How to connect two foundations together?

In construction projects where expansions or additions are planned, connecting two foundations is an essential step. It maintains stability and structural integrity by facilitating a smooth transition between the old and new foundations.

Depending on the particulars of the project and the kinds of foundations involved, there are a number of ways to join two foundations. Using footings or beams made of reinforced concrete that cross both foundation sections is one typical method. Differential settlement is avoided and loads are distributed efficiently with this technique.

Another method is to build a bond beam between the two foundations made of reinforced concrete. This beam strengthens the joint and adds extra strength and support in addition to joining the foundations.

Specialized connectors or anchor bolts are used for projects where the new foundation is made of steel or wood and the existing foundation is made of concrete. These connectors are made to withstand any differential movement and securely fasten various materials together.

When connecting foundations, careful planning and engineering calculations are necessary to guarantee that they can sustain the intended loads and environmental conditions over time. Builders can join foundations efficiently with the use of these techniques, guaranteeing the longevity and durability of the entire structure.

To connect two foundations together, follow these steps:	1. Prepare the surfaces of both foundations by cleaning them thoroughly.
2. Apply a bonding agent or primer to enhance adhesion.	3. Mix and apply an epoxy resin or mortar specifically designed for joining concrete.
4. Place the new concrete or mortar mix onto the prepared surface.	5. Smooth and level the joint to ensure a seamless connection.
6. Allow sufficient curing time as per manufacturer"s instructions.	7. Inspect the joint for any gaps or imperfections and make necessary adjustments.

Conditions for connection

Once all capital structure structures have been double-calculated, the various types of foundations are connected in accordance with the working design.

Initially, the bearing capacity is computed, the anticipated base deformation is identified, and the best new foundation type for the extension is chosen.

The purpose of the second stage is to assess how a new structural structure will affect already-existing objects in order to mitigate the possibility of non-design deformations forming, prevent tilt, and take prompt action to reinforce.

The difference in building settlement under their own weight must be considered when connecting two foundations. It is advised to use a monolithic reinforced concrete slab or a pile-grillage load-bearing foundation to connect two structures if a one-story structure or porch is attached to a high-rise building and the building is constructed on a strip foundation. This will reduce the possibility of steps forming as a result of settlement differences.

Depending on the details of the project, either a rigid or movable scheme can be used to connect the foundations.

It is advised to combine two foundations into a single structure in the following situations:

• Construction of two capital structures with similar space-planning and design parameters on homogeneous soils with sufficient bearing capacity.
• Construction of attached premises with different characteristics and weight, provided that measures were previously taken to compensate for the difference in settlement, for example, a lighter structure was built on piles.
• Construction of different buildings adjacent to each other, provided that the foundation soils are slightly compressible (dense sands, hard clays, loams with a deformation modulus of 40 MPa or more, as well as semi-rocky or rocky foundations).
• Construction of the extension after a long time has passed after the commissioning of the main facility, which indicates complete settlement of the structure, eliminates the risk of deformations and cracks between the combined foundations.
• The need to increase the contact plane of support of the base of the foundation on the foundation soil in order to prevent non-design settlements or correct an error in the design of the facility.

It is advised to forgo combining the two foundations and use alternative design solutions in relation to the structure in question if the capital construction project being designed or built does not satisfy any of the aforementioned requirements.

Draft

The difference in settlement is one of the primary issues a designer faces when combining two foundations to create a single structure. The following elements that lead to the formation of sediment differences must be considered when making such a design decision:

• Two structurally separated building blocks are designed and erected on heterogeneous soils, with a chaotic alternation of engineering-geological elements.
• The structures whose foundations need to be combined have different number of storeys, load-bearing frame layout and other characteristics, which leads to the application of different operational loads.
• The two structures are identical in design and space-planning parameters, but were built at different times, when the settlement of one foundation was already completed, and the deformation of the second foundation was just beginning.
• The combined foundations have different design solutions, dimensions, and depth.

