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PAGE
CONTENTS
ACKNOWLEDGEMENT
CHAPTER 1
1. INTRODUCTION 012. MANAGEMENT 023. ORGANISATION AND ORGANISATION CHART 03
CHAPTER 2
2.1 DEMAND MANAGEMENT 04
2.2 DISTRIBUTION SYSTEMS 06
2.3 TESTING WATER DISTRIBUTION SYSTEM 07
2.4 PRESSURE MEASURING DEVICES 08
CHAPTET 3
3.1 WATER RETAINING STRUCTURES 06
3.2 CONSTRUCTION JOINTS 06
3.3 CONCRETE TESTINGS DONE AT SITE 10
CHAPTER 4
4.1 FORMWORK 11
4.1.1 CHARACTERISTICS OF GOOD FORMWORK 11
4.1.2 MATERIALS FOR FORMWORK 12
4.1.2.2 TIMBER FORM WORK 12
4.1.3 TOOLS USED FOR FORMWORK 12
4.1.4 COVER BLOCKS 12
4.1.5 REMOVABILITY AND STRIKING 13
4.1.6 MAINTENANCE AND STORAGE OF FORMWORK 13
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4.2 TYPES OF FORMWORK 14
4.2.1 COLUMN FORMWORK 14
4.2.1.1 PLUMBING THE COLUMN 14
4.2.1.2 KICKER FORMWORK 14
4.2.2 BEAM FORMWORK 15
4.2.3 FORMWORK FOR STAIR CASE 15
CHAPTER 5
5.1 REINFORCEMENT 16
5.2 CONCRETING 17
CHAPTER 6
6 CONTROL AND SAFETY AT THE SITE 19
CHAPTER 7
PRACTICAL DIFFICULTIES ENCOUNTERED 19
CONSLUSION 19
ACKNOWLEDGEMENT
I would like to convey my special thank to all officers in National watersupply and drainage board (NWSDB), Town south office, Piliyandala and
Beijing municipal corporation (BMEC). Also I thank to the Industrial
Training Division of the faculty of engineering, University of Peradeniya andNational Apprentice and Industrial Training Authority.
Chapter 1
1.1 INTRODUCTION
The B.Sc. engineering undergraduates are employed for the industrial trainingafter first and third academic years. It is carried out by the Industrial Training
Division of the university under the approval of National Apprentice andIndustrial Training Authority. The training period is about 3 months. All thetraining appointments were handled by director training division at Telawela
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office (at Ratmalana). According to my preference they asked me to go to the
Town south office at Piliyandala. Project manager at Piliyandala appointed mefor Athurugiriya - Hokkandara worksite on 31stSeptember. Until that, for
about one week I was at Piliyandala site.
At Piliyandala site pipe laying work was being done at that time (mainly atBokkundara and Borelesgamuwa) and some finishing works at Miriswatawater tower. From Piliyandala office I gathered more information about Town
south project. Following organization chart describes the town south office
structure under the project manager.
Town south of Colombo water supply project has 2 main categories. They are,
1. On- going
2. Extension
Under the first one 4 sub projects, i.e. Homagama, Kesbewa main, Kesbewa
sub and Keselwatte were carried out. Similarly under extension project there
are 5 subprojects, i.e. Mattegoda, Hokkandara, Athurugiriya, Madapatha and
Godagama. My site comes under these extension projects.
Contract for principal civil works for those projects was awarded to Beijing
Municipal Corporation (BMEC) of China on 29th March 99 and expected to befinished about December 2000.
Design of mechanical & electrical works is being carried out by NWSDB.
Consultancy services for both projects are provided by the Nippon JogesuidoSekki of Japan in association with Parson engineering science of Pasadena,California of U.S.A. . Supervision and design of these sub projects were done
by NWSDB. However consultants were doing supervision work most of thetimes as its their duty to check the construction was according to the design.
