Determining G-γ Degradation Curve in Cohesive Soils by Dilatometer and in situ Seismic Tests

Authors: Ivandic Kreso, Spiranec Miljenko, Kavur Boris, Strelec Stjepan

Abstract:

This article discusses the possibility of using dilatometer tests (DMT) together with in situ seismic tests (MASW) in order to get the shape of G-g degradation curve in cohesive soils (clay, silty clay, silt, clayey silt and sandy silt). MASW test provides the small soil stiffness (G_o from v_s) at very small strains and DMT provides the stiffness of the soil at ‘work strains’ (M_DMT). At different test locations, dilatometer shear stiffness of the soil has been determined by the theory of elasticity. Dilatometer shear stiffness has been compared with the theoretical G-g degradation curve in order to determine the typical range of shear deformation for different types of cohesive soil. The analysis also includes factors that influence the shape of the degradation curve (G-g) and dilatometer modulus (M_DMT), such as the overconsolidation ratio (OCR), plasticity index (IP) and the vertical effective stress in the soil (s_vo'). Parametric study in this article defines the range of shear strain g_DMT and G_DMT/G_o relation depending on the classification of a cohesive soil (clay, silty clay, clayey silt, silt and sandy silt), function of density (loose, medium dense and dense) and the stiffness of the soil (soft, medium hard and hard). The article illustrates the potential of using MASW and DMT to obtain G-g degradation curve in cohesive soils.

Keywords: Dilatometer testing, MASW testing, shear wave, soil stiffness, stiffness reduction, shear strain.

Digital Object Identifier (DOI): doi.org/10.5281/zenodo.1316099

References:

[1] Lo Presti, “D.C.F. Discussion on threshold strain in soils”, In Proceedings of X ECSMFE, vol IV, Firenze, Italy, pp. 1282-1283, 1991.
[2] M. Vucetic, “Cyclic threshold shear strain in soils”, Journal of Geotechnical Engineering 120 (12), 2208-2228, 1994.
[3] M. Vucetic, R. Dobry, “Effect of soil plasticity on cyclic response”, Journal of Geotechnical Engineering, ASCE 117 (1), 89-107, 1991.
[4] I. Ishibashi, X. Zhang “Unified dynamic shear moduli and damping ratios of sand and clay”, Soils and Foundation 33 (1), 182-191, 1993.
[5] S. Likitlersuang, S. Teachavorasinskun, C. Suarak, E. Oh, A. Balasubramaniam, “Small strain stiffness and stiffness degradation curve of Bangkok Clays”, Japan Geotechnical Society, Elsevier B.V., 2013.
[6] TC16, “The flat dilatometer test (DMT) in Soil Investigation – A report by the ISSMGE Committee TC16”, 41 pp., Reprinted in proc. 2nd Int. Conf. On the Flat Diltometer, Washington D.C., 7-48, May 2001.
[7] S. Amoroso, B. M. lehane, M. Fahey, “Determing G- decay curves in sands from Seismic Dilatometer Test (SDMT)”, Geotechnical an Geophysical Site Characterization 4 – Coutinho & Mayne (eds), Taylor & Francis Group, London, ISBN 978-0-415-62136-6, 2013.
[8] S. Amoroso, P. Monaco, “Use of the seismic dilatometer (SDMT) to estimate in situ G- decay curves in various soil types”, Geotechnical an Geophysical Site Characterization 4 – Coutinho & Mayne (eds), Taylor & Francis Group, London, ISBN 978-0-415-62136-6, 2013.
[9] S. Marchetti, P. Monaco, M. Calabrese, G., “DMT-predicted vs measured settlements under a full-scale instrumented embankment at Treporti (Venice, Italy)”, Proc. 2nd Int. Conf. on Site Characterization, Porto, 2:1511-1518, Rotterdam: Millpress,2004.
[10] S. Marchetti, P. Monaco, M. Calabrese, G. Totani, “Comparision of moduli determined by DMT and backfigured from local strain measurements under a 40 m diameter circular test load in the Venice area”, Proc. 2nd Int. Conf. on the Flat Dilatometer, Washington D.C., 220-230, 2006.
[11] P. W. Mayne, “Stress-strain-strength-flow parameters from enchanced in situ tests”. In Proc. Int. Conf. on In Situ Measurement of Soil Properties and case Histories, Bali 27-47,2001.
[12] K. Ishihara, “Estimate relative density from in-situ penetration tests”, In Proc. Int. Conf. on In Situ Measurement of Soil Properties and case Histories, Bali 17-26, 2001.