The model of the building frame on an elastic foundation, which is developed based on the findings of the analysis of the official report on engineering and geological surveys, must be calculated in order to precisely forecast the amount of settlement over time.

In accordance with SP 22.13330.2016 "Foundations of buildings and structures," the maximum allowable differences in settlement and the extent of deformations can be ascertained. These parameters can then be compared with the outcomes of the calculation to determine whether combining two foundation structures is feasible.

Options for combining

In actuality, there are two methods used to combine various capital structure foundations into a single structure: rigid connections and connections made through expansion joints. The characteristics and subtleties of each of these approaches are described in detail below.

Rigid

The following scheme is followed when coupling a building’s load-bearing subterranean structures in this manner:

1. If such a solution is provided for by the project in advance, horizontal reinforcement outlets with a length of at least 70d bars are installed in the existing foundation to allow them to overlap with the reinforcement frame of the new foundation “in a run-up”.
2. If there are no outlets, since the extension with the combination of two foundation structures was not initially planned, the reinforcement outlets can be fixed with epoxy resin in pre-drilled holes of the required diameter in reinforced concrete.
3. The end part at the site of intended contact of the foundation structure is beaten with a pneumatic hammer or hammer drill until the torn plane is reached in order to increase the adhesion force during mating.
4. The reinforcement frame of the second foundation is knitted in accordance with the detailed design drawings, taking into account the overlap of the load-bearing horizontal rods of the lower and upper grids with outlets from the existing structure.
5. The new structure is covered with formwork panels before concreting.
6. The contact plane is wetted with cement laitance to ensure adhesion of the two materials.
7. Concrete of the required class is supplied to the formwork, the structure is compacted and vibrated, and the necessary time is waited for setting and strengthening of the entire structure.

The structure can function without issue for many years if all work was completed strictly in accordance with the technological map and the design prevents the occurrence of stresses that could cause cracks at the junction of structural elements after they are combined.

It should be considered that when rigid coupling is used, the internal forces generated in any of these structures due to operating loads are dispersed throughout the reinforced concrete volume. Under these circumstances, it is advised to create a single calculation model with two building volumes above these structures in order to verify the actual performance of the foundations.

With expansion joint

It is advised to join two foundations through an expansion joint if joining them to form a rigid unit is unacceptable because of a significant difference in settlement or for other reasons. The following algorithm is used to carry out this installation operation:

1. The foundation of the old building has already been built, has gained strength and has begun to settle on an elastic foundation.
2. The design of the second foundation for the attached structure is selected based on the date of commissioning of the old facility, as well as the design features of the combined real estate objects. For example, if a building has different number of storeys, and the old structure has been in operation for more than 2-3 years, it is allowed to install simple structures for an extension – a strip or slab foundation.
3. If the attached premises are erected immediately after the completion of the construction of a taller building, a stronger foundation should be provided to avoid large differences in settlement.
4. An elastic compressible insert is fixed to the old foundation, for example, extruded polystyrene foam with a thickness of 30 to 50 mm.
5. If necessary, an additional rubber flexible tape is installed, which will be located between the two foundations and act as a hydraulic insert, preventing groundwater from penetrating into the basement.
6. After the elastic insert, the formwork sheet is fixed so as not to damage the insulation during concreting or when tying the load-bearing reinforcement frame. The plywood sheet that acts as formwork cannot be removed after concreting the foundation.
7. The reinforcement frame of the foundation of the attached room is laid, the formwork is installed, after which the structure is filled with concrete.
8. After the concrete foundation of the attached room has gained strength, the structure is demolished, the expansion joint is cleared of build-up materials.
9. When the building is being finished, the seam is sealed with silicone, an elastic compressible cord, after which a decorative overlay is placed on top of it, at the level of the finished floor.

Nominally, a connection foundation is not implied by an expansion joint. Even though the seam may cross through the basement or basements, two buildings may be joined into a single functional space.

The compressible thickness of the soil base is the only way to observe the influence of either structure on the other; otherwise, both remain independent building structures. To address any heel and draft discrepancies, the designer must perform thorough calculations and take extra precautions.

