Foundations on a natural basis differ: by design - into separate, tape, solid and massive; by material - for concrete and reinforced concrete (prefabricated and monolithic), brick, rubble, sawn stone, etc.; by appointment - for foundations for buildings (residential, industrial, etc.), structures, equipment.

Separate foundations are pillars with a developed supporting part, transferring to the ground concentrated loads from columns, corners of buildings, frame supports, beams, trusses, arches and other elements. To install columns in the upper part of individual foundations, recesses - “glasses” are arranged. Such foundations are usually called separate glass type.

Strip foundations are used to transfer loads from extended elements of building structures - walls of buildings, structures, equipment support frames, etc. According to the arrangement in the plan, they differ into intersecting and parallel.

Solid foundations are built under the entire area of ​​the building. By constructive solutions they are divided into slab and box-shaped. Slab foundations, in turn, can be ribbed (caisson) and smooth.

Massive foundations are arranged for towers, masts, columns, heavily loaded supports of artificial structures (bridge supports), for machines, machine tools and other equipment.

The classification of foundations on a natural basis by design is shown in fig. IV-1, and according to the materials used - in table. IV-1.

Rice. IV-1.

Table IV-1

Classification of foundations on a natural basis according to the materials used

foundation type	Material
	concrete and reinforced concrete		but	brick	sawn stone
	made	monolithic
1. Individual: Glassless Glass 2. Tape 3. Solid 4. Massive	+ + + – –	+ + + + +	+ – + – +	+ – + – +	+ – + – +
Note. The + sign marks the materials used for the listed foundations.

Ministry of Science and Education of Ukraine

Odessa state academy construction and architecture

Foundations on a natural basis. Functions of the foundation as part of the structure. Depth of laying. Types of foundations (tape, columnar, solid slab)

Performed:

2nd year student gr.Mk-247

Yaroshenko Anna Igorevna

Introduction

Main part

Foundation types

Foundation functions as part of a structure

Depth

List of used literature

INTRODUCTION

Foundation - (Latin fundamentum) - an underground (underwater) foundation for houses, buildings and structures, which is usually made of concrete, stone or wood. Serves as an integral part of the building and is the main load-bearing structure, the main function of which is to transfer the load from the building to the ground base.

The base is considered to be the layers of soil lying below the base of the foundation and to the side of it, perceiving the load from the structure and affecting the stability of the foundation and its movement. The design of the foundations of buildings and structures depends on a large number factors, the main of which are: geological and hydrogeological structure of the soil; climatic conditions of the construction area; construction of the building under construction and foundation; the nature of the loads acting on the foundation soil.

The foundation for the foundations of buildings and structures can be natural, they are called soils that, in natural occurrence, have sufficient bearing capacity to withstand the load from the building or structure being erected. Natural foundations do not require additional engineering measures to strengthen the soil; their device is to develop a pit to the estimated depth of the foundation of a building or structure.

Soils suitable for the construction of natural foundations include rocky and non-rocky. Rocky soils are deposits of igneous, sedimentary and metamorphic rocks (granites, limestones, quartzites, etc.). They occur in the form of a continuous array or separate fractured layers. They have a high density, and therefore, water resistance and are a solid foundation for any type of structure. Non-rocky soils include coarse, sandy and clayey soils. Coarse-clastic soils (crushed stone, gravel, pebbles) are pieces formed as a result of the destruction of rocks, with a particle size of more than 2 mm. They are inferior in strength to rocky soils. If coarse-grained soils are not exposed to groundwater, they are also a reliable foundation.

sandy soils are particles of rocks with a particle size of 0.1 ... 2 mm. Sands with a particle size of 0.25 ... 2 mm have a significant. The strength and reliability of sandy foundations depend on the density and thickness of the underlying sand layer: the greater the thickness of the occurrence and the more uniform the density of the sand layer, the stronger the foundation. With regular exposure to water, strength sandy base decreases sharply.

Clay soils are finely dispersed scaly particles less than 0.005 mm in size. Dry clay base can withstand heavy loads from the mass of buildings and structures. With an increase in the moisture content of clay, its bearing capacity drops sharply. The influence of positive and negative temperatures in wet clay causes shrinkage during drying and swelling when water freezes in the pores of clay soil. A variety of clay soils are sandy loam, loam and loess.

