Contents
The construction of the fence begins with the solution of a difficult task: it is necessary to choose a foundation for the fence. On the one hand, it is necessary that it not be mowed down in the spring, during heaving, on the other hand, it is reluctant to bury extra money. So you have to solve the puzzle, choosing which of the bases is necessary – just put up poles, pour tape tape, or stop at an intermediate option – columnar with a grillage.
What can be the foundation for the fence
No matter how many fence designs there are, they all stand on several types of foundations. The depth of occurrence, the diameter or cross-section of pipes, the width and depth of the base may differ. These parameters depend on the climatic zone and the material from which the fence spans are made. And there are not very many designs and ways to implement them:
- A little sand and rubble is poured into the hole made in the ground, a pipe is inserted. The gap is clogged with stones and rubble, rammed.
- Wells are drilled in the same way, pipes are installed, only the filling around the post is concreted.
- The pipe is installed in a fixed formwork, the gap between it and the formwork is filled with concrete.
- Screw piles are used instead of pipes.
- The pillars are concreted, and a grillage is made between them. To provide the tape with sufficient strength, the grillage tape is reinforced by forming an air gap under it.
- They make a shallow strip foundation on pillars.
- Strip foundation to the depth of freezing.
Some ways to install fence posts
The designs are arranged in order of increasing cost: the least expensive is the first method, the most expensive is the fourth. The choice of foundation for the fence depends primarily on the type of soil and the level of groundwater. If the soils drain water well, and the GWL is low – below the freezing depth – you can put it on any structure. If groundwater is located high, you want a “serious fence” made of brick or rubble, for example, and even soil – clay or loam – you will have to make a more serious foundation, which costs a lot.
If you don’t know how deep they fit in a section of water, dig a pit near the planned fence. Its depth is 50-70 cm below the freezing depth for the region. If you dug to this level, but there is no water, then you are lucky and you can make a fence with a base of any design.
Installation of poles for easy fence
A light fence is one whose spans are closed with relatively materials with a relatively small mass: chain-link mesh, wooden of any design, from corrugated board, metal picket fence, metal boiled or forged mesh. Under them most often put pillars without plinths.
Poles for a mesh fence or picket fence
The cheapest and most versatile way is into a wide hole with crushed stone filling the gap. It works remarkably well on heaving soils with a high level of groundwater, it costs many times better than poured into concrete. Properly installed using this method, a light fence will never push out in the spring.
Holes for pillars of this type are obviously drilled much wider than the diameter of the pipe. Crushed stone or sand was poured at the bottom, it was tamped down (with a long pole or crowbar), a pole was placed, covered with rubble around, the pole was set up vertically and fixed with temporary struts. Pour crushed stone around in layers – 10 cm each, carefully tamp, to the maximum possible density. Everything, the installation is completed.
On normal soils
It is worth explaining why it is more stable and how such a pillar works on soils with normal drainage capacity. Water in any amount through the rubble well goes deep into, where it diverges in a natural way. When freezing, its amount around the post is not enough to have a tangible effect. The soil freezing around the post presses on the rubble, which, due to its mobility, almost completely compensates for it.
On such soils, crushed stone can be replaced with coarse sand. The coarser the grain, the better, and dusty or fine-grained sands will not work. Lay the sand in layers, spill thoroughly. The rest of the system works the same.
The key point here is the depth to which it is necessary to bury the post. If the windage is small, and the soil is well draining, it is enough to bury it at 1/3 of its height or a little more. At the same time, the hole needs to be made a little deeper: so that there is a pillow under the pipe of the order of 10-15 cm. Water will go into it and the column will remain almost dry. This is good for both its durability and stability.
Depth of holes for poles in heaving soils
If the soils are clayey, it is necessary to dig in below the freezing depth by 10-15 cm. Water will collect in this crushed stone cushion, since they do not always have time to leave on clay soils. If the pillow is below the freezing depth of the soil, there will be no heaving problems: there is still no water around the column, it has accumulated below and is in a liquid state.
If the freezing depth is very large – 2 meters or more, even such an “economy” option will be very expensive. Then you can make a drainage system around the fence to lower the groundwater level. The solution is correct, but the implementation is even more expensive.
Another option is to use screw piles. They can be drilled 2 meters much faster. But the piles themselves, and the services for their installation, are not the cheapest. You can, of course, first try manually, if it doesn’t work, call the technician.
