Repair of concrete foundation with piles and concrete strip

Do-it-yourself foundation repair: learning how to repair a foundation

Guaranteeing the longevity and strength of a private house or bathhouse is a reliable foundation. It would seem that it is enough to do everything according to the instructions, use only high-quality materials - and everything will be fine. What else do you need? But absolutely any bathhouse foundation can be deformed - and it’s not always even possible to accurately determine the reason. But the sooner all this is prevented, mistakes are corrected and the foundation is repaired, the better. Moreover, repairing the foundation with your own hands is just as feasible as building it.

In some cases, the lack of proper drainage was to blame, in others, the concrete poured into the belt was of frankly poor quality, and in others, the reinforcement was welded incorrectly.

So, even the most powerful foundation begins to collapse from too active construction in the area - especially in the neighborhood. In this case, it needs to be strengthened.

And even more often, problems begin in those buildings where the foundation drainage was not initially thought out. Let us explain: seasonal heaving of the soil gradually, over the course of several years, squeezes the bathhouse upward, or vice versa, due to insufficient soil research, one side of the building collapses somewhere. And this is fraught with distortions and complete destruction of the building later.

The article https://stroy-banya.com/fundament/fundament-na-razlichnyx-tipax-pochv.html will tell you more about how to choose the right foundation depending on the type of soil.

In a word, there can be many reasons - but the main thing is to take action in time.

If the foundation “squeezes” out of the ground

What to do if one of the corners of the building has risen? How is the foundation repaired under a house where there is no access?

The first thing to do is to drain the water from the walls and insulate the foundation itself. To achieve this, the groundwater level is reduced – thanks to the same well-designed drainage system. It is also necessary to provide storm drainage, if no one has taken care of this yet.

The article https://stroy-banya.com/fundament/uteplenie-fundamenta.html will tell you more about foundation insulation

By the way, if for some reason or lack of budget it is not possible to make a full-fledged blind area, then you can build a temporary one for the season: the slope from the walls is filled with soil, a film is placed on top and sprinkled with earth. This results in a temporary blind area that is effective.

How to save a foundation that continues to settle?

It often happens that the site for a bathhouse is carefully selected, construction is carried out according to all standards, but literally after a few years, for no apparent reason, the soil sags and the foundation cracks. Underwater waters are usually to blame.

But if settlement continues, it is necessary to strengthen the foundation. To check this, cement beacons are installed in its cracks - if over time they also crack, it means that the soil is still subsiding and repair of the foundation is urgently needed - otherwise the bathhouse itself will collapse.

If the foundation has sunk only slightly, several wells need to be drilled in problem areas of the soil in one-meter increments. Depth – 2.5 meters, diameter – 250 mm. If possible, some soil should be removed from under the foundation. All this is filled with concrete. As a rule, the problem is solved.

But what if the foundation continues to settle? What if the floor in the bathhouse has already tilted noticeably and the walls have begun to collapse? Then the repair can be in two options. First: divide the foundation into several sections along the length, and lay a new base. Second: along the entire perimeter, the old foundation is drilled to stable soil, and the voids are filled with cement mortar. This is done like this:

Step 1. Supporting the bathhouse. Before starting the repair itself, the bathhouse must be supported on temporary supports, fixed with boards with stakes nailed to the ground, so that they do not slide.
Step 2. The damaged area must be completely dug out and examined carefully.
Step 3. A trench is dug along the entire length of the foundation to a depth of at least a meter, which in the next step is filled with concrete or laid with bricks. So, under each such damaged area, its own additional foundation is built.

Here is the process itself: a hole is dug in front of the damage site to the very base, and then the earth is dug under the very base of the base. If the soil is hard, then the resulting void can simply be filled with concrete. But if the soil is wet and loose, then you need to dig a hole below the base and put a pipe 45 cm in diameter into it, filling it with liquid concrete. When the filling penetrates this loose soil, it will fill the void under the pipe, and as soon as the concrete stops going into the soil, you can stop the procedure. After half a meter, everything needs to be repeated - and there will be no more cracks in the foundation.

The same idea lies in the new Finnish foundation repair technology - literally in a day, workers drill holes directly in the ground and fill the spaces with a special mixture, at which point the bathhouse rises right before our eyes.

In the most difficult cases, and when you have to completely replace rickety pillars, only repairing the foundation with screw piles can save you.

What to do with a collapsing brick foundation?

