Naslov
The role of clay minerals in formation of sliding surface - a case study of Črešnjevec landslide (Zagreb, Croatia)

Autori
Martinčević Lazar, Jasmina ; Miklin, Željko ; Podolszki, Laszlo ; Durn, Goran ; Grizelj, Anita

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, kratko priopćenje, znanstveni

Izvornik
Conference Book of 9th Mid-European Clay Conference / Tibljaš, Darko ; Horvat, Marija ; Tomašić, Nenad ; Mileusnić, Marta ; Grizelj, Anita - Zagreb : Hrvatsko geološko društvo, 2018, 76-76

ISBN
978-953-6907-71-7

Skup
9th Mid-European Clay Conference (MECC 2018)

Mjesto i datum
Zagreb, Hrvatska, 17.09.2018. - 21.09.2018

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
clay minerals ; sliding surface ; landslide

Sažetak
Črešnjevec is one of the largest and long- active landslides in southern hilly zone of Medvednica Mt. that belongs to residential area of the City of Zagreb and where the problem with landslides occurs for decades. The first activity of Črešnjevec was recorded in 1960s and it continues until today. According to MIHALINEC et al. (2002) the landslide body consists of Pliocene – Pleistocene and Upper Miocene sediments with sliding surface at approximately 12 m of depth in zone of contact between two mentioned types of sediments. The aim of this paper is to represent a mineralogical composition of sediments from Črešnjevec landslide to see whether or not a mineralogical composition, especially clay minerals, has an influence on physical and mechanical properties of landslide sediments making them sensitive to sliding. Because of different environmental conditions during the Pleistocene and Upper Miocene periods (KOVAČIĆ & GRIZELJ, 2007 ; GRIZELJ et al., 2017), it was expected that the mineral composition would be also different. Furthermore, it was assumed that samples from shear zone would contain expandable clay minerals and high values of Atterberg limits and external specific surface area. Mineralogical and geotechnical analysis were conducted on 15 samples collected from Črešnjevec 35 m deep borehole drilled in 2016. during the project of Detail Engineering Geological Map of Podsljeme urbanized area M 1:5000 – Phase II (MIKLIN et al., 2016), in which three types of sediments were recognized: (a) heterogeneous Pleistocene sediments, (b) red sandy clays of presumed Upper Miocene- Pliocene age and (c) silts and sandy silts of Upper Miocene age. Atterberg limits were determined according to ASTM D 4318 – 10 (2010) standard proceeding. Residual shear strength parameters was obtained with standard direct shear test procedure. Specific surface area (SSA) was calculated from the Kozeny – Carman equation for hydraulic conductivity (URUMOVIĆ & URUMOVIĆ, 2016). Qualitative mineralogical analyses were performed by X-ray powder diffraction on random mounts of bulk samples and oriented mounts of < 2 μm fraction. Oriented mounts of the < 2 µm fraction were record after the following treatments: a) air drying, b) saturation with K+, c) solvation of K+ saturated mounts with ethylene-glycol, d) saturation with Mg2+, e) solvation of Mg2+ mounts with glycerol, f) heating to 400°C and g) heating to 550°C. Semiquantitative mineral composition of samples was obtained based on interpretation of bulk diffraction patterns and data processing in “RockJock” quantification program (EBERL, 2003). The main differences among all three sediment units are in carbonate and clay minerals content. Namely, heterogeneous Pleistocene sediments consist mostly of vermiculite, feldspars and quartz which are the main minerals in samples. Other mineral components in this unit are kaolinite, micas (illite and muscovite), goethite and amphiboles. Silts and sandy silts of Upper Miocene age consist mainly of quartz and micas in various quantitative ratios. They are in association with feldspars, carbonate minerals (dolomite, calcite), chlorite, smectite, kaolinite and goethite. Red sandy clays consist predominantly of quartz and micas in association with kaolinite, feldspar, goethite and small amount of vermiculite. Three of all samples match a shear zone with sliding surface. One of them is from units of heterogeneous Pleistocene sediments and other two from unit of red clays. They all have high clay content (38-76 %). The following mineral phases were detected in fraction < 2 µm: kaolinite, mica and two types of vermiculite (one with diffraction maximum on 18 Å and other with diffraction maximum on 14.5 Å, after solvation of Mg2+ mounts with glycerol). Furthermore, these samples have the highest values of liquid limits (41-86 %) and plasticity index (22-49 %) as well as SSA (60- 126 m2/g) and very low residual shear strength parameters (cr1=7 kNm-2, cr2= 6 kNm-2, φr1=13.5°, φr2=11.2°). According to obtained results it can be concluded that clay mineralogy, as a result of different sedimentation conditions, obviously had great influence on formation of sliding surface.

Izvorni jezik
Engleski

Znanstvena područja
Geologija, Interdisciplinarne prirodne znanosti

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