Excavation of Open Pit “Zagrad” in Rijeka, Croatia, A Case History

On the location Zagrad in Rijeka, Croatia, an open pit has been designed and constructed for the purpose of building the garageaccommodation- business complex. The location of the open pit is situated in the central area of the town Rijeka, and closely surrounded by the existing accommodation buildings, a traffic line and a railway. The open pit was designed and constructed four levels below the terrain surface, adjacent to the existing buildings and a traffic line. To secure the open pit walls during excavation, a support system with the selfdrilling rock bolts for the reinforcing of the rock mass and reinforced concrete grid structure on the excavated surface was designed. This paper presents the construction method for the open pit, with the application of active design concept during works execution. It also presents the set-up system for measuring, observing and monitoring of the support system behavior. This enabled, on the basis of the measurement results and performed back analysis, an active designing of the suitable support system during works execution, for the in situ conditions of the rock mass in excavation. Performed back analysis showed need for the additional correction in the correlation between deformation characteristics of the rock mass and rock mass classification

COMPLEX LANDSLIDE IN THE RJEČINA RIVER VALLEY

U radu su prikazani rezultati istraživanja prve faze složenog klizišta na sjeveroistočnoj padini doline Rječine između brane Valići i naselja Pašac. Bokovi doline oblikovani su u paleogenskom flišu i kvartarnim padinskim tvorevinama. Na vrhovima su zastupljene vapnenačke stijene tvoreći litice. Nastanak istražene kompleksne pojave klizišta predodređen je geološkom gradom i morfogenezom doline Rječine. To je složeno retrogresivno klizište, koje se počelo razvijati od stope prema vrhu kosine. Na padini je otkriveno 13 pojedinačnih kliznih tijela. Klizanjem je zahvaćen materijal padinskih tvorevina i dio kore fizičko-kemijskog raspadanja. Veći dio kliznog tijela saturiran je podzemnom vodom koja se procjeđuje kroz pokrivač po kontaktu s nepropusnom flišnom podlogom. Klizanje je relativno plitko budući da u hidroteh-ničkom tunelu, koji se nalazi ispod nožice klizišta, nisu uočena oštećenja prouzročena klizanjem. Pokrenuti su i megablokovi vapnenačke stijene koji, najvjerojatnije, klize po flišnoj podlozi. To je posebna pojava, netipična za klizišta na flišnim padinama u široj okolici Rijeke. Vapnenačka stijena na litici je jako dezintegrirana, a u njoj su vidljive svježe pukotine. Istraživanja su se sastojala od geodetskih mjerenja, geofizičkih, inženjerskogeoloških i geotehničkih istraživanja. Geodetsko snimanje obavljeno je metodom terestičke fotogrametrije. Rezultati su uspoređeni s aero-snimcima učinjenim godine 1981. Tako su se mogle otkriti promjene morfologije padine u razdoblju od 1981. do 1997. godine. Fotoskice su korištene i za dopunu inženjersko-geološkog kartiranja. Geofizičko mjerenje je obavljeno metodom plitkog seizmičko-refrakcijskog profiliranja.This paper presents the first phase investigation results of the complex landslide situated on north-eastern slope of the Rječina valley, between Valići damm and the village of Pašac. The valley slopes were formed in Paleogene flysch and Quaternary formations. The limestone rocks are present on the top sites, forming the scarps there. The complex landslide formation has been preconditioned by the geological structure and morphogenesis of the Rječina valley. This is the type of complex retrogressive landslide, starting with its development from toe to head. Thirteen individual landslide bodies were discovered on the slope. The material of slope formation and a part of weathering zone is caught by the landsliding. The larger part of landslide body is saturated by underground water penetrating through the covering zone in contact with flysch bedrock. The landsliding is relatively shallow, because there is no visible damage affected by sliding in the hydrotechnical tunnel, situated below the landslide toe. The mega-blocks of the limestone rock have also been moved and, most probably, are sliding down the flysch bedrock. This is a special phenomenon, atypical of the flysch slope landslide type in the area of Rijeka. The limestone rock on a scarp is extremely disintegrated, with new visible fractures in it. The site investigations comprised the surveying, seismic and engineering geological explorations. The surveying was performed by the method of terrestrial photogrammetry. The results are compared with aerial photos from 1981. In this respect, it was possible to discover the changes of slope morphology during the period 1981 — 1997. The photos were also used for the engineering geological mapping supplementation. The seismic surveying was performed by the surface seismic refraction method