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The concept of “strip foundation” characterizes only its shape. In practice, for low-rise buildings, there are several options for manufacturing a base of this shape. We will briefly talk about some and give instructions for the step-by-step construction of a monolithic foundation.
Tape Depth Options
There are two types of tape in depth. If the sole is no deeper than 60 cm, then this is a shallow foundation.
This also includes the bases when the sole is on the surface of the ground. To be more precise, a little lower, given that the site is leveled. In practice, such a foundation in its pure form is placed where there is no fertile layer. Such conditions are rare. In most cases, there is a humus layer on the construction site, so the scheme for arranging an unburied foundation looks like this:
- completely cut off the fertile layer along the entire base of the future structure;
- fill up a layer of sand (if necessary, improve the bearing capacity of the soil – also crushed stone);
- water, level and tamp the pillow;
- put the formwork for the tape.
And then there are two options:
- Concrete floors on the ground, brought out to the height of the base.
- Base / plinth with underground and floors overlap.
But the more common foundation is deepened into the ground up to 60 cm.
All these options are common in private construction, when the project does not provide for a basement. It has been proven that the heaving forces at a shallow depth are compensated by the weight of a low-rise structure, and the bearing capacity of a shallow tape is sufficient to withstand loads.
The sole of the buried one lies in the ground below the freezing point.
This type is the most durable, but it is also the most material-intensive. It is laid when you need a basement or an underground technical floor to accommodate engineering systems equipment.
Classification by technology
According to the manufacturing method, there are three types of base tape: prefabricated, monolithic, combined. And already these technologies have their own subspecies.
The prefabricated base is assembled, as a rule, from concrete blocks (FBS).
A smaller format is also used: ceramic brick or cinder block. But even for a foundation made of solid building blocks, the bearing capacity is weakened by the seams – and even the reinforcing belts cannot fully compensate for this. Therefore, in its pure form, a brick or cinder block foundation is rare, and building blocks go to the basement at the combined foundations.
If the FBS solution needs a spoon to fill irregularities and there are no special requirements for the brand (the adhesion strength of the blocks is ensured by the weight), then when using “small forms” a full-fledged masonry solution is required. In addition to assembling from FBS, foundations made of medium-sized natural stone are also popular..
And the popularity is simply explained – high decorative properties.
Combined foundations can also have different technological schemes. For example, an underground part made of reinforced concrete plus a brick basement.
Monolithic tape is of two types: with rubble stone, poured with concrete, and reinforced concrete.
In the first version, a small rubble stone is assigned a reinforcing role. Unlike a “clean” rubble foundation, rubble concrete provides: installation of formwork, laying a pillow, pouring a small layer of concrete, laying the first row of stone in it, pouring a layer of mortar, laying the second row, etc. The distance between the stones is kept about 5 cm, and the ratio of the volume of mortar and stone is approximately 1: 1.
The attractiveness of this type of foundation is in reducing the volume of concreting, and, consequently, the cost of materials.
But the most reliable is a monolithic concrete tape with a reinforcing frame.
Monolithic strip foundation
Manufacturing technology has the following sequence.
On the ground, markings are made of a pit (for a buried foundation) or a trench system (for a shallow foundation). Carrying out excavation work.
If the tape is shallow and the communications enter / exit under the sole, then they dig a trench for them and lay pipe sleeves under the tape. Level (plan) the bottom of the excavation or trenches. Fall asleep, level, moisten and tamp the sand and gravel cushion. The total thickness of the pillow is up to 30 cm (the ratio and volume of the parts depend on the characteristics of the soil), and the width of the pillow is 30 cm wider than the heel of the foundation. Assemble the formwork.
The materials are edged board and timber. It is allowed to use edged boards with wane, but so that there are no gaps between them.
To simplify the assembly procedure, you can make shields on the ground from boards and beams. The wall thickness of the formwork must withstand the concrete pressure. The strength of the formwork is increased by tying the posts horizontally with steel wire and reinforcing with side stops on the ground on one or both sides.
For a buried foundation, when arranging a basement, it is recommended to install a fixed formwork made of foam.
At the formwork of the recessed foundation, holes are cut out for sleeves for utilities. For sleeves, pieces of plastic or asbestos concrete pipes are used. The diameter of the sleeve is chosen based on the size of the passing pipes and the insulation layer. During the work on the arrangement of the foundation, the sleeves are filled with sand and the holes are closed.
Install the reinforcing frame. Reinforcement diameter, mesh parameters depend on the calculated bearing properties. The main purpose of the “iron” is to improve the resistance of the foundation to fracture and lateral loads, the compressive strength of the concrete stone is already high. The distance between the reinforcement and the walls of the formwork is at least 50 mm.
Pour concrete in layers. If there are access roads, and a concrete plant is nearby, then it is better to use a ready-made mixture.
Otherwise, the mixture is prepared by themselves, observing the proportions to obtain the required brand.
The optimal layer thickness is up to 20 cm. And the filling of the layer should be continuous along the entire perimeter. Each layer is compacted in one of the ways: with a deep vibrator or bayonet with a piece of reinforcement (for small volumes).
After pouring the last layer, it is covered with plastic wrap (this is a necessary condition for normal concrete hydration). It is allowed to cover the basement of the foundation with burlap and periodically moisten it. The first seven days are critical, when the concrete stone gains 70% of the calculated strength.
After four weeks, the formwork is removed. Then waterproofing is carried out. The choice of materials and technology depends on the nature of the soil and the water table. Popular roll materials that are deposited on the prepared surface.
Can you provide more detailed instructions on each step of building a strip foundation?