‘Geotech consultants should be held responsible for landslides’

Hindustan Times spoke to experts and leading geotech consultants in the city, who provided an insight into the probable causes of landslides at construction sites during the monsoon and the precautionary measures to be taken to prevent future mishaps

Mumbai: Last week, the piling work being done for a 30-storey SRA project’s saleable component building at Rahul Nagar in Chunabhatti East led to a massive landslide. Its impact was so great that a portion of a private road leading to the nearby Vasantdada Patil Engineering College caved in, burying 41 vehicles inside the excavation pit.

Mumbai, India - July 05, 2023 : Landslide in Rahul Nagar, Nr Vasantdada patil Engg College, Eastern express highway, Chunabhatti (E), As informed by MFB while piling work of Raunak group construction about 25ft of land slide thereby around 8-10 two wheelers and 4-5 four wheelers are trapped under debris. Area is evacuated, in Mumbai, India, on Wednesday, July 05, 2023. (Photo by Vijay Bate/HT Photo)

The SRA project was a planned and approved 30-storey free-sale component with a three-level basement. Last year too, the excavation work done for a two-level basement being constructed for an under-construction building led to a landslide at Pedder Road near Cadbury House, because of which residents of the adjoining Soham bungalow owned by mining baron Anil Agarwal were forced to evacuate.

Hindustan Times spoke to experts and leading geotech consultants in the city, who provided an insight into the probable causes of landslides at construction sites during the monsoon and the precautionary measures to be taken to prevent future mishaps.

Architect Shirish Sukhatme of Sukhatme & Associates said that the problem arose due to insufficient work done by geotechnical consultants. The latter play a crucial role and are essentially involved in all stages of the design of structures, from concept to construction. Their work is essential in the design and planning process as they assess the integrity of the soil, clay, silt, sand and rock prior to construction. In layman’s terms, they are also known as soil investigation contractors.

“To know about the condition under the ground, an opinion is sought from these experts, and whether there is a need for more trial bores to predict the nature of the soil,” said Sukhatme. “Geotech consultants might not have predicted the strata correctly in the recent landslides. Ultimately, it is the geotechnical consultant who should be held accountable for a landslide.”

Sukhatme added that the BMC had made it mandatory to appoint a geotechnical consultant even for ground-floor constructions. “They are supposed to certify the bearing capacity and the nature of the soil below,” he said. “This has become a part of the official approvals but is usually taken lightly.” Indeed, despite the civic body making it mandatory to appoint a geotech consultant, this is not always followed by builders.

Shekhar Vaishampayan, director, Ochre(Drillers) India(P) Ltd, a geotech expert, said that in the past, constructing one basement was a novelty but with increasing parking requirements, sewage treatment plants and fire water tanks, all of this was pushed below the ground to have a clean surface on top. “Because of this, one has to excavate deeper and deeper, and we come to a point where we often have three and even four basements below,” he said.

Gaurav Parab, partner at Global Geotech, said that when one constructed basements, one dealt with soil, which is a heterogeneous material. “More investigation programmes need to be planned whenever such deep excavations are planned since there are neighbouring plots involved, while you conduct soil investigation within your property at the exact centre where the building is being constructed,” he said. “The peripheral variation of the soil gets overlooked sometimes, which may lead to missing the parameters that need to be considered inside and outside the plot, and in turn leads to such consequences.”

According to Parab, the second reason for landslides is the services and utilities like cable trenches surrounding the plot. “The type of utility services present underground are unknown sometimes,” he said. “But the builders go ahead with the construction presuming uniform ground condition, and that may sometimes cause a problem because of leakages.”

Lastly, there are certain crucial factors for developers to keep in mind to prevent mishaps while constructing three-level basements. “We must consider a cycle of one calendar year while constructing a basement,” explained Vaishampayan. “There must be geotechnical investigation by a competent party for the tower and basement, followed by the evaluation of the design parameters. The geotechnical and structural consultants should sit together and finalise the system to be adopted for the given site, and then design the retaining system. There should be proper drawings and specifications for the retaining method and it should be executed properly. Post that, a resourceful and good project-monitoring consultant should be appointed who will monitor the work carefully. Only then will the chances of failure of the project be negligible.”