Replacement, replacement of weak soils under the foundation. How to make a foundation on heaving soils What is the procedure for replacing soil or
The question is especially typical for tired lands, clearing the area for a foundation, and horticultural areas. The latter tended to be distributed by “good” officials in those territories where there was no point in using agricultural enterprises due to poor soil. To understand all the features, you need to consider everything in order.
Replacing fertile soil for a lawn
Create a beautiful and smooth lawn It’s not easy, you need to bring the base into perfect condition. First, the earth is cleared of all flowers, roots, weeds, and flower beds. Vegetation is removed in two ways:
– herbicides, which cause severe harm to the land;
– bayonet shovel or an excavator.
Both methods have their pros and cons. The optimal, but difficult method is with a shovel. You should remove a minimally thin layer, while capturing everything growing from the roots. To turn the removed turf into, you need to leave it for three years in compost pit. The next steps: adding new clean fertile soil, leveling, replenishment.
Removing plant soil under the foundation
Before any construction begins, 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 rotting organic matter in the foundation and on the sides.
The boundaries and thickness of the layer being removed are determined by the project, or rather by preliminary analysis.
1. The minimum depth is 10 cm, the maximum is 50 cm.
2. Sand based vegetable soil lies to a depth of 5–10 cm.
3. On turfed areas - 12 cm.
4. On arable fields - 20 cm.
5. In forests up to 25 cm.
The process is difficult 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. The cut layers are placed in piles of 1.5–3 meters.
Replacement of tired soil in agricultural areas
The earth tends to become depleted. Therefore, it is necessary to carry out technical or biological reclamation. On large areas soil up to 10 cm is not removed. Special rules are established by GOST 17.4.3.02-85 “Requirements for the protection of fertile soil during excavation work.”
In the yard or garden, 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 area, you will have to remove part of it and refresh it with new high-quality soil. In built-up areas it is impossible to use heavy equipment; manual labor is used.
After the breakup Soviet Union Plots for dachas and vegetable gardens were distributed en masse. Most of in unsuitable swampy areas or with minimal topsoil. In these cases, it is necessary to clear the territory and purchase new fertile layers. If the fertile soil was removed during construction and no effort was made to return it, then new soil will have to be imported again.
Before planning the location of the foundation and determining its type, first of all, it is necessary to make geological soil survey. After all, the foundations on different soils will be completely different from each other. What will be good on sandy soil will be completely unacceptable on heaving or clayey soil. And if you build a house without taking into account all these nuances, then over time the building may “settle” or warp, breaking the walls and roof.
You can entrust geotechnical analysis to specialists, or you can save money by doing it yourself. You can do this in two ways: by determining the percentage of sand, clay and silt or by visual-tactile assessment. Let's consider the second, simplest, method.
Visual-tactile method for determining soils
Mechanics of soils and foundations
When assessing soils they have The following physical characteristics are of no small importance:
- the size of soil particles and their adhesion to each other;
- the presence of various inclusions;
- an indicator of friction between parts of the soil;
- ability to absorb and retain water;
- indicator of erosion and solubility;
- the property of shrinking and loosening.
The soils are loose and rocky. Structures are mainly erected on loose soils, which, in turn, are sandy and clay. Other types of loose soils are various combinations of clay and sand composition:
- sandy loam (5-10% inclusion of clay) - light, heavy, dusty;
- loamy (10-30% clay) - light, dusty and heavy.
Depending on the main physical properties sand and clay can be determined soil mechanics, on which it is proposed to build a dwelling. For example, when clay gets wet, it increases in volume, and when it dries, it decreases. Sand, when it dries, does not change its volume. Clay particles bond well with each other, sand particles do not. Sand practically does not compress under the influence of strong loads; clay, on the contrary, has excellent compressibility. Based on this, we can conclude that with the ability clay soils shrink strongly, swell when frozen and are easily washed away, it is best to lay the foundation to the entire depth of probable soil freezing. On sandy soils, you can deepen the foundation by only 50-70 cm.
Foundations can be piled and erected in specially dug pits. The latter are divided into strip foundations, solid foundations in the form of slabs for walls, foundations for columns along with foundation beams, and solid masses for the entire building. Pile foundations differ only in the way they are immersed in the ground: driven, pressed and screwed.
