Do-it-yourself foundation: step-by-step instructions for self-construction of the foundation. Solid foundation How a solid foundation slab works
They are divided into: separate - under each column; tape - under rows of columns in one or two directions, as well as under load-bearing walls; solid - under the entire structure. Foundations are erected most often on natural foundations (they are mainly considered here), but in some cases they are also performed on piles. In the latter case, the foundation is a group of piles, united on top of a distribution reinforced concrete slab - a grillage.
Separate foundations are suitable for relatively small loads and a fairly rare placement of columns. Strip foundations under rows of columns are made when the soles of individual foundations come close to each other, which usually happens with weak soils and heavy loads. It is advisable to use strip foundations for heterogeneous soils and external loads of different values, since they level uneven subsidence of the base. If the bearing capacity of strip foundations is insufficient or the deformation of the base under them is more than permissible, then solid foundations are arranged. They even out the subsidence even more. These foundations are used for weak heterogeneous soils, as well as for significant and unevenly distributed loads.
According to the manufacturing method, the foundations are prefabricated and monolithic.
28. Reinforced concrete foundations of shallow laying. Calculation of centrally loaded foundations.
Depending on the size, the prefabricated foundations of the columns are prefabricated and monolithic. They are made of heavy concrete of classes B15 ... B25, installed on sand and gravel compacted preparation 100 mm thick. In the foundations, reinforcement is provided, located along the sole in the form of welded meshes. The minimum thickness of the protective layer of reinforcement is 35 mm. If there is no preparation under the foundation, then the protective layer is made at least 70 mm.
The required area of the sole of the centrally loaded foundation in advance calculation
A=ab=(1.2…1.6)Ncol/(R-γ m d) R – design ground pressure; γ m is the average load from the weight of the foundation and soil on its steps; D - foundation depth
The minimum height of a square footed foundation is determined by conditional calculation of its punching strength, assuming that it can occur on the surface of a pyramid, the sides of which start at the columns and are inclined at an angle of 45°. This condition is expressed by the formula (for heavy concretes)
P<=Rbt ho u m
The pushing force is taken according to the calculation for the first group of limit states at the level of the top of the foundation, minus the soil pressure over the area of the base of the pushing pyramid: P=N-A1 p.
P=N/A1; A1=(hc+2ho)(b c +2h 0)
29. Reinforced concrete foundations of shallow laying. Features of the calculation of eccentrically loaded individual foundations.
Eccentrically loaded foundations. It is advisable to perform them with a rectangular sole, elongated in the plane of action of the moment.
Aspect ratio b/a=0.6…0.8. At the same time, the dimensions of the sides are rounded up to a multiple of 30 cm when using metal inventory formwork and 10 cm when using non-inventory formwork.
The maximum and minimum pressure under the edge of the sole is determined from the assumption of a linear distribution of stresses in the soil:
Pmax min=Ntot/A+-Mtot/W=Ntot/ab(1+-b*eo/a)
Ntot Mtot - normal force and bending moment at gamma f =1 at the level of the base of the foundation.
Ntot=Ncol+A gamma m N
Mtot=Mcol+Qcol H
Eo is the eccentricity of the longitudinal force relative to the center of gravity of the base of the foundation. Eo= Mtot/ Ntot
The maximum edge pressure on the ground should not exceed 1.2R and the average pressure - R.
In industrial buildings with overhead cranes Q<75 т принимают pmin>0, separation of the foundation from the ground is not allowed.
The height of an eccentrically loaded foundation is determined from the condition:
Ho=-hcol/2+0.5(Ncol/Rbt+P)^0.5
and design requirements
Hsoc=>(1-1.5)hcol+0.05
Hsoc=>lan+0.05
Hsoc - cup depth
Lan - the length of the anchoring of the reinforcement of the column in the foundation glass
Having determined the height of the foundation based on punching and design requirements, they take the largest of them.
