R&D Knowledge sharing session on ‘Cost Comparative study of Cased and Un-cased Columns in Marshy Soils’ & ‘GGBS and fly ash bricks’

The Civil Engineering department had its eleventh session under R&D cell on the 18^th February 2022 at 3.30 P.M. The two speakers for this session were Asst. Prof. Starina Dias and Asst. Prof. Oswyn Soares. The former presented a cost comparative study on cased and un-cased columns undertaken by her, while the latter presented on a GGBS and Flyash blocks.

Prof. Starina presented on ‘Cost Comparative study of Cased and Un-cased Columns in Marshy Soils’. She described how stone columns and granular piles derive their load carrying capacity from the confinement offered from the surrounding soil. But in very soft soil this lateral confinement from the surrounding soil may not be adequate for the stone column. Hence wrapping the granular pile with geotextile was one of the techniques to improve the performance of stone column.

She highlighted on how the bearing capacity of an encased column could be increased while reducing its settlement.  In her paper an attempt was made to investigate how the use of geotextile encasement for the stone columns at a bridge site at Mandur, Goa, having soft soil could be cost-effective over ordinary stone columns. The proposed improvement by encasement with a geotextile was done by a using finite element software, Plaxis 2D. After performing the analysis using both ordinary stone columns(OSC) and encased stone columns(ESC), for an area of 57.6 m², twelve OSC were required  at a cost of 9,00,000 rupees while nine ESC for an equivalent area, having a cost of 7,51,500 rupees. Hence comparing the cost of an OSC and ESC, the cost reduces by 16.5 percent for an ESC.

Prof. Oswyn presented on ‘GGBS and fly ash bricks’. He described the properties of fly ash, types of fly ash and its chemical composition. The presentation also showed a comparison between different classes of fly ash (Picture 2). He explained the major mechanical attribute of fly ash was to convert non-durable lime to Calcium Silicate Hydrate (C-S-H), which imparts strength and durability to the concrete. In his study, Prof. Oswyn is trying to activate Fly ash and GGBS with free lime, which will react with Silicon Oxide or Silicon Dioxide to form the cementitious material C-S-H.