In order for a building to stand unshakably and reliably, it will need to be provided with good support. The foundation, which is the foundation of the building, will serve as such a support. This structure is the part of the house that is responsible for transferring loads to the ground from elements that are located above.

The basis of any foundation is a high-quality sand cushion, which must be at least 10 cm thick and well compacted.

To install a sand cushion and a strip or other foundation you will need:

• fittings;
• gravelly sand of coarse fraction or clean river sand of medium fraction;
• heavy ramming;
• water;
• excavator;
• cement;
• lime or clay;
• gravel;
• crushed stone;
• sand;
• roofing felt;
• geotextiles;
• bitumen;
• building level;
• roulette.

Return to contents

Reasons why you should install a sand cushion under the foundation of a country house

1. It is possible to replace problematic soil under sand with sand. For example, there may be clay underneath. Heaving soil does not perform well during thawing and freezing.
2. Even a slight layer of sand makes it possible to level the bottom of a trench or pit, which is quite important for the subsequent stages of constructing any.
3. The sand cushion will resist compression. It is an intermediate link between the base soil and the foundation. Despite the fact that the soil becomes stronger with increasing depth (due to natural compaction under the influence of the mass of the overlying layers), replacing its surface layers with sand will help reduce the settlement of a private house. The cushion will break the capillary bridge and additionally protect the reinforced concrete from moisture.

Return to contents

What kind of sand should be used to create a base pad?

A sand foundation is the simplest and relatively cheapest type of foundation. There are several types of such structures, each of which has its own disadvantages and advantages. A sand base is a gravel-sand or sand bedding for the underground part of a house that does not have a basement. They are most often arranged for one-story single-apartment houses. These foundations are not suitable for buildings that are heavy. The cost of this design is much lower than that of any other type of foundation, which is why it is often used in the construction of small houses in the private sector.

First of all, to lay foundations on a sand bed, you need to dig a trench. Its depth should be such that the bottom is located on a dense base, which you will definitely need to reach. The resulting swarm must first be covered with coarse sand. This should be done in small layers 15 cm thick. Each layer will need to be well watered and thoroughly compacted using a heavy tamper.

The width of the sand backfill is most often made so that it exceeds the width of the wall by 10 cm. If necessary, this parameter can be increased. The foundation ends on a sand cushion 15 cm below the earth's surface. From this moment the construction of the basement begins. In order to increase the bearing capacity of the foundation, it should be poured with cement-lime, cement-clay or cement mortar.

Return to contents

Do-it-yourself foundation on a sand cushion using crushed stone

The construction of this type of sand foundation begins in the same way: the sand is laid in layers and compacted. Crushed stone is placed on top of the compacted sand. It is poured in a layer of 5-10 cm, which is first compacted and then poured with cement-lime or cement-clay mortar. Next, the next layer is poured and the procedure is repeated. Approximately 4 rows of bricks are laid above the ground level. Waterproofing from several layers of roofing material is installed on top, after which the base is placed.

A sand and gravel foundation can be arranged in a similar way. In this case, you will need to fill up the sand not in its pure form, but together with crushed gravel. This mixture is prepared in a 1 to 1 ratio. Most often, small stones made from durable gravel, broken bricks, and cobblestones are used. When backfilling, you should carefully ensure that the voids between pieces of broken brick or individual elements of gravel are completely filled with sand.

Return to contents

Strip foundation on a sand bed

Recently, the construction of strip foundations with a sand cushion has begun. The sand cushion plays a significant role in the design of the strip base: it will drain water from under the base and also reduce the effects of frost heaving forces.

The sand cushion will evenly transfer the load from the foundation to the underlying soil, increase the design resistance of the foundation and serve to level it. It is imperative to lay geotextiles before backfilling the sand-gravel mixture or sand. Geotextiles can protect the cushion material from siltation by heaving soil at high groundwater levels.

If there are basement premises, it is necessary to provide a connection between the concrete cushion and the body of the foundation strip using a profiled tongue-and-groove connection. Another option is to perform vertical reinforcement.

