/ 2406: FOUNDATION ENGINEERING I

LECTURE NOTES
EC E 2406: FOUNDATION ENGINEERING I LECTURE NOTES
Sb oring,
· Scaffolding and Und . .
Shonng. crp1nning
and scaffoldin ar
U d . . . g e the most frequent t
n erpmmng ts th_e install ation of temporary ernporary structures in building construction.
pSrhov1~e either addnional depth or an increase: pberrn_anent sup_pon to an existing foundation to
onng eanng capacity.
In multi-storey work, the shoring which su
supported by lower floors which may ppons freshly placed concrete is necessarily
not yet have an · d th •
not h ave been designed to c~rn, I d ame e1r full strength, and which may
constructton
• loads may exceed -desi·, oaI s as great as th. osc. imposed
·
during construction.
Therefore, shoring must be _dgnd oads by an appreciable amount.
prov, e for enough fl d
support the imposed loads wi·th . oors to evelop the needed capacity to
out excessive stress O d fl · W
reshores are used at the se al . r e ection. hether pennanent shores or
materials as well as the tverf reqULred low_er floor levels depends on job plans for reused of
ra e O strength gam m the structure
There are several types f d · bl . . . ·
clamin d . . o _a Justa e md1v1dual shores. The simplest of these, is based on
g ev1ce which permits the overlapping of two 2x4 members.

Figure 2 - Metal fittin gs are placed at the end of square lumber, making them adjustable shores.
A number of patented shoring systems have been developed with adjustable legs which
eliminate cutting, close fitting, and wedging. Figure 3 shows schematic diagram of one such
device.

Figure I - Using a clamping device, shores are made by joining two pieces of dimension lumber
which also facilitates length adjustment
A portable jacking tool is used to make vertical adjustments. Metal shore jack fittings are
available to fit over the end of 4x4 or 6x6 wood shore, thus transforming the piece of lumber
into an adjustable shore, as shown in Figure 2. These devices are capable of varying the shore Figure 3 - Shoring system with adjustable legs
Scaffold-Type Shoring
height as much as 12 inches.
Tubular steel form scaffolding was first designed to support loads imposed by the workers
getting to the work area. Since the system of jacks in the tubular steel scaffolding makes it easy
to adjust and level elevations, it is often used as a support for formwork. Since it is a modular
assembly, it makes it an attractive option for rapid utilization for formwork support. A
schematic diagram of a tubul ar steel scaffolding or shoring tower is shown in Figure 4.

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 LECTURE NOTES
ECE 2406: FOUNDATION ENGINEERING I LECTIJ RF. N<JTF_<;

Design Loads
According to OS HA and ANSI criteria and many years of np,:11cnu '-'Ith lllC>C 1y=~.
design load ratings for scaffold platforms arc as follow~
✓ Light-Duty Loading. 25 lb/lU maximum \\ Orkmg load for ~upport nf pcnplc 1n,t
tools (no equipment or matenal storage on the platfimn )
✓ Medi um-Duty Loading. 50 lb/Ill ma.x1mum working load for people an<I material
often described as applying lo bricklayers· and plaster.;' "'ork.
✓ Heavy-Duty Loading. 75 lb/Ill maximum " orkmg lo~d for people and ~tored matcndl
often described as applying to stone masonry \\ Ork

These ratings assume umform load distribution With the cxcepuon of the "'eight of stored
lock For materials, scaffol d loads most often consist of personnel. hoth stationary and transrtory lt 1s
Braces--.... important to remember that the OSHA and ANSI load-rating sy\tem 15 intended for :;u1d.:mct:
of field personnel in the construction and use of non-spcc1fically engineered \caffoldmg
applications.

