DELHI
METRO – COMPARISON OF TECHNIQUES
AND
METHODS FOR CONSTRUCTING ELEVATED
CORRIDOR
AND ITS ENVIRONMENTAL EFFECT
INDEX
1.
INTRODUCTION.
2.
GENERAL CRETIREN FOR SELECTION.
3.
SPECIAL REQUIREMENT OF ELEVATED
CORRIDOT.
4.
CONSTRUCTION METHODOLOGY.
5.
ERECTION OF SEGMENTS
6.
AIRPORT LINE.
7.
METHOD STATEMENT.
8.
PER KM COST.
9.
QUALITY CONTROLL.
10.
ENVIRONMENTAL IMPACTS
11.
CONCLUSION
1.0
INTRODUCTION
With
a view to reducing the problems of Delhi commuters like congestion on
roads, ever slowing speed, increasing accidents rate, fuel wastage,
and environmental pollution, Delhi Metro Rail Corporation Limited has
under taken the construction of Mass Rapid Transit System for Delhi.
The entire work of length approximately 413.83 km, planned so far is
divided into four parts-
- Phase I 65.10 km
- Phase II 128.06 km (110.98 km in Delhi + 17.07 in Non Capital Region)
- Phase III 112.17 km ( 62.30 km in Delhi + 49.87 in Non Capital Region)
- Phase IV 108.50 Km ( 97.00 km in Delhi + 11.50 in Non Capital Region)
The
phase I and Phase II of the system consists of 193.16 km route length out
of which a major portion, i.e. 142.31
km (125.23
km in Delhi and 17.08 km
in NCR) of the system is supported on the viaducts, 6.5km at Grade
and 44.35
under Ground.
The
construction of the superstructure of such long distance of viaducts
has not
only to meet the functional requirement but also to take care of the
site constraints
such as
i) Allowing free flow of vehicular traffic on the already congested along with chosen alignment,ii) Paucity availability of land,iii) Existence of charted and uncharted utilities,iv) Problems to pedestrians,v) Problems to existing residents, andvi) Environmental impact including noise and vibration etc.
Present
project report describes the comparison of various technique and methods
adopted in construction of the viaduct and examines together the various
factors influencing the design. The design solutions are presented
together with methods adopted to comply with very tight design
and construction period.
2.0
GENERAL
To
select the type of Metro Rail corridor -
I.
A comprehensive multimode mobility study, taking into account the various
transport means like Rail/Sub urban / Metro/Roads/Feeder services,
is required to be conducted to finalized the change over points.
II.
A combination of route i.e. elevated, at par, and under ground is
then selected
considering their –
· Construction cost· Maintenance cost· Aesthetical view· Environmental impact, and· Impact on the profile of the city
The
elevated corridor is planned by DMRC generally to cut across fairly densely
built up areas by virtue of its need to serve these area “Hence its impact
needed sensitive treatment and assessment. Thus, the sometimes conflicting
issues of operations and using requirements, construction appearance,
environmental impact, including noise and vibration had to be included
in the overall assessment of the most appropriate materials and form
of construction.
3.0
SPECIAL REQUIREMENTS OF ELEVATED CORRIDOR
3.1
DURING
CONSTRUCTION
As
stated in Para 1.0 above construction of the superstructure of such
long distance
of viaducts has not only to meet the functional requirement but also to
take care of the-
Site
constraints such as -
- Allowing free flow of vehicular traffic on the already congested along with chosen alignment,
- Paucity availability of land,
- Existence of charted and uncharted utilities,
- Problems to pedestrians,
- Problems to existing residents, and
- Environmental impact including noise and vibration etc.
Mitigation
Measures-
To
have minimum inconvenience to general public the following mitigation
measures
are required
· Fully barricading the construction corridor,· Providing proper signage and lighting arrangement,· Completing the construction in a minimum time frame and in a time bound manner,· Good house keeping of the surrounding area, and· Rais ing the confidence of the public by adopting safety measures, caring for public attitude
4.0
CONSTRUCTION METHODOLOGY
4.1
Structure Form Adopted
The
structural form adopted for the elevated Corridor (i.e. viaduct) constructed
so far by the DMRC is comprises of Pile
foundation - Group of bored piles of dia 1.0 m , 1.2m, and 1.5m.
