Challenge 1

Ans 1

A metro rail system is a network of public transport used for transit between places of high industrial and commercial activity within a city. The connecting stations are within a few kms. It is either elevated or underground. It is required in developing economies due to the high demand of commuter transit and the subsquent saturation of other modes of transport such as roads/conventional railway. It thus requires minimal amount of land (~ pier width) and can be engineered and constructed in heavy congested areas.

A conventional rail system, on the other hand, is a network of public transport connecting two different cities/places over long distances. Mainly it connects metro cities to non-metro cities. It is a network at ground level and the connecting stations can range from few kms to hundres of kms. Requires greenfield alignment since it is at ground level.

Ans 2

Currently operational metros in India - Kolkata, Delhi, Bangalore, Chennai, Mumbai, Nagpur, Hyderabad, Jaipur, Kanpur, Kochi, Lucknow,  Noida, Pune.

Recently we have also heard of Metrolite and MetroNeo proposals. MetroLite is proposed for cities with lower passenger density (Light rail transit) and costs ~ 40% of conventional metros. MetroNeo is also for cities with lower passenger density (Light rail transit) and costs ~ 25% of conventional metros.

The most important aspect is the assessment of the density (total) population that is going to travel in the different cities and their flow so that we come up with the most viable and economical solution.

Approximately 860 kms are under Construction and ~ 1000 kms proposed metro routes pan India.

Ans 3

DMRC is the busiest metro since during the time of its inception, public commute or transportation within the region was limited to roads and since its commissioning significant travel time reduction was witnessed.

Few facts: The lights and the AC go off at certain points in the metro journey. These are actually neutral zones, where the power supply switches from one sub-station to another. The United Nations has certified the DMRC as the first metro and rail-based system that gets carbon credits for reducing greenhouse gas emissions. It reduces about 6,24,000 tonnes of greenhouse emissions in Delhi every year.

Ans 4

1. Superstructure - It carries the train loads directly over it and connects two piers. Types based on span arrangement - U girders, I-girders, Box Girders, Composite Girders etc.
2. Bearings - Transfer the loads from the superstructure to the substructure. Types based on span and restraint requirements are Elastomeric, Spherical, Pot PTFE, etc.
3. Substructure - Consists of pier cap, pier and foundations (open/pile/well). Substructure transfter the loads from superstructure to the ground. Types are circular pier, rectangular pier, Cantilever pier caps, portal system. Rectangular piers are more efficient. The circular pier can be more efficient in water chanels.
4. Abutments - Substructure element provided at ends of a bridge to transfer loads and retain the slopes.

Ans 5

There are various aspects involved in choosing a particular type of metro system - elevated or underground.

Generally, it is observed that an elevated metro system is economical than an underground metro system. However, ground conditions are assessed for determining the solution. For instance, in areas of high rise building densities having deep foundations or ground conditions with high water table, an underground metro may not be economical / viable. For alignments with heavy density transit networks above ground like railways, roads and flyovers, existing metros, etc. one can explore underground metro. An elevated metro is ideal where tall piers can be constructed upto a certain height and have good soil strata.

Ans 6

Design Basis Report (DBR) of a metro project is prepared, sent for comments and finalized at the start of the project as per the planning so as to initiate design. DBR includes loadings to be considered, codal standards to be used during the detailed design. It acts as a guideline for design and approvals thus maintaining uniformity in the understanding of all stakeholders involved int he project.

Ans 7

Since DBR includes loadings, codal standards. it acts as a facilitator / reference document between stakeholders thus standardizing the design procedure. It can also easily capture variations, if any, during the design process.

Ans 8

Broadly, the chronology is as follows:-

1. Feasibility report - Checking the alignment for different underground utilities.

2. DBR finalization

3. Planning

4. Design - GAD approval followed by detailed design

5. Construction.

Ans 9

Topographical survey means practice of showing on maps or charts the heights and depths of the features of a place. In other words, contour mapping of a place can be done. Moreover, one can identify the existing raods, rails, water bodies, etc. With this, the design quantity cost estimate of structures is as close as possible to the actual to be constructed.

Ans 10

Hinderances possible are:- Rivers/Creeks,Tributaries,Nallahs etc., Educational institutions, Existing hospitals, Existing infrastructure-railways/transmission towers, etc, Religious place of importance, Existing Residential/Commercial/Industrial buildings.

Ans 11

Underground utilities are:- Electricity cables/ducts, Optical fibres, Sewage/Water/Gas pipelines, etc.

Ans 12

Solutions to underground utilities:-

1. Utility survey is an engineering option at a very initial stage to avoid / minimize those hinderances.
2. Utility diversion is an option where we divert/deflect the course which are fouling with the approved foundations up for construction. Requires lot of permissions outside the metro civil contract.
3. Revising the foundation arrangement:- This is an option where the utilities cannot be diverted at all. Here designer can relocate pile/s of a typical arrangement and design the pilecap for eccentric loadings if any.
4. Shifting of alignment- This is a last resort option where the network of utilities is so dense that no other option of the above 3 is possible.

Ans 13

Feeding of U-girders means supply of metro viaduct girders to its final location for the purpose of erection on pier caps/bearings. Generally, girders are transported (fed) to the location on the multi axle trailors. Once the girders are at the location of final erection, they are launched (erected) bt means of crane/ground supported staging/Launching girder, etc. depending on the method of construction adopted in planning. 

Ans 14

The main advantages of precast girders are as follows:-

1. Quality control at casting yard location can be achieved. Yard is designed and constructed and no settlement criteria is set. Hence there are no errors and if any can be rectified locally with good quality of girders.

2. Fast speed of construction i.e. better time cycle.

3. Traffic diversions may not be required or can be minimized.

For cast in-situ construction, staging arrangement is required at site and this man-material cost can escalate for taller piers and wider decks. It is difficult to control/rectify geometry even if there is minor settlement of ground. Accessibilty of concreting can be a major issue if tremie has to pass through complex box girder geometry.