What is the soil replacement procedure or. Appendix ii proposals for structural adaptations of columnar and strip foundations to the conditions of construction on heaving soils

The question is especially typical for tired lands, clearing a site for a foundation, and horticultural areas. The latter tended to distribute "good" officials in those territories where it makes no sense to use agricultural enterprises and because of the poverty of the soil. To understand all the features, you need to consider everything in order.

Replacing fertile soil for a lawn

It is not easy to create a beautiful and even lawn, you need to bring the foundation in perfect condition. First, the earth is cleared of all flowers, roots, weeds, flower beds. Vegetation is removed in two ways:

- herbicides, which cause severe damage to the earth;

- bayonet shovel or excavator.

Both methods have their pros and cons. The optimal, but hard way, with a shovel. The thinnest layer should be removed, while capturing everything growing from the roots. To turn the removed sod into, you need to leave it in the compost pit for three years. The next steps: adding a new clean fertile soil, leveling, recharge.

Removal of plant soil under the foundation

Before starting any construction, it is necessary to remove the sod for the following reasons:

- save on the purchase and delivery of soil;

- use the natural fertile layer;

- to prevent the process of decay of organic matter in the foundation and on the sides.

The boundaries and thickness of the removed layer are determined by the project, more precisely by preliminary analysis.

1. The minimum depth is 10 cm, the maximum 50 cm.

2. On a sandy basis, the vegetative soil lies at a depth of 5–10 cm.

3. In soddy areas - 12 cm.

4. On arable fields - 20 cm.

5. In forests up to 25 cm.

The process is carried out with heavy construction equipment: bulldozer or excavator, loader, dump truck or tractor for transportation. Bad soil often has a yellowish color, fertile soil can be gray-brown-black. The cut layers are placed in heaps of 1.5–3 meters.

Replacing tired land in agricultural areas

The earth tends to deplete. Therefore, it is necessary to carry out technical or biological reclamation. On large areas, land up to 10 cm is not removed. Special rules are established by GOST 17.4.3.02-85 "Requirements for the protection of the fertile soil layer during earthworks."

In the yard or in the garden, the owners try to constantly fertilize with organic matter, peat and minerals. If this process has not been carried out, then the soil has no fertile strength. In order not to raise the site, you will have to remove a part and refresh it with new high-quality soil. In built-up spaces, it is impossible to use heavy equipment, manual labor is used.

After the collapse of the Soviet Union, plots for summer cottages and vegetable gardens were distributed en masse. Most in unsuitable swampy areas or with a minimum amount of fertile layer. In these cases, it is necessary to clear the territory and buy new fertile layers. If the fertile soil was removed during construction and did not bother to return it, then you will again have to import a new one.

Before starting the construction of the foundation of the house, an operation such 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 a building during its construction at a given specific location is identified, measures can be taken to strengthen or replace soils.

Classification

All soils are subdivided into several basic 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 bases is practically not deepened. Coarse-grained soils, consisting of large ones, are also classified as rocky.
Bulk. Soils with a disturbed natural layering structure. Simply put, artificially poured. Buildings on such a foundation can be built, but first you should perform a procedure such as soil compaction.
Clay. They consist of very small particles (no more than 0.01 mm), absorb water very well and are considered heaving. Houses on such soils sag much more than on rocky and sandy ones. All are classified into loam, sandy loam and clay. These include, among other things, loess.
Sandy. Consist of large sand particles (up to 5 mm). Such soils are compressed very weakly, but quickly. Therefore, the houses built on them are upset at a shallow depth. Sandy soils are classified by particle size. The best substrates are gravelly sands (particles from 0.25 to 5 mm).
Quicksands. Silty soils saturated with water. Most often found in wetlands. They are considered unsuitable for the construction of buildings.

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

Basic physical characteristics

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

Humidity.
Porosity.
Plastic.
Density.
Particle density.
Deformation modulus.
Shear resistance.
Particle friction angle.

