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

The issue is especially typical for tired lands, cleansing the site for the foundation, and horticultural areas. The latter had the property of distributing "good" officials in those territories where it makes no sense to use agricultural enterprises due to the poverty of the soil. To understand all the features, you need to consider everything in order.

Replacement of fertile soil for a lawn

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

- herbicides, which causes 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 with roots. To turn the removed turf into, you need to leave it for three years in compost pit. The following steps: adding a new clean fertile soil, leveling, feeding.

Removal of plant soil under the foundation

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

- save on the purchase and delivery of soil;

- use the natural fertile layer;

– to prevent the process of decay organic matter at the base and on the sides.

The boundaries and thickness of the layer to be removed are determined by the project, or rather by preliminary analysis.

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

2. On a sandy base, plant soil lies to a depth of 5–10 cm.

3. On grassy areas - 12 cm.

4. On arable fields - 20 cm.

5. In forests up to 25 cm.

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

Replacement of tired land in agricultural areas

The earth has a tendency to deplete. Therefore, it is necessary to carry out technical or biological reclamation. On the large areas earth 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 power. 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 Soviet Union plots for dachas and vegetable gardens were massively distributed. Most of them are in unsuitable swampy areas or with a minimal amount of fertile layer. In these cases, it is necessary to clear the territory and purchase new fertile layers. If the fertile soil was removed during construction and did not bother to return it, then again you will have to import a new one.

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 it is revealed that there is a risk of a building collapsing during its construction at a given specific location, 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 also includes coarse-grained soils consisting of large ones. In the event that the stones are mixed with clay soil, the soil is considered to be weakly heaving, if with sandy soil - non-heaving.
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 particle density, one can also determine such an indicator as specific gravity 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 load 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 soil does 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 clay soils are also most often recognized as weak. a large percentage soil organic matter content.

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 pile foundation with depth 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, it should be done accurate calculations its dimensions in the horizontal and vertical planes. 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 its destruction. 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, this operation can also be done 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). Sometimes heat treatment soil is produced 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. For reinforcement, a solution is injected into the pipes liquid glass and Injection can be done to a depth of more than 20 m. The radius of distribution of liquid glass 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.

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

When it makes sense to raise the site

One of the worst geomorphological conditions is considered to be the rise of the GWL 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, pile-grillage. Shallow foundations do not work in such conditions, and full-fledged deepening requires support on a layer of soil 2.5-3 meters from the surface, above the foundation remains unstable and may be subject to precipitation due to high soil moisture.

This is not to say that geodetic site planning 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 soil eliminated problems with waterproofing, insulation and stabilization of the foundation and the resulting costs. This is usually true: planning allows you to solve the problem of poor geomorphology cheaper, and most importantly, faster, ultimately significantly reducing the shrinkage time of the foundation. This solution is especially shown in 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 the involvement of special equipment for pouring bored piles costs less blood, and yet among the foundations this one is one of the most difficult. In the area, there may also simply not be a sufficiently dense layer of soil to support a building of the required mass on it. Raising the site in such an environment will not give anything at all; in any case, you will have to make the foundation floating.

Is drainage necessary?

Drainage systems are shown for artificially leveled areas with significant elevation changes, where, as we know, the problem cannot be solved by conventional raising. However, erosion and washout phenomena can be expressed even on small slopes, so 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 (lower) receives water from a transverse section arranged along the upper boundary of the site. The bottom of the trenches is covered with rubble, 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 construction battle.

If the direction of the slope and the trenches diverge by more than 15º, you should be prepared for increased water flow. The bottom of the upper trench should be paved with bricks, even better - with trays. In such areas, it makes sense to level the ground locally exclusively for buildings. In this case, the plot for the garden is simply protected from erosion by a trench across the slope, along the upper slope of which a willow tree or several birches are planted. It is recommended to fill the bottom of the trench and its upper slope with crushed stone to prevent silting.

There is no point in lining the entire layer of the embankment with black soil, just as there is no point in throwing clay over the fertile layer. Upper layer you have to remove it to clean clay, and then return it to its place. If only part of the site is to be leveled, the excess soil is simply discarded onto the adjacent territory. If the site is planned completely, the work is carried out in two stages.