The most budgetary option in such a situation is to bury the pillars to the depth that is more or less acceptable, make the hole wider – about 50 cm in diameter or a square with the same side, that is, increase the damper layer. In winters with average temperatures, the fence will stand normally; in abnormally cold or little snow, some pillars may lead. But in most cases, light fences react normally to this, in the spring everything “sits down” in place. It is necessary to correct the situation only if the post has squinted.
Poles for a light, but “sailing” fence
If the spans have a continuous or almost continuous surface, a decent load is created on the pillars of the fence foundation with wind. But if the filling weight is still small – professional sheet, wooden panels – you can still get by with low costs. In this case, to compensate for the wind load, the upper part of the backfill must be concreted. The depth of the concrete block is about 30 cm.
To prevent the concrete block from being destroyed by gusts of wind, a reinforcing mesh is laid. You can use a ready-made mesh with a step of 5 cm, you can make it from a 6-8 mm rod. If the mesh is galvanized, it is laid so that it is buried in concrete by at least 30 mm (track the distance from the sides). When using ferrous metal, the concrete layer at the edges of the bars increases: at least 70 mm. In total, the dimensions of the concreted area with a black metal mesh are obtained: depth 30 cm, sides – at least 34 cm, with a galvanized mesh, the side of the square around the column is 30 cm.
Foundation for fences on loose soils
If the bearing capacity of the soil is very low – these are peat bogs, dusty, loose sands – in addition to backfilling with crushed stone, the hole must be concreted to the full depth. In this case, the measure is necessary. Concrete creates a much larger bearing surface, and this is important for these soils: the load from the fence is distributed over the entire surface and it stands normally.
Cheaper in this case, drilled piles: a hole is drilled, a sleeve is inserted into it from a roofing material rolled into a tube of a suitable diameter, preferably 2 or 3 layers.
If at the same time the groundwater level is high, but the inflow rate is low, you can try to pump it out of the hole and then pour it with concrete. If the water comes quickly, take a plastic bag of suitable length. It is lowered inside the formwork, the edges are fixed around the protruding sleeve. A pole is carefully placed in the bag, concrete is poured. Concrete gradually displaces water, filling the entire form.
The second method is suitable if below, under a peat bog or sand, there is a layer of soil with a normal bearing capacity. In this case, you can make a foundation for a fence on screw piles. They are twisted to the required depth – deepening 20-25 cm into the carrier layer. Fence posts are attached to protruding heads, or use the remaining length of the pile.
Fence foundation with brick pillars
If you want to make a fence on brick pillars, the work and costs will be more significant. Even if at the same time the weight of the span remains small – profiled sheet, wood, forging with some kind of material that comes in pairs or without it – it does not matter. You will have to make a serious foundation for the pillars themselves, because they themselves create a serious load.
Such fences do not respond well to uneven shrinkage. A mortgage is usually placed in brick pillars, which is then connected to the crossbars of the entire fence. The connection turns out to be rigid, and with uneven shrinkage, cracks appear in the places where the mortgage is fastened, and the destruction of the masonry begins. Therefore, the minimum allowable level of foundation for a fence with brick pillars is below the depth of soil freezing. This approach will ensure stability.
Normally draining, medium-heaving soils
Even if the water leaves well, in order for the fence to stand for a long time, you have to dig in below the freezing depth. But still, significant forces act on that part of the pile body that falls into the freezing zone. When freezing, the soil and concrete freeze into a single mass, and then the heaving forces are able to break the pile and squeeze out a piece of the fence.
To avoid such a situation, the foundation for the fence is made in fixed formwork. In this case, the soil cannot freeze with concrete and “works” on its own. As a formwork, you can use several layers of rolled roofing felt, polystyrene or expanded polystyrene (even packaging from household appliances will do), plastic or asbestos-cement pipes of a suitable diameter.
In any case, there must be reinforcement inside the pile. This is a construction of 4 bars of reinforcement 8 mm, connected by crossbars of 4-6 mm bars. It goes to the entire depth of the pile, with a release into the post. Further, if desired, you can increase the reinforcement, and fill the gap between the bricks in the column with concrete. The second option – a pipe is attached to the reinforcement, around which a column is placed. Recently, this is a more common way to build a brick pillar.
