home > Construction > Concrete pillars for the house. Columnar foundation: step-by-step do-it-yourself instructions. Entered into the concrete work log

Concrete pillars for the house. Columnar foundation: step-by-step do-it-yourself instructions. Entered into the concrete work log

This article continues the series of publications devoted to the construction of foundations. The time has come to pay attention to the columnar foundation, to figure out under what conditions it will show its best characteristics, understand how it is structured and by what principle it works, study the basic technological operations for its construction.

Features of columnar foundations

Columnar foundation can be considered the younger brother of the more industrial pile foundation, since it has a similar design and operating principle. In both cases, along the axes of the building there is a system of individual vertical supports of rectangular or round section, which are present at all intersection points of load-bearing walls, in corners, under especially loaded areas ( stone ovens, interior partitions grounds flights of stairs, columns). In both cases, a grillage can be used to connect the main elements of the foundation; the space between the racks is filled - the so-called “removal” is performed.

The main difference is the following - the pillars do not go below the freezing depth (these will already be piles, the length of which in the ground starts from 2 meters), so they only have a plantar compressive effect on the soil, while the friction force in the area of the side walls is insignificant. Based on this circumstance, technologically a columnar foundation can be not only solid/monolithic, but also assembled from ready-made piece elements. Agree, execute brickwork, for example, in a three-meter pit it is simply unrealistic, but with a depth of 40–70 cm - no problem.

The columnar foundation has its clear advantages:

· relatively low cost - it is approximately 1.5–2 times cheaper than its direct competitor, a shallow strip monolithic foundation ( less materials And earthworks, no equipment needed);

· low labor intensity;

· You can even build it alone, gradually manufacturing individual elements.

Naturally, this foundation is not universal, otherwise everything would be built on pillars, and there would simply be no other options. Let's not call this a disadvantage; it would be more correct to call it its specificity.

Due to the small total supporting surface, the columnar foundation cannot correctly transfer mass to the ground heavy house. The compressive forces under the soles of the supports turn out to be so great that the base is not able to support the weight of the structure; an increase in the number of pillars and their area is required cross section, which neutralizes the economic benefits of using such a foundation. Therefore, it is advisable to use columnar foundations only for lightweight houses made of wood (frame, timber, logs), for buildings made of lightweight mineral materials, only if they are small, low-rise, with wooden floors. In any case, the loads and soil resistance should be considered; this will be discussed below.

The limitation arising from the first point is that such a foundation cannot be laid on water-saturated, weak-bearing and heaving soils. Waterlogged and weak-bearing foundations cannot withstand concentrated loads and sag, and the possible forces of frost heaving easily overcome the small load on the foundation of a light building (we have already decided on the weight moment). In loose, unstable areas, piles that either “reach” dense rocks or, due to their length and large outer surface, cling using frictional forces, work better.

It is dangerous to use poles on steep slopes(if the height difference under the house is close to 1.5–2 meters). In such conditions, horizontally directed shear forces act too actively, which can simply overturn the structure. Moreover, the depth of the columnar foundation is small by definition, and, consequently, the house clings to the foundation relatively weakly.

Structurally, this foundation does not imply the construction of recessed rooms. If you need a basement or underground garage, then it is better (in all respects more profitable) to build a monolithic or prefabricated strip, which itself will form walls in the ground.

Well, to complete our introduction, we note that structurally and according to the material of manufacture, columnar foundations are divided into:

· wooden (in the pit there are logs with all kinds of extensions at the end - chairs);

· prefabricated (baked brick masonry, ready-made reinforced concrete products);

· monolithic (the most reliable, concrete is poured into the well directly on the site);

· rubble concrete (ruble stone is introduced into the solution).

Design of a columnar foundation

Development of a foundation design is the most difficult and very important task for a private developer. After all, we need to take into account the mass the most important moments, the main ones will be the properties of the soil on which we are building the house, as well as the level of loads that will be exerted on the house during operation. In the article " Strip foundation. Part 1: types, soils, design, cost” we talked in great detail about how to calculate loads, as well as determine the type and, accordingly, load-bearing characteristics of the soil. As for the columnar foundation, there are no less design issues here.

Length of column supports

It has already been said that a columnar foundation is laid above the freezing depth. With high-quality execution of each single support, even with a foundation depth of 40–50 cm, the house will normally cling to the natural foundation. It makes sense to go deeper a few tens of centimeters only if there are more stable layers below and you can rely on them. Let's still classify racks that extend below the freezing depth as cast-in-place piles and talk about them in the next article.

Now about the height above the ground. In order to remove the floor and wall structures from the ground at a sufficient distance, the heads of the pillars are raised approximately 30–50 cm above the surface. This has a positive effect on the moisture and thermal insulation of the first floor, allows you to create a base in the form of a fence, and thereby protect the lower part of the wooden walls.

Pillar cross-section

A prefabricated columnar foundation will have to be built in a rectangular or square pit; the monolith can be made with a round cross-section, and therefore, drills can be used to excavate the soil, making the work easier and allowing one to avoid the use of removable formwork.

In most cases, the cross-section of the supports is made uneven - expansion is organized at the bottom, and they come out to the surface with a smaller transverse size. Thanks to this design, the total support area of the entire foundation increases and the load on the ground decreases. There are several options:

For wooden post these are “chairs” (pieces of logs located perpendicular to the posts), a spot of concrete at the bottom of the well, where the support is sunk “damp” with its end, sometimes a large flat stone is simply placed in each hole.

For a brick foundation, these are extended 3-4 rows of two bricks, while subsequent rows are laid in one and a half bricks or one brick.

Monolithic pillars can start from flat plate approximately 100–150 mm thick, which is 200–250 mm wider than the stand itself, in the well-known TISE technology the support platform is spherical.

For prefabricated reinforced concrete foundations, larger blocks, or, for example, FL elements are sometimes used.

The width of the pillars leading to the head is, as a rule, no more than 60 cm, while the minimum width is 200 mm (for posts with a permanent steel shell). On average, the most common and technically justified cross-section of a pillar is 40–50 cm.

Number of pillars, distance between supports

In practice, the foundation pillars are spaced from each other at a distance of 1.5 to 3 meters. Accurate figures can be obtained if we know how many pillars to use. To carry out the necessary calculations, we must understand how much weight is transferred from each sole, and how much mass the soil can support.

First we calculate the supporting area of the pillar:

· for a square rack/slab with a cross-section of 40x40 cm - this is 1600 cm 2 (multiply the sides of the section);

· a round sole, for example, with a diameter of 40 cm, will be calculated using the formula S = πr 2 (3.14 * 202 = 1256 cm 2), or alternatively - S = 3.14D 2 /4.

We understand the type of soil (we pay special attention to the layers that will take the load - from 50 cm and below). Using the table, we determine the bearing capacity of the foundation. For example, loams of medium hardness/plasticity successfully resist loads of 2.5 kg/cm2.

It turns out that a square-section pole with a 40 cm base should be loaded on dense loam by no more than 4 tons (1600 * 2.5 = 4000 kg).

So that you can see the relationship between the type of soil and the design load on an individual column, we will give more examples for a rack of the same section: if we build on plastic loams (bearing capacity on average is 1.5 kg/cm2) - you can load no more than 2.4 tons , for very wet sands (1 kg/cm2) - no more than 1.6 tons.