Foundation on heaving soils
Heaving soils are one of the most problematic when constructing a foundation. Such soils, absorbing water and then freezing, increase in volume, which leads to deformation processes. Therefore, before starting work, it is recommended carry out careful design:
- Determine all possible loads that will fall on each section.
- Assess the soil properties and relief conditions of the built-up area.
- Select the approximate laying depth and the appropriate type of foundation.
- Calculate the dimensions of the foundation base, taking into account the pressure force of the structure and the deformability of soils.
- The possibility of foundation subsidence is assessed.
- Soil stability is checked.
How to make a foundation? Traditional way foundation construction on heaving soils involves the construction of a shallow version of the foundation with the formation of clay screens that serve as protection against water. As a rule, in this case, a strip foundation is used in the form of a rigid frame frame along the entire perimeter of the structure. At the depth of soil freezing, dig a trench of the required width and depth, make waterproofing and fill concrete mixture. This is perhaps the most economical way strengthening the house, but he does not exclude its partial deformations.
More reliable in this case is tiled or monolithic foundation . When the soil deforms, the slab seems to “float” along with the house, maintaining all the rigidity of the structure and preventing walls or ceilings from collapsing. The slab can lie directly on the ground or be deeply embedded in it. The dug pit is carefully compacted, covered with crushed stone, and then with sand, on which the waterproofing is laid. The waterproofing is covered with a small layer of concrete, reinforcement is installed, which is filled with another layer of concrete of the required height.
Another durable and less expensive method than a slab foundation is to build a foundation on screw piles, which are screwed to a depth below the soil freezing level. In addition, it is ideal for uneven surface terrain, such as a slope. And because of small area contact of piles with the ground, the foundation retains its immobility even with significant deformation of the soil.
Foundations on permafrost soils
The only and correct solution on permafrost soils is the construction foundation made of piles or pillars. Moreover, the pillars should be about one meter in diameter, and the piles should be approximately 40x40 cm. The lower part of such a foundation rests on permafrost soils, which will not allow it to deform. Such a foundation can be erected at any time of the year, which is important in permafrost conditions.
Foundation on sandy soil
Because the sandy soils practically do not retain water, which means that when freezing they remain in the same volume, therefore the foundation can be laid of absolutely any type: pile, columnar, strip or on a slab. And its careful insulation along the entire base and competent installation drainage system will solve the problem of close proximity to groundwater.
If you plan to build a house without a basement, then a shallow strip foundation is perfect. In addition, it is less expensive compared to other types. It is especially ideal for a wooden home. When planning a basement, it is recommended to make the foundation strip deeper.
Foundation on bulk soil
Bulk soil is heterogeneous in composition and has its own characteristics due to unpredictable further compaction. The most practical and reliable way to strengthen the foundation of a house is slab foundation installation, which will increase the support area and will not allow the structure to deform. Of course, this type of foundation requires dense reinforcement and requires a significant investment, but it is 100% worth it. A strip base is permissible only after a thorough examination of the embankment. Pile foundation is also acceptable, but only with a highly compacted embankment and a known depth of the embankment.
Foundations on subsidence soils
When designing foundations for planting soils Before starting work, it is necessary to evaluate the following components:
- quantity and properties of soil layers;
- soil subsidence under load;
- the distance at which groundwater flows;
- soil freezing depth;
- the dimensions of the foundation and the potential load on it at home.
Thus, after analyzing all this data, you can choose either a densely reinforced strip foundation, or a pile or tile foundation.
Foundations on clay soils
Clay soils are among the most difficult and the choice of foundation type for them will be directly depend on groundwater flow. If they go deep, it is possible to use a strip foundation with an expansion in the lower part and partial use of support piles.
However, the most durable option in case of significant amounts of water is to use a foundation on piles. If it is planned to build a house with several floors, then reinforced concrete slabs or beams that will hold the entire structure together. Piles are usually driven or screwed until they reach a layer of incompressible soil.
Foundation on rocky ground
Rocky soils are distinguished by the fact that they practically do not absorb moisture, do not freeze at all, and do not compress under load. Therefore, a particular difficulty lies in the formation of the foundation itself due to its special strength and resistance to destruction. In this case, it is possible to do without a foundation altogether, using slabs as a base that can serve as a floor. On clastic soil, you can make a foundation, deepening it by about half a meter.
Foundations on marshy, peaty soils
Swampy soil is complex in that it has a completely different structure in composition, density and water saturation, consisting of clay, peat and sand. Moreover, such soil is very unstable and fragile. Therefore it is very important to thorough drainage and water removal from the construction site.
