Measures for the construction of non-buried foundations on heaving soils. Replacing soils at the base of foundations Which foundation is better for non-porous soil

A characteristic feature of heaving soils is their susceptibility to frost heaving.

The process of soil heaving is the result of freezing of the moisture in it, which turns into ice.

The heaving force of clay soils can destroy any structure, therefore, construction on such soils requires a special technology for the production of work

Since the density of ice is less than that of water, its volume is greater. Heaving soils include three types of clay soils: sandy loam, loam and clay. Clay contains a lot of pores, which allows it to retain moisture. Accordingly, the more clay and water contained in the soil, the higher its heaving.

The degree of frost heaving is understood as a value showing the propensity of the soil to possible heaving. The degree of heaving is determined as the ratio of the absolute change in soil volume as a result of freezing to the height of the soil before freezing occurred.

Thus, here it is possible to determine how the process of soil freezing affects its volume. If the index of the degree of heaving of the soil is more than 0.01, then such soils are called heaving, that is, they increase by 1 cm or more when the soil freezes to a depth of 1 m.

Measures against heaving

The heaving force is so great that it can lift a large building. Therefore, on heaving soils, special measures are taken to reduce and prevent heaving. The following measures taken against heaving of soils can be distinguished:

All clay types of soils are subject to heaving.

1. Replacing the soil with non-rocky coarse or gravel sand. This will require a large pit, having a depth exceeding the depth of freezing of the soil. A heaving layer of soil is removed from the dug pit, which allows sand to be poured into it and thoroughly compacted. A material such as sand is very suitable for installation as it has a very high bearing capacity. This method is expensive because it requires a large amount of work.
2. You can also achieve stability by laying it on heaving soils at a level lower than the freezing depth. In this case, the heaving forces will act only on its lateral surfaces, and not on the base. Freezing to the side surface of the base of the house, the soil will move it up and down. As a result of the load, the heaving force per 1 sq.m of the side surface of the base of the house can reach 5 tons. If the house built on has a base equal to 6x6 meters, then the area of ​​\u200b\u200bits side surface will be 36 square meters. meters. The calculation of the tangential heaving force when laying to a depth of 1.5 meters will result in 180 tons. This is enough for the wooden house to rise, as the tree will not be able to resist the heaving force. Therefore, this method is used for the construction of heavy houses made of bricks or reinforced concrete blocks. They are based on tape types.
3. To reduce the influence of the tangential heaving force of the soil, a layer of insulation is used, which is laid on the soil layer. This method is suitable for light structures and shallow ones. The thickness of the insulation used is taken into account depending on the climatic conditions of the place where the house is being built.
4. Measures can be taken to divert water to prevent heaving. For this purpose, a drainage system is being arranged along the perimeter of the site. To do this, at a distance of half a meter from the foundation to the depth of its laying, a ditch of the same depth is laid. A perforated pipe is laid in it, which must be laid in a filter cloth with a slight slope. A ditch with a pipe wrapped in cloth must be covered with gravel or coarse sand. The water flowing from the ground must then flow through the drainage pipe into the drainage well through the hole. To ensure natural drainage of water, a sufficiently low area for drainage of water is required. This requires a blind area and storm sewer.

Strip base device

General requirements

The basic rules for constructing the foundations of buildings and structures are set out in SNIP 2.02.01-83.

For laying, it is required to create such a structure that would have an acceptable level of deformation throughout the life of the house. In this case, the condition of high stability under the influence of the tangential heaving force of the soil must be observed. The indicator of their deformation when laying on heaving soils should be zero. So that the sole of the foundation does not come off the base of the building, when laying it, follow the rule adopted in SNiP 2.02.01 - 83. Estimated freezing depth in relation to the laying depth for soils:

• non-porous - does not affect the depth of laying;
• slightly heaving - exceeds the depth of laying;
• medium and strong heaving - less than the depth of laying.

This rule ensures the exclusion of the action of large normal heaving forces on the sole of the base of the house for medium and strongly heaving soils. For weakly heaving, the effect of heaving forces is insignificant. The acting tangential heaving forces on the side surfaces of the foundation are crushed under the influence of the weight of the entire structure. Therefore, the heavier the construction object, the more feasible this condition.

The use of tape structures

The foundation, being the underground part of the building, takes the load from the weight of the structure and transfers it to the dense layers of soil, that is, the foundation. Its edge is a plane located in the underground upper part, which is in contact with the sole or base of the foundation.

Tape has high reliability and durability, therefore it is widely used in construction.

The device of strip foundations is simpler than others, although a large consumption of materials and the use of a truck crane will be required. The tape is a reinforced concrete strip laid under the walls of the building along its perimeter. When laying, it is necessary to ensure that the cross section in each section is of the same shape.

This type is applied to the following types of houses:

• with walls made of stone, brick, concrete, having a density of more than 1000-1300 kg / cu. m;
• with monolithic or reinforced concrete, that is, heavy floors;
• with a planned basement or basement, in which the walls of the basement are formed by the walls of the strip foundation.