Athurugiriya project comprises of a 920m3ground reservoir, 1000m3elevated
tower/tank (30m height) 9km long transmission main, a distribution network
of pipelines 28km in length, pumping station and ancillary facilities (underdesign). Treated water for the project is obtained by tapping the Labugama
transmission main. The design capacity is 4300m3/day and the total
population to be served by the design year of 2018 will be around 12500.
Hokkandara project comprises of 920m3ground reservoir 1000m3elevatedtower, 4.5m long transmission main, a distribution network of pipe line 15km.
In length, pumping station, and ancillary facilities (under design). Treatedwater for the project is obtained by tapping the Ambatale Jubilee-Batteramulla
transmission main. The design capacity is 6200m3/day and the total
population to be served by the design year of 2018 will be around 33000.
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During my training periods time most probably only pump house work and
tower work will be only carried out according to the work schedule. Mr.Thavandra kumar was the site engineer for both Athurugiriya and
Hokkandara. Mr. Mohan was Structural engineer for these sites (overall incharge).
1.2 Management
I) National water supply and drainage board (NWSDB)
Since NWSDB is a semi governmental organization, board of directors
managed it. Next to them a chairman and a general manager will be there and
balance follows as in the organization chart given above.
II) Beijing municipal engineering corporation (BMEC)
Similarly BMEC also have much similar management hierarchy. Site engineer
for this project by BMEC was Mr.Lieu(A Chinese engineer) .
III) General
NWSDB is the client for this project and BMEC is carries out the construction
works. In other words BMEC was paid by NWSDB under the contracts terms.Contract was offered by NWSDB by calling a tender world wide, and BMEC
offered the lowest cost for above specified projects.
Site office at Athurugiriya was facilitated (an air-conditioned container box
with necessary furniture). There were about 30 laborers employed by BMEC.
1.3 ORGANISATION
NWSDB comes under Ministry of urban development, housing andconstruction responsible for large development projects and system operation
and maintenance in the provision of water supply for domestic and industrial
uses. Co-ordinate rural water supply projects with the involvement of CBOsand local authorities. The National water supply and drainage board act
describes the statutory duty of the NWSDB to provide water supply for
public, domestic and industrial purposes. This is taken as right on the part of
the NWSDB to divert and use water for its purposes without other approval.The act administered by the NWSDB.
Chapter 2
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2.1 Demand management
Demand management involves measures to encourage the conservation ofwater by reducing water use, obtaining higher value of production from the
unit of water used and preventing losses and wastage. Saving andconservation of water in one sector not only reduce the financial burden on thesociety by delaying or foregoing new investment, but also provide water forother productive uses. Demand management covers surface water as well as
groundwater. Lower water usage and extraction implies an increase in water
for in stream uses. This can result in additional benefits to fisheries, tourismand other non-consumptive uses. Maintenance of minimum in-stream flows
could be important for both commercial fishery production and for protectionof indigenous fish species and other forms of bio-diversity. It will promote
recreational activities like fishing and swimming, help to protect sensitive
aquatic eco-systems and improve water quality through maintenance ofgreater pollution assimilative capacity.
Demand management consists of a wide range of activities carried out by
various agencies across a number of sectors. Recovery of water resource
management costs at the basin level is not carried out. Water service fees arecharged in the water supply sector for customers with piped water service.
Development of a cost recovery or cost sharing policy, applying to both waterresource management costs and co-ordination with sectoral cost recovery, is a
high priority, which is now being investigated by the water resources
secretariat.
Infrastructure rehabilitation is an important means of reducing water losses. In
urban systems rehabilitation for reduction of non-revenue water is important.
Water metering is another important demand management tool. Most
NWSDB consumers are metered and pay for water on a volume basis. In theirrigation sector water deliveries are controlled using gates and other devices.There is generally no control on the water used by the individual farmer, other
than availability of flow, and there is no system for labour or charges onvolume used.
NWSDB conducts school and general public awareness programs regarding
the value of water. It also has formed water consumer societies to reducewater losses through standpipe connections.