Knowing total weight of all building structures of the building, adding to this the mass of possible snow cover and operational loads (people, interior items...), we obtain the calculated mass of the building. For example, let's take a house of 100 tons.

At bearing capacity soil 2.5 kg/cm 2 a house weighing 100 tons will need to be installed on at least 25 pillars (100 tons/4 tons = 25 pcs.).

If our hypothetical building has an area of 10x10 meters, there is one central bearing wall, then the total length of all foundation axes will be 50 m. - this is a load of 2 tons per one linear meter. Knowing the maximum amount one pole should carry (in our case it is 4 tons), we can first calculate the minimum allowable distance between supports - 4 tons/2 tons = 2 meters.

Marking and preparatory work

Before starting work, it is imperative to: carry out soil research, take measurements of elevation changes, create a foundation plan, perform temporary drainage in the form of drainage ditches, and clear the site of turf.

When all the initial operations have been completed, they begin to take out the design marks in kind. The marking consists of linking the building to the red lines and dividing the axes of the future building, as well as the external and external contour of the foundation. As with a strip foundation, in the case of a columnar foundation it makes sense to make a cast-off with several control cords.

There are two main points when doing markup:

Maintain the rectangularity of the lines (use the Pythagorean theorem, the Egyptian triangle, laser angle builder, measure and compare the diagonals - they should be equal).

Maintain the top of the pillars at the same horizontal level (especially important for prefabricated options, since trimming the heads will be extremely difficult - pull the control cords exactly along the hydraulic level or level marks).

We described in detail the technology for preparing and placing marks in situ in the article “Strip foundation. Part 2: preparation, marking, excavation, formwork, reinforcement.”

Excavation

The volume of excavation work for a columnar foundation is one of the smallest among all types of foundations; the situation is better, perhaps, only with screw and driven piles. However, in most cases, pits or wells should be somewhat larger than it seems at first glance.

In order to create a brick support at a depth of, say, 70 cm, you will have to manually dig a rectangular hole, and its size at the very bottom will be approximately 15–20 cm larger than the stand on each side. The excavation should expand upward, since the slopes will prevent soil from falling into the pit. Approximately the same pits need to be prepared for the production of monolithic square pillars, since it will be necessary to install and unfasten the formwork, and then dismantle it. An undoubted advantage of enlarged pits is the opportunity to inspect the body of the pillar after stripping and waterproof it.

The situation is much simpler with round supports; their installation requires wells that can be dug using hand drills or special equipment - motor drills, pit drills. A clear advantage of this method is the ability to pour the monolith directly along the walls of the excavation, without the use of formwork. However, mechanized production of a well with a diameter of over 40 cm is impossible due to the lack of special tools, so round posts with a supporting heel are often installed in holes dug with a shovel.

Please note that a certain reserve of depth for the excavation is necessary; about 20 centimeters of the hole will be “taken away” by the pillow.

Pillow device

If for foundations in which the base is located below the freezing depth, a cushion as such is not needed (so TISE technology even prohibits doing it), then for a columnar foundation, always laid at half or even 1/3 of the height of the freezing soil, it is a mandatory element. Since in the event of possible frost heaving of the base, the soil will put pressure on the pillars from below, we replace it with a damping non-heaving material - coarse sand, a mixture of sand and crushed stone (40/60) or clean crushed stone, compacted in a ten-centimeter layer into the bottom of the well.

The sand cushion is made in a layer of at least 15–20 cm, and the material is placed in a sample from wall to wall. The mass must be spilled with water and thoroughly compacted.

Application of formwork

If we decide to build a monolithic columnar foundation with rectangular posts, we cannot do without the use of formwork, because it will not be possible to dig a hole exactly the size. Formwork panels are most often assembled from edged boards, although they fit perfectly sheet materials such as OSB or moisture-resistant plywood. In any option, it is necessary to very carefully loosen the shields in the well in order to prevent distortions during pouring.

notice, that building codes All tolerances are clearly regulated, so the deviation of the pillars along the axis cannot exceed 5 mm (at the heads), along the bottom of the pit the posts should not “diverge” from the axis by more than 30 mm, the permissible vertical difference is 1 cm per meter. The horizon line for all foundation heads must be maintained with a minimum error not exceeding 1.5 mm.

When developing a well with a drill, formwork can be omitted and concrete can be poured directly along the walls of the excavation. However, it is still necessary to somehow form a part of the pillar protruding above the surface of the earth. Usually the issue is resolved by using a shirt made of roofing felt. It is wound up to the very bottom of the well, the above-ground part of the jacket is reinforced with a mesh and fixed from the ground. On the surface, roofing felt will serve as formwork; in the ground, concrete will press it tightly against the walls, and the jacket will act as waterproofing material, in addition, it reduces the impact of friction forces that arise during frost heaving.

Reinforcement, head device

Using concrete like construction material, it is necessary to strengthen it with steel rods with a variable cross-section - reinforcement. Rods with a cross-section from 10 to 14 mm are combined into a frame with four longitudinal (vertical) threads, which are secured between clamps made of thin smooth reinforcement with a diameter of 6 mm. The frame elements are fixed using knitting wire or electric welding.

For reinforcing pillars of round cross-section (with a relatively small diameter), perhaps a frame made of three workers threads located inside triangular clamps. The main thing is that we need to maintain a minimum reinforcement ratio, which for monolithic columns is 0.4% (we consider the cross-sectional area of the column), a figure of 1–2% is considered normal.

If the foundation has a reinforced concrete grillage, then the longitudinal reinforcement bars are made 40–50 cm longer than the stand itself. The reinforcement is subsequently bent into horizontal plane and tied to the grillage frame. If a wooden beam or ready-made reinforced concrete lintels are used as a grillage, then the head can be formed with one central rod, including a embedded threaded rod.

Rubble concrete pillars are not reinforced; here the stone reinforces the mass, but such structures should not have rubble in the upper part, since in this part it is necessary to anchor the reinforcement intended for connection with the grillage.

To form protective layer concrete (about 5 cm) and securely fix the frame in the formwork, it is necessary to use special spacer elements. It is best to use factory-made plastic star limiters for these purposes, which are placed directly on the reinforcing bars. Read about the nuances of working with reinforcement in the section “Foundation reinforcement” of the second article about monolithic strip foundations, about the types of rods and frame design. There is something interesting in the section “Calculation of a reinforcement belt” of the first article about strip monoliths.

Assembly and concreting of the pillar

The assembly of columnar foundation racks must be carefully monitored in height after installing each row; this will be helped by properly tensioned cast-off cords, from which the necessary measurements can be taken with a tape measure. If a reinforced concrete pile can be “cut” to the required height and all the heads can be aligned in one horizontal line, then, for example, it is not so easy to cope with a brick. The same problems arise with foundations made of reinforced concrete blocks. Inside the prefab brick pillar, laid in one and a half or two bricks, a well is formed, which should be reinforced with a steel rod and filled with concrete.

Wooden poles are most often made from oak logs with a diameter of about 200–250 mm, which are fired over low heat until charred, treated with tar, bitumen or waste oils. The finished chairs are installed in pits or open pits and secured with backfill.

Rubble concrete foundations are assembled by alternately laying stone (diameter no more than 25 cm, compressive strength of at least the grade of coarse aggregate) and concrete. First, concrete is laid in a layer of 30–35 cm, then stones are placed on it and they are sunk until completely immersed. The approximate concrete/rubble ratio should be no more than 3:1. The minimum width of a rubble foundation is 500 mm.