Required
concrete pile cap, pier and cross heads( cast in situ/pre cast
pier heads )
Pre
cast Pre stressed concrete segments of type-
· single segmental U,· single segmental box,· segmental box,· segmental U,· Full U girder one for each track· Pre cast pre stress I girders cast in situ span, and Special span
4.2
SINGLE SEGMENT CONSTRUCTION
4.2.1
Constructivity Requirement for single segmental girders
·
Transportation of long
girders having spans more than 20m by trailor
will pose serious problem in crowded city roads and sharp curves.
·
Operation of Two cranes
to place girders in position will require traffic
block during night for a number of night which may not be acceptable
to traffic police and if agreed upon they will cause inconvenience
to general public.
·
The availability of
casting yard at suitable location as choice will be
governed by shifting, lifting and transportation of girders.
·
Cast in situ
construction, Where ever required, is time consuming and
cause inconvenience to public.
4.2.2
Advantage of single girder for two tracks over two girder
Single
girder for two tracks have got following advantage over two girders
i) 4m pier cap against 6 to 7 m for two girderii) 50% bearingiii) Gives a clean soffit and is preferable authentically
4.2.3
Disadvantages of single girder
i) Larger spans have to be cast-in-situ which will cause false work, shuttering and concreting problemii) It can not have curved surface in playiii) It is not idle suitable for carrying spans which are unavoidable in city due to road crossings, utilities and other constraints.
4.3
WHY SEGMENTAL CONSTRUCTION IS PREFERED?
The
various reasons arei)
If
a decision is taken to go for single girder for two tracks then
segmental casting is only option. It can be managed from
3 to 4 casting yards for one full leg of corridor located
at available land which may be a few km away.
ii)
Very fast Progress can e achieved.
iv)
Segments can be cast and stacked parallel to pile and pier construction
activity.
v)
Launching speed is very fast.
vi)
Cause minimum disturbance to traffic as segments can be fed
at selected location and launched with help of launched
spans moving it on completed deck to avoid lifting
of segment from trailor positioned on road.
vii)
It can have curved surface in plan and is suitable for carrying
span lengths.
viii)
In case some span have to be skipped due to local problems
segmental casting has got flexibility.
ix)
Cost of construction may be slightly more to start with but if
it is adopted on large scale it may come down and likely to
be comparable with conventional construction.
5.
ERECTION OF VIODUCT
The
superstructure is be erected entirely from below using an under slung erection
tackle.
Three
type of erection tackle are used
1.
BRIDGE CONEDesign by
Bombay based firm, moves pier to pier no ground support
is required.
2.
SPIC
Design
by Italy based Firm .Nois ing girder is supported on ground,
can not be used where R. L. as road vehicle can not be moved.
Much Safer and very use full for Railway x-ings.
3.
KHANOLKER
Design
by Bombay based firm, front leg is moved ground, can not
be used where x- ing is required.
.
6.
AIRPORT LINK
6.1
Different type of structure has been adopted due to special nature
of
requirement of airport link.
i)
Two types of super structure was adopted.
a)
25m long span U girder.
b)
Continuous span PSC solid slab at special. Locations i.e.
Dhoulakuan fly over. ii)
Pre cast Pier Cap
iii)
Other structure All foundation and other substructure works are
cast
in situ. This includes-
-foundation
pile and pile cap
-
Piers
-Abutments
-Extended
pier arm
-
Cantilever pier arms and portal piers
6.2
Bearing
-Elastomeric
bear ing are placed underneath U- girder for transfer of
vertical forces
-Concrete
shear keys are provided at top of pier cap which restrain the
movement of deck in transverse direction and acts as topper in longitudinal
direction.
A
gap of 25mm between deck and shear key each side of the deck is
maintained to allow thermal expansion of the deck.
6.3
Drainage of deck/ solid pier
Drain
pipe is located with in solid pier to avoid aesthetics problems.
The
top of deck soffit slab is profiled so as to collect run off water at
middle of slab by providing a cross slop of 1%. Two no of drainage
pipes at each end of U girder span have been provided on top
of the pier cap which will connect to the drainage pipe in pier.
6.4
SINGLE U-GIRDER
First
time in Delhi Metro
Advantages as compared to segmental box section
–
Cost
effective as the weight 11t/m where as it is 16t/m in segmental
box, overall savings is about 10% .
–
Fast
un erection it takes less than one day cycle in erection of one
span compared to 5-6 days required of conventional segmental
span.
–
Aesthetically
better looking as no joints.
- No site parapets required.
6.5 SINGLE SEGMENTAL GIRDER
Single segment for two tracks have got following advantage over two separate grinders :
Single segment for two tracks have got following advantage over two separate grinders :
-
4m pier cap head against 6 to 7m for the box girder.