All of these activities fall under various legal mandates for NWSDB. In mostcases demand management is a sectoral water management activity since, by
definition, demand occurs "downstream" of the point of diversion from
natural water bodies.
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2.2 Distribution system
Water is distributed to consumers in several different ways, as local conditionsor other considerations may dictate. The methods are :
i. Gravity distributionThis is possible when the source of supply is alake or impounding reservoir at some elevation above the city so that
sufficient pressure can be maintained in the mains.
ii. By pumping with storage - This is the most common method generallyused in practice. In this method the excess of water pumped during
periods of low consumption is stored in elevated tanks. During periodsof low consumption is stored in elevated tanks. This what our sites
construction purpose.iii. Direct pumpingIn this method pumps are used for supplying water
without any storage. The water is forced into the main and then toconsumers. It is the least desirable method.
2.2.1 Pipe laying
At Bokkundara site that is on the Borelesgamuwa Piliyandala Rd., some pipelaying
works was done.
Fig 02: 250VJFA connector
2.2.2 Valves in pipe line
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The importance of valves in pipe line should not be forgotten. Depending on
different situations and requirements, different types of valves are used. Someof the commonly used aresluice valves,
Sluice valvesThese are also known as gate valves and used to control the
flow of water through pipes. They facilitate the repair work in any portion ofthe distribution system.
Glove valveThis valve has a flatdisc which is parrallel to the flow directionand its seat is also parallel. Change in direction of flow through this valve
causes a rather high head loss. This valve is used in small sizes in buildingdistribution systems.
Pipe laying contract was awarded to sub contractors KDA Weerasinha andCo. Ltd. By BMEC according to the technical specification standard symbols
were used to denote specific parts as follows.
Fig 03: Standard symbols
2.3 Testing water distribution system
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Field hydrostatic pressure testing (AWWA C600) was also done at
Borelesgamuwa. All pipe line shall be thoroughly flushed out with water priorto testing , except that any pipe line having concrete thrust blocks shall be
thoroughly flushed out with water prior to testing, except that any pipe linehaving concrete thrust blocks shall be filled with water until a curing period of
at least 7days. Pipeline should be filled slowly left under working pressure for
about 24hrs.
After a pipe line has been laid, fitted with all appurtenances and accessories
painted both from inside as wellas outside by means of protective paints, etc;the pipe line will be tested for the soundness in its construction. The step by
step procedure adopted for testing pipes is described below:
1. The pipe line is tested from section section , thus at a time, only one
particular section lying between 2 sluice valves is taken up for testing2. The down stream sluice valve is closed and water is admitted into the
pipe through the upstream sluice valve. The air valves will be operatedproperly during filling up of the pipe.
3. The up stream valve, through which water was admitted is closed, so asto completely isolate the pipe section from the rest of the pipe.
4. Pressure gages are then fitted along the length of the pipe section atsuitable intervals (say 1km or so) on the crown, through holes left forthis purpose.
5. The pipe section is the connected to the delivery side of a pump
through a small by-pass valve, and the pump is started, so as to developpressure in the pipe. The operation is continued till the pressure insidethe pipe reaches the designed value, which can be read from the
pressure gages fixed on the pipe.
6. The by-pass vave in the closed, and the pump dis-continued7. The pipe is thus kept under pressure for 24 hrs, and inspected for
possible defects, leakage at joints, etc. This completes the pressure test.The pipe is finally emptied through, drain valves, and the observed
defects are rectified, so as to make the line fit for use. The pipe is again
tested by repeating the test, inorder to ensure proper rectification ofdefects, already done.
2.4 Pressure measuring devices
Since water needs to be delivered with adequate pressure, pressure measuringdevices are essential . Hydrostatic testing, similar to that performed when new
pipe is installed, can also be used test existing water systems. Kocol(1972)
and McPherson(1983) described use of these tests in Milwauke and
Rochester, and reported that the tests enabled them to find weak sections of
pipe and leaks by subjecting the pipe to high pressures(300 psi). This type oftesting can only be done in areas with few customers, as all service
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connections must be closed before repair crews are on hand is highly preferred
to having main fail at 3a.m on Saturday. This test can be helpful in detectinglarge leaks which enter sewers. Such water may, however indication of
infiltration of ground water.
