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

The effect of tunnelling work on the stability of approach cutting

U radu se opisuje stanje kada se u području predusjeka tunela nalaze dvije geotehničke konstrukcije, predusjek i tunel, u istom području djelovanja. Odgovara se na pitanje utjecaja iskopa tunela na stabilnost pokosa predusjeka. Prikazuje se proračun deformacija upotrebom numeričkog trodimenzijskoga modela, koji simulira stvarni proces iskopa predusjeka i tunela, kao i prijedlog tehnoloških rješenja za smanjenje utjecaja iskopa tunela na stabilnost pokosa u zoni predusjeka.The situation when two geotechnical structures, the approach cutting and tunnel, are situated in the same area of action, i.e. in the approach cutting zone of the tunnel, is described in the paper. The influence of tunnelling work on the stability of the approach cutting is studied. The strain analysis based on the three-dimensional numerical model, which simulates the actual approach cutting and tunnelling work, is presented. The technogical solution for reducing the tunnelling work impact on slope stability in the approach cutting zone is also proposed

Design and realization of side-cuts in flysch rock mass

Opisuje se metodologija projektiranja i izvedbe sustava za osiguranje stabilnosti zasjeka u flišnoj stijenskoj masi na riječkom području. Na temelju rezultata istražnih radova, iskustva tijekom izvedbe zahvata na osiguranju stabilnosti stijenskih zasjeka u naslagama fliša te mjerenja i promatranja tijekom izvođenja i provedbom povratnih analiza o stanju naprezanja i deformacija utvrđene su značajke stijenske mase s opisom realne veličine parametara čvrstoće i deformabilnosti.The methodology applied in the design and realization of the system used to stabilize side cuts in flysch rock formations in Rijeka area is described. Rock mass properties were determined, and strength and deformability parameters were described, on the basis of investigation results, experience gained during stabilization of side cuts in flysch formations, and using results of measurement and monitoring activities conducted during back analyses of stress/strain properties

Probabilistic Evaluations of Prescribed Safety Margins in Eurocode 7 for Spread Foundations

According to the design code Eurocode 7, analysis procedures require reaching a prescribed safety margin, based on the conditions of levelling design action and design resistance. Such semi-probabilistic procedures do not result in a consistent equivalent value of the Overall Factor of Safety (OFS), neither in individual analysis nor in different tasks in geotechnical engineering. Furthermore, the implementation of different calculation approaches in Eurocode 7 also does not guarantee an equal probability of the occurrence of a relevant limit state. A comparative analysis is conducted for an example of a centrically loaded spread foundation on homogenous, isotropic, and coarse-grained soil, according to procedures in Eurocode 7, Design Approach 3. An algorithm is developed to estimate failure probability, taking into consideration the relevant statistical characteristics of each calculation parameter. A significant influence of the statistical characteristics of the relevant sample is emphasized. The degree of required modification of the equivalent Overdesign Factor (ODF) and the Overall Factor of Safety (OFS), based on the criterion of the required reliability index β and failure probability pf , is quantified

European soil classification system for engineering purposes

U radu se predlaže nova europska klasifikacija tla (ESCS) za inženjerske potrebe koja koristi opis i simbole označavanja tla prema europskoj normi EN ISO 14688-1, a koju su se, kao članice CEN-a, obvezale implementirati 34 europske zemlje. ESCS je razvijena na načelima klasifikacije tla prema europskoj normi EN ISO 14688-2 i okvirno slijedi smjernice definirane USCS klasifikacijom prema američkoj normi ASTM D 2487. Prikazana je procedura za provedbu predložene klasifikacije i dani su primjeri usporedbe rezultata klasificiranja tla sa USCS klasifikacijom.This paper proposes the new European Soil Classification System (ESCS) for engineering purposes which uses soil description and symbols according to European standard EN ISO 14688-.1, and which 34 countries are bound to implement, as CEN members. ESCS is developed on principles for soil classification according to the European standard EN ISO 14688-.2, and it generally complies with guidelines defined by the USCS soil classification system in accordance with the US standard ASTM D 2487. The procedure for the use of proposed classification, and examples of comparison with the USCS classification system, are presented

The development of block theory in rock engineering

Klasična teorija blokova, službeno objavljena 1985. godine s objavom knjige „Block Theory and Its Application to Rock Engineering“ [1], sadrži niz pojednostavljujućih pretpostavki. Takve pretpostavke omogućile su stvaranje jednostavne metode koja uz prihvatljiva ograničenja daje zadovoljavajuće rezultate za inženjerske potrebe. Usprkos tome, tijekom godina se nastojalo unaprijediti klasičnu teoriju, kako bi se mogla akomodirati složenijim problemima, i/ili povećala pouzdanost proračuna realnijim opisivanjem stanja u stijenskoj masi. Cilj ovoga članka je napraviti pregled istraživanja provedenih u cilju unaprjeđenja određenih ograničenja klasične teorije blokova. Na temelju pregleda pretpostavki i ograničenja klasične teorije te dosadašnjih istraživanja, mogu se lakše identificirati područja za daljnji razvoj teorije blokova.Classic block theory, officially established in 1985 with the publishing of the book “Block Theory and Its Application to Rock Engineering” [1], takes a lot of simplifying and restricting assumptions. Such assumptions allowed for a simple method which with acceptable restrictions gave satisfying results for engineering practice. Despite that, there have been many improvements throughout the years which try to accommodate for more complex problems and/or increase the overall reliability of the method. The scope of this paper is to give an overview of said improvements over the classic block theory. Based on the overview of assumptions of the classic theory and on the researches to date, it’s possible to more easily identify areas of further research and improvement

