Faculty Publications

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Pore Water Pressure Analysis in Coir Mat-Reinforced Soil Incorporating Soil-Structure Interaction
(Springer Science and Business Media Deutschland GmbH, 2022) Sreya, M.V.; Jayalekshmi, B.R.; Venkataramana, K.
The proposed study investigates the effectiveness of reinforcing the soft soil by a coir mat, a natural material, to act as a seismic soil-isolation medium. A 3D finite element simulation in PLAXIS 3D software has been carried out on models of five-storey buildings resting on raft foundations in soft soil with and without the soil-isolation mechanism. This study also deals with the coir composites, coir–polyethylene and coir–rubber were proposed to increase the durability of the coir mat. The isolated soil-structure system was exposed to four different earthquake motions, such as the ground motions corresponding to the elastic design spectrum for Zone III as per the Indian standard code (IS 1893 (Part 1): 2016), the scaled Northridge earthquake (1994), El Centro earthquake (1940) and Chi-Chi earthquake (1999). A pore water pressure analysis of soil bed has been carried out to study the efficacy of these materials to reduce the excess pore water pressure generated in soil under earthquake loading. The other parameters, such as shear strain mobilized shear strength, effective stress in soil, and roof acceleration, in the building were analyzed. Isolation efficiencies of reinforcement materials to reduce the excess pore water pressure generated in soil under different earthquake motions obtained are 75–82%, 71–80% and 67–72% with coir, coir–polyethylene and coir–rubber, respectively. The resulting shear strain in soil reinforced by isolation mats is lower than that in unreinforced soil because the isolation mats strengthen the soil. Compared to the unreinforced soil, the mobilized shear strength and effective stress in the soil are increased when it is reinforced with coir and coir composites. The roof acceleration and bottom acceleration in the building got reduced by the isolation mechanism. © 2022, The Author(s), under exclusive licence to Springer Nature Switzerland AG.
Effect of Coir Reinforced Soil on the Seismic Response of RC Framed Buildings
(Springer, 2022) Sreya, M.V.; Jayalekshmi, B.R.; Venkataramana, K.
This study examines the effectiveness of reinforcing the soil with coir mat, a natural material, to act as a seismic soil-isolation medium. A 3D finite element simulation has been carried out on models of five-storey buildings resting on raft foundations in soft and stiff soil with and without the soil-isolation mechanism. The optimum values of the parameters such as the depth of embedment, width, and thickness of the coir mat have been analyzed. The isolated soil-structure system was exposed to two different earthquake motions, such as El Centro (1940) and simulated seismic excitation corresponds to the elastic design spectrum for Zone III as per the Indian Standard code (IS 1893 (Part 1): 2016). The optimum value for the depth of embedment, width, and thickness of the coir mat was identified as B/18, B/0.45 and B/36. The proposed study also deals with the coir (C) mat composited with other isolation materials such as polyethylene (PE) foam, rubber (RU) mat and geomembrane (G) to form C-PE, C-RU and C-G mats. These composites were proposed to increase the durability of the coir mat. The reinforcement of the C-PE mat shows a maximum of about 30% reduction in roof acceleration and 68% reduction in contact pressure. A pore water pressure analysis of soil bed also has been carried out to study the efficacy of these materials to reduce the excess pore water pressure generated in soil under earthquake loading. For that, a simple soft soil is modelled in Cyclic 1D software with and without the soil-isolation mechanism. The soil bed was exposed to El Centro (1940) and Northridge (1994) input motions. C-PE mat significantly reduces the excess pore water pressure by almost 93% and 88% in soil under El Centro and Northridge input motions, respectively. © 2022, Indian Geotechnical Society.
Site specific fragility modification factor for mid-rise RC buildings based on plastic energy dissipation
(Techno-Press, 2024) Mathews, M.; Jayalekshmi, B.R.; Venkataramana, K.
The performance of reinforced concrete buildings subjected to earthquake excitations depends on the structural behaviour of the superstructure as well as the type of foundation and the properties of soil on which the structure is founded. The consideration of the effects due to the interaction between the structure and soil-foundation alters the seismic response of reinforced concrete buildings subjected to earthquake motion. Evaluation of the structural response of buildings for quantitative assessment of the seismic fragility has been a demanding problem for the engineers. Present research deals with development of fragility curve for building specific vulnerability assessment based on different damage parameters considering the effect of soil-structure interaction. Incremental Dynamic Analysis of fixed base and flexible base RC building models founded on different soil conditions was conducted using finite element software. Three sets of fragility curves were developed with maximum roof displacement, inter storey drift and plastic energy dissipated as engineering demand parameters. The results indicated an increase in the likelihood of exceeding various damage limits by 10-40% for flexible base condition with soft soil profiles. Fragility curve based on energy dissipated showed a higher probability of exceedance for collapse prevention damage limit whereas for lower damage states, conventional methods showed higher probability of exceedance. With plastic energy dissipated as engineering demand parameter, it is possible to track down the intensity of earthquake at which the plastic deformation starts, thereby providing an accurate vulnerability assessment of the structure. Fragility modification factors that enable the transformation of existing fragility curves to account for Soil-Structure Interaction effects based on different damage measures are proposed for different soil conditions to facilitate a congenial vulnerability assessment for buildings with flexible base conditions. © 2024 Techno-Press, Ltd.

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