Knowing the density of particles, it is possible to determine such an indicator as the specific gravity of the soil. It is calculated primarily to determine the mineralogical composition of the earth. The fact is that the more organic particles there are 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 tests, it is revealed that the mechanical and physical characteristics of the soil do not allow constructing structures and buildings on it without the risk of their collapse or violation of the integrity of the structure, the soil is considered weak. For the most part, these include quicksands and bulk soil. Loose sandy, peaty and clayey soils with a high percentage of organic residues are also recognized as weak.

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

Substitution of soils: principle

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

Sometimes it happens that dense soil is located very deep. In this case, the pillow can 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 lower the load on soft soil due to pressure distribution will be. Such pillows can be used for the construction of foundations of all types.

When using such an artificial base, there is a risk of crushing the pillow under 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 piles are 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

Substitution of soils for the foundation should be carried out only with the preliminary conduct of appropriate studies and calculations. Of course, you won't be able to do this kind of work yourself. Therefore, most likely, you will have to invite specialists. However, when erecting not too expensive buildings, for example, household buildings, this operation can be performed "by eye". Although we would not recommend taking risks, for general development, let's take a closer look at this procedure. So, the stages of work in this case are as follows:

Excavation is carried out to a solid base.
Sand of medium size is poured into the trench to the level of the sole of the future foundation. Backfilling is carried out in layers of small thickness with each tamping. The sand must be moistened with water before compaction. Tamping should be done as carefully as possible. The sand itself should not contain any inclusions, especially large ones. Sometimes soil-concrete mixtures and slags are used instead.

In the event that an artificial foundation is used for 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.

Drainage system works

A moat is being dug a meter away from the building. In this case, the excavation is carried out below the depth of the foundation. Width - not less than 30 cm. The slope of the trench bottom should be at least 1 cm per 1 m of length.
The bottom of the trench is tamped and covered with a five-centimeter layer of sand.
Geotextiles are spread on the sand with the edges fixed on the ditch stacks.
A ten-centimeter layer of gravel is poured.
Lay a perforated drainage pipe.
Fill it with gravel with a layer of 10 cm.
Cover the "cake" with the ends of the geotextile and sew them together.
They fill everything up with soil, leaving viewing wells in the corners of the building.
At the end of the pipe, a receiver well is arranged. 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 installed there.
Take 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 soil reinforcement is done

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

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

Thermal method

The choice of the 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 amplification only if they belong to a non-rocky group.

Thermal amplification is one of the most common methods of amplification. It is used for loess soils and allows for 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 the heat treatment of the soil is carried out in a different way. Wells are dug into the ground. Then, flammable products are burned in them under pressure. The wells are previously hermetically closed. After such treatment, the fired 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 hammered into it, through which cement-clay mortars or cement suspensions are pumped. Sometimes this method is used to seal cracks and cavities in rocky soils.

Soil silicification

On quicksand, silty sandy and macroporous soils, the silicatization method is more often used. For reinforcement, a solution of liquid glass is pumped into the pipes and the injection can be done to a depth of more than 20 m. The radius of spread of liquid glass often reaches one square meter. This is the most effective, but also the most expensive, method of amplification. The low 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 silicatization.

Comparison of the cost of soil replacement and strengthening

Of course, the amplification operation will cost less than complete soil replacement. 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. The cost of crushed stone is $ 10. for 1 m 3. Thus, replacing a weak soil will cost $ 7. for the notch plus $ 7 for moving gravel, plus $ 10 for the gravel itself. Total $ 24 Strengthening the soil costs $ 10-12, which is half the price.

A simple conclusion can be drawn from all this. In the event that the soil on the site is weak, you should choose another place for building a house. In the absence of such an opportunity, it is necessary to consider the option of erecting a building on piles. Reinforcement and replacement of soil are performed 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 standards, are strengthened by methods suitable for their specific composition.

