Chrysanthos Steiakakis

Contribution of electrical tomography methods in geotechnical investigations at Mavropigi lignite open pit mine, Northern Greece

In this paper, the application of 2D and 3D electrical resistivity methods in geotechnical investigations is explored through a case study in Northern Greece. These two methods were employed at a lignite surface mining operation where fracture zones and discontinuities have been recently observed close to the pit boundaries. The main aim of the geophysical survey was to estimate the inclination of the contact between the Neogene and Schist/Carbonate formations near the southern limits of the pit, as well as to estimate the thickness of the carbonate rocks on top of the Schist formations to evaluate the stability of the southern slopes. Synthetic data were initially generated to help plan an efficient electrical tomography survey, in a region with complex geology and irregular terrain. Three configurations (Wenner–Schlumberger and dipole–dipole or pole–dipole) proved essential in such conditions and helped improving the resolution of the resistivity section. The sections were then calibrated by boreholes. Finally, the geophysical survey provided invaluable data regarding the geometry of the bedrock and possible faults, which was essential for the slope stability calculations.

Complementing geotechnical slope stability and land movement analysis using satellite DInSAR

This paper explores the potential of using satellite radar inteferometry to monitor time-varying land movement prior to any visible tension crack signs. The idea was developed during dedicated geotechnical studies at a large open-pit lignite mine, where large slope movements (10–20 mm/day) were monitored and large fissures were observed in the immediate area outside the current pit limits. In this work, differential interferometry (DInSAR), using Synthetic Aperture Radar (SAR) ALOS images, was applied to monitor the progression of land movement that could potentially thwart mine operations. Early signs of land movements were captured by this technique well before their visual observation. Moreover, a qualitative comparison of DInSAR and ground geodetic measurements indicates that the technique can be used for the identification of high risk areas and, subsequently, for the optimization of the spatial distribution of the available ground monitoring equipment. Finally, quantitative land movement results from DInSAR are shown to be in accordance with simultaneous measurements obtained by ground means.

Slope Stability Evaluation of Stiff Fissured Clays and Shales for Different Failure Conditions

This paper evaluates the utilization/mobilization of shear strength on failure surfaces located at different depths and in extension to different stress fields based on the current state of practice. Superficial failure surfaces are distinguished from deep seated ones regarding the utilization of shear strength parameters. Practical recommendations following the differentiation of stress field are proposed in the way that different shear strength parameters should be selected for different types of failures. Finally the difficulties and pit falls in evaluating the stability of high slopes in such materials is presented in order to help practicing engineers.

Land movement monitoring at the Mavropigi lignite mine using spaceborne D-InSAR

This paper examines the capability of remote sensing radar interferometry to monitor land movements, as it varies with time, in areas close to open pit lignite mines. The study area is the “Mavropigi” lignite mine in Ptolemais, Northern Greece; whose continuous operation is of vital importance to the electric power supply of Greece. The mine is presently 100-120m deep while horizontal and vertical movements have been measured in the vicinity of the pit. Within the mine, ground geodetic monitoring has revealed an average rate of movement amounting to 10-20mm/day at the southeast slopes. In this work, differential interferometry (DInSAR), using 19 Synthetic Aperture Radar (SAR) images of ALOS satellite, has been applied to monitor progression of land movement caused my mining within the greater area of “Mavropigi” region. The results of this work show that DInSAR can be used effectively to capture ground movement information, well before signs of movements can be observed visually in the form of imminent fissures and tension cracks. The advantage of remote sensing interferometry is that it can be applied even in inaccessible areas where monitoring with ground equipment is either impossible or of high-cost (large areas).

Integrating weather and geotechnical monitoring data for assessing the stability of large scale surface mining operations

Abstract The geotechnical challenges for safe slope design in large scale surface mining operations are enormous. Sometimes one degree of slope inclination can significantly reduce the overburden to ore ratio and therefore dramatically improve the economics of the operation, while large scale slope failures may have a significant impact on human lives. Furthermore, adverse weather conditions, such as high precipitation rates, may unfavorably affect the already delicate balance between operations and safety. Geotechnical, weather and production parameters should be systematically monitored and evaluated in order to safely operate such pits. Appropriate data management, processing and storage are critical to ensure timely and informed decisions. This paper presents an integrated data management system which was developed over a number of years as well as the advantages through a specific application. The presented case study illustrates how the high production slopes of a mine that exceed depths of 100–120 m were successfully mined with an average displacement rate of 10– 20 mm/day, approaching an almost slow to moderate landslide velocity. Monitoring data of the past four years are included in the database and can be analyzed to produce valuable results. Time-series data correlations of movements, precipitation records, etc. are evaluated and presented in this case study. The results can be used to successfully manage mine operations and ensure the safety of the mine and the workforce.

Integrated Evaluation of Rockfall Triggering Mechanism for Road Monitoring

Rockfalls in mountainous roads may result in increasing hazards for vehicles and people. Cases of rockfalls with fatalities or great disruption of traffic have been reported in the news and account for significant money loss. Unfortunately due to the complexity of the phenomenon of a single or a few rocks detachment, it has not been studied extensively and data relating to triggering of such phenomena are scarce. In this paper a first attempt is made to gather and analyze available published case studies where the triggering mechanisms of rockfalls are presented. The most significant triggering mechanisms are presented and the resulting rockfalls are analyzed based on the collected data. This work is part of a project aiming to monitor and evaluate rockfall phenomena in Greek highways.

Mapping the Bedrock Using ERT for Slope Stability Studies at Mavropigi Lignite Open Pit Mine, Northern Greece

The application of the electrical resistivity method in geotechnical investigations is explored through a case study in Northern Greece. This method was employed at a lignite surface mining operation where fracture zones and discontinuities have been recently observed close to the pit boundaries. The main aim of the geophysical survey was to estimate the inclination of the contact between the Neogene and Schist/Carbonates formations south of the pit. Two configuration arrays proved essential in such conditions, and helped improving the resolution of the geoelectrical section. The geoelectrical sections were then calibrated by boreholes indicating that the bedrock is dipping to the Northeast. Furthermore, the geophysical survey provided invaluable data regarding the geometry of the bedrock which was essential for the slope stability calculations.