and welcome once again to this series of lectures on the principles of construction management
and today we are at lecture seven where we will be talking about description of the items
so in the last class we had talked about finding out the quantities of different items in fact
previous to that we had identified the quantities and then we talked about how to find out the
quantities involved in the construction of a simple boundary wall it involved excavation
it involved a little bit of pcc then brickwork some amount of concrete shuttering the enforcement
work and so on
so we had said that in order to be able to estimate the cost of the boundary wall which
was the primary objective we should know the items the quantities and the rates of those
items for example a cubic meter of earthwork how much its going to cost a cubic meter brickwork
whats going to cost and so on now in order to determine the cost involved we should know
a little bit more about the actual description of the item and the finer details therein
and those finer details is what we are going to talk about today with that is what is called
the description of items so when we describe an item then we actually
tell the contractor or a bidder as to well there is earthwork involved and these are
the conditions under which the earthwork is to be carried out so thats something which
we are going to do today and coming back to this estimates there is the quantity of individual
items thats what we have done last time there is the rates of these items the quantities
are estimated using the measurements as given in the drawing and then as far as rates are
concerned they could be estimated using standard rates or the rate analysis of individual items
we are going to talk about it a little later perhaps in the next discussion and it largely
depends on the description or specifications of the work to be carried out
so this is what is the thrust of our discussion today the description of the items comes to
the unit cost of an item largely depends on the specifications of the work the specifications
describe the nature scope materials execution details and so on the description should be
as clear as possible to avoid conflicts and we will see in the discussion today where
we need to be careful when describing an item generally the clauses of the description of
item is included in the boq that is a bill of quantity sheet and that should be written
more or less in the order in which the work is to be carried out
so now lets go back to the example that we were working on the construction activities
in the boundary wall project were excavation brickwork concreting including pcc and rcc
plastering reinforcement and there was a small item of structural steel and so on shuttering
was included and all that kind of stuff so now lets look at some of the aspects relating
to description of these items as it should appear in a typical bill of quantities sheet
now the first thing is earthworks so now this picture here shows the earthwork being carried
out at a technical site thats not necessarily the kind of site that we will work with when
you are doing a boundary wall but this is illustrative to the extent that we come to
see what are the things involved in the earthwork so there is a certain height which is involved
there is a certain area which has to be available the surplus earth which is generated here
will have to be removed and it will have to be dumped somewhere so how far is the dumping
ground from the site where the earthwork is being carried out sometimes when we carry
out an excavation it is required that this part here the sites should be properly supported
in order to ensure that they do not cave in either we support the sites like this or we
allow for a slope here so what we must remember is that for every cubic meter of earthwork
involved there is a certain cost associated with it
so now the drawing will tell you only the minimum amount of earthwork that is required
to be carried out what from a construction point of view we have to understand is how
much is the earthwork that is payable how much should we pay for so if this is the earthwork
which is required and the client agrees to that then this becomes payable if not the
contractor has to keep this earthwork in mind when bidding for this quantity of earthwork
alone so in either case one has to be aware of the issues involved under what conditions
what kind of a slope is required if its a hard strata or us soft strata and so on and
so forth now typically therefore the item description
for earthwork should include digging suitable foundation trench which supports if required
so whether it is a trench or not is a issue so in our kind of a construction of a boundary
wall yes there is a trench that is the earthwork is largely linear so there is a boundary wall
which is like going to go like this and whether it is one point three meters or whatever the
width is so this will be a one point three meter wide earthwork or trench will be dug
for twenty meters because if you recall we have our boundary wall is like twenty meters
and ten meters in these sides so there will be a large twenty meter trench which will
turn here and so on and so forth so now it should include the trench the earthwork
really involves removal of that earth from the portion which has been excavated finishing
and dewatering so finishing really means that depending on the kind of equipment that you
use for the earthwork it may not be possible to maintain this ground at a certain level
across the entire length so how earthwork is typically carried out is that in a crude
form you come to about this depth and then do this final lets say hundred mm or hundred
fifty mm through a more precise kind of earthwork so that is what you do to get this bottom
fixed and then we need to make sure that the earth is properly ramped or it is properly
compacted before the pcc is laid on the ground then there is this issue of dewatering depending
on how deep the excavation is and where is the water table there can be an issue of some
amount of water seeping into our earthwork and now whether this dewatering is to be included
as part of the description of earthwork or not is something which we have to decide if
we do not include it and there is dewatering that comes in the contractor would be free