For h<450
мм фундамент выполняют одноступенчатым,
при 450 Then they check the bottom of the glass for punching, check the height of the step for the action of the transverse force along the inclined section and select the reinforcement. 30. Classification of one-story industrial buildings according to design features. The layout of the structural scheme of the building, the binding of elements to the center axes. The device of temperature-deformation seams. One-story industrial buildings are divided into: By the number of spans - single-span and multi-span; By the presence of crane equipment: buildings without crane equipment, buildings with overhead cranes, buildings with overhead cranes; Lantern and non-lantern buildings; Buildings with pitched roofs, buildings with low pitched roofs. Modern one-story industrial buildings in most cases are solved according to the frame scheme. The frame can be formed from flat elements working according to the beam scheme (truss structures), or include a spatial structure of the coating (in the form of shells supported on columns). The spatial frame is conditionally divided into transverse and longitudinal frames, each of which perceives horizontal and vertical loads. The main element of the frame is a transverse frame, consisting of columns fixed in the foundations, crossbars (truss beam arch), covering over them in the form of slabs. The transverse frame takes the load from the mass of snow, cranes, walls, wind and ensures the rigidity of the building in the transverse direction. The longitudinal frame includes one row of columns within the temperature block and longitudinal structures such as crane beams, vertical braces, column braces, roof structures. The longitudinal frame ensures the rigidity of the building in the longitudinal direction and perceives the loads from the longitudinal braking of cranes and the wind acting on the end of the building. The task of laying out a structural diagram includes: The choice of the grid of columns and the internal dimensions of the building Coating layout Breakdown of the building into temperature blocks The choice of the scheme of connections that provide the spatial rigidity of the building In order to ensure maximum typification of frame elements, the following bindings to the longitudinal and transverse coordination axes are adopted: 1. The outer edges of the columns and the inner surfaces of the walls are aligned with the longitudinal stakeout axes (zero binding) in buildings without overhead cranes and in buildings equipped with overhead cranes with a lifting capacity of up to 30 tons inclusive with a column spacing of 6 m and a height from the floor to the bottom of the supporting structures of the coating less than 16.2 m 2. The outer faces of the columns and the inner surfaces of the walls are displaced from the longitudinal center axes to the outside of the building by 250 mm in buildings equipped with overhead cranes with a lifting capacity of up to 50 tons inclusive, with a column spacing of 6 m and a height from the floor to the bottom of the supporting structures of the coating of 16.2 and 18 m , as well as with a column spacing of 12 m and a height of 8.4 to 18 m. 3. Columns of the middle rows (with the exception of columns adjacent to the longitudinal expansion joint, columns installed in places where the heights of spans of one direction differ, and also except for columns at transverse expansion joints and columns adjacent to the ends of buildings) are positioned so that the axes of the section of the crane parts of the column coincided with the longitudinal and transverse centering axes. 4. The geometric axes of the end columns of the main frame are displaced from the transverse staking axes into the building by 500 mm, and the inner surfaces of the end walls coincide with the transverse staking axes (zero binding). 5. Height differences between spans of the same direction and longitudinal expansion joints in buildings with a reinforced concrete frame should be carried out, as a rule, on two columns with an insert. 6. Transverse expansion joints are carried out on paired columns. In this case, the axis of the expansion joint is aligned with the transverse center axis, and the geometric axes of the paired columns are shifted from the center axis by 500 mm. 7. In buildings equipped with electric overhead cranes with a lifting capacity of up to 50 tons inclusive, the distance from the longitudinal center line to the axis of the crane rail is assumed to be 750 mm. 8. The junction of two mutually perpendicular spans should be carried out on two columns with an insert measuring 500 and 1000 mm. The height of the building is determined by technological conditions and is assigned based on the top of the crane rail. With a change in temperature, reinforced concrete structures are deformed - shortened or lengthened; due to shrinkage of concrete - are shortened. With uneven subsidence of the base, parts of the structures are mutually displaced in the vertical direction. In most cases, reinforced concrete structures are statically indeterminate systems, and therefore, from temperature changes, concrete shrinkage, as well as from uneven settlement of foundations, additional forces arise in them, which can lead to cracks or destruction of part of the structure. To reduce the efforts from temperature and shrinkage, reinforced concrete structures are divided along the length and width by temperature-shrinkage joints into separate parts - deformation blocks. Temperature-shrinkage joints are performed in the ground part of the building - from the roof to the top of the foundation, while separating floors and walls. The width of the temperature-shrinkage seam is 20-30 mm. Sedimentary seams, which simultaneously serve as temperature-shrinkage joints, are arranged between parts of buildings of different heights or in buildings erected on a site with heterogeneous soils; foundations are also divided by such seams. Sedimentary seams are arranged using an inset span of slabs and beams. The largest allowable distance between the temperature-shrinkage joints in reinforced concrete structures is standardized and is 72 m in heated one-story buildings made of precast concrete, and 48 m in unheated buildings. Solid foundations are: slab beamless, bar-beam and box-shaped (Fig. 18.1). Box-shaped foundations have the greatest rigidity. Solid foundations are made with especially large and