The use of a strip reinforced foundation ensures the reliability of the construction of the walls of a house built on heaving soils. At the same time, it redistributes the load from the area with one type of soil to the area with another type.

Kinds

Device diagram

Strip foundations are divided into two types: buried and shallow. Such a division depends on the load of the load-bearing walls of the building on their underground base. Both types are suitable for construction on heaving and slightly heaving soils, providing sufficient stability to the building. The strip foundation forms a reinforced concrete frame running along the entire perimeter of the building structure. The cost of building this structure allows you to achieve the optimal ratio of "reliability - savings". The budget for the device will be no more than 15-20% of the construction cost of the entire structure or building.

For the construction of buildings on slightly heaving soils, a shallow foundation is suitable. This type is used for the construction of foam concrete, wooden, small brick and frame houses. It is laid to a depth of 50-70 cm.

For the construction of structures on heaving soils, buried strip foundations are suitable. The ceilings and walls of houses for such a foundation should be heavy, and the weight of the entire structure will prevent the soil from heaving under the weight of the building or structure.

For houses built on heaving soils, they plan to simultaneously build a basement or garage. Laying is carried out to a depth of 20-30 cm lower than the freezing depth of heaving soil. The consumption of material for the second type will require more than for the first. Under the internal walls of the building can be laid with a depth of 40 to 60 cm.

The bottom of the strip buried foundation is laid lower than the freezing level of water in the soil. This can explain the high strength and stability compared to shallow-depth. However, the labor and material costs of a buried view are greater.

Device on heaving soils

A concrete mixer will help speed up the process of preparing a concrete mixture.

The strip foundation is laid in the warm season. Bookmarking does not require the use of expensive types of equipment, only a concrete mixer and small-scale mechanization are used.

Swelling and deeply freezing soils are not suitable for laying strip foundations. In such soils, its laying is carried out in rare cases. The site where a tape or other type of device is planned must undergo a series of engineering and geological surveys. They should include:

1. Determining the type of soil and its condition.
2. The degree of soil freezing.
3. Presence of water contained in soils.
4. The magnitude of the load from the building structure.
5. Basement available.
6. The service life of the building.
7. Necessary materials for laying.
8. Equipping the site for the construction of underground utilities.

A responsible and competent approach to choosing a type for a future building determines its quality. The future performance of the building depends on this. During the construction process, there may be unforeseen costs for correcting errors as a result of distortions. Bearing structures can be subject to vertical and horizontal deformations, uneven precipitation occurring in the soil. Groundwater problems may arise.

Laying a deep strip foundation

Preliminary stage and preparation of materials

Recessed strip foundations are structures with thick walls, the thickness of which is determined by the material used. The thickness of the walls is affected by the pressure force of the building and the degree of freezing and soil moisture. The strip foundation can be designed with an extension to the bottom or have a stepped look.

The design of the device on heaving soils is divided into two types:

The block strip foundation is mounted using special lifting equipment.

1. Belt prefabricated structures can be built using factory reinforced concrete blocks. Among the advantages of this type is the possibility of erection in any season. Such a foundation is simple when it is installed on heaving soils, which can be done in a short time. The disadvantage is the high price of the structure and the possibility of moisture transmission in conditions of insufficient waterproofing. This requires a blind area and drainage.
2. Tape, having a monolithic type, are built from high quality concrete solutions. Their structures, of any complexity, are equipped with a reinforced frame embedded in a single monolithic tape. The disadvantage of the design is the long duration of the masonry process.

In the course of preparatory work for laying a strip foundation installed on heaving soils, the following points must be taken into account:

The wooden formwork of the foundation must be securely fixed so that it does not collapse under the pressure of the poured concrete.

1. The width of the base should be taken more than the width of the walls of the building, taken into account in the design, by 15 cm.
2. Eliminate possible downtime by drawing up a work plan for the manufacture of a tape type with your own hands.
3. Equip warehouses by delivering the necessary materials to the construction site in order to pour the structure in one go.
4. Be sure to fix the position of all elements of the strip foundation using a cord with stakes.
5. Align all uneven terrain in advance at the site of the future foundation using rails and a level.

So, for laying a deep strip foundation, you will need tools and materials:

1. Level.
2. knitting wire.
3. Bayonet and shovels.
4. Cord for marking.
5. Ribbed reinforcement (section 10-14 mm).
6. Lumber, axe, hammer, nails and hacksaw for formwork.
7. Cement, sand, gravel.
8. Concrete mixer as equipment.

Step by step installation

The walls of deep trenches must be reinforced with spacers to avoid collapse of the soil.

The order of the bookmark involves the following work:

1. A layout plan of a building or structure.
2. Determination of the required depth of laying.
3. Trench preparation.
4. Laying a cushion of gravel and sand, if necessary.
5. Formwork installation.

Before starting work, after cleaning the construction site, a breakdown of the plan of the building or structure is carried out. At the same time, all dimensions of the planned foundation are transferred from the finished drawings to the surface of the land plot. Pillars are installed that serve as a cast-off, located at a distance of 1 to 2 meters from the future walls of the house, from the side of which boards are nailed. On these boards, the dimensions of the trenches of the pit, as well as the foundation and walls of the house, are marked. The distance is measured with a tape measure to ensure measurement accuracy, and the angles are calculated using a triangle. They define the location of the perpendicular axes.

