Construction and Infrastructure / | The foundation for homes |
Foundations are bearing part of the building and are designed to transmit the load from the upstream structures on the base (ground). From the reliable operation of the bases to a large extent depend on the performance of the building, its capital and durability. The cost of the construction of the foundations is 15 — 20% of the value of the house, and the correction of errors, usually busy and expensive, house foundation should be good, therefore, to the construction of his should be treated particularly responsible.
The figures show specific examples of foundations deformations arising from their wrong device.
Deformation of foundations:
SG - ground resistance MP - forces of frost heaving |
Drawdown foundation, ie. E. The gradual lowering of the ground under the influence of upstream loads in low-rise housing construction is a relatively rare phenomenon. Typically, the support area of the constructed foundations, especially the tape is much higher than the calculated on unsettled ground almost always ensures their stable state.
By building on soft ground and under heavy walls make pier foundation . To avoid subsidence footprint calculation and check the foundation if necessary to increase: in the strip foundation by broadening their bottom in the column, in addition, by reducing the distance between the posts.
In areas with high groundwater located on the foundations of low-rise buildings affected by the forces of frost heaving. In severe heaving soils (water-saturated clay, loam, sandy loam, silt and fine sand), these forces reach 100 — 150 kPa (10 — 15 tf/m2), and acting on the base upwards, often exceed the load upstream structures. This seasonal vertical movements of the surface layer of soil when it is freezing at 1 — 1,5 m is 10 — 15 cm. Skewed porch, terraces, verandas, and sometimes the walls of houses — in most cases it is the result of the forces of frost heaving soils.
The mistake many individual developers is to ensure that the deeper founded foundations for houses , the better, and that such a decision in itself ensures its reliable performance and stability. Indeed, at the location of the sole of the foundation below the frost line vertical forces frost heaving cease to act on it from below, but the tangential force frost heave acting on the lateral surface of the can and in that case pull the foundation together with the frozen soil or tear off the upper part of the bottom. Such cases are most likely to occur when the device foundations of stone, brick, or small blocks, especially for light buildings.
How to prevent the deformation of the foundation
To prevent deformation of the foundations on heaving soils, it is necessary not only to place them below the sole ground freezing and thus get rid of the immediate pressure of the frozen soil below, but also need to neutralize the shearing forces frost heaving, acting on the lateral surface of the basement. For this purpose, in the basement full height mounted reinforcing cage, rigidly connecting the upper and lower part of the foundation and the base broadened do, in the form of a support platform-anchor that prevents pull out the foundations of the earth in the frost heaving of the soil. This design ensures stable operation of the foundation for any vertical deformation of soil, but in practice it is only possible by using reinforced concrete. If the foundation erected of stone, brick, or small blocks without internal vertical reinforcement of the wall must be inclined to do (tapered side up). This method of device foundation pillars and walls with careful alignment of the surfaces significantly reduces the side effects of vertical heaving soils on the foundation.
Additional measures that reduce the impact forces of frost heaving can be: covering the side surfaces of the basement sliding layer (waste oil, plastic film), and the insulation of the surface layer of soil around the foundation (slag, expanded clay, polystyrene), which reduces the local depth of soil freezing. The last measure can be applied to previously built small-buried foundations need to be protected from frost heaving. During the construction of buildings on steep terrain is necessary to consider the lateral earth pressure and its possible shift. The magnitude of this pressure depends on many factors (the steepness of the slope, hydrogeological composition of the soil, and so on. D.) And difficult to transfer. Typically, these conditions are more reliable strip foundations, rigidly connected in the longitudinal and transverse directions. Columnar foundations in this case it is necessary to unite firmly on top belt reinforced concrete (raft) to all structural elements working together.
Depending on the form and manner bearing on soil foundations are columnar , belt and Plate :
Types of bases depending on the design
The most common and cheapest are pier foundation . According to material consumption and labor costs are in the 1,5 — 2 times, and at deep foundation of 3 — 5 times more economical than tape. Especially effective columnar foundations in heaving soils when deep freezing. However, at the pier foundation has features that prevent in some cases, their successful application. So, in a horizontally moving sufficient grounds to rollover stability and maturity required lateral shear device hard reinforced concrete raft foundation. Limit their use on soft soil during the construction of buildings with heavy walls. In addition, when the columnar foundations have problems with the device cap: if the strip foundation base is formed as if by itself, as its continuation, when columnar filling the space between the pillars, walls and earth (Zabirko) - a complicated and time-consuming business. & nbsp ;
Strip foundation are usually built during the construction of buildings with heavy walls and ceilings, a.takzhe when satisfied with a cellar under the house or warm underground. Possible and appropriate and the device strip foundation in their shallow dry soils iepuchinistyh, even if the building is built of lightweight structures without basement and underground. Strip foundation in these circumstances are, as it were recessed socket and consumption of materials and labor are close to that of the columnar foundations. On heaving deep freezing ground strip foundations device is technically feasible is difficult, busy and not economically justified. Slab foundation are a variety melkozaglublennyh belt, but unlike them have rigid spatial reinforcement throughout the carrier plane, allowing no internal deformation take alternating loads arising from the irregular and seasonal movements of soil.
On moving (heaving) soil foundations are in contrast to conventional, stationary, resting pa fixed base, have in common with the ground seasonal vertical movement and called floating . Their design is a solid or grid plates, made either of reinforced concrete or prefabricated concrete cross beams with tight sealing of joints. Device slab foundation requires a relatively large consumption of concrete and metal, and can be justified in a low-rise building in the construction of small and simple in the form of a plan of buildings and structures on heavy puchnnistyh, moving and subsiding soils, as well as in cases where not required devices of high base and top slab foundation can be used as a basement ceiling.
Types of foundations, depending on the material
Depending on the materials used bases are: sand, crushed stone, rubble, brick, concrete (monolithic and concrete blocks), concrete (monolithic and modular), as well as being of wood, concrete, metal and asbestos cement pipes and pillars. On dry and malovlazhnyh (nepuchinistyh) soils used all of the above types of foundations, and the cheapest of them are sand from coarse sand, crushed stone and brick. During the construction of buildings on the heaving soils (moisture saturation of clay, loam and sandy loam) foundations should establish concrete and reinforced concrete. Options tape and columnar foundations are shown in figures:
Columnar and strip foundations to still bottoms
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Columnar and strip foundations to heaving soils
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