Strengthening The Foundation

As a supporting structure of any building, the foundation experiences enormous loads, being under the pressure of the entire mass of the structure located above it. Strength indicators, bearing capacity, weaken over time under the influence of a number of destructive factors. There are several reasons, and they can be natural and man-made. It comes to violations of the integrity of the foundation, destruction of concrete protection. Subsidence occurs, cracks appear. Only timely reinforcement of the foundation will stop the vertical spread of cracks along the walls, unwanted deformations in the form of warped window and door units, and collapse of floors.

Foundation survey

Carrying out work to strengthen the foundations of buildings requires understanding the reasons that caused damage to them. Therefore, it is necessary to carry out a technical survey of the foundation. This is work for engineers of companies that have all the required licenses and certificates. Beforehand, specialists will need to ask the customer to provide comprehensive information about the history of the structure. Collecting technical documentation is especially relevant for strengthening the supports of long-built houses. It is necessary to collect:

• Information about the date of completion of construction of the facility;

• Data on the original appearance of the building, what changes were made (extension of areas, increase in the number of floors, redevelopment);

• Was the building in a state of disrepair?

• All information about the repair and restoration measures taken in the past.

Studying the building documents received by the surveying engineers helps to reduce the overall volume of research work at the site. Surveying the foundation of a building involves three stages - above-ground and underground parts, and the adjacent territory is also necessarily studied.

When engineers inspect the above-ground part, they determine the actual dimensions of the entire building, establish the value of real loads. The external damage received is inspected, first visually, then with the participation of devices and construction tools. Non-destructive testing methods are used: mechanical, radiometric, chemical, acoustic research.

Engineering work in the underground part is a very important stage. This is the foundation survey. Here its characteristics are determined: type of construction, material, dimensions. Strength parameters are determined, at what depth it lies. It is necessary to understand whether the foundation waterproofing has been completed, with what quality. In order to conduct a study of the foundation soils, it is necessary to dig pits. Depending on the condition of the building structures, their number may vary. If there are defects, pits are dug in the areas of suspected damage. The pit can be imagined as a rectangle, whose larger side is adjacent to the foundation.

The severity of the building's settlement is determined by instrumental methods. To measure the crack opening, two beacons are placed in the pre-cleaned area of ​​each crack opening. One - at the point of maximum opening, the other at the beginning of this area. On the installed beacons, made of plaster, sometimes glass or metal, no cracks should appear in about 2-3 weeks. In this case, it is considered that the deformation process of the building has stabilized.

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Methods of strengthening

Let's consider foundation strengthening technologies, and also talk about their advantages and disadvantages.The adjacent territory is examined to more accurately determine the causes of damage. These may be factors affecting the condition of the soil and the foundation base. Such as old river beds, reservoirs, filled-in ravines, improper drainage of surface water. This is an equally important part of the foundation survey.

Strengthening the foundation with piles

If serious flaws have crept into the building construction project, resulting in structures of insufficient strength and bearing capacity, the foundation is reinforced with piles. The same method is used to strengthen the foundation of a house when the soil has subsided, and this has started the process of its destruction. Also, when new construction has begun near the building or the structure needs an extension, piles are used.

This method is most often used to strengthen strip foundations, and reinforcement of pile foundations is also widespread. Piles can be screwed, bored, bored-injected, and driven.

Strengthening foundations with screw piles is a universal technique, in the sense that it can be used to strengthen foundations located on any type of soil except rocky soil. In this case, the building is slightly raised on jacks, and the previous foundation is dismantled. Screw piles, the number of which is calculated, are driven very close to the walls and screwed into the ground. Then a steel grillage made of I-beams or channels is installed, and the house is placed on a strong new metal frame.

It is advisable to use the method when there is a planned expansion of the area, i.e. when building an extension.Such foundation reinforcement has a drawback - it is necessary to replace the structures. Although often only part of the house is subject to reinforcement and replacement. Over time, the resulting pile support may sag, which will cause the need for new repairs.

