into construction practice, so you should be more careful when using dependencies established in the laboratory in natural conditions.

When designing, one should take into account the results of many years of stationary experimental data on the study of the interaction of freezing soil with foundations in natural conditions, and not for one winter, since climatic conditions for individual years with anomalous deviations are not typical for the average winter of a given area.

Engineering and reclamation measures are, in principle, fundamental, since they ensure drainage of soils in the zone of standard soil freezing depth and a decrease in the degree of moisture in the soil layer at a depth of 2-3 m below the depth of seasonal freezing. This measure cannot be implemented for almost all soil and hydrogeological conditions, and then it should be used only as a way to reduce soil deformation during freezing in combination with other measures.

Construction and structural measures against the forces of frost heaving of foundations are aimed mainly at adapting foundation structures and partially the super-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 foundation structures, the depth of their placement in the ground, the rigidity of structures above-foundation structure, load values ​​on foundations, anchoring of foundations in soils lying below the freezing depth and many other structural devices).

The design measures recommended in the Guide are given only 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.; More detailed recommendations are given on the size of filling the sinuses with non-heaving soil and on the size of thermal insulation pads, depending on the depth of soil freezing and local construction experience.

Calculations of foundations for stability under the influence of frost heaving forces, as well as calculations for structural measures are not mandatory for all structures used in foundation construction, therefore these measures cannot be considered universal in combating the harmful effects of frost heaving of soils in all cases.

Thermal and chemical measures are fundamental both to completely eliminate deformations from frost heaving and to reduce the forces of frost heaving and the magnitude of deformation of foundations when soils freeze. They include the use of recommended thermal insulation coatings on the soil surface around foundations, coolants for heating soils and chemical reagents that lower the freezing temperature of the soil with the foundation and reduce the tangential adhesion forces of frozen soil with the foundation planes.

When heated, the soil will not have a negative temperature, which eliminates freezing and frost heaving.

When treating the soil with chemical reagents, although the soil then has a negative temperature, it does not freeze, therefore freezing and frost heaving are also eliminated.

When prescribing anti-heaving measures, it is necessary to take into account the significance of buildings and structures, the features of technological production processes and operating conditions, soil and hydrogeological conditions, as well as the climatic characteristics of the area. When designing foundations on heaving soils, preference should be given to those measures that are the most economical and effective under the given conditions.

The measures outlined in this Guide to combat deformation of buildings and structures under the influence of frost heaving forces will help builders improve the quality of objects under construction, ensure the stability and long-term serviceability of buildings and structures, eliminate cases of extension of construction time, ensure the commissioning of buildings and structures in industrial operation in planned deadlines, reduce unproductive one-time and annually recurring costs for repairs and restoration of buildings and structures damaged by frost heaving.

The manual was compiled by Dr. Tech. Sciences M. F. Kiselev.

Please send all comments on the text of the Manual and suggestions for improvement to the Research Institute of Foundations and Underground Structures of the USSR State Construction Committee at the address: 109389, Moscow, 2nd Institutskaya St., 6.

1. GENERAL PROVISIONS

1.1. This Guide is intended for the design and construction of foundations of buildings, industrial structures and various special and. technological equipment on heaving soils.

1.2. The manual was developed in accordance with the main provisions of the SNiP chapters on the design of foundations and foundations of buildings and structures and foundations and foundations of buildings and structures on permafrost soils.

1.3. Heaving (frost-hazardous) soils are those soils that, when frozen, have the property of increasing their volume upon transition to a frozen state. Changes in soil volume are detected under natural conditions in the rise during freezing and the decrease during thawing of the daytime soil surface. As a result of these volumetric changes, deformations occur and cause damage to the foundations, foundations and superstructure of buildings and structures.

1.4. Depending on the granulometric composition of the soil, its natural humidity, freezing depth and groundwater level, soils prone to deformation during freezing are divided according to the degree of frost heaving into: highly heaving, medium heaving, slightly heaving and practically non-heaving.

1.5. Subdivision of soils according to the degree of frost heaving depending on the time-varying groundwater level and consistency indexI L accepted according to table. 1 adj. Chapter 6 of SNiP on the design of foundations and foundations of buildings and structures. Natural soil moisture during the design period must be adjusted according to paragraphs. 3.17-3.20 of the above-mentioned chapter of SNiP.

1.6. The basis for establishing the degree of soil heaving should be the materials of hydrogeological and soil surveys (the composition of the soil, its natural moisture and the level of groundwater, which can characterize the building site to a depth of at least twice the standard freezing depth of the soil, counting from the planning mark).

In the practice of designing foundations and foundations, great difficulties are often encountered when assessing soils based on the degree of frost heaving based on available materials from engineering and geological surveys, since usually the seasonal freezing layer is not considered the basis for foundations and the necessary soil characteristics are not determined for it. If the first 1.5-2 m in engineering-geological materials are characterized only as a “vegetation layer” or as “gray soil”, then in the absence of a groundwater level close to the freezing layer, it is not possible to determine the degree of soil heaving. If there are no characteristics of the freezing layer of soil, it is necessary to conduct separate additional surveys at the construction site, preferably for each standing building.

1.7. The design of foundations and foundations of buildings and structures on heaving soils should be carried out taking into account:

Table 1

Notes : 1. Consistency of clay soilsI L should be taken according to their natural humidity, corresponding to the period of the onset of freezing (before the migration of moisture as a result of the action of negative temperatures). If there are clay soils of different consistencies within the calculated freezing depth, the degree of frost heaving of these soils is generally taken based on the weighted average value of their consistency.

2. Coarse soils with clay aggregate containing more than 30% by weight of particles less than 0.1 mm in size, when the groundwater level is below the estimated freezing depth of 1 to 2 m, are classified as medium heaving soils, and less than one meter - as highly heaving.

3. Magnitude z- the difference between the depth of the groundwater level and the calculated depth of soil freezing, determined by the formula:z=N 0 – H, Where N 0 - distance from the planning mark to the groundwater level; N- estimated freezing depth, m, according to SNiP chapter II -15-74.

a) the degree of frost heaving of soils;

b) terrain, time and amount of precipitation, hydrogeological regime, soil moisture conditions and depth of seasonal freezing;

c) exposure of the construction site in relation to solar illumination;

d) purpose, terms of construction and service, significance of buildings and structures, technological and operational conditions;

e) technical and economic feasibility of the designated foundation structures, labor intensity and duration of work on the zero cycle and savings in building materials;

f) the possibility of changing the hydrogeological regime of soils, the conditions of their moisture during the construction period and over the entire life of the building or structure;

g) the available results of special studies to determine the forces and deformations of frost heaving of soils (if any).

