Steel support columns with a spiral tip are a reliable foundation for the construction of one-story buildings, cottages, garden houses, bathhouses and small outbuildings. Their installation significantly reduces construction time and reduces the cost of acquiring materials. However, despite a large number of advantages, their use has application limitations, as well as some operational disadvantages.
Technical description
A screw pile is a special metal drill that can be screwed into the soil during rotation. It is made of steel pipe with a radial inclined plate at the bottom, which is the main structural element. The presence of the blade ensures that the pile is immersed in the soil during installation, and after installation serves as the main support, distributing the weight of the building structures and fixing the position of the pipe during ground movements and frost heaving.
Different types of piles are determined by:
- screw terminal device;
- geometric parameters of pipes;
- intended purpose.
In addition, single-screw and twin-screw piles are distinguished, in which the second additional blade is located in the middle of the pipe. Twin screw supports have increased bearing capacity, resistance to soil heaving and shrinkage.
Welded blades
Welded-end screw columns are the cheapest products of relatively low quality. The lower part of the pipe has a pointed conical end, above which a wide drill blade is welded. The main disadvantage of the products is the lack of strength of the weld. If it hits a stone, the blade may be torn off or deformed. As a result, the correct installation of piles in depth and direction will become impossible.
Supports with a welded tip are taken only for light buildings for household purposes, canopies and fences (i.e., with the possibility of a small deepening). The use of welded piles for the construction of a residential building is recognized as dangerous.
Cast screws
Cast blades are made of high strength alloy steels using precision vacuum molding technology. To increase the strength of the material, each product is subjected to additional heat treatment, after which it is welded to a steel pipe. Manufactured industrially, cast tips are characterized by increased blade thickness and high manufacturing accuracy.
The price of cast screw piles is 25-30% higher, but the high quality of workmanship and the possibility of longer operation fully compensates for this. Each serious manufacturer issues a certificate and a technical passport to their products indicating the technical characteristics of the finished support.
The main varieties of piles
In the market of building materials, foundation supports with screws are represented by 4 different types, which differ significantly in their design.
- with one wide blade on the tip at the bottom of the pipe for wooden and frame buildings;
- two-bladed with increased bearing capacity for small stone houses and two-story frame-type buildings;
- narrow-bladed with a conical screw for mounting on rocky soils;
- with a straight toothed bottom edge for the installation of foundation foundations in permafrost.
In ordinary conditions of private construction, the most common are screw supports of the first type with one cast blade.
Existing sizes
Standard diameters of pipe columns range from 57 to 133 mm. The length is determined by the customer depending on the depth of soil freezing in the region of construction work. The width of the blade and the angle of inclination depends on the diameter of the pipe, the type of soil and the perceived weight loads.
Pile supports made of thick-walled tubing, corrosion resistant, are classified as a separate category. They are much more expensive than standard products, but have the best performance.
Key Benefits
A large number of advantages of steel pile supports contributes to the rapid growth of the popularity of these structures among private developers. Among the obvious advantages are the following factors:
- the possibility of building a foundation on most types of soils, including swamps and permafrost;
- quick and easy installation;
- good stability of building structures during heaving and ground movements;
- lack of influence of the depth of groundwater;
- the use of screw piles in areas with difficult terrain;
- installation work at any time of the year;
- use of concrete or steel grillage;
- low cost of materials available to most developers;
- lack of need for earthwork;
- durability and reliability of the foundation;
- the possibility of external insulation of floors in the house.
To speed up the construction of the foundation, there is the possibility of using special drilling equipment. In this case, you will have to pay for the service provided, but the work will be completed in 1 day without the application of great physical effort with high quality.
Few disadvantages
Despite the large number of positive qualities, screw piles have negative properties, including:
- the impossibility of erecting buildings and structures on rocky and rocky soils;
- restriction of bearing capacity determined by one-story construction;
- the need for measures to protect piles from corrosion and stray currents;
- difficulties with arranging a basement or cellar under the house;
- the need for concreting the internal cavity of the pipes and floor insulation.
All piles should be screwed to a depth below the freezing point of the soil. Therefore, it is necessary to ensure strict monitoring of installation work by the hired team.
Application options
Steel pipe columns allow you to build 4 types of foundations:
- installation of pile supports for each supporting element of the frame building;
- device of a pile tape in the form of a steel or reinforced concrete grillage;
- pile field for pouring reinforced concrete slab;
- single supports for the construction of an extension or individual elements of the building.
Given all the pros and cons of a pile-screw foundation, it can be considered the best option for installing gates, fences and other types of fences.
The intended use of metal piles is determined by the diameter of the pipe and the size of the blades. In product labeling, the first number indicates the size of the pipe string, the second indicates the blade. Depending on these indicators, it is recommended to use:
- 76 mm pipe for light railings and single posts;
- 89 mm for canopies, verandas, arbors and strengthening of brick columns;
- 108 mm for frame-type buildings and light timber houses;
- 133 mm for structures made of logs or foam blocks.
At the same time, twin-screw piles with a lower cast tip have the best bearing capacity. After screwing the supports, their inner cavity must be filled with concrete mixture without reinforcing.
The pile-screw foundation is considered the best solution for use on heaving soils, with a high level of groundwater and in wetlands.
Installation work
It is better to entrust the calculation of the pile field to a specialist who will take into account the existing type of soil on the site, the freezing depth, the bearing capacity of the supports, the option of protecting steel pipes from corrosion and other important factors. Here is a brief instruction on calculating the number of piles.
As a result, before starting work, you need to have on your hands an accurate plan for the arrangement of piles with an indication of their size. It is likely that before contacting an engineer, it will be necessary to carry out geological survey work to accurately determine the characteristics of soil layers and soil water.
Installation work consists of 5 successive stages:
- piling field marking;
- digging pits and screwing piles;
- pouring concrete mixture into the inner cavity of the pipes;
- trimming of pipe heads at the level of one horizontal plane;
- device of metal or reinforced concrete grillage.
All exposed welding areas must be painted or protected against corrosion in another way. To warm the house, the space between the grillage and soil must be sheathed with boards or sheet building material. Due to the lack of a basement, the construction of the blind area can be simplified and have a small thickness. We have described the technology in more detail here and here.