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

FOREWORD

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

This Guide contains engineering-reclamation, construction-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 briefly provides instructions for the production construction works on the zero cycle and measures to prevent bulging of non-buried and shallow foundations for low-rise stone buildings for various purposes and one-story prefabricated wooden houses in countryside.

The most common damage to foundations and destruction of structures above the foundation of buildings and structures from frost heaving is due to the following factors: a) the composition of soils in the zone of seasonal freezing and thawing; b) the state of natural moisture content of soils and the conditions of their moisture; c) the depth and rate of seasonal soil freezing; d) design features of foundations and above-foundations; e) the degree of thermal influence of heated buildings on the depth of seasonal soil freezing; f) the effectiveness of measures applied against the effects of the forces of frost bulging of foundations; g) methods and conditions for the production of construction work on a zero cycle; h) conditions of operational maintenance of buildings and structures. Most often, these factors affect the foundations in total with their 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 by the method of modeling in laboratory conditions, still do not bring a positive effect when these results are transferred to construction practice, therefore, one should be more careful when using the dependencies established in the laboratory in natural conditions.

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

Engineering and reclamation measures are, in principle, fundamental, since they ensure the drainage of soils in the zone of the standard freezing depth of soils and a decrease in the degree of moistening of the soil layer at a depth of 2-3 m below the depth of seasonal freezing. This measure can be carried out practically not for all soil and hydrogeological conditions, and then it should be used only as reducing the deformation of the soil during freezing in combination with other measures.

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

The constructive 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 and 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 and local construction experience.

Calculations of foundations for stability under the action of frost heaving forces, as well as calculations for constructive measures are not mandatory for all structures used in foundation engineering, therefore, these measures cannot be considered universal to combat the harmful effects of frost heaving of soils in all cases.

Thermal and chemical measures are fundamental both in the complete elimination of deformations from frost heaving, and in reducing the forces of frost bulging and the values ​​of deformation of foundations during freezing of soils. They include the use of recommended thermal insulation coatings on the soil surface around the foundations, heat carriers for heating the soil and chemicals that lower the freezing temperature of the soil with the foundation and reduce the tangential forces of adhesion of frozen soil to the planes of the foundations.

When heated, the soil will not have a negative temperature, which excludes 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 excluded.

When appointing anti-heath measures, it is necessary to take into account the importance of buildings and structures, the peculiarities of 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 such measures that are most economical and effective in these conditions.

The measures outlined in this Guide to combat deformations of buildings and structures under the influence of frost heaving forces will help builders improve the quality of facilities under construction, ensure the stability and long-term serviceability of buildings and structures, exclude cases of lengthening the construction time, ensure that buildings and structures are put into industrial operation in planned terms, to reduce unproductive one-time and annually recurring expenses for repair and restoration of buildings and structures damaged by frost heaving forces.

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

All comments on the text of the Guide and suggestions for improvement, please send to the Research Institute of the grounds and underground structures Gosstroy of the USSR at the address: 109389, Moscow, 2nd Institutskaya st., 6.

1. GENERAL PROVISIONS

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

1.2. The manual has been 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. Heavily (frost-hazardous) soils are soils that, when frozen, have the property of increasing their volume when passing into a frozen state. The change in the volume of the soil is found in natural conditions in the rise in the process of freezing and lowering during the thawing of the day surface of the soil. As a result of these volumetric changes, deformations and damage to the bases, foundations and superstructure of buildings and structures occur.

1.4. Depending on the granulometric composition of the soil, its natural moisture content, the depth of freezing and the level of standing of groundwater, soils prone to deformation during freezing, according to the degree of frosty heaving, are divided into: strongly 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 the consistency indicatorI L taken according to table. 1 app. Chapter 6 of SNiP on the design of foundations and foundations of buildings and structures. The natural moisture content of soils for the period of operation during design 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 heaving of soils should be the materials of hydrogeological and ground surveys (soil composition, its natural moisture content and the level of groundwater standing, which can characterize the building site to a depth of at least twice the standard depth of soil freezing, counting from the planning mark).

In the practice of designing foundations and foundations, there are often great difficulties in assessing soils according to the degree of their frost heaving on the basis of the available materials of engineering and geological surveys, since usually the layer of seasonal freezing 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 "vegetative layer" or as "gray soil", then in the absence of a groundwater level close to the freezing layer, it is not possible to establish the degree of heaving of soils. In the absence of the characteristics of the freezing soil layer, additional surveys should be carried out separately at the construction site, preferably for each standing building.