Chapter 3
3.1 Water retaining structures
Water retaining structures are structures which are required to contain, orexclude, any or non aggressive aqueous liquid. Common structures of this
type include water towers and reservoirs storage tanks including sewage
disposal and treatment systems, and floors and walls of basements and otherunderground constructions where it is necessary to prevent ingress of
groundwater.
As it is important to restrain cracking so that leakages do not take place thedesign is generally governed by the requirements of the serviceability limitstate, but stability considerations are particularly important and design must
take careful account of the construction methods to be used.BS8007 gives the
guidance on design and construction of these water retaining structures based
on the limit state philosophy embodied in BS8110.
BS8007 recommends some modification to BS8110. They are
a. Use of f= 1.4 for liquid loads.b. Use of concrete grade 35c. Exposure classification of internal members(within water) and
recommends a minimum cover of 40mm.d. Maximum crack width limited to 0.2mm unless the aesthetic
appearance is critical, when 0.1 mm is required to avoid staining of
concrete.e. Maximum bar spacing of 300mm.f. Anchorage bond stresses for straight horiontal bars in sections
subjected to direct tesion must be reduced to70 per cent of the usual
values.g. At least 75mm blinding concrete is required below ground slabs.
3.2 Construction joints
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All concrete structures must inevitably contain joints, although the need for
joints to accommodate movement in water retaining structures is governed bythe likelihood of, and need to restrict, unacceptable cracking principally due to
shrinkage and thermal movements. Frequently it may be possible to combinethe two categories of joint.
Principal characteristics of jointsare4 that they must be watertight, and in thecase of movement joints must also permit repeated movements to take place
as freely as possible. Water bars will be generally incorporated, either the
surface type in slabs, or commonly the centre bulb type in walls. These mustbe held effectively in position during concreting, while allowing good
compaction of the concrete to be still possible. Such water bars mustfurthermore be able to accommodate anticipated movement without tearing,
and with stand considerable pressure.
All movement joints must be sealed with a flexible compound which
effectively is watertight and also prevents dust and grit from entering and thusblocking the joint. Jointing materials must be durable under the condition of
exposure to which they may be subjected, but routine replacement is likely tobe necessary.
construction joints, contraction and expansion joints are possible source ofwater leakage if not made water-tight. Therefore, any such joint coming underwater should be provided
Fig 04: Construction joint
with a suitable water stop (bar). Common water bars may be classified in three
categories metal, rubber and mastic types.
Construction joint is defined as a joint in the concrete introduced, for
convenience in construction at which special measures are taken to achievesubsequent continuity without provision for any relative movement.
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As per the technical specification manual, It was stressed that the contractor
(BMEC) should submit to the engineer(water board representative),construction joints should be located as not to impair the structural strength of
the completed structure.
3.3 Concrete testing done at the site
All the testing of concrete was done according to BS1881: part 2: 1970published in 1989 amended on 1983. This also complies with ISO4109.
For different levels of workability different methods were handled to evaluate
Workability Method
Very low Vebe time
low Vebe time, compacting factor
high Compacting factor, slump flow
Very high Flow
Table 01: Workability test methods
There are no unique relationships between the values yielded in 4 test.
International construction consortium (ICC) supplies all the concrete mix.
Allowed slump range was 8-12cm; even though there are 3 types of slump,top value was taken. Three types slumps are,
a. True slumpb. Shear slumpc. Collapse slump
Stringent quality control ensures have taken by BMEC. Check list anddetailing of concreting was filled out and checked by NWSDB representative.Checklist was prepared by Lieu(BMEC site engineer) and detailing of
concreting form was filled by Mr.Hikkandra. Cube test done for 7 day and 28day at Malabe lab.