Sandy loamy soils are a mixture of sand and clay particles in the amount of 3 ... 10%. Loamy soils consist of sand and contain 10...30% clay particles. These types of soils can be used as natural bases (if they are not subject to moisture). In terms of their strength and bearing capacity, they are inferior to sandy and dry clay soils. Some types of sandy loam, regularly exposed to groundwater, become mobile. Therefore, they received the name quicksand. This type of soil is unsuitable as a natural base.

Loess soils are particles of silty loams with a relatively constant granulometric composition. Loess soils in a dry state can serve as a reliable foundation. When moistened and exposed to loads, loess soils are strongly compacted, resulting in significant subsidence. Therefore, they are called landing.

The name of soils, as well as the criteria for identifying soils with specific properties and their characteristics are given in SNiP “Foundations of buildings and structures. Design standards".

Foundations are usually laid below the freezing depth of the soil, in order to prevent them from buckling. On heaving soils in the construction of light wooden buildings, shallow foundations.

foundation supporting structure depth

MAIN PART

Currently, the following types of foundations are used for the construction of residential buildings - columnar, tape and solid slab. The choice of foundation design depends mainly on the soil conditions of the construction area, the loads on the foundations and the design features of the building being designed.

Tape

Tapefoundations are used for houses with a large mass of walls: brick, stone, concrete, as well as under wooden ones, which are planned to be faced with bricks.

The foundation is laid around the entire perimeter of the house, including internal and external capital walls. Masonry can be of various shapes: rectangular, trapezoidal, stepped, or with an expanded lower part, otherwise called a pillow. For optimal load compensation from a massive building, a trapezoid shape is used. When using brick or rubble as a foundation material, the angle of inclination of the side face to the vertical should not exceed 30 °, and for concrete - 45 °.

Strip foundations are divided into: monolithic and prefabricated. For the construction of a monolithic foundation, concrete and reinforced concrete are usually used. For the manufacture of their construction, formwork is necessary - a reinforcing structure, or the so-called form for concrete, which is installed at the bottom of the pit. It can be mobile, collapsible and portable, volume-block. Wood or metal is used as a material for its manufacture. Inside the formwork, as a rule, thermal insulation sheets, expanded clay, mineral wool boards, or foam plastic are laid. Concrete is poured in an even layer, without fail compacting. The advantages of a monolithic foundation are not only in its strength and durability, but also in the fact that it is suitable for building houses of any shape.

The material for prefabricated foundations are concrete or reinforced concrete blocks (FBS), which are laid on the mortar and fixed together with a thick steel wire. They are built faster and easier than monolithic ones and are not inferior to them in strength, but they have a high cost, and can also let water through at the junction of the plates.

brick foundation- less durable and more laborious than monolithic. During its construction, a full-bodied moisture-resistant red brick is used.

rubble foundation considered the most durable, but too costly, since the rubble stones used for its construction are difficult to select and adjust in size. But the construction of such a foundation is simply necessary on wet soils, due to the moisture resistance of rubble stone.

In general, the disadvantages of strip foundations are their massiveness, high labor costs, materials and, accordingly, funds. However, they are widely used due to their simple construction technology.

columnarfoundations for walls are suitable for light loads and solid foundations. They are used, as mentioned above, mainly in industrial construction in frame buildings. In residential and civil, they are designed, as a rule, in low-rise buildings without basements. Column foundations are made in the form of wooden chairs and in the form of pillars of square, rectangular and trapezoidal sections made of ceramic bricks, rubble, concrete, reinforced concrete and other materials.

Pillar foundations are used for the construction of houses with wooden, chopped, frame shield walls, that is, walls that are light in weight. The construction technique is very simple: a well is drilled in the ground, reinforcement is installed in it, and then cement or other provided material is poured. Especially successful is the addition of the foundation with a reinforced grillage tape, it is almost 2 times more economical.

However, if some rules for installing a columnar foundation are not followed, it will not be able to perform its functions. It is fundamental that the well should be drilled to a depth of at least 2 m, that is, deeper than the level of soil freezing. Secondly, a sand cushion is arranged at its bottom, or a special stone or concrete slab is installed, in extreme cases - a plate of wooden beams 10 cm thick, 20 cm wide and 50 cm long. Its functions are to ensure the stability of the foundation and reduce the pressure of the house on the ground. Thirdly, the pillars are installed at all corners of the building, as well as at all intersections of the capital and non-capital walls. The gaps between the posts should be no more than 1.2-2.5 m, in which a jumper should be arranged, which serves to tie the supports between themselves and the base for the base. If the distance between the pillars is greater than the specified one, it is necessary to erect end beams, reinforced concrete or metal.