-
50% bearing.
-
Gives a clean soffit & is preferable aesthetically.
-
Segmental construction can achieve very fast progress.
Segment
can be cast & stacked parallel to pile & pier construction
activity.
-
Cost of construction may be s lightly more to start with but
if it is adopted large scale it may come down & is likely to
be comparable with conventional construction.
-
In case of some problem, if a few spans have to be skipped,
segmental cast has got flexibility.
11.0
METHOD STATEMENT
A
method statement is detailing the procedure of casting various
elements of the structure.
It
is to be prepared by the contractor and get it approved by the client
or their nominated consultants well before starting the construction
work at site.
It is a written document, available at site, to be referred by the client and contractor, as and when required by them, to ensure availability of required infrastructure and proper sequence of
the
construction activities ,so as to get the work done with desire
progress and quality.
7.1 Preambles: Casting of proposed U –Shaped girders of 25.0 m nominal length for Air Port express link of DMRC.
7.2 Casting Yard- Located near Airport in Mahipalpur with an area of 315m X 50 m approx. Constructed as per Drawing No 267/Cy/01. Other details to be mentioned herein are details of
casting
beds, no of different moulds, Jigs, Batching Plant, Rebar
Yard, Stacking Area, water tanks ,Excess Road, Office Block,
Laboratory, Over Head Gantry, Sheds to Keep var ious
Tools
and Plants etc.
7.3 Reference Drawing:- Details of the drawings illustrate the complete casting and stacking scheme is to be given under this head.
7.4 List of Moulds and Equipments in casting Yard
7.5
Mould: Under this head Details of casting beds along with details
of Approved reference Drawing, Sequence of fixing the various
shutters is to be given here.
7.6
Time Cycle for Casting-
Sr.No
Description Time Remark
1
Cleaning of casting beds and oiling 5 hrs. Day
2
Fixing of outer shutter 10 hrs. Day 1
3
Placing of rebar cage 10 hrs Day 1
4
Threading of strands 12 hrs Day 2
5
Initial pretensioning 6 hrs Day 2
6
Final pretensioning of all strand 2 hrs Day 2
together
7
Placing of inner mould and 15 hrs Day 3
8
Inspection by client 2 hrs Day 3
9
Pouring of concrete 10 hrs Day 4
10
Curing 72 hrs Day 4 – 6
11
Removal of inner shutters * 4 hrs Dar 4
12
Transfer of pre- stress 2 hrs Day 7
13
Cutting of strands 2 hrs Day 7
14
Lifting of girder 10 hrs Day 7
*
Inner shutters must be available for casting of 2nd long line on day
5th so that casting is possible on day 6th
7.7
Rebar cage- No of Jigs required to achieve the planned progress per
week and frequency of checking the condition of jigs as mutually
agreed to be mentioned here.
7.8
Rebar cage – method of cutting and bending of re-bars, their checking
procedure and shifting to casting bed is to be given here.
7.9
Cover block- Procedure of their casting, required shape (semi circular)
is to be given here.
7.10
Concreting- The sequences of concreting to be mentioned here for
example- Soffit - Web1 - Web2 then top flange on both sides
7.11
Fixture in girder – here the details of all the fixture to be provided
are to be given.
7.12
Curing of the Girder- method and time period of curing , alternate
method etc.
7.13
shuttering- Method and time of shuttering, their placement and cleaning
etc to be mentioned here. Transfer of prestress
7.14
Lifting of girder- Procedure of lifting and placement as per drawing
with required no of pre decided type of cranes to be given
here.
7.15
Inspection before dispatch to the erection site.
Enclosures
- For example Risk assessment, inspection test plan formats
etc.
8.0
PER KM COST
Viaduct
Phase
I
Rs.
24 crore/km
Phase
II
Rs.
22 crore/Km
Dwarka
to Dwarka city Sect. 21
Rs.
19 crore /km (open Foundation)
Tunneling
Rs.110
crore /Km
9.0 Quality Control
9.1
FACTORS FOR SUCCESS
- Understand the Client’s Requirements
- Identify and manage risks
- Team building
- Develop good communication and co-ordination
- Be one step ahead of the client
- Identify problems early
- Establish procedures
9.2
DMRC QUALITU STRUCTURE
- ISO 9001 Standard
- Contractors are responsible for QA and QC
- Consultants carry out audit roles
- Client make decisions
- High prior ity given to safety & quality (inspections, audits & training)
- Structured contractor’s record keeping, monitoring, and reporting
9.3
GENERAL AND
SPECIAL CONDITIONS
Detailed
ISO 9001 Quality Assurance Manual demonstrating the proposed
method to achieve the required quality standards of the Employer,
DMRC
The
Engineer shall be entitled to audit any aspect of the system
Compliance
with the quality assurance system does not relieve the Contractor
of any of his duties, obligations or responsibility in the Contract.
