Shoring is used to support a structure to prevent a collapse. The
most common shoring techniques that we encountered are during the early stage
of construction which is an excavation. Shoring is intended to support a deep
excavation to prevent the retained soil overturns and eventually cause a
project mishap. Depending on the soil type, shoring support is usually provided
when we need to support an excavation with at least a 1.20-meter difference in
levels from our gate level or the +/- 0.00 level. In construction, shoring is
completely different from a retaining wall, as this is used only to retain the
soil during the excavation and as far as the structural design is a concern; it
is not used primarily for the purpose of a retaining wall.
As a
structural engineer, we should be able to know and decide which type of shoring
suited the construction project that we are engaged at the early stage of
design. To help you decide which is which, the author lists down its type and
uses to help you narrow down the selection process. The five common types of
shoring that we usually encountered in the construction project are:
- H or I-Beam Shoring
H or I-Beam Shoring also
known as soldier pile walls are the most common type of shoring that we usually
encountered in a construction project. It is constructed by driving
prefabricated steel I or H sections into the ground. Soil conditions may allow
for the sections to be vibrated directly into the ground instead of the
pre-drilling of the soil before installing the beam. The full wall is formed by
installing a pre-cast concrete panel between the driven steel beams to
construct the shoring walls.H or I-Beam Shoring was used to support an excavation ranging from 1.2
to 5.0 meters deep or excavations equivalent to at least one basement and
depending on the design, its toe length ranges from 10 meters to 12 meters
depth from 0.00 levels. You can go beyond 5 meters provided that it is properly
designed and calculated to sustain the given surcharge load along its outside
perimeter.
- Secant Pile
Shoring
Secant Pile Shoring was formed of intersecting two combinations of
piles, with a “reinforced”, also called as secondary and “un-reinforced” or
primary pile interlocking each other to form a continuous wall. A guide beam is
constructed first prior to installation to keep the alignment in place. This is
usually used in deep excavations. After casting the “primary” pile, the
temporary casing is extracted while the concrete has not fully set and the
heavy casing is then driven into the intervening pile location cutting into the
fresh concrete of the adjacent pile. The “secondary” piles are then immediately
drilled. The steel cages of the “secondary” pile are inserted and the
structural concrete is poured to form a continuous wall.
Secant Pies are the best choice to use when there is no room for open
excavation or when space is limited because of an existing structure that was
too close in proximity. In this case, surcharge loads due to the neighboring structure are considered in the design.
- Contiguous Pile
Shoring
Contiguous or Tangent Pile Shoring is composed of closely spaced piles
wherein the faces of the piles are almost touching or tangent with each other.
This is used in areas where water is not significant or the water pressure is
very minimal. This is usually proposed in clay soils and can use to
retain dry granular material or fills. Although water seepage between the gaps
of the pile is more likely to occur when used in water-bearing granular soils,
it can be prevented by grouting these gaps to form a water-tight retaining
wall. This type of shoring is not recommended to use in a high groundwater
table without dewatering works. Construction of contiguous pile is very similar to that of the secant
piles as prior to the installation, a guide beam should be constructed to serve
as a guide for the contiguous wall to install in place.
- Sheet Piles
Although it can be used to retain soil to soil excavations, this type of
shoring is bests to use when we need to isolate our excavation from the bodies
of water specifically a creek, a pond or on a sea-side. It is commonly seen in
a port and harbor construction. Similar to soldier piles, it can be constructed
by driving prefabricated Z or U steel sections into the ground using a Vibro
hammer. The full wall was formed connecting the Z or U steel sections or the
sheet piles. Depending on the depth of excavation, the end of the sheet piles
if not long enough can be welded together to reach the desired depth in the
ground.
- Diaphragm Walls
When the excavations are too deep for the type of shoring that is above mentioned
above, diaphragm walls can be used. It is made of reinforced concrete designed
primarily according to loads that need to be resisted. It can be the element
for a temporary or permanent retaining wall or both. For the deep
excavation of the basement and tunnels, the diaphragm wall is the best option.