The construction begins with the construction of a sand cushion at the bottom of the trench.

It is very important for heaving soils to determine the depth of their freezing, the presence of groundwater, and to calculate the soil load on the foundation. It is laid to a depth below the freezing of heaving soils, therefore it is buried.

Laying technology at the initial stage is associated with digging a trench. You can prepare it using an excavator or do it yourself with a shovel. The trench will be the base, which is required at the end of the preparation to be made even without collapses and irregularities. A trench is dug up to a depth of 1 meter, while not installing fasteners. Its walls must be vertical. If the depth is more than a meter, then slopes are made so that soil does not shed from the spacers.

The finished trench should be laid in layers of gravel and sand, each 12-15 cm high. Both layers are compacted with water after laying. The finished pillow is laid with a layer of polyethylene film. An alternative option is to pour concrete mortar, which is aged for a week. As a result, a more liquid concrete mortar firmly sets.

Stage of formwork preparation and reinforcement knitting

The diameter and number of rows of longitudinal reinforcement in the frame depends on the design of the structure being erected.

For the construction of formwork, planed boards are taken, the thickness of which is from 40 to 50 mm. You can use shield formwork moistened with water before pouring the concrete solution. Slate, plywood and other suitable materials are used for this purpose. When erecting the formwork, it is simultaneously kept under control to the correct level of verticality. For the plant, pipes made of asbestos concrete are laid in the formwork in the sewerage structure with water supply.

As the formwork is being arranged, a reinforced frame is laid in it. The reinforcement is mounted in the formwork, receiving a frame around the entire perimeter of the future foundation. The reinforcing bars used must have the same diameter everywhere. The reinforcement frame is mounted using knitting, which should be done in accordance with the design documents. During its installation, the technology of the device of the selected type, prefabricated or monolithic, is carefully observed.

In the absence of a special project, a standard reinforced frame is made in a vertical position. Two rows of reinforcing bars are taken along the width of the foundation, which are fastened horizontally using knitting wire. The required amount of reinforcement is determined by the width of the foundation and is carried out every 10, 15 or 25 centimeters.

Pouring a structure

An internal vibrator should be used to compact the concrete mixture placed in the formwork.

After preparing the formwork and knitting the reinforced frame, concrete is poured. The thickness of each layer of the fill should be about 15-20 cm. The fill should be rammed with a special wooden rammer. So, in order to exclude all voids in the structure, the walls of the formwork are tapped with the help of or a wooden hammer.

Concrete mortar is prepared on site using a concrete mixer. In this case, cement, sand and crushed stone are taken in a ratio of 1: 3: 5, respectively. This composition varies depending on what season and what complexity the structure has.

The consistency and composition of each layer should be the same. In winter, they use a concrete heater, lining the entire structure with mineral wool and using special frost-resistant additives. Concrete is poured from a small height using gutters, otherwise the pouring may result in concrete delamination.

To remove air from concrete, it is pierced at the end of all pouring work in different places with a probe. In order for the strip foundation to become strong evenly, it is covered with a film.

At the final stage, the formwork is removed 4-6 days after the concrete has been poured. The term depends on the temperature at which the filling was performed, and on its thickness. After the formwork is removed, backfilling is carried out using clay and sand. The backfill is compacted with water and leveled.

In the upper part, the foundation is treated with a special waterproofing solution. The type of composition depends on how deep the structure lies. Thermal insulation is carried out, if necessary.

When constructing a deep strip foundation on heaving soils, the freezing depth is taken into account, which is a constant value for each locality. It depends on climatic conditions and humidity levels. Unlike the shallow foundation used for slightly heaving soils, the buried one does not include a sand cushion. Buried strip foundations are supported by an unresolved soil structure that is not waterlogged.

Shallow on heaving soils

The construction of buried strip foundations in terrain with heaving soils is expensive. It requires large financial costs. The increased influence of the tangential heaving force on the structure, which exceeds the load from the structure itself, complicates the construction technology. Therefore, the most promising solution is the construction of basement-free low-rise buildings on heaving soils. Such buildings are characterized by the use of tape monolithic reinforced concrete shallow foundations. They require an anti-rock sand cushion. At the slightest load from the house, its foundation rests on the ground, which is close to the surface. Due to the absence of the need for additional measures, the cost of arranging this type of foundation is significantly reduced.

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Before starting the construction of the foundation of the house, such an operation as checking the bearing capacity of the soil must be carried out without fail. Research is carried out in a special laboratory. In the event that the existence of a risk of collapse of the building during its construction in this particular place is revealed, measures can be taken to strengthen or replace soils.