1.8. The volume and types of special studies of soil properties and general engineering-geological and hydrogeological surveys are provided for by the general survey program or additional buildings to the general program in agreement with the customer, depending on the geological conditions, design stage and specifics of the buildings and structures being designed.

2. BASIC DESIGN CONSIDERATIONS

2.1. When choosing soils as natural foundations within the designated area for development, preference should be given to non-heaving or practically non-heaving soils (rocky, semi-rocky, crushed stone, pebble, gravel, gruss, gravelly sand, large and medium-sized sand, as well as fine and silty sand, sandy loam, loam and clay of a solid consistency with the groundwater level below the planning mark by 4-5 m).

2.2. For stone buildings and structures on highly and moderately heaving soils, it is more expedient to design columnar or pile foundations anchored in the soil based on the calculation of heaving forces and rupture in the most dangerous section, or to provide for the replacement of heaving soils with non-heaving ones for part or the entire depth of seasonal freezing of the soil . It is also possible to use bedding (pillows) of gravel, sand, burnt rocks from waste heaps and other drainage materials under the entire building or structure in a layer to the calculated depth of soil freezing without removing heaving soils or only under the foundations with a proper feasibility study calculation.

2.3. All basic measures aimed at preventing deformation of structural elements of buildings and structures during freezing and heaving of soils should be provided for when designing foundations and foundations, including all costs in the estimated cost of work on the zero cycle.

In cases where measures against frost heaving are not provided for by the project, and the hydrogeological conditions of the soil of the construction site during the period of work on the zero cycle turned out to be inconsistent with the survey results or worsened due to unfavorable weather conditions, representatives of the designer's supervision must draw up an appropriate report and raise the issue before the design organization about the appointment, in addition to the project, of measures against frost heaving of soils (such as draining the soil at the base, compaction with crushed stone compaction, etc.).

2.4. Calculation of the basis for the action of frost heaving forces should be carried out based on stability, since the deformations of frost heaving are alternating in sign and are repeated annually. On heaving soils, the design should provide for backfilling of the excavation pits before the soil freezes in order to avoid frost heaving of the foundations.

2.5. Strength, stability and long-term serviceability of buildings and structures on heaving soils are achieved by using engineering, reclamation, construction, structural and thermochemical measures in the practice of design and construction.

2.6. The choice of anti-heaving measures should be based on reliable and very detailed data on the presence of groundwater, its flow rate, the direction and speed of its movement in the ground, the topography of the waterproof layer, the possibility of changing foundation designs, methods of construction work, operating conditions and features of technological production processes.

3. ENGINEERING AND RECLAMATION MEASURES TO REDUCE DEFORMATION FROM THE ACTION OF FREEZE HEAVENING FORCES OF SOILS

3.1. The main reason for frost heaving of soils is the presence of water in them, which can turn into ice when it freezes, therefore measures aimed at draining soils are fundamental, as they are the most effective. All engineering and reclamation measures come down to draining soils or preventing their saturation with water in the seasonal freezing zone and 2-3 m below this zone. It is important that the foundation soils be as dehydrated as possible before freezing, which is not always possible to achieve, since not all soils are capable of quickly release the water they contain.

3.2. The choice and purpose of reclamation measures should depend on the conditions of the moisture source (atmospheric precipitation, high water or groundwater), the terrain and geological strata with their filtration capacity.

3.3. When drawing up construction projects and their implementation in situ on sites composed of heaving soils, one should, if possible, avoid changing the direction of natural drains and take into account the presence of vegetation cover and the requirements for its preservation.

3.4. When designing foundations on a natural foundation with heaving soils, it is necessary to provide for reliable drainage of underground, atmospheric and industrial waters from the site by performing timely vertical planning of the built-up area, installing a storm sewer network, drainage channels and trays, drainage and other drainage and reclamation structures immediately after completion of work on zero cycle, without waiting for the complete completion of construction work.

3.5. General measures to drain the site include measures to drain the pits. Before excavating a pit, it is first necessary to protect it from the runoff of atmospheric water from the surrounding area, from the penetration of water from neighboring reservoirs, ditches, etc. by constructing berms or ditches.

3.6. Water should not be allowed to stagnate in pits. If there is a small influx of groundwater, it should be systematically removed through the construction of wells 1 m deep below the bottom of the pit.

To lower the groundwater level, it is recommended to install vertical drains made of sand and gravel mixture along the perimeter of the pit.

3.7. Backfilling of sinuses in clayey soils should be carried out with careful layer-by-layer compaction using manual and pneumatic or electric rammers to avoid the accumulation of water in the backfill, which increases the soil moisture not only of the backfill, but also of the natural soil.

3.8. Bulk clay soils when planning terrain within a building must be compacted layer by layer with mechanisms to a volumetric mass of the soil skeleton of at least 1.6 t/m 3 and a porosity of no more than 40% (for clayey soil without drainage layers). The surface of the bulk soil, as well as the surface of the cut, in places where there is no storage of building materials and traffic of vehicles, it is useful to cover it with a soil layer of 10-15 cm and sod.

The slope for hard surfaces (blind areas, platforms, entrances, etc.) must be at least 3%, and for turfed surfaces - at least 5%.

3.9. To reduce uneven moisture in heaving soils around foundations during design and construction, it is recommended to: carry out excavation work with a minimum amount of disturbance to natural soils when digging pits for foundations and trenches for underground utilities; It is necessary to arrange waterproof blind areas at least 1 m wide around the building with clay waterproofing layers at the base.

3.10. On construction sites composed of clay soils and with a terrain slope of more than 2%, the design should avoid installing water tanks, ponds and other sources of moisture, as well as locating sewerage and water supply pipelines entering the building on the upland side of the building or structure.

3.11. Construction sites located on slopes must be protected from surface water flowing down the slopes by a permanent upland ditch with a slope of at least 5% before digging pits.

3.12. During construction, the accumulation of water from damage to the temporary water supply system must not be allowed. If standing water is detected on the ground surface or when the ground is moistened due to damage to the pipeline, it is necessary to take urgent measures to eliminate the causes of water accumulation or soil moistening near the location of the foundations.

3.13. When backfilling communication trenches on the upland side of a building or structure, it is necessary to install lintels made of crumpled clay or loam with careful compaction to prevent water from entering (through the trenches) to buildings and structures and moistening the soil near the foundations.

3.14. The construction of ponds and reservoirs that can change the hydrogeological conditions of the construction site and increase the water saturation of heaving soils in the built-up area is not allowed. It is necessary to take into account the projected change in water level in rivers, lakes and ponds in accordance with the long-term master plan.