For the convenience of pouring concrete into narrow wells, with or without formwork, it makes sense to first make a loading funnel with a diameter of 700–800 mm from sheet metal. Concrete is placed in formwork in layers of 30–35 cm and subjected to vibration or bayonet. After concreting is completed, the product is covered with polyethylene and until the formwork is removed (about 5 days) it needs care - humidification, heating, etc. In terms of compressive strength, concrete of class B15 or more, with coarse aggregate with a fraction of up to 70 mm, will be most suitable. For self-cooking concrete mixture It is worth taking as a basis the ratio 1: 3: 5: 0.5 (cement, sand, crushed stone, water). We outlined all the main points regarding concreting foundations in the article “Strip foundation. Part 3: concreting, final operations.”

backfilling

This operation is mandatory unless you poured concrete directly into a round hole dug with a drill. The bosoms of the pit should be filled in stages, with each layer, about 20 centimeters thick, being compacted with a tamper. It is best if the material for filling the sample is coarse sand or a mixture of crushed stone and sand, which are non-heaving, low-compressible soils.

Grillage arrangement

The grillage is a system of beams or a solid slab that passes through the heads of all the pillars and connects them into a single whole. The grillage structure allows the weight of the building to be evenly distributed across all supports (each axis of the house can be loaded differently). Note that for wooden houses There may not be a grillage in the usual sense, but then its role is played by a beam or log of the lower frame.

In some cases, the grillage is assembled by welding or bolting from steel beams. This design is very reliable with respect to compression and tension forces, but if there are flaws in processing, it is highly susceptible to corrosion.

Most often, the grillage is made of reinforced concrete - prefabricated or monolithic. A prefabricated grillage is obtained by laying ready-made reinforced concrete lintels, type 5PB-25–37 P, on top of the pillars, which are joined at the centers of the pillars and connected by welding the released reinforcing elements.

To install a monolithic grillage, U-shaped boxes should be made for the entire perimeter of the building; they are installed on top of the heads and securely secured with struts from stakes driven into the ground. To prevent the structure from bending under the weight of concrete, supports are made in the spans between the pillars under the box. Some craftsmen prefer to create a ridge of sand around the perimeter on which the formwork will rest.

Depending on whether there will be a gap between the ground and the grillage, or whether it will rest on the ground with its lower edge, high and low grillages are distinguished. In the first case, free space (minimum 100 mm) ensures movement heaving soil, and he will not act “to break away”, raising the grillage. The second option is suitable for stable sandy soils, then the grillage transfers the load to the natural foundation, not only through the pillars, but also in the spans. The low grillage is even deepened a little and a leveling cushion of sand is made under it.

Obviously, a monolithic grillage must be reinforced; as a rule, 4 reinforcing threads with a diameter of 10–14 mm are sufficient for it. The technology for manufacturing a reinforcement frame, as well as concreting, is no different from the installation of a strip foundation or monolithic belt, so we again recommend that you refer to the article “Strip foundation. Part 3: concreting, final operations.”

As for the cross-section of a monolithic grillage, it usually has the shape of a square, with a side equal to the width of the walls, but not less than the width of the pillars in the head area.

Pickup

This element of the columnar foundation is installed last, often already at the final stages of building a house. The fence is needed to isolate the space under the lower ceiling from external influences - moisture, snow, low temperatures. The essence of the pick-up is that masonry is made between the pillars piece materials(brick, rubble, blocks...), a concrete wall is poured, or a frame is created that is sheathed sheet panels, type basement siding. Ventilation holes must be installed through the intake array.

This is what the technology for constructing a columnar foundation looks like. This type of foundation has firmly taken one of the leading positions among all structures. And the point here is not only about saving effort and material resources, but a correctly calculated and skillfully constructed columnar foundation can easily last no less than the house itself. This has already been tested by time.

Turishchev Anton, rmnt.ru

http://www. rmnt. ru/ - RMNT website. ru

STANDARD TECHNOLOGICAL CARDS (TTK)

(collection)

K-1-20

CONSTRUCTION OF PILE FOUNDATIONS
UNDER SUPPORTS OHL 35-500 kV

Standard technological maps (collection) K-1-20 were developed by the department of organization and mechanization of the construction of power transmission lines (EM-20) of the Orgenergostroy Institute

Compiled by: Voinilovich N.A., Kogan E.N., Kolosov Yu.A., Ssorin E.A., Smirnova E.G., Kapischeva G.V., Sorokina E.N.

The maps were developed in 1978, approved by the State Technical University for Construction of the USSR Ministry of Energy, protocol No. 239 dated July 26, 1979.

The maps cover the breakdown of the axes of foundations and places for immersion of piles, the immersion of reinforced concrete piles when constructing foundations and the installation of grillages when installing pile foundations for steel supports of 35-500 kV overhead lines.

Section 1
Layout of foundation axes and pile immersion locations
for standardized steel supports of overhead lines 35-500 kV

A COMMON PART

0.1. Section 1 of the collection K-1-20 consists of four technological maps K-1-20-1, K-1-20-2, K-1-20-3 and K-1-20-4 for work on laying out the axes of foundations and places for immersion of piles for standardized steel supports VL 35-500 kV.

0.2. Before starting work on laying out the axes of foundations and places for immersion of piles, the following work must be completed, which is not taken into account in this map:

a) arrangement of entrances to the “picket”;

b) clearing the site of stumps and bushes (in forested areas);

c) in winter, the site must be cleared of snow with a bulldozer;

d) site layout in work area piling unit.

0.3. The layout of the foundation axes and pile immersion sites is carried out by a specialized team of workers as part of an integrated foundation installation team.

Squad composition

0.4. To set out on the ground, the team leader (foreman) must have a layout drawing for each picket indicating the axis of the overhead line, the axis of the traverse, and the axes of the centers of the foundation blocks.

0.5. To secure the main alignment axes, stakes 600-700 mm long and 60-80 mm in diameter are used, which must be preserved until the installation of the support is completed, including its alignment and fastening.

0.6. For auxiliary signs indicating the places of immersion of piles, it is recommended to use wooden pegs 200 mm long with a section of 30 in the summer.´ 30 mm, and in winter, metal pins with a diameter of 10-12 mm.

0.7. Requirement for tools, devices, materials (per link)

Name		GOST, brand, Drawing no.	Unit	change	Qty.
	Note	10529-70	Theodolite with tripod
	setLeveling staff l	1158-65	= 3.5 m
	PC.	7253-54
	Folding metal meter	3620-63
	Pointed digging shovel
	Construction steel scrap	1399-73
	Carpenter's ax	979-70
	Cross saw
	Metal tape measure				Axial stakes 60-80 mm
	for one shift				Wooden center pegs
	for one shift (summer time)				Metal studs

for one shift (winter time)

This statement does not include brigade safety equipment (first aid kit, helmets, etc.), provided for by the report card for small-scale mechanization equipment.
Section 2
Driving reinforced concrete piles when constructing foundations

A COMMON PART

for steel supports of 35-500 kV overhead lines

0.2. Technological maps have been developed in relation to standardized piles of square section 25´ 25 cm and 35´ 35 cm with a length of 6, 8, 10 and 12 m, manufactured according to the album standard designs series 3.407-115 (approved by the Ministry of Energy on January 18, 1977). A general view of the piles is shown on.