Tub, and Coupler Scaffolds

Tube and coupler scaffolds are assembled from three basic structural clements·
✓ The uprights, or posts, which rise from ground or other w lid \uppon.
✓ The bearer, which supports the work platforms and / or provide transverse hor1Lonul
connections between the posts;
✓ The runners, which attach to the posts directly below the b,:arcrs llld provide
longitudinal connections along the length of the scaffold
Adjustable Jacks These three clements arc usually connected with standard or fixed coupler.; which pro~1dc a
90° connection in two places and are shown in Figures 5a and 5b F1gwc Sc show5 the tube and
Figur, 4 - A shoring tower is made by assembling end frames with diagonal braces coupler scaffold used on a job site.
Scaffolding
Scaffolding has been used for many centuries to provide access areas for building and _.......
...

-..
decorating structures taller than people who work on them.
The word ~scaffolding" refers to any raised platform or ramp used for ingress and egress for
..-•·
pedestrian movement and/or the passage of building materials. Since the mid-I 920s the concept ---...:~
of using steel pipes fastened together with metal-form or cast clamps (couplers) instead of poles
and ropes was introduced.
Aluminum alloy pipes and couplers were developed for their lighter weight and speedier
construction. Aluminum alloy is onl y two-thirds as strong as steel, but it is only one-third lo
one-halfns weight. Because of the higher initial cost, aluminum is restricted mostly to building
maintenance scaffolds and suspended platforms.
C,ner2I Design Co nsideration!
It is a common practice to use a minimum factor of safety of four in the design of all
scaffoldings, meaning that scaffolds and their components can support four times the maximum Figur, Sa - The basic assembly of tub.: and coupler scaffol<ls
design load without experiencing failure. For this reason, the design load is multiplied by a
factor of 4, before and determ ining limiting strength and yield stress of the metal used in the
engineering design of scaffolds and their componcnls.

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 ,r ~400: 1-v UM >A I lllN ENGINEERJNG I
LECTURE NOTES ECE 2406: FOUNDATION ENGINEERJNG I 1.F.CTURF. ~OTF--~

Mrthods of stabilizing agai nst a building

~
a) Wall tic and anchorage
b) Window reveal tube
c) Reveal between pilasters
1"1

Tube and Coupler Scaffolds: APPLICATION

Q::)::>ffi
r. ... ._
Tube and coupler scalTolds can be assembled in many different ways because of the nexibihty
of their assembly dimensions in the horizontal and vcnical planes Tube and coupler scaffolds
••I
are more adaptable since they are not restricted by frame width in the transv= d,rcct,on or by

,.._ ..
1----··
0
--,.1 j
C.-•---D.41111f
Ill
I brace length in the longitudinal direction or by frame height in the ven ical direction (unlike
sectional frame scalTolds which is going to be discussed later m this lesson).
Therefore, for cases of irregular dimensions and contours. such as churches or old auditoriums.
It!

' =~-C::
r.,...,...... .....1111 . . .
r,,
~ tube and coupler scaffolds become the preferred option smce 1t makes access 10 the worlc plxe
easier.
Tube and Coupler Scaffolds: BASlC CONFIG URATIONS
Figure Sb · The basic components of tube and coupler scalTolds
l11e basic configurations are as follows:
I ) Double Pole. Double Pole or Independent Pole Scaffold is a scaffold supported from
the base by a double row of uprights, independent of support from the walls and
constructed of uprights, ledgers, horizontal platform bearers, and diagonal bracmg.
2) Single Pole. Single Pole Scaffold is a platform resting on putlogs (putlog 1s a scaffold
member upon which the platform rests) or crossbeams, the outside ends of which are
supponed on ledgers secured to a single row of posts or uprights and the inner ends of
which are supported on or in a wall.
3) Tower Scaffolds. These consist of one or few bays m either horizontal plane..
conslructed to required height for access to ceilings or for specialized load support
requirements not conveniently achievable with sectional frames. They may be mounted
on casters and become mobile scaffolds or rolling towers. An application of to\\er
scaffolds is to provide stair access to unusual structures such as cooling towers.

