A balanced decision, or which foundation is better – pile or strip

Selecting the appropriate foundation is essential for constructing a strong, long-lasting structure. Strip foundations and pile foundations are two popular choices that are frequently discussed. The choice between the two is crucial to construction planning because each type has pros and cons of its own.

Pile foundations are generally utilized in regions with difficult soil conditions or where deeper structural support is required. They are made up of long, thin columns, or piles, that are driven deeply into the ground and end when they come to rock or stable soil. By distributing the building load over a greater area and decreasing the chance of settlement, this kind of foundation pushes the weight of the structure deep into the ground.

Strip foundations, also referred to as shallow foundations, on the other hand, distribute the building’s weight over a larger surface area at a shallower depth. These foundations are more frequently utilized in locations with stable soil conditions close to the surface or in buildings with lower weight capacities. They are made up of continuous masonry or concrete strips that run the length of the building, supporting the walls and distributing the weight equally.

The type of soil, the weight and design of the building, as well as local building codes, are some of the factors that often influence the decision between pile and strip foundations. Because pile foundations can reach deep into the stable soil or rock below, they are preferred in regions with soft, compressible soil or high water tables. In contrast, strip foundations are less expensive and simpler to build in regions with stable, firm soil near the surface.

In the end, choosing between strip and pile foundations comes down to striking a balance between structural needs, soil characteristics, and financial constraints. Each type has advantages and works well in certain situations. Builders can make an informed decision that guarantees the stability and longevity of the building for many years to come by being aware of the benefits and drawbacks of each.

Pile Foundation Strip Foundation
A pile foundation is suitable for areas with unstable soil conditions, where traditional strip foundations may not provide adequate support. Strip foundations are commonly used where soil is stable and can support the weight of the building evenly across the entire perimeter.

Foundation on screw piles – what is it??

Originally, screw mounts were meant for military applications. It was necessary to quickly lay the groundwork for defensive structures.

In the latter part of the 20th century, screw piles became more popular in the civil engineering domain.

A metal pipe with a screw-shaped shank is called a screw pile. Two workers manually screw small-length (1.5 – 1.8 m) supports into the ground.

The technological hole in the upper portion of the pipe is threaded with a long-lasting object (metal tube or fittings) to function as a rotating lever. In order to give the support a rotational-translational movement into the soil’s depths, curved blades bite into the ground.

Rifle piles are used on practically all types of soils because of their versatility. Well, rocky and rocky foundations are an exception.

The installation speed of a pile-screw foundation (VF) is faster than that of a pile-grillage foundation. A small private house’s supports can be installed by two workers in a single shift.

It can take one and a half to two months to dig trenches, install formwork and reinforcement, pour concrete, and let it cure.

When it comes to construction, the decision between pile and strip foundations comes down to weighing budget, schedule, and soil conditions. In order to ensure stability in unstable soils, pile foundations distribute weight deeper into the ground. Large structures requiring robust support against shifting ground are best suited for them. Strip foundations, on the other hand, are appropriate for smaller buildings and stable soils because they distribute loads equally across the soil’s surface. They frequently show to be quicker and more affordable to install. Making the best decision requires an awareness of the local soil behavior, project size, and financial factors in order to provide a foundation that will withstand environmental changes and the test of time.

What is LF?

Strip foundations (LF) are the most popular kind of foundation for tasks and structures. Both prefabricated foundation blocks and monolithic reinforced concrete are used in its construction. The tape is shaped like masonry for small buildings, consisting of brick, cinder blocks, and natural stone.

Sometimes a strip foundation is the only appropriate option for the type of foundation used in the construction of private homes, particularly those that are two to three stories tall.

For a monolithic tape, formwork must be installed in trenches dug, reinforced, and concrete poured. This is the case if a pit needs to be dug for a prefabricated reinforced concrete foundation. Both approaches are applied to small buildings on compacted soil or large-scale construction projects.