The material for the pillars can be wood, brick, stone, concrete. As for wood, it is recommended to use pine or oak, the service life of which is at least 6 and 13 years, respectively. Burnt or bitumen-coated poles will last 1.5-2 times longer. Their diameter should be about 20 cm. Red brick is not suitable for building a foundation, but iron brick, obtained by firing ordinary brick, is perfect. The dimensions of the pillars when using rubble stone are 60x60 cm, iron bricks - 50x50 cm, concrete or rubble concrete - 40x40 cm.

At present, the method of combining columnar and strip foundations has become widespread, although many experts believe that the foundation should be homogeneous, since only in this case can its service life, response to climatic and other conditions be accurately predicted.

The advantages of the columnar foundation are: its efficiency and low labor intensity. It is especially convenient to use this foundation in climatic zones with deep soil freezing. However, the following are considered serious disadvantages of this type of foundation: insufficient stability in horizontally moving soils, difficulty in building a basement, unacceptability for construction on weakly bearing soils, especially with a large mass of walls.

Solidfoundation. The need to build a solid foundation arises during construction on the so-called "floating" soils, as well as on soils with a high groundwater table. For example, on sandy pillows, compacted landfills, swelling soils.

Slab foundations are constructed under the entire area of ​​the building in the form of either monolithic slab, or reinforced concrete lattice. Such a foundation is appropriate for the construction of small compact structures that do not require a high base, for example, garages, baths, workshops. For the construction of more massive buildings, they resort to the use of ribbed slabs or reinforced cross tapes.

The advantages of a solid foundation include: its ability to level the vertical and horizontal movements of soils, to exclude the penetration of groundwater into the basement even under high hydrostatic pressure, as well as the simplicity of construction. Most often, this type is used to give the foundation the quality of spatial rigidity. But due to the high consumption of materials for its construction, it is very expensive for a consumer with an average income.

Depending on the loads acting on the foundation, piles are placed in it: one at a time - under separate supports; in rows under wall structures; bushes - under the columns; pile fields - for buildings and structures of a small area with significant loads.

The main function of the foundation is to transfer the load from the walls and roof to the foundation to transfer the load of the building to the soil surface.

Depthfoundations depends on a number of conditions: the type of structure (house, bathhouse, garage, outbuildings) and its design features (the presence of a basement, basement floor, etc.); the magnitude and nature of the loads acting on the foundation; geological and hydrogeological conditions of the site; the possibility of heaving of the soil during freezing and precipitation during thawing.

The minimum depth of foundations for the external structures of structures erected on all soils, except for rocky ones, should be at least 0.5 m from the surface of the site layout. In buildings with basements, the reduced depth of the foundation footing relative to the floor must be at least 0.5 m; with dense or compacted soils, it is allowed not to bury the foundation into the ground, i.e. take the laying depth equal to the thickness of the preparation for the floors and the basement floor (Fig. 1).

Soil type

Groundwater level

Freezing depths.

The type of soil has a very strong influence on the depth of laying. First of all, it is important the property of the soil to change its volume in the wet state during freezing (the so-called frost heaving of the soil), according to this characteristic, the following types of soils are distinguished:

Rice. 1. The depth of the foundation in relation to the basement floor:

Sand preparation under floors h1;

Basement concrete floor h2;

Basement floor level;

Foundation depth relative to the basement floor Np;

Not heaving - rocky and semi-rocky rocks.

Slightly heaving - coarse clastic soils, gravelly sands, large and medium.

Heaving - fine sands, silty sandy loams, loams.

The level of groundwater is also important in the design of foundations and is entirely determined by the hydrogeological conditions of the area. High groundwater level at heaving soil may require such expensive solutions for the construction of foundations and basement waterproofing that it would be more profitable to abandon such a site for construction.

