engleski

Landslide investigation without the application of exploratory drilling

Landslide investigations often are based on exploratory or rotary core drilling, which has its drawbacks. Borehole investigations are expensive and long term. It is a kind of point test so that important soil layers can remain undetected by drilling. Inaccessible and steep terrains on landslides are often a significant problem for drilling rig applications. Therefore, in recent years, this standard investigation method has been supplemented or, in specific cases, replaced by modern methods of geotechnical and geophysical investigations. This paper presents just such a case of landslide investigation without the application of exploratory drilling. The investigations were carried out in village Petrovsko (north-western Croatia), on a landslide of the rotational-translational type, with a total area of 5000 m2. This instability potentially threatened the D206 state road corridor. Engineering geological and recent geotechnical-geophysical investigations were applied to define the boundaries of instability, the lithological composition of sediments in the subsurface and locating the sliding surface. According to the results of investigations with a Dynamic Probe Light (DPL) and Cone Penetration Test (CPTu), the depth of the sliding surface was determined. Geophysical investigations performed using Electrical Resistivity Tomography (ERT), Seismic Refraction (SRF) and Multichannel Analysis of Surface Waves (MASW) confirms and perfectly complement the results of in situ geotechnical surveys. The unfavourable geological structure was determined, as silty sands and clays predominate in the surface layers, and organic clays of low shear strength appear immediately before contact with marl. The main cause of landslides is the decreased strength of clay in contact with marl, due to the rise of ground water level and effect on pore pressure and effective pressure of the deeper layers of the clay. Finally, the gravel drainage trenches have been proposed as a conceptual remedial solution through the upper lying layers to hard marl.

Landslide investigation ; Sliding surface ; Slope sliding trigger ; Landslide remediation

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