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Chapter 4
4.1 Formwork
Formwork is a mould or a box, temporary support to pre-cast or insitu
concrete structures. It holds the concrete and finally set to the inner profile ofthe structure. So the inner profile must be fit to the required shape and
dimensions. The Formwork should be supported until it curves sufficiently tobecome self-supporting.
The Formwork includes the actual material in contact with the concrete (form
face) and all the necessary associated supporting structure.
4.1.1 Characteristics of good Formwork
To successfully carry out its functions formwork must achieve a balance ofthe following requirements.
1. It should be sufficient in strength to support the weight of wet concreteplaced on it, the weight of workers and their equipments, the force ofvibration and the force of wind and rain.
2. It must have sufficient tight joints to prevent loosing of grout because
grout leakage cause honeycombing of the surface.3. It should be built in such a way that it can be easily removed and stripafter concreting.
4. It should be capable of being re-used. To ensure this, the formworkmay be coated with oil to permit easy striking off and it should be clean
before storing immediately after striking
4.1.2 Materials for formwork
Various factors should be concerned when selecting a material for formwork
1. It must be durable material because it should be able to re-use severaltimes. As such it is economical.
2. The material should be impervious to water to prevent loss of waterfrom the face of the formwork.
3. It should be able to form the desired shape and easy to handle4. Material surface should be even and free from knots because fair face is
important.
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Normally, formwork is made in timber, plywood or metal.
4.1.2.1 Metal formworkMetal formwork has a very high reuse potential. So it is more economical than
timber where repetitive work is necessary. In these all four subprojectsdimensions are somewhat exactly same. Therefore most of formworks are
metal formworks. However it should be handled correctly and thoroughlycleaned, oiled and maintained after each use. It gives smooth concrete finish.
Metal formwork is made up from spatially made shallow rectangular pans ofvarious sizes. These are clipped or bolted together to form the required shapes.The main disadvantage is rusts under humid condition.
4.1.2.2 Timber Formwork
Timber is the most commonly used material for general formwork because it
is easy to cut in to shapes, fix and dismantle and cheap. Timber formwork is
usually made from softwood free from excessive knots and other defects.
A problem some times caused by the timber formwork is the rapid absorption
of the moisture from the concrete.
So before concrete is placed timber should wet. Therefore moisture will not be
absorbed too fast from the wet concrete. But timber should not be too wet
because the timber with high moisture content will shrink which may resultopen joints and leakage of grout. If the timber is dry it will absorb the
moisture from the wet concrete which could weaken the resultant concrete
member.
4.1.2.2.1 Plywood formwork
Thick plywood, which is, smooth, fairly rigid and in large sizes is most
suitable for formwork. The advantage of using plywood in formwork is that itgives a good surface finish. Therefore it does not require any further
treatment. Plywood formwork can be used many times and easy to handle. But
Plywood formwork can be used many times and easy to handle. But Plywoodsheets are very expensive. Curved formwork is most satisfactorily constructed
by forming plywood to the required curve and fixing it to a rigid timber frame.
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4.1.5 Tools used for formwork
1. Hammers2. Plumbob
3. Chisel4. Hacksaw5. Try square6. Ruler and tape
4.1.6 Cover blocks
Cover block is a small block of cement with blinding wire in middle. It helpsto maintain the right amount of concrete cover during construction. Theyshould be made to the thickness of the clear cover required for the job.
After the reinforcement are set, the cover blocks should be tied to the outer
bars from all sides i.e. cover blocks should be placed between thereinforcements and the formwork. Cover blocks also help to keep the bars in
position when concreting.
It is very important to check the cover blocks before starting concreting.
Generally 1:2 mix proportions should be used for cover blocks. Because highstrength is required as concrete. But in the site, 1:3 mix proportions of mortar
was used. Cover blocks should be cured on time to gain the required strength.