Basic car	Tractor T-100 MBGP
Load capacity, tf
Machine weight, t
Weight of attachments (without hammer), t
Specific ground pressure, kgf/cm 2
Maximum length of the driven pile, m
Fuel consumption, kg/hour

e) place the pile under the hammer and lower the cap onto it;

f) drive the pile, monitoring the verticality of its immersion (at the end of driving, failure is determined as the average value of the last 10 hammer blows);

g) remove the hammer from the pile;

i) check the compliance of the position of the driven pile with the design (in height and in plan);

j) move the unit to the place of immersion of the next pile.

0.9. When carrying out work on driving piles, it is necessary to strictly observe the safety rules set out in the main regulatory documents, as well as in the instructions for servicing the piling unit and for working with the hammer.

Particular attention should be paid to meeting the following requirements:

When moving the unit over a distance of more than 100 m (from picket to picket), the boom should be placed in the transport position and the hammer should be lowered to the stop;

When moving the unit from pile to pile, the hammer should be at a height not exceeding 1-2 m from the ground;

Slope work site allowed no more than 5°;

The first lifts of the hammer and pile must be carried out carefully; if malfunctions occur, immediately lower the load;

The main axis of the falling part of the hammer during impacts must coincide with the longitudinal axis of the driven pile;

If the eccentricity of the hammer and pile is detected, it is necessary to align the hammer or slightly shift the machine itself while the hammer is running;

If there is a danger of pile destruction, the hammer operation should be stopped immediately;

It is not allowed to simultaneously carry out two working operations - lifting a hammer and a pile;

During pile lifting and installation, people are prohibited from remaining in the area where the pile may fall (one and a half length of the pile).

0.10. Work on driving piles is carried out by a team of workers consisting of:

0.11. MATERIAL AND TECHNICAL RESOURCES

Requirement for machines, tools and materials for driving piles (per link)

Name	GOST, brand, N of drawing	Unit	change	Qty.
1. Pile driving unit	SP-49	= 3.5 m
2. Diesel hammer	S-330
3. Headband				For piles with a cross section of 350´ 350 and 250 ´ 250
4. Folding meter	7253-54
5. Metal tape measure
6. Universal sling
7. Plumb
8. Assembly crowbar	1405-72
9. Pointed digging shovel	3620-63
10. Level

This statement does not include brigade safety equipment (first aid kit, etc.), provided for by the report card for small-scale mechanization equipment.

Section 3
Installation of grillages when constructing pile foundations
for standardized steel supports of 35-500 kV overhead lines

A COMMON PART

0.1. Section 3 of the collection K-1-20 - from two technological maps K-1-20-9 and K-1-20-10 for the installation of grillages when installing pile foundations for standardized steel supports of power lines with a voltage of 35-500 kV.

0.2. Technological maps have been developed in relation to standardized grillages manufactured in accordance with the album of standard designs of the 3.407-115 series (approved by the USSR Ministry of Energy on January 18, 1977). General view of pile grillages for foundation blocks of supports different types shown on , and .

a) Double pile	b) Four-pile

4. Assembly crowbar

5. Sledgehammer 5 kg

6. Level

7. Geodetic rod

8. Electrodes

E-42A

Rice. 0-7. Slinging grillages

1 - Cable 15 mm, Leveling staff= 6 m; 2 - Grillage

The statement does not include the brigade safety equipment (first aid kit, etc.), provided for by the report card for small-scale mechanization equipment.

CALCULATION
expected economic efficiency
from the implementation of technological maps K-1-20

Expected reduction in the number of workers in the construction of pile foundations for standardized supports of 35-500 kV overhead lines as a result of the use of technological maps K-1-20. 3 people per year, which is 3´ 235=705 hour days, where 235 is the average annual number of days off work.

The annual economic effect in accordance with the instructions for determining the annual economic effect SN 423-71 is calculated using the formula

E = (A 1 -A 2)+(A 1 -A 2)(0.15+0.5)+0.6D+0.12(G 1 -G 2)750,

where A 1 -A 2 is the annual saving of the basic salary (with the cost of one person-day 10 equal to 705´ 10=7050 rub.)

0.15 - coefficient taking into account the reduction of overhead costs for the basic salary

0.5 - coefficient taking into account payments for the mobile nature of work

0.6 - overhead cost savings from reducing the labor intensity of construction and installation work by 1 person-day, rub.

D - annual savings in labor costs, man-days

0.12 - standard efficiency coefficient for energy construction

G 1 - G 2 - reduction in the number of workers, people.

750 - specific capital investments in non-productive assets per 1 worker.

The annual economic efficiency from the implementation of technological maps K-1-20, calculated using the above formula, will be:

E = 7050+7050·0.65+0.6·705+0.12·3·750=12325 rub.

Page 6 of 17

Laying depth foundations on a natural basis for bridge supports does not exceed 3-4 m. The peculiarity is that they are erected in pits, previously dug to full depth. This is how they differ from deep foundations, the construction technology of which is fundamentally different. Another distinctive feature is that the calculation does not take into account the soil resistance along the lateral surface.

Foundation work must begin immediately after the commission has accepted the foundation and signed an act authorizing the commencement of laying the foundation.

Immediately before laying the foundation, the bottom of the pit must be cleared to the design level (the excavation of the pit with a bulldozer or excavator should be carried out with a gap of 0.1-0.3 m, so as not to disturb the natural structure of the soil).

The foundation must be laid dry. During the construction of the foundation, groundwater is constantly pumped out so that it does not flood the fresh masonry until the concrete acquires a strength of at least 2.5 MPa.

Shallow foundations for bridge piers can be made of class B20 concrete, rubble concrete (containing rubble stone in a volume of up to 20% of the volume of the masonry) and reinforced concrete.

For the supports of large and medium-sized bridges, concrete rigid massive foundations(Fig. 2.16, a), characterized by the fact that the line of foundation ledges forms an angle with the vertical, not exceeding the angle of pressure distribution from vertical loads (about 30°). In this case, no tensile stresses arise in the foundation body.

Rice. 2.16 - Shallow foundation: a - rigid concrete; b - flexible reinforced concrete; 1 - soft plastic loam; 2 - semi-solid clay; 3 - level of maximum erosion; 4 - reinforcing mesh

For overpasses and overpasses they are often erected reinforced concrete flexible foundations, which require less materials, but require reinforcement mesh in the area of the foundation base (Fig. 2.16, b).

Foundation depth in heaving (clayey) soils should exceed the calculated value for of this region freezing depth of at least 0.25 m. For foundations on coarse-grained, gravelly and coarse-grained soils there is no this requirement.

Foundation mark on a natural basis in the river should be at least 2.5 m below the bottom mark, taking into account local erosion.

The procedure for reinforcing and concreting the foundation regulated by the work project. Project organization determines the class of concrete in terms of strength, grades in terms of frost resistance and water resistance. During the construction of the foundation, quality control of the work must be carried out to ensure the specified properties of the structure.

To reinforce the foundation, it is necessary to ensure a thickness of the protective layer of concrete of at least 50 mm.