unevenly distributed loads. The configuration and dimensions of the solid foundation in the plan are set so that the resultant of the main loads from the structure passes approximately the center of the sole. In some cases of engineering practice, when calculating solid foundations, the approximate distribution of the reactive pressure of the soil according to the law of the plane is sufficient. If on a solid foundation, loads are rarely distributed, unevenly, it is more correct to calculate it as a slab lying on a deformable foundation. Under the action of the reactive pressure of the soil, a solid foundation works like an inverted reinforced concrete floor, in which the columns; serve as supports, and the foundation structural elements experience bending under the action of soil pressure from below. In accordance with what is stated in subchapter 17.3, for solid foundations, the calculation of slabs on a compressed layer of limited depth and, in some specified cases, based on bed coefficients, is of practical importance for solid foundations. The solution of such problems is beyond the scope of the course. Fig.18.1. Solid reinforced concrete foundations a - slab beamless; b - slab-and-beam; c - box-shaped In buildings and structures of great length, solid foundations (except for end sections of small length) can be approximately considered as independent strips (ribbons) with a width, the main unit, lying on a pliable foundation. Their calculation on a base with a bedding coefficient corresponds to that described in subchapter 17.3, and the calculation on a compressed layer of limited depth is explained below. Beamless foundation slabs are reinforced with welded meshes. Grids are accepted with working reinforcement in one direction; they are stacked on top of each other in no more than four layers, connecting without overlapping in the non-working direction and overlapping - without welding in the working direction. The upper grids are laid on the frame-stands. Slab-and-beam solid foundations are reinforced with welded meshes and frames. On fig. 18.1 shows an example of reinforcing the foundation of a multi-storey building. Double longitudinal and transverse meshes are laid in the thickness of the slab. The most stressed zone is additionally reinforced with a double layer of longitudinal meshes. For local bending, the slab is reinforced with top reinforcement grouped into grids of three working rods; gaps are left between them for access to the lower reinforcement. In the ribs, flat frames are combined into spatial frames by welding of transverse rods and are connected with slab reinforcement with pins. A slab of unit width, isolated from a solid foundation together with a base, is considered as a plane problem under plane deformation according to the classification of the theory of elasticity. 1 - columns; 2 - ribs; 3 - plates Fig.18.1. An example of the construction of a solid slab-and-beam foundation a - diagram of the foundation design in plan; b-layout welded grids in plan; c - details of reinforcement of foundations; g - welded Today, any more or less serious building, erected in accordance with current technological standards, requires a foundation. Depending on the characteristics of the soil, the number of storeys of the building and some external factors, the type of foundation used is selected. A monolithic solid foundation is poured in the case of building a building on loose soils with low bearing capacity and in places where groundwater is close to the surface. Examples of places where you can not do without the use of such a foundation are old landfills, soils prone to swelling, sandy areas. This type of foundation belongs to shallow, in addition, its use allows the building to obtain an acceptable footprint on a small plot of land. This type of foundation is quite versatile - it is built both under heavy multi-storey buildings and under prefabricated panel structures of light weight. The main difference will be in the way the reinforcing bars are placed and the layout of the additional stiffeners. A solid (slab) foundation is a solid reinforced concrete slab placed over the area of the entire building. It has a high bearing capacity and resists soil displacement well, actually moving along with the soil. It also enhances the resistance of the house to the loads that are likely to occur during land subsidence or temperature fluctuations. The slab foundation is focused on complex types of soils: Work on the formation of a slab (solid) foundation allows both the pouring of concrete at the construction site, and the use of standard reinforced concrete slabs, which are used for laying roads. The main condition is a thickness within 20-30 cm. Depending on this, the construction includes several stages: It consists in the development of documentation, the calculation of estimates, accurate planning and clearing the territory. In order to eventually receive a complete package of documents, it is best to contact specialists working in the profile. This will save time and money, as well as a professional approach to building a house, taking into account the type of recommended foundation. This is especially true when erecting the rear on soils with surface moisture. In addition, the foundation for the foundation requires a balanced approach and clarification of all the details. Equally important is the ideal evenness of the surface. To do this, the site is first freed from shrubs and other vegetation, stumps and roots are removed, large stones and boulders are collected. Next, level it with a shovel and a level, removing protrusions and recesses. This stage consists in transferring the plan to the area. For this, a geodetic breakdown and setting of key marks of the future building is carried out. Next, the entire top layer of the earth is removed. It has a low bearing capacity and a high compressibility. That is why it is removed to a depth of half a meter. The work is carried out with the help of an excavator. To fill the pit, a gravel-sand or crushed-stone-sand mixture is used at the rate of 60:40, respectively. It is tightly packed. This pillow: In addition, the sandy base does not retain water, and the low “seated” structure does not allow the soil to freeze during the cold season, providing the structure with increased stability. Then trenches are laid across the foundation (for reservoir drainage) and lined with geotextiles. Gravel is poured