Performance evaluation of geogrid reinforced soil walls with marginal backfills through centrifuge model tests S. Balakrishnan 1 , B.V.S. Viswanadham * Department of Civil Engineering, Indian Institute of Technology Bombay, Powai, Mumbai 400 076, India article info Article history: Received 9 October 2014 Received in revised form 1 June 2015 Accepted 2 June 2015 Available online xxx Keywords: Geosynthetics Reinforced soil walls Model tests Marginal fills Centrifuge modelling Pullout tests abstract Marginal fill materials that do not follow the guidelines are used in constructional activities due to ease in its availability and economic benefits. But several cases of geogrid reinforced soil wall failures indicate the loss of interfacial shear resistance due to wetting of backfill as a possible reason. In the present study, centrifuge tests were performed on geogrid reinforced soil wall models with wrap-around facing using a 4.5 m radius large beam centrifuge facility available at IIT Bombay at 40 gravities. A marginal soil with 21% fines was chosen as backfill in the study. Two geogrid types of different stiffnesses were modelled based on scaling considerations and used in the study. The models were prepared at wet of optimum to simulate wet backfill conditions. The surface settlements of the models during centrifuge tests were monitored with the help of Linear Variable Differential Transformers (LVDTs). Digital Image Analysis (DIA) was performed on photographs of the front elevation of the model captured during flight, to obtain face movements and reinforcement strain distribution along geogrid layers during centrifuge tests. In- terpretations of centrifuge model test results reveal that the soil wall reinforced with low stiffness geogrid layers was observed to deform excessively and undergo pullout failure along soilegeogrid interface. However, the provision of geogrid layers with higher stiffness limited the excessive outward deformations of geogrid reinforced soil walls with marginal backfills. Further, the effect of moulding water content and stiffness of the geogrid on the mobilization of pullout resistance was evaluated through pullout tests in the laboratory. Based on the observations made from pullout tests and centrifuge tests, provision of stiffer geogrids in geogrid reinforced soil walls was found to be one of the viable options to mitigate the problems posed by marginal backfills. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction A wide spectrum of fill materials is available and they are generally classified on the basis of gradation, plasticity, clay mineralogy and chemical composition. Selection of a fill type for a particular project depends on various factors such as strength and deformation requirements, availability and interaction with rein- forcement. Grain size, plasticity, permeability, shear strength (un- der short term and long term conditions) and compaction characteristics are also evaluated to select a material as backfill. The fill material should be reasonably free from organic or other dele- terious materials. The use of well graded, freely draining granular fill in reinforced soil wall is important to achieve good soil- reinforcement interaction and proper drainage. Koerner et al. (1998) recommends a backfill material which is completely free from fines. AASHTO (2009) allow a backfill material with less than 15% of fines passing No. 200 (0.075 mm) sieve and plasticity index not exceeding six. But due to the ease in availability, on-site (or locally available) soils are widely used. They also result in saving 20e30% of cost compared to use of permeable or granular fill material (Christopher and Stuglis, 2005). Such soils do not follow the specifications and are termed as marginal soils, low permeable or poorly draining in literature by Mitchell and Zornberg (1995), Koerner et al. (1998), Christopher et al. (1998) and Raisinghani and Viswanadham (2010, 2011). The problems posed by marginal backfills have been a topic of study by these researchers. It was indicated by Koerner et al. (1998) that without drainage, the total force against the wall can be twice as that of a properly drained reinforced fill soil. * Corresponding author. Tel.: þ91 22 25767344. E-mail addresses: sreejabalakrishnan@iitb.ac.in (S. Balakrishnan), viswam@civil. iitb.ac.in (B.V.S. Viswanadham). 1 Tel.: þ91 22 25764345. Contents lists available at ScienceDirect Geotextiles and Geomembranes journal homepage: www.elsevier.com/locate/geotexmem http://dx.doi.org/10.1016/j.geotexmem.2015.06.002 0266-1144/© 2015 Elsevier Ltd. All rights reserved. Geotextiles and Geomembranes xxx (2015) 1e14 Please cite this article in press as: Balakrishnan, S., Viswanadham, B.V.S., Performance evaluation of geogrid reinforced soil walls with marginal backfills through centrifuge model tests, Geotextiles and Geomembranes (2015), http://dx.doi.org/10.1016/j.geotexmem.2015.06.002