Sectional Scaffolding
Sectional scaffolding is available in many frame configurations. Most frames are available m
1he widths of 2, 3, and 5 feet Some special purpose frames are available m 4 and 6 fe..--t widths
(6-fi frames are used in sidewalk canopies). Standard frame heights are 3. 4. 5, 6, and 6.5 feet
Figure Sc• Tube and coupler scalTolds used in the cons1ruction high for sidewalk canopies. The frames are also available in heights of 7.5. 8. and 10 fc:et

Diagonal bracing is used to stiffen the structure as necessary, most imponant in the longitudinal The most common material used in the fabrication of steel framt-s is 1 5/8-in.- OD cubing wi!h
direction. Bracing is generally connected to the posts with "adjustable" or "swivel" couplers a wall thickness between 0.086 and 0.105 in_ The most common gr:idc of steel used for this
wl11ch have the facility of adjusting a full 360°. Diagonal bracing should always be attached to purpose is ALSI designation A 1050, a high-carbon alloy having a nunimum ) 1eld stress of
the posts as closely as practical to the "node'' points forrn1:d by the runner-bearer connections. 50,000 psi with a corresponding ultimate stress of over 75,000 psi. The higher carbon ste.:l ts
Another imponant structural clement is the building tic which connects the scalfold to the wall generally preferred because its lower ductilit)' and g1eatcr rigidity make it more resistant to
or structure and is needed to provide rigidity and w1chorage of the scaffold in the transverse damaging and bending of the members and because 1t has greater strength.
direction. Scaffolds need to be laterally supponcd; otherwise, they arc unstable: because of their Underpinning
height-to-width ratio and have low strength to resist wind and other lateral forces. Underpinning is the installation oftempordf)' or pemumcnt support to an existing foundation to
provide .:ither additional depth or an increa.,;e m bearing capacit) Then: ar~ SC\"eral existmg

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/ 2406: FOUNDATION ENGINEERING I LECTURE NOTES ECE 2406: FOUNDATION ENGINEERJNG I