over it. Rotary sealed wells are installed at the corners of the resulting “structure”, since the slab bases lie mainly on soils with a high moisture content and the maximum proximity of groundwater. Then proceed to the basic formwork. According to calculations, it should go beyond the perimeter of the foundation by 15 centimeters. The bottom of the pit is covered with granite gravel of a fraction of 4-6 cm. The maximum thickness of the layer can reach 20 cm. A small 4-cm layer of concrete is formed on top of it, which is the first screed. But before that, the crushed stone is shed with a liquid mixture of sand and concrete so that the outer layer forms an even “crust”. Next, move on to waterproofing. These can be special rolled materials with adhesions or a conventional bituminous primer that is coated with cement. Any rolled waterproofing agent is glued onto it. On top of the mastic in 2 layers, a gluing built-up waterproofing spreads. If desired, you can make and insulating layers. Then they begin to form the formwork for a monolithic reinforced concrete slab. To do this, racks are dug in around the entire perimeter of the structure and any plank materials are nailed to them. During this operation, a level is required. The base of the foundation slab is a special metal frame with reinforcement over the entire area. For these purposes, two iron grids are used - lower and upper. Their bundle is performed with special hooks and annealed steel wire. Then, between the main mesh rods, additional ones are installed, at a distance of 20 cm from each other. Plastic compensators or clamps are also mounted, ensuring the best location of the steel bars. Pouring concrete is the final stage of work on the slab foundation. In the course of its implementation, both ready-made dry mixes and self-mixing solutions can be used - based on cement, sand and gravel (crushed stone). They fill the formwork strictly to the height of the sides. After drying, the plates proceed to the next stage of construction. Slab foundations are recommended to be made in the form of monolithic reinforced concrete flat or ribbed slabs. In buildings with a wall structural system, it is recommended to arrange a slab foundation under the entire building; in buildings of shaft-wall and frame-stem structural systems, it is allowed to arrange a slab foundation only under shafts (stiffening cores). For slab foundations with ribs, the intersections of the ribs serve to install the frame columns. The space between the ribs, if they are directed upwards, is filled with sand or gravel, and concrete preparation is arranged on top. When using a ribless foundation, the columns are installed as follows: Rice. 17 Solid beamless foundation for supporting columns For slab foundations for frameless buildings of small height (or weight), a foundation pit is required, with a depth of 50-70 cm. 12-16 mm, and all this is poured with the first layer of concrete 20-25 cm high. Waterproofing is laid on the prepared base. Along the perimeter of the house and under all internal load-bearing walls, a strip foundation is constructed using formwork. A second, protective layer of concrete 10-15 cm is poured over the waterproofing, and the surface of the future floor is leveled with a cement-sand screed. The final stage will be the installation of waterproofing between the foundation and the ceiling of the basement. Reinforced concrete slabs are reinforced by calculation. The height of the slabs for multi-storey buildings is about a meter. With a large deepening of solid foundations and the need to ensure their greater rigidity, it is possible to design box-shaped foundation slabs with the placement of cellars between the ribs and ceilings of the boxes. Solid (slab) foundations are used in the following cases: The site has weak soils and significant loads that cannot be taken by single or strip foundations; Uneven settlement of buildings or structures is not allowed or is strictly regulated. Foundation slabs significantly redistribute forces to the base, and make precipitation and pressure on it uniform; Technological necessity of creating a solid foundation (for example, installation of process equipment); The need for external protection of the base from water penetration (the slab can be used as a waterproofing; the bottom of the tank, etc.); Justified in low-rise construction with a small and simple form of the building. Solid foundations are calculated as slabs on an elastic foundation. Advantages: relative simplicity of construction; the possibility of their implementation in heavy heaving, mobile, subsidence and karst soils. Disadvantages: quite expensive (due to the high consumption of concrete and metal for reinforcement). Rice. 17 Solid (slab) foundations To date, another design of a solid foundation is proposed - with a heater introduced into the composition of the slab. Such a foundation allows you to get a warm floor structure at no additional cost. Photo 1. The device of a slab foundation for a residential building 1a - for an apartment building, 1b - for an individual residential building Pile foundations Pile foundations are widely used in construction on weak highly compressible soils, as well as with increased load on the foundation. So, in the construction of high-rise buildings and others with significant loads, pile foundations are used instead of conventional ones, regardless of the type of soil. Pile foundations are more economical than strip foundations by 32-34%, by 40% in terms of concrete costs, by 80% in terms of earthworks. A pile is a rod immersed in the ground and designed to transfer the load from the structure to the ground. According to the pile material, there are reinforced concrete, wooden, concrete, metal, combined, soil piles. Depending on the method of immersion in the ground, driven, stuffed, bored, screw and shell piles are distinguished. Driven piles are driven using pile drivers, vibratory pile drivers and vibro-pressing units. Reinforced concrete piles can be of solid section (square and round) and hollow - shell piles (d=800mm). Piling machine After immersion to failure, the top of the pile is cut off. A stuffed pile is arranged by filling pre-drilled, punched or punched holes with a concrete or other mixture. The lower part of the well can be expanded using explosions (camouflaged heel piles). This method is effective under the influence of holding forces; on subsiding soils. Bored