to say that well the cost of dewatering is not included in the description and therefore
that becomes an extra item if it is included then we do not have to pay for dewatering
because thats part of the earthwork itself moving forward there will be a certain amount
of back filling its not necessary for example that all the earth that is removed will be
taken away see for example in our case what we did was we are going to excavate something
like this and create a wall which will look something like this
so what happens to this part this part will have to be backfilled so only this amount
of earth which is generated will need to be carted away so that is why we have this term
called disposal of surplus earth at a given location very often the surplus earth may
need to be disposed of at a distance which may be hundred meters or a kilometer away
from the site so the cost of carting this earth to that dump location has also to be
specified and accounted for in the description or the cost of the earthwork so that is what
is earthwork all about and therefore the description of an earthwork item could typically be earthwork
in excavation including dressing of sides and ramming of the bottoms dewatering providing
timber shoring if necessary with lift up to two meters including getting out the excavated
soil and disposal of surplus excavated soil as directed within a lead of two kilometers
so we are talking of a depth and we are talking of a lead among other things so this depth
can also be different so obviously if the depth of excavation increases or changes then
the unit cost of worth work will also change so we can have a situation where so we can
always have another item of worth work in a typical boq which would say same as above
but with a lift between two and five meters so what we are declaring is that if the lift
is between two meters and five meters what is the cost or we can have a situation where
same as above with a lead between two kilometers and five kilometers so the contractor knows
and he bids for the earthwork item depending on what are the kind of conditions that are
given in the boq let me also add a few other things which are highlighted in blue here
using hydraulic excavator we do not need to specify equipment when we are writing a boq
but sometimes we may do it when we say foundations in trenches now what we are saying here is
that the excavation is being carried out in a trench or in a drain where the width involved
is not necessarily very large the picture that was given to you right in the beginning
let me go back to that picture if we are excavating something like this so the calculation of
length versus breadth more into height will give you a certain amount of excavation as
far as quantities is concerned but if the area was not this large and the same amount
of excavation was to be carried out in a trench or a drain kind of a configuration then the
situation will be quite different so thats something which again we can include
in the description and thats whats being done here that in foundations or drains so if it
was a rough foundation we can say that its a rough foundation or its a foundation which
measures so much area and plan and so on and of course we have already talked about the
issues relating to dewatering so now moving forward what about brickwork so this picture
here shows brickwork being carried out we can see that it involves placing of bricks
in layers and we have what is called a bed joint and this joint is typically filled with
mortar so we need to specify what is the composition of this mortar what is the thickness of this
brick wall and sometimes we also may specify the strength of the masonry unit or we may
just specify the quality of the bricks and the composition of the mortar and assume that
the strength of the masonry unit will be automatically met
so now the brickwork description could include items such as the thickness of the wall proportion
of the mortar to be used in the bed joint the class of bricks to be used compressive
strength of the brick unit and details of curing and scaffolding if necessary so obviously
once we have a brick wall being made there is the issue of what is the height of the
wall if the wall is lets say more than two meters or two point five meters then it is
not possible for a mason to reach the top here and be able to do the brickwork for that
we will need to erect a scaffolding up to lets say about one one and a half meter the
brickwork can be done without scaffoldings so whether scaffolding is to be included not
included would depend on the nature of the job that we are talking about so long as lets
say we are talking about one point five one point seven meters its not necessary perhaps
to make elaborate scaffolding and we can just make do with a stool or something like that
for an item of that nature we need not include the cost of scaffolding and thats what we
can do with our boundary wall you will recall that the brickwork that we calculated in the
last lecture was in cubic meters and we used the length breadth and height of the brickwork
now please remember that if we specify the thickness of the wall we say that the wall
is hundred fifteenth thick or two hundred and thirty thick in that case the breadth
dimensioned need not be given then we are only talking in terms of a square meter representation
of the masonry unit or the brickwork so more formally the description of brickwork in a
typical boq would be something like providing hundred fifteen mm thick wall with first class
bricks with one is to six cement mortar in straight or curved in plan walls at all levels
including curing scaffolding if required as directed by engineer in charge so in this
case we have given the wall thickness the class of bricks the composition of the mortar
is specified that it could be straight or curved in plan including curing scaffolding
all levels as directed by the engineer so from a contractual point of view if we
write all levels and there is indeed a huge variation in the height then it becomes difficult
for the bidder to understand how much brickwork is being done at one one and a half meter
and how much of it will require scaffolding and thats why it becomes important for us
to have the drawings ready at the time of tendering so that the bidder is able to look
at the drawings and look for himself in what portion of the brickwork scaffolding will