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

Table 1

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

2. Coarse-grained soils with clay filler, 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 from 1 to 2 m, refer to medium-loamy soils, and less than one meter - to strongly puffy.

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

a) the degree of frosty heaving of soils;

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

c) exposition construction site in relation to sun exposure;

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

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

f) the possibility of changing the hydrogeological regime of soils, the conditions of their moistening during the construction period and for the entire service life of a 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 exploration program or additional buildings to the general program as agreed with the customer, depending on the geological conditions, the design stage and the specifics of the projected buildings and structures.

2. BASIC PROVISIONS FOR DESIGN

2.1. When choosing soils as natural foundations within the allotted building area, preference should be given to non-rocky or practically non-rocky soils (rocky, semi-rocky, gravelly, pebble, gravel, gravelly, gravelly sands, coarse and medium-sized sands, as well as fine and dusty sands, sandy loam, loam and clay of solid consistency when the groundwater level is below the planning mark by 4-5 m).

2.2. For stone buildings and structures on strongly and medium-heaving soils, it is more expedient to design columnar or pile foundations anchored in the soil based on buckling forces and rupture in the most dangerous section, or to provide for the replacement of heaving soils with non-heaving soils for part or the entire depth of seasonal soil freezing ... It is also possible to use bedding (cushions) 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 foundations with a proper feasibility study by calculation.

2.3. All the main measures against deformations of structural elements of buildings and structures during freezing and heaving of soils should be provided for in the design of bases and foundations with the inclusion of all costs in the estimated cost of work on a zero cycle.

In cases where measures against frost heaving are not provided for by the project, and the hydrogeological conditions of the soils of the construction site during the period of work on the zero cycle turned out to be inconsistent with the survey results or deteriorated due to unfavorable weather conditions, representatives of the field supervision should draw up corresponding act and to raise a question before the design organization on the appointment, in addition to the project, of measures against frost heaving of soils (such as drainage of soils at the base, compaction with crushed stone tamping, etc.).

2.4. The calculation of the bases for the action of the forces of frost heaving should be made according to stability, since the deformations of frost heaving are alternating signs, repeated annually. On heaving soils, the project should provide for backfilling the sinuses of the pits before the onset of freezing of the soils in order to avoid frosty bulging of the foundations.

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

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

3. ENGINEERING AND RECLAMATION MEASURES TO REDUCE DEFORMATION FROM THE EFFECT OF THE FORCES OF FROZEN SOILS

3.1. The main reason for the frost heaving of soils is the presence of water in them that can turn into ice when freezing, therefore, measures aimed at draining soils are fundamental, as the most effective. All engineering and reclamation measures are reduced to draining the soils or preventing their water saturation in the zone of seasonal freezing and below this zone by 2-3 m. quickly give away the water contained in them.

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

3.3. When drawing up construction projects and their implementation in nature on sites formed by heaving soils, it is necessary to avoid, if possible, changing the direction of natural drains and take into account the presence of vegetation and the requirements for its preservation.

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

3.5. The general measures for draining the site include measures for draining the pits. Prior to the excavation, it is first of all necessary to protect it from the flow of atmospheric waters from the surrounding area, from the penetration of water from neighboring water bodies, ditches, etc. by arranging berms or ditches.

3.6. Do not allow stagnation of water in the pits. With a small inflow of groundwater, it should be systematically removed through the device of wells 1 m deep below the bottom of the pit.

To lower the groundwater level, it is recommended to install vertical drains from a sand-gravel mixture around the perimeter of the pit.

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

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

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

3.9. To reduce the uneven moisture of heaving soils around foundations during design and construction, it is recommended: to carry out earthworks with a minimum amount of disturbance of natural soils when digging foundation pits and underground trenches engineering communications; it is imperative to arrange waterproof blind areas with a width of at least 1 m around the building with clay waterproofing layers at the base.

3.10. On construction sites, composed of clay soils and with a slope of more than 2%, when designing, it is necessary to avoid the construction of reservoirs for water, ponds and other sources of moisture, as well as the location of the sewerage and water supply pipelines in the building from the upland side of the building or structure.

3.11. Construction sites located on the slopes must be fenced off before the start of excavation from surface waters flowing down from the slopes by a permanent upland groove with a slope of at least 5%.

3.12. It is impossible to allow accumulation of water during construction from damage to the temporary water supply system. If standing water is found on the surface of the soil or when the soil is moistened from damage to the pipeline, it is necessary to take urgent measures to eliminate the causes of water accumulation or soil moisture near the location of the foundations.