It is often possible to preliminarily determine the level of groundwater without conducting serious physical studies. Such information can be obtained in neighboring populated areas. In this case, its sources can be: local firms involved in the study and testing of soils; local engineers advising in the field of construction; city ​​building departments; local real estate agents; owners of adjacent lots.

The depth of the foundation for rocky and semi-rocky rocks can be any and does not depend on the level of groundwater or the depth of freezing. If the soil consists of gravel, coarse or medium sands, then the depth of the foundation should be 0.5 meters, regardless of the level of groundwater and the depth of freezing.

When the soil is heaving, then, depending on the level of groundwater, three options are possible:

If the groundwater level exceeds the calculated depth of soil freezing by more than 2 m, it is enough to deepen the foundation by only 0.5 meters.

If the groundwater level exceeds the soil freezing depth by less than 2 m, then the laying depth is about 75% of the soil freezing depth, but should not be less than 0.7 meters.

If the groundwater level is less than the calculated depth of soil freezing, then the depth of laying should not be less than the depth of soil freezing.

The foundation is supporting structure the whole house. It is on him that the strength and durability of the house depend. The functions of the foundation include transferring the load from the building to the ground, as well as resisting the influence of groundwater and frost.

The main requirements for foundations are: strength, stability, resistance to the influence of atmospheric conditions and negative temperatures, durability corresponding to the service life of the above-ground part of buildings and structures, industrial design of structures, cost-effectiveness.

The main function of the foundation is to bear the entire load of the main architectural components of the structure, preventing their premature destruction, decay, subsidence, cracking, deformation and other negative processes that occur under the natural influence of gravity or negative climatic conditions.

Tape foundations are made in the form of continuous walls, columnar foundations - in the form of a system of free-standing pillars and solid - in the form of a solid slab of rectangular or ribbed section for the entire building.

The depth of the foundation is directly dependent on three factors:

Soil type

Groundwater level

Freezing depths.

The strength and stability of any structure primarily depend on the reliability of the base and foundation.

LIST OF USED LITERATURE

1. Anatoly Sergeevich Shcherbakov "Fundamentals of the construction business"

Foundation Depth: [#"justify">.

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Foundations on a natural basis. Scope, design features, classification. Engineering-geological surveys and their assessment. Design principles.

Foundations- this is an underground or underwater part of a structure that receives loads from upstream structures and transfers them to the foundations.

Foundations can be divided into varieties: foundations shallow on a natural basis pile foundations and foundations deep.

Foundations of shallow laying on natural grounds.

Shallow foundations on natural bases they call such foundations that are built in open pits with a depth of at least 5-6 m. requirement to the foundations - they are sufficient strength, durability, frost resistance, stamina against aggressive impact groundwater.

The foundation must be of such dimensions that the average pressure along the sole (under the sole) of the foundation does not exceed the design soil resistance of the base. In addition, the calculated values ​​of absolute settlements and settlement differences between individual foundations of one structure should not exceed the limit values ​​established by design standards.

Used for foundations reinforced concrete, concrete, rubble concrete, rubble masonry , Sometimes - cement soil.

Varieties of shallow foundations:

1) individual foundations under the columns in combination with foundation beams(random beams);

2) columnar foundations under brick walls;

3) tape foundations under brick walls(continuous);

4) tape foundations under the columns;

5) foundations from cross bands for columns;

6) foundations in the form solid slab;

7) massive foundations.

1). Separate foundations under the columns in combination with foundation beams(random beams) are usually used in industrial buildings with not too large loads on the ground, it is enough durable And little compressible soils, a flexible scheme of operation of the above-ground part of the building, when the column and crossbars or the column and the truss are hinged.

They differ in the method of attaching the foundation to the column.

More often:

A) monolithic(small columns) (Figure 1:1).

Figure 1.1. 1 - concrete on fine aggregate not lower than the class of concrete of the foundation itself (not lower than B20); 2 - glass;

b) large columns - without a glass, rigid joint- Welding and joint is monolithic with concrete.

Figure 1.2.

2). Separate foundations under brick wall (glassless, columnar). They are used for low-rise buildings, under good soil conditions, as a rule, for private individual construction.

Figure 1.3. Separate foundation for a brick wall (glassless, columnar)

Figure 1.4. Cross sections columnar foundations

3). Tape foundations under brick walls.

Strip foundations are sometimes called continuous. Applicable for uniform load from the walls to the ground and permanent along the wall ground conditions(plane deformation condition (l/b ≥ 10).