piles differ from rammed piles in that ready-made reinforced concrete piles are installed in the well with filling the gap between the well and the pile with a cement-sand mortar. Screw piles can be with a steel or reinforced concrete tip, as well as piles with articulated stops. They are used, as a rule, for the construction of unique buildings with significant horizontal loads. The design prevents pulling out of the pile and overturning of the foundation. Depending on the properties of the soils, piles can transfer the load from the building to practically incompressible soils, resting on them with their lower ends - rack piles, or transfer the load with the side surfaces and the lower end due to friction forces - "hanging" piles. Rice. 18 Types of piles depending on the method of transferring loads To evenly distribute the load in compressible soils, distribution beams or grillage slabs, which can be either monolithic or prefabricated, are laid directly on them or on specially arranged heads at the upper ends of the piles. Monolithic grillages are used for brick buildings, prefabricated - for large-panel ones. Recently, non-grilled pile foundations have been widely used (for large-panel buildings with a small step), floor slabs and basement panels in these cases are based on prefabricated pile heads. Grillages are high - the lower plane is located above the surface of the earth, and low - when the lower plane rests on the ground or is buried in it. Pile foundations in the plan can be: Tapes with the location of piles in one or two rows at a distance from each other 3d -8d (when transferring small loads (for buildings of medium and low rise), the distance between the piles is 1.5-1.8m (8d)), where d is the diameter or pile side; Under the supports - single piles or located in a bush; In the form of a continuous pile field - for heavy structures with uniform loads. Piles must be placed at all corners of the building and at the intersection points of the axes of the walls. With cohesive soils (clay, loam, sandy loam), under the monolithic grillage of the outer walls, an underlying layer of materials used in the blind area (slag, crushed stone or coarse sand) with a thickness of 0.2 m is laid, and under the grillage of the inner walls - preparation of lean concrete, crushed stone or slag 0.1 m thick. The coupling of the grillage with piles is allowed to be provided both freely supported and rigid. Advantages: Gives less shrinkage economical (reduce the consumption of materials, for example, concrete by 40%), less labor-intensive (during their construction, the volume of earthworks is significantly reduced), Possibility of construction on soils with low bearing capacity). Rice. 19 Types of piles a - transverse: Rice. 20 Pile foundation with monolithic grillage Photo 2. Pile foundation made of metal pipes Fig. 20 Pile foundation: pile placement options, foundation section Fig. 21 Pile foundation for a column Rice. 22 Pile foundation options With significant slopes or difficult terrain, as well as with a high level of groundwater, buildings are placed on a combined strip-pile foundation. In this case, the piles are buried beyond the depth of soil freezing. Foundations are the supporting part of the building and are designed to transfer the load from the overlying structures to the foundation. The foundations of the building must meet the following basic requirements: have sufficient strength and resistance to tipping and slipping in the plane of the sole, resist the influence of atmospheric factors (frost resistance), as well as the influence of ground and aggressive waters, correspond in terms of durability to the service life of the building, be economical and industrial in manufacture . Having broken a place under the foundation of the building, proceed to excavation. The construction of the foundation is recommended to be carried out immediately after excavation. Drying, the earth in the trench crumbles and it takes a lot of time to remove it. By design, the foundations are: solid, tape, columnar and pile. solid foundations They are a solid non-block or ribbed reinforced concrete slab "under the entire area of the building. Solid foundations are suitable in cases where the load transferred to the foundation is significant, and the base soil is weak. This design is especially appropriate when it is necessary to protect the basement from the penetration of groundwater at a high level if the basement floor is subjected to high hydrostatic pressure from below. Rice. 1 Solid beamless foundation: 1 - reinforced concrete foundation slab They are arranged under the walls of the building or under a number of individual supports. In the first case, the foundations have the form of continuous underground walls (Fig. 3a), in the second - reinforced concrete cross beams (Fig. 3b). In its outline in the profile, the strip foundation under the stone wall is in the simplest case a rectangle (Fig. 4e). The rectangular section of the foundation in height is permissible only with small loads on the foundation and a sufficiently high bearing capacity of the soil. In most cases, in order to transfer pressure to the base that does not exceed the normative pressure on the soil, it is necessary to expand the base of the foundation. The theoretical sectional shape of the foundation with an expanded sole is a trapezoid (Fig. 46). The expansion of the sole should not be too large in order to avoid the appearance of tensile and shear stresses in the protruding parts of the foundation and the appearance of cracks in them. Rice. 3. Foundation structures: A - foundation in the form of continuous underground walls: 1 - strip foundation; 2-wall; b-in the form of cross reinforced concrete beams: I - strip foundation for columns; 2 - reinforced concrete column On the basis of experience, the angles of inclination of the theoretical side face of the foundation to the vertical were established, along which there are no dangerous tensile and shear stresses. The limiting angle, conventionally called the pressure distribution angle in the foundation material, is 45 ° for concrete, masonry with a cement mortar of composition 1: 4 - 33 ° 30 ", for rubble masonry with a complex mortar of composition 1: 1: 9 - 26 ° 30?. In buildings with basements, the section of the foundation within the basement is arranged in a rectangular shape with an extension below the basement floor, called a pillow (Fig. 