3.13. When backfilling communication trenches from the upland side of a building or structure, it is necessary to arrange lintels of crumpled clay or loam with careful compaction to prevent water from entering (through trenches) to buildings and structures and moistening soils 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 the heaving soils of the built-up area is not allowed. It is necessary to take into account the projected change in the water level in rivers, lakes and ponds in accordance with the long-term master plan.

3.15. Avoid the location of buildings and structures closer than 20 m to existing dispensers for refueling diesel locomotives, washing cars, supplying the population and for other purposes, and also do not design dispensers on heaving soils closer than 20 m to existing buildings and structures. The areas around the dispensers should be planned with water drainage.

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

3.17. Particular attention should be paid to the season of periodic flooding of the territory, since the flooding of the territory in the autumn period most unfavorably affects the frost heaving, when the water saturation of soils increases before freezing. It is also necessary to predict an artificial increase in the level of groundwater and natural soil moisture due to the influx 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, their flow rate, direction and speed of their movement in the ground, topography of the roof of the waterproof layer. Without these data, the constructed drainage and drainage structures may be useless. If it is not possible to get rid of groundwater and drain the soils of the freezing layer, then one should resort to the design of constructive or thermochemical measures.

4. CONSTRUCTION AND CONSTRUCTION MEASURES AGAINST DEFORMATION OF BUILDINGS AND STRUCTURES DURING FREEZING AND SOIL FLOW

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

With full balancing of the normal and tangential forces of frost heaving of soils, measures against deformation are reduced to constructive solutions and calculation of loads on foundations. Only for the construction period, when the foundations overwinter unloaded or have not yet 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 apply such constructive measures that are aimed at reducing the forces of frost heaving and deformations of structural elements of buildings and the adaptation of 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 reckon with possible vertical alternating stresses from frost heaving of soils (raising of soils during freezing and their sedimentation 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 soils with different degrees of heaving cannot appear under the foundations of one building. If it is necessary to construct a building on soils with varying degrees of heaving, constructive measures should be taken against the action of frost heaving forces, for example, with strip prefabricated reinforced concrete foundations, arrange a monolithic reinforced concrete belt along the foundation cushions, etc.

4.4. When designing buildings and structures with strip foundations on highly heaving soils at the level of the top of the foundations, constructive reinforced concrete belts with a width of at least 0.8 wall thickness, 0.15 m in height and reinforced belts above the openings of the last floor should be provided for 1-2-storey stone buildings along the perimeter of the outer and inner walls.

Note. Reinforced concrete belts must have a concrete grade of at least M-150, reinforcement with a minimum 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 strongly and medium-heaving soils, it is necessary to take into account the effect of the normal forces of frost heaving of soils on the sole of the grillage. Precast reinforced concrete sub-wall randbeams must be monolithically interconnected and laid with a gap of at least 15 cm between the randbeam and the ground.

4.6. The depth of laying foundations in construction practice should be considered as one of the fundamental measures to combat deformations from uneven settlement of foundations and from frost bulging during freezing of soils, since the purpose of deepening foundations into the ground is to ensure the stability and long-term operational suitability of buildings and structures.

When designing, the depth of the foundations is assigned depending on the factors provided for in clause 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 state of soils at their base.

The depth of the foundation is meant the distance measured vertically, counting from the day surface of the soil, taking into account the filling or cutting to the base of the foundation, and if special training from sand, crushed stone or lean concrete - to the bottom of the preparation layer. The bottom of the foundation is the lower plane of the foundation structure, which rests on the ground and transfers pressure to the ground from the weight of the building and structure.

4.7. When determining the depth of the foundations, one should take into account the purpose and design features of buildings and structures. For unique buildings (e.g. high-rise buildings and the Ostankino television tower in Moscow), the soil properties serve as the criterion for deepening the foundations. It is known that at greater depths the soils are denser and can take significantly higher loads.

Prefabricated typical foundations of civil buildings of mass construction (for example, residential multi-storey buildings) are deepened according to the conditions of stability. It is not possible to give a typical solution to the depth of the foundations for all types of soils at the base, 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 ultimate deformations on non-heaving soils and stability on heaving soils.

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

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

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

4.8. Foundations for heavy equipment and machines, 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 the addition of soils increases with depth, and therefore, in order to increase the pressure on the base and reduce the size of the settlement of foundations when compaction of soils, a greater depth of foundation is taken compared to the depth of foundation under the conditions of freezing and heaving of soils.

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

4.9. There are cases when the natural relief of the site changes in the built-up area by diverting the channels of streams and rivers outside the construction site, and the old channel is backfilled with soil, or the site is leveled by cutting off the soil in one area and backfilling on the other.