Bored piles are a framework of reinforcement and concrete mortar. First, holes are drilled using auger drills, reaching dense soil layers, where the soil is removed and the old foundation is exposed. Formwork is placed in the hole using a casing pipe, inside which a reinforcement frame is mounted. The structure increases the load-bearing capacity of the pile. Using steel beams, reinforcement outlets, the frame is connected to the foundation. Finally, the entire hole, right up to the foundation and frame junction, is filled with concrete - foundation cementation is performed. This is how prefabricated, strip types of foundations are mainly reinforced.

Bored injection piles have been used relatively recently. They are useful in the presence of building subsidence, in some other situations. By means of mechanisms, holes for piles are drilled directly through the old foundation. It is necessary to accurately calculate the angle of inclination and drilling depth. Then, by injection, a cement-sand solution is fed inside. The soil near the future location of the pile is strengthened.

Then, using vibration immersion technology, a reinforcement cage is immersed into the filled borehole. The work is done quietly, quickly, and such piles can be used on sliding slopes. Large diameter boreholes can be formed and drilled to significant depths. But this is a rather expensive method. The cheapest method is to strengthen the foundations with screw piles.

Cementation

Strengthening foundations by cementation is the simplest and cheapest technology. When it is implemented, the cement composition is injected into the voids under sufficient pressure. Bentonite or cement-sand mortar is used. The zones where the holes will be made and the number of injections that should be made into one hole are calculated.

The mixture is supplied by special injectors through pre-formed wells drilled in the foundation or soil. The method is also good for its versatility. It is quite applicable to different types of foundations. It can be slab, pile, strip, columnar. The size of the structure does not play a special role either. It is possible to carry out cementation reinforcement of the foundations of large and powerful buildings, or to perform this method of reinforcement of the foundation of a small private house in the suburbs.

The sand used in the solution should be fine or with a medium fraction content. The choice is determined by the composition of the base materials. When each pore is filled with solution, you need to wait until it hardens. At the end of this process, the entire structure will be a single durable monolith.

Widening the foundation sole

The essence of the method is that the support area is increased by installing additional concrete or reinforced concrete elements from the side faces. They can be installed on one or two sides using the increase method. Or on three or four sides of the foundation base. In the latter case, collars or reinforced concrete shirts are used. We will tell you why reinforced concrete shirts and collars are used in the next section.

The load is distributed over a slightly larger surface. In this way, the settlement is removed, the risk of the foundation losing its bearing capacity is reduced, and more significant loads can be applied to the foundation. The method of widening the foundation sole is capable, in particular, of stabilizing its tilt, equalizing the difference in contact pressures.

The technology of widening the foundation sole is not applicable or is only partially possible in cases where there is a significant rise in groundwater. In addition, it is not recommended on water-saturated soil, on weak, structurally unstable soils.

The composition of the elements for extension (they themselves are called "extensions") includes prefabricated banquettes. Monolithic parts are also used, which are installed close to the side edge of the foundation. The technology of widening the sole involves the installation of extensions along the entire length. Sometimes reinforcement is placed under the most loaded sections of the foundation.

The work on installing prefabricated elements (banquettes) involves preliminary compression of the soil under the sole. They ensure that the base contributes to the strengthening of the rest of the foundation. After preliminary compression of the soil and reinforcement, additional elements are connected to the work.

Jacks operating on the hydraulic principle are used. They are secured with special wedges. Preliminary compression can also be created by turning the prefabricated element around the lower edge.

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Reinforcement with a reinforced concrete jacket or collars

The "shirt" is a three-dimensional frame structure. During installation, it is welded to the exposed reinforcement of the foundation. It turns out that it covers the existing foundation from all sides. We have already mentioned reinforced concrete shirts in the previous section - they are used to expand the base.

Before concreting the structure, the soil under its base is compacted. This is done to ensure strength, because installing the shirt involves widening the base of the foundation. The fasteners used in the method are anchor joints. They are driven into the foundation to increase the bearing capacity of the reinforced concrete shirt.

Reinforced concrete collars are completely closed structures that cover the entire surface after installation, not just the problematic part of the foundation. Installation of the collar allows you to correct shortcomings and errors made during the construction stage. Such shortcomings are compensated for by collars without increasing the area of ​​the base. They are used if it is necessary to strengthen individual fragments of the foundation, and only in cases where the walls have sufficient load-bearing capacity.

