Performance assessment of mechanically stabilised earth walls with sustainable backfills Pushpraj Mandloi MTech MSc student, Department of Civil and Environmental Engineering, Indian Institute of Technology Patna, Patna, India (Orcid:0000-0002-5976- 5513) Sanjana Sarkar MTech Research Scholar, Department of Civil and Environmental Engineering, Indian Institute of Technology Patna, Patna, India (Orcid:0000-0002-3336- 5837) Amarnath Hegde PhD Assistant Professor, Department of Civil and Environmental Engineering, Indian Institute of Technology Patna, Patna, India (corresponding author: ahegde@iitp.ac.in) The growing depletion of natural geomaterials has forced scientists and engineers to look for alternate sustainable backfill materials for large-scale practical applications. This study presents an experimental and numerical investigation of the performance of two sustainable backfills – namely, steel slag and construction and demolition waste (CDW) – for possible mechanically stabilised earth (MSE) wall backfill application. A detailed characterisation followed by the performance evaluation of the materials using extensive laboratory experiments, encompassing strength and drainage criteria, is presented. Results of the triaxial and California bearing ratio strength tests highlighted the superior performance of the sustainable backfill materials compared with that of the traditional backfill material. The adequate drainage capacity of slag and CDW reflected the encouraging possibility of utilising the materials as alternate backfills. Additionally, the strength enhancement options of sustainable backfills using geogrid reinforcement were evaluated. Finally, the feasibility of utilising the materials in a prototype MSE wall was investigated with the help of finite-element numerical analysis. The hardening soil model was used to capture effectively the non-linear stress–strain behaviour of these materials. Results obtained from finite-element analysis demonstrated multiple benefits of sustainable backfill materials. In comparison with the standard backfill, MSE walls with slag and CDW backfill demonstrated 56 and 70% reductions in horizontal wall displacements, respectively. Moreover, lower reinforcement strains were observed in walls with sustainable backfills. Keywords: construction & demolition waste/finite-element modelling/geosynthetic-reinforced soils walls & slopes/hardening soil model/MSE wall/Plaxis/recycling & reuse of materials/steel slag/sustainability/UN SDG 7: Affordable and clean energy/UN SDG 9: Industry, innovation and infrastructure Notation C c coefficient of curvature C u uniformity coefficient c cohesion (kPa) D 50 average particle size (mm) E 50 stiffness modulus at 50% failure stress (kPa) E oed oedometer stiffness (kPa) E ref 50 reference stiffness modulus at 50% failure stress (kPa) E ref oed reference oedometer stiffness (kPa) E ref ur reference unloading/reloading stiffness (kPa) E ur unloading/reloading stiffness (kPa) e i initial void ratio e max maximum void ratio e min minimum void ratio H height of soil above the base of the wall (m) I D relative density K nc o coefficient of earth pressure at rest m modulus exponent p ref reference confining pressure (kPa) R f failure ratio g unit weight (kN/m 3 ) n Poisson’s ratio f friction angle (°) y dilation angle (°) s 3 minor principal stress (kPa) 1. Introduction Mechanically stabilised earth (MSE) walls are retaining structures that have been widely adopted worldwide for supporting highways, roadways, bridge abutments and so on. More than 200 000 MSE walls had been constructed by 2018, due to their low space requirement, cost-effectiveness, higher resistance to dynamic loading and greater durability compared with those of traditional retaining walls (Koerner and Koerner, 2018). The performance of MSE walls is governed by the quality of the backfill and its interaction with reinforcements embedded in 1 Cite this article Mandloi P, Sarkar S and Hegde A Performance assessment of mechanically stabilised earth walls with sustainable backfills. Proceedings of the Institution of Civil Engineers – Engineering Sustainability, https://doi.org/10.1680/jensu.22.00012 Research Article Paper 2200012 Received 24/02/2022; Accepted 01/07/2022 ICE Publishing: All rights reserved Engineering Sustainability