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

When assigning the depth of the foundations, it is necessary to take into account the 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 level of groundwater and the consistency of clayey soils. Loose soils, water-saturated and containing in their composition a large number of organic residues cannot always be used as natural bases.

On weak and highly compressible soils, it is required to take measures to improve the properties of soils or to design pile foundations.

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

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

4.10. Periodic fluctuations in the level of groundwater in the stressed zone of the foundation of foundations strongly affects the bearing capacity of soils and causes deformation of the foundations and foundations. In addition, the close location of the groundwater level to the frozen soil layer determines the amount of frost swelling of the soil due to the suction of moisture from the underlying water-saturated soils.

A special type of groundwater is the so-called top water with a limited distribution in the plan and an unstable level of standing. ground water, contained in the soil in the form of separate foci. Quite often, perching water is found in the thickness of the seasonally freezing soil and causes a large unevenness of frost heaving of soils and bulging of foundations. Even within the same construction site, there are several centers of upstream water with different levels of groundwater standing, sometimes even pressurized.

It is necessary to take into account the depth of freezing and the degree of heaving of the soils when assigning the depth of the foundations, but as according to the condition of stability, freezing of heaving soils below the foot of the foundations should not be allowed.

4.11. The depth of the foundations of stone civil buildings and industrial structures on heaving soils is taken not less than the calculated depth of freezing of soils according to table. Chapter 15 of SNiP on the design of the 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 according to table. 1 chapter of SNiP on construction climatology and geophysics, and in the absence of data in it for a specific point or area of ​​construction based on the results of observations of a hydrometeorological station located in similar conditions to the construction site;

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

m t - coefficient taking into account the influence of the thermal regime of a 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 the foundations of buildings and structures.

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

In the practice of foundation construction, under the actual depth of soil freezing, it is customary to consider a layer of solid-frozen soil vertically from the surface to the bottom of the solid-frozen soil layer. The hydrometeorological service for the actual depth of soil freezing takes the depth of temperature penetration of zero degrees into the soil, since for agricultural purposes it is required to know the depth of freezing of the soil to zero temperature, and for the purposes of foundation construction, it is required to know how deep the soil is in the frozen state. Since the actual depth of freezing of soils depends on climatic factors (even at the same point in different years, the depth of freezing of soils fluctuates), then the average value is taken for the standard depth of freezing of soils in accordance with clause 3.30 of the SNiP chapter on the design of the foundations of buildings and structures.

It is necessary to subdivide the freezing of the soil under the base of the foundation into a one-time one when performing work on a zero cycle in winter and an annual one during the entire life of the building, when sign-changing deformations appear during seasonal freezing and thawing of soils during the period of operation. When assigning the depth of the foundations on the condition of excluding the possibility of freezing heaving soil under the base of the foundation is meant the annual freezing during the operation of buildings and structures, since according to the condition of freezing of the soil during the construction period, the depth of the foundation is not determined.

As mentioned above, the measure for the depth of laying the foundations against the prevention of freezing of the soil under the base of the foundation refers 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 the non-completion of construction works on the zero cycle.

In cases where the natural moisture content of soils does not increase during the construction and operation of buildings on weakly loosened soils (semi-solid and tough-plastic consistency), the depth of the foundations, subject to the possibility of buckling, should be taken at the standard freezing depth:

up to 1 m - not less than 0.5 m from the planning mark

up to 1.5 m - not less than 0.75 m from the planning mark

from 1.5 to 2.5 m - not less than 1.0 m from the planning mark

from 2.5 to 3.5 m - not less than 1.5 m from the planning mark

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

4.12. Based on the experimental verification of non-buried and shallow foundations at construction sites for last years in the practice of energy and agricultural construction, reinforced concrete foundations are used in the form of slabs, beds and blocks, laid without deepening on heaving soils under temporary buildings and structures of construction bases for thermal power plants and for equipment of outdoor switchgears of electrical substations. This completely eliminates the tangential forces of frost bulging and the accumulation of residual irreversible deformations of frost bulging. This method significantly reduces the cost of construction and at the same time ensures the serviceability of buildings and special equipment.

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

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

When cutting off the soil from the outside of the building walls, the standard depth of soil freezing is considered from the soil surface after cutting, i.e. from the planning mark. When adding soil around the walls from the outside, it is impossible to allow the construction of the building before filling the soil around the foundations 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 during freezing can damage the building due to lateral pressure on the basement walls.