The first step is to remove the plaster. And the whole situation with the foundation will immediately be in full view - how serious its damage is. If so, you will have to dig an additional trench and secure the metal mesh with anchors. Next, the formwork is built and filled with concrete. As soon as the concrete hardens, the formwork is removed, and the trench itself must be backfilled and compacted well.

If the damage turns out to be minor, you can simply replace individual sections and restore the blind area. It is only important that both the new and the old masonry are connected.

And in order to further strengthen the base of a brick bath, you need to use a reinforced concrete cage, attaching it to the support using through anchoring. It is important to equally distribute the load between the new and old parts of the base. And for convenience, the entire base can be divided into two-meter zones, each of which can be changed in stages.

If you want to find out which bathhouse is better: brick or log, we recommend reading the article https://stroy-banya.com/karkas/kakaya-banya-luchshe-kirpichnaya-ili-iz-brevna.html

Old bathhouse? It will last another hundred years!

Have you inherited a good, but slightly dilapidated Russian bathhouse? There is no need to worry - our ancestors always built “to last forever”, and such steam rooms are successfully outlived even by neighboring cottages. There is only one thing that needs to be done - a good inspection and repair of the foundation, because something, and the zero level is the first to suffer from time and rain.

So, here's what you'll need to do:

Step 1. Preparation. In the bathhouse, all objects, furniture and even the stove are removed - after all, the steam room will have to be raised.
Step 2. Lifting. To raise a small wooden bathhouse, you will need 2-3 jacks and beams to further fix the walls in the desired position.

How to pour a foundation for a house - tips, schemes and ways to save money

The process of laying any foundation involves several stages:

Site preparation and foundation marking
Excavation work, trench digging, pillar drilling
Preparing a pillow for the foundation
Installation of reinforcement cage and construction of formwork
Pouring concrete and leveling

In this article I will talk in detail and step by step about pouring the most popular today - strip foundation and about the distinctive features of the stages of pouring other types.

Pouring the foundation yourself

There are several types of strip foundations, but the do-it-yourself pouring technology is almost the same for everyone.

You can read about pouring a shallow strip foundation, as well as about a non-buried strip foundation, in my previous articles.

Site preparation and marking for strip foundation

The site preparation process is not difficult at all. First of all, you need to clear the site, or at least the place where you are going to build a house, from excess vegetation, debris, large roots, etc.

When the area is clean, we mark the future foundation strip according to the project.

If you don’t have a level or other special devices, don’t despair; for high-quality marking we only need a tape measure, pegs, a cord and, possibly, a sheet of paper.

We mark all external walls by installing pegs in the corners of the future house. After installing the pegs, measure the diagonals of each rectangle. It should turn out that the opposite sides of the rectangle and its diagonals are equal. If this does not happen, then we draw a sketch of the house on paper, put down the resulting dimensions and think about where and which peg needs to be moved. After corrections, be sure to repeat the measurements. And so on until you have all the sizes.

Try to make the markings of the future structure as accurately as possible, this will help in the future to avoid some difficulties with aligning the corners when building the walls of the house. And for those who want to learn more about marking the foundation for a house, read my article about this, which describes in detail the marking process with examples.

Digging a trench for a monolithic strip foundation

You can dig a trench for a strip foundation manually or mechanically.

It’s quick and cheap to dig with an excavator, but it doesn’t really adhere to dimensions; in some places it can end up being a little wider, in others a little deeper, which will subsequently affect the volume of concrete poured. The savings in this case are very doubtful.

If you don’t want to dig yourself, then it’s better to hire workers and ensure that all dimensions are observed, this will subsequently help you save on the volume of concrete you order.

You can easily calculate the depth of laying a strip foundation by studying one of my articles. It describes in detail all types of strip foundations, their depth and what factors it depends on.

We build a sand cushion for the foundation of a house

The foundation cushion is laid from washed sand, without various admixtures of clay, etc.

Sand, unlike the soil in which the foundation is laid, is much less susceptible to heaving and will evenly distribute water under the foundation, which will eliminate uneven shrinkage of the foundation.

Sand is poured into the trench and compacted. The layer of such a sand cushion should be at least 20cm.

If you do not have special devices for compacting sand, then you need to at least spill it well with water before pouring.

We reinforce the future foundation strip and construct the formwork

For the reinforcement cage, reinforcement with a diameter of 8-14 mm is used, and in order to more accurately determine the diameter and amount of reinforcement, you can use the calculation of reinforcement for a strip foundation. With it you will select the correct diameter and amount of reinforcement for your foundation.

