PART 1: SCAFFOLDING, SHORING & UNDERPINNING.

1. SCAFFOLDING.
When temporary structures are provided to support platform for workmen, structural material
and appliances required during construction at raised height (normally more than 1.5 m) it is
called scaffolding.

Within the framework of a scaffold, there are work platforms placed at varying heights and
locations to enable workers to access different areas for construction or repair purposes. It is built
solely for the purpose of elevating workers, materials, and equipment.

Its components are:-

 Standard – these are vertical members of framework, supported on the ground or drum, or
embedded into ground.
 Ledgers – these are horizontal members, running parallel to the wall.
 Braces – these are diagonal members fixed on standards.
 Putlogs – these are transverse members, placed at right angle to the wall one end
supported on ledgers and other on the wall.
 Transoms – these are those putlogs whose both ends are supported on ledgers.
 Bridle
 Boarding
 guard rail
 Toe board.
TYPES OF SCAFFOLDING
The following different types of scaffolding are in common use.
1) Single scaffolding or bricklayers scaffolding
 2) Double scaffolding or masons scaffolding
3) Cantilever or needle scaffolding
4) Birds cage scaffolding
5) Ladder or trestle scaffolding
6) Suspended scaffolding

KEY POINTS TO CONSIDER DURING SCAFFOLDING

1) Construction and design of scaffold comes under safety regulation of building site. For
example when a person is liable to fall from more than 2m, the platforms of the scaffolds
are to be provided with a guard rail to a height of 1m and also a tie board at least 200 mm
above the platform.
2) About 35 to 40 percent of all the accidents that takes place in building construction sites
is due to faulty scaffolding. Therefore strict supervision should be followed according to
standard practice during scaffolding erection.
3) All scaffolding should be properly fixed so that they do not fall away from wall laterally.
Similarly it should be stable longitudinally also.
4) The platform should be wide enough to accommodate a person working on it. It should
not be less than 425 mm in width when the height is more than 1.8 m.
5) When materials are to be stored on the platform then the width of the platform should not
be less than 850 mm.
6) Workmen should not work under the scaffolding.

APPLICATIONS OF SCAFFOLDS
1) Supporting the working platforms where masons can stand and carry on their duties such
as plastering, brick laying or painting etc.
2) Scaffolding is also provided where demolition or maintenance work of the building has to
be carried out.

2. SHORING.
Construction of temporary structures to support an unsafe structure is called shoring. Like
scaffolds, shoring systems are also temporary. However, they’re intended to support the building
or bridge, not the workers. Shoring systems are made of heavy-duty modular steel components.

Structural shoring is used during construction, renovation, and demolition projects. It’s an
essential tool for tasks such as bridge repairs. Since the shoring system holds up the weight of the
structure, workers can safely perform repairs without risking the shifting or caving of the
structure itself.
TYPES OF SHORING
Depending on the supporting characteristic or their positions in the space, shorings are classified
into following 3 types.
a) Raking or inclined shores
Ranking shores is a system of giving temporary support to an unsafe wall. A raking shore
consists of Rakers/inclined members, wall plate, needle, cleats, bracing and sole plate

b) Flying or horizontal shores.

In this type horizontal supports are provided for supporting temporarily the parallel walls of
the two adjacent buildings, which may tend to collapse or damage when one of the
intermediate buildings has to be pulled down and rebuilt.
 c) Dead or vertical shores
In this system of shoring, the vertical members known as ‘dead shores’ are used to support
temporarily the walls, roofs, floors, etc., by providing horizontal members known as needle.
Objectives:
1. To rebuild the lower part of a defective load bearing wall.
2. To rebuild (or replace) or deepen the existing foundations, which have either become unsafe
or require strengthening for carrying heavier loads.
3. To provide large openings in the existing walls such as doors, windows, shop fronts or
garages at a lower level.

KEY POINTS TO CONSIDER DURING SHORING

1) Temporary support by means of shores to unsafe structures may be given externally or
internally or may be from both sides.
2) To maintain equilibrium, it is essential that the lines of actions of overturning forces in
floors and roofs, the forces in walls and the reaction of the shores must meet at a single
point.
3) Shoring can be made of timber or steel considering the load it has to withstand.
4) Shoring should be strong enough to resist the acting forces, consistent with economy

APPLICATIONS OF SHORING
Shoring is provided in following situations
1) When a building wall shows sign of bulging or leaning outward
2) At the time of dismantling or reconstructing a defective building wall, shoring is provided to
support the floors or roofs connected to that wall.
3) Shoring is also provided to support super structure when large openings are required to be
made in the walls.
 3. UNDERPINNING
Structures provided underneath of an existing foundation to maintain its stability is termed as
underpinning. Underpinning is used to repair, strengthen or renewal of the foundation of an
existing building.

