Services on Konkan Railway were disrupted today after a wall of the Pernem tunnel, located just north of Pernem railway station partly collapsed.
As a result, several trains have been diverted via the Miraj-Pune route. Sources suggest that the restoration of the line could take days. The tunnel runs from chainage Km 383.506 to Km 385.067 on KR.
UPDATE: Several trains diverted till 15th and 20th of August 2020. See details below:
The tunnel already had a 50 km/h permanent speed restriction. A 20 km/h restriction was imposed at the spot of the collapse since last year. Since the location of the collapse is not far from the southern end of the tunnel, thus improving chances of speedy restoration.
But this isn’t the first time that the Pernem tunnel has shown its displeasure.
Collapses during construction
On October 10, 1997, three months before the Pernem tunnel was completed, a major collapse took place. Thirty-year-old Executive Engineer Ravi Kapoor was lucky to survive. The collapse took place just above him. He found himself in chest-deep soil, his helmet crushed, and a boulder on his foot.
His colleague V Jayasankaran stayed back to rescue him. It was a lucky escape. Again on August 26, 1997, it was Jayasankaran’s timely warning which saved several workers when another collapse occurred at the Pernem tunnel. Thus time the workers were safely evacuated.
Konkan Railway has 91 tunnels in adding up to 84 km in length. However, tunnels totalling 3,500 metres of length in weak soil, mainly in Goa and Karnataka, posed the most problems during construction, wrote Menka Shivdasani and Raju Kane in the book Konkan Railway- A dream come true.
There are five soft soil tunnels on the Konkan Railway. They are Pernem (1561 m), Old Goa ( 544 m), Padi (1917 m), Bhatkal (863 m), and Byndoor (1962 m).
Water Diviners and Water Tables
To solve the soft soil problem, engineers also thought of lowering the water table at Pernem as a possible solution. They wanted to do this by drilling borewells along the tunnels and drying out the.soil. But that could not be done.
An 85-year-old water diviner who had helped out at the Natuwadi tunnel (between Karanjadi and Diwankhavati) refused to travel to Pernem. Another diviner died in an accident while travelling to Pernem and the idea was given up.
Challenges in the construction of soft soil tunnels like at Pernem
Draining water out in an around a soft soil tunnel was the biggest challenge faced by Konkan Railway engineers during construction. The region receives very heavy rainfall during the monsoon.
For five months, that is the monsoon and the ensuing three months, soft soil tunnels which landed in lithomargic clay strata underlying hard laterite soil saw problems of mudflow, collapses, cavity formation and squeezing of supports.
Techniques such as fore-poling, insertion of perforated pipes for draining out water, and grouting were tried out.
At Pernem, engineers faced the most unpredictable conditions. According to Vinod Kumar, the then Chief Engineer (Tunnel). “Every day at Pernem reveals different strata – like a chameleon. It alters between soft schist rock, slanting rock, hard laterite and soft clay and water seepage is ever-present.”
Tunnelling works at Pernem was hampered for several days as a single roof collapse meant a set back of one month.
Works on this tunnel on the Maharashtra Goa border commenced in mid – 1992 and was completed on January 10, 1998. Post this the last section on the Konkan Railway between Sawantwadi and Pernem (22 km) was opened fpr traffic on January 26, 1998.
Excerpted from Konkan Railway – A Dream Come True
Featured Image Courtesy: Incredible Indian Railways Youtube Channel