As a rule, vertically laid rods are 8-10mm in diameter, and horizontal longitudinal rods are 12-14mm in diameter. The rods along the trench are always thicker because they will be subject to a greater load, and they, in turn, must cope with it.

In what way to knit the reinforcement frame, in a trench or next to a trench, and then lower the finished frame into it, you must decide for yourself what is more convenient for you. The disadvantage of tying reinforcement in a trench is that if the trench is not wide enough, you will cover it with your body.

It is advisable to construct a reinforcing cage using knitting wire, and not using a welding machine, because weak spots appear in the welding areas of the reinforcing rod.

Formwork for the foundation, if necessary, is constructed using boards 10-20 cm wide and 2.5 - 4.0 cm thick.

When constructing the formwork, it is necessary to eliminate large holes in the formwork and firmly secure it. Opposite formwork panels must be tied together with pins, thus preventing the formwork from bursting when pouring concrete.

The corners of the formwork also need to be firmly fixed, because these are the weakest points.

How to pour concrete for a foundation

Pouring concrete for any type of foundation is the same. As a rule, for large volumes purchased concrete is poured, since a monolithic reinforced concrete strip can only be achieved if the foundation is poured at one time.

And so, all the preparatory work has been done, now it is necessary to pour concrete for the future foundation of the house.

For pouring, concrete grades M200 - M400 are used, which depends on the composition of the concrete.

Pouring concrete into a trench always starts from the corners, and then the remaining voids are filled.

The ideal conditions for pouring the foundation for a house is that the mixer has access to all corners of the house.

The mixer drives up to the corner and the pouring process begins. At this time, one person should hold the gutter, guiding it, and the other (preferably two) should help the concrete to be evenly distributed throughout the trench using a shovel, for example.

In order to expel air from concrete, you need to use a deep vibrator; if you don’t have one, then you need to vibrate using improvised methods. You can vibrate with a bayonet shovel, this vibration is called the bayonet method. A good result can be obtained by tapping with a hammer on the reinforcement frame, or on the formwork (not too much!).

Types of repair work

Currently, there are various ways to reconstruct the base or strengthen it. Since various materials are used to build houses: wood, brick, reinforced concrete, etc., repairing the foundation of a house with your own hands will be carried out according to a certain method.

Most often, during the construction of buildings, strip foundations are laid. If we look at it in more detail, it looks like an integral structure, in some areas of which it is unacceptable to exceed construction loads. Heaving soil can deform the base of such a structure, so before laying the foundation of a house, you need to carefully study the soil and the depth of its freezing.

To repair the foundation of a wooden house, the house will need to be completely raised and only after lifting the foundation of the building will be laid. However, this reconstruction method is only suitable for wooden buildings.

The foundation of a wooden house needs repairs

If the structure has tilted due to subsidence of the soil, then as a result of the repair it is necessary to balance the impact force by increasing the area of the structure. The start of repairs should be carried out where the highest level of roll is detected. Instructions for repair work:

It is necessary to mark a two-meter section of the structure and dig a trench near it. Its depth (one meter) must exceed the lowest point of the damaged part;
The part of the base that is exposed to the ground must be cleaned of adhering dirt, plaster and other deposits;
The cleaned wall surface must be treated with a primer designed for deep penetration;
Holes are prepared on the damaged wall into which anchors are screwed. The minimum number of vertical rows is 3, the horizontal space between the elements should be 60-120 cm;
A reinforcing mesh welded from metal rods is welded to the anchors. Their diameter should not exceed 10-14 mm;
A liquid solution of concrete mixture is poured into all formations that appear as a result of destruction;
If the resulting damage has a wide area, in this case it is necessary to install formwork that is filled with concrete;
Some time after the solution has dried, a layer of waterproofing is attached to it;
The trench is compacted with layers of soil, and each layer must be compacted.

Replacing the foundation in parts

When repairing the structure of a wooden building, the buildings are supposed to be raised; in all other cases, concrete is poured or the area of the structure is increased. It all depends on the degree of damage and the cause of its formation. It is recommended to periodically check the condition of the structure for integrity, which will avoid severe damage to the surface of the walls.

Ways to correct defects in the foundation of a house

Every person who owns his own home will sooner or later encounter problems with cracks in the walls of the building, curvature of the foundation, and distortions. First of all, these problems come from damage to the base of the foundation, which, even with proper construction, can significantly decrease over a long period of time.

