‘Maha Metro should deposit ‘drill cores’ with GSI for geo-scientific studies’

Source: The Hitavada      Date: 07 Jan 2019 10:12:08


Staff Reporter,

For past few years, Nagpurians have been watching Maharashtra Metro Rail Corporation Limited (Maha Metro) drilling various bores in various parts of the city. Though the drilling was done to know more about the soil texture and strength of the ground to bear the load of pillars being erected for the project, the ‘drill cores’ preserved by Maha Metro may be useful for a number of geo-scientific studies including earthquake studies. For the purpose, Maha Metro will have to deposit the drill cores with National Core Library of Geological Survey of India (GSI), Nagpur.

Dr Anjan Chatterjee, former Additional Director General, GSI, sought information under the Right to Information (RTI) Act from Maha Metro and after studying the information received, has suggested that it would be worthwhile ‘if the cores are deposited by Metro authorities after completion of their studies in National Core Library at GSI’.

According to Dr Chatterjee, thousands of meters of drill cores have been preserved at National Core Library of GSI.
“If the cores are deposited there, all stakeholders can have access to the preserved cores of Nagpur Metro for their respective studies. The National Core Library at GSI, Nagpur is very well equipped, with preserved drill cores of boreholes from various localities in India and is among the two such libraries in India,” he said. The drilling work done within Nagpur city with borehole cores properly labeled and preserved is of utmost importance, as no such recent work by any agency is on record, Dr Chatterjee told ‘The Hitavada’.

The borehole data is very important for stakeholders, mainly geological agencies that have Nagpur city in their domain, as their designated area of study.
Standard Penetration Test (SPT) data generates ‘N’ values that are the number of hits of the auger drill hammer on the strata being drilled, explained the senior scientist. SPT is an in-situ dynamic penetration test designed to provide information on geotechnical engineering properties of soil and rocks drilled.

The more the hits by the hammer in the auger drilling rig, higher are the ‘N’ values, indicating a stable and solid rock sub-strata. Lesser the hammer hits generated by sub-strata, lower are the ‘N’ values, indicating a soft and friable strata, with vulnerability to earthquakes. This data is available as per the map that has been generated by Maha Metro. “SPT data is very important for earthquake studies, especially to study the foundation rock tenacity and their vulnerability during earthquakes and soil liquefaction,” Dr Chatterjee said. Geotechnical properties of the foundation rock are quite important, as this has a direct bearing to give due strength to civil structures that are built upon them.

Geotechnical engineering properties like bearing capacity, shear test properties of the soil cover, underlying bed rock and the rock strata below and Young’s Modulus (a modulus of elasticity of a material) are also quite valuable for sub-surface engineering studies. The thickness of the soil cover that usually varies is also available for different localities in the city, where drilling has been carried out. The water table depths are quite useful for groundwater studies, though many other agencies may have such data. Besides, the drill cores will be useful for studies in earthquake geology, Deccan volcanism, petrology, paleontology and other disciplines of geology, said Dr Chatterjee while shedding light on the utility of the drill cores.