The area of the City of Zagreb is relatively large (~ 640 km 2 ) and urbanized (> 800,000 residents). The general geomorphological setting of the City is on the alluvial plane of the Sava River, on the southern slopes of Medvenica Mountain and on the northern slopes of Vukomeričke Gorice, i.e. hilly area. Within this area geohazard events occur, for example: numerous landslides during last decades, great flood in 1964 and on 22 nd March 2020 Zagreb was struck by an M5.5 earthquake. These events cause great damages and can endanger or even take lives. Seismic and geological zonation of the part of the City of Zagreb area (~ 175 km 2 on the southern slopes of Medvednica Mountain) was carried out as one of the geohazard mitigation measure. The zonation was financed by the City of Zagreb government and performed according to Eurocode 8 in the period of 2017-2019. The results of zonation were presented in Study where the geological, geotechnical, geophysical and seismic characteristics of the research area were compiled and addressed. The data sets were organized and presented in GIS project, i.e. in form which is easily usable by officials or public users. At the same time the Study contributes to better understanding of soil and rock properties of the research area and increases the available data and knowledge fund. The research results were also presented on developed Seismic zonation map in accordance with Eurocode 8 in scale of 1:25,000 where areas of equal soil amplification relative to the bedrock are depicted. The developed map can provide (thematic) basic seismic background info necessary for urban planning. Different thematic (geohazard) zonation maps are necessary in modern and quality urban development and they are prerequisite in development of quality hazard and risk management.

Water Treatment Plant for the city of Osijek is situated on the riverbank of Drava River. The soil at the location consists of alluvial deposits with layers of soft soil to the depth of 16 m. One part of the construction area is covered with 4 m high fill material. For heavy loaded structures and large area basins and tanks, deep foundation was designed with full displacement concrete piles. The piles of d=40 cm are installed by using lost cone technique down to 2 m in the bearing stratum of dense sand. Bearing capacity of the piles is calculated according to geotechnical investigation works which consists of geotechnical borings, laboratory tests, in‐situ SPT and CPTU. The calculation methodology is given, regarding the selection of design values for pile skin and base resistance. The effect of addition filling on the construction area is evaluated by using finite element method in Plaxis 2D, to calculate the negative skin friction on the piles. After the pile construction, pile capacity was tested by dynamic load test. The comparison of predicted and tested results is given in the paper.

Abstract:The behavior of sand largely depends on the initial state, water content, drainage conditions, and type of action on the sand. The dominant mechanism that governs sand behavior is dilatancy, the volume change during shearing. Owing to dilatancy, dense sand samples attain greater strength during shearing compared to loose samples. Investigation of the sand behavior shows that the final strength during shearing, for the sand samples starting from the same initial state of stress, tends to be independent of the initial void ratio. This final state is called the critical state, or steady state, and can be well described by the critical state line. The main goal of this research is to investigate the behavior of clean sand from Jerovec under triaxial shearing and to derive its critical state line. The behavior of sand is investigated for different initial states (initial densities and state of stress) and for different drainage conditions (consolidated isotropically drained (CID) test and consolidated isotropically undrained (CIU) test). The test results are presented along with all the laboratory tests performed on Jerovec sand (grain-size distribution, specific gravity, minimum and maximum void ratio). The critical state line is compared with those of other sands available in the literature.Keywords: triaxial test; drained and undrained conditions; initial state of compacted sand; isotropic compression; shear stress-strain curve; stiffness and strength ISPITIVANJE PIJESKA JEROVEC I ODREĐIVANJE LINIJE KRITIČNOG STANJA Sažetak: Ponašanje pijeska znatno ovisi o stanju u kojemu se pijesak nalazi, sadržaju vode u pijesku i uvjetima dreniranja vode, te vrsti djelovanja na pijesak. Dominantan mehanizam koji utječe na ponašanje pijeska je dilatacija, svojstvo zrnatog materijala da mijenja volumen zbog djelovanja čistog smicanja. Zbog djelovanja dilatacije, zbijeni uzorci pijeska postižu veću čvrstoću prilikom smicanja u odnosu na rahle. Ispitivanja pokazuju da neovisno o početnoj zbijenosti, uzorci pijeska koji se smiču iz istog početnog stanja naprezanja, postižu jednaku čvrstoću za konačno stanje. Navedeno stanje naziva se kritičnim stanjem, a može se dobro opisati linijom kritičnog stanja. Svrha istraživanja u ovome radu bila je ispitivanje ponašanja pijeska Jerovec u uvjetima troosnog smicanja, te određivanje linije kritičnog stanja. Ispitano je ponašanje uzoraka za različito početno stanje zbijenosti i izotropnog naprezanja te različite uvjete dreniranosti (drenirani -CID pokus, nedrenirani -CIU pokusi). U radu su prikazani rezultati ispitivanja u troosnom uređaju te rezultati ispitivanja fizičkih karakteristika pijeska (granulometrijski sastav, minimalna i maksimalna zbijenost, specifična težina čvrstih čestica). Linija kritičnog stanja uspoređena je s kritičnim stanjem za slične pijeske dostupne u literaturi.Ključne riječi: ispitivanje u troosnom uređaju; drenirani i nedrenirani uvjeti; početno stanje zbijenosti pijeska; izotropna kompresija; naponsko deformacijska krivulja smicanja; krutost i čvrstoća.