Of course, these problems must be solved without the slightest delay. This will save your time and money, and will prevent your home from deteriorating further. Therefore, below we will describe the main ways to improve the foundation of a house.

METHOD ONE: STRENGTHENING THE FOUNDATION

Let's start with the simplest thing: strengthening the foundation. Typically, reinforcement is carried out when the foundation begins to subsidence. If you cannot correct the foundation of your house in time with the help of reinforcement, then it can result in a large amount of money with the complete replacement of expensive parts of both the foundation itself and the entire building.

First, you will need to dig a trench around the entire perimeter of the house. It is better to make the trench as deep as possible. Its width should be such that it is as comfortable as possible for you to work with the underground part of the foundation while in the trench.

Now, using a trowel, carefully clean the surface of the foundation of the entire house from dirt and debris, after which you can begin strengthening. To strengthen the foundation reliably, you will need rigid reinforcing wire. Take it and nail it firmly to the foundation to its full possible height. The other end of the wire is lowered and secured on the other side to the ground.

In order for this entire structure to remain strong, you need to make formwork along the width of the trench and fill the whole thing with concrete. The solution must be made as thick as possible. It is also advisable to add small pieces of reinforcement to it.

Fill the trench with the solution so that about 15 cm remains to the surface of the earth. After the concrete hardens to this height, you will need to add earth and sand and compact everything well. If there are places on your foundation with very large cracks, it is necessary to make through anchoring on them and connect it with an additionally laid row of brick or cinder block. This will subsequently ensure an even load on all parts of the building.

METHOD TWO: RAISING THE FOUNDATION

The next option is to raise the base of the foundation. This is an ideal option for how to correct the foundation of a house if it has sunk too much, thereby causing large cracks in the walls of the house and distortions in the openings of doors and windows.

To raise the foundation, you will need a very strong pad to support the foundation on, and two fairly strong jacks. Start by lifting the most damaged corner of the house using jacks. Carefully place a spacer under the raised part and immediately begin working on the next corners.

When lifting corners with a jack, it is very important to consider two main points. The first is the lift height. The most damaged area should be raised first and above the other corners. But with all this, the maximum lifting height should not exceed two cm. The second is the possible distortion of the log house. Therefore, in the process of raising the corners, it is necessary to carefully ensure that the frame does not warp. Otherwise, it may lead to even greater destruction.

After raising all the corners, check that in the end all the corners are raised exactly the same distance. If you have checked and all the lifting heights are the same, proceed directly to the process of correcting the foundation. To do this, near the corners and in the middle of each wall we make recesses for pillars, the height of which is approximately 1 m.

After this, very strong reinforcement is inserted into the recesses. Try to squeeze the reinforcement so that it rests well on the walls of the recesses. When you are finished with the reinforcement, install the formwork. But after this, mix a thick solution with pieces of reinforcing wire and fill the recesses with reinforcement with it. As a result, you should get so-called reinforcement columns, which will prevent the foundation from sagging in the future. After the solution has hardened, you can sprinkle the flooded areas on top with soil, compacting it well with a roller.

Reconstruction of the foundation of a country house

Strengthening the foundation by installing a monolithic slab: 1 – existing foundation; 2 – reinforcement plate; 3 – fines for sealing the reinforced frame of the slab; 4 – reinforced frame for embedding the slab into the wall; 5 – slab stiffeners; 6 – level of soil development for slab construction; 7 – crushed stone preparation for the slab; 8 – load-bearing wall of the building; 9 – electric welding of slab reinforcement frames.

The least expensive would be to repair or strengthen the columnar foundation of an old wooden house or auxiliary building. Wooden stands called chairs are used as pillars. First, you need to partially disassemble the base and dig a pit near the chair to be replaced. A temporary support is made nearby, at a distance of about 1 m. Now you need to use a jack (lifting at least 10 tons) or a powerful lever to hang the wall so that the lower crown comes out of the tenon of the old chair. At the same time, a temporary, higher support is placed under the wall. All that remains is to install a new chair; it is better if it is brick or concrete.

Repairing, strengthening, or replacing part of a brick or stone foundation will require the preparation of a solution. Replacement of weakened areas is carried out one by one. In this case, one of the possible methods of strengthening or repairing the foundation of the house is used.