The upper surface of the strip foundation on a sand cushion will need to be waterproofed. When installing a prefabricated strip foundation on excessively heaving and highly heaving soils on top of foundation blocks, it will be necessary to reinforce the structure with a reinforced concrete or reinforced belt.

If you plan to build a frame wall, anchors must be cast into the body of the base strip during concreting. This must be done in order to frame the walls. The presence of threaded anchors to secure the vertical reinforcement that connects the foundation to the interfloor reinforced belt may be necessary for some technologies for constructing walls made of cellular concrete. Bent reinforcement outlets from the base body will be needed in order to connect the foundation with monolithic walls and monolithic floors.

On top of the sand cushion you will need to lay a layer of waterproofing (bitumen-polymer roll material or thick plastic film). After the reinforcement has been completed, it is necessary to cast it in the formwork.

It is worth paying attention to the thickness of the protective layer of the concrete tape on the side of the sand cushion. The requirements of American and domestic standards are almost identical: the thickness of the protective layer of concrete on the side of the sand cushion must be 70 mm. If you plan to use concrete preparation, the thickness of the protective layer will be reduced to 35-40 mm.

font size

STATE ELEMENTAL ESTIMATED STANDARDS FOR CONSTRUCTION WORKS - COLLECTION 31 - AERODROMS - GESN-2001-31 (approved by the State Construction Committee of the Russian Federation... Relevant in 2018

Table GESN 31-01-039 Construction of a sand base

Scope of work:

01. Leveling sand with a bulldozer (standard 1).

02. Leveling and leveling sand with a motor grader (standard 2).

03. Installation and removal of tracer strings (standard 1).

04. Construction of a sand layer using a high-performance kit profiler (standard 1).

05. Rolling the sand layer with rollers on pneumatic wheels with watering.

Meter: 100 m3 base

Sand base construction:

31-01-039-1 high-performance kit profiler

31-01-039-2 motor grader

Resource code	Cost element name	Unit measured	31-01-039-1	31-01-039-2
1	Labor costs of construction workers	person-hour	7,18	8,21
1.1	Average job level		2	2,3
	Driver labor costs	person-hour	4,4	2,51
3	MACHINES AND MECHANISMS
070149	Bulldozers when working on other types of construction (except water) 79 (108) kW (hp)	mach.-h	1,04	-
120910	Self-propelled road rollers with pneumatic wheels 16 t	mach.-h	1,37	1,04
121309	Base profilers with sliding forms	mach.-h	0,67	-
121601	Watering machines 6000 l	mach.-h	0,65	0,66
120202	Medium motor graders 99 (135) kW (hp)	mach.-h	-	0,81
4	MATERIALS
101-1682	Polyamide twisted cord, diameter 2 mm	T	0,0001	-
408-9040	Natural sand for construction work	m3	110	110
411-0001	Water	m3	5	5

In general, the technological sequence of work on the installation of the underlying layer in winter conditions includes: preparation of the surface of the working layer; preparing the quarry for sand excavation; development of sources for obtaining sand in a dry frozen or thawed state with loading into vehicles, transportation and unloading it at the site of installation of a frost protection layer (FPL); cleaning the surface of the working layer from snow and ice immediately before filling; leveling, leveling (if necessary, loosening); compaction to the density (degree of compaction) established by a test compaction for dry frozen or thawed soils.

Preparation of the surface of the working layer includes clearing of snow, ice and all objects that interfere with the normal process of work;

It is recommended to take the approximate length of the grip depending on the air temperature: up to - 10°C, the length of the grip is 40-50 m; from -10°C to -20°C the length decreases to 30 m. The performance of the sealing agents also decreases. In each specific case, the grip length is determined based on the results of test dumping and test compaction, taking into account the overall rate of dumping associated with the distance of sand transportation and the number of vehicles, as well as taking into account the shifting productivity of the compacting agents used.

Leveling of the poured volumes of sand is carried out by bulldozers, followed by the formation and preparation by a heavy motor grader of the design layer of thickness (in a loose state) established by the project, for subsequent compaction with cam and smooth drum vibratory rollers.