The primary distinction between LF and VF is the absence of significant labor and material costs during screw pile installation. Tens of times less concrete is needed for pipe pouring.

It should be mentioned that almost immediately following their installation, a screw support pile foundation can be utilized for additional construction. Within thirty days of pouring, monolithic tape can be loaded with upper structures.

Comparison

The following standards are applied in order to assess the merits of both kinds of support bases:

  1. Construction budget.
  2. Construction time.
  3. Purpose and limitations.
  4. Labor costs and maintainability.
  5. Environmental friendliness and project scaling.
  6. Manufacturability and seasonality.

Construction budget – which is cheaper?

We need to take into account an example of an object’s construction in order to evaluate the costs of each type of foundation objectively.

Assume you have to construct an aerated concrete foundation for a house:

  • plan size 6 x 6 m;
  • soil freezing depth – 400 mm;
  • groundwater level – 2.2 m;
  • distance to the load-bearing soil layer from the ground surface – 500 mm;
  • masonry thickness of load-bearing walls in 1 aerated block – 200 mm.

Costs for constructing the belt

You must ascertain the tape’s volume in order to compute its cost. The depth of the foundation base is 800 mm, as determined by the data above. This is above groundwater and below the freezing line. In accordance with the guidelines, the foundation is submerged 300 mm down into the layer of load-bearing soil.

The depth of the sole is multiplied by a minimum base height of 150 mm to find the height of the LF. The developer has the option to raise the base significantly. The tape’s width is equal to the walls’ masonry material thickness plus 30 mm on each side (the minimum standard).

A monolithic foundation will be the following total size:

  • tape width – 200 + 30 + 30 = 260 mm = 0.26 m;
  • the length of the LF will be 4(6000 + 200 + 30 + 30) = 6260 x 4 = 25040 mm = 25.04 m;
  • the height will be equal to 800 + 150 = 950 mm = 0.95 m;
  • the volume of the foundation will be – 0.26 x 25.04 x 0.95 = 6.18 m3.

As per the State Elementary Estimate Standards (GESN 81-02-06-2017), approximately 60 kg of periodic profile reinforcement with a diameter of 10 mm and 20 kg of smooth rods with a diameter of 6 mm are required to reinforce 6.2 m3 of concrete. You can see the average cost of 1 m3 of ready-mixed concrete (M 300) with delivery – 2,600 rubles, 1 m of reinforcement (ø 10 mm) – 32 rubles, and 1 m of smooth wire (ø 6 mm) – 12 rubles by looking at online advertisements.

As a result, the following will be the cost of material resources needed to construct the LF:

  • concrete – 6.26 x 2600 = 16,300 rubles.;
  • fittings ø 10 – 190 rub.;
  • smooth rods ø 6 mm – 250 rub.

A total of 16740 rubles.

Concrete preparation in a mixer solution is much less expensive if you do it yourself. The most important thing to keep in mind is that you can only use cement M 400 – 500 to prepare cement sand-crushed stone mortar M 300.

Building a shallow strip foundation is shown in the following video:

Cost of pile-screw

Determine the number of screw supports based on the house’s layout. The marking perimeter is supported by four points at each corner, with intermediate piles spaced 2000 mm apart. There are twelve supports in all.

Based on the foundation base design depth of 800 mm and the height of the above-ground portion of 300 mm, the screw pile measures 1100 mm in total length.

A factory-made screw support with an æ of 57 mm and a length of 1500 mm with a tip will typically cost 1370 rubles (source: internet). It will cost 16,440 rubles for 12 screw piles.

The price factors are about equal in this instance. Naturally, this conclusion is not infallible; each unique situation must take into account all relevant unanticipated expenses as well as the going rate at the construction site.