Possible difficulties

The designer or contractor may encounter numerous challenges when merging two foundations for distinct capital construction projects, which frequently results in a number of unfavorable outcomes.

The following lists all potential obstacles and mistakes that could arise during this construction and installation process, along with the best solutions to address the issues at hand:

• Unevenness of the soil base – before combining the foundations, provided that a strip or slab foundation is installed for the extension, it is recommended to carry out a complete or partial replacement of weak soils, ensuring the same operating conditions for both structures.
• If the main object was erected not much earlier than the extension, and settlement of the foundation continues, you should not organize a rigid connection with the supporting structures of the extension. In such situations, it is recommended to organize an expansion joint.
• The tilt of the foundation of an already constructed structure under the influence of loads from the extension. In such situations, the best solution would be to plan the extension in advance, that is, to provide for the extension of part of the base of the foundation structures of the existing building or to arrange a series of piles at the junction. If this is also not possible, it is recommended to perform a calculation and provide for a shift in the center of gravity of the attached structure, or strengthen the structure at the junction point in order to minimize its effect on the compressible thickness of the soil under the adjacent object.
• Formation of water in the basement, which penetrates through the expansion joint. When connecting structures in this way, it is recommended to provide a hydroviste in the form of a rubber elastic harness, as well as the device of waterproofing sealant after pouring and a set of design strength of concrete.
• Formation of cracks along the length of a rigid foundation junction. In case of rigid mating and monolithic joint, it is necessary to analyze the design in detail, and also make the necessary design decisions that eliminate the risk of formation of settlement differences.

It’s advised to develop a project only after reviewing the official report on the engineering and geological surveys that have already been completed. This will help to completely prevent issues with discrepancies in settlements or mistakes when merging two foundations. It’s also advised to make sure that every installation procedure is continuously monitored.

This is a succinct and unambiguous main thesis statement for your paper: For structural stability and integrity in building and renovation projects, connecting two foundations is essential. The right methods, such as doweling, grouting, or using structural connectors, are crucial when connecting new and old foundations or integrating various types, such as concrete and steel. The practical techniques, factors, and detailed instructions in this article will help you connect two foundations in an efficient and long-lasting manner.

Features of attaching different bases

The connection of each of the various foundation structure types that are used during the construction of capital construction projects has unique characteristics.

It should be noted that there are specific requirements and subtleties for the proper organization of the joining seam for each type of foundation, including columnar, strip, slab, and pile-grillage.

The basic guidelines for matching strip, slab, pile, and column foundations for different types of capital construction projects are as follows.

Ribbon

Strip foundations, which are composed of a base and a vertical portion, can be monolithic or prefabricated. They are positioned in the shape of an unbreakable tape, slightly thicker than the wall structures, under the building’s internal load-bearing vertical elements and along the entire perimeter of the structure.

The following characteristics need to be considered when matching and connecting such foundations:

1. First of all, you should take into account the date of pouring the old foundation, as well as the number of floors of the building being added. If more than 2 – 3 years have passed, and the difference in number of floors does not exceed 1 – 2 floors, it is allowed to join the strips without forming a complex unit, with a rigid interface and monolithic joint.
2. If buildings have fundamentally different designs and differ significantly in height, or are erected with a short time interval, it is recommended to provide an expansion joint in advance to prevent the formation of cracks.
3. To create a rigid joint, at the end of the old tape you need to drill at least 4 holes – 2 from below, 2 from above, into which reinforcing bars are inserted and fixed in them with epoxy resin. If the width of the tape is more than 600 mm, 6 to 8 reinforcing bars should be fixed.
4. A monolithic connection with the formation of a rigid unit is carried out both along the sole and along the wall of the strip foundation.
5. In order to avoid tilting of the extension due to non-design settlements at the junction, it is recommended to install a tooth in this section of the tape – a monolithic section up to 500 – 800 mm long, immersed in the ground 300 – 500 mm deeper than the main base of the structure.

