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Abstract A rock bolt represents the most important element in ensuring stability of rock mass excavations. This paper presents weaknesses and strengths of methods which deal with evaluation of rock bolts. Most widely used is pull-out test, conducted for capacity determination in destructive manner. To overcome ‘destructivity’, a method of acoustic emission shows that the force close to the failure point can be determined, so that the rock bolt will remain usable for strengthening purposes. Another NDT system, called GRANIT, is developed in order to determine load level inside rock bolt by analyzing its natural frequencies. When it comes to evaluation of grouting quality, efforts were made in order to find reliable solution, but existing methods still have weaknesses which limit their applicability. First developed and today still widely used is Boltometer which is based on emission of energy in rock bolt and on analyzing returned energy. However, dissipation of energy, due to karstic phenomena may not yield good results. Some efforts in improvement of weaknesses of Boltometer have been conducted and are presented in paper. A basic concept is given for novel method for NDT evaluation of grouting quality, which is in development at Faculty of Civil Engineering in Zagreb.
Abstract The aim of this paper is to examine and compare the results of engineering geological exploration works in the design phase and during the construction of tunnel Stražina. Tunel Stražina is located near the city of Omiš on Zagreb-Split-Dubrovnik highway in Croatia. The interactive design method was applied in the tunnel design. This methodology integrates the empirical, rational and observational approaches in the geotechnical design of the tunnel. It allows for the thorough and comprehensive overview and problem solving during the construction. In addition, it minimizes the errors that may occur due to the limitations of each individual approach. Predicted underground excavation support solutions were done based on site investigation activities and other bases using the empirical and rational approaches. Geomechanical and Q classification were performed as a part of the empirical approach. Engineering-geological tunnel mapping was done during the excavation activities as a part of the geotechnical monitoring. Verification of the tunnel support system during the construction phase was done using the actual data obtained from the engineering-geological mapping and the monitoring. Thus, the actual rock mass quality along the tunnel was determined and the tunnel underground excavation support measures were optimized. Due to the complex conditions present in the rock mass, the discrepancy between estimated and actual rock mass conditions can hardly be avoided, and likewise, a certain amount of discrepancy between the predicted and actual support systems is also to be expected. The interaction of site investigation, design and construction, in addition to introducing the risk analysis, is essential for a more rational, safer and more economical construction. Development of methods and procedures for the preparation and control for each of the phases is important for a successful operation of each participant performing a completion of a particular phase, as well as for the project investor.
Abstract Tunnel "Vrata" is a part of the Rijeka—Zagreb high way, section Oštrovica—Vrata. Right tube of the tunnel "Vrata" is 262 m long. During excavation works for the right tunnel tube, underground hall (cavern) was found along the tunnel cross section, and outside of it as well. The longest hall cross section which is parallel with tunnel, in horizontal projection is 51 m long. Total volume of this caving object is estimated to be approx. 55,000 m, but most probably this cavern and the cave channel are going further along the fault, above the narrow and covered up fissures under the talus material. Investigations, design solution, numerical simulation, remedy works and monitoring of the caving object remedy works are shown in this paper.
Abstract Viaduct "Kotezi" is designed over the polje Bunina, on the highway A1, Zagreb –Split – Dubrovnik, section: Ravča – Vrgorac – Ploče 1 (Karamatići), from the chainage km 83 + 652.9 to km 84 + 867. Span complex consists of 32 spans with lengths 37.10 + 30 × 38.00 + 37.10 = 1214.20 m. The height from the base of the highest pillar foundation to the elevation of the grade line is 36.0 m. In this paper the methodology of the investigations, the investigation results and rough copy of the viaduct foundation is described, as well as the real engineering geological conditions on the site of every foundation, which were determined after the excavation. The comparison between the prognostic and the real cover thickness is presented, as well as the way of building the substitution layer of the crushed stone.
Abstract The Konjsko tunnel is an integral part of the Zagreb-Split-Dubrovnik highway, section Prgomet-Dugopolje. It consists of two tunnel tubes having 1326.0 and 1133.8 meters in length. The greatest overburden amounts to 150 m. This paper presents geotechnical measurement results and back numerical analyses. Back numerical analyses in combination with geotechnical measurements enable safer and more rational approach to designing and performing underground constructions. They contribute to the development of cognition on rock massifs and to determining its physically-mechanical parameters, joining it with rock classifying results. They can help to verify or to modify characteristics of the primary support system, of the foreseen progress length, estimated time of non-supported ranges, as well as time and schedule of performing all works regarding the excavation stability.