Formwork for foundations most often it is wooden (stationary or prefabricated panel). The moisture content of lumber should not be more than 25%. Deviations from the vertical of the formwork over the entire height of the foundation should not exceed 20 mm, and the displacement of the formwork axes should not exceed 15 mm. Installed formwork monolithic structures accepted by a commission with the participation of a foreman and a representative of the customer’s technical supervision. The following are subject to verification:

correct installation of formwork and fastenings;
compliance of formwork elements with the project;
the density of connections between the formwork elements among themselves and with previously laid concrete.

Armature for horizontal lower meshes is accepted by calculation (calculation scheme - a slab on an elastic base, loaded with pressure from a rack). The installed reinforcement of the structure is accepted with the drawing up of an act for hidden work. When installing reinforcing mesh must be ensured maximum deviations at distances between rods of no more than 0.5 d (d- diameter of the rod).

Concrete works

Concrete works require increased attention from construction personnel. Quality control consists of checking:

quality of concrete constituent materials;
the quality of the concrete mixture during its preparation, transportation and placement;
compliance with the rules of concrete care, terms of stripping and loading of structures.

Quality control of concrete works carried out by construction technical personnel, construction laboratory, representatives of the customer and the design organization.

Cement, sand And coarse aggregates must have factory passports certifying that the quality of materials meets the requirements of GOSTs. The content of dust or clay particles in natural sand should not exceed 1%. Crushed stone and gravel that are more contaminated than allowed by GOST must be washed. Application of natural gravel-sand mixtures without preliminary fractionation is not allowed. The maximum cement content during the construction of massive foundations should not exceed 300 kg/m 3 for concrete and 350 kg/m 3 for reinforced concrete structures. Cement is allowed only class DO (without additives).

Before laying the concrete mixture, the following must be checked and the relevant reports drawn up:

all hidden work (base preparation, reinforcement, installation of embedded parts, etc.);
correct installation of formwork and scaffolding for concreting, reliability of their fastening.

Consequently, as soon as they are ready, inspection and acceptance certificates for the installed formwork and reinforcement are drawn up. In addition, before concreting, it is necessary to draw up test reports for cement, sand, crushed stone, as well as maps for selecting the composition of concrete.

During the process of concreting structures, logs of concrete work and concrete maintenance should be kept.

The following is entered in the concrete work log:

start and end dates of concreting;
composition of the concrete mixture, indicators of its mobility, given concrete strength class;
volume of work performed;
numbers of reports on taking control samples and data on the results of their tests;
outside air temperature during concreting;
temperature of the concrete mixture during concreting in winter conditions and during the construction of massive structures;
date of demoulding of structures.

Delivery of concrete mixture to the laying site is carried out by dump trucks or concrete mixer trucks, which are loaded at the concrete plant ready-made mixture or its dry components. Required amount motor transport units (pcs.) is determined by the formula

where T 1 is the duration of loading and unloading of the vehicle, min;

T 2 - travel time (round trip), min;

T 3 - the delivery interval of the concrete mixture is determined by:

where V is the useful capacity of the vehicle, m3;

I - accepted concreting intensity, m 3 /h.

So, at T 1 = 10 min, T 2 = 60 min, V = 4 m 3, I = 6 m 3 / h required quantity transport units will be:

N= (10 + 60)/(60 4/6) + 1 = 3 pcs.

and the interval between successive deliveries of concrete mixture is 40 minutes.

Concrete mix supply can be done in various ways:

directly into the concrete structure with cranes using a tub (cube) with a capacity of 0.5-8 m 3;
on trays;
through pipelines using concrete pumps and pneumatic blowers.

The height of free drop of concrete mixture into the formwork should not be more than 2 m when concreting reinforced structures and 3 m when concreting unreinforced structures. To prevent the concrete mixture from stratifying (when coarse aggregate settles below) when dropping from a great height, link trunks are used. They consist of links in the form of truncated cones, which are suspended from one another.

When the concreting intensity is 6 m 3 /h or more, it is more advisable to use concrete pumps. In the construction of dispersed facilities with small volumes of work, it is economically profitable to use concrete mixer trucks, which allow you to combine the processes of transportation, production and laying of concrete mixture.

Laying concrete mixture is carried out after preparing the base: rock surfaces and working joints must be cleaned of debris, dirt, oils, snow, ice, as well as cement film (for example, by notching). Immediately before installation, cleaned surfaces must be rinsed with water and dried with a jet. compressed air. For non-rocky foundations, crushed stone preparation is carried out with a layer thickness of at least 10 cm.

The concrete mixture is laid in horizontal layers without technological interruptions with the laying direction in one direction. The thickness of the layer when working with manual deep vibrators should remain within 25-40 cm.

If they concrete large areas, it is allowed to lay and compact the concrete mixture in inclined layers, forming a horizontal leading section 1.5-2 m long. The angle of inclination of the surface of the laid layer to the horizon before compacting the mixture should not exceed 30°. Compaction is carried out starting from the leading layer.

Each subsequent layer must be laid before the concrete of the previous layer begins to set (approximately 2-3 hours). If, however, there was a break, and it exceeded the time when the concrete began to set (that is, if the concrete lost its ability to thixotropically liquefy), a working seam is required. In this case, it is possible to continue laying the concrete mixture only after the concrete has gained strength:

0.3 MPa when cleaning the base from the cement film with a water or air jet;
1.5 MPa when cleaning with a wire brush.

Strength of concrete Depending on the temperature and hardening time for Portland cement, it can be taken approximately according to the table. 2.4.

Table 2.4 - Determination of concrete strength depending on hardening time

The concrete mixture must be laid with compaction using deep vibrators. The step of rearrangement of vibrators should not exceed 1.5R (R is the radius of action of the vibrator).

The operating radius of a deep vibrator is on average 4-5 outer diameters of the vibrating tip (for vibrators IV-112 and IS-476 this diameter is 51 and 76 mm, respectively).

The maximum water-cement ratio to ensure the required grade of concrete for frost resistance should not exceed 0.45-0.50 in a non-aggressive environment for parts of the foundation that are periodically exposed to wetting and drying (zones of variable water levels in the river or freezing).

When concreting a structure, it is necessary to select a series of concrete samples measuring 10×10×10 or 15×15×15 cm (concrete structures and samples are molded using the same technology):

1 series - 3 samples to determine the strength before loading the structure (maintained under conditions of hardening of the concrete of the structure);
Series 2 - 6 samples to determine strength at 28 days of age and to determine the grade of concrete for water resistance (maintained under standard conditions);
Series 3 - 12 samples for determination frost resistanceconcrete(kept under normal conditions).

The volume of the batch of concrete from which samples are taken is no more than the volume of concrete of the structure molded within one day, and no more than 50 m3.

Curing is to keep it moist and protect it from sudden temperature changes (especially in the first days). After finishing concreting, exposed surfaces of freshly laid concrete (including during breaks in laying the mixture) should be protected from water evaporation and precipitation (for example, by covering with film). To do this, you can use reinforced polymer films, dornite in 2-3 layers, etc. The surfaces must be protected while concrete reaches at least 70% of the design strength. For normal hardening of concrete, a temperature of about 20 ° C is required and relative humidity air at least 90%. Under these conditions, after 7-14 days, concrete gains 60 - 70% strength (Table 2.4).

It is important to ensure temperature regime holding concrete and its control. Special wells are made in the array to measure temperature. Measurement data is recorded in a temperature control log.

It is prohibited to periodically pour water on the exposed surfaces of hardening concrete and reinforced concrete structures.