4.1.7Removability and striking
Forms may have to remain undistributed until the concrete reaches a
minimum strength until it is sufficiently cured, of the required colour or toprotect it. Formworks should be struck slowly and must not be struck untilconcrete is strong enough to self-supporting because edges can be damaged.
The appropriate time at which it is safe to remove the formwork depends on
the type of element. The minimum striking time varies from 1-28 days.
Location Minimum
period
Sides of the slab and
staircase01 day
Sides of the walls and
beams
03 days
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Soffit of beam and lintels 14 days
Soffit of the slab and staircase
21 days
Table 02: Formwork strikability periods
But striking time vary according to
1. Weather conditions2. Type, size, shape, and position of the element in the structure3. Guidance given in the B.O.Q.
4.1.8 Maintenance and storage of formwork
Provision must be made for the removal and storage large sections of
formwork. A level storage area is required to store formwork after striking.They should be well cleaned before storing because the grout remaining on
the forms become hard and stubborn. Then it is difficult to reuse. Metal panels
need a light coating of oil before storage to prevent rust.
All forms need to be carefully stacked and stored. Panels of forms should bekept horizontal and face to face. The forms need to be carefully stacked and
face to face. The forms and components should be clearly marked and kepttogether for easy identification on re-use. A tidy store reduces wastage,damage and losses.
4.2 Types of formwork
Formwork is used for beams, Staircases, Slabs, Columns, Lintels, drains,Retaining walls and etc. When striking formwork of all types of works said
above should strike slowly and must not be struck until concrete is strongenough to be self-supporting. Because edges can be damaged.
4.2.1 Column formwork
Column formwork is a vertical mould assembled by boards as shown on
figure. It is also called as column box. Usually vertical boards are 25mmthick. The widths of the boards vary depending on the section of the column.
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The boards internal dimensions should be equal to the external dimensions of
the column. Timber or steel struts can be used as supports. The struts shouldbe able to resist the vibration and pressure of casting.
The side of the box are secured firmly together by using tie-bolts. Tie-bolts
are rods of about 6mm diameter, which hold the formwork in place. The endsof the rods are treated, so that the work can be steadily secured by using nuts.Important to remember to check whether the required dimensions are in the
inner profile of the column box, after plumbing and align the formwork.
Formwork should be located against a Kicker. Concrete specification forcolumn is usually 1:2:4(3/4") with a clear cover of 50 mm.
4.2.1.1Plumbing the column
The most important thing is plumbing the column in both directions. Inwooden formwork, two batons are fixed to both top and bottom ends of the
formwork. So suspending a plumbob from a baton at top to the bottom does
this. Adjustments could be done by the props should be adjusted until thedistance between form and line at top and bottom are equal. After that using
the try square should check the angles of the formwork. The plumbing shouldalso repeat to the adjacent edge. Finally all the props should be checked for
tightness.
Immediately after the concrete is poured, the column should be checked forplumb and carefully adjusted if necessary.
4.2.1.2 Kicker formwork
Kicker is a 3" height wooden frame as shown in figure. It should be made to
the dimensions of the column.
Before set the kickers first mark the centre of the column and draw two cross
lines through centre point of the column. Then mark the centres of the foursides of kicker formwork by nails and tie two crosses strings and find out the
centre of the kicker formwork. After that coincide the formwork centre with
the column centre by helping the two cross lines marked earlier. At the correctposition fix the formwork to column reinforcements by wooden pieces as
shown in figure.
Laying kicker is essential to ensure accuracy of the column and prevent
loosening of grout from the bottom edge of the form. It also acts as an
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anchorage against up thrust for the column shuttering. Kicker formwork
should be removed before column box is set.
4.2.2 Beam formwork
A beam formwork consists of a three sided box which is supported by cross
members and which are propped to the under side of the soffit board. Thestrength of the soffit board should be greater than the strength of two
sideboards. In some cases the beam formwork is prepared separately to fit the
each beam length and fix the beam formwork by bamboo props.
In our site using two strings, which fixed to the columns, aligns formwork.
