CMRL: Under the corridors
Notwithstanding the traffic chaos, pollution and other problems, the Metro services have been gaining popularity and acceptance by the denizens.
CHENNAI: Life in the city has been thrown out of gear for months due to the construction work of the Chennai Metro Rail Limited (CMRL). Notwithstanding the traffic chaos, pollution and other problems, the Metro services have been gaining popularity and acceptance by the denizens.
As heartening as that is, officials at the CMRL have no time to dwell on the success, as they’re busy battling and resolving challenges that crop up every day, and often, multiple times a day.
Catching up with the lost time in awarding tenders, CMRL officials and respective contractors of corridors — C3 and C4 — have been hastening the construction process at all possible places.
But, some tasks in the construction of underground (UG) stations are proving to be more challenging than anticipated, so much so that the CMRL had to revise the original plans and shell out a large amount of money for diversions.
Speaking to DT Next, officials and contractors say that most of the challenges arise due to unchartered utilities, lack of land area, vehicular movements, and rocky terrain. So far, Metro stations in Purasawalkam, Tiruvanmiyur and Sterling Road have been the most demanding for various reasons.
One of the most challenging factors in this station is the diversion of utilities and the interconnections, and these works need to be done in a rather tight space. As there are major underground pipes supplying water to Purasawalkam and its neighbouring areas, the diversions had to be meticulously planned out.
For utilities, there are two types for diversion – wet and dry. Wet utilities consist of water pipes and sewer pipes, and dry utilities comprise transformers, electric and telecom cables.
In Purasawalkam, after identifying the utilities in February 2022, contractors have been held up diverting them for more than 18 months. In July, the contractor, Tata projects, finished the interconnection of a major 1,000-mm diameter water pipeline. Another 1,000 Metro Water pipe interconnection will be completed by the end of August.
Explaining the diversion process, the official said, “Initially, while making a trench for the diaphragm wall, numerous cables were found. They were not diverted; instead, they were taken out, bundled up and once the work was finished, it was put back inside the ground. It’s called localised diversions, which require a great deal of time. When the ground is exposed for trenching, cables are often intertwined. Sorting them out takes time.”
Besides this, procurement for the right materials to meet the standard is a challenge, they say. And, in the case of wet utilities, getting the materials and calibrating the angles for diversions and interconnections is hectic and time-consuming. The larger the diameter of the pipeline, the strenuous task it is to divert.
The utility challenge
The wet utilities in Purasawalkam are brick arch sewer 1,000 diameter, two 1,000 mm diameter water lines, 750 diameter sewer pipeline and 600 mm sewer main line. Additionally, there are also a few 200 and 100 diameter water lines, which are already diverted. Dry utilities are 11 KV Egmore feeder, TVH feeder, GM office feeder, 11 KV local feeder, 11 KV water works feeder, 33 KB electrical line and three transformers.
The most challenging utility in Purasawalkam is the brick arch drain, that runs from Millers Road to Brickklin Road, where workers did not have enough space for diversion. The drain is the main line feeding from Millers Road to Brickkiln Road. “The limiting constraint was the land. As the brick arch was interchanging with two parallel 1,000 mm diameter pipes, an adequate gap was required to carry out the diversion work, within the road and roof slab-level,” explained the official.
Adding to this, utilities diversions are also linked with traffic diversions. Keeping in mind the dense vehicle movement and limited land area, traffic diversions were approved in three stages for the overall station box in Purasawalkam High Road. “To save time during utility diversions, we have proactively begun working on the diaphragm panels. As the whole 400-metre station is divided into panels, with each panel being 2.8 metres, we have built three so far,” he said.
To further mitigate the delay, CMRL officials are re-considering the contractor’s proposal of changing the sequences of launching and retrieval of tunnel boring machines (TBMs).
Due to lack of land area, Tiruvanmiyur Metro station has been planned out as an on-road UG station, forcing construction to be done in stages. Besides this, the contractor (L&T) found massive uncharted utilities connected to techno parks like Tidal Park and Ramanujan IT Park.