5 a). Often, foundations are made with a stepped section (Fig. 5 b). The depth of the foundation should correspond to the depth of that layer of soil, which, by its qualities, can be taken for a given building as a natural foundation. When determining the laying of the foundation, it is necessary to take into account the depth of soil freezing. It is recommended to lay foundations below the freezing depth. If the base consists of moist fine-grained soil (dusty or fine sand, sandy loam, loam, clay), then the base of the foundation is located no higher than the freezing level of the soil. The level of soil freezing is taken at a depth where a temperature of 0 ° C is observed in winter, with the exception of clay and loamy soils, for which the level of freezing is taken at a shallower depth, where a temperature of about -1 ° C occurs. The standard freezing depth of loamy and clayey soils is indicated in SNiP 2.02.01-83 on a schematic map in which lines of the same standard freezing depths are plotted, expressed in centimeters. The standard freezing depth of silty and fine sands, sandy loams, silty clays and loams is also taken from the map, but with a coefficient of 1.2. Fig 4. : Fig 5. Strip foundations: A - rectangular with a pillow; b - stepped with a pillow (1) Studies have established that the soil under the foundations of the outer walls of regularly heated buildings with a room temperature of at least +10 ° C freezes to a lesser depth than in an open area. Therefore, the estimated depth of freezing under the foundations of a heated building is reduced against the standard value by 30% with floors on the ground; if the floors are on the ground on logs - by 20%; floors laid on beams - by 10%. The depth of laying under the internal walls of heated buildings does not depend on the depth of soil freezing, it is assigned at least 0.5 m from the basement floor or ground level. The depth of laying the foundations of the walls of buildings with unheated basements is assigned from the basement floor, it is equal to half the calculated freezing depth. The assumption that the deeper the foundation is laid, the greater its stability and reliability of operation, is incorrect. When the base of the foundation is located below the level of freezing of the soil, the vertical forces of frost heaving cease to act on it from below, but the tangential forces of frost heaving acting on the side surfaces can pull the foundation together with the frozen soil, and tear it off under light buildings when building foundations made of bricks and small blocks. Therefore, for the successful operation of the foundation, in order to prevent its deformation in heaving places, it is necessary not only to place the sole below the level of soil freezing, which will relieve the direct pressure of the frozen soil from below, but also to neutralize the tangential forces of frost heaving acting on the side surfaces of the foundation. Inside the foundation, a reinforcing cage is laid to its entire height, rigidly connecting the upper and lower parts of the foundation, the base is made expanded in the form of a supporting platform-anchor, which does not allow the foundation to be pulled out of the ground during frost heaving of the soil. This constructive solution is possible when using reinforced concrete. When building a foundation of bricks or small blocks, without internal vertical reinforcement, the walls are made sloping-tapering upwards. The above method of constructing foundation pillars and walls, with careful alignment of their surfaces, significantly weakens the lateral vertical effect of heaving soils on the foundation. The influence of frost heaving forces is reduced by: coating the side surfaces of the foundation with a sliding layer of polyethylene film; used engine oil; insulation of the surface layer of soil / around the foundation with slag, foam plastic, expanded clay, which reduces the local depth of soil freezing. The latter is also applicable to shallow foundations built earlier and in need of protection from frost heaving. On a large-falling terrain, during the construction of a building, it is necessary to take into account the lateral pressure of the soil and its probable shift. Strip foundations rigidly connected in the longitudinal and transverse directions work more reliably under these conditions. Columnar foundations must be rigidly united on top with a reinforced concrete belt - a grillage, for more efficient joint work of all structural elements. In gravelly, coarse and medium-sized sands, as well as in coarse-grained soils, the depth of the foundation does not depend on the freezing depth, but it must be at least 0.5 m, counting from the natural level of the soil (planning mark when planning by cutting and backfilling). In modern construction, the most industrial are prefabricated concrete and reinforced concrete foundations from large foundation blocks. The use of prefabricated foundations can significantly reduce construction time and reduce the complexity of work. The prefabricated foundation (Fig. 6) consists of two elements: a pad of reinforced concrete blocks of a rectangular or trapezoidal shape (Fig. 7)t laid on a carefully compacted sand preparation 150 mm thick, and a vertical wall of blocks in the form of concrete rectangular parallelepipeds. Rice. 6. Prefabricated strip foundation of concrete blocks under the walls of the house with a basement and a technical underground: I - foundation slab; 2 - concrete wall blocks; 3 - coloring hot Rice. 7. Foundation block cushion When building on weak highly compressible soils, in prefabricated foundations, to increase resistance to tensile forces and rigidity, reinforced concrete belts 100-150 mm thick or reinforced seams 30-50 mm thick are arranged, placing them between the pillow and the lower row of foundation blocks, as well as at the level of the upper foundation cut. Foundation walls, assembled from large blocks, despite their great strength, are sometimes thicker than the above-ground part of the walls. As a result, the strength of the material is used by only 15-20%. Calculations show that the thickness of the walls of prefabricated foundations can be taken equal to the thickness of the above-ground walls, but not less than 300 mm. Savings in building materials can be achieved by installing discontinuous foundations, consisting of reinforced concrete pillow blocks, not laid close, as provided for