Changing the dimensions of the laying depth is possible only in certain sections of a limited length. Areas that have different sizes foundations, separated sedimentary seams.

They are used with significant loads and rather weak soils. Significantly change the rigidity of the structure. Almost do not work for bending in the longitudinal direction (with high rigidity of the walls).

Figure 1.5. Prefabricated strip foundation under the wall

Figure 1.6. Strip foundations:

a - monolithic; b - prefabricated solid; in - prefabricated intermittent;

1- reinforced tape; 2 - foundation wall; 3 - building wall; 4- foundation cushion; 5 - wall block

Figure 1.8. Foundation slab designs:

a - solid; b - ribbed; c - with corner cutouts

4) Tape foundations under the columns.

Used for column spacing no more than 6 m and if available weak soils.

Reduce uneven settlement of individual columns.

5) Cross strip foundations for columns. It is applied at a small step of columns, at big loadings and weak soils. Cross tapes allow you to equalize the settlement of not only individual columns in a row, but also the building as a whole.

Figure 1.9. Cross strip foundations for columns

6). Solid slab (smooth) foundation. Foundations in the form of a solid slab, both under columns and under brick walls, are arranged under the entire structure or part of it in the form of reinforced concrete slabs under a grid of columns and walls. Such foundations bend in two mutually perpendicular directions, have a small uniform settlement, they are not afraid of surface water flooding, and they also protect the basement parts of the building. The dimensions of such foundations are determined by the dimensions of the structure in plan.

Figure 1.10. Solid slab (smooth) foundation for columns

Figure 1.11. Solid slab (smooth) foundation

Figure 1.12. Solid slab foundation

Figure 1.13. Slab foundations with prefabricated cups

Figure 1.14. slab foundation with monolithic glasses

Figure 1.15. Slab ribbed foundation

Figure 1.16. Solid foundation for a group of columns

Figure 1.17. solid box foundation

7) Massive foundations- these are the foundations of massive structures with a massive underground part (foundations of dams, bridge supports, blast furnaces, chimneys, under machinery with dynamic loads). They create a large inertia, prevent oscillations, reduce the amplitude, speed, acceleration of oscillations, etc.

Figure 1.18. Massive foundation for a blast furnace

Figure 1.19. Blast slab foundation

Figure 1.20. Bases for furnaces located on the lower floor of the building:

a - at the stone walls of the building; b - in the openings of the walls on the broadening of their foundations 1 - oven; 2 - waterproofing; 3 - pre-furnace steel sheet; 4 - wooden floor; 5 - brick rubble or concrete foundation; 6 - sand; 7 - open retreat; 8 - Brick wall; 9 - grouting; 10 - wall lintels; 11 - blind cutting half a brick thick

According to the method of constructing foundations in the pit, they distinguish monolithic And prefabricated.

Natural foundations are soils or rocks that are in the conditions of their natural occurrence and perceive the load from the foundations.

Choice construction site for a building or structure is determined primarily by the geological and hydrogeological conditions of the foundation. At the same time, the nature of the strata of soils and the thickness of each layer, their physical and mechanical properties, the level of groundwater, the possibility of erosion, etc. are established.

Soils are explored by drilling or pitting. Drilling makes it possible to take soil samples from various depths. Samples are taken at least every 0.5 m in height. This is the fastest and easiest way of geological exploration of the base.

Drilling allows you to directly examine the soil in natural conditions and test it on samples of significant size with an undisturbed structure. The pits are rectangular wells dug to various depths.

To obtain a geological profile of a certain soil section, the boundaries of homogeneous layers that are found in pits or wells located along the same axis are connected to each other. Several such vertical sections give an idea of ​​the geological structure of this soil massif.

The calculation of the base consists in limiting the deformations of the structures of buildings, determined by the magnitude of the load, which is called the design resistance of the base. This load must correspond to such a subsidence of the base, at which the deformations that occur in the structures of a building or structure do not exceed those permissible for their normal operation.

The settlement of the base under the foundation depends on the ratio between the load on the soil and its deformation, as well as on the distribution of pressure in the soil. The sole of the foundation, transferring the load to the base, causes corresponding stresses in it. With increasing depth, these stresses spread to ever larger volumes of soil, but their magnitude decreases. If we consider the horizontal plane, then the stresses in it are distributed unevenly. Their greatest value is observed in the center of load application with a gradual decrease towards the periphery (Fig. 53).