Classification

All soils are divided into several main types:

• Rocky. They are a solid rock mass. They do not absorb moisture, do not sag and are considered non-porous. The foundation on such grounds is practically not deepened. Rocky soils also include coarse-grained soils consisting of large ones. In the event that stones are mixed with clay soil, the soil is considered weakly heaving, if with sandy soil it is non-rocky.
• Bulk. Soils with disturbed natural layering structure. In other words, artificially poured. Buildings on a similar basis can be built, but first you must perform a procedure such as soil compaction.
• Clayey. They consist of very small particles (no more than 0.01 mm), absorb water very well and are considered heaving. Houses sink on such soils much more strongly than on rocky and sandy ones. All are classified into loams, sandy loams and clays. These include loess.
• Sandy. They consist of large sand particles (up to 5 mm). Such soils are compressed very weakly, but quickly. Therefore, houses built on them settle down to a shallow depth. Sandy soils are classified according to particle size. Gravel sands (particles from 0.25 to 5 mm) are considered the best bases.
• Quicksand. Dusty soils saturated with water. Most often found in wetlands. For the construction of buildings are considered unsuitable.

Such a classification by type is carried out in accordance with GOST. Soils are examined in laboratory conditions with the determination of physical and mechanical characteristics. These surveys are the basis for calculating the capacity of foundations for buildings. According to GOST 25100-95, all soils are divided into rocky and non-rocky, subsidence and non-subsidence, saline and non-saline.

Main physical characteristics

When conducting laboratory studies, the following soil parameters are determined:

• Humidity.
• Porosity.
• Plastic.
• Density.
• Particle Density.
• Deformation modulus.
• Shear resistance.
• Friction angle of particles.

Knowing the density of particles, it is possible to determine such an indicator as the specific gravity of the soil. It is calculated, first of all, to determine the mineralogical composition of the earth. The fact is that the more organic particles in the soil, the lower its bearing capacity.

What soils can be classified as weak

The procedure for conducting laboratory tests is also determined by GOST. Soils are examined using special equipment. The work is carried out only by trained specialists.

If, as a result of testing, it is revealed that the mechanical and physical characteristics of the soil do not allow the construction of structures and buildings on it without the risk of their collapse or violation of the integrity of the structure, the soil is recognized as weak. These for the most part include quicksand and bulk soil. Loose sandy, peaty and clayey soils with a high percentage of organic residues are also most often recognized as weak.

If the soil on the site is weak, the construction is usually transferred to another place with a better foundation. But sometimes this is not possible. For example, on a small private plot. In this case, a decision can be made to build a pile foundation with a laying depth of up to dense layers. But sometimes it seems more appropriate to replace or strengthen the soil. Both of these operations are quite expensive in terms of both financial and time costs.

Soil replacement: principle

The process can be done in two ways. The choice of method depends on the depth of dense layers. If it is small, weak soil with insufficient bearing capacity is simply removed. Next, a poorly compressible cushion of a mixture of sand and other similar materials is poured onto the dense base of the underlying layer. This method can only be used if the thickness of the soft soil layer on the site does not exceed two meters.

Sometimes it happens that dense soil is located very deep. In this case, the pillow can also be laid on a weak one. However, in this case, accurate calculations of its dimensions in the horizontal and vertical planes should be performed. The wider it is, the less will be the load on weak soil due to the distribution of pressure. Such pillows can be used when constructing foundations of all types.

When using such an artificial base, there is a risk of crushing the pillow with the weight of the building. In this case, it will simply begin to bulge into the thickness of the weak soil from all sides. The house itself will sag, and unevenly, which can lead to the destruction of its structural elements. In order to avoid this, sheet piling is installed around the perimeter of the pillow. Among other things, they prevent waterlogging of the sand and gravel mixture.

Is it possible to change the soil on the site yourself

The replacement of soils for the foundation should be carried out only with the preliminary conduct of appropriate studies and calculations. Doing this on your own, of course, will not work. Therefore, most likely, it will be necessary to invite specialists. However, when erecting not too expensive buildings, for example, household ones, this operation can be performed “by eye”. Although we still would not advise taking risks, but for general development, let's look at this procedure in more detail. So, the stages of work in this case are as follows:

• Excavation is carried out to a solid foundation.
• Medium-sized sand is poured into the trench to the level of the sole of the future foundation. Backfilling is done in layers of small thickness with ramming of each. The sand must be moistened with water before compaction. Tampering should be carried out as carefully as possible. There should be no inclusions in the sand itself, especially large ones. Sometimes soil-concrete mixtures and slags are used instead.

In the event that an artificial base is used under the foundation, it is also worth arranging. This will slightly increase the density of the soil surrounding the pillow and prevent it from being squeezed out to the sides.

Works on the creation of a drainage system

• A ditch is dug a meter from the building. Excavation is carried out below the depth of the foundation. Width - not less than 30 cm. The slope of the bottom of the trench should be at least 1 cm per 1 m of length.
• The bottom of the trench is rammed and covered with a five-centimeter layer of sand.
• Geotextiles are spread on the sand with the edges fixed on the moat stacks.
• Pour a ten-centimeter layer of gravel.
• Lay perforated drainage pipe.
• Cover it with gravel with a layer of 10 cm.
• Cover the "pie" with the ends of the geotextile and sew them together.
• They cover everything with soil, leaving manholes in the corners of the building.
• A receiver well is arranged at the end of the pipe. It is necessary to divert the drain at least five meters from the wall of the building.
• Gravel is poured at the bottom of the well and a plastic container with holes drilled in the bottom is placed there.
• Lead the pipe into the container.
• From above, the well is covered with boards and sprinkled with earth.