Abstract The remaining oil reserves in Croatian oil fields amounted to 11.0 million cubic meters at the end of 2007. This, together with high oil prices on the world market, represents a good basis for the implementation of enhanced oil recovery methods. Between 1978 and 1991, detailed laboratory research of carbon dioxide usage for oil displacement was performed. That research, coupled with simulation studies, has proved that water alternate gas - WAG process achieves the best oil recovery from Croatian oilfields (e.g. Ivanic oilfield). The CO2 pilot project on the Ivanic oilfield started in 2001 by injecting salt water into the reservoir in order to increase reservoir pressure. The injection of carbon dioxide lasted between 2003 and 2006.Final results and in situ data from the field will be presented in the paper. During the injection of carbon dioxide into the reservoir, some thermodynamic changes occurred in the tubing string as well. The most important factors during CO2 injection are the knowledge of CO2 physical characteristics and thermodynamic conditions during the injection. PT conditions during the CO2 injection on the pilot project have been measured and will be presented in the paper. Based on the results of the pilot project, a decision to set up the first Croatian full-field EOR project on Croatian oilfields was made. Introduction In the past 20 years a large group of scientists has conducted theoretical laboratory research. The next phase was using numerical simulation methods for increasing oil recovery from oil reservoirs in Croatia. Almost all EOR methods have been analysed but carbon dioxide usage method was selected as the most appropriate. That research identified the Ivanic oil field as the main candidate for the implementation of CO2 injection. The Ivanic Oilfield, situated 35 miles east of Zagreb, the capital of Croatia, was discovered in 1963. Oil production was established from the Miocene Iva-sandstones at an average depth of 1,600 m. The reservoir rock consists of small to middle sized grain sandstones crossed through with grey midstone. The original oil in place was estimated at 21.6210 m. The Ivanic crude oil gravity is 850 kg/m (33.4°API). The initial reservoir pressure was 183 bar, and reservoir temperature is 97.7 °C. The reservoir rock characteristics are: porosity in the range of 21.5–23.6 %, and permeability in the range of 14.6–79.6 mD. Tectonically, Ivanic structure is an asymmetrical brachianticline with axes running in the northwest-southeast direction, and with an inclination of the 3 - 4 %. Crossectional geological profiles of Ivanic oil field structure are given in Figure 1. In the upper and lower parts of the structure there are shale zones which divide the formation into two reservoirs. The lower reservoir is divided into 7 intervals of sandstone, named Gamma. From the top they are named Gamma: 5, 4, 3, 2/1, 2/2, 2/3 and 2/4. The Ivanic oil field naturally flowing oil production started in 1963. Solution gas drive was the dominant reservoir drive mechanism in the primary phase. In 1966, primary production peeked at 1,200 m of oil per day and by 1972 it declined. The recovery factor realized in the primary phase amounted to 10.4 % of OOIP. Because of that, at the beginning of 1972, water flooding was for first time in Croatia performed on the Ivanic oil field. The reservoir pressure at that moment was 107 bar. A secondary production peak was reached in 1977, again with oil production of 1,200 m. Realized oil recovery in secondary phases (end of the 2007) was 26.1% of OOIP. Over 40 years, through primary and secondary phases, 8,747,841 m of oil, and 1,250 x 10 m of gas was produced on the Ivanic oil field. The production of oil in primary and secondary phases is given in Figure 2. Injection of carbon dioxide in the pilot project was performed in the deepest part of Gamma reservoir - Gamma2/4. From the upper production intervals, Gamma2/4 is separated by midstone (1.5-4 meters). The original oil in place in Gamma2/4 reservoir was estimated at 68310 m. From CO2 injection point of view, that oil reserve was the target of the pilot project.
