Institute of Hydro Engineering

Gdańsk, Poland

Institute of Hydro Engineering

Gdańsk, Poland
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Sawicki A.,Institute of Hydro Engineering | Swidzinski W.,Institute of Hydro Engineering
Journal of Theoretical and Applied Mechanics | Year: 2010

The incremental model describing the pre-failure behaviour of granular soils is proposed. Firstly, the constitutive equations are derived from the extensive set of experimental data, for the triaxial configuration. The following features are included into the model: initial anisotropy, initial state of sand (i.e. either dilative or contractive), instability line. Then, the incremental constitutive equations are generalized to the 3D case, using techniques of tensor algebra. Finally, the model is re-derived for the undrained conditions in order to predict such phenomena as, for example, static liquefaction. The approach presented is an alternative to already classical approaches as the elasto-plasticity or hypoplasticity. The paper consists of two parts. Part I deals with the formulation of the model and its calibration, whereas Part II is devoted to verification of the model against experimental results.

Bossi G.,CNR Research Institute for Geo-hydrological Protection | Zabuski L.,Institute of Hydro Engineering | Pasuto A.,CNR Research Institute for Geo-hydrological Protection | Marcato G.,CNR Research Institute for Geo-hydrological Protection
Geotechnical and Geological Engineering | Year: 2016

In order to assess the stability of a landslide, continuous or discontinuous models have been proposed. Here, we compare the two methods in their capability to provide a reliable hazard assessment. Both models have been applied to long term monitoring data obtained from a landslide located in Passo della Morte (Eastern Italian Alps). The availability of accurate data obtained in a long-term campaign is a pre-requisite to correctly understand the dynamics of the process and to implement a sound numerical model. First, a detailed geological investigation located the different soil layers and rock formations with their distribution along the slope, allowing the identification of the structural controls of the unstable rock mass. Then, landslide long term monitoring data provided information on the type of failure mechanism. Both the continuous and discontinuous numerical solutions describe the kinematics for the landslide and allow to delineate a hazard assessment for the investigated area. The continuous model is better in delineating the development of the deep slip surface while the discontinuous allows to recreate the toppling phenomenon. © 2016 Springer International Publishing Switzerland

Sawicki A.,Institute of Hydro Engineering | Swidzinski W.,Institute of Hydro Engineering
Archives of Civil Engineering | Year: 2013

This paper presents numerical simulations of the behavior of a sandy layer subjected to a cyclic horizontal acceleration in shaking table tests, with a particular attention focused on the settlements of a dry sand layer, and on the liquefaction of saturated sand. A compaction/liquefaction model (C/L) is applied to these simulations. The infl uence of specifi c parameters of the model on the compaction and liquefaction of a sandy layer is shown and discussed. The results of simulations are compared with selected experimental data.

Sawicki A.,Institute of Hydro Engineering
Archives of Mechanics | Year: 2014

THE PROBLEM OF PORE WATER PRESSURE changes in the seabed is considered. Two mechanisms of pore pressure changes are distinguished. The first is caused by external excitations, such as earthquakes, when pore pressure is gradually generated, leading to liquefaction. The second mechanism is caused by water waves, and it leads to cyclic changes in pore water pressure and the mean effective stress. Under certain conditions, when the effective stress path tends to exceed the failure condition, the regrouping of effective stresses takes place, as the soil should accommodate to new conditions. Then, the mechanism of resolidification of the seabed is described. It is concluded that after resolidification, the seabed is in a virgin state, as liquefaction erases the previous history of the seabed structure. A critical discussion of selected existing approaches to the problem of pore-pressure changes and the mechanism of liquefaction is presented in detail, in the form of extensive appendices. Some of these appendices deal with the crucial aspects of the mechanics of liquefaction such as, for example, the drained/undrained conditions. Copyright © 2014 by IPPT PAN

Sawicki A.,Institute of Hydro Engineering | Kulczykowski M.,Institute of Hydro Engineering
Journal of Earthquake Engineering | Year: 2014

Experimental results showing the frequency-dependent behavior of both dry and saturated sandy layers subjected to a horizontal excitation on a shaking table are presented. The largest settlements of a dry layer correspond to two specific frequencies. In the case of a saturated layer, there is a single peak frequency corresponding to the largest depth of sinking of a measuring plate in liquefied subsoil. The first peak of settlements coincides with the single peak of sinking in liquefied soil. The eigenfrequencies of the layer were estimated. A modification of the compaction law was proposed for low shaking frequencies. Copyright © A. S. Elnashai.