During underpinning, the existing structure is required to be temporary supported by means of

raking shores.
TYPES OF UNDERPINNING
There are several methods of underpinning of foundation of which the three popular methods are
as follow.
a) Pit method.
It involves strengthening by excavation and building below the existing foundation. The entire
length of foundation is divided into sections of 1.2 to 1.5 m lengths. One section is taken at one
time.
For each section, a hole is made in the wall, above plinth level, the needle is inserted in the hole.
Needle may be made up of timber or steel section. Bearing plates are placed above needle to
support the masonry above it. The foundation pit is then excavated to desired level and new
foundation is laid. When the work on one section is over, work on next section is taken up.
b) Pile method.
It involves supporting the building on newly built piles of various types without excavation. Piles
are driven at regular interval along both the side of wall. The piles are connected by concrete or
steel needle, penetrating through the wall.

These beams incidentally acts as pile caps also. This method is very helpful in clayey soil, and
water logged areas. The existing foundation is very much relieved of the load.

KEY POINTS TO CONSIDER DURING UNDERPINNING

1) Building should be first examined for presence of any weakness such as poor brickwork or
masonry and for effects of settlement which may arise during the underpinning operation.
2) Temporary support should be provided by adequate shoring and by strutting up of openings
and inside of floors.
3) In case of underpinning below high rise buildings, check must be made to measure any
movement of the building by means of plumb bob or total station.

APPLICATIONS OF UNDERPINNING
The following situations demand underpinning.
1) When defective foundation of wall is to be replaced with new foundation or when existing
foundation of a wall is required to be strengthened to enable it to carry more loads.
2) To strengthen shallow footings of the existing building when a building with deep foundation
is to be constructed adjoining to it.
3) To safe guard against the danger of excessive or differential settlement of foundations of
existing structure.
4) To increase depth of foundation to increase its bearing capacity so as to sustain heavier loads.
5) During construction of basement of an existing building structure.

PART 2: DEWATERING EXCAVATIONS AT CONSTRUCTION SITE

Construction dewatering is the range of techniques used to control groundwater to allow
excavations, shafts, tunnels and other structures to be constructed below groundwater level in
workably dry, stable and safe conditions.

If a planned programme of construction dewatering is implemented, a construction project will

typically see several benefits, including:
1) Improved geotechnical stability and safety, including allowing steeper side slopes and
preventing the softening or disruption of the excavation formation level due to upward
groundwater pressures or uncontrolled seepage.
2) More efficient excavation and construction conditions, including firmer excavation
conditions less prone to rutting or bogging down of plant and machinery. The drier
working conditions created by dewatering will improve the efficiency of construction
operations such as excavation, concreting or pipe laying.
3) Less risk of adverse environmental impacts because correctly engineered dewatering
systems produce ‘clean’ water with very little suspended solids, reducing the risk of
water pollution.
The methods of dewatering at construction sites are:
1. Wellpoint method of dewatering.
2. Eductor wells.
3. Open sump pumping.
4. Deep wellpoint method.

1. WELLPOINT METHOD OF DEWATERING EXCAVATIONS

In this method, a series of wells of required depth are created in the vicinity of the excavated area
from where the water has to be pumped out. The wells are arranged either in a line or a
rectangular form where the wellpoints are created at a distance of at least 2m from each other.

Riser pipes or dewatering pipes are then installed into those closely spaced wells which on the
surface are connected to a flexible swing pipe which is ultimately appended to a common header
pipe that is responsible for discharging the water away from the site.

The purpose of using a flexible swing pipe is just to provide a clear view of what is being
pumped and the purpose of header pipe is to create suction as well as discharge the water off the
working area.
One end of the header pipe is connected to a vacuum pump which draws water through notches
in the wellpoint. The water then travels from the wellpoints through the flexible swing pipe into
the header pipe to the pump. It is then discharged away from the site or to other processes to
remove unwanted properties such as contaminants.

2. EDUCTOR WELLS METHOD OF DEWATERING EXCAVATIONS.

The method is very similar to the wellpoint method of dewatering; the only difference lies in the
usage of high-pressure water in the riser units instead of vacuum to draw out water from the
wellpoints. The method uses the venturi principle which is the reduction in fluid pressure that
results when a high-pressure fluid flows through a constricted section of a pipe.

A high-pressure supply main feeds water through a venturi-tube just above the well-screen,
creating a reduction in pressure which draws water through the riser pipe. The high pressure
main feeds off the return water. This method is economically competitive at depth in soils of
low permeability.