. . d is transferred from the w ucturc into the pile through a steel

conditions wl11ch may lead to the need for underpinning. They arc: Jean sand-cement mix . fhc Joa . ' f 1 plates wedge~, and drypack 1~
✓ Construction of a
✓
· Wll· h a decper foundation adjacent to an existing building
new proJcct bracket welded to the side of the pile. A comb1nauon o s1cc ,
Settlement of an existing structure . Ii11 b the structure and the bracket
installed to ensure a tight etwccn_ . 10
two stones high, depending on
✓ Change in use of a structure This type of underpinning can be uulized for :trluct~rcs l~p material at suhgradc or the new
✓ Addnion of a basement below an existing structure the weight of the building and the quality o 11e ; gb . the e~i~1mg structure Die
SettIemcnt of existing
· · structures m · many cases is caused by lowering of the waler table due to structure. The spacing oftl1c piles depends on the load istn uiion m
tidal Ouctuations, wells for a water district, etc. This lowering of the water table can cause Ilic maximum spacing should not exceed 8 feel.
lops of timber piles to decay over time and will require remedial underpinning. With certain
Ground Water Dewalering . . • . below groundwater level.
soil profiles, nsing of the water table can effect a decrease in bearing capacity of the soil causing Many civil engineering or smaller proJects involve excavations . I . I. d
seulemcnt and require underpinning. Construction of structures on unsuitable bearing material Dewalering is a term to describe the removal of groundwater from wlll11n a soi mate~a /n
0
or over compressible layer (peat, organic silts, or poorly compacted backfill) may cause is carried oul 10 ensure excavations arc undertaken in dry and stable conditions The _n s _ nol
settlement controlling groundwater can have catastrophic cfTccts by groundwater ingress and ui.-.tabilny.
or excessive groundwater pore pressures resulting in heave or quick cond1t1ons
Ddtrmining the need for underpinning
Underpinning is the direct support of an existing building foundation. fl provides the Construction Dew>1tering is a common lcnn used to describe the 1cmporary lowering of
opportunity to preload (i.e., jacking) to limit settlement and improve poor foundations. When a groundwater level within an aquifer or dcpressurising a sub-artesian or 11rtcsi:rn hud.
structure stans showing signs of settlement or distress, it is of utmost importance lo precisely
monitor the seltlcmcnt or movement by a professional on a daily, weekl y, or monthly basis, Permanent Dewatcring covers 1hc installation of continuing groundwater control system.
depending on the severity of the movements. Plotting these readings will indicate if the Ground conditions and objectives d1cta1c dewntcring rcquircmcnL~ and appropriate method can
movements arc decreasing or increasing, and by analyzing the resulls, a decision can be made be dc1cm1ined by pumping testings. The dewatcring mechanism can encompass gravity
whether or not underpinning (or other measures) arc required lo safeguard the structure. drainage such as deepwells using submersible borehole pumps or applying a vacuum to a soil
malerial using ejectors or vacuum wellpoinl systems.
Prior to the Sl311 of excavation for a new structure, it is advisable to have a professional examine
all structures in close proximity to the construction site, to determine whether or nol A deep well typically consists of a borehole fitted with a sloued Iiner aml an electric submersible
undcrpmnmg 1s necessary. pump. As water is pumped from a deep well, a hydraulic gradient 1s formed and waler nows
inlo 1he well fanning a cone of depression around the well in which there is little or no wa1er
underpinning Mtlhod~ remaining in the pore spaces of the surrounding soil.
Temponary ~upport with Maintenance .Jacking
Light structures (for example, wood-frame garages) that fall within the innucncc line of the Deep wells work best in soils with specific permeability profiles with the amount of drawdown
adjacent excavation and which do not warrant the expense of an underpinning installation may that a well can achieve is limited only by the size of the pump. Deep Wells arc typically drilled
me supported on timber or concrete mats. using cable percussive or rotary drilling methods, lenninating typically ma 300mm or 250nun
ff settlement occurs, the structure will be kepi al the same level by means of mechanical or bore.
hydraulic jacl(j At completion of the work in the adjacent lot, the jacks arc replaced with short
steel columns, and the void is filled with concrete. Wcllpoin1ing or v:truu m wcllpuinls arc ,t very versatile and economic method of groundwater
Sttp J: Shore existing construction, excavate approach pit, and expose existing timber piles. conlrol and have an advan1agc of being installed relatively qui,kly and at close ccnlrL'S arc very
Remove top ponion of the piles and cul piles al new cut-off elevation. cflcctivc in fine grained or stratified soils. Well points consist of small diameter tubes with a
Step 2: Install , t~ I plates, drypack, and wedging &trul Transfer load into pile by means of steel lillcr intake at the bottom, they arc typically installed around the perimeter of an excavation or
wcdgci parallel lo a pipeline by jetting or auguring techniques. Varnum and Oow is generated by a
Sttp l: Placcmt-nl of concrete encasement, backfill approach pit. dcwatering pump, which in turn limits drawdown lo - 5-6111 dqith For greater depths a second
stugc wellpoinling system can be installed at a lower level. l'roject D<•Wal.-rin,: can olTer
IJndtrpinning Method, - Hracktl Pile Underpinning stainless steel 'scll~jetting' wcllpoin1s as wdl as conve1t1ional disposable ,1cllpoints
When btJrh the cxi~ting and future struclUres belong lo the same owner, the use of brnckel piles
i1 very ce<mom,cal (mo, 1municipal huilding codes do nol allow a building to be supported on Ejcclors or E1luclors urc very cITcct in soils oflow to medium permeability where the pump in~
the founrlalion that is located on iomconc elSc'~ property). The steel bruckct pile~ ore driven or waler level is too deep for wcllpoints but yields too small 10 allow the use of a electric
placed ..i!Jil«nt IJJ the luturc Nfructurc in pre-augured hole~ which urc lhen backfilled with a suhmcrsihlc borehole pump. Ej1·1·tors arc commonly used up to deptl1s of5(hn. can run at times