“While trenching at the Tiruvanmiyur stretch, on the station location, we found unknown utilities like 2,200 mm gravity sewer line, water supply pipes, 110 KV cables and optical fibre cables running to nearby IT parks. Each one required stage-by-stage diversions due to lack of space, and heavy traffic,” stated the official.
Due to space constraints, the 2,200 mm gravity sewer of the Chennai Metropolitan Water Supply and Sewerage Board (CMWSSB), 110 KV cables of the Tamil Nadu Generation and Distribution Corporation Limited (Tangedco) and other utilities had to be diverted above the proposed station building. The official explained that diversions could have been done easily if there was ample space.
“But, in Tiruvanmiyur, there is MRTS on one side and IT parks on the other. There was a severe dearth of space. Hence, for diverting 2,200 mm sewer line, a portion of the station building had to be constructed before the utility diversion work commenced. The diversion of the 2,200 mm sewer line alone was done at an estimated Rs 2.5 crore,” the official added.
On the other hand, the temporary one-time diversion of 110 KV line cost CMRL Rs 4 crore including Rs 2 crore on diesel to keep the generators running until diversion was completed.
Additionally, the geological condition in the Tiruvanmiyur stretch posed a complication. Due to the rocky underground, construction of the diaphragm wall and station was complex, said officials.
“Due to certain challenges, after the work for the station’s diaphragm wall was completed on one side of the road, traffic was diverted before the station work began on the other side. This had to be carried out a few times to enable the station construction,” said the official.
This Metro station is located at the junction of four roads with Valluvar Kottam on the south and Poonamallee High Road on the north. L&T has already commenced the TBM work in Chetpet, which will be retrieved at the Sterling shaft in the north by August next year.
“For completing the shaft before the retrieval time, we’ve requested L&T to prepare the launching shaft on priority. RVNL is the contractor for UG construction, which has just mobilised the work. But since we cannot hold for long, L&T will construct the shaft alone, before the UG contractor comes on board,” said the official. CMRL has already begun the process of road diversions for digging trenches and identifying utilities, which are being done in eight stages.
Dry & wet problems
Subsequently, CMRL has also began diverting the utilities that were infringing with the proposed shaft.
Some of the large wet utilities found infringing were 750 diameter water pipeline and 900 diameter water pipeline. Both were overlapping each other.
Besides this, a small water pipeline 150 mm diameter had been diverted away from the shaft. And, a 250 mm diameter sewer line has been diverted till now.
The dry utilities in Sterling are 11 KV electric cable and telecommunication cables, for which the work is still in progress, starting July 2023.
“After diverting the pipes, we can connect new pipes to the existing ones. Then, we’ll be able to cut off the portion infringing with the shaft. This interconnecting process is a long one,” noted the official.
During the interconnection, the CMWSSB must give approval. But, as several interconnecting work requests are pending with the CMWSSB, there is delay in carrying the work.
Due to the interconnection at Kaliamman Koil Street in Koyambedu that was completed recently and maintenance work at Chembarambakkam Lake, the approval for Sterling is getting further delayed, said officials.
Once the interconnection work is completed, the land will be back-filled, followed by road restoration and traffic diversion. Trenching for the interconnection of the 750 mm diameter pipeline will commence after that.
Major interconnection is a long process as it goes on in stages from approvals, inspections, and informing the public through media on water supply cuts.
Another challenging factor faced in Sterling Road is the traffic. Due to its prominent location, multi-directional flow of traffic and approvals are required for traffic diversions.
“To better regulate traffic, we’ve laid a 5-metre temporary concrete road at the entrance of the station work to minimise the impact of traffic. This was done additionally, which is not part of the original construction plan,” the official said.
Struck by rock
Another construction-based difficulty was the rock. Like the UG phase I construction, CMRL is also encountering rock in the diaphragm wall. The construction through the rock-bed largely delays the work.