3.15. It is necessary to avoid locating buildings and structures closer than 20 m to existing pumps for refueling diesel locomotives, washing vehicles, supplying the population and for other purposes, and also not to design pumps on heaving soils closer than 20 m to existing buildings and structures. The areas around the pumps must be designed to ensure water drainage.

3.16. When designing foundations, both seasonal and long-term fluctuations in the level of groundwater (and high water) and the possibility of forming a new increase or decrease in the average level should be taken into account (clause 3.17 of the chapter on designing the foundations of buildings and structures). An increase in the groundwater level increases the degree of soil heaving, and therefore it is necessary when designing to predict changes in the groundwater level in accordance with the instructions in paragraphs. 3.17-3.20 chapters of SNiP on the design of foundations of buildings and structures.

3.17. Particular attention should be paid to the season of periodic flooding of the territory, since the most adverse effect on frost heaving is flooding of the territory in the autumn, when the water saturation of the soil increases before freezing. It is also necessary to predict an artificial increase in groundwater levels and natural soil moisture due to the supply of industrial water during technological processes associated with high water consumption.

3.18. The design of engineering and reclamation measures should be based on reliable and detailed data on the presence of groundwater, its flow rate, the direction and speed of its movement in the ground, and the topography of the roof of the aquifer layer. Without this data, constructed drainage and drainage structures may be useless. If it is not possible to get rid of groundwater and drain the soil of the freezing layer, then you should resort to designing constructive or thermochemical measures.

4. CONSTRUCTION AND CONSTRUCTION MEASURES AGAINST DEFORMATION OF BUILDINGS AND STRUCTURES DURING FREEZING AND HEAVING OF SOILS

4.1. Construction and structural measures against the deformation of buildings and structures from frost heaving of soils are provided in two directions: completely balancing the normal and tangential forces of frost heaving and reducing the forces and deformations of heaving and adapting the structures of buildings and structures to the deformations of foundation soils during freezing and thawing.

With the normal and tangential forces of frost heaving of soils fully balanced, measures against deformation are reduced to design solutions and calculation of loads on foundations. Only during the construction period, when the foundations overwinter unloaded or do not yet have the full design load, should temporary thermochemical measures be provided to protect the soil from moisture and freezing. For low-rise buildings with lightly loaded foundations, it is advisable to use such constructive measures that are aimed at reducing the forces of frost heaving and deformation of structural elements of buildings and adapting buildings and structures to deformations during freezing and thawing of soils.

4.2. The foundations of buildings and structures erected on heaving soils can be designed from any building materials that ensure their operational suitability and meet the requirements of strength and long-term preservation. In this case, it is necessary to take into account possible vertical alternating stresses from frost heaving of soils (raising of soils during freezing and settlement during thawing).

4.3. When placing buildings and structures on a construction site, it is necessary, if possible, to take into account the degree of heaving of soils so that under the foundations of one building there cannot be soils with different degrees of heaving. If it is necessary to construct a building on soils with varying degrees of heaving, constructive measures should be taken against the effects of frost heaving forces, for example, with strip prefabricated reinforced concrete foundations, install a monolithic reinforced concrete belt over the foundation pads, etc.

4.4. When designing buildings and structures with strip foundations on highly heaving soils, at the level of the top of the foundations, it is necessary to provide for 1-2-story stone buildings along the perimeter of external and internal main walls, structural reinforced concrete belts with a width of at least 0.8 of the wall thickness, a height of 0.15 m and above the openings of the last floor there are reinforced belts.

Note: Reinforced concrete belts must have a concrete grade of at least M-150, reinforcement with a minimum cross-section, three rods with a diameter of 10 mm with reinforced joining along the length.

4.5. When designing pile foundations with a grillage on highly and moderately heaving soils, it is necessary to take into account the effect of normal forces of frost heaving of soils on the base of the grillage. Prefabricated reinforced concrete sub-wall rand beams must be monolithically connected to each other and laid with a gap of at least 15 cm between the rand beam and the ground.

4.6. The depth of foundations in construction practice should be considered as one of the fundamental measures to combat deformations from uneven settlement of foundations and from frost heaving when soils freeze, since by deepening foundations into the ground the goal is to ensure the stability and long-term serviceability of buildings and structures.

When designing, the depth of foundations is assigned depending on the factors provided for in paragraph 3.27 of the SNiP chapter

When designing foundations for buildings and structures, the purpose of deepening foundations into the ground is a rather complex and important issue of foundation engineering, therefore, when solving it, one should proceed from a comprehensive analysis of the complex influence of various factors on the stability of foundations and on the condition of the soils at their base.

The depth of laying foundations means the distance measured vertically, counting from the daytime surface of the soil, taking into account backfilling or cutting, to the base of the foundation, and in the presence of special preparation from sand, crushed stone or lean concrete - to the bottom of the preparation layer. The base of the foundation is the lower plane of the foundation structure, resting on the ground and transmitting pressure from the weight of the building and structure to the ground.

4.7. When determining the depth of foundations, the purpose and design features of buildings and structures should be taken into account. For unique buildings (for example, high-rise buildings and the Ostankino television tower in Moscow), the criteria for deepening the foundations are the properties of the soil. It is known that at greater depths soils are denser and can bear significantly greater loads.

Prefabricated standard foundations of civil buildings of mass construction (for example, residential multi-storey buildings) are buried according to stability conditions. It is not possible to give a standard solution for the depth of foundations for all types of foundation soils; they are possible only for similar soil conditions.

Low-rise buildings with lightly loaded foundations, such as civil and industrial buildings and structures in rural areas, are designed taking into account maximum deformations on non-heaving soils and stability on heaving soils.

The depth of foundations for temporary buildings and structures is taken on the basis of technical and economic considerations using lightweight shallow foundations.

The depth of foundations for large industrial buildings is taken depending on technological processes, foundations for special equipment and machines, as well as the conditions of operational maintenance of the building.

The depth of foundations depends on the combination of permanent and temporary loads on the foundation, as well as on dynamic effects on the soils at the base of the foundations, especially these conditions must be taken into account when deepening foundations under the walls of the external fence in industrial buildings with large dynamic loads.

4.8. Foundations for heavy equipment and machinery, as well as for masts, columns and other special structures, are installed to a depth in accordance with the requirement to ensure stability and economic feasibility. As a rule, the density of soils increases with depth, and therefore, in order to increase the pressure on the foundation and reduce the amount of foundation settlement during soil compaction, a greater depth of foundations is taken in comparison with the depth of foundations under the conditions of soil freezing and heaving.

Foundations subject to horizontal or pull-out loads are laid to a depth depending on the magnitude of these loads. For buildings with heated basements, the depth of foundations is taken according to the conditions of foundation stability, regardless of the depth of soil freezing.