When the load on the load-bearing walls increases, the foundation is simply expanded, increasing its area. To do this, they dig holes on both sides and partially hollow out the old foundation from the sides. This is done in order to ensure a monolithic connection between the new foundation of the house and the old one. A sand cushion is poured onto the ground, and everything is filled with mortar. Sometimes, for greater strength, reinforcement in the form of large diameter rods (15-20 mm) is inserted into the old foundation. They can be strengthened on each side or pass through the base. In the latter case, care must be taken, otherwise too large holes can lead to destruction

Strengthening the foundation using a monolithic frame: 1 – existing foundation; 2 – “extendable” reinforced frame of the foundation; 3 – “shorts” made of reinforcing steel for connecting reinforced frames; 4 – electric welding of working frame rods; 5 – monolithic concrete “jacket”; 6 – “key” for exposing the reinforcement; 7 – “short ones” and 3 rods of 12-16 mm each; 8 – reinforced frame of the shirt.

The second option, which involves repairing or strengthening the base, is to expand the area under the sole. This is a more labor-intensive job that cannot be done alone. You will have to dig out the foundation and install a monolithic reinforced concrete slab underneath it.

The installation of a new foundation, its repair or strengthening, restoration begins from weaker places or under walls with openings (doors, windows). After completion of the work, it is necessary to thoroughly compact the soil in order to increase the bearing capacity of the entire foundation. The easiest way to do this is by compacting 10-15 cm layers of crushed stone. The soil must be compacted until the pebbles begin to break.

If the walls do not seem strong enough, they are reinforced with metal beams. First, a horizontal groove is punched into the foundation, where an I-beam or channel is inserted. To prevent them from turning inside out, beams are installed across them, for installation of which through holes are punched in the base of the house. The transverse beams are welded to the horizontal ones. The resulting structure is filled with cement-sand mortar (1:3).

When dismantling old masonry, it is necessary to evaluate the further suitability of its individual elements. The simplest way is to evaluate hardness. To do this, run a piece of slate or a piece of asbestos cement over the surface of the rubble or brick. If no pronounced scratch remains, the material is suitable for further use. When selecting a brick, pay attention to its spoon edges: they should not have cracks more than 3 cm deep.

How to strengthen the foundation of your own house with your own hands

Very often, owners of country houses are interested in strengthening the foundation - no wonder, because everyone wants to be confident in the reliability and durability of their home. Carrying out work to strengthen foundations is a whole story, the outcome of which depends on theoretical knowledge and practical experience. But don’t be afraid, strengthening the foundation of a private house can be done with your own hands, of course, if you are not faced with a situation where it is easier to build a new house than to repair an old one.

Strengthen the foundation or eliminate the cause

The conclusion that suggests itself: first eliminate the reasons that cause changes in the foundation (its destruction) and natural violations of the integrity of the house built on it. Let's look at the most common reasons:

the foundation was initially built in violation of technology. In this case, it is definitely necessary to strengthen it;
changes in the foundation of the house are associated with increased soil moisture. In this situation, much attention is paid to the blind area of the foundation; if necessary, drainage of the foundation is arranged. We will talk about the latter solution in one of the following articles;
The site chosen for construction has a heterogeneous soil composition, which leads to local deformations of the foundation of the house. As an effective solution, a set of measures is used, including strengthening and insulating the foundation, drainage, and, if possible, replacing part of the unstable soil with crushed stone and sand.

To summarize the above: first, you should take care of additional thermal insulation of the soil layers located under the foundation and next to it (this measure will reduce heaving phenomena, if such are typical for your site), and also ensure minimal humidity of the site near the base by developing a drainage system. Only after this can you think about serious work to strengthen the foundation.

Ways to strengthen the foundation of a house

Let's start with the fact that the house can be stone (made of bricks, blocks, etc.) or wooden. In one of the previous articles, we talked in some detail about repairing and strengthening an old wooden house, for example, here you can find some useful solutions.

If with wooden buildings everything is simple - they can be “raised” if desired (what can I say, even replacing the foundation under a wooden house is quite possible), then with stone houses things are somewhat different: they are heavy, and in order to change their position, you will have to spend a lot of time and money.

Therefore, the approach here is different.

Most stone houses are built on a strip or slab foundation. In the latter case, problems with the foundation are extremely rare, so we will only consider strengthening the monolithic tape.

