Delhi Metro Construction Methodology

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-

1. Phase I 65.10 km
2. Phase II 128.06 km (110.98 km in Delhi + 17.07 in Non Capital Region)
3. Phase III 112.17 km ( 62.30 km in Delhi + 49.87 in Non Capital Region)
4. 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 :

- 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.

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