Construction time

Regarding the amount of time required to construct the foundation, screw piles are superior to monolithic strips in many ways. The following are the approximate timelines for building a house with a 6 x 6 m plan for both types of foundations:

Strip foundation Screw piles
LF construction schedule in days:
  • marking – 1;
  • earthworks (manual digging of channels for formwork) – 3;
  • installation of formwork – 3;
  • reinforcement – ​​2;
  • preparation and pouring of concrete – 2;
  • solidification of the monolith – 30.
  • marking – 1;
  • screwing in supports – 2;
  • cutting off the tops of piles to one level and filling pipes with concrete – 2;
  • installation of heads -1;
  • foundation exposure – 14.

For light buildings, the pipes are filled with crushed stone or dry sand when a screw foundation is installed. The cavities are frequently left empty and then painted from the inside with an anti-corrosive paint. Here, the foundation is built in a matter of five to seven days.

Labor costs and maintainability

The labor expenses incurred in building the LF and WF are not similar. While building a strip foundation takes a lot of labor, screw supports that can be quickly installed need less physical labor.

With the exception of sporadic repairs that remove tiny breaches in the monolith’s integrity, the destroyed strip foundation is essentially never restored.

It is possible to fix screw piles. The HF is improved by welding new metal into pipe sections that have been corroded.

Purpose and limitations

The limitations and purpose of the base govern the use of LF and VF. High bearing capacity dense soils are used for the construction of strip foundations.

If the foundation is built on poor soil, its monolithic perimeter will soon sink and collapse. As a result, these kinds of foundations are not constructed on heaving soils that have a deep freezing depth. Additionally, it should be mentioned that LFs can withstand loads from multi-story homes.

It is highly probable that the screw foundation is designed for buildings composed of lightweight materials, such as:

  • panel,
  • frame,
  • timber house construction.

Soils that are saturated with coarse rocks and rocky foundations are the limitations of WF. The pipe blades break without reaching the design mark when they come into contact with such soil.

Manufacturability and seasonality

Both types’ foundation construction technologies are very different from one another. If producing a monolithic tape involves a lot of work in relation to:

  • digging trenches,
  • installation of formwork,
  • reinforcement and pouring concrete,

Therefore, installing screw piles just requires workers’ physical strength.

Environmental friendliness and project scaling

When comparing environmental friendliness between pile and strip foundation projects, screw supports come out on top.

The surrounding flora suffers when a LF is being built because the natural soil surface layer is disturbed. There is still a ton of waste from the building process, including leftover trash and concrete mortar leaks.

Strip foundations are still among the most widely used and dependable foundations in individual construction, despite this. There is no need for extra scaling in LF projects.

Screw piles essentially don’t disturb the pristine landscape when they appear on a construction site. According to what VF considers to be the greenest foundation supports.

In terms of scaling, screw piles are growing in popularity daily due to the introduction of new materials and design elements.

There are a few things to consider when choosing between a strip foundation and a pile foundation for your building project. For locations where the load needs to be distributed farther into the ground or for sites with unstable soil conditions, pile foundations are perfect. By moving heavy loads to deeper, more stable layers of rock or soil, they provide stability and are capable of supporting heavy loads.

Strip foundations, on the other hand, distribute the weight uniformly across the ground and are appropriate for structures with stable soil conditions and a uniform weight distribution. In locations where the soil is firm and can support the weight of the building without experiencing excessive settlement, they are less expensive and simpler to build.

Selecting the appropriate kind of foundation is primarily determined by the unique features of your construction site. Important considerations include soil type, building design, anticipated loads, and financial limitations. Finding the type of foundation that best fits the needs of your project can be accomplished by performing a thorough site investigation and consulting with structural engineers.

The choice between a strip foundation and a pile foundation ultimately comes down to striking a balance between structural integrity, affordability, and appropriateness for the site’s circumstances. Each type has benefits, and the best option is selected to meet the project’s practical and financial requirements while ensuring the building’s longevity and stability.

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Milan Yashina

Design engineer, specialist in development of design documentation. I will help you correctly design your home or other building.

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