Movement of people on concreted structures and installation of formwork on overlying structures is allowed once the concrete reaches a strength of at least 1.5 MPa.

Formwork of vertical surfaces according to SNiP 3.03.01-87, it can be removed after the concrete reaches a strength of at least 0.2-0.3 MPa (Table 2.4).

Minimum strength of concrete unloaded monoliths horizontal structures supported by the entire contour, when stripping the formwork, it must be at least 70% of the design for spans up to 6 m and at least 80% for spans over 6 m.

After construction foundation The spacer fastenings of the pit fencing are removed. Instead (if necessary, determined by calculation), short pieces are installed between the fence wall and the foundation (the strength of the masonry must be at least 5 MPa). After dismantling the formwork and covering coating waterproofing The surfaces of the foundation that will come into contact with the soil are filled layer by layer with local soil into the spaces between the foundation and the fence, with each layer being compacted.

From this article you will learn what advantages and disadvantages support-column bases have; we will consider in detail technological features foundations of this type and we will understand the main nuances of constructing support-column foundations with our own hands.

Types of support columnar bases

In small-scale construction, when constructing small buildings made of wood or frame panels, the arrangement of support-columnar foundations is resorted to quite often.

Rice. 1.1: Support-column foundation made of FBS blocks

There are several types of support-column foundations, each of which has its own advantages and disadvantages. Let's consider the main ones:

Brick;

This is the simplest option, which is perfect for building light houses on dense soil (sandy loam or dry sandy soil) with a low level of groundwater. The load-bearing capacity of brick racks will be sufficient for any utility room and for small one-story wooden houses.

Fig 1.2: Construction of a support-column foundation made of bricks

Columnar supports made of steel pipes;

Concreted metal pipes have the greatest load-bearing capacity among all types of columnar supports. For the construction of a columnar foundation, pipes with a wall thickness of at least 4 millimeters are used, and it is mandatory to coat the pipes with an anti-corrosion metal primer, which is necessary to protect the steel from damage under the influence of groundwater.

Columnar supports made of asbestos pipes;

Made of wood;

Logs can be used for the construction of a columnar foundation, but due to the many disadvantages of this material (susceptibility to rotting, exposure to groundwater and low load-bearing capacity), this type of foundation is quite rare.

Fig 1.5

Support-column foundation advantages

First, let's figure out under what conditions it makes sense to equip columnar foundations.

The use of any type of columnar foundation is limited by the weight of the building being erected - such foundations are not intended for the construction of heavy brick or concrete houses. This is a good option for light one-story buildings made of wood, panel panels and insulated frames.

Rice. 1.6: Construction of a house made of timber on a support-column foundation

Among characteristic advantages All types of support-column bases can be distinguished:

Minimum construction time - a full-fledged support-column foundation can be erected in 2-3 working days;
Minimum cost, in comparison with strip and slab bases, due to a significantly smaller amount of required materials;
Possibility of arrangement with your own hands, without the use of special equipment;
Good resistance to frost heaving of the soil, due to which it is rational to resort to the arrangement of columnar foundations when constructing auxiliary buildings on soils with a large freezing depth;

Disadvantages of a columnar foundation

Low load-bearing capacity limits the application potential - suitable only for light buildings;
Minimal resistance to horizontal movement of soil, resulting in a high risk of pillars warping - such a foundation requires a reliable grillage strapping;
The support-column foundation does not provide for the possibility of creating ground floor or basement.

Fig 1.7

Pillar foundation made of concrete blocks

The most common type of support-column foundation is a foundation made of concrete blocks, for the creation of which reinforced concrete or expanded clay concrete blocks industrial production.

Reinforced concrete block structures are heavy (up to 3 tons), which is why their installation is carried out by construction cranes (special loop-shaped hooks are provided on the surface of the block). In small-scale construction, such blocks are used extremely rarely.

Expanded clay concrete blocks are much smaller in size and weight; creating a columnar base using such blocks can be done with your own hands.

Fig 1.8

The technology for constructing a support-columnar foundation provides for a pillar spacing of 2-3 meters (the pitch may be smaller if the building is built on problematic soil), while the supporting pillars must be evenly placed along the perimeter of the walls of the building and must be present at the intersection points of the walls and at the corners of the house .

The height of one pillar may vary depending on the slope of the construction site - according to technology, on terrain with natural slope the supports must have uneven penetration into the ground; there are often cases when on one side of the building the support pillar is made of two FBS blocks, and on the other - from five.

Fig 1.9

Pillar foundations made of FBS, as a rule, are created with a minimum level of immersion in the soil (within 15-30 centimeters). Required condition is the presence of a compacting cushion of sand and crushed stone, the thickness of which must be at least 20 centimeters (10 centimeters for each layer).

When laying FBS concrete pillars, the blocks are connected using cement-sand mortar or a special adhesive composition. Upon completion of installation, the pillars are covered with waterproofing material - roofing felt or roofing felt and the installation of the piping begins.

The grillage on supporting pillars made of FBS blocks can be made in the form of a monolithic reinforced concrete strip, or it can be a prefabricated structure made of timber, I-beam or channel.

DIY columnar foundation

Let's consider the main stages of constructing a support-column foundation from FBS blocks with our own hands:

Preparatory work - the area is cleared of vegetation and debris, the top fertile layer of soil is removed to the depth of one shovel bayonet;
Marking - according to the design data, the contours of the walls of the house are transferred to the soil, along which the locations of the support pillars are marked. The marking is carried out using pegs driven into the ground from reinforcement scraps and twine stretched between them;

Fig 2.0: Marking the area for the foundation

Excavation work - next you need to dig holes in which the support pillars will be located.

Backfilling - a 10-centimeter layer of sand is poured into the pits, which is spilled with water and compacted; a layer of fine crushed stone of a similar thickness is placed on top of the sand;

Fig 2.1: Scheme of compacting bedding under the foundation

Concreting - a cement-sand mortar based on M300 cement is poured into the pits, the surface of which is carefully leveled, after which 2-3 days are waited until the residual hardening of the concrete;
Masonry of blocks - FBS masonry is carried out using a similar cement-sand mortar; upon completion of the masonry, the height of the pillars is leveled to the same level and the blocks are covered with rolled waterproofing material or coated with bitumen mastic. Then the free space in the pits is backfilled, while the soil is further compacted using a manual tamper;

Figure 2.2

The column foundation can be considered the younger brother of the more industrial pile foundation, as it has a similar design and operating principle. In both cases, along the axes of the building there is a system of separate vertical supports of rectangular or circular cross-section, which are present at all points of intersection of load-bearing walls, in the corners, under especially loaded areas (stone stoves, interior partitions, bases of staircases, columns). In both cases, a grillage can be used to connect the main elements of the foundation; the space between the racks is filled - the so-called “removal” is performed.

The main difference is the following - the pillars do not go below the freezing depth (these will already be piles, the length of which in the ground starts from 2 meters), so they only have a plantar compressive effect on the soil, while the friction force in the area of the side walls is insignificant. Based on this circumstance, technologically a columnar foundation can be not only solid/monolithic, but also assembled from ready-made piece elements. Agree, it is simply unrealistic to do brickwork, for example, in a three-meter pit, but with a depth of 40-70 cm - no problem.

The columnar foundation has its clear advantages:

relatively low cost - it is approximately 1.5-2 times cheaper than its direct competitor, a shallow strip monolithic foundation (less materials and excavation work, no equipment needed);
low labor intensity;
You can even build it alone, gradually manufacturing individual elements.