After acquiring building land, it often turns out that the relief and geology of the area are not quite suitable for long-term use and agricultural activities. We will talk about raising and leveling the ground, from markings to protective landscaping.

When does it make sense to lift a site

One of the worst geomorphological conditions is considered to be the rise of the groundwater level above the depth of soil freezing. In such areas, heaving is especially pronounced, which is why there is a need for complex types of foundations, for example, in pile-grillage. Shallow foundations do not work in such conditions, and full-fledged deepening requires support on a soil layer 2.5-3 meters from the surface, above the foundation remains unstable and can be subject to precipitation due to high soil moisture.

This is not to say that site surveying is a cheap method to get rid of soil problems. However, the usefulness of such a solution can be expressed economically in favor of the developer, if the raising of the ground eliminated the problems with waterproofing, insulation and stabilization of the foundation and the resulting costs. This is usually the case: planning allows for a cheaper, and most importantly, faster solution to the problem of poor geomorphology, significantly reducing the resulting shrinkage time of the base. This solution is especially shown during the construction of a log house or the installation of prefabricated foundations.

But raising the level on the site does not always solve the problem. With a large slope (more than 5-7%), terracing should be performed, and not raising the soil, and this is a completely different technology. On such slopes, even attracting special equipment for pouring bored piles costs less blood, and this is one of the most difficult foundations among the foundations. In the terrain, there may also simply not be a sufficiently dense layer of soil to support the building of the required mass on it. Raising the site in such an environment will do nothing at all; in any case, you will have to make the foundation floating.

Do you need drainage

Drainage systems are shown for artificially leveled areas with significant elevation differences, where, as we know, the problem cannot be solved by ordinary uplift. However, the phenomena of erosion and washout can be expressed even on small slopes, therefore, minimal backfilling and surface drainage will have to be done.

On both boundaries of the site, located along the slope, it is necessary to dig rain trenches, one of which (the lower one) receives water from the cross-section arranged along the upper border of the site. The bottom of the trenches is covered with rubble, and shrubs are planted along the slopes. Periodically, the trenches will have to be cleaned, usually the owner of the site has the one that is higher in level. In depth, the trenches should reach the upper aquiclude and cut it a little - about 20-30 cm. In order to less disturb the terrain, the depth of the trenches can be adjusted with hygroscopic material - the same rubble or building battle.

If the direction of the slope and the trenches diverge by more than 15º, be prepared for increased water inflow. The bottom of the upper trench should be paved with bricks, even better with trays. In such areas, it makes sense to level the soil locally exclusively for buildings. In this case, the plot for the garden is simply protected from erosion by a trench across the slope, on the upper slope of which willow trees or several birches are planted. It is recommended to fill the bottom of the trench and its upper slope with rubble in order to prevent siltation.

There is no point in covering the entire layer of the embankment with chernozem, just as there is no point in throwing clay over the fertile layer. The top layer will have to be removed to clean clay, and then put back in place. If only part of the site is to be leveled, the excess soil is simply thrown into the adjacent area. If the site is planned completely, the work is carried out in two stages.

Excavation is carried out in order to eliminate the plastic washed-out layer between two dense layers, because the likelihood of the embankment sliding under its own weight is so great. The only exception is when the site is located simply in a lowland without a slope 20-30 cm below the adjacent territory. Here it is reasonable to limit ourselves to increasing the thickness of the fertile layer.

After exposure of the dense layer, a series of geodetic measurements is carried out. Knowing the configuration of the upper confining layer, you can determine the required volume of soil and start bringing it in. At the same time, the volumes of crushed stone for filling are calculated and the arrangement of the drainage system is planned.

How to fill up the hill

To create the embankment, a swollen tough-plastic clay, loam or sandy loam is used. The ability of the bedding to pass water is determined by geomorphology: if, with an abundance of water, it is impossible to fill up a tightly rammed terrace, or the filling is carried out over a porous layer, the embankment should be limited to letting water through. It is optimal if the bearing capacity of the clay corresponds to the underlying layer, so do not be too lazy to take samples.

