Matej Maček

Mechanism of Active Landslides in Flysch

Triggering mechanisms and active landslide dynamics are to a large extent a function of rock and soil types involved. Among different types of active landslides in Slovenia, in the last few years, those in flysch have been of specific research interest. Different field and laboratory investigations have been carried out on several active landslides in flysch, mainly on the Slano Blato landslide in SW Slovenia. The research activities have been focused on the prevailing mechanisms of active landslides in flysch, specifically they have been directed into investigations on soil suction and its relationship with water content and shear-strength characteristics. These research activities have been carried out in the framework of the World Center of Excellence “Mechanisms of landslides in over-consolidated clays and flysch” of the Faculty of Civil and Geodetic Engineering of the University of Ljubljana, and the IPL-151 Project “Soil matrix suction in active landslides in flysch – the Slano Blato landslide case”. This paper presents the main results obtained.

Monitoring of the Stogovce Landslide Slope Movements with GEASENSE GNSS Probes, SW Slovenia

Open image in new window Landslide Stogovce had been triggered by an extreme precipitation event in September 2010, and destroyed a local road. Measurements in inclinometers along the newly constructed road have indicated movements in 2011 and 2016. GEASENSE GNSS probes, which were installed on the landslide body below the new road, have also measured movements in range of several cm/month in the 2012–mid 2015 period, with cumulative movement of 45 cm in this period. Depth to the slip surface was from 13 to 25 m, and groundwater occurs in most of the boreholes, approximately half meter above the slip surface. The displaced material has been also detected by the calculation of surface difference in GIS, from the 2010 and 2014 lidar DEMs. The displaced material is composed mostly of debris of fractured Upper Triassic limestone and dolomite and weathered flysch, and due to its measured movements, is still capable of being transformed into a debris flow.

WCoE: Mechanisms of Landslides in Over-Consolidated Clays and Flysch and IPL-151 Project: Soil Matrix Suction in Active Landslides in Flysch—The Slano Blato Landslide Case

The Faculty of Civil and Geodetic Engineering of the University of Ljubljana (UL FGG), Slovenia, Europe, was voted in 2011 at the 2nd World Landslide Forum in Rome, Italy to be one of the 14 new World Centres of Excellence (WCoE) in Landslide Disaster Reduction for the period 2011 to 2014. This successful nomination followed the period 2009-2011, in which UL FGG successfully fulfilled the role as one of the WCoEs for the first time. The title of the activities of the WCoE was selected to be “Mechanisms of landslides in over-consolidated clays and flysch”.

Landslide Monitoring Techniques Database

An ICL thematic network Landslide Monitoring and Warning Thematic Network (LaMaWa TheN) was established in 2011 and includes ten ICL member organizations and two ICL supporters from eight countries. Of the different proposed activities of this ICL thematic network, we at the University of Ljubljana, Faculty of Civil and Geodetic Engineering (UL FGG) have started to set up web pages showing advanced landslide monitoring techniques and giving case examples of landslide monitoring and early warning systems. In the first phase, we started to put together a literature review on landslide monitoring systems with the description of landslides—a landslide monitoring database. The database will later be used as a base for formulating a web questionnaire to be filled by landslide experts worldwide to gain a broader knowledge on the expertise available in the world on the topic of landslide monitoring.

Soil-Water Characteristic Curve of Residual Soil from a Flysch Rock Mass

Depending on the nature of the material and suction range, laboratory measurements of the soil-water characteristic curve (SWCC) can be time-consuming and expensive, especially for residual soils, in which a wide range of particle sizes and soil structures typically results in SWCCs that cover a wide range of suction. Investigations of the SWCCs of residual soil from flysch rock masses are rare, and so far, no results were presented in the literature which were obtained by performing measurements on undisturbed specimens. In this paper, a detailed examination of water retention characteristics is performed for a specific type of residual soil (CL) formed by the weathering of a flysch rock mass. Measurements performed by using different techniques and devices on intact specimens were successfully combined to obtain the SWCC during both drying and wetting processes, under different stress conditions, and from saturated to air-dried conditions. Used procedures are suitable for the determination of SWCCs of soils that undergo volume changes during the drying or the wetting process, since instantaneous volumetric water content can be determined. Results presented in this paper can be used to assess the influence of desaturation of the residual soil covering flysch slopes during dry summer periods by providing key-in material properties required to analyze the transient rainfall infiltration process.

