Three-Dimensional Analysis of the Mirogoj Landslide in Zagreb

Klizište Mirogoj je malo translacijsko klizište koje se pojavilo u proljeće 2013. i prouzrokovalo štetu na pristupnoj cesti groblja Mirogoj. Klizište se nalazi na obroncima Medvednice u jugoistočnom dijelu groblja Mirogoj. Osnovu naslaga čine glinoviti materijali kvartarne starosti ispod kojih se nalaze pliokvartarne naslage zastupljene šljuncima, pijescima i siltitima. U njihovoj podini nalaze se glinovito pjeskoviti lapori i gline gornjeg ponta koji u mlađem dijelu postupno prelaze u slabovezane do nevezane glinovite pijeskove i slitove. Dimenzije klizišta su ukupne duljine od 65 m te 80 m maksimalne širine. Klizište je maksimalne dubine od 7 m do klizne plohe. Padina se pruža u smjeru sjeveroistok – jugozapad s nagibom između 20° i 25°. Sredina područja je šumovita, a na djelu klizišta vegetacija upućuje na dugotrajno klizanje terena koje je uočeno na savinutim stablima poznatim kao pojava „pijanog drveća“. U okolici klizišta nema pojave stalne površinske vode. Stalna razina površinske vode od 3,50 m dubine zabilježena je na dvije bušotine prema istražnim radovima. Za povratnu analizu klizišta uzet je karakteristični presjek za klizište Mirogoj. Povratnom 2D analizom stabilnosti u programskom paketu FLAC 7.0 određeni su parametri triju geotehničkih jedinica: glina mekane do čvrste konzistencije, glina krute konzistencije i glina vrlo krute konzistencije. U diplomskom radu korištena je za isto klizište 3D metoda analize stabilnosti prema Hungru (1987). Nakon proračunatih vrijednosti razmatrane su metode sanacije klizišta te je predloženo rješenje prema kojemu se sanira postojeće klizište i to kombinacijom pilotske stijene i dreniranja terena.The Mirogoj Landslide (City of Zagreb, Croatia) is a small, translational landslide occurred in spring 2013 caused damages of the access road to the Mirogoj Cemetery. The landslide is located at the slope of the Medvednica Mountain. The geological setting of the slope is consisted of the quaternary clayey layer over layers of gravels, sands and silts in the superficial deposit while the bedrock is consisted of clayey marls, clays, silts and sands. The dimensions of the landslides are 65 m of total length, 80 m of maximum width and 7 m of maximum depth to the slip surface. The orientation of the slope is to southwest with inclination from 20 to 25 degrees. The wider area of the landslide is forested and in the signs of old sliding are visible on the existed trees (“trunk” forest). In surround area there are no presences of surface water phenomena. The ground water level was identified in two boreholes during the field investigation and the average depth to the ground water level from the surface is 3,50 m. The geotechnical model was established for the proper longitudinal cross section of the landslide and three geotechnical units were selected as applicable layers in the model: the high plasticity clay of solid consistency and semi-solid consistency layers in superficial deposit, and low plasticity clay of solid consistency as the bedrock layer. The 2D back analyses using FLAC V 7.0 software were conducted to confirm accepted shear strength parameters of different soil layers. The 3D analyses were conducted using Hungr’s method (1987) to identify impact of spatial impact of shear resistance on existing factor of safety. As a remedial measure the drainage using longitudinal drainage trenches and pile wall in the foot were considered. For both proposed remedial measure constructions the 2D and 3D slope stability analyses were conducted. It was concluded that the 3D analyses provide better insight in effectiveness of applied remedial measures in order to stabilize the Mirogoj Landslide