Analysis of the Possible Reactivation of the Krbavčići Landslide in Northern Istria, Croatia

Abstract

The Krbavčići landslide occurred in January 1979 near the town of Buzet, Croatia, after a long period of heavy rainfall. It is located in Northern Istria in the area built of flysch rock mass where numerous mass movements in the past and recent history have been recorded. A flysch rock mass is highly susceptible to weathering, which leads to material disintegration, changes in geotechnical properties, and shear strength decrease, finally resulting in instability processes in flysch slopes. This paper describes existing information about the Krbavčići landslide occurrence, laboratory testing of siltstone samples from a flysch rock mass, and numerical slope stability analyses of a possible landslide reactivation caused by possible long rainy periods and further weathering of the flysch rock mass. Slope stability analysis using the Rocscience, Slide software, as well as landslide numerical simulations using the LS-Rapid simulation software were performed on the basis of the digital elevation model (DEM) and laboratory test results of siltstones with different weathering grades. A DEM of the Krbavčići landslide was obtained on the basis of the unmanned aerial vehicle (UAV) survey conducted in March 2016. The residual shear strength of siltstones to predict a reactivation of landslides is of highest importance and was determined by ring shear and direct shear tests on siltstone samples with different weathering grades. The results of the numerical simulations show that an increase of the groundwater level in the landslide body in combination with the further weathering of the flysch rock material at the sliding surface would have the main influence on a possible landslide reactivation and the further development of the landslide displacement.

Influence of Carbonate-Flysch Contact and Groundwater Dynamics on the Occurrence of Geohazards in Istria, Croatia

“…Increased short-term precipitation should lead to increased material weathering and slope processes that increase landslide risk. The decrease in the factor of safety with the increase in the degree of flysch weathering was discussed in [36]. From the 2D stability analyses performed, the authors concluded that the fresh flysch rock material had a factor of safety of 1.175, the factor of safety for the slope built in the moderately weathered material decreased slightly to 1.132, and to 1.064 for the completely weathered material.…”

“…Fine-grained flow is not a typical instability phenomenon in this area, but is geomorphologically predetermined by the presence of deeply incised fossil ravines filled with clayey or weathered rock material. The analysis of the possible reactivation of the Krbavčići landslide was further discussed in Vivoda Prodan and Arbanas [36].…”

Weathering Effects on Engineering Geological Properties of Trachydacitic Volcanic Rocks from the Monte Amiata (Southern Tuscany, Italy)

“…While lithology depends on the rock-forming environment and does not evolve over time, the degree of weathering may be time-dependent, and it may show different degrees of intensity in space. Rock weathering may play an important role on the evolution of landforms [5,6], slope instability [7][8][9][10][11][12][13] and engineering geological properties [14][15][16]. Namely, strength parameters are strictly dependent on both intrinsic lithology and secondary weathering degree [4], the latter being often evaluated through expert-based visual properties [17,18] and/or mineralogical characteristics determined by modal analyses [19].…”

Large Shear Strength Parameters for Landslide Analyses on Highly Weathered Flysch

“…The main input for a landslide stability analysis is the shear strength parameters of the soil materials that form the failure surface. In order to determine the relevant shear strength parameters for design purposes, the widely commonly used laboratory tests are the direct shear box test, even though they have several limitations [1][2][3][4][5][6], as well as the triaxial compression test [7][8][9]. Moreover, for the determination of the residual shear strength, the ring shear apparatus is used [10][11][12][13][14][15].…”