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 . vu . , u. ' i 1vN l::l'-11..il.NEERING I
LECTURE NOTES LECf URE NOTES
ECE 2406: FOUNDATION ENGINEERlNG I

of zero water entry into the well d .f

efficiency an I scaled can generate a vacuum in the ,veil I . Interior basement waterproofing systems should be prepared to work m the case of a power
· o increase
outage, the failure of a sump pump, and in the face of overwhelming torrential ram. A proper
Basement Dewatering sump pump, backup sump and/or battery backup sump pump should be installed in a large sump
Basement dewatering d pit with an airtight lid for safety and to keep humidity from seeping through to the basement
an waterproofing refers to techni
from entering the basement of h ques used to remove and prevent water environment, where it can promote mold growth. This ainight practice will also reduce the
a ouse or other commerc· 1 b •td·
waterproofing will include both dr . ia ui mg. Effective below -ground possibility of dangerous radon gases for entering the living space. Despite widespread sump
amage and sealers
Waterproofing is needed anytime a structu . . . pump failures, top-of-the-line sump pump systems are more reliable than ever.
W aterproofino and drain .d . re is built at ground level or below ground. Exterior Waterproofing
" age cons1 erations are especiall d d.
is Iikely to build · h . Y nee e m cases where ground water Exterior waterproofing prevents wate r from entering foundation walls therefore preventing the
up m t e soil and raise th I bl • -
hydrostatic pressure to be exe e wa er la e . This higher water table causes wicking and moulding of building materials. Waterproofing a structure from the exterior is the
Hydrostatic pressure ~ rted underneath basement floors !l!ld against basement walls. only method the IBC (International Building Code) recognises as adequate to prevent structural
ca d b . orces water m through cracks m foundation walls through openings
era:: J :l)ans'.on and contraction of the footing-foundation wall joint a:id up through floor
· . Y OSlattc pressure can cause maJor structural damage to foundation walls and is likely
damage caused by water intrusion. Prior to the l 980's much of the original exterior
waterproofing was actually damp-proofing using a degradable asphalt-based covering. Today,
however, Polymer products will completely waterproof an exterior foundation wall. This
to contnbute to mould, decay and other moisture-related problems.
material has a half-life in the thousands of years which makes it ideal for a long term exterior
Methodologies waterproofing solution. Asphalt and tar based compounds are affected by soil pH. and break
down after 10-20 years, thus making that type of waterproofing ineffective over time.
The three _measures developed to prevent this problem differ greatly in ideology and design.
Polymer-based compounds
Th~ first is mtenor wall and floor scaling, with the other two methods being interior water
Over the past ten years, polymer-based waterproofing products have been developed. Polymer
drainage and exterior drainage combined with waterproofing coatings.
Interior Sealants based products last for the lifetime of the building, and are not affected by soil pH. Polymer
based waterproofing also has the advantage of a low enough viscosity that it can be sprayed
Interior sealers will not provide permanent protection from water infiltration where hydrostatic
directly onto a wall.
pressure is present_ Interior sealers are good for preventing high atmospheric humidity inside
the basement, from absorbing into the porous masonry and 10 prevent spalling. Spalling is a
condition where constant high humidity or moisture break down masonry surfaces causing
deterioration and shedding of the concrete surfaces.
Interior water drainage
Although interior water drainage is not technically waterproofing, it is a widely accepted
technique in mitigating basement water and is generally referred to as a basement dewatering
solution. They function by draining underground water from alongside the foundation footers
and underneath the basement floor. They then channel it with a French drain, PVC pipe, or
through a patented product to a sump pump system, which will then pump the water from the
basement. Foundation sump pumps are best installed by a professional dewatering contractor
to ensure maximum effectiveness and project reliability.
ln a simplified model, the following would occur:
1) Water enters the home via the basement wall/floor joint, through cracks in the
foundation walls and/or holes created by faulty or decaying masonry/brick.
2) A perimeter trench drain such as a French drain collects the water before it enters into
the basement.
3) Wall vapour barriers/retarders and drip mouldings are used and incorporated into the
subslab perimeter drain to collect water coming from wall cracks and other foundation
wall defects, such as pipe protrusions.
4) The drain directs the water to a sump pump.
5) The sump pump directs the water out of the house.

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