Due to the small total supporting surface, a columnar foundation cannot correctly transfer the mass of a heavy house to the ground. The compressive forces under the soles of the supports turn out to be so great that the foundation is not able to support the weight of the structure; an increase in the number of pillars and their cross-sectional area is required, which neutralizes the economic benefits of using such a foundation. Therefore, it is advisable to use columnar foundations only for lightweight houses made of wood (frame, timber, logs), for buildings made of lightweight mineral materials, only if they are small, low-rise, with wooden floors. In any case, the loads and soil resistance should be considered; this will be discussed below.

It is dangerous to use poles on steep slopes (if the height difference under the house is close to 1.5-2 meters). In such conditions, horizontally directed shear forces act too actively, which can simply overturn the structure. Moreover, the depth of the columnar foundation is small by definition, and, consequently, the house clings to the foundation relatively weakly.

Well, to complete our introduction, we note that structurally and according to the material of manufacture, columnar foundations are divided into:

wooden (in the pit there are logs with all kinds of extensions at the end - chairs);
prefabricated (baked brick masonry, ready-made reinforced concrete products);
monolithic (the most reliable, concrete is poured into the well directly on the site);
rubble concrete (ruble stone is introduced into the solution).

Design of a columnar foundation

Development of a foundation design is the most difficult and very important task for a private developer. After all, we need to take into account a lot of important points, the main ones among them will be the properties of the soil on which we are building the house, as well as the level of loads that will be exerted on the house during operation. In the article “Strip foundation. Part 1: types, soils, design, cost” we talked in great detail about how to calculate loads, as well as determine the type and, accordingly, load-bearing characteristics of the soil. As for the columnar foundation, there are no less design issues here.

Length of column supports

It has already been said that a columnar foundation is laid above the freezing depth. With high-quality execution of each single support, even with a foundation depth of 40-50 cm, the house will normally cling to the natural foundation. It makes sense to go deeper a few tens of centimeters only if there are more stable layers below and you can rely on them. Let's still classify racks that extend below the freezing depth as cast-in-place piles and talk about them in the next article.

Now about the height above the ground. In order to remove the floor and wall structures from the ground at a sufficient distance, the heads of the pillars are raised approximately 30-50 cm above the surface. This has a positive effect on the moisture and thermal insulation of the first floor, allows you to create a base in the form of a fence, and thereby protect the lower part of the wooden walls.

Pillar cross-section

For a wooden pole, these are “chairs” (pieces of logs located perpendicular to the posts), a spot of concrete at the bottom of the well, where the support is sunk “damp” with its end, sometimes a large flat stone is simply placed in each hole.
For a brick foundation, these are extended 3-4 rows of two bricks, while subsequent rows are laid in one and a half bricks or one brick.
Monolithic pillars can start from a flat slab approximately 100-150 mm thick, which is 200-250 mm wider than the post itself; in the well-known TISE technology, the support platform is spherical.
For prefabricated reinforced concrete foundations, larger blocks, or, for example, FL elements are sometimes used.

Number of pillars, distance between supports

First we calculate the supporting area of the pillar:

for a square rack/slab with a cross-section of 40x40 cm - this is 1600 cm 2 (multiply the sides of the section);
a round sole, for example, with a diameter of 40 cm, will be calculated using the formula S = πr 2 (3.14 * 202 = 1256 cm 2), or alternatively - S = 3.14D 2 /4.

It turns out that a square-section pole with a 40 cm base should be loaded on dense loam by no more than 4 tons (1600 * 2.5 = 4000 kg).

Knowing the total weight of all building structures of the building, adding to this the mass of possible snow cover and operational loads (people, interior items...), we obtain the estimated mass of the building. For example, let's take a house of 100 tons.

With a soil bearing capacity of 2.5 kg/cm2, a house weighing 100 tons will need to be installed on at least 25 pillars (100 tons/4 tons = 25 pcs.).

If our hypothetical building has an area of 10x10 meters, and there is one central load-bearing wall, then the total length of all foundation axes will be 50 m. - this is a load of 2 tons per linear meter. Knowing the maximum amount one pole should carry (in our case it is 4 tons), we can first calculate the minimum allowable distance between the supports - 4 tons/2 tons = 2 meters.

Marking and preparatory work

There are two main points when doing markup:

Maintain the rectangularity of the lines (use the Pythagorean theorem, the Egyptian triangle, laser angle builder, measure and compare the diagonals - they should be equal).
Maintain the top of the pillars at the same horizontal level (especially important for prefabricated options, since cutting the heads will be extremely difficult - pull the control cords exactly along the hydraulic level or level marks).

We described in detail the technology for preparing and placing marks in situ in the article “Strip foundation. Part 2: preparation, marking, excavation, formwork, reinforcement."

Excavation

In order to create a brick support at a depth of, say, 70 cm, you will have to manually dig a rectangular hole, and its size at the very bottom will be approximately 15-20 cm larger than the stand on each side. The excavation should expand upward, since the slopes will prevent soil from falling into the pit. Approximately the same pits need to be prepared for the production of monolithic square pillars, since it will be necessary to install and unfasten the formwork, and then dismantle it. An undoubted advantage of enlarged pits is the opportunity to inspect the body of the pillar after stripping and waterproof it.

The situation is much simpler with round supports; their installation requires wells that can be dug using hand drills or special equipment - motorized drills, hole drills. A clear advantage of this method is the ability to pour the monolith directly along the walls of the excavation, without the use of formwork. However, mechanized production of a well with a diameter of over 40 cm is impossible due to the lack of special tools, so round posts with a supporting heel are often installed in holes dug with a shovel.

Please note that a certain reserve of depth for the excavation is necessary; about 20 centimeters of the hole will be “taken away” by the pillow.

Pillow device

If for foundations in which the base is located below the freezing depth, a cushion as such is not needed (TISE technology even prohibits its use), then for a columnar foundation, which is always laid at half or even 1/3 of the height of the freezing soil, it is mandatory element. Since in the event of possible frost heaving of the base, the soil will put pressure on the pillars from below, we replace it with a damping non-heaving material - coarse sand, a mixture of sand and crushed stone (40/60) or clean crushed stone, compacted in a ten-centimeter layer into the bottom of the well.

The sand cushion is made in a layer of at least 15-20 cm, and the material is placed in a sample from wall to wall. The mass must be spilled with water and thoroughly compacted.

Application of formwork

If we decide to build a monolithic columnar foundation with rectangular posts, we cannot do without the use of formwork, because it will not be possible to dig a hole exactly the size. Formwork panels are most often assembled from edged boards, although sheet materials such as OSB or moisture-resistant plywood are also excellent. In any option, it is necessary to very carefully loosen the shields in the well in order to prevent distortions during pouring.

Note that the building codes clearly regulate all tolerances, so the deviation of the pillars along the axis cannot exceed 5 mm (at the heads), along the bottom of the pit the posts should not “diverge” from the axis by more than 30 mm, the permissible vertical difference is 1 cm per meter. The horizon line for all foundation heads must be maintained with a minimum error not exceeding 1.5 mm.