Watch this video to learn how to join two foundations and build up a foundation slab:

Plate

Typical universal foundation designs that work well for building on loose soil. evenly distributes the weight across the whole construction site. They are placed to resemble a single, monolithic reinforced concrete slab, which may be composed of all of the individual blocks or may have deformation seams separating them.

The following subtleties must be considered when designing docking units for slab foundations:

1. In the case of a deformation seam, it is necessary to ensure the distance between the two foundations of at least 30 – 50 mm.
2. The seam is filled with an elastic insert of compressed insulation.
3. The recommended thickness of the slab for the organization of rigid conjugation should be at least 400 mm.
4. When creating a rigid node, reinforcing issues should be sparkled into the end of the old slab structure along the entire length, with a step, a multiple of the main background reinforcement of foundations for attached rooms.
5. If buildings have different masses and heights, creating a rigid monolithic unit is not recommended, as this will lead to the structures tilting.

Watch this video to learn how to join two foundations and build up a foundation slab:

Piles

The most dependable, long-lasting, labor-intensive, and costly foundation structures are pile foundations. They are composed of vertical rod elements, or piles, driven through weak layers by reinforced concrete or metal piles submerged in the soil base’s thickness.

The main load-bearing structures of the structure are built on the grillages that unite the pile heads in the upper section. Such bases are docked in accordance with the following specifications:

1. When joining two pile foundations, it is not recommended to use driven rod structures for an extension, since vibration can affect the decorative properties of the foundation for an existing capital construction project.
2. The nearest piles should be mounted no closer than 5 diameters and no less than 500 mm from the planned interface line.
3. When constructing a pile field under a new foundation, it is imperative to install beacons and reference points on existing structures in order to monitor settlement and tilt.
4. Considering that two pile foundations give minimal settlement even over a long time, if they do not belong to unique high-rise objects, it is possible to join grillages both to form a rigid unit and through an expansion joint.
5. To prevent non-design differences in back settlement, an optimal balance should be ensured between the number of piles operating under the foundations and the operational loads on the soil foundation from each of the two joined objects.
6. In the event that foundations made of metal screw piles for small private country houses, porches, verandas or other premises are subject to joining, provided that the characteristics of the elements immersed in the ground comply, no additional requirements or restrictions are provided for the joining of grillages.

Columnar supports

One of the most basic types of foundations is a columnar one, which is typically utilized for summer cottages or attached auxiliary spaces like porches, verandas, terraces, and summer kitchens that are attached to the structure.

They are made up of metal pipes or asbestos-cement pipes submerged in pre-drilled ground wells with reinforced concrete filling the interior spaces.

Although they are designed and operate similarly to pile foundations, the pipes are only submerged two to three meters below the surface, so they cannot increase the structure’s load-bearing capacity. If pairing such foundations is required, the following characteristics need to be considered:

1. The distance between adjacent columnar supports of an existing and an attached facility must be at least 1000 mm to prevent the foundations from influencing each other when the pillars are immersed.
2. It is recommended to drill wells under the pillars of a joint foundation in the dry season, with a minimum groundwater level, in order to eliminate the risk of sudden movement of water-saturated soil.
3. Considering that pillars, unlike metal screw piles, work primarily under the lower end of the ground support area, they can give slight settlement or be subject to seasonal heaving, which is especially important for clay foundations. In this regard, it is recommended to join such foundation structures through expansion joints.
4. In other aspects, columnar supports work on the same principle as piles, so there are no other requirements or distinctive features for them.

Ideal pairing method

Selecting the best and most universal way to join foundations is difficult because different engineering-geological components with unique mechanical and physical properties make up each soil foundation, and design schemes within the structures can vary as well.