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

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

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

Cases in the practice of foundation engineering are not uncommon when it is required to lay foundations on frozen soils. Under favorable soil conditions, it is possible to allow the laying of foundations on frozen soils without preliminary warming them up, but at the same time it is necessary to have reliable physical characteristics of soils in a frozen state and data on their natural moisture content in order to make sure that the soils are really very dense and low moisture with a solid consistency and according to the degree of frosty heaving, they are practically non-heaving. An indicator of the density of frozen clay soil is the volumetric mass of the skeleton of frozen soil more than 1.6 g / cm 3.

4.16. In order to reduce the forces of heaving and prevent deformations of foundations, due to freezing of heaving soils with the lateral surface of the foundations, you should:

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 the foundations;

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

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

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

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

h) apply full or partial replacement of heaving soil with non-heaving soil.

4.17. The calculation of the stable position of foundations on the effect of frost heaving forces of the base soils should be carried out in cases where the soils are in contact with the lateral surface of the foundations or are located under their soles, are heaving and their freezing is possible.

Notes (edit) ... 1. When designing capital buildings on deep foundations with high loads, the stability calculation can be made only for the construction period, if the foundations overwinter unloaded;

2. In the design and construction of low-rise buildings with structures that are insensitive to uneven precipitation (for example, with wooden chopped or cobbled walls), as well as for agricultural structures such as vegetable and silos made of wood materials, calculations for the effect of frost heaving forces can be avoided and do not apply measures against radiation.

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

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

Q n - the normative value of the force that keeps the foundation from buckling due to the friction of its lateral 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 - the standard value of the specific tangential heaving force, taken equal to 1; 0.8 and 0.6, respectively, for highly heaving, medium-heaving and slightly-heaving soils;

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

4.19. The normative value of the force that keeps the foundation from buckling,Q n due to friction of its lateral surface against thawed soil is determined by the formula

where - normative value resistivity displacement of thawed soil of the foundation along the lateral surface of the foundation, determined according to 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 anchor-type foundations, the forceQ n holding the foundation from buckling should be determined by the formula

where γ with p - the 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 - the 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 anchoring part of the foundation from its upper surface to the leveling mark, see.

4.21. Determination of 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 and generally buildings with lightly loaded foundations, especially for the use of monolithic non-stepped foundations.

Example... It is required to check the foundation slab made of expanded clay concrete with dimensions of 100 × 150 cm for 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 bed without burying it into the ground. According to the degree of frost heaving, the soil at the base of the slab is medium-heaving.

Substituting the values ​​of the quantities into the 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 cm 2; h 1 = 50 cm; σ n = 0.02 (by); 0.9 x 18> 1.1 x 150 x 50 x 100 x 0.02; 16.2<16,5 т.

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

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

MEASURES FOR THE DEVELOPMENT OF NON-DEPLOYABLE FOUNDATIONS ON HEAVY SOILS

6.3. When constructing non-buried foundations, tangential forces of frost bulging 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 are reduced to the preparation of the soils of the foundations for laying foundations on them in order to reduce frost heaving deformations and adapt the structures of the foundations and the above-foundation structure to alternating deformations.

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

Depending on the availability of non-porous soils or materials near the site, coarse and medium-sized sand, gravel-pebble, fine gravel, boiler slag, expanded clay and various mining waste can be used for the construction of cushions for foundation slabs.

On sites with fill or alluvial soils, the design of non-buried foundations in the form of slabs and beds should be performed in accordance with the requirements of Sec. Chapter 10 of SNiP on the design of the 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 the axes, sand is laid, filling under the outer walls with a thickness of 5-8 cm and a width of 60 cm. Formwork is installed, reinforcement is laid (three rods with a diameter of 20 mm) and concreting is performed (section of the tape is 30 × 40 cm). On excessively heaving soils, especially in low relief elements, it is recommended to lay a monolithic strip foundation on backfills with a thickness of 40-60 cm, but at the same time, the backfill soil should be compacted as much as possible;

b) after the completion of the foundation work, it is necessary to complete the layout of the site around the house, ensuring the flow of water from the building;

c) on medium-porous, slightly porous and practically non-porous soils, it is possible to arrange strip foundations from prefabricated reinforced concrete blocks with a section of 25 × 25 cm and a length of at least 2 m;

d) according to the standard design, it is imperative to lay a blind area outside the house with a width of 0.7 m, plant ornamental shrubs, prepare a soil layer around the house and sow seeds of sod-forming grasses. The planning of areas for sodding should be done with a ruler.

MEASURES FOR THE DEVICE OF LOW-DEPTH 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 abyssal soils. Local compaction of soils is achieved by driving foundation blocks into the ground or by installing prefabricated blocks in nests, rammed with an inventory compactor in a dynamic way, which increases the degree of industrialization of construction work, reduces the cost, labor costs, and costs of building materials.