in strip foundations, but at a certain distance from one another, approximately from 0.2 to 0.9 m. blocks are covered with soil. Pillar foundations They have the appearance of separate supports arranged under walls, pillars or columns. With minor loads on the foundation, when the pressure on the ground is less than the standard, it is advisable to replace the continuous tape walls of low-rise buildings with columnar ones. Foundation pillars made of concrete or reinforced concrete are covered with reinforced concrete foundation beams on which the wall is built. To eliminate the possibility of bulging of the foundation beam due to swelling of the soil located under it, a sand or slag cushion 0.5 m thick is arranged under it. The distance between the axes of the foundation pillars is assumed to be 2.5-3 m. The pillars must be placed at the corners of the building, at the intersection and junction of the walls and under the walls. Columnar foundations for walls are also erected in high-rise buildings with a significant depth of foundation - 4-5 m, when the construction of a strip continuous foundation is unprofitable due to its large volume and, consequently, greater consumption of materials. The pillars are covered with prefabricated reinforced concrete beams, on which the walls are erected. Columnar single foundations are also arranged for individual supports of buildings. Figure 8a shows a prefabricated foundation for a brick pillar, made of reinforced concrete pillow blocks. A more economical option is to lay reinforced concrete blocks-slabs under brick pillars (Fig. 8 b). Prefabricated foundations for reinforced concrete columns of frame buildings can consist of one reinforced concrete glass-type shoe (Fig. 8c) or from a reinforced concrete block-glass and a base plate under it (Fig. 8d). Pile foundations They consist of separate piles, united from above by a concrete or reinforced concrete slab or beam, called a grillage (Fig. 9). suit in cases where it is necessary to transfer significant loads to weak soil. Fig 8. Prefabricated foundations for individual supports: Piles are differentiated according to the material, method of manufacture and immersion in the ground, the nature of work in the ground. According to the pile material, there are wooden, concrete, reinforced concrete, steel and combined. According to the method of manufacturing and immersion in the ground, piles are driven, immersed in the ground in finished form, and stuffed, manufactured directly in the ground. Depending on the nature of the work in the ground, two types of piles are distinguished: piles - racks and hanging. Piles-racks with their ends rest on solid ground, for example, rock and transfer the load to it (Fig. 10). They are used when the depth of solid soil does not exceed the possible length of the pile. Pile foundations on pile-racks practically do not give sediment. If solid soil is located at a considerable depth, hanging piles are used, the bearing capacity of which is determined by the sum of the resistance of the friction forces along the side surface and the soil under the pile tip (Fig. 11). Rice. 9. Types of piles in the ground: A - hanging piles; b - pile-racks: 1 - dense limestone; 2 - silty plastic loam; 3 -.silt; 4 - silty sand; 5 - peat; 6 - plant layer Wood piles are cheap, but because they rot quickly if they are in soil with varying moisture, the heads of wood piles should be placed below the lowest level. However, in areas with a high level of groundwater, wooden piles last a very long time if they are constantly in the water. In world practice, there are examples of four-hundred-year-old buildings on wooden piles, which are still in good technical condition. Reinforced concrete piles are durable, more expensive than wooden ones, but they can withstand significant loads. The scope of their application has been significantly expanded due to the fact that the design mark of the heads of reinforced concrete piles does not depend on the level of groundwater. The distance between the axes of the piles is determined by calculation. Within the limits of the most common pile insertion depths - from 5 to 20 m, these distances for ordinary pile diameters range from 3...8d, where d is the pile diameter. Fig 10. Driven pile-stand of the foundation: Rice. 11. Stuffed hanging pile foundation: Pile foundations, in comparison with block foundations, give less settlement, which reduces the likelihood of uneven soil deformations. When preparing the foundation, sometimes old filled-in wells, pits, random weak layers of soil are found in the ground. In order to avoid uneven settlement of foundations, these places must be cleared and filled with masonry, lean concrete or compacted sand, and when building foundations, reinforced seams should be applied over these places. Foundations are exposed to moisture seeping through the ground atmospheric moisture or groundwater. Due to capillarity, moisture rises up the foundation and dampness appears in the walls of the first floor. To block the penetration of moisture into the walls, an insulating layer is arranged in their lower part, most often from two layers of bituminous rolled materials (roofing material, etc.), glued together with waterproof bituminous mastic. Cellars One of the important conditions for the safety and integrity of the house is waterproofing the basement. The walls and floors of basements, regardless of the location of groundwater, must be isolated from surface water seeping through the soil, as well as from capillary groundwater rising up. In basements, when the groundwater level is below the basement floor, sufficient waterproofing of the floor is its concrete preparation and a waterproof floor made on it, and waterproofing the walls is covering the surface in contact with the ground with two layers of hot bitumen. If the groundwater level is above the basement floor, in this case the water pressure is created the greater, the greater the difference between the levels of the floor and groundwater. In this regard, for waterproofing the walls and floor of the basement, it is necessary to create a shell that could resist the effects of hydrostatic pressure. An effective measure to combat the penetration of groundwater into the basement is a drainage device. The essence of the drainage device is as follows. Ditches are arranged around the building at a distance of 2-3 m from the foundation with a slope of 0.002--0.006 