First mark the height to the beam from the floor, on the columns and the propsare adjusted to that height. Then two runners are fixed in between the twocolumns. After that short runners are fixed (nailed) on the runners,
perpendicularly with 4 spacing. Then two string are tied leaving the beam
width in between them, between the two columns and the soffit board is fixedon the short runners with helping the strings. Finally the two sideboards arefixed and supported as shown on figure.
4.2.3 Formwork for stairs
A stair case provides a link between floors in building s. It should constructedto provide, easy comfortable and safe access up and down with steps that arenot difficult to climb.
When constructing formwork for stairs, the landing is first set in position.
After the landing is fixed two strings are tied between the landing and theground (upper) floor. Those two strings should maintain the width and the
inclination of the flight. Then joists (2x4 timber batons) place the soffit board
underneath and the props are nailed to the joists.
The sideboards are set in positions. On the sideboards the step height is
marked leaving the waist thickness from the baton by using strings. After that
marks the going & risers in between the two lines by using chalk and trysquare and riser boards are nailed to the sideboards by supporting hangers.
The splayed bottom edges of riser boards are nailed to the sideboards by
supporting hangers. The splayed bottom edge of riser boards help to completetrowelling of the tread surfaces and to make sure that air is not trapped underthe bottom edge of riser boards. The riser boards are supported by struts to
prevent the sideboards from falling apart when concrete is poured or due to
vibration.
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Chapter 5
5.1 Reinforcement
Steel reinforcement material requirements
1. Tensile strength2. Easy to bent up to any required shape3. Effect to temperature changes
Therefore steel is the most suitable 3 basic types of steel bars,
1. High yield (torque steel) which has ribbed appearance and may betwisted tensile strength of 450N/mm2. In drawing normally denoted as
Y.
Bar bending was according to design requirement by a group of labourers whowere specialised in bar bending. Main source material, i.e. Steel is Steel
Corporation of Srilanka. To bend the bars steel pipes were used and to cut a
electric cutter and some times manual cutters were used for small diameterbars. For base of bending normally following simple shapes are used.
1. Straight2. Right angle bend3. Cranked4. Stirrups
In addition to these simple shapes BS4466 shapes are also used.
5.2 Foundation
Foundation is a part of a structure which transmits loads directly to theunderlying soil.If the soil near the surface is capable of adequately supportingthe structural load it is possible to use either footings or a raft.A footing is a
relatively small slab giving separate support to the structure.
Depending on the transmission of forces , foundations can be classified intotwo:
1. Shallow foundationstermed footings, spread footings, or mats.Foundation depth is generally D < B
2. Deep foundations - piles or caissons with D > 4 to 5B
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Foundation types and typical usage
Foundation type Use Applicable soil conditions
Spread footing,
wall footings
Individual columns,
walls bridge piers
Any conditions where bearing capacity is
adequate for applied load. May use onsingle stratum: Firm layer over soft layer or
soft layer over firm layer.
Mat Foundation Same as spread and
wall footings. Very
heavy column loads.
Usually reduces
differential
settlements and total
settlement
Generally soil bearing value is less than for
spread footings; Over one-half area of
building covered by individual footings.
Check settlements
Pile foundations
floating
In groups (at least 2 )
to carry heavy
column, wall loads;
requires pile cap
Poor surface soils. Soils of high bearing
capacity 2050m below basement or
ground surface, but by distributing load
along pile shaft soil strength is adequate.
Corrosive soils may require use of timber or
concrete pile material.
Bearing In groups (at least 2)
to carry heavy
column, wall loads;
requires pile cap
Poor surface and near-surface soils; soil of
high bearing capacity (point bearing on) is
8-50m below ground surface
Caissons (shafts
75cm or more in
diameter)
generally bearing
or combination of
bearing and skin
resistance
Larger column loads
than for piles cap by
using caissons as
column extension
Poor surface and near-surface soils; soil of
high bearing capacity (point bearing on) is
8-50m below ground surface.