Of course, a drainage system should be installed on the building itself.

How is soil reinforcement done?

Since soil replacement is a rather laborious and costly operation, it is often replaced by the procedure of strengthening the base for the foundation. In this case, several different ways. One of the most common is soil compaction, which can be surface or deep. In the first case, a rammer in the form of a cone is used. It is lifted above the ground and dropped down from a certain height. This method is usually used to prepare bulk soils for construction.

Deep soil compaction is carried out using special piles. They are hammered into the ground and pulled out. The resulting pits are covered with dry sand or poured with soil concrete.

thermal method

The choice of soil reinforcement option depends, first of all, on its composition, the procedure for determining which is regulated by GOST. which was presented above, usually require strengthening only if they belong to a non-rock group.

One of the most common amplification methods is thermal. It is used for loess soils and allows strengthening to a depth of about 15 m. In this case, very hot air (600-800 degrees Celsius) is injected into the ground through pipes. Sometimes heat treatment of the soil is done in a different way. Wells are dug into the ground. Then combustible products are burned in them under pressure. Wells are hermetically sealed. After such treatment, the burnt soil acquires the properties of a ceramic body and loses its ability to absorb water and swell.

Cementation

Sandy soil (a photo of this variety is presented below) is strengthened in a slightly different way - cementation. In this case, pipes are clogged into it, through which cement-clay mortars or cement slurries are pumped. Sometimes this method is used to seal cracks and cavities in rocky soils.

Silicization of soils

On quicksand, dusty sandy and macroporous soils, the silicification method is more often used. To enhance this, a liquid glass solution is injected into the pipes and the injection can be done to a depth of more than 20 m. The liquid glass propagation radius often reaches one square meter. This is the most effective, but also the most expensive way to amplify. A small specific gravity of the soil, as already mentioned, indicates the content of organic particles in it. In some cases, such a composition can also be enhanced by silicification.

Comparison of the cost of replacement and soil reinforcement

Of course, the amplification operation will cost less than the complete replacement of the soil. For comparison, let's first calculate how much it will cost to create artificial gravel soil per 1 m 3. Selecting land from one cubic meter of area will cost about 7 USD. The cost of crushed stone is 10 USD. for 1 m 3. Thus, the replacement of weak soil will cost 7 c.u. for the recess plus 7 c.u. for moving gravel, plus 10 c.u. for the gravel. Total 24 c.u. Strengthening the soil costs 10-12 USD, which is two times cheaper.

From all this one can draw a simple conclusion. In the event that the soil on the site is weak, you should choose another place to build a house. In the absence of such an opportunity, it is necessary to consider the option of building a building on piles. Strengthening and replacing the soil is carried out only as a last resort. When determining the need for such a procedure, one should be guided by SNiP and GOST. Soils, the classification of which is also determined by the regulations, are strengthened by methods suitable for their specific composition.

In some cases, it is economically feasible, instead of deepening the foundation through a small thickness of weak (silty, peaty, bulk, etc.) soils or strengthening weak soils located under the foundation, to remove these soils and lay a pillow of sand, gravel, stone in their place , cement-soil, lime-soil mixture or other low-compressible material.

Rice. 5.3. Pillow device diagram
on the left - with a small thickness of the layer of weak soil; on the right - with a large thickness of the layer of weak soil; 1 - foundation; 2 - a pillow from a low-compressible material; 3 - layer of solid soil; 4 - weak ground

With a layer of soft soil 1.5-2 m thick, it is advisable to lay the pillow directly on the underlying layer of stronger soil (on the left in Fig. 5.3). If weak soil extends to a considerable depth, the dimensions of the cushion are determined from the condition that the pressure under it decreases to a value not exceeding the design resistance of this soil. In this case, the thickness of the pillow and its width at the bottom are taken based on the distribution of pressure at an angle a to the vertical from 20 to 40°. The value of the angle a depends on the physical and mechanical properties of the cushion material.

It is advisable to use pillows for single and strip foundations with a sole width of 1-1.5 m in clay, loamy and sandy soils with a design resistance of 0.10-0.15 MPa above the level. For the device of the pillow, a material with a calculated resistance under the base of the foundation of 0.20-0.25 MPa is used. In sandy and sandy loamy soils, non-cohesive soils are used for the construction of pillows. In loamy and clayey soils, in order to avoid the accumulation of water in the pit, pillows are made from compacted cohesive soils, or a mixture of soils with cement or lime is used for their construction.

To eliminate the possibility of lateral expansion of the soil under the foundation, to prevent bulging of weak soil, as well as to protect the base from underwashing, sheet piles are used, which in some cases are left in the soil for the entire period of operation of the structure. Sheet piling can also be used in the construction of soil pads to reduce the amount of work to remove weak soil from the pit and fill the pad.

