DOI: 10.3303/CET2184008 Paper Received: 4 July 2020; Revised: 27 November 2020; Accepted: 11 February 2021 Please cite this article as: Mangifesta S., Sebastiani D., Napoleoni Q., 2021, The Effect of Nanomaterials Injection on the Mechanical Characteristics of Coarse-grained Soils, Chemical Engineering Transactions, 84, 43-48 DOI:10.3303/CET2184008 CHEMICAL ENGINEERING TRANSACTIONS VOL. 84, 2021 A publication of The Italian Association of Chemical Engineering Online at www.cetjournal.it Guest Editors: Paolo Ciambelli, Luca Di Palma Copyright © 2021, AIDIC Servizi S.r.l. I SBN 978-88-95608-82-2; I SSN 2283-9216 The Effect of Nanomaterials Injection on the Mechanical Characteristics of Coarse-Grained Soils Sara Mangifesta a,* , Diego Sebastiani a , Quintilio Napoleoni b a GEEG Geotechnical and Environmental Engineering Group, Startup of Sapienza University of Rome, Corso d’Italia, 97, 00198, RM, Italy b Dept. of Civil, Constructional and Environmental Engineering of Sapienza University of Rome, Via Eudossiana, 18, 00184, RM, Italy sara.mangifesta@geeg.it Modern technologies offer nowadays a great variety of solutions for soil stabilization, as low- or high-pressure injections of fluid mixtures. There are many different products suitable for this purpose, depending on the properties of the soil to be treated: for sand, in particular, suspensions of nanoparticles, made available by modern industrial technologies, can be considered among the fluid mixtures potentially suitable for its treatment. This work presents the preliminary results of a wider study developed to verify the potential beneficial effects of the injection of natural based micro- and nano-materials on the mechanical properties of coarse-grained soils. To verify the improvement in sand strength, standard geotechnical tests, such as direct shear tests, were performed on soil samples before and after the injection of micro- and nano-particles of natural materials (sand, clay and graphite). The results proved that the injection in sand of a mixture of water and micro-sized sand improves the mechanical characteristics of the samples. By adding clay nanoparticles and graphene to this mixture the results showed an even greater increase in the shear strength. The results of this work proved that natural based micro- and nano-materials seems to have promising properties to become a competitive resource in the field of geotechnical engineering as soil stabilizers, as a valid alternative to widely used materials. 1. Introduction In the past few decades many different techniques have been used to improve the physical properties and the mechanical characteristics of the soil to prevent natural and anthropogenic undesired phenomena. Thanks to technological developments (Bavasso et al., 2016), nowadays it is possible to choose from a great variety of solutions for soil stabilization, as low- or high-pressure injections of fluid mixtures: in literature there are several examples of studies on the improvement of the mechanical characteristics of soils through injections of mixtures of nanomaterials. According to the recommendation adopted by the European Commission in 2011, a nanomaterial is “a natural, incidental or manufactured material containing particles, in an unbound state or as an aggregate or as an agglomerate, and where for 50% or more of the particles in the number size distribution, one or more external dimensions is in the size range 1 nm – 100 nm”. Nanomaterials typically show different behaviours or properties when compared to larger particles of the same material (Nohani & Ezatolah, 2015). In literature, most of the works refers to a clay matrix in which mixtures composed of different nano-sized elements are injected, as nano-aluminum oxide (Luo et al., 2012), SiO2 nanoparticles with both cement (Bahmani et al., 2014) and recycled polyester fiber (Changizi & Haddad, 2015), nanosized silica (Eswaramoorthi et al., 2017) and nanosized flyash (Sanchin Prabhu et al., 2017). Few studies have been conducted on coarse-grained matrices instead (Ghasabkolaei et al., 2017) and the suspensions of nanometric particles can be included among the fluid mixtures suitable for the treatment of medium-sized sand (Proia et al., 2017). In all these studies, the results of the experiments demonstrate that the addition of nanomaterials increases the values of the strength parameters investigated, such as the uniaxial compressive strength and the shear strength. Next future technologies will allow to micronize materials, that is to produce particles with diameters smaller than 100 µm, or to synthesize them (Bavasso et al., 2018) at increasingly lower costs and 43