Tunneling ops between Washermenpet-Mannadi metro rail stretch to be completed in three days

C Shivakumar

Chennai:

The tunneling operations between Washermenpet to Mannadi is likely to be completed within three to four days even as metro rail is leaving no stone unturned to ensure safety of residents and buildings.

Chennai Metro Rail General Manager (construction) V Somasundaram told Express on Tuesday that in the stretch between Washermenpet to Mannadi 18 of the 740 buildings developed cracks. Fourteen of them were minor and four were major which were being rectified, he added.

Interestingly, metro rail is frequently monitoring the buildings using modern gadgets installed in streets and buildings while the tunnel boring machines are operating beneath.

The tunnel boring works from Washermenpet to Mannadi has progressed smoothly and Somasundaram is hoping for a similar success between Seven Wells to Mannadi, another congested area in north Chennai.

It is likely the tunnel-boring machine would complete the stretch in next two months. But then it won’t be smooth sailing for metro rail. “Everything thing depends on the geology of the building. We expect more settlements during the comings days and it all depends on the structure of buildings,” he said.

Interestingly, metro rail said that they had carried out a survey before the tunnel boring works started. “We shared the information with owners of the building and said any deterioration from the present state would be rectified,” he added.

And to ensure a smooth operation and transparency in settlements, metro rail has fitted several equipments to ascertain whether the building is safe while the tunneling operations are on.  These include tilt meters, crack meters, tape extensometer and inclinometer. “The reading are taken every four hours or at times during morning and evening,” said Somasundaram.

He said if the geology has rock beneath, then the building would not be affected.

Box:

The instruments used by metro rail to monitor buildings while tunnel boring machines drill beneath.

The ground settlement point is used to monitor the vertical settlement on the surface of embankments, soil, masses, etc. It may also serve as a deep ground settlement point for monitoring of vertical displacement of utilities and in some cases as a benchmark.

Inclinometer or clinometer: It is an instrument for measuring angles of slope (or tilt), elevation or depression of an object with respect to gravity.  Clinometers measure both inclines (positive slopes, as seen by an observer looking upwards) and declines. It is also known as a tilt meter, tilt indicator, slope alert, slope gauge, gradient meter, gradiometer, level gauge, level meter, declinometer, and pitch and roll indicator.

Building settlement marker: The building settlement marker is used to monitor the vertical settlement or movement of any structure. These reflective markers can be monitored either using total-station or digital level equipment for the most precise readings.

Crackmeters: it is intended to measure movement across surface cracks and joints. It is installed by grouting, bolting, or bonding two threaded anchors (with ball joints) on opposite sides of the crack and then attaching the ends of the guage to the anchors.

Tape extensometer: It is used to detect and monitor changes in the distance between two reference points. Typical applications include -- monitoring convergence of tunnel walls and deformations in underground openings besides  monitoring displacement of retaining structures, bridge supports, and other structures.