The best options for these soils would be a pile foundation with a metal shell or a heavily reinforced slab foundation. It is also permissible to use a shallow strip base, but only for light buildings such as a bathhouse or wooden frame houses.
Strengthening and replacing soil under the foundation
To increase the strength of the soil under the foundation, widely use artificial soil fixation:
- cementing on special piles to compact sand;
- silicization or filling the soil under the base with a chemical solution;
- thermal firing with gases at high temperatures;
- transmission electric current through clayey wet soils in order to drain it;
- the electrochemical method combines the electric method with the simultaneous injection of chemicals into the soil;
- mechanical compaction of soil or production of soil cushions.
However, there are cases when strengthening obviously weak soil is very costly and economically unprofitable. Then replacing the soil itself will be the only way out of this difficult situation. This happens as follows: weak soils under the base are removed, and instead a sand-gravel layer is laid, and then a soil-cement layer with a minimum compression ratio of the material.
You can build a house on absolutely any soil. To do this, you just need to study its properties and choose the appropriate type of foundation, which will allow your home to stand for many decades, without causing any trouble to the owner. major repairs walls, roof and other ceilings.
In some cases, it is economically feasible to replace the deepening of the foundation through a small thickness of weak (silt, peat, bulk, etc.) soils or strengthening weak soils located under the foundation, remove these soils and in their place lay a cushion of sand, gravel, stone, 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 soft soil layer; on the right - with a large thickness of the soft soil layer; 1 - foundation; 2 - cushion made of low-compressible material; 3 - layer of durable soil; 4 - soft ground
When the thickness of the weak soil layer is 1.5-2 m, it is advisable to lay the cushion 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 based on the condition of reducing the pressure under it 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 pressure distribution at an angle a to the vertical from 20 to 40°. The magnitude of the angle a depends on physical and mechanical properties pillow material.
It is advisable to use pillows for single and strip foundations with a base width of 1 -1.5 m in clayey, loamy and sandy soils with a design resistance of 0.10-0.15 MPa above the level. To construct the cushion, 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 to construct cushions. In loamy and clay soils To avoid the accumulation of water in the pit, the cushions 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, and also to protect the foundation from erosion, sheet piling fences are used, which in some cases left in the ground for the entire period of operation of the structure. Sheet piling can also be used when constructing soil cushions to reduce the amount of work required to remove soft soil from the pit and fill the cushion.
Depending on the design of the fence, the depth of driving the sheet piling into the soil below the base of the foundation, as well as the physical and mechanical properties of the foundation soil, its load-bearing capacity as a result of the use of sheet piling can be increased up to 2 times, and foundation settlements can be reduced by 2-3 times. Best design The fence that absorbs the thrust force of the foundation soil is a round fence made of flat steel sheet pile.
4. In what cases is replacement of weak soils used?
5. What is the role of sheet piling in soil stabilization?
6. What is cementation, bitumenization, silicatization, resinization of soils?
After acquiring land for development, it often turns out that the terrain and geology of the area are not entirely suitable for long-term use and agricultural activities. We will talk about raising and leveling the soil, from marking to protective landscaping.
When does it make sense to raise a site?
One of the worst geomorphological conditions is considered to be a rise in 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 foundations, for example, in pile-grillage foundations. Shallow foundations do not work in such conditions, and full deepening requires support on a layer of soil 2.5-3 meters from the surface; above that, the foundation remains unstable and can be subject to precipitation due to high soil moisture.
It cannot be said that geodetic site planning is cheap method get rid of soil problems. However, the usefulness of such a solution can be expressed economically in favor of the developer, if raising the soil eliminates problems with waterproofing, insulation and stabilization of the foundation and the associated costs. This is usually true: planning allows you to solve the problem of poor geomorphology cheaper and, most importantly, faster, ultimately significantly reducing the period of foundation shrinkage. This solution is especially indicated when building a log house or installing 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 done rather than raising the soil, and this is a completely different technology. On such slopes even the use of special equipment for pouring bored piles costs less blood, but among the foundations this is one of the most complex. There may also simply not be a dense enough layer of soil in the area to support the construction of the required mass. Raising the site in such a situation will not give anything at all; in any case, you will have to make the foundation floating.
Is drainage necessary?