TISE piles are more reliable in such a situation. They have a cylindrical extension at the end, which greatly increases the resistance to buoyancy. Such foundations for a fence can be made on weakly and medium heaving soils.
For the manufacture of this type of pile, a drill with a folding blade is used, which leans back after reaching the required depth. In order for such a foundation to work normally, it is desirable to expand below the freezing depth.
But it is not always possible to drill with a hand drill. On very dense clays, soils with crushed stone, it is unrealistic to drill a hole. And if there is also a freezing depth of the order of 2 meters or more, then it can be unrealistic to cope with such a task. In such cases, there are several solutions:
- Use galvanized screw piles. It is much easier to screw them in even by hand, in extreme cases there is special equipment.
- Make a pile foundation with a pillow. In this case, dig a larger hole. A crushed stone pillow is made at the bottom, a reinforcing belt is placed on it in the formwork (from an 8 mm bar). The belt is made in such a way that outlets go into the post from it (about 30 diameters of reinforcement in height, that is, for 8 mm reinforcement, the outlets should be 240 mm). After the concrete of the pillow has set, the formwork is placed and the pile is poured. It must also be reinforced, and the release from it goes to the pole.
An example of the formation of a pillow and outlets for a pole
After pouring the piles on normal soils, they backfill from the “native” soil; on those prone to heaving, it is better to fill it with crushed stone. Thus, a damping backfill will be created around the pile, compensating for the lateral pressure of the soil on the pile. And the pillow will resist vertical extrusion.
Heavily heaving soils
If the freezing depth is too great or the soil is very puffy, another solution is required. It is necessary to tie the foundation pillars to distribute the resulting loads. For fences with stone pillars, but easy filling, this is done using a grillage – a reinforced concrete tape. In order to prevent it from being bent by heaving forces, an air cushion about 10 cm thick is arranged under it.
Such a foundation for the fence is built as follows: after pouring the piles, a trench is dug, which is larger in size than the required grillage: it will be necessary to install the formwork. A low-density foam plastic, 10 cm thick, is laid at the bottom of the trench and around the piles. A reinforcing frame is made: four bars 10 mm in diameter, connected by a 4-6 mm bar. Pile protrusions are combined with grillage reinforcement. Everything is filled with concrete. After setting, the formwork is removed, the foam remains under the grillage. It provides the required air gap: at low density, it is 90% air. After the winter, of course, it will be compressed, but this is not scary: the air will remain. But in order to prevent sand or debris from falling into the crack, it is necessary to bury flat slate on both sides, which will block this gap, preventing it from silting.
The same grillage can be made on screw piles. If they suit you more, everything remains in force – their cutting parts are deepened below the freezing level, and then, everything is like with a grillage, ditch, formwork, foam plastic, reinforcement, pouring.
Why is it not worth pouring sand or gravel under the grillage? Because in this case it will be wet and most likely, when freezing, it will not help much. As a result, the grillage will burst.
Foundation for a heavy fence
In principle, the same foundation is suitable as for a medium-weight fence. Only thicker reinforcement is required: 12 mm. When reinforcing, it is necessary to position the bars so that they are in the thickness of the concrete by at least 70 mm. Based on this, and the requirement that the minimum distance between the reinforcement bars should be at least 2 filling diameters, we obtain the minimum width of the grillage – 250 mm. This is if the concrete is filled with crushed stone of a fraction of 20-40 mm.
In addition to the usual reinforcement of the grillage, it is desirable to lay a layer of metal mesh on the upper longitudinal bars with a step of 5 cm. It will give greater strength to the upper zone of the tape. And you will be able to start masonry filling in 2 weeks after pouring, and not in 4.
The grillage is done in exactly the same way: with the formation of a damper layer of foam under it. After the concrete has gained most of its strength, it is advisable to coat it with bituminous mastic. This is necessary not so much for waterproofing, but to reduce adhesion to the soil. Since the grillage under a heavy fence is most often in the ground, tangential heaving forces also act on it. To reduce them, coating is necessary.
Do not forget also about the sheet that blocks access to the damper zone under the grillage. Without it, after some time, the gap will silt up, which will lead to heaving under the tape, and this will lead to cracks in the fence.
Is it possible to make a foundation for a stone or brick fence strip foundation? Can. If you make it below freezing, it will stand great, but it costs a lot more.