Depending on the design of the fence, the depth of driving the sheet pile into the soil below the base of the foundation, as well as the physical and mechanical properties of the base soils, its bearing capacity as a result of using the sheet pile can be increased up to 2 times, and the base settlements can be reduced by 2-3 times. The best design of the fence, which perceives the forces of expansion of the base soil, is a fence made of flat steel sheet pile, round in plan.
4. In what cases is the replacement of weak soils used?

5. What is the role of sheet piling in soil stabilization?

6. What is cementation, bitumization, silicification, soil tarring?

When creating a project for development, first of all, the type of soil is determined, since the type of foundation directly depends on this. So, columnar - the least expensive in financial plan(up to 18% of the budget of the entire construction), but not on every soil it may be applicable. Sandy soils and sandy loam are suitable for such a foundation, but loam, peat and clay areas, as well as soils subject to horizontal displacements, require additional strengthening.

How to determine the type of soil yourself

To independently determine the type of soil, you should do some manipulations:

1. Take some earth and moisten it with water. Make a ring out of the mixture. If there is a lot of sand in the soil, it will not work. The sandy loam will be divided into small fractions. In the presence of clay, the ring will remain intact.
2. Pour soil from the site into a glass of water (1/3 per 250 ml) and shake. The cloudier the suspension, the more clay is contained in the soil.
3. To detect the presence of moisture, you need to take a part of the earth and put it on a thin sheet of paper. Let it lie down for 7-10 minutes, then shake off the earth and assess the degree of its wetting. The larger the wet spot, the more water-saturated the soil.
4. You can estimate the degree of groundwater depth by measuring the water level in nearby wells or boreholes. As well as the height of their placement relative to the building site.

The columnar foundation is suitable for light buildings ( frame houses, outbuildings, dachas, baths) without basements and cellars. It can be laid on all types of soil, as long as the water table is not too high. Depending on the type of soil, it can be:

• buried. Such a foundation is lowered up to 1 m below the soil freezing line. This is a suitable option for wet heaving soils (swampy, with a high groundwater horizon, soils on clay);
• shallow (or shallow). It is laid to a depth of up to 70 cm from the level of freezing. It is applied on sandy and rocky soils;
• not buried. Depth is not more than 50 cm. The foundation is installed on strong soils with a flat surface.

Also, columnar foundations are supported-columnar, columnar from pipes or columnar-tape.

Foundation laying on non-rocky and heaving soils

Non-rocky soils are areas of land formed for the most part from the remains of destroyed rocks (gravel, crushed stone, sand), which are coarse-grained material. The more particles such soil has, the less impact it will have on the strength of the foundation. These are the safest soils for any type of buildings.

The columnar foundation on such soils is laid shallow (I use shallow or shallow masonry). In some cases, 20-30 cm is enough.

Heaving soils include sandy loam, dusty sands, clays with high humidity and loams. The main characteristic is the increase in soil volumes when the water that is in its composition freezes. For such soils, the most successful foundation is a columnar structure. It minimizes the action of tangential forces, and the base is not destroyed when the soil freezes.

If unstable soil has a very high percentage of moisture, when laying the foundation, its upper ball is replaced with a non-porous one (upper 2/3 layers). For heated houses - from the outside, for unheated houses - from the outside and inside.

With very heaving soils or a weighted structure (made of brickwork), it is recommended to use a dressing (ryndbeam). It can be located on the surface of the soil or have a slight depth. This will help to avoid the influence of heaving of the soil or its movements as much as possible.

Laying the foundation on clay

Clay soils (with a clay content of about 10-30%) are very plastic, subject to erosion, do not hold their shape and can move. The stability of houses on them depends on the correct laying of the foundation.

Ways to strengthen the soil:

• mechanical ramming with the help of technical equipment (skating rink);
• electroosmosis. Rod terminals are introduced into the soil ball under voltage up to 5 A \ m 2. After exposure to current, the required area becomes denser, dry, which minimizes swelling;
• electrochemical effect. In addition to the current, special mixtures are added to the soils (for example, calcium chloride);
• partial replacement of the soil. To a depth of up to 1 m, the top layer of soil is removed and a stronger one is filled up, which is compacted in layers.

In the presence of slopes, they are reinforced with concrete stops or panels, at a slope of 50-60 relative to the slope.

bookmark technology

For heaving soils, it is preferable to choose pillars with an extension at the bottom, in other cases, designs in the form of a parallelepiped or cylinder are suitable. There are several ways to bookmark column foundation.

First way. Holes are dug under the pillars, which exceed the dimensions of the pillars by 30–40 cm, then formwork and a frame of reinforcement are installed in them. Next, the concrete is poured. After it hardens, the formwork is removed, and the pillar is covered. The technology makes it possible to create monolithic iron poles of high strength and stability, but requires a large amount of work.

