Calculation of the foundation for a multi-storey building. Design of shallow foundations and pile foundations. - PP, Drawings
- Added: 09.07.2014
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1. Analysis of the initial data on the above-foundation structure
2. Analysis of geotechnical and hydrogeological conditions
2.1. Determination of physical and mechanical properties of base soils
2.2.Determination of foundation laying depth
2.2.1.By purpose and design features of the designed
2.2.2.By depth of foundations of adjacent structures
2.2.3. on loads and impacts on bases and foundations of engineering
geological conditions of the construction site
2.2.4. By existing and projected terrain to be built
2.2.5. By depth of soil freezing
2.2.6. According to hydrogeological conditions during construction and
operation of the facility
3. Foundations of shallow laying
3.1. Sizing of shallow foundation foot
3.2. Construction of shallow foundations
3.3. Calculation of sediment of shallow foundations according to the diagram linearly
deformable half-space by layer-by-layer summation method
4. Pile foundations
4.1. Purpose and operation of the pile
4.2. Basis of pile classification
4.3. Determination of pile foundation parameters
4.4. Pile Foundation Design
4.5. Pile foundation settlement calculation sequence
5. Feasibility comparison of options
List of used literature
2. Analysis of engineering-geological and hydrogeological conditions of the construction site
Reference the building in plan and height. In the plan, we show the direction of the geological section .
Geological section is made on scale: vertical (1:500) horizontal (1:500).
The section shows the following data:
- Layer numbers (top to bottom)
- Age and genesis (origin of soil)
- Relative elevations of the bottom of each layer (from wellhead)
- Soil sampling places with number
- Outline of underground part of the building with indication of absolute elevations
the clean floor of the first floor, the bottom of the foundations of shallow laying and pile pile, the lower ends of the piles.
- Vertical axes, calculated foundations
- Layout mark.
To illustrate the features of each soil layer, a vertical scale Ro is created to the right of the geological section along the axis of one of the specified foundations.
After the building reference is made in plan and height and the geological section is constructed, we compile summary table 2 based on table I and the geological section. To do this, you need to sort soil samples by layer numbers using the number, wells, and sample depth. From soil layers represented by chernozem or its impurity, cultural layer, samples are not taken because they cannot serve as a basis.
For these layers, only the specific gravity required to calculate transport costs is represented.
We define derivatives and indexation characteristics and the name of soils according to GOST 25001 - 82. The mechanical characteristics of soils are determined by SNiP 2.02.01 - 83.
2.2.3. In terms of loads and impacts on bases and foundations, engineering and geological conditions of the area on which the construction sites are located.
First of all, we select the bearing layer (in which the foundation floor will be located). Weak soils cannot be a bearing layer, such as peat, a vegetation layer. We determine the absolute elevation of the roof of the bearing layer and accept the value of deepening, we determine the absolute elevation of the foundation floor.
When choosing a bearing layer, it is necessary to take into account the values of forces on the upper sample of the foundation and the physical and mechanical characteristics of each layer of soils. The bearing layer will be 3 layer - dark brown loam
R0 = 250 kPa.
The preliminary area of the foundation can be determined by the formula: A = Fv/Ro = 388/250 = 1.55 m ². We take in advance the width of the strip foundation 1.5 m. The minimum deepening of the foundations into the bearing layer should be 10...... 50 cm on the other side should not leave a layer of soil of low thickness under the base of the foundation, if the building properties are much worse than the properties of the underlying layer. The foundation is buried in the bearing layer by 0.7 m under the base of the foundation there remains a mass of the bearing layer of 2.8 m.
2.2.4. According to the existing and projected relief of the built-up area.
The existing relief of the territory is calm (a slight deviation of marks, the absence of ravines) it does not impose restrictions. In case of a sharp change in relief (presence of a steep slope), the structure is divided by a sedimentary seam into separate compartments (sections).
2.2.6. According to hydrogeological conditions during the construction and operation of the structure.
After considering each condition separately, the depth of foundation laying is assumed to be 3.2 m.
Elevations of the pedestal sole are assigned on the basis of the same conditions, excluding item 2.3 by design conditions the height of the pedestal = 50 cm the height of the pile sealing into it is 100 mm.
Absolute elevations of soles of all foundations of the structure are located at one elevation. This reduces the cost of land work .
3.2. Construction of shallow foundation
The foundations of buildings, as a rule, are made concrete and reinforced concrete, therefore they are designed on the basis of SNiP according to concrete and reinforced concrete structures.