4.9. There are cases when the natural topography of the site is changed in the built-up area by diverting the beds of streams and rivers beyond the construction site, and the old bed is filled with soil, or the site is leveled by cutting off the soil in one area and filling it in another.

Despite the compaction of bulk soils, the settlement of foundations on them will be greater compared to the settlement of soil of natural composition, and therefore the depth of foundations cannot be assumed to be the same for bulk soils and soils of natural composition:

When determining the depth of foundations, it is necessary to take into account hydrogeological conditions as a decisive factor in many cases of foundation design. The depth of the foundation depends on the physical state of modern geological deposits, the homogeneity and density of the soil, the groundwater level and the consistency of clay soils. Loose soils, water-saturated and containing a large amount of organic residues, cannot always be used as natural foundations.

On weak and highly compressible soils, it is necessary to take measures to improve soil properties or design pile foundations.

The depth of foundations in complex hydrogeological conditions should be decided in several options, and the most rational decision is made from their comparison based on technical and economic calculations.

An extremely unfavorable factor in foundation building is the presence of groundwater and the location of its level close to the surface. This factor determines not only the depth of foundations, but also their design and the method of carrying out work on the construction of foundations.

4.10. Periodic fluctuations in the groundwater level in the stressed zone of the base of foundations greatly affect the bearing capacity of soils and cause deformation of bases and foundations. In addition, the close location of the groundwater level to the layer of frozen soil determines the amount of frost heaving of the soil due to the suction of moisture from the underlying water-saturated soils.

A special type of groundwater is the so-called perched water with a limited distribution in the plan and an unsustainable level of standing groundwater, contained in the soil thickness in the form of separate pockets. Quite often, perched water occurs in the thickness of seasonally freezing soil and causes greater unevenness of frost heaving of soils and heaving of foundations. Even within the same construction site, there are several pockets of perched water with different levels of groundwater, sometimes even pressure water.

When setting the depth of foundations, it is necessary to take into account the depth of freezing and the degree of heaving of soils; as a condition of stability, heaving soils should not be allowed to freeze below the base of the foundations.

4.11. The depth of foundations of stone civil buildings and industrial structures on heaving soils is taken to be no less than the calculated depth of soil freezing according to Table. Chapter 15 of SNiP on the design of foundations of buildings and structures.

The estimated depth of soil freezing is determined by the formula

Σ| T m | - the sum of the absolute values ​​of average monthly negative temperatures for the winter in a given area, taken from the table. 1 chapter of SNiP on construction climatology and geophysics, and in the absence of data in it for a specific point or construction area based on the results of observations of a hydrometeorological station located in similar conditions to the construction site;

N 0 - soil freezing depth at Σ|T m |=1, depending on the type of soil and taken equal, cm, for: loams and clays - 23; sandy loams, fine and silty sands - 28, gravelly, coarse and medium-sized sands - 30;

m t - coefficient taking into account the influence of the thermal regime of the building (structure) on the depth of soil freezing at the foundations of walls and columns, taken according to table. Chapter 14 of SNiP on the design of foundations of buildings and structures.

There are three different depths of soil freezing: actual, standard and calculated.

In the practice of foundation building, the actual depth of soil freezing is usually considered to be a layer of hard-frozen soil vertically from the surface to the bottom of the hard-frozen soil layer. The Hydrometeorological Service takes the depth of penetration of zero degrees temperature into the soil as the actual depth of soil freezing, since for agricultural purposes it is required to know the depth of soil freezing to zero temperature, and for foundation building purposes it is required to know at what depth the soil is in a hard frozen state. Since the actual depth of soil freezing depends on climatic factors (even at the same point in different years the depth of soil freezing fluctuates), the average value is taken as the standard depth of soil freezing according to clause 3.30 of the SNiP chapter on the design of foundations of buildings and structures.

Freezing of the soil under the base of the foundation should be divided into one-time freezing during zero-cycle work in winter and annual freezing during the entire life of the building, when alternating deformations appear during seasonal freezing and thawing of soils during operation. When assigning the depth of foundations based on the condition of excluding the possibility of freezing of heaving soil under the base of the foundation, this means annual freezing during the operation of buildings and structures, since the depth of the foundation is not determined based on the condition of soil freezing during the construction period.

As mentioned above, the measure of the depth of foundations to prevent freezing of the soil under the base of the foundation applies only to the operational period, and during the construction period protective measures are provided to protect the soil from freezing, since during the construction period the base of the foundations may end up in the freezing zone due to incomplete construction zero cycle work.

In cases where the natural soil moisture does not increase during the construction and operation of buildings on slightly heaving soils (semi-solid and hard-plastic consistency), the depth of foundations, based on the possibility of heaving, should be taken at the standard freezing depth:

up to 1 m - at least 0.5 m from the planning mark

up to 1.5 m - at least 0.75 m from the planning mark

from 1.5 to 2.5 m - at least 1.0 m from the planning mark

from 2.5 to 3.5 m - at least 1.5 m from the planning mark

For practically non-heaving soils (hard consistency), the calculated depth can be taken equal to the standard freezing depth with a coefficient of 0.5.

4.12. Based on experimental testing of non-buried and shallow foundations at construction sites in recent years, in the practice of energy and agricultural construction, reinforced concrete foundations in the form of slabs, beams and blocks are used, laid without deepening on heaving soils under temporary buildings and structures of construction bases of thermal power plants and under open distribution equipment electrical substation devices. In this case, the tangential forces of frost buckling and the accumulation of residual irreversible deformations of frost buckling are completely eliminated. This method significantly reduces the cost of construction and at the same time ensures the usability of buildings and special equipment.

4.13. The depth of foundations for internal load-bearing walls and columns of unheated industrial buildings on highly and moderately heaving soils is taken to be no less than the calculated depth of soil freezing.

The depth of laying the foundations of walls and columns of heated buildings with unheated basements or underground areas on highly heaving and medium-heaving soils is assumed to be equal to the standard freezing depth with a coefficient of 0.5, counting from the surface of the basement floor.

When cutting soil from the outside of the walls of a building, the standard freezing depth of the soil is calculated from the surface of the soil after cutting, i.e. from the planning mark. When adding soil around the walls from the outside, the construction of the building must not be allowed until the soil around the foundations is filled to the design level.

When cutting and dumping soil, special attention should be paid to draining the soil outside the building, since water-saturated soils, when freezing, can cause damage to the building due to lateral pressure on the basement walls.

4.14. As a rule, freezing of the soil below the base of the foundation of stone buildings and structures and the foundation for special technological equipment and machines on highly heaving and medium-heaving soils is not allowed, both during construction and during operation.