The number of roller passes and the thickness of the compacted layer are established on the basis of a test compaction. The recommended initial number of passes of compaction agents (6-8 passes along one track) is taken depending on the condition of the sand used (thawed or dry frozen), the mass of the rollers, the configuration of the rollers, the nature and degree of impact (dynamic or static), outside air temperature, ground temperature .

Test compaction, necessary for implementation for both dry-frozen and thawed sands according to a separate scheme, is recommended to be carried out for the following thicknesses (in a dense body) of layers: full or half thickness of the underlying layer (UBS). The indicated values ​​are specified depending on changes in specific conditions (temperature, mass of rollers, compaction scheme, sources of sand and its condition).

The trial compaction is carried out according to the following regulations:

transport thawed or dry frozen soil to the prepared surface of the working layer;

level and form a layer of the thickness required by the project (or half the required layer thickness);

roll with a crawler bulldozer or smooth roller (no more than two passes);

determine the initial degree of compaction (compaction coefficient TO upl);

compact the sand layer after rolling with heavy vibratory rollers with cam rollers; in this case, after every two passes of a heavy vibratory roller, the surface of the layer is rolled with a smooth pneumatic roller and samples are taken with a cutting ring to determine the compaction coefficient.

For a layer of a given thickness, roller mass, number of passes, sand and air temperature, a dependence graph is constructed K upl = f (N), where TO compaction - compaction coefficient; N- the number of passes of the skating rink along one track.

The maximum achieved compaction coefficient for each layer is determined by the dependence K upl = f ( N) based on the condition when K upl does not depend on the number of passes. For further work, the thickness of the layer and the number of passes of a roller of a given mass are accepted, at which the maximum possible compaction coefficient for the given conditions is achieved, which is accepted as the required one. In this case, the reasons are established why it is not possible to achieve the required value of the compaction coefficient according to SNiP 2.05.02-85 (see Table 22), namely: natural humidity, degree of sand heterogeneity, temperature, weight of the roller, etc. It should be borne in mind that according to the standard compaction curve of the sand used, depending on the natural humidity, you can pre-set the maximum possible compaction coefficient.

Based on the results of the trial compaction, a report is drawn up, which is approved by the management of the construction organization and agreed upon by the engineering support service and the design organization. In the event of a sudden change in weather conditions or replacement of compaction equipment, it is recommended to perform a repeat test compaction.

The largest linear size of frozen lumps should not exceed 20 cm, and their number should be no more than 10% of the total volume of sand being laid. The presence of snow and ice in the poured sand is not allowed. Oversized clods must be removed from the dumping site. It is also not allowed to clear dump truck bodies of snow and clods of frozen soil in dumping areas.

Backfilling and leveling of the transported volumes of sand on the catch are carried out in a time frame that allows completion of compaction before it begins to freeze, that is, in a thawed state. After the formation of a layer of frozen crust 3-4 cm thick on the surface of the compacted layer, further compaction is ineffective, and therefore additional loosening is necessary. When compacting sand with pad rollers, before freezing of the prepared layer begins, the perforations from the mark are cut off with a motor grader, and the surface at the mark of the working layer is rolled with pneumatic rollers.

In case of heavy snowfalls and blizzards, as well as when the air temperature is below -25°C and the wind force is over 10 m/sec, sand filling must be stopped and the surface must be insulated with a layer of snow. When resuming work and transporting sand for the next technological layer, snow and ice are removed from the surface on which subsequent backfilling is carried out and the surface is loosened to a depth of at least 0.3 m.

Construction of the foundation is one of the key stages of building a house. The correct choice of foundation design and adherence to construction technology are important here. The installation of a sand cushion under the foundations is an integral part of the construction of the base of the building.

Why do you need a sand cushion for foundations?

The sand cushion performs important functions that will further affect the integrity and durability of the structure as a whole:

• levels the bottom of a trench or pit;
• serves as a kind of drainage system;
• increases the shock-absorbing qualities of the foundation, which is important for heaving soils.