When developing a well with a drill, formwork can be omitted and concrete can be poured directly along the walls of the excavation. However, it is still necessary to somehow form a part of the pillar protruding above the surface of the earth. Usually the issue is resolved by using a shirt made of roofing felt. It is wound up to the very bottom of the well, the above-ground part of the jacket is reinforced with a mesh and fixed from the ground. On the surface, the roofing material will serve as formwork; in the ground, the concrete will press it tightly against the walls, and the jacket will act as a waterproofing material; in addition, it reduces the impact of frictional forces that arise during frost heaving.

Reinforcement, head device

Using concrete as a building material, it is necessary to reinforce it with steel rods of variable cross-section - reinforcement. Rods with a cross-section from 10 to 14 mm are combined into a frame with four longitudinal (vertical) threads, which are secured between clamps made of thin smooth reinforcement with a diameter of 6 mm. The frame elements are fixed using knitting wire or electric welding.

For reinforcing pillars with a round cross-section (with a relatively small diameter), a frame of three working threads located inside triangular clamps may be better suited. The main thing is that we need to maintain a minimum reinforcement ratio, which for monolithic columns is 0.4% (we consider the cross-sectional area of the column), a figure of 1-2% is considered normal.

If the foundation has a reinforced concrete grillage, then the longitudinal reinforcement bars are made 40-50 cm longer than the stand itself. The reinforcement is subsequently bent into a horizontal plane and tied to the grillage frame. If a wooden beam or ready-made reinforced concrete lintels are used as a grillage, then the head can be formed with one central rod, including a embedded threaded rod.

To form a protective layer of concrete (about 5 cm) and securely secure the frame in the formwork, it is necessary to use special spacer elements. It is best to use factory-made plastic star limiters for these purposes, which are placed directly on the reinforcing bars. Read about the nuances of working with reinforcement in the section “Foundation reinforcement” of the second article about monolithic strip foundations, about the types of rods and design of the frame; there is something interesting in the section “Calculation of a reinforcement belt” of the first article about strip monoliths.

Assembly and concreting of the pillar

The assembly of columnar foundation racks must be carefully monitored in height after installing each row; this will be helped by properly tensioned cast-off cords, from which the necessary measurements can be taken with a tape measure. If a reinforced concrete pile can be “cut” to the required height and all the heads can be aligned in one horizontal line, then, for example, it is not so easy to cope with a brick. The same problems arise with foundations made of reinforced concrete blocks. A well is formed inside a prefabricated brick pillar, laid in one and a half or two bricks, which should be reinforced with a steel rod and filled with concrete.

Wooden poles are most often made from oak logs with a diameter of about 200-250 mm, which are fired over low heat until charred, treated with tar, bitumen or waste oils. The finished chairs are installed in pits or open pits and secured with backfill.

Rubble concrete foundations are assembled by alternately laying stone (diameter no more than 25 cm, compressive strength of at least the grade of coarse aggregate) and concrete. First, concrete is laid in a layer of 30-35 cm, then stones are placed on it and they are sunk until completely immersed. The approximate concrete/rubble ratio should be no more than 3:1. The minimum width of a rubble foundation is 500 mm.

For the convenience of pouring concrete into narrow wells, with or without formwork, it makes sense to first make a loading funnel with a diameter of 700-800 mm from sheet metal. Concrete is placed in formwork in layers of 30-35 cm and subjected to vibration or bayonet. After concreting is completed, the product is covered with polyethylene and until the formwork is removed (about 5 days) it needs care - humidification, heating, etc. In terms of compressive strength, concrete of class B15 or more, with coarse aggregate with a fraction of up to 70 mm, will be most suitable. To independently prepare a concrete mixture, you should take as a basis the ratio 1: 3: 5: 0.5 (cement, sand, crushed stone, water). We outlined all the main points regarding concreting foundations in the article.

backfilling

Grillage arrangement

The grillage is a system of beams or a solid slab that passes through the heads of all the pillars and connects them into a single whole. The grillage structure allows the weight of the building to be evenly distributed across all supports (each axis of the house can be loaded differently). Note that for wooden houses there may not be a grillage in the usual sense, but then its role is played by a beam or log of the lower frame.

In some cases, the grillage is assembled from steel beams by welding or bolting. This design is very reliable with respect to compression and tension forces, but if there are flaws in processing, it is highly susceptible to corrosion.

Most often, the grillage is made of reinforced concrete - prefabricated or monolithic. A prefabricated grillage is obtained by laying ready-made reinforced concrete lintels, type 5PB-25-37 P, on top of the pillars, which are joined at the centers of the pillars and connected by welding the released reinforcing elements.

Depending on whether there will be a gap between the ground and the grillage, or whether it will rest on the ground with its lower edge, high and low grillages are distinguished. In the first case, free space (minimum 100 mm) provides movement for the heaving soil, and it will not act “to pull away”, raising the grillage. The second option is suitable for stable sandy soils, then the grillage transfers the load to the natural foundation, not only through the pillars, but also in spans. The low grillage is even deepened a little and a leveling cushion of sand is made under it.

Obviously, a monolithic grillage must be reinforced; as a rule, 4 reinforcing threads with a diameter of 10-14 mm are enough for it. The technology for manufacturing a reinforcement frame, as well as concreting, is no different from the installation of a strip foundation or a monolithic belt, so we again recommend that you refer to the article “Strip foundation. Part 3: concreting, final operations".

As for the cross-section of a monolithic grillage, it usually has the shape of a square, with a side equal to the width of the walls, but not less than the width of the pillars in the head area.

Pickup

This element of the columnar foundation is installed last, often already at the final stages of building a house. The fence is needed to isolate the space under the lower ceiling from external influences - moisture, snow, low temperatures. The essence of the fence is that piece materials are laid between the pillars (brick, rubble, blocks...), a concrete wall is poured, or a frame is created, which is sheathed with sheet panels, such as basement siding. Ventilation holes must be installed through the intake array.

Turishchev Anton, rmnt.ru

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Concrete pillars for the house. Columnar foundation: step-by-step do-it-yourself instructions. Entered into the concrete work log

Section 1 Layout of foundation axes and pile immersion locations for standardized steel supports of overhead lines 35-500 kV

A COMMON PART

This statement does not include brigade safety equipment (first aid kit, helmets, etc.), provided for by the report card for small-scale mechanization equipment. Section 2 Driving reinforced concrete piles when constructing foundations

A COMMON PART

Section 3 Installation of grillages when constructing pile foundations for standardized steel supports of 35-500 kV overhead lines

A COMMON PART

CALCULATION expected economic efficiency from the implementation of technological maps K-1-20

Concrete works

Types of support columnar bases

Support-column foundation advantages

Disadvantages of a columnar foundation

Pillar foundation made of concrete blocks

DIY columnar foundation

Design of a columnar foundation

Length of column supports

Pillar cross-section

Number of pillars, distance between supports

Marking and preparatory work

Excavation

Pillow device

Application of formwork

Reinforcement, head device

Assembly and concreting of the pillar

backfilling

Grillage arrangement

Pickup

Section 1
Layout of foundation axes and pile immersion locations
for standardized steel supports of overhead lines 35-500 kV

This statement does not include brigade safety equipment (first aid kit, helmets, etc.), provided for by the report card for small-scale mechanization equipment.
Section 2
Driving reinforced concrete piles when constructing foundations

Section 3
Installation of grillages when constructing pile foundations
for standardized steel supports of 35-500 kV overhead lines

CALCULATION
expected economic efficiency
from the implementation of technological maps K-1-20