On practically non-heaving soils, freezing of soils below the base of the foundations can be allowed only if the soils of natural composition are dense and at the time of freezing or during freezing their natural moisture does not exceed the moisture content at the rolling boundary.

4.15. As a rule, it is prohibited to lay foundations on frozen soil at the base without conducting special studies of the physical state of the frozen soil and a conclusion from a research organization.

It is not uncommon in the practice of foundation construction when it is necessary to lay foundations on frozen soils. Under favorable soil conditions, it is possible to lay foundations on frozen soils without first warming them up, but in this case it is necessary to have reliable physical characteristics of the soils in the frozen state and data on their natural moisture content in order to make sure that the soils are indeed very dense and low-moisture with a solid consistency and according to the degree of frost heaving they are considered practically non-heaving. An indicator of the density of frozen clay soil is the volumetric mass of the frozen soil skeleton of more than 1.6 g/cm 3 .

4.16. In order to reduce heaving forces and prevent deformations of foundations due to freezing of heaving soils with the side surface of foundations, the following should be done:

a) take the simplest forms of foundations with a small cross-sectional area;

b) give preference to columnar and pile foundations with foundation beams;

c) reduce the area of ​​freezing of soil with the surface of foundations;

d) anchor the foundations in the soil layer below seasonal freezing;

e) reduce the depth of soil freezing near foundations using thermal insulation measures;

f) reduce the values ​​of tangential forces of frost heaving by using lubrication of foundation planes with polymer film and other lubricants;

g) make decisions to increase the loads on the foundation to balance the tangential buckling forces;

h) use complete or partial replacement of heaving soil with non-heaving soil.

4.17. Calculation of the stable position of foundations under the influence of forces of frost heaving of foundation soils should be carried out in cases where the soils are in contact with the side surface of the foundations or are located under their base, are classified as heaving and freezing is possible.

Notes . 1. When designing permanent buildings on deep foundations with heavy loads, stability calculations can be made only for the construction period if the foundations are overwintered unloaded;

2. When designing and constructing low-rise buildings with structures that are insensitive to uneven precipitation (for example, with wooden chopped or cobblestone walls), as well as for agricultural structures such as vegetable and silo storage facilities made from wood materials, calculations for the effects of frost heaving forces can be avoided do not carry out or apply anti-radiation measures.

4.18. The stability of the position of foundations under the action of tangential forces of frost heaving on them is checked by calculation using the formula

Where N n - standard load on the foundation at the level of the base of the foundation, kgf;

Q n - standard value of the force that keeps the foundation from buckling due to friction of its side surface against thawed soil located below the calculated freezing depth (determined by );

n 1 - overload factor taken equal to 0.9;

n- overload factor taken equal to 1.1;

τ n - standard value of the specific tangential force of heaving, taken equal to 1; 0.8 and 0.6, respectively, for highly heaving, medium heaving and low heaving soils;

F- area of ​​the lateral surface of the part of the foundation located within the estimated freezing depth, cm (when determining the valueFthe calculated freezing depth is accepted, but not more than 2 m).

4.19. The standard value of the force that keeps the foundation from buckling isQ n due to the friction of its side surface on thawed soil, it is determined by the formula

Where - standard value of the specific shear resistance of thawed foundation soil along the lateral surface of the foundation, determined based on the results of experimental studies; in their absence the value it is allowed to take 0.3 kgf/cm 2 for sandy soils and 0.2 kgf/cm 2 for clay soils.

4.20. In the case of using anchor-type foundations, the forceQ n , which keeps the foundation from buckling, should be determined by the formula

where γ with p - average standard value of the volumetric weight of the soil located above the surface of the anchor part of the foundation, kgf/cm 3 ;

F a - area of ​​the upper surface of the anchor part of the foundation, taking the weight of the overlying soil, cm 2;

h a - deepening the anchor part of the foundation from its upper surface to the planning level, see

4.21. Determining the forces of frost heaving of soils acting on the lateral surface of foundations is of great importance for the design of foundations and foundations of low-rise buildings and, in general, buildings with lightly loaded foundations, especially for cases of using monolithic non-step foundations.

Example. It is required to check a foundation slab made of expanded clay concrete with dimensions of 100×150 cm under the column of a one-story frame building. The depth of soil freezing below the base of the slab is 60 cm, the load on the column resting on the slab is 18 tons. The slab is laid on the surface of the sand bedding without being buried in the ground. The soil at the base of the slab is classified as medium heaving according to the degree of frost heaving.

Substituting the values ​​of the quantities into formula (), we obtain the value of the normal forces of frost heaving of soilsN n =18 t; n 1 =0,9; n=1,1; F f =100×150=15000 cm2; h 1 =50 cm; σ n =0.02 (by); 0.9×18≥1.1×150×50×100×0.02; 16.2<16,5 т.

An experimental test showed that with such a load on the foundation of a frame building, when the soil froze by 120 cm, vertical displacements of the foundation slabs from 3 to 10 mm were observed, which is quite acceptable for frame one-story buildings.

The limits of applicability of measures to prevent heaving of non-buried and shallow foundations are drawn up on the basis of a generalization of existing experience in the construction and operation of buildings and structures erected as experimental ones on heaving soils.

MEASURES FOR CONSTRUCTING NON-FULL FOUNDATIONS ON HEAVY SOILS

6.3. When constructing non-buried foundations, tangential forces of frost heaving do not appear and, therefore, the possibility of the occurrence and accumulation of residual uneven deformations during freezing and thawing of soils is excluded. Thus, the main measures to ensure the stability and serviceability of buildings and structures come down to the preparation of foundation soils for laying foundations on them in order to reduce frost heaving deformations and adapt foundation structures and superstructures to alternating deformations.

Normal frost heave forces in most cases exceed the weight of the superstructure, i.e. they are not balanced by the load on the foundation and then the main factor influencing the heaving of the foundation will be the amount of deformation or heaving of the soil. If the magnitude of frost heaving is not proportional to the values ​​of normal heaving forces, then measures should be aimed not at overcoming the normal forces of frost heaving, but at reducing the values ​​of heaving deformation to the maximum permissible values.

Depending on the availability of non-heaving soils or materials near the site, coarse and medium-sized sand, gravel and pebbles, small crushed stone, boiler slag, expanded clay and various mining wastes can be used to install cushions under the foundation slabs.

On sites with bulk or alluvial soils, the design of non-buried foundations in the form of slabs and beds should be carried out in accordance with the requirements of Section. Chapter 10 of SNiP on the design of foundations of buildings and structures.