Capillary moisture rises to the concrete foundation pad along the soil. This is extremely undesirable, since in the same way the water will continue to rise further upward, reaching the reinforcement and overlying structures.

A layer of sand cuts off capillary moisture from the foundation. The sand cushion under the foundation protects the base of the house and from groundwater, which, depending on the season

change their level.

A sand cushion is used in the construction of shallow foundations, when the foundation is laid below the depth of soil freezing. This is based on the fact that sand does not change its volume when frozen and after thawing.

In some cases, it is much more profitable to replace the layer of problematic soil completely or partially with sand. For example, when a layer of weak soil extends to great depth. It is unprofitable to deepen the foundation to the load-bearing soil layer. A sand cushion with a given degree of density performs the function of good soil.

Rules for constructing a sand cushion

Before laying sand, the bottom of the pit (trench) is covered with roofing felt or geotextile. This action protects the sand cushion from mixing with the main soil and increases the service life of the base. It also prevents siltation of sand when the groundwater level rises.

Only coarse-grained or gravel fractions are suitable for constructing a sand cushion. It is possible to use river sand. Silty and fine fractions are prone to heaving and are therefore not suitable for protecting foundation structures.

To create a reliable foundation and prevent its subsidence in the future, the sand is carefully compacted. It is poured in layers 20 cm thick and must be pre-wetted. You should not spill sand on site, as there is a high probability that the soil underneath will be washed away. This circumstance leads to uneven shrinkage of the building.

Sand compaction is carried out using a vibrating plate or a hand vibrator. You can do the work with improvised means, but there is a risk of getting a low-quality, poorly compacted foundation base. The result should be a strong monolithic base, on which even the imprint of an adult’s shoes does not remain - this is a kind of test of the quality of the seal. It is important to ensure that the sand surface is level and level; a building level is used for this purpose.

When do you need a sand cushion for the foundation?

A foundation on a sand cushion is carried out if individual construction of a house, cottage, bathhouse or garage is underway. Heavier buildings require other materials to strengthen the foundation.

To level the bottom of the trench, a layer 20 cm high will be sufficient. Studying the following factors will allow you to accurately determine the thickness of the bedding:

• soil composition at the construction site;
• freezing depths;
• occurrence of groundwater level;
• climatic conditions of the region;
• loads transmitted from the structure.

When constructing a building on weak soils, an increase in the thickness of the cushion is required. If under the plant layer there are silty or fine sands, clay or loams, peat or silt soils, the height of the sand cushion will increase to 80 cm. Such soils, as a result of freezing and thawing, sharply change volume and are deformed.

The maximum thickness of the sand cushion is limited: it should not exceed three times the width of the concrete blocks. The shape of the sand cushion is also important: it is made in the shape of a trapezoid, with an inclination angle of 30º.

The sand cushion is not always suitable. In some cases, its use is inappropriate:

• in areas flooded with water, then the sand will simply be washed away;
• if the foundation soils are made of coarse sand.

The sand base is erected under different types of foundations: strip, slab, pile, columnar.

Strip foundation

It is possible to determine the type of foundation in each specific case only by calculating the foundation on a sand cushion. In most cases, small, fairly light buildings are erected on a strip foundation.

Regardless of whether it is made of concrete blocks or a monolithic structure, its width will be an important parameter. This size affects the width of the trench, and, consequently, the dimensions of the sand cushion under the strip foundation.

As a rule, 10-15 cm are added to the width of the concrete base on both sides. Knowing all the parameters, it is easy to calculate the volume of sand required for the foundation. For example, the width of the concrete base is 30 cm, then the sand cushion will be 60 cm. Multiply the width by the height and the total length of the foundation. It should also be taken into account that compaction increases the volume of material consumed. Therefore, another 15% is added to the result obtained.

The width of the sand cushion increases if wall drainage is installed. Another distance equal to the diameter of the pipe is added.