towards the prefabricated drainage ditch. Pipes (concrete * ceramic or others) are laid along the bottom of the ditches with a slope. There are holes in the walls of the tubes through which water penetrates. Ditches with pipes are covered with a layer of coarse gravel, then a layer of coarse sand and top-open ground. Through pipes laid in ditches, water flows down into the lowland (ditch, ravine, river, etc.). As a result of the drainage device, the groundwater level decreases. When the groundwater level is not higher than 0.2 m from the basement floor, waterproofing of the basement floor and walls is arranged as follows. After coating the walls with bitumen, they arrange a clay castle, that is, before filling the trenches, crumpled greasy clay is hammered close to the outer wall of the basement. Concrete floor preparation is also laid on a layer of crumpled greasy clay. At a height of the groundwater level from 0.2 to 0.5 m, gluing waterproofing is used from two layers of roofing material on bituminous mastic (Fig. 12). The insulation is laid on the concrete preparation of the floor, the surface of which is leveled with a layer of cement mortar or asphalt. Since the floor structure must withstand a sufficiently large hydrostatic pressure from below, a concrete load layer is laid on top of the insulation, which balances the water pressure with its weight. On the outer side of the walls, insulation is glued on bituminous mastic and protected with 1/2 brick masonry of iron bricks on cement mortar and a layer of wrinkled greasy clay 250 mm thick. The gluing insulation of the outer walls of the basement is placed 0.5 m above the groundwater level, taking into account its possible fluctuation. Fig 12. Waterproofing strip foundation in a building with a basement: 1 - layer of load concrete; 2 - concrete preparation; 3 - roll waterproofing; 4 - crumpled greasy clay 250 mm; 5 - masonry of iron bricks on cement mortar 120 mm; 6 - double layer of bitumen Rice. 13. Waterproofing strip foundation in a building with a basement: 1 - concrete preparation; 2-reinforced concrete slab; 3-roll waterproofing; If the groundwater level is located more than 0.5 m above the basement floor, then a reinforced concrete slab is laid on top of the floor waterproofing, which is made of three layers of roofing material or hydroisol (Fig. 13). The slab is embedded in the basement wall, which, working on bending, perceives the hydrostatic pressure of groundwater. With a high level of groundwater, the external waterproofing device sometimes causes difficulties. In such cases, it is performed along the inner surface of the basement walls (Fig. 14). The hydrostatic head is perceived by a special reinforced concrete structure - a caisson. Rice. 14. Basement waterproofing at high groundwater pressure; 1 - roll insulation; 2 - concrete preparation; 3 - cement layer; 4 - cement screed; 5 - reinforced concrete box structure; 6 - clean floor; 7 - cement plaster over bituminous coating; 8 - waterproofing Necessary features that are taken into account in the construction of foundations and the construction of plinths When laying foundations of any type, the following rules must be observed: Most foundation structures use concrete. Concrete has the property of "maturation", 28 - 30 days. After laying the concrete structure, it must be kept for a given time without loads and it is desirable to close it either with roofing felt or other available material from drying out the top layer. During the concrete setting period, periodically water the foundation with water to prevent uneven drying. So building a house on a newly erected foundation is fraught with danger, defects will not keep you waiting. Foundation waterproofing is essential. It consists in coating with hot bitumen the entire surface in contact with the ground. Walls are also insulated. For this, two layers of roofing material are laid (1st layer - between the basement and the zero level; 2nd layer - between the basement and the main wall of the house). This protects the walls of the house and the basement from moisture. Protection of the outer side of the plinth from atmospheric influences. This is achieved by plastering or tiling. To grout the foundation, rubber-containing components (ash from burnt tires) are added to the mixture. It turns out a "fur coat" for the base. She is beautiful and reliable. During the construction of the plinth, ventilation holes are provided. In summer they serve to ventilate the underground, and in winter they are closed so that dampness does not get into the house. The blind area is necessary to protect the foundation from the effects of surface water. The width of the blind area is from 0.75 to 1 meter with a slope from the basement wall. As materials are used: reinforced concrete, asphalt, concrete or well-compacted clay. The device for draining rainwater from roofs also affects the strength of the foundation. Rainwater from the roof enters the blind area, breaks it and the basement gradually, unevenly moistens the soil near the foundation. This affects the bearing capacity of the foundation and contributes to subsidence of the foundation.
Solid (slab) foundation technology
General characteristics
Stages of work
Preparation
Plot breakdown
Formwork and reinforcement
Pouring concrete
A 
b
1 - square; 2 - square with a round cavity; 3 - round hollow; 4 - rectangular; 5 - channel; 6 - I-beam;
b - longitudinal:
7 - prismatic; 8 - cylindrical; 9 - pyramidal;
10 - trapezoidal; 11 - diamond-shaped; 12 - with a broadened heel.
ext in pic 20
a - rectangular; b - trapezoidal: 1 - cut
bitumen; 4 - cement-sand mortar; 5 - blind area; b - two layers of roofing paper go
hydronsol on bituminous mastic; 7 - basement
a - under brick pillars from blocks of strip foundations; b - the same, from special reinforced concrete slabs; c - under a reinforced concrete column from a glass-type shoe; g - the same, from a glass block and a base plate
I - waterproofing; 2 - the surface of the earth; 3 - reinforced concrete grillage beam; 4 - driven pile of rectangular section; 5 - dense soil
1 - waterproofing; 2 - reinforced concrete beam grillage; 3 - stuffed pile; 4 - tip of the casing pipe; 5-weak soils
During the operation of the foundations, it is necessary to monitor the settlement of the base and possible deformations.
4 - crumpled greasy clay 250 mm; 5 - iron brick masonry on cement
solution 120 mm; b - double layer of bitumen