In places where the site plan rises more than 30-40 cm above the adjacent territories, it is necessary to carry out retaining dumping with road crushed stone of fraction 70-90 cm. It is also used in surface drainage. Crushed stone is dumped immediately after excavation under the formed side. The width of the dump in the lower part must be at least half the height of the crushed stone shaft. On the sides of the site along the slope, you can immediately form the bottom of the drainage trenches with rubble.

The supports with a height of more than a meter are covered with geotextiles, which are immediately pressed down with a small layer of clay. After that, the imported soil is started and distributed over the site. The easiest route for laying is starting from the shaft, laid from the place of entry of the equipment to the opposite point, and then to the dump in both directions.

It is not recommended to pour more than 0.7-0.8 meters of clay embankment at a time. If it is necessary to raise more, wait for heavy rain or give the embankment time for wintering. But with the use of ramming and excavating equipment, you can quickly fill in even more impressive dumps.

Whether tamping or rolling is necessary

It is optimal if the imported clay is sequentially unloaded completely at the upper level of the dump, and then collides with the bucket into the unfilled areas. This is how a high-quality compaction occurs, in which the final shrinkage takes place in one or two wetting.

The rammer is used when there is a need for a high speed of work, for example, when the optimal time for filling an embankment is limited by season or weather. With alternate tamping, layers of clean clay can be poured in 0.6-1.0 layers one after the other without preliminary wetting. Note again that only swollen clay is suitable for compaction, dry clay will not take on waterproof properties until swelling and subsequent compaction.

Layers of 30-40 cm can be compacted by rolling, but wheeled vehicles are poorly suited for these purposes. A crawler excavator is irreplaceable if the site is raised to a height of more than a meter, in other cases it is wiser to resort to manual delivery and leveling, and entrust the compaction to precipitation.

Note that it is often not necessary to manually tilt the site. Under the influence of the movement of surface water, the fresh embankment will eventually assume a natural slope. With an abundant flow of water, sometimes it is even necessary to slightly raise the embankment in the lower part of the slope in advance.

If you hurry up and bring in chernozem before the final compaction of the clay, erosion will quickly have its destructive effect and the site will greatly lose its fertility. Unfortunately, only plowing the soil in spring and autumn saves from such a phenomenon, and even then in part.

It is better to fill chernozem or fertile layer dry and not roll it, preferably manual distribution and leveling of the soil. Technique must deliver chernozem in the reverse order than the one in which the clay was poured. The area is filled from the edges to the central one. At the end of the backfill, it is also filled.

This is the most time-consuming stage of raising the site: in addition to the fact that it is necessary to level the soil not only in one plane, but also with uniform compaction, the upper fill layer may not be uniform. Usually, before unloading the black soil, formwork is mounted, the foundation is cast and waterproofed, then sprinkled with crushed stone. The embankments of the surface backwater are also arranged before the formation of the fertile layer.

Protection against erosion, strengthening of the embankment on the slope

In addition to backfill and drainage, there are other ways to prevent soil erosion. Of these, the most famous and quite effective is planting along the upper and lower boundaries of the planned site of plants with a developed root system, and in the upper part - actively absorbing water.

Shrubs are planted along the slopes of drainage trenches to strengthen their walls. Plants from blackberries and rose hips to reeds are suitable here: they do not create much shade and at the same time they pump water out of the soil well. From the upper tier, in addition to birch and willow, you can use undersized elderberry and sea buckthorn. On steep slopes, it is recommended to strengthen the embankment with geogrids and an underground drainage network.

But with a small difference in the ground level, filling and protective landscaping will be quite enough.

Foundations are the basis of engineering structures, ensuring their strength, stability and durability. It is important that the soils at the base have the required strength and low compressibility. To determine the soil characteristics and the conditions for laying the foundation, a complex of engineering-geological and hydrological surveys is mandatory.