Pile foundations

In some cases, installation of a pile foundation is necessary even in individual construction. Problematic soils, deep freezing depth, high groundwater levels are the main factors that influence the decision in favor of foundations on piles.

The technology for constructing a sand cushion under pile foundations is no different from constructing a bedding under a strip foundation. In this case, the area of ​​the sand cushion will be much larger, since it is placed not only under the external and internal walls, but under the entire building.

Before driving piles, a pit is dug on the site. Then, according to the plan, the piles are installed and the caps are filled with concrete. The next stage is compacting the sand cushion. The thickness of the sand base here can also be different.

Regardless of the type of foundation, it is important to correctly calculate the height of the sand cushion and accurately follow the technology for its construction. Along with the construction of the foundation, it performs an important function: it is responsible for the integrity of the structure. Errors in calculations, incorrectly selected fraction, and poor-quality sand compaction will lead to uneven settlement, cracks in walls, and distortions in door and window openings during operation.

The installation of a sand cushion under all types of foundations allows you to save building materials: in particular concrete. Sand is one of the most accessible and cheapest materials. In cases where the use of a sand cushion under the foundation is advisable and justified by calculations, the result is a relatively simple foundation and significant financial benefits.

In preparation for construction of the road base remove the top layer of soil with a bulldozer, and then strengthen the base with a soil vibratory roller. The base of the roadway can be sand, crushed stone, crushed stone-sand, cement concrete, and can also be made of black crushed stone and mixtures reinforced with binders. This or that type of foundation has its advantages and disadvantages in terms of operational characteristics and capital costs. The underlying layer of sand serves to reduce the load on the earthen base from vehicle traffic, accumulates moisture, and performs a drainage function on clay soils. Compaction of the sandy base is carried out with rollers weighing 5-6 tons, vibratory compactors or pneumatic rollers. When constructing a sandy base, in order to add moisture to the sand, it is watered.

Device crushed stone foundations has a number of advantages compared to bases made of other materials. The crushed stone base can be laid in any weather, without blocking vehicle traffic. Also, crushed stone can be stored for a long time on the road or in the highway area. The quality of the crushed stone base determines the strength of the road pavement, which is influenced by the rigidity of the crushed stone base layer and the compressive stress during compaction that occurs under the influence of automobile traffic. The crushed stone base is compacted using heavy pneumatic and vibratory rollers. The rigidity of the base is increased by using easily compacted crushed stone. It is very important to choose crushed stone of a certain shape, since the shape of the grains affects the bearing capacity of the crushed stone layer. Compaction of the crushed stone base occurs due to the filling of pores with proppant materials, due to the spatial reorientation of grains, and also due to the fine-grained fractions of the main placer.

Device crushed stone-sand base optimal for the construction of road foundations. Laying a crushed stone-sand base eliminates the possibility of “reflected” cracks appearing on the road surface. The possibility of long-term preservation in the open air under any weather conditions characterizes the crushed stone-sand mixture as a high-tech raw material for laying the foundation. The base of the roadway made of crushed stone-sand, gravel-sand, crushed stone-gravel-sand, ash and slag mixtures can be strengthened with binding materials. Binders fill voids, increase adhesion between particles of mineral material, while increasing the density and water resistance of the mixture. When compacting mixtures with binders, choose a binder that could bind the loose material into a monolith and, at the same time, lay as a thin film over the surface of the material.

When constructing bases from black crushed stone, the crushed stone is prepared in mixers with forced mixing. Depending on the laying temperature and the type of binder used, black crushed stone is divided into hot, warm and cold. Accordingly, the temperature for laying a mixture of black crushed stone varies from 150 ° C to sub-zero temperatures. Binders can be used from viscous and liquid bitumen and bitumen emulsions. Compaction of the base of black crushed stone occurs first with medium rollers and then with heavy rollers (combined vibratory roller or soil roller for rent).

Road bases made of cold black crushed stone are usually compacted with self-propelled pneumatic rollers. If you want to learn in detail about the design and compaction of cement concrete foundations and other types of foundations, contact our specialists.