Abstract Tertiary CO2 injection is planned at Ivanic oil field, Croatia, in order to recover some of more than 12×10 Sm (75 MMSTB) of remaining oil in place. The field was discovered and put to production in 1963, secondary waterflooding was started in 1972, and today the field is facing a considerable decline in oil production and an increasing water cut. A revised geological model of Ivanic field, based on 3D seismic data acquired in 1998, was used as a ground for building a full field numerical simulation model. 40 years of production history were matched sucessfully by using black oil formulation. Compositional simulation was applied for 18 tertiary injection scenarios, which investigated impact of number and position of injection wells, number of CO2 slugs, and prior repressuring of the reservoir on the predicted production profile and final tertiary oil recovery. All tertiary injection cases were compared to the base case of continued waterflooding. Simulation results indicate possibility of recovering more than 2.5×10 Sm (15.7 MMSTB) of incremental oil in 20 years of future production. One of the possible sources of CO2 is the gas treatment plant in Molve, Croatia, which daily releases into atmosphere large quantities of carbon dioxide extracted from natural gas produced in northern Croatian gas fields. Sequestering a considerable amount of this CO2 in Ivanic oil field is a welcome additional benefit of the planned tertiary injection project. Introduction Ivanic oil field is situated in the north-western part of the Sava depression, about 35 km to the east of the Croatian capital of Zagreb. It was discovered in 1963 by drilling the exploratory well Iva-4, which confirmed the existence of commercial quantity of 33.4°API oil in Miocene sandstones inside an assymetrical brachianticline, at the absolute (subsea level) depth of approximately 1600 m. Porosity of the reservoir rock is in the range 21.5–23.6%, permeability is in the range 14.6–79.6 mD, initial reservoir pressure was 183 bar, and reservoir temperature is 97.7°C. Original oil in place was estimated at 21.62×10 Sm. Total of 88 wells were drilled during the field history. Currently there are 43 oil producers (all equipped with sucker rod pumps), 11 observation wells and 14 water injectors; 20 wells were abandoned. 7 oil producing sandstone intervals, named Gamma, were identified during the field development phase. Starting from the topmost, they are Gamma 5, 4, 3, 2/1, 2/2, 2/3, and Gamma 2/4. A presence of initial gas cap was confirmed in Gamma 5, while PVT analyses of a number of downhole and surface fluid samples taken from Gamma 4 through 2/4 indicate that oil is undersaturated, with saturation pressure of 137.2 bar common in those intervals. Initial PVT properties of reservoir oil are shown in Table 1. Production started in late 1963, and peaked in 1966 with slightly more than 1200 Sm of oil per day. Soon after that, lack of aquifer support caused a substantial decrease of reservoir pressure and, consequently, oil production decline typical for inefficient solution gas drive. It was therefore decided to support the reservoir energy by water injection. Waterflooding was started in 1972, and oil production response was noted early in 1973, together with water production increase. Secondary production peak was reached in 1977 with oil production reaching almost 1200 Sm/day, which was followed by a more or less regular trend of oil production decline and water cut increase. Cumulative oil production until end of year 2003 is 8.68×10 Sm. Oil and water production history is shown in Figure 1. Ivanic as an EOR Candidate During the late 1970s and beginning of 1980s, majority of Croatian oil fields were comprehensively evaluated in terms of applicability of various EOR technologies. The basic screening criteria applied were taken from the available technical references. During this screening process, Ivanic oil field was identified as a good candidate for application of CO2 injection. This lead to an extensive laboratory research program aimed at quantifying the thermodynamical interaction between CO2 and Ivanic reservoir oil and the ability of CO2 to mobilise the capillary trapped oil from the pore space of actual reservoir rock samples. Several sets of slim-tube tests performed by injecting CO2 into sandpacks saturated by recombined Ivanic oil according to Yellig and Metcalfe laboratory procedure showed that minimum miscibility pressure (MMP) is in the range of 190–200 bar, close to the initial reservoir pressure.
Abstract INA Oil Company, Plc. Zagreb is a Croatian company engaged in the exploration and production of oil and gas, refining and distribution of petroleum products. An enormous quantity of hazardous waste is generated in oil and gas production and thus has to be disposed in a permanent and safe manner. In recent years, INA has been disposing waste by injection into exploration dry wells and production depleted wells. A specific waste disposal problem has arisen in the process of gas and condensates in Molve, Kalinovac, Stari Gradec and Gola fields. Namely, mercury-sulfide, sulfur slurry and heavy metals have been separated during the production of gas and condensate. Mercury-sulfide has been separated in the process of active coal utilization. The disposal of active coal saturated with mercury-sulfide is a very complex issue. So far, the methods of mercury-sulfide disposal have not been ecologically acceptable. However, on the basis of new experience and knowledge in that field, waste dispersed in a bentonite suspension may be disposed in a permanent and safe manner into appropriate geological formations. In the same way, when combusting various types of industrial and municipal waste, the problem of residual ash disposal emerges. Such residual ash contains heavy metals which may be permanently disposed by using the above mentioned method. This paper deals with the experience of waste disposal by deep well injection in the Republic of Croatia. Introduction The exploration of hydrocarbons in the Republic of Croatia started some hundred years ago, and significant oil and gas reserves have been discovered. More