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

Experimental studies to determine the deformation of frost heaving under pressure in natural conditions have established that when a locally compacted base freezes 60-70 cm below the base of the foundation, the value of frost bulging of the foundation is: with 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 vertical displacements at the foundation were not observed for two winters.

The use of local compaction of soils, at the base on medium and weakly loamy soils, makes it possible to use the freezing soil as a natural base with a foundation depth of 0.5-0.7 from the standard freezing depth of soils. So, for example, for the middle zone of the European territory of the USSR, the 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 vegetative-sod layer and filling, soil that does not contain plant inclusions;

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

c) a breakdown of the axes of the location of compacted foundations should be made after the equipment for local compaction of soils under detached foundations is delivered to the site;

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

for buildings in which vertical movements from 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 displacements 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 the permissible deformations.

Before installing shallow foundations on sites with a complex geological structure, it is necessary to clarify the settlements of foundations installed on a locally compacted base by static tests. The number of on-site tests is set by the design organization c. depending on hydrogeological conditions.

The technology for the construction of shallow foundations is described 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 INSULATING MEASURES TO REDUCE THE DEPTH OF FREEZING OF SOILS AND NORMAL FORCES OF FROST BLOWING OF LOW-DEEP FOUNDATIONS

EXPERIENCE IN THE APPLICATION OF THERMAL INSULATION MEASURES IN THE PRACTICE OF CONSTRUCTION

7.1. Thermal insulation measures used in the practice of foundation construction are subdivided into temporary (only for the construction period) and permanent (taking into account their effect during the entire service life of buildings and structures).

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

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

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

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

In some cases, instead of installing a blind area, sodding of the soil surface is used at the outer walls 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 DEVICE OF THERMAL INSULATION MEASURES TO REDUCE THE DEPTH OF FREEZING OF SOILS

7.2. In order to ensure the safety of the blind area and their heat-insulating effect, instead of the blind area on heat-insulating cushions, it is recommended to use expanded clay concrete for the blind area with a dry bulk density from 800 to 1000 kgf / m 3 with a calculated value of the thermal conductivity coefficient, respectively, in a dry state 0.2-0.17 and in water-saturated 0.3-0.25 kcal / m · h · ° С.

Laying the blind area of ​​expanded clay concrete should be done only after careful compaction and leveling of the soil near the foundations at the outer walls.

It is advisable to lay the expanded clay concrete blind area on the surface of the soil with the calculation of its lower water saturation. Claydite concrete should not be laid in an open trough in the ground to the thickness of the blind area. If, due to the 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 construction of expanded clay concrete blind area is taken in the simplest form in the form of a tape, the dimensions of which are assigned depending on the estimated depth of soil freezing according to table. 5.

Table 5

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

The proposed dimensions of expanded clay concrete blind area 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 need the same experimental verification at construction sites.

8. INSTRUCTIONS FOR PRODUCTION OF CONSTRUCTION WORKS FOR ZERO CYCLE

8.1. The following requirements are imposed on the production of zero-cycle works: to avoid excessive water saturation of heaving soils at the base of the foundations, to protect them from freezing during the construction period and to finish excavation work on filling the sinuses and planning the site around the building under construction in a timely manner.

In the practice of construction, sometimes on lowered sites, soil filling is used by refluxing fine-grained or dusty sand from the bottom of the reservoir. Since the sand with water jet is poured from the pipes onto the site (from which the water rolls down and the soil settles), it is necessary to provide for the drainage of the reclaimed sand layer in order to self-compact it and reduce water saturation.

Usually reclaimed fine and silty sands are in a water-saturated state for a long time, therefore, when frozen, such soils turn out to be highly porous and at the same time poorly compacted.

When using refilled soils as natural bases, it is impossible to prevent freezing of soils under the foundations and lay the foundations on frozen soil, even for low-rise buildings.

Where buildings have already been built or are under construction, it is necessary not to allow the reclamation of heaving soils closer than 3 m from the foundations of the outer walls.

