Geotechnique A microscale-based model for small-strain stiffness in unsaturated granular geomaterials --Manuscript Draft-- Manuscript Number: 17-P-238R3 Full Title: A microscale-based model for small-strain stiffness in unsaturated granular geomaterials Article Type: General Paper Corresponding Author: Arianna Gea Pagano University of Strathclyde Glasgow, UNITED KINGDOM Corresponding Author's Institution: University of Strathclyde Order of Authors: Arianna Gea Pagano Alessandro Tarantino Vanessa Magnanimo Corresponding Author's Secondary Institution: Order of Authors Secondary Information: Manuscript Region of Origin: UNITED KINGDOM Abstract: Stiffness at very small strains G0 is commonly assessed via laboratory and field methods and used to design a wide range of infrastructure. When stiffness is inferred from field measurements, its value depends on the soil suction and state of saturation at the time of the measurement, and models are needed to infer G0 at varying suction and degree of saturation. When stiffness is measured on saturated specimens in the laboratory, models are needed to extrapolate the laboratory 'saturated' stiffness to the field 'unsaturated' stiffness. This paper presents an experimental investigation of G0 of unsaturated sand using the hanging water column method and the bender element technique. Experimental results revealed that wave propagation velocity and, hence, stiffness is not controlled by the product ‘suction times the degree of saturation’. A microscale-based model was formulated to interpret the experimental results, and to elucidate the mechanisms underlying different patterns of G0 in unsaturated materials observed in the literature. According to the proposed model, the evolution of G0 is controlled by the evolution of the suction/degree of saturation-induced intergranular stress during drying-wetting cycles. The breadth of the water retention curve and the magnitude of the intergranular stress due to the presence of the menisci were found to be responsible for the different patterns of G0. Suggested Reviewers: Eng Choon Leong Nanyang Technological University cecleong@ntu.edu.sg For his contribution to the improvement of bender element tests interpretation; knowledge and experience in laboratory and field testing for saturated and unsaturated soils Fernando A. M. Marinho Universidade de Sao Paulo fmarinho@usp.br For his contribution to the investigation of the small strain stiffness behaviour of unsaturated soils using bender elements David Mašín Charles University masin@natur.cuni.cz For his contribution to the modelling of shear stiffness of unsaturated soils at very small strains Powered by Editorial Manager® and ProduXion Manager® from Aries Systems Corporation