Moreover, while other stations have to slow down the work during the day, Sterling Road can carry on the work throughout the day because of its confined location. Yet, the soil disposal from trenching cannot be done during the day.
To speed up the construction of the shaft and to reduce the waiting time of TBM arriving next year, CMRL has altered the station construction methodology from top-down to bottom-up.
Explaining further, the official added, “We changed the construction design to bottom-up, where the base-slab of the station will be constructed first, slowly progressing upwards.”
Toiling towards a breakthrough
As the elevated line of the Metro Rail phase 2 construction is reaching its advanced stage, CMRL has simultaneously expedited the underground (UG) constructions in all 3 corridors (C3, C4 and C5).
But, as the awarding of tenders and packages were delayed for the construction of UG stations, CMRL officials confirm that the commissioning of the UG service has also been delayed by one-and-half-years. And, the UG station operations will start in 2028.
However, the contractors and officials have been toiling to reduce the delay to one year.
After the phase 1 and extension (C1 and C2), been in operation in the city since 2015 for 54 km with 41 stations (20 elevated stations and 21 UG stations), CMRL has been engaged with phase 2 construction for overall 116.1 km with 119 stations (43 UG stations and 76 elevated stations). The expenditure has been revised to Rs 61,843 crore by dropping nine non-feasible stations and reducing the station sizes.
For the construction work of phase 2 UG, CMRL recently awarded nine out of 10 packages for corridors 3 and 4. But, for corridor 5, where the soil testing was completed in March 2019, CMRL is yet to award tenders for five UG stations. But officials confirm that the tenders will be awarded within a month.
After completing the soil testing in August 2019, CMRL awarded seven packages for corridor 3, two tunnelling packages (TUO1 and TU02) and 5 packages for UG station constructions. For corridor 4, two UG packages have been awarded to contractors after winding up the soil testing in February 2020.
One tunnelling package has been awarded to Tata Projects, which will build around 9 km twin-bored tunnels from tunnel boring machine (TBM) retrieval shaft near Venugopal Nagar station to Kellys station. It will also construct the diaphragm walls of the station box and entry/exit structures of Madhavaram Milk Colony, Murari Hospital, Ayanavaram and Purasaiwakkam High Road stations.
The second tunnelling package was awarded to L&T for building around 12 km twin-bored tunnels from Kellys station to Taramani Road junction station. L&T will also construct diaphragm walls of the station box and entry/exit structures of Chetpet, Royapettah GH, Tiruvanmiyur Metro stations, along with part of the diaphragm wall of Greenways Road station.
On the progress of tunnelling 21 km from Madhavaram Milk Colony to Taramani, a CMRL official said, “15 TBMs are working in corridor 3 for constructing the network of underground tunnels. These TBMs shall be launched and retrieved multiple times until completion from the shafts at various locations. Out of 15 TBMs, eight have been launched and the remaining will progressively start tunnelling within the next eight months. Currently, both upline and downline (3.26 km) segment installation works have been completed.”
The first breakthrough was achieved in June after completing tunnelling from Madhavaram Milk Colony to Venugopal Nagar. For 30 UG stations, diaphragm wall works are in progress, noted official sources.
For building an UG station in corridor 3, contracts have been awarded to Dineshchandra-SOMA JV, Tata Projects and Rail Vikas Nigam in June 2023. These three contractors will work on construction of underground station from Madhavaram Milk Colony to Perambur Metro, six stations from Ayanavaram to Kellys, seven stations from KMC to Royapettah GH, five stations from Radhakrishnan Salai to Adyar Junction and four stations from Adyar Depot to Taramani.
For corridor 4, the tender construction of UG stations was accepted by ITD Cementation India in January 2022.
For the UG station from Light House to Kodambakkam, two contracts for 10 km tunnelling, including the construction of nine UG stations between Lighthouse to Kodambakkam, has been awarded and diaphragm wall construction work is going on, say CMRL officials.
For this stretch alone, four TBMs have arrived and the launch of the first TBM is expected in September this year.