The second way. A special foundation drill is used - TISE-f, with its help it is possible to make wells up to 20 cm in diameter, with an expansion at the bottom up to 60 cm. This is a simpler method that allows you to lay the foundation yourself.

What to pay attention to? At the intersections of the walls (points of greatest loads), under the frame rack, poles are erected at a distance that is a multiple of the pitch of the beams of the lower trim (1.5 − 2.5 m). The cross section of concrete blocks or brick pillars must be at least 50x50 cm. The thickness of the walls with a ball of thermal insulation is up to 25 cm, the ceilings (except for the basement) are made of wood.

The pillars are mounted vertically, concrete blocks are placed on them. A fence is installed between the pillars - a light wall that insulates the underground and protects it from moisture. It should be the same around the entire perimeter of the building (as a rule, it is brick or concrete). The wall thickness is 12 cm, the level of penetration into the soil is 25 cm. If the soil is clay and very heaving, the pick-up is placed on a sand cushion 20 cm high and 30 cm wide.

With or without grillage

Grillage - the upper part that connects the pillars into one structure, it is made of reinforced concrete tape, which gives the building greater stability on moving soils, and also evenly distributes the weight of the house on all pillars.

Its presence is not always necessary, since the lower crown of a wooden frame performs this role. But for frame houses built on heaving soils or in areas with a slope, a grillage is needed. The main thing is that the grillage must be mounted so that it does not go deep into the soil and does not rest on it. Otherwise, in winter, it can break away from the pillars and the foundation is deformed.

The absence of a grillage is the most economical and easiest way to lay the foundation. It is used if the soils are not too heaving, and the buildings are light, small-sized and do not require tape support (wooden frame, frame house).

If the foundation is on clay under the pillars to the freezing depth, the soil is replaced with a mixture of coarse sand, crushed stone or gravel, watered and tamped.

The heavier the structure, the more powerful the pillars should be chosen and the step should be taken more often (1.5 m). It is irrational to do less, but the step cannot be exceeded over 3 m. The cross section of the pillars can be different, depending on the material (brick, monolith, wood). On clay, the best option is reinforced concrete.

Why reinforce a monolithic columnar foundation

Concrete pillars are strong in compression, but do not withstand tensile or bending loads well. To avoid such deformation, the foundation must be reinforced in areas where stretching can occur. For example, when heaving, the upper part of the pillars will push up, while the lower part will be held in a non-freezing soil layer, as a result, the pillars may crack. This is where vertical reinforcement comes in handy.

The rebar frame consists of vertical ribbed bars (class A-3) with a diameter of 1.2 cm. The ribbed bars are selected to provide better contact with the concrete. They are connected using thin smooth mounting fittings (diameter 0.6 cm), which in itself does not perceive the load, but only connects the rods into one structure.

When reinforcing pillars with a diameter of up to 20 cm, 2 rods are required. If the height of the column is about 2 m, the ribbed reinforcement is tied up with a mounting one every 80-100 cm, that is, in 3-4 places.

If there is a grillage, it is also reinforced. They make 2 belts (lower and upper), each of which includes at least 2 longitudinal rods. For such reinforcement, reinforcement with a diameter of 1.2 cm and a cross section is used. The reinforcing cage is completely immersed in concrete, the level above the grillage surface is 3-5 cm.

If we take into account all the engineering and technological features of laying a columnar foundation, know the type of soil, the level of groundwater and the nature of the future building, such a foundation will be durable and wear-resistant for decades.

Most houses are built in regions with a temperate climate, but this does not mean that there are no problems during the construction of buildings. Heaving soils are one of them. The fact is that in conditions of frost heaving, the fundamental foundation of the building can quickly crack, as a result of which its integrity will suffer, and, accordingly, the strength of the foundation.

There are many methods for solving such problems. However, before starting to take any action, it is necessary to take into account the features of the heaving of the earth.

How does swelling happen

Since the density of water is greater than that of ice, in the process of freezing its volume changes upwards. Based on this, the moisture in the soil becomes the cause of the expansion of its mass. Hence, such a concept as the forces of frost heaving appeared, that is, the forces that affect the process of soil expansion. The soil itself in this case is called heaving.

Healthy! The soil expansion level is typically 0.01. This means that if the top layer of the earth freezes to a depth of 1 m, then the soil volume will increase by 1 cm or more.

Frost heaving itself occurs for several reasons:

• Due to the depth of the upper aquifer. If the water is located close to the surface, then even if the clay is replaced with gravelly sand, it will be ineffective.
• Based on the depth of freezing of the earth during the cold period in a particular region.
• Depending on the type of soil. Most water is found in clay and loam.

Based on the composition of the soil and climatic conditions, heaving and non-heaving soils are distinguished.

What is the difference between heaving and non-heaving bases

According to GOST 25100-2011, there are 5 groups of soils that differ in the level of heaving:

• Excessively heaving (the level of soil expansion is more than 12%);
• Strongly foamy - 12%;
• Medium heaving - about 8%;
• Slightly heaving - about 4%;
• Non-porous - less than 4%.

The last category is considered conditional, since there is practically no soil that does not contain water in nature. Only granite and coarse-grained rocks can be attributed to such bases, but in our conditions such soils are extremely rare.