Retaining walls ,
bridge abutments
Permanent retaining
structure
Any type of soil, but a specified zone in
back of wall usually of controlled backfill
Sheet-pile
structures
Temporary retaining
structures as
excavations,
waterfront structures,
cofferdams
Any soil; waterfront structure may require
special alloy or corrosion protection.
Cofferdams require control of fill material.
Table 03: Foundation types
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In my site (Athurugiriya) 2 constructions were going on simultaneously.They
are
1. Pump house2. Elevated water tower(insitu)
In the following drawings I have illustrated their foundation details
Fig 05: Pump house front elevation
Following drawings represents the elevated tower base foundation details.
Following chart provides the information regarding the piles information.
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Fig 06 : Chart of pile configuration detail
However use of piles depends on several conditions as described in Table no03.And in the Athurugiriya site no piles were used.
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Fig 07: Elevated tower base details
Fig 08: Elevated tower base slab reinforcement details
5.2 Concreting
Splay area concreting:
For each part of construction BMEC will prepare a procedure detailing which
is called method statement. Method statement for splay area is asfollows.(summarised)
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Section elevation 44.10(T.B.M. 27.70)
Volume of 2parts 14m3,22m3 16mm steel cables were used hold the formworks. Distance between
steel cables 300mm
Splay area was covered with 24 pieces of plywood 10 X 10m timber
supported by the top screwed steel pipe
Works of second part done after 1st900mm high flat steel forms. In onesegment 24 groups and totalling 48 for both segments.
ICC will supply the grade 30 concrete with slump 8-12cm.
Temperature 32C
Tremie pipe always is within the form and allowed free fall is 1m. Thiscondition was maintained in order to prevent segregation.
Concreting will be worked circularly in order to maintain the level of
concreting. Mark of the level was marked with red colour anticorrosive,
which was used for maintenance of formworks. At each layer of circlewas maintained 30cm as the maximum.
For curing gunny bags were used.
Method statement of construction of bottom dome and conical section.
1. Bottom dome 900X400, 900X300, 900X200 steel shutters( connectedwith 48dia. Steel pipes)
2. About 48 trusses will be fixed kickerAn extended part of previouslyconnected structure(here it is 10cm)
3. 5 mixers will supply volume of concrete 48m3, and 2 pump trucks willbe used. Detailed drawings of the constructions are as follows,
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Fig 09: Elevated tower part sectional elevation
Fig 10: Elevated tower part sectional elevation
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Chapter 6
6.1 Control and safety at the site
Each item of work control and safety was carefully mentioned in the contractconditions book. It is also important to have a copy of this at each site office.
Office equipment and temporary office facilities such as air-conditionedcontainer box were supplied by BMEC (contractors). BMEC has the authority
to prevent the trespassing of unauthorised persons. Land was acquired byNWSDB from Steel Corporation. Wooden ladder (as a temporary measure)
was provided along the tower for inspection of engineer (clientNWSDB).
Nylon net was used to cover almost entire tower (even covering the scaffolds)in order to prevent the personals falling from the tower in the case of
accidents. Medical expense for the labourers in the case of accidents on thesite was covered by BMEC.
Labourers were categorised by the work they are specialised and handled byseparate Chinese Forman as follows,
1. Barbending labourers -10
2. Carpentry labourers -153. General labourers -5
Basic salary was 250 per day per labourer and overtime was 100/= per hour
per labourer. Since employeeemployer contract laws are not so handledstringently there are can be seen many time that these employers are abusing
the employees. One good example is that removal/cleaning collapsed
boundary wall. Where the boundary wall had some broken glass pieces.
Chapter 7
PRACTICAL DIFFICULTIES ENCOUNTERED
As the work is given to more and more sub-contractors, it becomesmore and more difficult for the executive engineer to control the work.
All brought-in items such as cement, sand, timber etc. must be
inspected carefully, as sub-standard items can be brought in to get moreprofit by the contractors.
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