Can you please update us on the current status of the East-West Metro project? What are the timelines Afcons have set for completing the works on the project?
The Kolkata East-West Metro – also known as Line 2 of the Kolkata Metro – is currently under construction. The 16.6km corridor will have 12 stations between Salt Lake Sector-V and Howrah Maidan.
Time lines of completion:
- Twin Bored Tunnels including tunnelling works below river Hooghly: Already completed by Nov 2018.
- 8 numbers Cross passages: Already completed by Nov 2019.
- Howrah Maidan Station (includes finishes): March 2021.
- Howarh Station (including finishes): September 2021.
- Mahakaran Station (including finishes): Entry Structures pending clearance from Archaeological Survey of India (ASI).
- Ventilation Shaft at Strand Road: Deepest Ventilation Shaft (40 meters deep below ground level) already constructed. Adjoining super structure to be completed by August 2021.
As we know, the COVID-19 has hit operations and construction of Metro projects across India. According to you, what is the main impact of COVID-19 on the Metro projects construction in Kolkata? What kind of major challenges are being faced by the Afcons staff and workers during these days and what are the safety precautions they are following at the project sites?
Construction activities had to be stalled in March due to the lockdown. It restarted again after the relaxations were announced.
1. Precautions to be taken before starting work at sites / offices:
- All Sub-Contractors and interfacing contractors should have approved Protocol from KMRCL.
- COVID-19 response protocols as laid out here in below will be communicated to all concerned.
- All Interface contractors will share the workmen quarantine and isolation details, COVID-19 test report/result and workmen accommodation, transportation details with GC/ KMRCL with copy to TTAJV.
- Only personnel with negative RT PCR test/ COVID-19 test will be allowed come in system starting with induction.
- All negative tested workmen shall stay in company provided accommodation/ labour camp of respective interface contractors.
- Separate quarantine and isolation facility shall be arranged by Interface contractors for emergency purpose. The Detail of such facilities shall be submitted to GC/ KMRCL and same shall be shared with TTJV.
- Mandatory medical check-up as per guidelines to be arranged for all workers. The detail of such arrangement shall be submitted to GC/KMRC and same shall be shared with TTJV.
- Only medically fit workers will be deployed at site and medical assistance arranged for unfit workers, if necessary. The fit certificate issued by competent person shall be submitted to GC/KMRC and same shall be shared with TTJV.
- Photo Identity cards to be given to all workers and staffs;
- All workers and staff of interface contractor must have Aarogya Setu app and it shall be functional.
- Aarogya setu app will be checked at Entry by gate by security guard, failing which entry will not be allowed at workplace.
- Hospital shall be identified who treat COVID-19 patients in consultant with GC and KMRCL.
- Suitable signage at construction site shall be displayed, spelling out safety practices in the language which is understood by most of the worker.
- Non-touch garbage bins with biodegradable garbage bag will be installed for waste collection near rest room and dining area. Proper disposal of garbage bags along with daily cleaning and sanitization of bins to be ensured by Interface Contractor.
- Separate drinking water arrangement shall be provided by Interface contractor for their workers/staff.
- Separate touch free hand washing arrangement with soap shall be provided by Interface contractor with company name mention on it.
- Areas with a probability of bigger gathering, e.g. Entry-exit points, lobbies, walking paths, water dispenser, toilets, lunch areas etc. to be identified and all arrangements to be made to ensure social distancing.
2. Precautions to be taken after start of work:
2.1 Precautions at site, common areas and utilities:
- Everyone entering the site mandatory to wear mask.
- Thermal scanning shall be done by TTA JV for Interface contractor. Separate register shall be maintained for record of temperature.
- If temperature is found as more than 99°F, then the person will not be allowed to enter in the site.
- If anyone leaves and re-enters the site during the shift, re-screening of the individual will be done prior to re-entry into the worksite.
- Shift Start time/ end time on the site shall be made staggered for staff as well as workmen to avoid congestion at the entry exit points.
- Proper queue shall be maintained at the entry- exit gate, social distancing to be followed.
- Daily Tool Box Meeting will be done to spread the awareness about COVID 19 and its preventive measures during toolbox talk, training and other sessions, social distancing guidelines shall be followed.
- A safety Team will be formed along with TTAJV and interface contractor to oversee implementation of these guidelines. The safety team will do daily site visit, conduct meeting and generate report to review the system is working or not.