Speaking about what heaving soil is and how to determine it, it is worth considering its composition and groundwater level.

How to independently determine the degree of heaving of the soil

In order to determine “at home” whether there are heaving soils on your site, the easiest way is to dig a pit (vertical working) about 2 m deep and wait a few days. If no water has formed at the bottom of the dug pit, then it is necessary to drill (a garden drill is used for this) a well for another 1.5 m. When water appears in the well, the distance from the groundwater level to the surface is measured using a bar.

To determine the type of soil, it is enough to make a visual inspection of the soil. On the basis of these data, it is possible to draw approximate conclusions about the degree of land expansion in the cold season.

If the soil is slightly heaving, then the GWL will be below the estimated freezing depth. This value directly depends on the type of soil:

• silty sands - 0.5 m;
• sandy loam - no more than 1.0 m;
• loam - 1.5 m;
• clay - 2 m.

If the soil is medium-heavy, then the groundwater level will be below the freezing depth by:

• 0.5 m if sandy loam prevails;
• 1.0 m - loam;
• 1.5 - clay.

If the soil is strongly heaving, then the GWL will be lower by:

• 0.3 m - if the soil mainly consists of sandy loam;
• 0.7 m - loam;
• 1.0 m - clay.

If clay and loam are located quite close to the estimated depth of soil freezing, this is not the best foundation for a shallow foundation. However, this does not mean that it is impossible to build on such soils.

How to solve the problem of heaving soils

There are many ways to reduce the level of soil heaving. Consider the most common.

Soil replacement

Replacing the heaving soil is considered the most labor-intensive and expensive process, since it assumes the complete removal of the soil located at the site of the future construction. After that, new earth or coarse-grained sand and gravel is filled in, and the foundation is laid on non-rocky soil.

Building weight

The lower the weight of the building, the more likely it is that the earth that swells during the cold season will exert pressure on it. To prevent this from happening, it is recommended to build more massive buildings. However, it also leads to serious financial costs.

Construction of a slab foundation

To add additional weight to the building and prevent ground pressure, you can install a slab foundation as the foundation for the house. A solid monolithic slab with a height of more than 20 cm, buried in the ground, will be subjected to frost heaving forces, however, in this case, it will simply rise evenly in winter and take its original position when the air temperature rises.

Technically, it is not difficult to build a slab foundation (difficulties can arise only at the stage), however, such a foundation will also be expensive.

Pile foundation installation

If you want to get by with little bloodshed, then the cheapest way is to install a pile foundation. However, it should be borne in mind that such structures are only suitable for light-weight houses (frame, sip-panel structures, and so on).

As a fundamental basis, fit:

• screw piles that are screwed into the soil just below the freezing level;
• reinforced structures (in this case, it is necessary to prepare wells and install rods wrapped in roofing material and a metal frame in them).

After installing the piles, the elements are connected using load-distributing slabs or beams (grillage), which are laid around the perimeter of the future building and insulated with polystyrene foam or expanded polystyrene.

Some builders erect brick columnar structures up to 60 cm high on heaving soils and deepen them by about 15 cm, but such bases are only suitable for gazebos, summer kitchens and other structures not intended for living.

Permanent home heating

If we compare the temperature of the soil located under a heated and unheated house, then in the first case it will be almost 20% higher. Accordingly, if people live in the building year-round and the building is heated, then the heaving force will be minimized.

Soil drainage

To prevent soil expansion, the water content of the soil can be reduced. To do this, it is necessary to build a drainage well, which will be located at some distance from the building. To build such a system, you need:

• Dig a trench around the house.
• Lay pipes in it with small holes on the sides. In order for water to be drained from the house by gravity, it is necessary to lay pipes at a slight slope towards the drainage well. Accordingly, the closer the pipeline is located to the well, the deeper it is laid.
• Sprinkle pipes with gravel and cover with geotextile.

Ground insulation

To reduce the heaving of the soil, you can build a blind area. Typically, such a structure is made around the perimeter of the building in order to protect the foundation from rainwater. But, if you make more powerful thermal insulation of the blind area, it will be possible to reduce the level of land expansion in the winter.

To make an insulated blind area, you must adhere to the following recommendations:

• The width of the blind area should be 1-1.5 m more than the width of the soil freezing.
• As the basis for the blind area, it is recommended to use sand, which is carefully rammed and spilled with water.
• Expanded polystyrene or any other insulation is laid on the sand with a layer of about 10 cm.
• Waterproofing (roofing material) is laid on top.
• Crushed stone is laid on the waterproofing layer and everything is poured with concrete.
• Before concreting, it is recommended to reinforce with a steel mesh with a diameter of 4 mm and a mesh size of 15 x 15 mm.

In custody

Knowing which soils prevail on the site, you can calculate the level of their heaving, respectively, you can choose the best option for arranging the fundamental foundation or reduce the amount of moisture in the soil. Some builders additionally insulate the foundation, as this also reduces the level of moisture affecting the concrete base of the house.