For prefabricated foundations, separate typical elements are used, for example, foundation slabs, wall blocks, sub-column parts of foundations, row foundations for columns, foundations for spacer structures, etc.
4. pile foundations
4.1. Purpose and operation of the pile
Piles are round or multifaceted rods (wooden, concrete, reinforced concrete or metal) immersed in the ground. In length, they can be of constant cross section (cylindrical and prismatic) and variable (conical and pyramidal).
A group of piles forming a pile foundation is connected to the surface by a rigid structure in the form of a beam or plate, which ensures the transfer of pressure from the structure to all piles and prevents horizontal movement of the upper part of the latter.
Structures linking the heads of piles are called pile pits and are made depending on the material of the piles and the constant level of groundwater made of wood, concrete or reinforced concrete. There are tops high and low. Tall are called pedestals, the lower plane of which lies above the surface of the ground. Such pedestals are arranged when the surface of the soil is covered with water, for example, during the construction of embankments, bridge supports, etc. However, it is possible to arrange high pedestals in the construction of civilian buildings, for example, in the construction of a technical underground.
Low are called pedestals with a lower plane buried in the ground. In industrial and civil engineering, low pines are usually used. The elevation of the deepening of the low pile into the ground depends on the presence of basements and underground communications passing in it, the possibility of bundling of soils, the depth of laying of neighboring foundations and a number of other reasons.
Pile with its lower end can rest on practically incompressible soils: rock, dense large-breaking, dense sandy, dense low-compressible clay in a solid state (with consistency index IL < 0). In such cases, all pressure on the ground of the base is transmitted only through the lower end of the pile, along the area of its cross section. Such piles are called rack piles.
However, far from always the lower ends of the piles can be supported on non-compressible soils. For the most part, the lower ends of the piles remain in compressible soils. In such cases, the load from the pile is perceived by the soil both in the cross-sectional area of the pile and on its side surface, therefore, the point should be located in stronger soil when buried in it by 2-3 m, i.e. the length of the piles is determined based on engineering and geological conditions. Such piles are called hanging, or friction piles. This name was given to piles in connection with the development of friction forces on the side surface of piles
4.2. Basis of pile classification
Piles can be wooden, metal, concrete and reinforced concrete. Recently, soil concrete or soil cement piles have begun to be used.
According to the method of introduction into the soil, finished piles submerged into the soil by clogging, crushing, screwing, etc., and stuffed, made directly in a well made in a pound, are distinguished. Finished piles immersed in the ground using hammers and vibration loaders are called driven.
The cross section of piles can be solid (full-body piles) or hollow (hollow piles and shell piles). There is no fundamental difference between hollow piles and shell piles. If the diameter (side) of the cross section of the pile is up to 800 mm and there is an internal cavity of the pile, it is called hollow. Under the same conditions, but with a diameter of more than 800 mm, piles are called shells.
Hollow piles and shell piles can be with an open or closed lower end, which affects the method of work and the bearing capacity of the pile.
To increase bearing capacity of pile, widened heel is arranged at its lower end (by drilling or camouflage explosion). The arrangement of the widened heel in one way or another is possible in driven piles, but is most often used in padded piles.
The structures of finished piles, as can be seen from the above, are more or less standard. The structures of padded piles are extremely different-shaped. Wells for the arrangement of padded piles can be made directly in the soil by drilling or punching, under the protection of the casing or without it, or with the casing removed after concreting the pile or remaining as the outer shell of the pile. It is possible to combine various methods of arrangement of pile shaft and widened heel.
As part of the course work, we consider hanging driven reinforced concrete piles.
Driven reinforced concrete piles have become the most widespread and are used in various structural modifications. Reinforced concrete piles are made of conventional or pre-stressed reinforced concrete.
The most common reinforced concrete prismatic piles of a continuous square section. Such piles are used with section sizes from 200x200 to 400x400 mm, 3-24 m long.
Length intervals for such piles are taken for lengths of 3-6 m in 0.5 m and for lengths of 6-24 m in 1 m. Non-stressed piles are made with a length of 3-16 m, and pre-stressed - more than 16 m long. Continuous prismatic reinforced concrete piles are reinforced according to the calculation by longitudinal rods from hot-rolled reinforcement of steel of a periodic profile with a diameter of 12-22 mm of class A300 and transverse reinforcement with spirals, grids in the head of the pile and loops made of ordinary reinforcement wire of class A240 with a diameter of 5-6 mm. Concrete for piles with non-stressed reinforcement is accepted as class B15, and for piles with pre-stressed reinforcement - class B30. Crushed stone with size not exceeding 40 mm is used as coarse aggregate for concrete.
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