- Individual working areas to be identified and barricade these area with proper display board, disinfection of theses area to done by interface contactor before starting and closing of work.
- Common area need to be identified, one disinfection agencies will be hired for disinfection and cleaning of common area (Entry exit point, staircase, tally token area, common passage etc) on daily basis. The cost will be beared by the entire interface contractor.
- There will be strictly ban on sitting in common areas.
- Every machine and equipment will be disinfected in daily basis and vehicle will be disinfected every time while entering in site. Such arrangement will be made by respective interface contractors for their equipment and vehicles.
- Vehicle should be parked in designated area and 4 ft distance to be maintained from other vehicles.
- Driver mandatory wear masks and do not roam in site premises.
- There will be strict ban on Gutka, Tambaku, Paan etc. on site and spitting shall be strictly prohibited.
2.2. Precaution at Worker Restroom and Toilets:
- Individual toilet and rest room shall be provided by interface contractors and demarcate the area. Bio toilet shall be provided in site premises.
- Regular cleaning and disinfection of toilet shall be done.
- Non-touch garbage bins with biodegradable garbage bag will be installed for waste collection at all common access areas. Proper disposal of garbage bags along with daily cleaning and sanitization of bins to be ensured.
- Rest room areas will be segregated from other contractors. Dedicated rest room will be arranged by respective interface contractors and by their on resources.
- Foods shall be consumed at designated areas only.
- Post lunch waste shall be disposed in designated bins by individual interface contractor and area shall be cleaned on daily basis.
2.3 Workmen and Staff Transportation:
- Public Transport vehicles strict ban for transportation of staff and workmen.
- Self transport vehicle shall be arranged and disinfected after entering in site.
2.4 Precautions for vehicles, equipment and tools & tackles:
- Visitor’s vehicles, Staff’s need to be disinfected by individual Interface Contractor.
- Wipe down interiors and door handle of machines or construction vehicles, the handles of equipment and tools that are shared after its every use with disinfectant.
- Re-usable equipment to be thoroughly cleaned and should not be shared with others.
2.5 Precautions for incoming material:
- All construction materials arriving at site must be kept isolated for minimum 3 days before taking into use. In case of emergency requirement of the material shall be disinfected thoroughly.
- Hire/ own vehicle shall be disinfected thoroughly before unloading at site.
- Paper/cardboard packaged parcels to be isolated for at least 24 hours. Plastic packages parcels should be isolated for at least 72 hours.
- Quarantine/isolation material area shall be identified, segregated and know to all Interface Contractor.
2.6 Precaution for external visitors:
- Prior detail of visitor and purpose of visit shall be shared with TTAJV.
- Visitor must install Aarogya Setu App and it shall be functional.
2.7 Precaution after completion the work:
- After completion of work, individual working area to be disinfected.
- All the barricade, signages and material need to be remove from site after completion of work.
- And ensure common area to be disinfectant by all Interface contractor.
Please brief us more about how tunneling for the East – West Metro project in Kolkata is more challenging than the other Metro project in India? What are the tunneling technologies being adopted for completing this challenging project?
The 16.6 km long Kolkata Metro’s East-West Metro Corridor will have an underground stretch of 10.8 km. The route will include a 520m tunnel under the river Hooghly. We view this section as a major challenge of the project.
Key challenges includes:
i. Alignment Fixing:
a) Sufficient cover above Tunnel Crown:
The tide runs rapidly on the Hooghly, and produces a remarkable example of the fluvial phenomenon known as a tidal bore. This consists of the head-wave of the advancing tide, hemmed in where the estuary narrows suddenly into the river, and often exceeds 7 ft (2.1 m) in height. It is felt as high up as Kolkata, and frequently destroys small boats. The difference from the lowest point of low-water in the dry season to the highest point of high-water in the rains is reported to be 20 ft 10 in (6.35 m).
So this tidal phenomenon causes scouring of River bed and considering the same the Tunnel crown required the sufficient cover of soil above it. By studying various parameters of Tidal phenomenon, Scouring details, Life of tunnel structure, etc. it is decided to provide a cover of 13.0m above tunnel crown.
b) Straight Alignment:
To maintain geometrical parameters of tunnel, minimum tunnel length and speedy mining it was required to keep the alignment of tunnel below river straight.
ii. Soil Investigation:
a) Boreholes away from Alignment:
To avoid the passage of water during tunneling the bore holes were kept away from the Tunnel alignment. It was also considered that it should not infringe due to future change in alignment if any.
b) Special Investigations:
The Bhagirathi-Hooghly river system is an essential lifeline for the people of West Bengal. It was through this river that the East India company sailed into Bengal and established their trade settlement, Calcutta, the capital of British India. People from other countries such as the French, Dutch, Portuguese, etc. all had their trade settlements by the banks of this river.
