Faculty Publications
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Item Numerical Modelling of 2D Geogrid Reinforced Sand Bed(Springer Science and Business Media Deutschland GmbH, 2020) Sreya, M.V.; Makkar, F.M.; Sankar, N.; Chandrakaran, S.The use of continuous geosynthetic inclusions is involved in traditional soil reinforcing techniques such as geotextiles or geogrids, which are strong in tensile resistance. They protect the environment and promote a stronger planet by conserving energy and the earth’s resources through the production of durable and sustainable structures. In the present investigation, a numerical analysis is performed to understand the behavior of a square footing resting on geogrid reinforced soil. The numerical simulations were carried out using a three-dimensional FEM software, PLAXIS 3D. The numerical model was systematically validated with the results obtained from experimental studies. The effect of various factors such as embedment depth of first layer, spacing between consecutive layers and the multi-layers of the reinforcing elements are studied. It is observed that, four numbers of geogrid elements give the maximum bearing capacity ratio of 3.51 for an optimum depth of first layer and the spacing of 0.25B. © 2020, Springer Nature Singapore Pte Ltd.Item Performance of Footing on Clay Bed Reinforced with Coir Cell Networks(American Society of Civil Engineers (ASCE) onlinejls@asce.org 1801 Alexander Bell DriveGEO Reston VA 20191 Alabama, 2020) Kolathayar, S.; Narasimhan, S.; Kamaludeen, R.; Sitharam, T.G.Geocells are three-dimensional polymeric hexagonal pockets that provide lateral confinement to the soil, thereby increasing the bearing capacity of the soil bed. This paper briefly reviews past studies on geocell reinforcement of soil and presents a new product, cells made out of natural coir fiber, as an alternative to commercially available high-density polyethylene (HDPE) geocells. A series of model plate load tests were conducted on unreinforced soil and on soil reinforced with coir geocells to understand the soil reinforcement mechanism. It was observed that with the introduction of coir geocells, the load-bearing capacity of the soil bed increased up to three times and a significant reduction in the settlement was observed in the underlying weak soil bed. The study also presents a comparative performance evaluation of the natural coir cell-reinforced soil with conventional HDPE geocell-reinforced soil. Further, this paper analytically demonstrates the influence of the lateral resistance effect and vertical load dispersion effect incorporated by coir cells in strengthening the soil bed. © 2020 American Society of Civil Engineers.Item 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.Item Model Footing Tests and Analytical Studies on Clayey Soil Bed Reinforced with Coconut Shell Mat(Springer Science and Business Media Deutschland GmbH, 2022) Kolathayar, S.; Gadekari, R.S.The cellular confinement systems are becoming popular in ground improvement because of their efficiency in improving the bearing capacity of soil due to the lateral confinement effect. The commercially available geocells are made from polymer materials and they are costly. This study presents the performance evaluation of coconut shell mat as a cellular confinement system in clayey soil. It is the first of its kind application of coconut shells for soil reinforcement through a lateral confinement mechanism. This soil reinforcement system using coconut shells is termed “Geococoshell” by the authors. A series of model plate load tests were conducted on unreinforced soil, soil reinforced with High-Density Polyethylene (HDPE) geocells, and soil reinforced with coconut shell mats to evaluate the performance of coconut shell mat reinforced soil bed. The results of the experiments showed that coconut shells reinforced clayey soil improved bearing capacity up to 1.5 times compared to HDPE geocell reinforced clayey bed. The effect of different patterns of placing coconut shell mat was also studied and discussed in the paper. The analytical studies have been conducted considering the reinforcement mechanisms of coconut shell mat embedded in the soil bed. © 2022, The Author(s), under exclusive licence to Springer Nature Switzerland AG.Item 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.Item Seismic response analysis of RC framed buildings on geo-reinforced soil(Springer Science and Business Media Deutschland GmbH, 2023) Sreya, M.V.; Jayalekshmi, B.R.; Venkataramana, K.Geotechnical seismic isolation is a recently emerged isolation technique to prevent the damaging effects of the earthquake on the building structures and nonstructural components. The study analyzes the effectiveness of different materials such as epoxy polystyrene, polyethylene foam, coir mat, rubber mat, and coir composites as a soil isolation medium to reduce the seismic energy transferred, thereby reducing the dynamic response of buildings under earthquake loads. Finite element analysis was carried out to evaluate the soil–structure interaction (SSI) effect in low-rise reinforced concrete structures with raft foundations subjected to various earthquake motions. Two kinds of soil, namely soft and stiff soil, were considered based on their flexibility to study dynamic soil–structure interaction effects. Roof acceleration and base shear of the building and contact pressure distribution and settlement at raft foundation–soil interface were the parameters evaluated for the different soil properties. The linear elastic behavior was assumed for the integrated building–foundation–soil system. This system was exposed to ground motions corresponding to scaled El Centro (1940) earthquake and simulated seismic excitation, which corresponds to the elastic design spectrum for Zone III as per the Indian standard code (IS 1893 (Part 1): 2016). The results indicate that the soil isolation provided by the high stiff polyethylene foam and coir mat substantially reduced the earthquake energy transmission to the superstructure. It is also observed that the seismic response of the buildings and raft is dependent on the flexibility of underlying soil. Seismic responses increase as the soil flexibility increases. Compared to stiff soil, the reinforced materials are very efficient in reducing seismic responses in soft soil. © 2023, Springer Nature Switzerland AG.