When installing non-buried strip foundations for prefabricated one-story buildings, the following recommendations should be followed:

a) on the planned site, after breaking out the axes, sand bedding is laid under the outer walls 5-8 cm thick and 60 cm wide. Formwork is installed, reinforcement is laid (three rods with a diameter of 20 mm) and concreting is done (ribbon cross-section 30x40 cm). On excessively heaving soils, especially in low relief elements, it is recommended to lay a monolithic strip foundation on bedding 40-60 cm thick, but the bulk soil of the bedding should be compacted as much as possible;

b) after completion of the foundation work, it is necessary to complete the planning of the area around the house to ensure water drainage from the building;

c) on medium-heaving, slightly heaving and practically non-heaving soils, strip foundations can be constructed from prefabricated reinforced concrete blocks with a cross-section of 25×25 cm and a length of at least 2 m;

d) according to the standard project, it is necessary to lay a blind area outside the house 0.7 m wide, plant ornamental shrubs, prepare the soil layer around the house and sow the seeds of turf-forming grasses. The layout of areas for turfing should be done according to the ruler.

MEASURES FOR CONSTRUCTING SHALLOWED FOUNDATIONS ON HEAVY SOILS

6.4. Shallow foundations on a locally compacted base have found application in the construction of buildings and structures for agricultural purposes on medium- and slightly heaving soils. Local soil compaction is achieved by driving foundation blocks into the ground or installing prefabricated blocks into nests compacted using an inventory compactor in a dynamic way, which increases the degree of industrialization of construction work, reduces cost, labor costs, and consumption of building materials.

The locally compacted soil base under the foundation acquires improved physical and mechanical properties and has a significantly greater load-bearing capacity. As a result of increased pressure on the soil and its greater density, deformations of the base during freezing and thawing of the soil are sharply reduced.

Experimental studies to determine the deformation of frost heaving under pressure in natural conditions have established that when a locally compacted base freezes below the base of the foundation by 60-70 cm, the amount of frost heaving of the foundation is: at a pressure on the ground of 1 kgf/cm 2 - 5–6 mm ; 2 kgf/cm 2 - 4 mm; 3 kgf/cm 2 - 3 mm; 4 kgf/cm 2 - 2 mm and at a pressure of 6.5 kgf, no vertical movements at the foundation were observed during two winters.

The use of local soil compaction in foundations on medium- and low-heaving soils makes it possible to use freezing soil as a natural foundation with a foundation depth of 0.5-0.7 from the standard soil freezing depth. So, for example, for the central zone of the European territory of the USSR, the laying of foundations can be taken at 1 m from the planning mark with the condition of local soil compaction.

Preparation of foundations for shallow foundations should be carried out in the following order:

a) cutting off the plant-turf layer and backfilling, soil that does not contain plant inclusions;

b) local soil compaction at the base of columnar foundations by driving in an inventory compactor to form nests for prefabricated foundations;

c) the layout of the axes of the location of compacted foundations should be carried out after equipment for local compaction of soils under free-standing foundations has been delivered to the site;

d) the depth of shallow foundations is taken from the following conditions:

for buildings in which vertical movements due to frost heaving of soils are not allowed, depending on the specific pressure on the soil under the base of the foundation in the range from 4 to 6 kgf/cm 2 ;

for light buildings, in the presence of vertical movements that do not interfere with normal operation (temporary, prefabricated panel, wooden and other buildings), the depth of soil freezing under the base of the foundation can be taken based on permissible deformations.

Before constructing shallow foundations on sites with complex geological composition, it is necessary to clarify the settlements of foundations installed on a locally compacted foundation by static tests. The number of tests at the facility is established by the design organization. depending on hydrogeological conditions.

The technology for constructing shallow foundations is set out in the “Temporary recommendations for the design and construction of shallow foundations on heaving soils for low-rise agricultural buildings” (NIIOSP, M., 1972).

7. THERMAL INSULATION MEASURES TO REDUCE THE DEPTH OF SOILS FREEZATION AND NORMAL FORCES OF FROST BULKING OF SHOW-DEPTH FOUNDATIONS

EXPERIENCE IN APPLYING THERMAL INSULATION MEASURES IN CONSTRUCTION PRACTICE

7.1. Thermal insulation measures used in foundation construction practice are divided into temporary (only for the construction period) and permanent (taking into account their effect throughout the entire life of the building and structure).

During construction around the foundations of buildings and structures, it is recommended to use temporary thermal insulation coatings made of sawdust, slag, expanded clay, slag wool, straw, snow and other materials in accordance with the instructions for protecting soils and subgrades from freezing.

Permanent thermal insulation measures include blind areas laid on a thermal insulation pad made of slag, expanded clay, slag wool, foam rubber, pressed peat slabs, dry sand, etc. other materials.

The laid thermal insulation blind areas around a building under construction are usually destroyed during further installation work by the movement of mechanisms and after the construction work is completed they need to be rebuilt, which is not always done, and therefore conditions are created for uneven water saturation of the soil and the depth of soil freezing near the foundations.

The greatest thermal insulation effect is achieved in cases where the cushion material is in a dry state, but often the thermal insulation material laid in the trough is saturated with water in the fall before freezing and this reduces the thermal insulation effect.

In some cases, instead of constructing a blind area, sodding of the soil surface at the outer walls is used and, as experience shows, the freezing of the soil under the vegetation cover is reduced by half compared to the depth of freezing of the soil under the bare surface of the soil.

RECOMMENDATIONS FOR THE APPLICATION OF THERMAL INSULATION MEASURES TO REDUCE THE DEPTH OF SOIL FREEZING

7.2. In order to ensure the safety of the blind area and their thermal insulation effect, it is recommended that instead of blind areas on thermal insulation pads, use expanded clay concrete for blind areas with a volumetric weight in a dry state of 800 to 1000 kgf/m 3 with an estimated value of the thermal conductivity coefficient, respectively, in a dry state of 0.2-0.17 and in water-saturated 0.3-0.25 kcal/m·h·°С.

Laying a blind area made of expanded clay concrete should be done only after thoroughly compacting and leveling the soil near the foundations of the external walls.

It is advisable to lay the expanded clay concrete blind area on the ground surface with the expectation of lower water saturation. Expanded clay concrete should not be laid in an open trough in the ground to the thickness of the blind area. If, due to design features, this cannot be avoided, then it is necessary to provide drainage funnels to drain water from under the expanded clay concrete blind area.

The design of the expanded clay concrete blind area takes the simplest form in the form of a strip, the dimensions of which are assigned depending on the estimated depth of soil freezing according to table. 5.

