A suspended pile is used on loose soils when it is necessary to install the foundation. Such piles are able to hold the load due to the friction forces of the soil on the side and end parts of the support. The lack of support from below is compensated by the length of the pile and lateral friction. If we consider a conical hanging screw pile, then its lateral surface will take a load of up to 70%.
Description
A hanging pile differs from a pile-rack in that the latter is installed by resting on the soil. The length of the compacts the earth on the side walls. Over time, adhesion only increases. Precipitation occurs due to compaction of the soil under the tip of the support. There are differences between a single hanging pile and a bush. At the same load, the bush shrinks harder. Sediment increases with a close arrangement of bush piles.
The amount of draft will depend on the ratio of the distances between piles and their length. The length of the piles can be determined taking into account the characteristics of the soil. The looser the ground, the longer the pile should be. Design loads should also be taken into account. The pile will be longer than the greater load it will have to take. When the usual length is not enough, hanging composite supports are used.
Installation Methods
A hanging pile can be immersed in several ways, which are selected by researchers and designers during geodetic surveys. Among the main methods of diving should be highlighted:
- shock;
- vibrating;
- vibration shock;
- indentation;
- screwing up;
- vibration pressing.
Description of the methods
With the vibration method, the support is immersed by the method of directional vibration, which allows to discharge the soil. As soon as the installation is stopped, the soil collapses. Tightening is suitable for screw suspension supports. The method with undermining for such piles is excluded, since loose soil will degrade its characteristics and it will not be possible to achieve the necessary adhesion. There will be no friction between the side surface of the support and the soil.
Installation of hanging supports on a finished foundation
Sometimes a situation arises when the exploited foundation requires strengthening. In this case, the technology of bored piling is used. In the foundation or close to the base, holes are made in the soil with a step of 2 m. Their depth should be greater than the line of the main piles, if you have to work with a double base. The difference between these values can reach 2.5 m.
Drilled holes should be located in pile gaps or near old supports. If the slab foundation requires strengthening, then drilling is carried out along the entire perimeter of the slab. In this case, the plate is drilled through. Since the foundation support is located at the bottom of the basement or in the basement, work is done there.
The next step is compaction of the soil under the influence of pressure. Concrete mortar is poured into the mines. It is recommended to use a concrete pump, since it can be used to obtain the desired mixture pressure. This allows you to strengthen the finished foundation of any type. This method has some advantages. For example, earthwork is minimal. Complex manipulations are excluded. The technology itself allows you to get a pile foundation bored type. Used concrete pump and drill rig. The soil is compacted under high pressure, due to this the frictional force between the pile and the soil increases.
If we make a comparison with a traditional driven support, the described one allows you to get a support that is held in the ground more reliably. This technology allows you to strengthen the finished foundation if it began to sag or collapse. However, there are also disadvantages. One of them is that the installation of piles of this type is quite difficult to perform. This is especially true if you do not have a special technique.
Pile calculation
The calculation of the hanging pile is carried out according to the formula: P = km (RH × F + u∑f ⁿili). Supports can have different sections:
- square;
- rectangular;
- round.
In determining the main parameters, the following quantities are used: k is the soil uniformity coefficient. F is the area of the stop, which is taken over the cross-sectional area. The resistance of the underlying soil is RH. For clay soil of medium consistency, this value is 0.3 tons per square meter. Here you should observe a driving depth of 5 m.
The coefficient of working conditions is indicated by the letter m. The thickness of the soil layer on the sides of the pile in meters is indicated in the formula by the letters li. Normative resistance - f ⁿi. The perimeter of the cross-section of the support in meters is indicated by the letter u.
Hanging grillage
Pile foundations are usually erected under light buildings. That is why the most popular high pile grillages, which are also called hanging. They are made in the form of a monolithic reinforced concrete tape, the height of which reaches 40 cm. Its width can be the same, everything will depend on the type of wall material.
The device of a hanging grillage on piles begins with the installation of formwork. It is built using technology that will depend on the type of grillage chosen. It can be undecked, deepened or high. During the construction of a buried grillage, a sand and gravel cushion is laid at the bottom of the trench. Top formwork for grillage is installed. In dense, stable soil, formwork can only be installed for its ground part. When building a ground grillage, the formwork is installed on a sand and gravel pillow. Its base should be located at ground level. When installing a hanging grillage, you can install the formwork in several ways. In some cases, it is mounted on a pillow, which is first crumbled and tamped. Its height should correspond to the height of the sole of the grillage. Once the concrete has hardened and the formwork has been removed, the pillow from under the grillage is removed.
Pile Racks
When considering hanging piles and piles, you need to know how their bearing capacity is determined. This parameter for a suspended pile was calculated above. Now you can find out which formula is used for the rack. It looks like this: Fd = Yc × R × A. The difference here is only in the fact that the value of R, which determines the soil resistance under the lower part of the support, is taken not according to the tables, but calculated independently.
Reinforced concrete construction can work in the soil in two ways. One of them is a support stand. Such a pile gets stability due to the fact that its end part rests on a ball of incompressible soil. The hanging type of support is stable due to the resistance of the earth to the tip and the friction of the soil with the side walls of the pile. In practice, you can understand that the difference is expressed in the length of the support. The one that works in the form of racks has an impressive length. Its tip passes through a layer of surface low-density soil. Then it rests against a ball of soil.
Increase in bearing capacity. Sizes of a support
The bearing capacity of a hanging pile is determined by the formula that was presented above. But if it is not enough, then the problem can be solved in several ways. The first is to increase the diameter of the support; in some cases, the length also increases. Bushiness can also be increased by one unit of the base area of the building.
Products sometimes expand in the pit area. This increases the friction area at the end. If, when determining the bearing capacity of the hanging piles, it was found that this value should be increased, the problem can be solved by using modern technologies. For example, a pulse-discharge technique. But it is worth remembering that an increase in the size of the product can cause a rise in the cost of construction. The price of the foundation will be the sum of the prices of each element. The thicker the support, the more difficult it will be to dig it into the soil. The number of driven piles for reinforcement can contribute to the weight of the structure, both literally and financially. You may not get the desired benefits.
Sometimes a hanging driven pile requires more load bearing capacity. But if you use bushiness for this, then the design will sit more than one support. The length of a standard pile is 7 m.
There is a practical observation: if the step between the supports is more than 3 diameters, then a single pile and a bush are settled approximately the same. By reducing this distance, you can increase shrinkage.
Finally
When arranging foundations on weak soil, different piles are used. They may differ in immersion method, material of manufacture, shape and size of the cross section. By the method of interaction with soil layers, structures can be represented by racks or hanging products. In the latter case, the pillars rest on compressible soils, transferring loads to the tip and lateral surfaces.