Disaster strikes, alarm bells ring

Hill building norms listed

By Saurav Bora in Guwahati
  • Published 23.04.16

Guwahati, April 22: Building structures in the hills here are as safe as on the plains provided they are designed for structural safety after studying the soil characteristics and drainage patterns according to engineering practices, experts said today.

"Unlike in the plains, construction in the hills involves not just a preliminary study of the soil characteristics or water load-bearing capacity but also a contour study to document the slopes and prepare a design for their stability against natural phenomena. Once the parameters are taken into consideration aided by geo-technical engineering, any structure, whether in the hills or plains, can be considered safe for living," P.K. Sharma, president of the Assam Real Estate and Infrastructure Developers Association, told The Telegraph today.

A retaining wall, which can hold back a hillside and turn steep slopes into living spaces, is imperative.

"But if the construction/cutting of a slope is unscientific, you are asking for disaster to strike and cause damage. A retaining wall can only be constructed after devising a water drainage that keeps pressure off it. The water run-off is high on slopes that are not disturbed and layered with vegetation. But when the vegetation is removed and earth cut haphazardly, water percolates into the soil and there is an active earth pressure," Sharma said.

"There is a greater earth pressure on retaining walls in the hills coupled with the pressure of water running down from a slope.

The Kamrup (metro) district administration had sealed five unsafe residential structures located in a hilly area at Akashi Nagar in Bamunimaidam here on Wednesday after a retaining wall collapsed following a landslide the previous night. There were no casualties.

"All the structures were unsafe for living and hence sealed. Four of them are on government land and hence unauthorised," Lakhi Nandan Saharia, circle officer, Guwahati revenue circle, who had inspected the site, said.

The district administration recently instituted a team comprising circle officers, who have been directed to conduct a survey and identify landslide-prone areas in their respective circles.

The administration said need-based relocation of people in such areas would be carried out.

Throwing more light on structural safety, city-based consultant engineer J.N. Khataniar said, "Construction of a retaining wall involves engineering. The weight of the wall should be more than the water pressure from all sides. The depth of a structure on a slope depends on the flowing water pressure (that varies with the wall height) and the saturated soil pressure."

There is no water pressure on structures in the dry season. "So, the water pressure during the monsoon has to be considered before construction, particularly in the hills. Building structures in the hills are more complicated than on the plains for which special technical care has to be taken for their safety," Khataniar said.

There are at least 25 landslide-prone areas in and around the city. Apparently, lessons still have not been learnt as the authorities take a reactive approach after disaster strikes. Over the years, instances of rain-triggered landslides in the hilly areas and the subsequent loss of lives and damage to property have been a common occurrence, particularly during the monsoon.

"There is expert help at Assam Engineering College, Jalukbari, and IIT Guwahati is the right place for getting suggestions and solutions to the geo-technical problems related to constructions," he said.