The distribution of pressure depends on the shape of the foundation in plan. Under strip foundation the pressure in the soil with depth will decrease much less than under a square foundation, where it immediately spreads evenly in four directions, and not in two, as under a strip foundation. For example, at a depth of 1 m the value of the average pressure in the soil under the strip foundation will be equal to 0.55 R, and under a square foundation 0.34 R at depth 2 and 3 m respectively 0.31 R and 0.21 R, 0,11 R and 0.06 p(p- the value of the average pressure in the soil under the base of the foundation).

Estimated soil resistance at a foundation depth of 1.5 to 2 m and foundation width 0.6-1 m the following are installed:
clay soils - from 1 to 6 kg/cm2(depending on porosity and humidity);

Rice. 53 Graph of pressure in soils

Sands - from 1 to 4.5 kg/cm2(depending on particle size, humidity and density);
- coarse soils - from 3 to 6 kg / cm 2;
- rocks - 1/6 of the compressive strength of the rock (regardless of the size and depth of the foundation).

With a foundation depth of less than 1.5 m the design resistance is reduced, and at more than 2 m- increase, since soils become denser with increasing depth under the influence of the weight of the overlying layers.

In addition, with a foundation width of less than 0.6 m the design soil resistance should be reduced, and if more than 1 m- increased.

The strength and stability of any structure is ensured, first of all, by the strength and stability of the foundation, which must be laid on a solid foundation.

foundation called the thickness of natural strata of soils, directly perceiving the load and interacting with the foundation of the structure under construction.

The grounds are called natural if the soils under the base of the foundation remain in their natural state. In case of insufficient soil strength, measures are taken to artificially strengthen them. Such grounds are called artificial. natural foundation

can serve as a variety of soils that make up the upper part of the earth's crust. Natural soils used as natural foundations are divided into four types: rocky, coarse, sandy and clayey.

The bearing capacity of clay soil is highly dependent on moisture content. The bearing capacity of dry clays is quite high and such soils can serve as a good base, with an increase in humidity, their bearing capacity drops significantly.

Sandy loam and fine-grained sands, when liquefied by water, become so mobile that they flow like a liquid, and are called quicksand.

The construction of buildings on such soils is associated with significant difficulties.

Clay soils also include loess, which, when soaked in water, have subsidence properties or swell. The use of their soils as bases requires the use of special measures.

In addition to these types, there are also soils with organic impurities (vegetable soil, peat, swampy soil, etc.), permafrost and bulk soils. Soils with organic impurities are not used as natural bases, since they are heterogeneous in composition, loose, and have significant and uneven compressibility. Filled soils are also heterogeneous in composition and compressibility, and their use as foundations requires special justification.

Strengthening of soils by means of surface silt and their deep compaction is carried out by tamping with pneumatic rammers with tamping of crushed stone, silt and gravel. Compaction with tamping plates and a mass of 1 ton or more, which are dropped from a height of 3–4 m, reaches a depth of 2–2.5 m. For compaction of large areas, compaction of the soil with heavy rollers is used.

Sandy and silty soils are well compacted by vibrating with special and surface vibrators, and such compaction is carried out much faster than when tamping.

Deep soil compaction is carried out using sand or soil piles. Inventory steel pipes with a diameter of 400-500 mm with a pointed drop-down steel shoe at the end are introduced into the ground with a vibratory hammer. The pipes immersed to the required depth are filled with sand and then removed with vibration. With this extraction, the sand is compacted and well fills the well.

Strengthening the weak soil of the base (its strengthening) is also achieved by the use of plugging (cementation, silicification and bituminization).

foundation(Fig. 1.1) is the underground part of the structure, erected on natural silt and artificial foundations and serving for transfers and loads from structures to the foundations. The constructive shape of the foundation allows for a more even distribution of pressure from the structure to the ground.

The upper boundary between the foundation and the ground part of the structure, as well as the boundaries between the separate and ledges of the foundation, is called edged foundation. The lower plane of the foundation resting on the ground is called base of the foundation. The distance from the ground level near the finished building (layout mark) to the sole is called foundation depth.