Strengthening the MLF

Despite the fact that the MZF - a shallow strip foundation - works as a single structure that redistributes loads throughout the foundation, it is not protected from local heaving phenomena, which may be associated with differences in the composition of the soil under the foundation. It is due to the prevailing action of lifting forces on one side that the foundation (and house) can tilt to the other. This is accompanied by the appearance of cracks in the foundation with all the ensuing consequences.

Obviously, in order to balance the action of the lifting forces, it is necessary to increase the area of the sole. This work is carried out from the heeling side, which is divided into several sections up to 2 meters long. Further, the sequence of strengthening the MLF can be presented as follows:

digging a trench for the first reinforcement element. Its depth should be greater than the depth of the old foundation (for the construction of a sand cushion), the width is taken based on calculated data and, as a rule, it is not less than the width of the old tape;
in the old foundation, holes are drilled (holes for reinforcement, thanks to which the old foundation and the reinforcing element will be combined) and grooves (recesses in the monolith, increasing the adhesion area of the concrete solution);
then the reinforcement frame of the element is knitted, the rods entering the old foundation are cemented;
formwork is installed and the first reinforcement element is poured with concrete mortar.

Only after the concrete reaches 70% strength do they begin to develop new reinforcement elements. The work is being carried out in the same way. Subsequently, all elements are combined into a single system due to the release of reinforcement from each part of the reinforcing tape.

Upon completion of the work, the foundation is dug in at the places where cracks appear, which are sealed with cement mortar and waterproofed.

Strengthening the strip foundation buried below the GPG

As a rule, a monolithic strip base, the base of which is below the soil freezing depth (SFD), is not subject to uneven lifting influences from the soil. Otherwise, work to strengthen it is carried out in the same way as described above.

In some cases, problems with such foundations are caused by the action of groundwater, which literally washes away the soil from under the foundation. The same can be said for the monolith itself, which, under the influence of high humidity, loses its strength characteristics.

The only feasible solution in such situations is to arrange a drainage system for the foundation. If the buried foundation is badly damaged and the concrete begins to crumble, then the upper damaged layers should be removed, treated with cement laitance and then thoroughly waterproofed.

In case of significant damage, the tape must be expanded by installing additional reinforcing elements, as described above.

Repairing the foundation of an adobe house

Question:

Hello. We decided to do a major renovation of an adobe house, a house built in 60, only two parallel corners at the end have sagged (and even then a little, but noticeably); from the street you can see that there is a foundation (if there is one) along the perimeter of the house. We decided to strengthen the bay with cement mortar in some places, and in some places by simply laying monolithic blocks on top of the ground!

Do you think there is a foundation, given the year it was built? And if it is not there, is it worth removing the cement mortar and monolith and laying a new foundation? There are no cracks anywhere!

Polina, Omsk.

Answer:

Hello, Polina from Omsk!

Without inspecting your adobe house, which is more than half a century old, it is difficult to advise or recommend anything.

For this purpose, local builders are usually invited, who are familiar with the features of adobe buildings and are determined locally about possible repair and reconstruction work.

Your remark that there are no visible cracks anywhere on the walls of the house inspires some optimism. Therefore, there is still some kind of foundation or a bearable foundation under the walls. Or the soil under the house is strong enough and the weight of the house is not so great.

And so, often in several places under the walls they make point diggings in order to determine - what is there after all? This is done very carefully and in limited areas, so as not to violate the integrity of the walls and prevent them from collapsing.

The presence or absence of a foundation under adobe houses is dictated by many conditions - the characteristics of the soil, the weight of the building, its design, the presence of high groundwater, etc. and so on.

The option of laying blocks and pouring concrete under the base of the walls of an adobe house is sometimes used in such cases. Naturally, the main attention should be paid to the sagging two corners, where the main efforts to strengthen them are directed.

Sometimes they follow the path you mentioned, that is, they remove the cement mortar in those places where it is not continuous, but consists of separate fragments. And fill the cavities and depressions in the foundation base with a new concrete solution.

Therefore, I repeat once again - you should carry out a professional inspection and, based on it, make a decision whether to leave everything as is with minimal strengthening of the foundation. Or carry out drastic work at high financial costs.

In practice, most often, if the old foundation is in a tolerable condition and there are no deformations and cracks, and provided that the old adobe house will not be lined with new brick walls and no work will be done on the construction of an attic and all kinds of extensions, then they do the minimum. That is, they correct the sagging corners sufficiently and stop there.

I won't say anything else.

Good luck!