then 4,300 exploration and production wells were drilled in the onshore and offshore sedimentary deposits. In the nineties, there was initiated to dispose waste, generated in the process of exploration, drilling, production, refining and distribution of hydrocarbons by injection into dry exploration or depleted production wells. At the time, the liquid waste component was injected into an abandoned, specially selected well, while its solid part was neutralized by solidification and it was disposed at the location of wells, namely in the existing mud pits or specially built waste disposal sites. Nowadays, by improving the referred technology, liquid and solid parts of waste have been permanently disposed by injection into geological and technically appropriate wells. The technology mentioned above enables not only the disposal of waste generated in oil industry but also that generated in other industries such as food industry, chemical industry, leather and pharmaceutical industries. By the application of the referred technology, waste may be permanently and safely disposed into geologically appropriate wells, as well as heavy metals which contain almost all kinds of waste, thus meeting the principles of environmental protection. The overall waste disposal cost and the possibility of polluting potable water by heavy metals from solidificated solid part of waste are reduced. Currently, the technological waste created during drilling, workover, oil and gas production and refining processes is permanently disposed by applying a specific procedure developed in Croatia. For that purpose, an adequate law regulation to enable the application of the referred procedure is under preparation. This paper deals with the possibility of hazardous waste disposal generated in the process of oil and gas production and by incineration treatment (residual ash). Many dry and depleted wells are particularly appropriate for a permanent disposal of industrial waste generated in various industries since there is no need for additional investment in the creation of new wells. Selected geological formations at the depth of 1,500 to 5,000 meters are covered with impermeable bed rock and cap rock without vertical regional faults, which prevents waste from migrating into the aquifer of potable water. Waste disposal by injection into deep wells is a unique method which may be used for a permanent disposal of hazardous waste without having a single impact on the environment, since waste is disposed out of the biosphere.
ABSTRACT: The solution used for the design of foundations for a wild animal crossing over a deep trench during the construction of a highway in Croatia is presented. The foundation design of the crossing arch structure had to be changed after the excavation works revealed that the foundation rock, consisting of upper Triassic dolomite, was greatly heterogeneous. Several limit equilibrium and stress-strain analyses were carried out after the rock classification resulted in four rock and soil categories. Three different foundation types, satisfying the requirement of uniform rock deformations, were finally chosen. Horizontal displacements measured at the arch abutment show very good agreement with predicted values. RÉSUMÉ: La solution utilisee dans l'etude des fondations d'un ouvrage prefabrique en arc destine au passage de gibier travers de l'autoroute Zagreb - Rijeka est presentee. II fallait modifier les etudes pour ces fondations apr s qu'une forte heterogeneite du bedrock, compose des dolomites provenant du trias superieur, a ete revelee pendant les travaux de construction de l'autoroute. Suivant les crit res de la classification geotechnique des sols, le bedrock a ete divise en quatre categories. Les analyses de capacite portante par methode d'equilibre limite et les analyses de contrainte-deformation ont ete effectuees, Trois types de fondations, determines selon Ie principe d'harmonisation des deformations, ont ete choisis. Les mesures des deplacements horizontaux au pied de I'arc ont montre une bonne correspondance avec les deplacernents prevus. ZUSAMMENFASSUNG: Die Gruendungsbestimmung der Montagebogenkonstruktion des, fuer die wilde Tiere im tiefen Einschnitt ausgefuerten Übergangs ueber die Autobahn Zagreb-Rijeka, ist in diesem Atikel beschrÍeben. Der Gruendungsentwurf der Bogenkonstruktion sollte verandert werden, nachdem die Ausgrabungsarbeiten gezeigt haben, daß der Grundfels - Dolomit aus Keuper, hauptsachlich ungleichartig war. Die Analysen der Tragfahigkeit durch Grenzzustand und die Spannung/Deformation Analysen wurden durchgefuehrt,, Nach der Felsenklassifikation wurde Fels- und Bodenkategorisation gemacht und vier Kategorien wurden bestimmt. Drei verschiedene Gruendungsarten, welche die Beanspruchungen der gleichformigen Felsdeformationen befriedigten, wurden endlich gewahlt. Die im Strebepfeiler gemessenen horizontalen Verschiebungen, zeigen gute Übereinstimmung mit den prognostizierten Werten. INTRODUCTION A crossing for wild animals was constructed over a 20 m deep trench along the Zagreb-Rijeka highway in Croatia The crossing is half a prefabricated arch structure, 100 m wide, with a span of 30 m. The foundations were constructed in the upper Triassic dolomite. It was first decided to construct a three-joint prefabricated arch with 1.5m wide elements, and small foundations adequate for the good quality rock mass. After the cut-off was made, it was determined that there were significant variations in the quality of the rock. It was thus, decided to design a two-joint arch with cross-enforcement to pass over weaker zones. The two prefabricated elements were fixed at the crown. ANALYSIS OF FOUNDATION DESIGN Geological structure of the region The rock mass consists of the upper Triassic late diagenetic dolomites of different texture types. Wide clay beds exist in the fault zones. The uniaxial compressive strength of the basic rock is 50 MPa. There are three basic groups of discontinuities. The interbedding has the position of 30–35/20–40°, and the layer thickness varies between 10 and 60 cm. The layer surfaces are deflected and rough, and they often have a limonite coating.
