Screw pile foundation technology is very popular among private homeowners, largely due to its ease of implementation. However, even professionals can encounter problems when installing this type of foundation for a house or other structure. One of the most common is when a screw pile hits a rock. Preventative measures can be taken to reduce the likelihood of this risk and address the problem after it has already occurred. Let's take a closer look at what needs to be done to accomplish this.
Geological Site
Survey
Any foundation requires a preliminary study of the
construction site, particularly the soil and topography. The following
parameters are particularly important for pile technology:
•
Soil characteristics. Not only the composition
(i.e., the presence of clay, sand, and peat) is important, but also the
structure—the arrangement of layers, their thickness, and their extent within
the site. Each soil type has its own physical and chemical properties, which
affect the load-bearing capacity and condition of structures within it (e.g.,
metal). Each layer can have a heterogeneous composition (construction debris,
rock inclusions), have a loose structure (bulk), or be rich in rhizomes—all of
these characteristics influence the design calculations.
•
Frost depth. The length of the steel supports
depends on how deeply the ground freezes: according to technical requirements,
the tip of each support must pass the freezing level and penetrate the
underlying load-bearing layer (usually 10-15 cm deeper). This parameter varies
depending on climatic conditions and is specific to each region. For example,
for the Leningrad Region, average values are 1.5-1.7 m.
•
Groundwater level. All pile supports are
protected with an anti-corrosion coating. However, proximity to groundwater
should be avoided if possible, and to do so, it is necessary to know its
location.
•
Obstacles. Rocks, strong roots, and fragments of
old buildings, while not preventing the installation of the pile foundations,
may delay the installation of the pile foundation.
The most complete and objective results can be obtained by
ordering a geological survey from a specialized company. Professionals will
conduct this survey, providing a detailed report and a survey report. A test
boring procedure will provide less comprehensive information, but the soil
composition and characteristics will still be accurate. You can dig several
holes up to 2 m deep yourself or drill them with a motorized auger, but it is
better to entrust the evaluation of the samples to specialists. Another
alternative is to get information from neighbors if they are undertaking or have
completed construction (the accuracy may be low, since even within a
construction site, characteristics often vary).
Problem-solving
algorithm
Even if a screw pile hits a rock during installation, don't
give up – there are ready-made solutions to resolve the situation:
•
If
the boulder is located below the frost line, the support can be left in place. The
lower you can screw the shaft, the more stable the foundation will be.
•
If
the pile hits a rock above the frost line, it must be unscrewed, the
obstruction removed, the soil compacted, and the screwing repeated, offsetting
the pile by a few centimeters.
•
If
the boulder cannot be removed, the screw-in point is shifted by a distance
permitted by the design and not interfering with the foundation bracing.
•
If
such a shift is not possible, one support element is replaced with several,
which are screwed in according to the plan developed by the designer.
Such cases are rare, but they can disrupt the installation
plan. Therefore, it is important to thoroughly prepare for installation and
follow all procedures strictly.
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