really be required that will help him bid more realistically so now coming to the concrete
in work lets see this is what the concreting is this picture here shows concreting being
carried out trying to find out what will be the cost of this concrete being poured what
is the most logical unit in which it can be measured and paid the most logical unit as
we did in the estimation exercise last class was in cubic meters where we try to find out
that ok for the footing what is the length breadth and height for the pillars what is
the length breadth and height and we find the total volume of concrete involved
so now in order to be able to do that we should specify other details such as the material
storage and batching so the contractors or the bidder will have to get all the ingredients
store them safely so that they are not contaminated with leaves or any other extra material way
them batch them in a mixing plant it should include mixing whether it is by hand or machine
or it could be the details of the structural element much as the same discussion that we
had for excavation to get a cubic meter of concrete in a open area which is like a slab
or a raft is quite different than getting the same cubic meter of concrete into a beam
or a column we should specify the details of the structural element where the concrete
is being placed a regular quality control testing at site and curing and also the grade
of concrete the transportation of concrete from the mixing plant to the site of placing
and vibration so all this has to be part of the concreting
work then we know that ok in order to do ten cubic meters of concrete which involves the
material the mixing the quality control the curing transportation and vibration what is
going to be the cost and obviously thats also related to the grade of concrete whether its
m two five or its m thirty possibly there will be differences in cement content there
could be differences in admixtures and so on and so forth so once all these things are
known then we can submit a realistic cost for the cubic meter of concrete and thats
the unit cost that we are talking about so a formal description of the concreting work
would be reinforced cement concrete work in beams slabs columns and so on up to tenth
floor level or specify a certain height that obviously once the height increases different
equipments will come into play so the contractor or the bidder should know
whether pumps have to be mobilized or not what is the kind of placing method that is
going to be used including the cost of mixing transportation placing in position vibration
and finishing with the mixed details as provided in drawings or as directed by the engineer
in charge the rate should also include cost of storage and regular quality testing and
curing till the minimum stripping time as per any standard it could be i s four five
six or any other standard that we are doing the construction with so thats how we go to
the description of concreting works and coming to plastering this is the picture of plastering
being carried out and there the description would be providing fifteen mm thick cement
plaster in one is to six mortar to brickwork in superstructure including surface preparation
texturing and curing for ten days so that is how the plastering item goes and
now coming to the reinforcing steel we have seen some pictures in the last lecture and
this is another picture which shows that what we are talking about is to find out what should
be the cost per lets say metric ton for putting these kind of reinforcements in position for
that the description would really be providing fabricating and placing reinforcement steel
fe five hundred or any grade of steel of various diameters so what we are saying is that we
are putting in all the diameters together and submitting a quotation in terms of tons
alone of grade fe five hundred hysd bars conforming to respective is codes or any other codes
that we are talking about which would include is straightening cutting bending hooking lapping
and or welding wherever required as directed placing in position tying with eighteen g
black annealed binding wire double fold cost of binding wire and anchoring to the adjoining
members wherever necessary all laps and waste is complete as per structural drawings
so this really is the complete description of the reinforcing work because it also includes
the rate will include cost of all materials cost of labor cost of equipment machinery
loading and unloading transportation all incidental charges at work at all leads and lifts so
once we say this we are also declaring that regardless of the height of placing the reinforcement
the rate will be the same so much as we did with the earthwork we could again here also
have a situation we can divide this item into heights at the same reinforcement item up
to a height of say three meters beyond three meters up to say ten meters greater than ten
meters so if we are able to do that the contractor or the bidder knows that in certain cases
the reinforcement will be placed up to three meters in certain cases it will be up to ten
meters and beyond ten meters so depending on how much is the reinforcement being placed
in these three heights or at these three heights the rates applicable would be different
similar is the situation with handling diameters you can imagine that handling an eight mm
diameter bar or a thirty two mm diameter bar is not really the same thing as far as the
ease of operations is concerned bending the bar cutting the bar jointing the bar all these
things are different when it comes to different diameters so of course it becomes very difficult
to say that for each diameter we have a different rate but yes engineering judgment can be exercised
and one can say that ok we will apply a rate up to sixteen mm bars and then four bars greater
than sixteen mm there will be a certain other rate applied so these are the kind of refinements
that we need to do in preparing a very precise description in the bill of quantities and
please remember that the more precise we are in our description the easier it becomes for
the bidder to bid and the more accurate is your estimate and with this we come to an
end to the discussion today these are some of the references which you could use to understand
the topic further and i look forward to seeing you in another lecture next time
thank you