ABSTRACT: Based on many years of research focusing on a number of significant structures (bridges, tunnels, dams, high rock slopes, etc.) designed and realized in the Adriatic coastal area, we have collected a large quantity of engineering-geological and geotechnical information. To devise engineering geological (IGM) and geotechnical models (GM), it is indispensable to conduct engineering rock-mass classification using one of the widely recognized methods. Starting from the existing RMR and Q classifications, we have developed a new "n" classification which enables a more complete limestone classification and categorization, using a relatively simple procedure. RÉSUMÉ: En se basant sur plusierus annees de recherches portant sur un grand nombre de grands ouvrages (ponts, tunnels, barrages, talus rocheux eleves, etc.) etudies et realises dans la zone côtiere de I'Adriatique, nous avons ramasse une grande quantite des donnees geologiques et geotechniques. La classification de la masse rocheuse selon une des meethodes reconnues dans Ie monde est indispensable pour I'etablissement des modeles de geologie de l'ingenieur (IGM) et des modeles geotechniques (GM). En partant des classifications existantes "RMR" et "Q", nous avons developpe une nouvelle classification "n" qui perment une categorisation des calcaires plus complete, a l'aide d'une procedure relativement simple. ZUSAMMENFASSUNG: Auf Grund unserer langjahrigen Forschungen an einer Reihe großer Objekte (Bruecken, Tunnels, Staudamme, Felswande usw.) die in der adriatischen Kuestenregion errichtet wurden, haben wir eine große Menge von ingenieurgeologischen und geotechnischen Angaben gesammelt. Um ingenieurgeologische (IGM) und geotechnische (GM) zu entwerfen, ist es notwendig, eine Ingenieur-Klassifikation von Gesteinsmassen nach einer der anerkannten Methoden durchzufuehren. Ausgehend von bestehenden Einordnungsverfahren "RMR" und "Q" haben wir eine neue "n" Klassifikation entwickelt, die ein vollstandigeres Einordnen und Kategorisieren von Kalksteinen ermöglicht und verhalnismassig einfach ist. 1. INTRODUCTION Croatia's development in the period after 1990 is marked by an increasing global trend of investing in transportation infrastructure. According to estimates presented in various design solutions, approximately 30 to 50 km of road tunnels are to be built on the following highway routes: Zagreb-Maribor, Zagreb-Split (Zadar), Zagreb-Varaždin, Rijeka-Karlovac, Rijeka- Trieste, Rijeka-Dubrovnik. In addition, about 50 km of tunnels are to be built along the approx. 150 km long valley railway line Zagreb-Karlovac-Rijeka. Furthermore, a tunnel approx. 12–15 km in length is to be built through Ćićarije on the railway line stretching from Rijeka to Pula [Jašarević, 1993]. It should also be noted that an intensive urban development of medium-sized and large cities-aimed at revitalizing the existing city centers-has brought about significant traffic and environmental problems that may be resolved in a rational manner by building appropriate underground structures. This particularly applies to large cities situated along the Adriatic coast (Rijeka, Split, Dubrovnik, Šibenik). From the engineering-geological and geotechnical standpoint, the rational and cost-effective design and construction of underground structures must be based on the knowledge of essential rock-mass properties: occurrence of fissures (discontinuous environment), heterogeneity, anisotropy, and natural (primary) stress. In fact, the fissuring exerts the greatest influence on geotechnical properties, i.e. on the design and construction of underground structures in rock massif, which is why this element has been given an appropriate significance in the rock-mass classification (5 out of 11 classification parameters-Table 2). As to traffic corridors, it is important to note that most significant underground structures have been designed and are to be built in the coastal area of Croatia. Limestone formations from the Jurassic and Cretaceous period are present on over 50% of the total coastal area of the Republic of Croatia. Several classifications and categorizations of limestone formations, based on international experience and many years of research conducted in our country, are presented. In addition, the procedure for determining (selecting) geotechnical parameters required in the corresponding calculations is given.