The river is navigable and a major transport system in the region with a large traffic flow. For a long time, the Calcutta Port was the biggest port of India. So by considering history of River it was necessary the Special Investigations to ensure there is no hidden obstacles in the form of Ship wreckages, lost anchors etc.
iii. Uncertain Geology:
There were some chances of encountering water bearing strata at it was sitting just above the Tunnel crown in some areas.
iv. Surface Management For Non-Stop Tunnelling:a) Vehicular Movement:
a) Vehicular Movement:
The tunnel launching shaft is situated in the very busy and crowded area of Howrah city. As it is busy and crowded, there is no space for storage of muck so here muck disposal was a serious concern as daily 1200 cum of muck disposal was required without fail and mucking quantity could go even higher in case of emergency. To cater this muck quantity 150 trips of dumpers were required which was a major task through this area.
b) Spares & Material Arrangement:
It was necessary to arrange the Spares of TBM & Materials in advance before entering below the river. AFCONS has arranged 3 months material stock and strategically run 1 TBM at a time so that there will not be any emergency situation due to unavailability of Spares.
Can you please share with us about the types of tunneling methods and technologies being used in the construction of tunnels for the Metro projects globally?
Afcons faced with several challenges when it took up a project of this magnitude.
Make or Break Moments:
I. Completion of First Transportation Tunnel Under Any Mighty River In India in 67 days against a Plan of 120 days:
Under river tunneling has been undertaken in different parts of the world. There have been failures and there have been successes. A study was conducted to understand the mode of the failure that has taken place and appropriate arrangement was made to avoid the possible challenges which are discussed in detailed below:
A. Tunnel Flooding:
While tunneling under water there will be chances of Tunnel Flooding due to various reasons. To avoid the Tunnel Flooding situation detailed study was done and referred the case studies where Tunnel Flooding was occurred and accordingly strategy were made to Avoid the Tunnel Flooding condition.
The following Case Studies were refereed during Planning phase for Tunneling under River:
Case Study 1: DENMARK – STOREBAELT CROSSING – 1991:
It is 8 Km Sub sea Railway Tunnel. Tunnelling was done with HOWDEN EPB TBM’s. While doing cutter head intervention which lasts for a week long and at the same time Tunnel flooding was occurred. The sea water flood was occurred through Man lock doors which were obstructed by Supply lines and result of which twin TBM’s, Tunnels and Portals get submerged. This incident caused a +1 year delay to the project.
Case Study 2: QATAR – 2015:
It was not a river or sea crossing but same principles were applied. It is red line part of 100-KM of Metro tunnels. For tunnelling HERRENKNECHT EPB TBM’s were used. While TBM advancement huge Groundwater flood was occurred through Screw Conveyor and One TBM & Tunnel get submerged. This incident caused a 5 months delay to the project. The reason behind the incident was failure to close the screw conveyor gate.
Lessons taken from above Case Studies:
- Cutter head intervention before entering below river Hooghly.
- Ensured that there is no obstruction at man lock door.
- Ensured working pressure in accumulator.
- Ensured test gate operations on daily basis.
- Identified source of leakages like Articulation Joint and prepared for sealing of the same in case of emergency.
- Identified fare geology in during Alignment fixing and design stage. Stiff clay strata has been selected during finalization of alignment.
- All bore holes for soil testing executed away from the tunnel alignment.
- Tunnel crown was kept 13m below river bed to avoid obstructions in form lost anchors/ship wreckage.
C. Non Stop Mining:
- Non stop mining has been done to reduce ground movement.
- Additional dump yards and transporters were identified for muck disposal.
- Additional routes and help of police & administration has been taken for muck disposal in extreme traffic congestions.
- All critical materials required for river portion were arranged well in advance.
- Minimum stock of material & other requisites was maintained inside tunnel and launching shaft to allow tunneling works smoothly.
D. Crew Deployment Pattern:
- Maintained no shift change till crossing the river.
- Kept minimum watch crew inside the TBM all the time.
- Kept standby staff and managers.
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