Mode of production earthworks with the use of hydromechanization, it can be harmlessly used in the southern regions of our country, where the standard freezing depth of soils is not more than 70-80 cm, as well as in non-porous soils throughout the USSR. But on sites formed by heaving soils, the development of soils using hydromechanization should not be carried out, since this method saturates the soils with water, which violates the requirements of paragraphs. 3.36-3.38, 3.40 and 3.41 of the SNiP chapters on the design of the foundations of buildings and structures on the protection of soils from excessive water saturation with surface waters. In principle, there is no categorical prohibition in the use of soil development by hydromechanization, but with this method it is necessary to take the necessary irrigation and drainage measures to drain the soil at the base of the foundations, and give appropriate 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 earthworks. Trenches should be torn off for laying strip prefabricated and monolithic foundations of small width so that the width of the sinuses can be covered with an indentation or a waterproofing screen. After installing prefabricated foundations or placing concrete in a monolithic foundation, immediately backfill the sinuses with careful compaction of the soil and ensuring drainage from the accumulation of surface water around the building, without waiting for the final layout of the site and laying the blind area.

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

It is advisable to carry out all work on laying foundations and filling the sinuses in the summer, when work can be done quickly and with high quality at a relatively low cost of earthworks. It would be useful to observe the seasonality of work on the zero cycle 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 solid-frozen state, it is often necessary to resort to artificial thawing of the soil in various ways, which speeds up excavation and does not impair the building properties of soils at the base of the foundations. Thawing of heaving soils by letting water vapor into drilled wells should not be used, as this sharply increases soil moisture due to water vapor condensate.

8.4. The filling of the sinuses should be carried out after the end of the concreting of monolithic foundations and after the laying of the basement 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, create favorable conditions for the deformation of the foundations and the superstructure by the tangential forces of frost bulging. It is even worse when the sinuses are backfilled in winter with frozen soil and without compaction. The laid revenge near the foundations usually fails after thawing and self-compaction of the soil in the sinuses.

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

The use of mechanisms for compacting the soil when filling the sinuses is difficult due to the presence of basement walls, which create cramped conditions for the operation of the mechanisms.

8.5. According to the requirement of the SNiP chapter on the design of the foundations of buildings and structures, it is necessary to apply measures to prevent freezing of heaving soil below the base of the foundation during the construction period.

In the case of overwintering of the laid foundations and slabs, one should not forget about the protection of the soil from freezing, especially when the foundations will be loaded during the laying or installation of the walls of the building before the soil thaws below the sole of the foundations. In order to protect the soil from freezing at the base of the foundations, various methods are used, starting with backfilling with soil and ending with covering the foundations and slabs with heat-insulating materials. Snow deposits are also a good thermal insulation 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 should be covered with a standard freezing depth of more than 1.5 m with mineral slabs in one layer, slag-wool magicians or expanded clay with a bulk density of 500 kgf / m 3 and a thermal conductivity coefficient of 0.18 layer 15 -20 cm.

If the building has been erected, and the soils at the base of the foundations are frozen, then it is necessary to take care of ensuring uniform thawing of the soils under the base of the foundation by laying heat-insulating coatings on the outer sides of the foundations and heating the soils inside the building, for which you can use electricity or heating the air in the underground with heaters and temporary heating stoves.

For uniform thawing, the walls of winter masonry on the south side have to be covered with matting, shields, tar paper, plywood or straw mats to protect them from collapse during rapid and uneven thawing.

Storage of concrete blocks, bricks, crushed stone, sand, expanded clay and other materials can be used as thermal insulation for the period of thawing of soils near the foundations outside the building for 1-1.5 months from the southern side.

Due to the uneven thawing of soils under the outer and inner transverse load-bearing walls, through cracks form under and above the openings on the transverse internal load-bearing wall. These cracks usually widen and sometimes reach tens of centimeters at the top, while at the outer longitudinal walls there is a roll with a deviation of the upper part away from the building. With large rolls, large sections of the outer and inner walls have to be disassembled.

The roll of the outer walls is often formed during the freezing of the soil in January-March, when the foundations of the outer walls are laid at the calculated depth of freezing of the soil, and the foundations are laid shallowly under the inner bearing walls (by half or even one third of the standard depth of freezing of soils).

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

8.6. At the first detection of even small hair 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 appeared under the action 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 thawing of the soil inside the building under the foundations of the internal load-bearing walls, which will cause the foundation to settle and the cracks will close partially or completely. It is necessary to refrain from continuing the erection of walls or erection of prefabricated houses with a frozen base until the soil under the foundations has completely thawed and until the settlement of the foundations has stabilized after the soil has thawed.

8.7. At construction sites, during the production of work, the soils at the base are locally saturated with water from the leakage of water into the ground from the faulty water supply network. This leads to the fact that in some areas, clayey soils from non-porous and slightly porous, turn into highly porous, with all the ensuing consequences.

To protect the soils at the base of the foundations from local water saturation during the construction period, the temporary water supply lines of construction sites should be laid on the surface so that it is easier to detect the appearance of water leakage and timely repair damage to the water supply network.