Table 5

According to an experimental test of the thermal insulation effect of a blind area on an expanded clay cushion 0.2 m thick and 1.5 m wide, the depth of soil freezing near the fence of winter greenhouses decreased by 3 times and the thermal influence coefficient of a heated greenhouse with a blind area on an expanded clay cushionm t obtained an average of 0.269.

The proposed dimensions of expanded clay concrete blind areas and structures of non-buried and shallow reinforced concrete foundations on expanded clay for temporary buildings and structures of construction bases of thermal power plants require the same experimental verification at construction sites.

8. INSTRUCTIONS FOR ZERO CYCLE CONSTRUCTION WORK

8.1. The following requirements are imposed on the production of zero-cycle works: avoid excessive water saturation of heaving soils at the base of foundations, protect them from freezing during the construction period and promptly complete excavation work to fill the cavities and level the site around the building under construction.

In construction practice, soil is sometimes added to low-lying areas by refilling fine-grained or silty sand from the bottom of a reservoir. Since hydraulic monitors pour sand along with water from the pipes onto the site (from which the water rolls off and the soil settles), drainage of the sandy layer should be provided in order to self-compact it and reduce water saturation.

Usually, washed-up fine and silty sands are in a water-saturated state for a long time, so such soils, when frozen, turn out to be highly heaving and at the same time weakly compacted.

When using refilled soils as natural foundations, the soils under the foundations must not be allowed to freeze and foundations must not be laid on frozen soil, even for low-rise buildings.

Where buildings have already been built or are under construction, heaving soils should not be allowed to flow closer than 3 m from the foundations of the external walls.

The method of excavation work using hydromechanization can be safely used in the southern regions of our country, where the standard freezing depth of soils is no more than 70-80 cm, as well as in non-heaving soils throughout the USSR. But on sites composed of heaving soils, soil development using hydromechanization should not be carried out, since this method saturates the soil with water, which violates the requirements of paragraphs. 3.36-3.38, 3.40 and 3.41 chapters of SNiP on the design of foundations of buildings and structures on the protection of soils from excessive water saturation with surface water. In principle, there is no categorical prohibition on the use of soil development using hydromechanization, but with this method it is necessary to take the necessary drainage measures to drain the soil at the base of the foundations and provide proper feasibility studies.

8.2. When constructing foundations on heaving soils, it is necessary to strive when digging pits with earth-moving mechanisms to comply with the requirements of the current regulatory and technical documents for the production and acceptance of excavation work. It is necessary to tear out trenches for laying strip prefabricated and monolithic foundations of small width so that the width of the sinuses can be covered with a cover or a waterproofing screen. After installing prefabricated foundations or laying concrete in a monolithic foundation, you should immediately backfill the sinuses with careful compaction of the soil and ensure drainage from the accumulation of surface water around the building, without waiting for the final planning of the site and laying of the blind areas.

8.3. Open pits and trenches should not be left for a long time before installing foundations in them, since a large time gap between opening the pits and laying foundations in them in most cases leads to a sharp deterioration of the soil at the base of the foundations due to periodic or constant flooding of the bottom of the pit with water. On heaving soils, opening a pit should only begin when the foundation blocks and all the necessary materials and equipment have been delivered to the construction site.

It is advisable to carry out all work on laying foundations and filling cavities in the summer, when work can be done quickly and with high quality at a relatively low cost of excavation work. It would be useful to observe the seasonality of zero-cycle work on heaving soils.

If it is necessary to open pits and trenches to a depth of more than 1 m in winter, when the soil is in a hard-frozen state, it is often necessary to resort to artificial thawing of the soil in various ways, which speeds up the excavation work and does not impair the construction properties of the soil at the base of the foundations. Thawing heaving soils by releasing water vapor into drilled wells should not be used, since this sharply increases soil moisture due to condensation of water vapor.

8.4. Backfilling of the sinuses should be carried out after finishing concreting monolithic foundations and after laying the basement floor for prefabricated block foundations. It should be borne in mind that filling the sinuses near the foundations with a bulldozer does not ensure proper compaction of the soil and, as a result, a large amount of surface water accumulates, which unevenly saturates the soils near the foundations and, when frozen, creates favorable conditions for deformation of the foundations and the above-foundation structure due to the tangential forces of frost heaving. It happens even worse when the sinuses are filled in winter with frozen soil and without compaction. The laid fill near the foundations usually fails after the soil in the cavities thaws and self-compacts.

The sinuses should be filled with the same thawed soil with careful layer-by-layer compaction.

The use of mechanisms for soil compaction when filling cavities is difficult due to the presence of plinth walls, which create cramped conditions for the operation of the mechanisms.

8.5. According to the requirement of the head of SNiP for the design of foundations of buildings and structures, measures must be taken to prevent freezing of heaving soil below the base of the foundation during the construction period.

In the case of overwintering laid foundations and slabs, one should not forget about protecting the soil from freezing, especially when the foundations will be loaded during the laying or installation of building walls until the soil below the base of the foundations thaws. In order to protect soil from freezing at the base of foundations, various methods are used, from backfilling with soil to covering foundations and slabs with thermal insulation materials. Snow deposits are also a good insulating material and can be used as a thermal insulator.

Reinforced concrete slabs with a thickness of more than 0.3 m on highly heaving soils must be covered with a standard freezing depth of more than 1.5 m with mineral slabs in one layer, slag mags or expanded clay with a volumetric weight of 500 kgf/m 3 and a thermal conductivity coefficient of 0.18 layer 15 -20 cm.

If the building is erected, and the soils at the base of the foundations are in a frozen state, then care must be taken to ensure uniform thawing of the soils under the base of the foundation by laying thermal insulation coatings on the outside of the foundations and heating the soils inside the building, for which you can use electricity or heating the underground air with air heaters and temporary heating stoves.

To ensure uniform thawing, winter masonry walls on the south side have to be covered with matting, panels, roofing felt, plywood or straw mats to protect them from collapse during rapid and uneven thawing.

As thermal insulation for the period of thawing of soil near the foundations outside the building for 1-1.5 months on the south side, you can use the storage of concrete blocks, bricks, crushed stone, sand, expanded clay and other materials.

Due to uneven thawing of the soil under the external and internal transverse load-bearing walls, through cracks form under and above the openings on the internal transverse load-bearing wall. These cracks usually expand and sometimes reach tens of centimeters at the top, while the outer longitudinal walls tilt with the upper part deviating away from the building. With large rolls, it is necessary to dismantle significant sections of the external and internal walls.

The tilt of external walls is often formed during the process of soil freezing in January-March, when the foundations of external walls are laid at the calculated depth of soil freezing, and under the internal load-bearing walls the foundations are laid shallowly (at half or even one third of the standard soil freezing depth).