Drainage systems are indicated for artificially leveled areas with significant elevation differences, where, as we know, conventional elevation cannot solve the problem. However, the phenomena of erosion and washout can be expressed even on small slopes, so minimal backfilling and surface drainage will have to be done.
Along both boundaries of the site, located along the slope, you need to dig rain trenches, one of which (the lower one) receives water from a cross-section arranged along the upper border of the site. The bottom of the trenches is filled with crushed stone, and shrubs are planted along the slopes. Periodically, the trenches will have to be cleaned; usually the owner of the site will have to clean the one that is higher in level. The depth of the trench should reach the upper aquitard and cut it a little - about 20-30 cm. In order to disturb the terrain less, the depth of the trenches can be adjusted with hygroscopic material - the same crushed stone or construction debris.
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, or 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, along the upper slope of which willow or several birch trees are planted. It is recommended to fill the bottom of the trench and its upper slope with crushed stone 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 on top of the fertile layer. Upper layer you will 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 thrown into the adjacent area. If the site is planned completely, the work is carried out in two stages.
Soil excavation is carried out in order to eliminate the plastic washable layer between two dense layers, since there is a high probability of the embankment sliding under its own weight. 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 dense formation is exposed, a series of geodetic measurements are carried out. Knowing the configuration of the upper aquitard, it is possible to determine required volume soil and begin its delivery. At the same time, they calculate the volume of crushed stone for backfilling and plan the installation of a drainage system.
How to fill the hill
To create an embankment, hard-plastic clay in a swollen state, loam or sandy loam is used. The ability of the bedding to pass water is determined by geomorphology: if, when there is an abundance of water, it is not possible to fill a tightly compacted terrace or the bedding is carried out on top of a porous layer, the embankment should have limited water permeability. It is optimal if bearing capacity the clay matches the underlying layer, so take the time to take samples.
In places where the site plan rises above the adjacent areas by more than 30-40 cm, it is necessary to perform backfill road crushed stone fractions 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 fill 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, crushed stone can be used to immediately form the bottom of drainage trenches.
Supports more than a meter high are covered with geotextiles, which are immediately pressed down with a small layer of clay. After this, imported soil is brought in and distributed throughout the site. The simplest route for laying is starting from the shaft, laid from the point of entry of the equipment to the opposite point, and then into 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, you should wait for heavy rain or give the embankment time to overwinter. But with the use of compaction and excavator equipment, you can quickly create more impressive dumps.
Is compacting or rolling necessary?
It is optimal if the imported clay is sequentially unloaded completely onto upper level blade, and then pushes the bucket onto unfilled areas. This is how high-quality compaction occurs, in which the final shrinkage takes place in one or two wettings.
Tamping is used when there is a need for high speed work, for example when optimal time to perform embankment is limited by season or weather. With alternate tamping, you can pour 0.6-1.0 layers of pure clay one after another without prior wetting. Let us note once again that only swollen clay is suitable for compaction; dry clay will not acquire water-resistant properties until swelling and subsequent compaction.
Layers of 30-40 cm can be compacted by rolling, but wheeled vehicles are not suitable for these purposes. A crawler excavator is indispensable if the site is raised to a height of more than a meter; in other cases, it is wiser to resort to manual transport and leveling, and leave compaction to precipitation.
Please note that it is often not necessary to manually grade the site. Under the influence of movement surface waters a fresh mound will take over time natural slope. If there is an abundant supply of water, sometimes it is even necessary to slightly raise the embankment at the bottom of the slope in advance.
If you rush and bring in chernozem before the final compaction of the clay, erosion will quickly have its detrimental effect and the area will greatly lose its fertility. Unfortunately, only plowing the soil in spring and autumn can save you from this phenomenon, and even then only partially.
It is better to pour the chernozem or fertile layer dry and not roll it, preferably manual distribution and leveling of the soil. The equipment must import chernozem in the reverse order from the order in which the clay was poured. The area from the edges to the center is filled. At the end of the backfill, it is also filled.
This is the most labor-intensive 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 top bulk layer may not be uniform. Usually, before unloading chernozem, formwork is installed, the foundation is cast and waterproofed, and then covered with crushed stone. Surface support mounds are also installed before the fertile layer is formed.
Protection against erosion, strengthening the embankment on the slope
In addition to backfills 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 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 pump water out of the soil well. From the highest tier, in addition to birch and willow, you can use low-growing 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 soil level, backfilling and protective landscaping will be quite sufficient.