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

9.1. During the industrial operation of buildings and structures erected on heaving soils, changes in the design conditions on the bases and foundations should not be allowed. To ensure the stability of the foundations and the serviceability of buildings, it is necessary to take measures against an increase in the degree of heaving of soils and the appearance of deformations of structural elements of a building from frost bulging of foundations. These measures are reduced to meeting the following requirements: a) not to create conditions for increasing soil moisture at the base of the foundations and in the zone of seasonal freezing closer than 5 m away from the foundations; b) to prevent deeper freezing of soils near the foundations in relation to the calculated depth of freezing of soils adopted during the design; c) do not allow cutting the soil around the foundations when redeveloping a settlement or a building site; d) not to reduce the design load on the foundation.

In order to combat an increase in the natural moisture content of soils at the base of foundations during the industrial operation of buildings and structures, it is recommended to: drain all industrial, domestic and storm water into lowered places away from the foundations or into storm sewer receivers and keep the drainage structures in good condition; every year, all work on cleaning surface drainage systems, i.e. upland ditches, ditches, trays, water intakes, openings of artificial structures, as well as storm sewers, should be carried out before the beginning of autumn rainy weather. It is necessary to periodically monitor the condition of drainage structures, all work to correct damaged slopes, violations of planning and blind area should be performed immediately, without delaying these works until the soil freezes. If this damage has formed stagnant water on the surface of the soil near the foundations, it is necessary to urgently ensure the drainage of surface water from the foundations. In case of detection of storm water erosion on the ground, it is necessary to urgently eliminate soil erosion and strengthen the areas along the drain with a large storm water drop.

9.2. The heat-insulating coatings provided for by the project and carried out by the construction at the foundations around the buildings in the form of blind areas on slag or expanded clay cushions, turfing of the soil surface or other coatings must be maintained in the same condition as was done according to the project during construction. When carrying out major repairs of buildings, it is impossible to allow overwintering of heated buildings without heating, as well as replacing the blind area around buildings with thermal insulation coatings with blind areas without thermal insulation coating.

During major repairs of buildings, it is impossible to allow lowering of the planning marks for built buildings on highly heaving soils, since the depth of the foundation may turn out to 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 off should be at least the estimated freezing depth of the soil, and if conditions allow, then leave a strip of untouched soil (i.e., without cutting) near the foundations 3 m wide. such cases, when the distance from the planning mark to the base of the foundation, after cutting off 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 waters and other irrigation and drainage devices, which made it possible to prevent water saturation of soils near the foundations of buildings and structures.

9.3. During the 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 frosty bulging of foundations and the pressure on the foundations from the weight of the building.

Often, when the loads on the foundations increase, it is necessary to apply the reinforcement of 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 bulging increase in proportion to the increase in the area of ​​freezing of the foundation with the ground. Consequently, when designing the reinforcement of foundations (especially columnar ones), it is necessary to check the stability of the foundations for the action of the tangential forces of frost buckling.

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

9.4. The areas with grass cover provided for by the project require annual maintenance, which consists in timely preparation of the soil layer, over-sowing of sod-forming grasses and replanting of shrubs. The presence of a sod layer reduces the depth of freezing of soils by almost half, and shrubs accumulate snow deposits, which reduces the depth of freezing by more than three times compared to the depth of freezing in an open area. It is better to carry out all work on the care of both the sod cover and the shrub plantations in the spring without violating the territory planning adopted by the project. Where the sod cover and the leveling of the soil surface are disturbed as a result of excavation work to eliminate accidents of underground communications or the passage of vehicles, it is necessary to restore the leveling, loosen the vegetation layer and sow the seeds of sod-forming grasses again. The best grasses are considered to be the mixtures of the local flora. During the hot and dry months, it is necessary to water the sod cover 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 found in the form of cracks in the walls of brickwork and distortions at the openings of large-block or panel fences. At the first detection of deformation of structural elements of a building, it is necessary to establish a systematic observation of the change in these deformations according to the beacons installed on the cracks and according to the leveling data of the established marks. All fundamental measures to eliminate existing deformations should be prescribed only after the causes of these deformations have been established. In especially difficult cases, the administration of the enterprise should contact a design or research institute to establish the causes of deformation and develop measures.

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 standard 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 temperature of the soil and the adhesion forces of the frozen soil with the planes of the foundations.

When appointing anti-seam 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 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 containing aggregate particles less than 0.1 mm in size in an amount of more than 30% by weight, freezing under humidified 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

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.

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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.

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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 base of the foundation. 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 ().

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