The Loosefooter has righfully expressed a deep concern about the institutional disfiguring, defacing and mangling of the Telangkhedi promenade in recent years. He has covered the sequence of events, the politics behind and the now issued show cause notices to authorities by the National Green Tribunal, Pune, quite well. The lake constructed by Gyanoji Bhosle in 1799 (just 23 years after the American war of Independence ended in 1776), is a Grade– I heritage structure vide a gazette notification issued by the state government on October 18, 2003. Grade-I category accords the highest level of protection given to buildings and precincts of national or historic importance. Incidentally, on June 13, 2020, a large part of the retaining wall of the lake had collapsed, sending danger signals. The Supreme Court on January 25, 2024 has ordered a status quo on the ongoing civil works at the lake.

 

The Maharashtra Government and the Maha Metro were refrained from carrying out any further civil works on the lake’s embankment. The petition was filed by the NGO Swachh Association through its President, Anusuya Chhabrani. The Bench had warned, “Don’t mess around with nature. There are a few wetlands left in the country.” It is not yet clear whether geotechnical feasibility studies were undertaken to ascertain the suitability of the visitor’s gallery construction over the embankment of the lake.

 

The geotechnical properties of soil, such as the grain-size distribution, plasticity, compressibility, and shear strength needed to have been assessed by proper testing in an accredited laboratory. Shear strength is the most important geotechnical property of soils that help in stability of civil engineering structures on or below the earth. Moreover, geotechnical properties of underlying basement rocks, below the embankment needed to have been ascertained by drilling boreholes and retrieving the drilled core samples of basement rocks for testing. Tests that include rock texture (grain/particle size), rock stability (strength) whether commensurate with its load-bearing capacity, permeability of the rock and degree of weathering undergone, rock resistance to weathering and mineralogical composition of the rock, needed to have all been undertaken in one or more accredited geotechnical and petrological laboratories. It is not known what all geotechnical feasibility studies were done? The above cited geotechnical feasibility studies are essential for ascertaining the suitability of the earthen embankment on the promenade and for its basement rocks, post the civil works. It is important to know whether these can withstand load/s of the huge mass of the cement concrete structure/s that has been constructed.

 

The term “piling” in engineering geology refers to the process of installing deep foundation elements, known as piles. The piles enable transfer of structural loads to the soil if compact and invincible, or to the subsurface, basement rock layers as desired. Piling is much desirable if the upper soil layers are weak or unsuitable to support the weight of a structure. The piles act as columns, distributing the load and preventing unforeseen factors from becoming a causative factor for instability of the structure. The earthen embankment built on the lake has a wall of soil, sand, clay and rock boulders (mainly basalt) that have all been compacted to form a retaining structure, behind which the lake water is retained. Gravity dams include the huge ones constructed lately and are usually much larger than such embankments or earthen dams and are made of concrete.

 

These rely on their weight to resist the horizontal pressure of the water column that they hold behind. For both types of dams viz. earthen and gravity, the soil and underlying basement rock strata studies are very important, with the view to understand their load bearing capacity for any proposed civil structure. Earthen dams/embankments fail sometimes if the retained water’s level reaches high above, overtopping it. Water column pressure may also be an important causative factor triggering such failures. Incessant and heavy rains create such failures. Besides, earthquakes, erosive forces weakening the structure and undue human interference are other causes of embankment/earthen dam failures.

 

The spillways also need to be cleared from time to time to drain away excessive water, if any. And desilting exercises undertaken from time to time is another viable remedy to avoid such failures. To avoid a catastrophe may be for future generations, we cannot ignore the importance of testing geotechnical parameters of the Telangkhedi embankment and its basement, just given the fact that it is now 226 years old. With the new civil structures constructed atop the embankment, such tests have become all the more necessary in public interest.