9.4
CONTRACT REFERANCE
- GCC (General Conditions of Contract)
- SCC (Special Conditions of Contract)
- Special Specifications
- IS and International Standards
- Contractor’s Quality Assurance Manual
- Contractor’s Quality Control Procedures
- (ITPs, Pre-pour and Post Pour Checklists, Sign-offs, As-builts, Completion Certificates)
9.5
QUALITY RESPONSIBILITES
9.1
Contractor
is responsible for QA & QC
9.2
Contractor submits Quality Plan for approval: -
9.3
Method Statement
a) Work Proceduresb) Inspection Test Plans (Witness, Hold & Document Points)c) Inspection Checklists
9.4
BASE OF ACCEPANCE CORRIDOR
a)
Concrete workability
b)
Shrinkage and Swelling
c)
Strength
d)
Durability
–
(Water
permeability)
–
Cracking
–
Cover
on reinforcing steel
–
Aesthetic
9.5
REQUIREMENT
a)
The pour procedure and schedule
b)
Anticipated problems and possible solutions
c)
The formwork design
d)
The concrete mix design
e)
The quality control procedure and the facilities provided by
Contractor.
9.6
FIELD INSPECTION
-Formwork
-
Reinforcing
-
Concrete Handling and Placing
-
Plastic Concrete Finishing
-
Shrinkage Cracks
-
Curing
-
Formwork Removal
9.7
TESTING
LABORATORY
-
Contractor provides its own testing Laboratory
-
All equipment provided as listed in the contract
-
Test results verified for accuracy during inspection and periodic audit
9.8
CONCRETE BATCHING PLANT
-
Periodic calibration
-
Equipment Preventive Maintenance Program
-
Mixer blade end gap from face of drum (max= 7 mm) checked daily
-
Compliance to concrete uniformity (ASTM C-94)
9.10
CONCRETE PLACEMENT
The
concrete is placed with help of the concrete pump
10.0
ENVIRONMENT IMPACT:
At locations where pollution level has already exceeded the permitted level or is on higher side, every construction activity needs very close scrutiny to ensure that there is no further environmental degradation. Planning for method of construction and type of materials used plays a very vital part in containing the adverse environmental impact.
At locations where pollution level has already exceeded the permitted level or is on higher side, every construction activity needs very close scrutiny to ensure that there is no further environmental degradation. Planning for method of construction and type of materials used plays a very vital part in containing the adverse environmental impact.
10.1
ACTION TAKEN TO REDUCE NAGETIBVE ENVIRONMENT IMPACT
a)
The
pre-stressing technique, was used extensively on the elevated track
to bind the segments, reduces the weight and volume of structure thus
correspondingly reducing pollution in manufacturing, transporting,
and assembling, etc.
b)
Use of high strength concrete to optimum level substantially reduced
not only transportation and erection cost but also mitigated pollution.
Similarly, by appropriate use of ‘pre-stressing’ in concrete structure,
economy is invariably achieved as there is reduction involume
from 20% to 40% in most of the cases, which in turn results in a
positive impact on environmental during construction.
c)
Some of the other environmentally friendly construction practices employed
during the construction of the metro included
1. Tyre washing facility at site exits,2. provision of oil separators,3. Recycle of bentonite and reuse /recycle of curing waste productive.4. Use of dewatered water etc.5. Maintenance of equipment is mandatory and requirements for use of silent DG sets is made more stringent.6. Segregation of wastes at sites was initiated and handling of waste as per legal requirements was introduced.
11.0
CONCLUSION
Apart from the advantages mentioned in the beginning of this report there are a number of environmentally sustainable advantages of DMRC
1.
In operation, it is a non polluting and environmental friendly system
2.
It has a very high carrying capacity to cater to huge passenger
demands thus drastically reducing land acquisition for
the same load
3.
It requires much less space to carry same number of passengers
4.
Energy requirement per passenger kilometer is one fifth than for
other modes
5.
Finally, it is fast, reliable, safe and comfortable, all at the same time
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