UNCORRECTED PROOF Deformation characteristics of lacustrine carbonate silt in the Julian Alps S. Lenart * Section for Earthquake Engineering, Slovenian National Building and Civil Engineering Institute, Slovenia Received 30 June 2004; revised 31 December 2004; accepted 20 February 2005 Abstract The deformation characteristics, shear moduli and damping ratios of reconstituted lacustrine carbonate silt samples were investigated in different kinds of laboratory tests. Material from a landslide that occurred in a seismically very active area in Slovenia was used in the tests. The initial values of this material’s deformation characteristics and the extent to which these values change due to increasing shear strain depend on a number of factors, such as the degree of saturation, the initial void ratio, over-consolidation, and the effective stresses. The use of a volumetric threshold strain has proved to be the best way of describing the shear modulus reduction curve irrespective of any other factors, and it fits well with the data obtained in the experiments. The critical state and consolidation lines for the investigated material are presented in the paper as deformational characteristics at critical strain levels. The material’s liquefaction potential was studied for certain in situ conditions. q 2005 Published by Elsevier Ltd. Keywords: Lacustrine carbonate silt; Deformation characteristics; Shear modulus; Damping ratio; Liquefaction; Critical state; Volumetric threshold strain 1. Introduction The different glaciations which have covered the Alps several times in the Earth’s history have produced glacial detritus in large quantities, particularly in Alpine valleys. Post-glacial deposits are common in regions where melting water formed post-glacial lakes. Fine silts and clays were brought down from the mountains by water and settled in lakes, resulting in the formation of various kinds of lacustrine sediments. Such sediments were formed not only in the European Alps but also in North America and the Himalayas, and in other regions which have been covered with ice in the past. Descriptions of lacustrine clay soils [1,2,3] and of lacustrine gravelly fines [4] have been given by various authors, together with some of their characteristics. In some cases [2] the authors have dealt with the mineralogical and mechanical characteristics (e.g. static behaviour) of these soils, whereas in other cases dynamic tests like liquefaction tests [4] as well as in situ measurements [5] have been performed. Most of the test results have shown that the behaviour of such lacustrine material of glacial origin is very sensitive to various factors such as water content and loading conditions, including seismic effects. 2. Reasons for the investigation of lacustrine soils in the Julian Alps Lacustrine soils can be found in many parts of Slovenia, but mostly in the region of the Julian Alps, which is located in the western part of the country and is seismically very active. During the strong earthquake which occurred in April 1998, with its epicenter in the Krn mountains and a magnitude of M WA Z6.0, an approximately 100 m long section of the shore of the 20 km distant Lake Bohinj collapsed due to liquefaction of fully-saturated lacustrine carbonate silt. At the same time the earthquake, in amplified form, caused serious damage to several buildings in the village of Mala vas near Bovec, which were founded on lacustrine soil. These failure cases, which occurred during a seismic event, drew our attention to the sensitive behaviour of lacustrine carbonate silts. Soil Dynamics and Earthquake Engineering xx (xxxx) 1–12 www.elsevier.com/locate/soildyn 0267-7261/$ - see front matter q 2005 Published by Elsevier Ltd. doi:10.1016/j.soildyn.2005.02.010 * Corresponding author. Tel.: C386 1 2804 555; fax: C386 1 2804 484. E-mail address: stanislav.lenart@zag.si. SDEE 2883—20/5/2005—00:47—MURALIDHARAN—148521—XML MODEL 5 – pp. 1–12 DTD 5 ARTICLE IN PRESS 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112