Waldemar Świdziński

Elastic moduli of non-cohesive particulate materials

The problem of determining the elastic moduli of some particulate materials (granular, non-cohesive) is analysed. First, a brief survey of existing laboratory methods and a literature review are presented. Some basic shortcomings regarding the interpretation of commonly accepted tests and the determination of material parameters are discussed. Then an original method of determining the elastic moduli of particulate materials is proposed. The method is based on a new interpretation of oedometric tests, with additional measurement of lateral stresses. An original feature of this interpretation is that the first phase of unloading is elastic. The elastic moduli for various particulate materials, such as soils, grains, powders and metal balls, are determined. It has been shown that the elastic moduli of particulate materials do not significantly depend on either the initial density of the material or the stress level, in contrast to some widely accepted opinions.

Monitoring of landslides in the Brda river valley in Koronowo (Polish Lowlands)

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.

Apparent Creep of Saturated Sand Caused by Intrinsic Cyclic Loading

AbstractAn 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.

Response of Partially Saturated Non-cohesive Soils

Abstract This paper analyses and discusses experimental results of undrained triaxial tests. The tests were performed on non-cohesive partially saturated soil samples subjected to monotonic and cyclic loading. The tests were aimed at determining the influence of saturation degree on soil’s undrained response (shear strength, excess pore pressure generation). The saturation of samples was monitored by checking Skempton’s parameter B. Additionally, seismic P-wave velocity measurements were carried out on samples characterized by various degrees of saturation. The tests clearly showed that liquefaction may also take place in non-cohesive soils that are not fully saturated and that the liquefaction potential of such soils strongly depends on the B parameter.

Stability Analysis of Żelazny Most Tailings Dam Loaded by Mining-Induced Earthquakes

The paper presents the stability analysis of Żelazny Most tailings dam subjected to mining-induced paraseismic events. The tailings dam as well as foundation have complex geotechnical structure. The foundation of the dam is built of series of tertiary and quaternary formations affected in the past by three glaciations whereas the complexity of tailings structure results from the method of its deposition within the pond. Simplified dynamic displacement analysis of the dam is performed based on Newmark’s approach using GeoStudio2007 software. The paper highlights the necessity of proper domain and time discretization, especially in the case of complex geological structure. Dynamic response of the tailings dam was obtained for the equivalent linear one-phase soil model. Stability calculations were performed for Coulomb-Mohr model and Stress History And Normalized Soil Engineering Properties (SHANSEP). The applied input signals were selected by Arias intensity criterion from huge set of signals recorded on the ground surface caused by mining tremors. The peak ground acceleration value was scaled to the values predicted by hazard analysis. The results of the calculations carried out for three selected acceleration signals have revealed no permanent deformations.

Modelling of Post-flotation Tailings Liquefaction Induced by Paraseismic Events

Abstract This paper presents and discusses the results of numerical modelling of pore water pressure build-up in post-flotation saturated tailings deposited at the Tailings Storage Facility “Żelazny Most”, caused by seismic-induced dynamic loading. Numerical simulations were based on the compaction/liquefaction model proposed by A. Sawicki. The model parameters were determined in the laboratory for tailings sampled at the TSF “Żelazny Most”. The sensitivity of the numerical model was verified in a series of numerical tests for various horizontal acceleration amplitudes. In the main calculations, an accelerogram recorded during a real paraseimic event was assumed. The results obtained show that, with the current seismic activity near the TSF “Żelazny Most”, some pore water pressure is generated within the saturated tailings layer, but it does not trigger the liquefaction phenomenon.

Simplified Probabilistic Analysis of Settlement of Cyclically Loaded Soil Stratum by Point Estimate Method

Abstract The paper deals with the probabilistic analysis of the settlement of a non-cohesive soil layer subjected to cyclic loading. Originally, the settlement assessment is based on a deterministic compaction model, which requires integration of a set of differential equations. However, with the use of the Bessel functions, the settlement of a soil stratum can be calculated by a simplified algorithm. The compaction model parameters were determined for soil samples taken from subsoil near the Izmit Bay, Turkey. The computations were performed for various sets of random variables. The point estimate method was applied, and the results were verified by the Monte Carlo method. The outcome leads to a conclusion that can be useful in the prediction of soil settlement under seismic loading.

Stabilization of the Landslide in the Brda River Scarp at the Abutment of the Historical Bridge of the Narrow-Gauge Railway (Koronowo, Poland)

The paper presents the analysis of the catastrophic landsliding that affected the embankment at the western bank of the Brda river and the bridge abutment of the abandoned narrow-gauge railway from Bydgoszcz to Koronowo (central Poland). The bridge (18 m max. height, 120 m long) was set in use in 1895. It is the highest truss bridge in Europe and it is assigned a technical monument status according to Polish legislation. The railway trail was closed in 1992, so after the bridge served as a pathway. The catastrophic landsliding occurred as effect of unfavourable lithology (loose soils underlain by clay), river valley-side geometry and cumulative triggering action of rain and melt-water. The initial slide exceeding a 10 m displacement developed almost perpendicularly to the embankment axis. Following slips, developed under the bridge, resulted in removal of buttressing and the abutment exposure. The sliding process was simulated using Universal Distinct Element Code and applying a back analysis procedure. Based on the above, a remedial treatment was worked out which comprises stabilizing by retaining, slope profiling around the abutment as well as artificial drainage of the landslide area.

Discussion of “Cyclic Strength of Sand under Sustained Shear Stress” by J. Yang and H. Y. Sze

In their technical paper, the authors study the effect of initial shear stress on the cyclic strength and liquefaction potential of sand. They introduce the concept designated as thresholda, inwhicha represents the sustained shear stress level, and they suggest that this parameter can be related well to a state parameter c. A linear relationship between cyclic strength andc is proposed, and the line representing this relationship rotates as a changes. The authors present extensive results fromexperiments performed on themodel Fujian sand, onwhich they base their generalizations. They also mention a lack of sufficient data from other sources that would enable a better understanding of the problemconsidered, especially because someofficial geotechnical organizations, for example the National Center for Earthquake Engineering Research (NCEER) committee, still do not recommend existing approaches as geotechnical standards. In order to meet these needs, we would like to add information about the similar behavior of another model sand, called Skarpa. The discussers hope that our limited results will be included in respective databases concerning the effect of sustained shear stress on the cyclic behavior of sands. We have also found some inconsistencies in the paper by Yang and Sze, and have addressed these in additional comments.