The hanging pile is used on loose soils when it is necessary to install a foundation. Such piles are able to hold the load due to the forces of friction 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 side surface will take a load of up to 70%.
Description
A hanging pile differs from a pile-rack in that the latter is supported by the soil. Along the length, it compacts the earth on the side walls. Over time, the bond only increases. Settling occurs due to compaction of the soil under the tip of the support. There are differences between a single hanging pile and a bush. With the same load, the bush shrinks more strongly. The draft increases with the close location of the bush piles.
The amount of settlement will depend on the ratio of distances between piles and their length. The length of the pile can be determined taking into account the characteristics of the soil. The looser the earth, 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 compound supports are used.
Mounting Methods
A hanging pile can be driven in several ways, which are selected by researchers and designers during geodetic surveys. Among the main ways of immersion should be highlighted:
- drum;
- vibrating;
- vibroimpact;
- indentation;
- screwing;
- vibropressure.
Description of methods
With the vibration method, the support is immersed by the directional vibration method, which allows the soil to be discharged. As soon as the installation is stopped, the soil collapses. Screwing is suitable for screw hanging posts. The flushing method for such piles is excluded, since loose soil will degrade its characteristics and the necessary adhesion cannot be achieved. There will be no friction between the side surface of the support and the soil.
Installation of hanging supports on the finished foundation
Sometimes a situation arises when an exploited foundation needs to be strengthened. In this case, the technology of bored hanging piles 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 occurrence 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 shouldlocated in pile gaps or near old supports. If strengthening requires a slab foundation, 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, the work is done there.
The next step is to compact the soil under pressure. Concrete mortar is poured into the mines. It is recommended to use a concrete pump, as 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, earthworks are minimal. Complex manipulations are excluded. The technology itself makes it possible to obtain a pile foundation of a bored type. Used concrete pump and drilling rig. The soil is compacted under high pressure, which increases the friction force between the pile and the soil.
When compared with a traditional driving support, the described one allows you to get a support that is held in the ground more securely. 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 this type of pile is quite difficult to perform. This is especially true if you don't have special equipment.
Pile calculation
Calculation of a hanging pile is carried out according to the formula: P=km (RH × F + u∑f ⁿili). Supports can have different sections:
- square;
- rectangular;
- round.
When definingThe following values are used for the main parameters: k is the coefficient of soil homogeneity. F is the stop area, which is taken from 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, a driving depth of 5 m should be observed.
The working conditions coefficient is denoted 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. Regulatory resistance - f ⁿi. The perimeter of the support section in meters is denoted by the letter u.
Hanging grillage
Pile foundations are usually erected under light buildings. That is why the most popular are 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 installation of a hanging grillage on piles begins with the installation of formwork. It is built according to technology, which will depend on the type of grillage chosen. It can be shallow, deep or high. When constructing a buried grillage, a sand and gravel cushion is laid at the bottom of the trench. A formwork for the grillage is installed on top. In dense stable soil, formwork can only be installed for its ground part. When constructing a ground grillage, the formwork is installed on a sand and gravel cushion. Its base should be at ground level. When installing a hanging grillage, you caninstall formwork in several ways. In some cases, it is mounted on a pillow, which is previously crumbled and compacted. Its height should correspond to the height of the sole of the grillage. As soon as the concrete hardens and the formwork is removed, the pillow from under the grillage is removed.
Stand piles
When considering hanging piles and rack piles, you need to know how their bearing capacity is determined. This parameter for a hanging pile was calculated above. Now you can find out what formula is used for the rack. It looks like this: Fd=Yc × R × A. The only difference here is that the value of R, which determines the resistance of the soil under the bottom of the support, is not taken from tables, but is calculated independently.
Reinforced concrete structure can work in soil in two ways. One of them is a stand. Such a pile gains 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 point and the friction of the soil with the side walls of the pile. In practice, it can be understood 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 low-density surface soil. Then it rests on a ball of soil.
Increased bearing capacity. Support Dimensions
The bearing capacity of a hanging pile is determined by the formula that was presented above. But if it's not enough, thenThe 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 area unit of the base of the building.
Products sometimes expand in the pita area. This increases the area of friction 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, the discharge-pulse technique. But it is worth remembering that an increase in the size of the product can cause an increase in the cost of construction. The price of the foundation will be the sum of the prices for each element. The thicker the support, the more difficult it will be to dig it into the soil. The number of piles driven in for reinforcement can contribute to the weighting of the structure, both in the literal sense and from a financial point of view. The desired benefit may not be obtained.
Sometimes a hanging driven pile requires more bearing capacity. But if you use bushiness for this, then the structure will shrink 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 settle approximately the same. By reducing this distance, shrinkage can be increased.
In conclusion
When arranging foundations on weak soil, different piles are used. They may differ in the method of immersion, the material of manufacture, the shape and dimensions of the cross section. According to the method of interaction with the soil layers of the structurecan be represented by racks or hanging products. In the latter case, the posts rest on compressible soils, transferring loads to the tip and side surfaces.