Sawicki A.,Institute of Hydro Engineering | Mierczynski J.,Institute of Hydro Engineering | Swidzinski W.,Institute of Hydro Engineering
Journal of Geotechnical and Geoenvironmental Engineering | Year: 2014

An interesting phenomenon, designated as an apparent creep of saturated sand, is described on the basis of experimental data obtained from triaxial quasi-drained-controlled tests. In such tests, external stresses were kept constant while the pore pressure was cyclically changed (intrinsic cyclic loading). It is a kind of cyclic loading that takes place in seabeds, where the pore pressure changes cyclically because of the action of water waves. During the experiment, both vertical and horizontal strains were recorded. It is shown that these strains gradually increase as functions of the number of loading cycles in such a way that the volume of the specimen is constant, and only the deviatoric strain increases. The experimental curve resembles the creep curve for solid materials, in which real time is replaced by the number of loading cycles. The experiments are described and discussed, and a simple model of the phenomenon observed is proposed. © 2013 American Society of Civil Engineers.

Zabuski L.,Institute of Hydro Engineering | Swidzinski W.,Institute of Hydro Engineering | Kulczykowski M.,Institute of Hydro Engineering | Mrozek T.,Polish Geological Institute National Research Institute | Laskowicz I.,Polish Geological Institute National Research Institute
Environmental Earth Sciences | Year: 2015

The paper discusses landslides investigated in a Brda river valley in the region of the town Koronowo near Bydgoszcz (Kujawsko-Pomorskie Voivodeship) in the Polish Lowlands. Due to morphologic and geologic setting the area is prone to slope instability. Out of 32 identified landslides, 9 were selected for detailed examination. To register a nature and rate of failures a complex monitoring system was installed on slopes where the selected landslides resulted in damages to municipal infrastructure. The system was facilitated with inclinometers and piezometers, supported by a network of GPS-RTK geodetic benchmarks as well as with a recording station. The performed examination revealed that the most unfavourable arrangement of the layers is, when under a non-cohesive soil lies a cohesive impermeable layer. The landslides are rather shallow ones (except for two incidents) with slow rate of displacement. The landslide-triggering factor is water originating from precipitation and snow melting. Influence of water was especially significant in early spring 2011, due to the combined effect of snow melting and infiltration of thawing water originating from the former, as well as exceptionally high rainfalls. The influence of hydrologic conditions on slope deformations is complex. There is a significant time lag between a movement initiation and unfavourable hydrometeorological conditions. That is exemplified with the landslide that was initiated in February–March 2011 in consequence of atmospheric conditions of November–December 2010. The results formed the background for inventing engineering treatment measures aiming at current remedial stabilisation of slopes and mitigation of possible landsliding in the future. © 2015, The Author(s).

Sawicki A.,Institute of Hydro Engineering | Swidzinski Waldemar W.,Institute of Hydro Engineering
Computers and Geotechnics | Year: 2010

A simple incremental model describing the pre-failure behaviour of granular soils is presented. The model describes both the dry/fully drained and undrained response. It takes into account an initial anisotropy of soil and an initial state defined as either contractive or dilative. A physically sound definition of loading/unloading is assumed, which differs from elasto-plastic approaches. The model is based on extensive empirical data and gives predictions conformable with experimental results. It also describes pre-failure instabilities of granular soils, both dry/fully drained and undrained. The Hill's criterion was used to examine stability. It was shown that this condition can be formulated either in terms of the effective stresses or by the total stresses. In the extreme cases of either dry/fully drained or undrained conditions, these alternative formulations are equivalent. This is not so in the case of partial drainage of pore water and associated volumetric deformations as well as pore pressure changes. The model describes the pre-failure instabilities well, and additionally allows for analytical derivation of the instability line. It was shown that the second order work, appearing in the Hill's condition, is equivalent to the entropy source. © 2010 Elsevier Ltd.

Sawicki A.,Institute of Hydro Engineering
Geotechnical Engineering | Year: 2011

Possible links between certain aspects of pre-failure instabilities of sand (instability line) and plastic dilation are studied. The starting point is experimental results obtained from triaxial investigations, which are approximated separately by analytical formulae for initially contractive and dilative sands. The irreversible strains are deduced from the condition that plastic work (dissipation) should be positive. Then, analytical formulae for plastic dilation are derived and presented in graphical form. In the case of initially contractive sand, a possible link between the instability line and maximum of the plastic dilatancy function is demonstrated. This condition is equivalent to the minimum dilation parameter or maximum of Rowe's function. In the case of initially dilative sand, it is shown that the negative work done by a mean stress on expanding (dilating) soil should not be treated as dissipative because of thermodynamical requirements. Consequently, the plastic dilation function is zero for shearing stress exceeding the instability line.

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