The reliability of CPTu and DMT for the mechanical characterisation of soft tailings

Nowadays, the stability and the safe cover and closure of soft tailings has become one of the most challenging topics in geotechnical and environmental engineering. For appropriate analysis and modelling, geotechnical properties of tailings should be well defined. Due to low strength, viscous nature and poor trafficability, as well as due to the specific geometrical properties of fine particles and pore water chemistry in tailings, different test methods and their modification and improvements must be used for valid and reliable characterisation of tailings. This paper analyses and compares the results of different field test methods, piezocone penetration test (CPTu), flat dilatometer test (DMT) and field vane test (FVT), performed on the red gypsum sludge and complementary laboratory tests. CPTu and DMT measurements were evaluated using procedures developed for soils and the obtained mechanical properties were compared with those measured in the laboratory. The significant distinctions between different test methods and different empirical correlations were analysed taking into account differences in index properties of soils and the red gypsum sludge. Based on analysis, some modifications of conventional empirical correlations were proposed for field tests results interpretation and sludge characterisation. The obtained data also show the advantages and limitations of some conventional methods and prove the need for further development in that field of geotechnical investigation.

Identification of Landslides as Debris Flow Sources Using a Multi-model Approach Based on a Field Survey—Koroška Bela, SloveniaOpen image in new window

The landslide as a debris flow source identification is an important but often complex step in debris flow hazard assessment. Landslides are an important source of debris flows and this paper presents a multi-model approach of identification. The village of Koroska Bela in NW Slovenia has a history of debris flows and active landslides in the watershed of the Bela torrent, which presents a sediment source for potential debris flows in the future. Two models were applied for landslide identification in the watershed. A detailed field survey was carried out for model results validation. A GIS-based landslide susceptibility model was applied to identify areas susceptible to landslides and the LS Rapid triggering model was applied also to identify landslides and simulate the triggering phase. The study results show good agreement of the field survey and the models, particularly considering the completely different origin of both models and their development. These results show the possibility of applying numerical models to identify landslide sources and encourage their implementation in debris flow hazard assessment. But as with all models, a high level of expert knowledge and users’ experience is required to get useful, and what is more, reliable results.

Mechanisms of Landslides and Creep in Over-Consolidated Clays and Flysch (WCoE 2014–2017)Open image in new window

The Faculty of Civil and Geodetic Engineering of the University of Ljubljana (UL FGG), Slovenia, Europe, was voted in 2014 at the 3rd World Landslide Forum in Beijing, China to be one of the 15 new World Centres of Excellence (WCoE) in Landslide Disaster Reduction for the period 2014–2017. This successful nomination followed the period 2011–2014, in which UL FGG successfully fulfilled the role as one of the WCoEs for the second time. The title of the activities of the WCoE in this third term was slightly modified to be “Mechanisms of Landslides and Creep in Over-Consolidated Clays and Flysch”. We can divide the activities of the WCoE at UL FGG into international and national research activities. The international ones consisted of the ICL related activities with the main task of being the main organizer of this 4th World Landslide Forum 2017, international cooperation, European research activities, and bilateral cooperation. The national ones consisted of the national projects and the national research program “Water Science and Technology, and Geotechnics”. In the paper, these activities of the WCoE at UL FGG are elaborated in more detail, with a comprehensive list of publications to show the dissemination and capacity building efforts.

Influences of Rheometer Size and the Grain Size on Rheological Parameters of Debris Flow

Open image in new window Debris flows are non-Newtonian fluids. Theirs rheological parameters depends on the volume concentration, grain size composition, fines content and fines plasticity. To get realistic data for modelling of debris flows, the rheological parameters had to be measured at different volume concentrations, taking into account the whole grain size distribution. Rheometers for fluids are limited with the gap size and usually only fine grained suspensions could be investigated. The results measured in such device on coarse grained soils may not be representative. The paper presents the study in which two shear rate controlled coaxial cylinder rheometers were used to investigate the influence of maximum grain size to the rheological parameters of the Stože debris flow: the larger ConTec Viscometer 5, in which the maximum grain size is 22.4 mm and the smaller Brookfield DV3T HB rheometer. Rheological parameters obtained by using both devices were compared based on water content, volume concentration and maximum grain size.

Geotechnical and Environmental Characterization of Boiler Slag as Fill Material

AbstractBoiler slag is a by-product that is derived from coal combustion in wet bottom boilers. Due to its low bulk density, in the compacted state it is an attractive alternative for use as structural fill material. Compared with other coal combustion by-products, the geotechnical and leaching properties of boiler slag are less known. This paper presents the results of laboratory and field investigation of boiler slag, produced in boilers where brown coal is used as fuel. Chemical and mineralogical composition, as well as mechanical properties were studied in the laboratory. A test embankment was constructed in order to identify compaction behavior and the achieved layer stiffness. A lysimeter was installed as part of the test embankment for the long-term monitoring of the quality and quantity of percolated water.