Repair and reinforcement of the foundation with screw piles

Recommendation points

• What foundations can be repaired using screw piles
• Strengthening the foundations of multi-storey buildings
• Preparing an obsolete structure for vertical development
• Emergency foundation repairs due to abnormal soil subsidence
• Stage one. Geo-environment study and bearing capacity calculations
• Stage two. Reinforcement of corner modules “bulls”
• Preparation of the object. Expose the foundation
• Screwing in piles
• Reinforcement and pouring
• Stage three. Strengthening the strip foundation
• Earthworks during the repair of the foundation around the entire perimeter
• Partial dismantling
• Driving in piles by a mechanized method
• Concreting
• Prefab and log houses
• Lifting the building with jacks
• Foundation device

A crack in the foundation is a nightmare for any conscious owner. Fortunately, there is a proven and reliable way to fix defects and strengthen the foundations of houses. We will tell you about the possibilities of screw piles and methods of strengthening the foundation with their help..

The technology of reinforcing concrete foundations using piles is not new, but thanks to the development of the technical base in the construction industry, it has become available for use in private households. This method of strengthening the foundation is not cheap, but provides the best results in the shortest possible time..

The use of piles ensures maximum strength and stability of the building’s supporting structure to changes in soil density: winter heaving, groundwater erosion and natural shrinkage. The whole range of works can be really completed in one season, and the result will surpass everything, even the wildest expectations. Pile technology gives the foundation characteristics that cannot be achieved even with a complete replacement. Excellent mechanical strength and structural stability make it possible to construct the second and third floors of the superstructure even on those buildings that were considered emergency before reinforcement..

What foundations can be repaired using screw piles

The intended use of the aircraft is the device of a bearing support in areas of soil with low or uneven density. Thanks to the original design of the blade, the screw pile has a larger area of ​​support on the ground than reinforced concrete, and therefore is able to withstand significant pressure – up to 25 tons. However, the use of screw piles is not limited to difficult geological conditions: they perfectly cope with most of the common tasks that can be assigned to supporting structures..

Strengthening the foundations of multi-storey buildings

Screw piles are perhaps the only relatively safe method of strengthening the foundations of multi-storey buildings. Due to the high load, the concrete base is difficult to open, and there can be no talk of its full or partial replacement. Using the sun, you can with the utmost care get to the bottom plane of the foundation and prop it up without clearing it from the soil.

Preparing an obsolete structure for vertical development

A similar situation occurs when strengthening the foundations of old buildings. During the construction of houses in the post-war period, there was an acute shortage of building materials, and therefore the quality of the foundation foundations leaves much to be desired. When trying to open such a foundation, collapses and complete deformation of the supporting array very often occur, implying its complete replacement. Screw piles are capable of supporting the foundation without significant interference in its fragile structure due to the heads of a special design.

Emergency foundation repairs due to abnormal soil subsidence

Due to the erosion of the soil by groundwater, areas of different density appear, due to which the foundation is subject to the consequences of uneven distribution of the load: fractures, deformation, crumbling. The only alternative to the use of VS in this case is a complete replacement of the soil under the foundation or its compaction with a rare cement mortar. In this case, VS are not only the least expensive solution, but also the most durable: they do not rely on the upper layers of the soil, but keep the force at the depth where the effect of water erosion is minimal..

Stage one. Geo-environment study and bearing capacity calculations

If you want to strengthen the foundation with screw piles, you should observe a clear step-by-step operation. The first step is to conduct a thorough survey, which determines:

1. Density of soil around the entire perimeter of the building. For this, numerous samples are taken from the soil and compared with each other for density and moisture. Sampling is carried out, as a rule, by the point method. When excavating soil at subsequent stages, additional samples are taken, according to the results of the analysis of which additional adjustments can be made.
2. The required number of piles, their placement points, the degree of penetration, the type of blades and heads, as well as the thickness of the bearing mast.
3. The current state of the foundation, the type and rate of its destruction. The examination also establishes measures, the adoption of which is guaranteed to restore the strength of the supporting structure..
4. The need for additional pouring, the calculation of the reinforcing mesh and the composition of concrete.

Engineering and geological surveys and the issuance of conclusions on the properties of soil are carried out by specialized laboratories and enterprises. Such types of work are subject to compulsory licensing and are considered a narrowly focused area of ​​technical expertise. It is enough to carry out a soil survey according to six indicators, however, an expert opinion on physical and mechanical properties is drawn up for eleven. In general cases concerning urban and rural construction, focus on the lower price segment.

Stage two. Reinforcement of corner modules “bulls”

You should start by strengthening those sections of the foundation that account for the bulk of the distributed mass. The corner parts of the building support are subject to the greatest load, which comes from the geometry of the structure. Often, only strengthening the corners of the foundation is enough to prevent further destruction and reduce the degree of natural deformation.

Preparation of the object. Expose the foundation

In order to gain access to the concrete base, it is required to dig a pit, taking into account the following features:

1. Dimensions not less than 100×100 centimeters and deepening below the level of the foundation.
2. The fourth part of the pit should fall directly on the corner of the concrete structure.
3. The ditch for the foundation should not be too large: it is enough to provide a gap of 10 centimeters.
4. When the foundation is opened, dirt should be washed off from it and allowed to dry for 24 hours.