Excavation is carried out in order to eliminate the plastic washable layer between two dense layers, because the probability of the embankment sliding under its own weight is so high. 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 the tight formation is exposed, a series of geodetic measurements is carried out. Knowing the configuration of the upper aquiclude, it is possible to determine the required volume of soil and start its delivery. At the same time, the volumes of crushed stone for backfilling are calculated and the drainage system is planned.

How to fill up the hill

To create an embankment, hard-plastic clay in a swollen state, loam or sandy loam is used. The ability of the backfill to pass water is determined by geomorphology: if, with an abundance of water, it is impossible to fill a tightly compacted terrace or the backfill is carried out over a porous layer, the embankment should pass water to a limited extent. Optimally, 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 above the adjacent territories by more than 30-40 cm, it is necessary to carry out retaining filling with road gravel of a fraction of 70-90 cm. It is also used in surface drainage. Crushed stone is dumped immediately after excavation of the soil under the formed board. The width of the filling 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 with crushed stone, you can immediately form the bottom of the drainage trenches.

Supports more than a meter high are covered with geotextile, which is immediately pressed down with a small layer of clay. After that, imported soil is started up and distributed over the site. The easiest laying route is starting from the shaft laid from the vehicle entry point 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 necessary, raise more should wait for heavy rain or give the embankment time to overwinter. But with the use of tamping and excavating equipment, more impressive dumps can be quickly poured.

Is tamping or rolling necessary?

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

Rammer is used when a high speed of work is required, for example, when optimal time to fulfill the embankment is limited seasonally or by the weather. With alternate tamping, layers of pure clay can be poured 0.6-1.0 one after the other without prior wetting. We note once again that only swollen clay is suitable for tamping, dry clay will not take on water-resistant 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 caterpillar excavator is indispensable if the site is raised to a height of more than a meter, in other cases it is more reasonable to resort to manual transportation and leveling, and entrust the compaction to precipitation.

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

If you hurry and bring in black soil before the final compaction of the clay, erosion will quickly have its detrimental 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 only partially.

Chernozem or a fertile layer is better to be poured dry and not rolled, preferably manual distribution and leveling of the soil. Machinery must deliver black soil to reverse order than the one in which clay was poured. The area is filled from the edges to the center. 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 bulk layer may not be uniform. Usually, before unloading the chernozem, formwork is mounted, the foundation is cast and waterproofed, then sprinkled with rubble. Mounds of surface backwater are also arranged before the formation of a fertile layer.

Protection against erosion, strengthening 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 plants with a developed root system along the upper and lower boundaries of the planned area, and actively absorbing water in the upper part.

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 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 level of the soil, dumping and protective landscaping will be quite enough.

Foundations - the basis engineering structures providing their strength, stability and durability. It is important that the soils at the base have the necessary strength and low compressibility. To determine the soil characteristics and conditions for laying the foundation, a complex of engineering-geological and hydrological surveys is carried out without fail.

Of particular importance are:

type of base soils;
location and thickness of layers;
the depth of seasonal freezing;
groundwater level.

One of effective methods foundation device with the required characteristics is the replacement of unreliable soils.

Heaving or swelling rocks

Heaving bases are characterized by the ability to increase in volume during freezing, which leads to the rise of the soil surface and the occurrence of frost heaving. Subsequent thawing leads to the opposite effect - soil precipitation. The result is the appearance and development of cracks in the foundation structure and the walls of the building, the slope of the structure and even its destruction.

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

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

Soils are considered non-rocky when their degree of heaving is ≤ 0.01, that is, when freezing to a depth of 100 cm, an increase in their size occurs ≤ 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 upper two thirds of the layers.

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

If the house is heated in winter, then it is enough, at the same time as replacing the foundation soils, to cover the sinuses with draining 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 install a pillow made of sand if, within its height:

there is a variable level ground water. The pillow works as a drainage, turning into the form of ordinary heaving soil;
there are ground pressure waters, and the foundation sole is made at a depth above seasonal freezing. Under the influence of water pressure, heaving of sand can occur.

Peat types of soil

Replacing peat is economical under two conditions:

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

Otherwise, you should think about the need to build in the area or move on to the construction of a pile or slab foundation.

rock formations

Durable rock has excellent bearing capacity, resistance to frost heaving and resistance to temporary flooding. Replacing the rocky soil under the foundation is necessary only if there are upper fractured layers. After their disassembly, concrete is laid on top.

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 clay 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 washing away, 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 ground 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. best design the fence, which perceives the forces of expansion of the soil of the base, 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?