Of particular importance are:

type of foundation soil;
location and thickness of layers;
the depth of seasonal freezing;
groundwater level.

One of the effective methods for constructing a foundation with the required characteristics is the replacement of unreliable soils.

Heapy or swelling rocks

Heavy foundations are characterized by the property of increasing in volume during freezing, which leads to a rise in the soil surface and the occurrence of frost heaving. Subsequent thawing leads to the opposite effect - soil sedimentation. The result is the appearance and development of cracks in the structure of the foundation and walls of the building, the inclination of the structure and even its destruction.

Heavy types of rocks - fine and silty sands, loams, clays (with high humidity at the time of freezing).

Erection of foundations on such soils is dangerous, therefore, the heaving soil under the foundation is replaced with non-heaving (coarse or medium-grained sand, gravel, crushed stone).

Soils are considered non-heaving if their degree of heaving is ≤ 0.01, that is, when they freeze to a depth of 100 cm, their size increases ≤ 1 cm.

It is not always advisable to replace the soil at the entire freezing depth, because it is known from practice that freezing in the lower third of the layer is insignificant and practically does not lead to heaving. Therefore, it is sufficient to replace only the top two thirds of the layers.

But, the correct conclusion in each specific case can only be given by a qualified specialist.

If the house is heated in winter, then it is enough, simultaneously with replacing the base soils, to fill up the sinuses with drainage soil. This will reliably protect the foundation structures from lateral soil influences. If heating is not planned, then backfilling is carried out outside and inside.

It is unacceptable to create a sand cushion if within its height:

there is a variable groundwater level. The pillow works like a drain, turning into a kind of ordinary heaving soil;
there is groundwater confined, and the foundation base is made at a depth higher than seasonal freezing. Sand swelling can occur under the influence of water pressure.

Peat types of soils

Peat replacement is economical if two conditions are met:

its thickness does not exceed 2 m;
there is a layer of sufficiently strong rocks under the peat.

Otherwise, it is worth considering the need for construction in the area or go to the construction of a pile or slab foundation.

Rocks

The solid rock has excellent bearing capacity, resistance to frost heaving and immunity to temporary flooding. Replacement of rocky soil under the foundation is necessary only in the presence of upper fractured layers. After disassembling them, concrete is laid on top.

In a number of cases, it is economically feasible to remove these soils and put a cushion of sand, gravel, stone in their place instead of deepening the foundation through a small thickness of weak (silty, peaty, bulk, etc.) soils or strengthening weak soils located under the foundation. , 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 soft soil; on the right - with a large thickness of a layer of soft soil; 1 - foundation; 2 - a pillow made of low-compressible material; 3 - a layer of solid soil; 4 - soft 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 more durable soil (on the left in Fig.5.3). If the soft soil extends to a considerable depth, the dimensions of the pillow are assigned from the condition of reducing the pressure under it to a value that does not exceed the design resistance of this soil. In this case, the thickness of the pillow and its lower width are taken based on the pressure distribution 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 pillow material.

It is advisable to use pillows for single and strip foundations with a base 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 design resistance under the base of the foundation of 0.20-0.25 MPa is used. In sandy and sandy loam soils, non-cohesive soils are used for making pillows. In loamy and clayey soils, in order to avoid the accumulation of water in the pit, the pillows are made of 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 soft soil, as well as to protect the base from undermining, sheet pile fences are used, which in some cases are left in the ground for the entire period of operation of the structure. Sheet piling can also be used when installing soil cushions to reduce the volume of work on removing soft soil from the pit and filling the cushion.

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 the use of sheet piling can be increased by up to 2 times, and the subsidence of the base is reduced by 2-3 times. The best design of the fence, which absorbs the forces of expansion of the soil of the base, is a round-shaped fence made of flat steel sheet piling.
4. In what cases is the replacement of weak soils used?

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

6. What is cementation, bitumization, silicatization, resinization of soils?