Under the influence of normal forces of frost heaving of soils, upwardly expanding through cracks also appear at the base of the foundations of internal load-bearing walls, while the top of the external walls noticeably deviates from the vertical. The cream of the outer walls depends on the height of the rise of the inner stone wall and the opening width of one or two cracks at the top of the inner wall.

8.6. When you first detect even small hairline cracks on the walls of stone buildings, it is necessary to establish the cause of their appearance and take measures to stop the expansion of these cracks. If cracks appear under the influence of normal forces of frost heaving, then these cracks should not be allowed to be sealed with cement mortar. The main event in this case will be the thawing of the soil inside the building under the foundations of the internal load-bearing walls, which will cause settlement of the foundation and the cracks will close partially or completely. Continuing the construction of walls or installation of prefabricated houses with a frozen foundation should be refrained until the soils under the foundations have completely thawed and until the settlement of the foundations has stabilized after the soils have thawed.

8.7. At construction sites, during work, the soils at the base become locally saturated with water due to water leaking into the ground from a faulty water supply network. This leads to the fact that in some areas clay soils turn from non-heaving and slightly heaving into highly heaving ones with all the ensuing consequences.

To protect the soil at the base of the foundations from local water saturation during the construction period, temporary water supply lines should be laid along the surface to make it easier to detect the occurrence of water leaks and timely repair damage to the water supply network.

9. MEASURES FOR THE PERIOD OF OPERATION OF BUILDINGS AND STRUCTURES TO PROTECT SOILS BASED ON FROM EXCESSIVE WATER SATURATION

9.1. During the industrial operation of buildings and structures erected on heaving soils, changes in the design conditions of the bases and foundations should not be allowed. To ensure the stability of foundations and the serviceability of buildings, it is necessary to take measures aimed at preventing an increase in the degree of soil heaving and the occurrence of deformations of the structural elements of a building due to frost heaving of foundations. These measures boil down to fulfilling the following requirements: a) not to create conditions for increasing soil moisture at the base of the foundations and in the seasonal freezing zone closer than 5 m to the side of the foundations; b) prevent deeper freezing of soils near foundations in relation to the calculated depth of soil freezing adopted during design; c) do not allow cutting off the soil around the foundations when redeveloping a populated area or a built-up site; d) do not reduce the design load on the foundation.

In order to combat the increase in natural soil moisture at the base of foundations during the industrial operation of buildings and structures, it is recommended to: drain all industrial, domestic and storm water to low places away from the foundations or into storm sewer receivers and maintain drainage structures in good condition; annually all work on cleaning surface drainage systems, i.e. upland ditches, ditches, chutes, water intakes, openings of artificial structures, as well as storm drains, must be carried out before the onset of autumn rainy weather. It is necessary to carry out periodic monitoring of the condition of drainage structures, all work to correct damaged slopes, layout violations and blind areas should be carried out immediately, without delaying this work until the soil begins to freeze. If these damages have caused stagnation of water on the ground surface near the foundations, it is necessary to urgently ensure the drainage of surface water from the foundations. If erosive activity of storm water is detected in the area, soil erosion should be urgently eliminated and areas along the drainage system with a large drop in storm water should be strengthened.

9.2. Thermal insulation coatings provided for by the project and implemented by construction at the foundations around buildings in the form of blind areas on slag or expanded clay cushions, sodding of the ground surface or other coatings must be maintained in the same condition as it was carried out according to the project during construction. When carrying out major repairs of buildings, it is prohibited to overwinter heated buildings without heating, as well as to replace blind areas around buildings with thermal insulation coatings with blind areas without thermal insulation coating.

During major repairs of buildings, lowering the planning marks of buildings built on highly heaving soils should not be allowed, since the depth of the foundation may be less than the calculated depth of soil freezing. The distance from the outer wall of the building to the place where the soil is cut must be no less than the calculated depth of soil freezing, and if conditions permit, then a strip of untouched soil (i.e. without cutting) should be left near the foundations 3 m wide. The only exception to this requirement can be such cases when the distance from the planning mark to the base of the foundation, after cutting the soil, will be no less than the calculated depth of soil freezing. During these works, it is impossible to violate the conditions of surface drainage of atmospheric water and other irrigation and drainage devices, which prevented water saturation of soils near the foundations of buildings and structures.

9.3. During the period of operation of buildings, it may be necessary to change the load on the foundations of industrial buildings during reconstruction when changing equipment or changing production processes, which can disrupt the relationship between the forces of frost heaving of the foundations and the pressure on the foundations from the weight of the building.

Often, when the load on foundations increases, it is necessary to strengthen the foundations. At the same time, the area of ​​freezing of the soil with the lateral surface of the foundation increases, the tangential forces of frost heaving increase in proportion to the increase in the area of ​​freezing of the foundation with the soil. Consequently, when designing the strengthening of foundations (especially columnar ones), it is necessary to check the stability of the foundations under the influence of tangential forces of frost heaving.

It is also necessary to check by calculation the foundations for equipment in cold workshops or in the open air, when heavy equipment is replaced with lighter equipment, i.e. when the load on the foundation is reduced. If the calculation shows that the tangential forces of frost heaving exceed the weight of the structure, then, in relation to specific conditions, constructive or other measures should be taken against heaving of the foundations.

9.4. The areas with grass cover provided for by the project require annual maintenance, which consists of timely preparation of the soil layer, reseeding of turf-forming grasses and replanting of shrubs. The presence of a turf layer reduces the depth of soil freezing by almost half, and shrub plantings accumulate snow deposits, which reduces the freezing depth by more than three times compared to the freezing depth in an open area. It is better to carry out all work on caring for both the turf cover and shrub plantings in the spring without violating the territory layout adopted by the project. Where the turf cover and the layout of the soil surface are disturbed due to excavation work to eliminate accidents of underground communications or the passage of vehicles, it is necessary to restore the layout, loosen the plant layer and re-sow the seeds of turf-forming grasses. The best sods are considered to be mixtures of local flora. During hot and dry months, it is necessary to water the turf and ornamental shrubs so that they do not die from lack of moisture.

9.5. Sometimes, during the period of industrial operation, deformations of buildings are detected in the form of cracks in the masonry walls and distortions at the openings of large-block or panel fences. When deformation of the structural elements of a building is first detected, it is necessary to establish systematic monitoring of changes in these deformations using beacons installed on cracks and according to the leveling data of installed marks. All radical measures to eliminate existing deformations should be prescribed only after the causes of these deformations have been established. In particularly difficult cases, the enterprise administration must contact a design or research institute to establish the causes of deformation and develop measures.