It is advised to consider the following details and subtleties in order to connect two foundation structures with the best possible outcome:

• The ideal solution would be the simultaneous design and construction of both the main building and attached premises with a preliminary calculation of draft, their difference, roll, development of drawings for all joints of structures.
• If the project involves an extension that is to be built later, the building site underneath it should be protected in advance from erosion, flooding and other negative environmental factors.
• If attached premises are erected after the construction of the main building, it is recommended to wait 1 to 2 to 3 years for the foundation to settle completely. This will save the owner of the property from many problems in eliminating the difference in draft and stabilizing the roll subsequently.
• If the building is already established, and the property owner decides to organize a rigid connection between two foundations, load-bearing structures for the new structure should be provided in advance, allowing for minimal settlement. In such cases, it is recommended to use screw or bored piles, as well as columnar supports, if the soil conditions, as well as the structural and volumetric planning parameters of the object allow them to be installed without reducing the bearing capacity.

Whatever the advice, engineering and geological surveys must be conducted on the construction site in order to arrange the best possible pairing of two foundation structures.

Additionally, create a thorough project that analyzes internal joint stresses as well as potential settlement variations.

This will accomplish maximum savings on investments made in the installation of the aforementioned structures while also removing the possibility of unfavorable outcomes for the facility owner.

What material to choose for the extension?

When discussing private country real estate, an auxiliary structure is an addition to the main house. The following construction materials can be used to construct it, depending on its intended use and the materials used in the previously built and commissioned structure:

• Beam or log – it is recommended to use only if the main structure is built from similar building materials in order to provide a single architectural ensemble for the entire building. The best type of foundation is strip, slab or metal screw piles.
• Frame-panel technology – optimal design for attached rooms with both warm and cold circuits. Suitable for organizing an extension to any wooden house. Such structures are most often arranged on poles or on screw piles.
• Clay brick masonry – can be used as cladding for lightweight blocks or in the construction of the main load-bearing walls of attached premises. The use of such masonry is advisable if the main building is built of brick, or involves the construction of a wet facade made of plaster and painting. The type of foundation is determined by calculation, and can be strip, slab or pile-grillage.
• Masonry made of porous lightweight blocks – ceramic stones, aerated concrete, foam concrete, expanded clay concrete and other modern building materials. Suitable for the construction of any warm extension for stone buildings, regardless of the type of façade cladding. Foundations are assigned by analogy with a brick extension.
• Monolithic reinforced concrete frame – it is advisable if the attached premises require the organization of large spans or have a non-standard configuration, and it is impossible to implement such complex individual design solutions using other building materials. Regardless of the frequency of location of the supports of the supporting frame, the enclosing structures between them are made of brick or building blocks. It is recommended to install the foundations of the structure on bored piles or in the form of a monolithic reinforced concrete slab.

It is recommended that the supporting structures beneath the attached structures have light rafters or beams made of wood or metal. The roof of the attached structures can be pitched or flat.

The roofing pie and the main rear should be identical. The joints of structural load-bearing elements below the zero level and the foundation structures are typically unaffected by the roof.

Of course! For your article on "How to connect two foundations together?" here is a brief conclusion:

Any structure that spans two foundations must connect them in order for it to be stable and long-lasting. Whether you’re retrofitting an existing foundation or joining new construction, the process requires precise planning and execution.

Determine the kind of foundations that are involved first. The composition and load-bearing capacity of any material, be it masonry, concrete, or another, must be understood. The selection of connecting techniques and materials is guided by this knowledge.

Then, decide on a suitable method to join the foundations. Using epoxy resin, steel bars (rebar), or specialty connectors made for foundation linking are common techniques. Depending on variables like environmental conditions and structural requirements, each method has a different set of advantages.

Make sure there is a smooth and safe transition between the foundations. In order to avoid shifting or settling over time, proper alignment and sufficient reinforcement are essential. To preserve structural integrity, abide by engineering guidelines and manufacturer specifications.

Finally, once the connection is complete, carry out careful examinations to confirm the strength and longevity of the joint. Resolve any disparities as soon as possible to avoid further issues that can jeopardize the structure’s overall stability.

This conclusion aims to summarize the key considerations and steps involved in connecting two foundations effectively, ensuring clarity and accessibility for your readers.

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