The choice of foundation design for any building depends on the soil characteristics, which are determined during a geodetic survey. The parameters obtained during this survey include not only the bearing capacity and structure of the soil, but also the groundwater level and freezing depth. In our article, we will discuss the soil types suitable for pile foundations, as well as the properties of each type, installation considerations, and recommended driving depth.
Soil Types
The composition and structure of the soil at the
construction site significantly influence the installation process. Even within
a small area, the parameters can vary significantly. Therefore, it is important
to consider the recommendations of specialists in each specific case.
Rocky
It practically does not absorb moisture, therefore it does
not become soggy, and is not subject to heaving or deformation. It consists of
limestone, quartz, and sandstone. These types include both volcanic rocks (a
single monolith) and layered areas containing various soil components.
Installation is only possible in the second type of location—until the tip hits
solid rock. With monolithic construction, screw piles cannot be driven into solid
rock.
Marshy terrain
Such areas are characterized by a shifting topsoil (peat),
which shrinks significantly when drying. Construction on peatlands is
challenging because it is impossible to bring in heavy equipment. In some
cases, installation can be simplified by systematic preparation:
•
constructing
a "sleep road" (excavating the access road, laying logs, backfilling
with sand and crushed stone), laying plank shields;
•
pre-draining
the construction area and installing a suitable drainage system.
In such conditions, using metal poles is the most
cost-effective solution—quick, reliable, and inexpensive. Foundation depths can
reach 10-12 meters. To achieve maximum stability and prevent vibration, the
foundation is braced with an angle brace.
Heaving Soil
Heaving soil is the degree to which its volume increases
when it freezes. If the ground surface rises by 1 cm after freezing at 1 m, it
is considered heaving, a phenomenon known as frost heave. According to
technology, this phenomenon can be avoided by driving the piles below the
freezing point into a dense soil layer.
Every type of soil contains moisture to varying degrees.
However, sand allows moisture to pass through to the lower layers, while clay
retains moisture due to its numerous small pores. The higher the clay content
of the soil, the more heaving it will be. Such soils include pure clays and
loams. Driving screw piles into heaving soils is easy, and in most cases,
installation can be done manually. If the clay is dense, machinery or the
digging of deep pits may be required. The installation depth averages 1.5-1.6
to 2 m.
Sandy Loam
This is a mixed soil containing up to 10% clay, with the
remainder consisting of sand and silt particles. Under the influence of
moisture (precipitation, flooding, changes in groundwater level), such areas
can shift and are often referred to as "quicksand." Beneath the
surface shifting layers, there will be a dense layer at depth, which has
already compacted under the pressure of the fertile soil. In such areas, the
most reliable method for building a house or outbuildings is using screw piles
(a depth of 1.7-2 meters is usually sufficient).
Sandy
Medium and coarse sand is sand in which more than 50% of the
mass consists of particles 0.25 mm or larger. All types, including gravelly
sand (25% of particles 2 mm or larger) and fine silty sand (more reminiscent of
clay), are optimal for pile foundations. However, fine sand, especially when
saturated with water, can cause difficulties with screwing. The average
foundation depth is 1.5-1.7 meters. This may also require deep pits, extended
ends of the lever when screwing, or the use of specialized equipment, followed
by the construction of additional bracing after installation.
Permafrost
Installing reinforced concrete foundations on frozen ground
is difficult—it requires specialized equipment and professional construction,
which significantly increases costs. To create a reliable foundation, specially
manufactured screw piles for permafrost soils are used. Special design
requirements are imposed on the support models used: strength and high
maneuverability. Most often, SVS piles with increased metal thickness (up to 6
mm) and a tapered blade are selected. The installation depth depends on the
degree of freezing. In regions located further north, the freezing depth will
be greater, meaning longer supports will be required.
Rocky
Soils of all types can be found in any region of our
country, including rocks, rubble, and limestone layers. The presence of
obstacles makes foundation installation more challenging, but still feasible.
When driving screw piles into rocky soil, both manual labor and machinery are
used. If the rocks are large, they will have to be removed and then
construction will proceed according to the technology. If the rocks are not
very large, mechanical screwing and the use of appropriate metal supports (such
as self-tapping screws) will hardly slow down the process. The average depth is
1.6-1.9 meters.
Reservoirs
Screw pile
technology is the simplest and most effective method for constructing piers,
docks, walkways, and marinas. Steel supports can be installed from pontoons in
the summer, but it's much easier to install them from ice in the winter. The
soil at the bottom of the reservoir often has a dense structure beneath a layer
of silt, and the blades are securely anchored in it. The only difficulty with
screwing is the reservoir's depth; at greater depths, extensions are
unavoidable. Constant exposure to water does not affect the durability of
prefabricated products—they have durable anti-corrosion protection.
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