Seismic quality index (SQi) of rock mass

Postojeće klasifikacije stijenske mase su, u manjoj ili većoj mjeri, manjkave obzirom na specifičnosti pojedine lokacije. Ni jedna klasifikacija, međutim, ne koristi brzine seizmičkih valova kao ulazne parametre u postupku klasifikacije. U radu se uvodi pojam indeksa seizmičke kvalitete (SQi) kao komparativnog pokazatelja stanja diskontinuiranosti stijenske mase koji potvrđuje potencijal brzina uzdužnih valova kao klasifikatora, naročito karbonatnih stijena u zoni trošenja. Polje numeričkih vrijednosti SQi generira se iz odnosa sporost - seizmička impedancija – poroznost, u pojedinoj ćeliji matrice brzine. Promjene polja indeksa seizmičke kvalitete SQi uzrokuju promijenjene vrijednosti brzine u promatranoj ćeliji i susjednim ćelijama. Procedura određivanja indeksa seizmičke kvalitete prikazati će se na primjeru stvarnog tomografskog seizmičkog presjeka, na kojem su prethodno definirani diskontinuiteti standardnom procedurom geološko - geofizičke procjene. Primjena SQi kao polja vrijednosti omogućiti će preciznije zoniranje i određivanje važnosti diskontinuiteta u postojećim klasifikacijama karbonatnih stijena krša.The existing rock mass classifications are, to a smaller or larger extent, deficient in regards to the specifics of particular locations. No classification, however, uses the velocity of seismic waves as initial parameters in the classification procedure. This paper introduces the term seismic quality index (SQi) as a comparative indicator of the discontinuity state of rock mass which confirms the potential of velocity of longitudinal waves as a classifier, especially for carbonate rock mass in weathering zones. The field of numerical values for SQi is generated from the relationship slowness – seismic impedance – porosity, in a particular cell of the velocity matrix. Changes in the field of seismic quality index SQi cause changes in velocity values in an observed cell and neighbouring cells. The procedure to determine the seismic quality index will be shown on the example of an actual tomographic seismic profile for which discontinuities were previously defined using a standard geological-geophysical evaluation procedure. Use of SQi on the basis of fields of values, will allow to define more precisely zoning and determine the significance of discontinuities in terms of existing classification of carbonate rock mass in karst regions

Selection of a field testing method for karst rock mass deformability by multi criteria decision analysis

The rock mass deformation modulus is an essential parameter for any numerical analysis and prediction of deformation in geotechnical engineering. Experience acquired using a large number of geotechnical projects in Croatia and the world indicates a somewhat unreliable determination of rock mass deformability based on correlation of classification results. The method of field testing for deformability can provide a more reliable insight into rock mass behaviour under loading conditions. The paper presents the most frequently used methods for field testing rock deformability. The benefits and disadvantages are shown of each particular method used in determining criteria and forming a ranking list of test methods using the multi criteria decision analysis. This ranking list of terrain testing for the rock mass stiffness is acquired on the basis of set criteria, assumes guidelines for compiling an exploratory works plan necessary for designing complex geotechnical structures in karst. Appropriate analyses of the sensitivity to changes in the significance of particular criteria was carried out including its effect on selecting the field method for testing karst rock mass deformability

Geotechnics as an unavoidable segment of earthquake engineering

Ovaj rad daje širi pregled uloge geotehnike u potresnom inženjerstvu te obuhvaća niz praktičnih primjera kvantifikacije geotehničkih seizmičkih pokazatelja za potrebe izgradnje pojedinih objekata, kao i osvrt na nadolazeće promjene u sadašnjim projektnim normama koje evaluiraju utjecaj tla na građevine u potresnim uvjetima. S obzirom na seizmičku aktivnost područja Hrvatske, istaknuta je nužnost sveobuhvatnog pristupa seizmičkom mikrozoniranju koji uzima u obzir čitav niz pokazatelja, od litoloških, inženjerskogeoloških i hidrogeoloških karakteristika te položaja aktivnih rasjeda, do identifikacije nestabilnih padina i zona izraženog likvefakcijskog potencija, za što je potrebna provedba opsežnih geofizičkih i geotehničkih istraživanja.A broader overview of the role of geotechnics in earthquake engineering is given, and a set of practical examples of the quantification of geotechnical seismic indicators for construction of individual buildings is provided. An overview of oncoming changes to the current design standards for evaluating the effect the soil has on buildings in earthquake conditions is also given. Considering the level of seismic activity in Croatia, the need for adopting a comprehensive approach to seismic microzoning is emphasized, which involves a whole array of indicators, from lithological, engineering geological, and hydrogeological properties, and position of active faults, to identification of unstable slopes and zones of pronounced liquefaction potential, for which extensive geophysical and geotechnical investigations are required

Applying the analytic network process for risk assessment in sustainable ground improvement

Temeljenje teških građevina u mekom tlu može se riješiti poboljšanjem tla. Održivo poboljšanje tla postiže se miješanjem tla sa sintetiziranim vezivima - geopolimerima. Prirodno tlo se na taj način pretvara u novi materijal. U radu je prikazana primjena analitičkog mrežnog procesa (ANP) za procjenu rizika u održivom poboljšanju tla. Analize osjetljivosti pokazale su izrazitu stabilnost rezultata odlučivanja.Constructing foundations for heavy buildings on soft ground can be carried out by ground improvement. Sustainable ground improvement is achieved by adding synthesised binding materials - geopolymers. Natural ground composition in this way is transformed into new material. This paper presents the implementation of the Analytical Network Process (ANP) for assessing risk in sustainable ground improvement. Sensitivity analyses have shown exceptionally stable decision making results