A study on rock-falls on the Mumbai-Pune Expressway found that a risk assessment on the busy roadway should be done every three years, considering that approximately 43,000 vehicles ply on the stretch daily.
An assessment of the 93-km long expressway between 2002 and 2012 by the Indian Institute of Technology-Bombay (IIT-B) found that an average of seven people die each year on the road because of rockslides.
Researchers said a series of safety measures such as wire mesh that can bear the weight of rocks, drainage channels and a regular check for weak areas on the rock-face can make the lane expressway completely safe.
“No care seems to have been taken after the hill was blasted to construct the expressway, neither were experts consulted by the contractors. As a result, rocks have been left hanging and new fractures created. The wire mesh used to cover the rock is not sufficient to hold the load,” said professor TN Singh, department of earth sciences, IIT-B. “There are wire meshes that can hold even 500kg weight. There has to be effective management to handle the problem.”
Between 2002 and 2012, the Mumbai-Pune Expressway witnessed 115 rock-fall incidents with 17 such events recorded in 2005 alone.
Based on the traffic density on the expressway, the three-member team studied three scenarios and found that the probability of the impact of moving vehicles on a fallen rock was the cause for most deaths, taking an average of five lives every year. This is followed by rocks falling on stationary vehicles, which is likely to take the lives of two people a year, while falling rocks hitting vehicles on the move could kill one person annually.
“The expressway is a busy road and continuous movement of vehicles can cause vibration in the hills and create new fractures. Water ingress inside the slopes deteriorates the strength of the rock. Soft soil inside the fractures will also get washed away resulting in widening of the cracks,” said Singh. “Any water inside slopes is dangerous.”
Other suggestions include drilling 8mts to 9mts rock bolts that can hold rocks together as done along some stretches of the city’s eastern freeway. Additionally, mixture of cement, water and fibre can be injected into the fractures that will prevent water ingress.
The study, Rockfall Risk Assessment along Mumbai-Pune Expressway, Maharashtra, India, was published in the International Journal of Science and Research last year.