3. OPEN SUMP PUMPING METHOD OF DEWATERING EXCAVATIONS

This is the most common and economical method of dewatering as gravity is the main playing
force. Sump is created in the excavated area into which the surrounding water converges and
accumulates facilitating easy discharge of water through robust solid handling pumps.
Its application is however confined to the areas where soil is either gravelly or sandy.

4. DEEP WELL METHOD OF DEWATERING EXCAVATIONS

Just like the wellpoint method, wells are drilled around the excavated area, but the diameter of
wells, in this case, varies between 150-200mm. By creating deep wells around the vicinity, the
groundwater is made to fall into them under the influence of gravity. The water thus accumulated
is pumped out using a submersible pump or a centrifugal pump

As a result, the groundwater level in the surroundings would decline. According to the type and
arrangement of pumps, the depths of the wells could reach up to 30m. This method is generally
adopted when a heavy amount of water from the ground has to be drawn out.

PART 3: FOUNDATION CHARACTERISTICS OF TROPICAL AND RESIDUAL

SOILS.
1. RESIDUAL SOILS.
Residual soils are found in many parts of the world and re used extensively in construction,
either to build upon, or as construction material. They are formed when the rate of rock
weathering is more rapid than transportation of the weathered particles by e.g., water, gravity and
wind, which results in a large share of the soils formed remaining in place.
The soils typically retain many of the characteristics of the parent rock. In a tropical region,
residual soil layers can be very thick, sometimes extending to hundreds of meters before
reaching un-weathered rock.

Residual soils are products of chemical weathering and thus their characteristics are dependent
upon environmental factors of climate, parent material, topography and drainage, and age. Thus,
the geological origins greatly affect the resulting engineering characteristics of the soils.

Both lateritic soils (residual soils in well-drained regions) and andosols (residual soils in poorly-
drained regons) are susceptible to property changes upon drying, and exhibit compaction and
strength properties not indicative of their classification limits. Both soils have been used
successfully in earth dam construction, but attention must be given to seepage control through
the weathered rock.

Conversely, black soils are unpopular for embankments. Lateritic soils respond to cement
stabilization and, in some cases, lime stabilization. Andosols should also respond to lime
treatment and cement treatments if proper mixing can be achieved. Black expansive residual
soils respond to lime treatment by demonstrating strength gains and decreased expansiveness.
Rainfall induced landslides are typical of residual soil deposits.

2. TROPICAL SOILS.
Tropical soils are soils that exhibit physical, chemical, mineralogical and mechanical
characteristics that differ from those of temperate zone soils as a result of factors such as
weather, humidity and other conditions of the tropics. They are formed primarily by in
situ weathering processes, and hence are residual soils.

Tropical soils are highly structured materials, both at macro and micro levels. The micro-
structure is produced by leaching out of minerals during weathering, leaving an open structure.
They are also likely to be cemented soils due to deposition of minerals either during or after
weathering.

The highly structured nature of tropical soils, combined with the fact, they often exist in an
unsaturated state, makes them difficult to deal with as engineering materials. However, they
often have good engineering properties.

Some tropical soils can be problematic, demonstrating collapse or shrink–swell movements.

Ground investigation for tropical soils poses some difficulties due to their heterogeneous nature.
Sampling of tropical soils so that the original structure is maintained can be a major challenge,
and hence there is a strong emphasis on in situ testing methods.
REFERENCES.
1. “Differences between Scaffolding, shoring and underpinning” by Surykanta.
Retrieved on 3rd June 2019 from
“https://civilblog.org/2015/09/24/difference-between-scaffolding-shoring-underpinning/”
2. “Engineering and Construction in Tropical and Residual Soils” by Geotechnical
Engineering Division, ASCE (American Society of Civil Engineers), New York, NY.
3. “Geotechnical characteristics of residual soils” by Frank C. Townsend. Retrieved on 5th
June 2019 from
“https://ascelibrary.org/doi/abs/10.1061/%28ASCE%2907339410%281985%29111%3A
1%2829”
4. “Handbook of Tropical Residual soils” by Bujang B.k, David G. Tall and Arun Prasad.
5. “Methods of dewatering excavation at construction site” Retrieved on 4th June 2019 from
“https://theconstructor.org/practical-guide/methods-of-dewatering-excavation-
construction-site/13849/”
6. “Understanding the difference between scaffolding and shoring”. Retrieved on 3rd June
2019 from
“https://www.scaffoldingresource.com/blog/2018/03/understanding-the-differences-
between-scaffolding-and-shoring/”