Screwing in piles

The immersion of corner piles can, if necessary, be done manually: the dimensions of the pit and the absence of restrictions on the side of the walls make it possible for the knob to move freely. The piles must be immersed to a depth determined by the peculiarities of the existing structure so that the flat head is flush with the bottom edge of the foundation. The pile insertion point should be located as close to the corner of the building as possible. The project may provide for the use of two piles on opposite sides of the corner of the foundation.

Reinforcement and pouring

A concrete block called “bull” must be poured into the dug pit. To do this, you need to assemble a frame from steel reinforcement:

1. Under the foundation, rods of profile reinforcement with a diameter of 12 mm are brought in and do not reach the border of the digging by 5-10 cm. The best option would be to prop the reinforcement to the foundation with stones or broken bricks.
2. The outward-facing ends of the reinforcement should cover at least half of the excavation area. In general, 6–7 rods are enough, which are laid flat on the pile head and welded to it. After fixing the reinforcement on the heads, the fixing stones should be removed.
3. Several reinforcement rods are vertically welded to the pile head.
4. In accordance with the specified parameters, a frame is formed from reinforcing rods and reinforcing mesh.

Pouring concrete should be done in two stages. At the first stage, the concrete mixture is poured to a level not lower than the middle of the existing foundation and subjected to vibration ramming. At the second stage, it is possible to reduce the consumption of concrete mixture by reducing the size of the pit by 30-40% using external formwork.

Note: if additional filling is not provided by the project, an angle bracket is used as a head and additional reinforcement is not carried out..

Stage three. Strengthening the strip foundation

If the technology requires strengthening the supporting structure along the entire perimeter, the third stage of work is carried out. Strengthening the strip foundation is the most time consuming and complex process. In addition, due to the small size of the trench, it should be possible to use small-scale mechanization for screwing in piles..

Earthworks during the repair of the foundation around the entire perimeter

Digging is done manually:

1. Digging a trench up to 50 centimeters wide around the entire perimeter of the building.
2. The opening and subsequent strengthening is carried out gradually: you cannot open more than half the length of one wall, but to speed up the process, work can be carried out on different sides of the house.
3. The depth of the trench must match the bottom of the foundation. If the project involves pouring an additional array, the bottom of the trench should be lowered 15–20 centimeters lower, without affecting the soil layer directly under the foundation.

Partial dismantling

In the process of opening the foundation, you can often find completely detached concrete fragments, which must be removed. In addition, the concrete layer can be subjected to defectoscopy and in case of unsatisfactory results, it is worth dismantling the damaged areas. At the same time, a number of adjustments are made to the layout of the pile entry points into the ground..

Driving in piles by a mechanized method

The piles are screwed in using a portable gearbox or a drilling and crane mechanism on a self-propelled unit. The reach of the last link of the boom must be sufficient to drive the pile into the trench to the specified depth, otherwise special shanks will have to be used. The point of entry of the piles into the ground is located at a well-defined distance. A spacer bracket is used as a head, the heel of which should go under the foundation to be strengthened by at least?. The bracket must be reinforced with gussets from the bottom side.

Concreting

If necessary and possible, partial concreting is carried out, the process of which is in many respects similar to the pouring of corner fragments of the foundation, but still has differences:

• reinforcement is introduced under the foundation without support on the head;
• a longitudinal reinforcing frame is formed, the rods are welded to the brackets at the ends of the piles. The longitudinal reinforcement should be at least 6 meters long, and the transverse reinforcement should not reach the pit walls by 10–15 centimeters;
• the frame has a rectangular cross-section and is formed on wire frames.

Pouring the concrete mixture can be done in one step, but you should make sure that the concrete flows into the tunnel area. The best option would be to apply vibration shrinkage.

Prefab and log houses

It is easiest to equip light buildings and structures with a foundation on screw piles. In the process of replacing or strengthening the foundation, only the grillages remain intact, the level of which should be guided by when installing the headings.

Lifting the building with jacks

To carry out the replacement of the foundation, the building must be raised. For this, special hydraulic equipment and fixing supports are used. Often, the re-equipment of the foundation is carried out in two stages: first, one side of the structure is raised and a new support is mounted under it. Then the building is raised from the other side, relying on the new structure and the strengthening of the foundation is completed, after which the structure is completely lowered. If the house has the shape of a rectangle, it is better to lift it from the wider side, in order to avoid the appearance of a break point.

Foundation device

The piles are inserted into the ground at the smallest distance from the building symmetrically from two opposite sides in accordance with the position of the support bollards, using any of the available immersion methods.

Flat heads are mounted on the screwed-in piles, while their horizontal level is clearly checked with the grillages.

Opposite piles are connected using T-beams or U-beams by arc welding.

The grillages are strengthened: they should be covered with a metal substrate and fastened around the perimeter with a steel band.

If it is required to strengthen the foundation from all four sides, the lifting of the building is carried out in four stages: first, relative to the transverse and then to the longitudinal axis. The connection of the supporting beams is allowed to be made at a distance from the nearest grillage not more than 50 cm.