A foundation on rocky soil provides a reliable foundation
for a structure of any weight. For construction, it's important to select the
most optimal type of supporting structure.
Rocky soils are quite common in Russia. These rocks are
composed of crystals bound together by a rigid structure. This type of soil has
high load-bearing capacity. These rocks are virtually indeformable and can
withstand pressures of 120 MPa. All of these factors make them ideal for
construction.
Rocky soil has the following properties:
•
does not freeze;
•
does not compress;
•
is
not subject to frost heave;
•
can withstand significant loads.
This type of rock is suitable for various types of
foundations. However, it is still better to avoid installing piles.
Foundation designs on rocky soil can be very simple. For
example, a shallow strip foundation. Any type of support can support the heavy
weight of the structure, since the rock itself becomes the foundation.
A shallow columnar foundation on rock is considered the
optimal option. The columns are installed in drilled holes. To increase the
strength of the structure, an extension is added at the end of the support.
When building on solid rock, deep foundations are not required, since the rock
itself provides good load-bearing capacity.
The structure is connected by a grillage. The resulting
foundation is reliable and stable. Its advantages include low costs and quick
construction.
Other types of
foundations are also built on rocky soil:
•
recessed strip foundation. This type of
foundation is created if its boundaries are not on solid rock. In this case,
excavation work involves excavating soil to a depth of approximately 70
centimeters. Next, the site is leveled, trenches are dug, a sand cushion is
laid, and waterproofing is applied. Formwork is installed on the prepared
foundation, a reinforced belt is created, and concrete is poured.
•
shallow strip foundation. For this type of
foundation, a 30-centimeter-deep excavation pit is sufficient. A sand cushion
is not required. On level ground, a reinforced belt is not required. This type of
foundation is more economical.
•
slab foundation. When constructing this type of
foundation, there are many factors that increase the cost of construction and
make this project too expensive.
More economical options are common. In many cases, a shallow
structure is built on rock. This type of foundation is reliable. It is
protected from destruction by the strength of the rock itself, which also has
undeniable advantages such as water resistance and durability. The rock becomes
a natural support for the house built on it.
However, there are also disadvantages. Drainage systems and
utility lines are difficult to install on rocky soil. Rocky soil is typically
found in seismically active zones. Strengthening the foundation to protect it
from tremors requires additional interventions. Therefore, holes are drilled in
the rock. Fasteners are installed into these holes, to which a reinforced belt
is attached.
The difficulties of working on such soils determine the
specific nature of building houses on cliffs. Conventional tools are
insufficient for this type of construction, requiring the use of specialized
equipment. This increases the cost of construction.
Types of Rock Soil
Rocky soil is primarily found in mountainous areas, forming
as a result of the disintegration of rock masses. However, it is also present
on plains. In these areas, the rock is located beneath sedimentary masses at
some depth.
The following types of soil exist:
•
igneous (granite, diorite, andesite);
•
slate,
quartzite, gneiss, marble, and iron ore, which are of metamorphic origin;
•
cemented
sedimentary masses (conglomerate, sandstone);
•
marl, gypsum.
The bearing capacity of such rocks is assessed by the
compressive strength of the soil in a saturated state. Important
characteristics include solubility, weatherability, and softening coefficient.
These determine the bearing capacity. These parameters are also taken into
account during structural design and the justification for the use of
specialized equipment.
When constructing a foundation, the geological and physical
properties of the rock are taken into account. Many types can support 50 tons
of load per square meter. Columnar, strip, and slab foundations are suitable
for them.
Piles are not recommended for forming foundations on rocky
soils. The following are reasons why this should not be done:
•
the
process of screwing them into rocky soil is too difficult. Rocks
encountered along the way prevent the screwed-in support from freely driving to
the required depth;
•
high
risk of pile column deformation. The pile can bend when hitting a large
rock. The soil may be quite soft;
•
in
rocky soil, blade breakage, corrosion protection coating, and welds may be
damaged. Such risks reduce the load-bearing capacity and strength of the
foundation;
•
natural
weathering of dispersed soils. Such rocks prevent the pile tip from
properly strengthening.
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