If an extension to the house is needed (or the walls in the building are not thick enough), the base of the foundation must be widened. First, a trench is dug along the base of the house, and the house is thoroughly cleaned along the perimeter. Holes are drilled for the reinforcement bars, on which the frame is later formed. It is welded with sheet metal, and concrete is poured under pressure into the empty areas of the foundation and into all the cracks. When the solution hardens, it is used to completely fill the entire metal formwork.

Shotcreting

This method is widely used during reconstruction, which involves increasing load values. During shotcreting, sand is mixed with cement in a ratio of 2 to 1 or 6 to 1. Under high pressure created in a compressor by compressed air, the solution is fed by a shotcrete gun. Dry mixture and water are fed into its nozzle from different lines. A coating up to one and a half centimeters thick is formed. This is the version of the "dry" shotcreting method.

The "wet" method uses crushed stone with larger particles than the "dry" method. However, the size of the fractions should not exceed 8 mm. The ready solution is fed to the problem surface. The thickness of one layer is much greater, more than 10 centimeters. For large volumes of work, a concrete pump is used.

The rebound, that is, the output of the supplied mixture in the opposite direction, is low. The place of work remains practically clean. Finishing is also possible. Some disadvantage of this method is low maneuverability. The work requires high speed of execution, the concrete solution in the sleeve of the unit must not be allowed to dry out.

The "dry" method of strengthening foundations by shotcreting is distinguished by high productivity, as well as significant distances to which the components of the composition can be supplied. However, the implementation of the method leads to a large percentage of rebounds, so the work site must then be removed. The work requires concentration and extensive experience.

Carbon fiber reinforcement

This foundation reinforcement technology is innovative and relatively young. It is now very often used in construction practice. Carbon fiber sheets are applied to problem areas - planes, bends, edges. As a rule, this method involves computer modeling of the foundation, with the desired result embedded in the program. Based on such calculations, the number of required carbon fiber sheets is determined. Design documents also include diagrams, drawings, and a step-by-step work plan.

The foundation surface is cleaned of foreign particles and dust. The area around the foundation is also prepared. Sometimes large cracks are treated (by gunning), the surface is leveled, then treated with a primer. Then the areas where the canvases will be attached are marked out, and the adhesive composition necessary for reliable adhesion of the carbon fiber to the surface is mixed. After the canvases are correctly positioned on the foundation (the fibers are directed along the line of greatest force), the surface is treated with protective compounds. After the work is accepted by the customer, final finishing is possible.

Injection

This method is also an innovation. In addition to strengthening, it gives the foundation excellent water-repellent properties. Micro Cements are used in the work. This is the name given to a very finely ground mineral binder obtained in factories using the air segregation method.

Preparation for injections consists of drilling holes at a certain angle and at an optimal distance. Special tubes with sockets will then be placed in them, through which the mixture will flow under pressure. These can be packers or assembly columns. The depth of the hole is two-thirds of the depth of the foundation, but they should be about half a meter from the base.

A water mixture is prepared, for which a high-speed mixer is used. Another representative of technical equipment is a screw or plunger pump. It feeds the suspension into the foundation through packers, until it returns or the pressure increases to critical. Even the smallest cracks (shrinkage, hair) are filled in this way.

What is better after all?

Carbon fibers - foundation reinforcement with their help, has now almost completely replaced the traditional methods already described by us. Advanced building materials made of carbon fiber have become the most popular among builders. Foundation reinforcement with carbon fiber is so popular because:

• The material perfectly resists various types of loads: stretching, compression, bending, twisting; in terms of elastic properties, carbon fiber surpasses steel;

• No welding or fire work required;

• There is no need for special equipment and lifts;

• The work is carried out by small teams and in a short time;

• Carbon fiber does not change the weight of the structure or its geometry;

• Carbon fiber reinforcement involves only non-destructive technologies;

• The material is chemically inert and resists corrosion;

• Carbon fiber is absolutely safe and does not contain toxins;

• There is no need to interrupt production processes or change the site visit schedule when working using these technologies.

The use of innovative technologies, first of all, the strengthening of the foundation with carbon fiber can replace any of the "classic" strengthening methods. Moreover, due to the high physical and chemical characteristics of the building material, such strengthening eliminates all the shortcomings of traditional methods.