Roller cone drill bit efficiency time during drilling depends, to a large extent, on the properties of the materials from which the components of the roller cone bit are made. The faster the roller cone bit is worn, due to the effects of the rock material through which we drill and the drilling regimes used during the drilling, the worse is the efficiency of drilling and the higher is the number of drill bits needed to drill the well. The aim of our research was to determine the mechanisms of wear on roller cone bit materials according to the characteristics of the steel material of the roller cone bit and the characteristics of the rock material, in this case, sandstone on the drilling regime. The results of the discovered wear mechanisms help us to anticipate the possible improvement of the resistance of the unprotected roller cone bit steel material to excessive wear and, consequently, the longevity of the roller cone bit. For this purpose, we examined the steel materials of the roller cone bit, which we used during well drilling and the rock material, sandstone, through which we drilled with the roller cone bit under consideration. The results of our analysis present the mechanisms that result in the wear of the roller cone bit material under the given conditions of the rock material and the drilling regime. The results of the discovered wear mechanism can be used to improve the material of the roller cone bits in order to achieve a longer operating life and decrease the related costs of drilling.
COBISS.SI-ID: 1762399
In order to improve the hot workability of AISI D2 tool-steel ingots during several heats hot-deformation process, laboratory hot-compression tests as well as industrial investigations of the carbides' behaviour were carried out. The conditions that led to the occurrence of undesired, oversized carbides in the matrix were estimated and explained. The area fraction of carbides with respect to their size, their number per µm2 and their sphericity after each hot-deformation cycle were determined. It was found that too high soaking temperature results in an increased size of carbides which decreases hot workability. The results of industrial investigations show that area fraction of carbides after the end of each deformation cycle remains almost constant, but their mean size more than double during deformations in several heats which implies that the final microstructure is not dependent primarily on the last soaking-deformation cycle but depends on entire processing history, i.e. hot workability over several hot-deformation cycles can change considerably from cycle to cycle.
COBISS.SI-ID: 1287775
The article presents a comparative analysis of an optimal design for conventional and geothermal energy piles, based on mixed-integer and non-linear programming (MINLP) optimizations. To complete this analysis, a MINLP optimization model OPTPILE was constructed. The model is based on structure production costs, while the piles are made of more than one material. It was subjected to geotechnical designs, structural resistance and settlement constraints that satisfy the requirements of the ultimate and serviceability limit states of the Eurocode specifications and recommendations for design and analysis of geothermal energy piles. The optimal design of a conventional and geothermal energy pile was investigated for various soil and load conditions. A comparative analysis of MINLP optimizations were performed over a wide range of alternative scenarios: different vertical loads on the pile, alternatives of discrete cross-sections as well as different Young's moduli of the soil. Based on the calculated results, a recommended optimal design for a conventional pile and a geothermal energy pile were developed.
COBISS.SI-ID: 21635606
Due to intrinsic characteristics of aquifers groundwater frequently passes between various types of aquifers without hindrance. The complex connection of underground water paths enables flow regardless of administrative boundaries. This can cause problems in water resources management. Numerical modelling is an important tool for the understanding, interpretation and management of aquifers. Useful and reliable methods of numerical modelling differ with regard to the type of aquifer, but their connections in a single hydrodynamic model are rare. The purpose of this study was to connect different models into an integrated system that enables determination of water travel time from the point of contamination to water sources. The worst-case scenario is considered. The system was applied in the Soča/Isonzo basin, a transboundary river in Slovenia and Italy, where there is a complex contact of karst and intergranular aquifers and surface flows over bedrock with low permeability. Time cell models were first elaborated separately for individual hydrogeological units. These were the result of numerical hydrological modelling (intergranular aquifer and surface flow) or complex GIS analysis taking into account the vulnerability map and tracer tests results (karst aquifer). The obtained cellular models present the basis of a contamination early-warning system, since it allows an estimation when contaminants can be expected to appear, and in which water sources. The system proves that the contaminants spread rapidly through karst aquifers and via surface flows, and more slowly through intergranular aquifers. For this reason, karst water sources are more at risk from one-off contamination incidents, while water sources in intergranular aquifers are more at risk in cases of long-term contamination. The system that has been developed is the basis for a single system of protection, action and quality monitoring in the areas of complex aquifer systems within or on the borders of administrative units.
COBISS.SI-ID: 1712479
This article discusses the basic findings that enable a determination of the thicknesses of the adsorbed water layers on the external surfaces of clay minerals and their dependence on the total water content in soils. The thicknesses of the water films were first determined indirectly from tests of the undrained shear strength of clay mineral samples. A comparison between these thicknesses and the total quantity of water in the samples showed that this ratio is exactly defined and can be expressed by a non-linear function in which the type of soil is determined by two parameters, which depend on the size and the quantity of the clay minerals. A test of the correctness and usefulness of the established expression was made on two samples of clays. The thicknesses of the water films, calculated using the proposed equation for different moisture contents, were compared with the thicknesses determined from the adsorptive potential of the soils. These results showed a good agreement. The possible application of the proposed expression is shown for the case of an estimation of the soil–water characteristic curve in the range between the water content at the air-entry value and the residual water content.
COBISS.SI-ID: 19417110
The assessment for realistic CO2-adsorption capacities of different rocks is important for understanding the processes associated with CO2 storage. This paper investigates the adsorption characteristics of rocks for CO2 (limestone, sandstone, marl, claystone, clay, siltstone and metamorphic rock) by using a gravimetric method. The measurements were performed at 21°C with pressures from 1 up to 4 MPa. Sandstone (and clay with sand/sandstone) showed the largest adsorption capacity at 21°C. The highest amount of in situ CO2 contents in measured samples was 21.4 kg/t. The CO2-adsorption capacities were lower than past results in different coal samples. The results indicate that adsorption of CO2 into rocks may play an important role in storing CO2 in subsurface rock.
COBISS.SI-ID: 7007097
The physical and mechanical properties of fine-grained soils, especially clay minerals, are greatly influenced by the specific surface area. Many investigations were conducted to examine the relationships between the specific surface area of soils and their engineering properties. We have previously shown that there were relationships between the external specific surface area of the soils and their Atterberg limits. These relationships, based on the test results from soils prepared artificially in the laboratory, were presented in a general analytical form. As Atterberg limits are the most distinctive and the easiest property of soils to measure, it would be a very convenient basis for estimating the specific surface area. The aim of these investigations was to identify the possibility of practical applications. Five heterogeneous soil samples were selected, the liquid and plastic limits were measured as well as the grain size distribution, the mineral and chemical compositions and the specific surface area. The external specific surface area of the soils measured by the BET method ranged between 17 m2/g and 54 m2/g. The estimated values using Atterberg limits were slightly higher. The calculated and measured values of the external specific surface area differed by 0.6-6 m2/g.
COBISS.SI-ID: 16216854
The paper presents the cost optimization of an underground gas storage (UGS), designed from lined rock caverns (LRC). The optimization is performed by the non-linear programming (NLP) approach. For this purpose, the NLP optimization model OPTUGS was developed. The model comprises the cost objective function, which is subjected to geomechanical and design constraints. The geotechnical problem is proposed to be solved simultaneously. Geomechanical rock mass parameters are determined from geological conditions of a selected suitable UGS location and a special FE model is generated. The rock mass strength stability and safety of the system are then analyzed for various combinations between different design parameters like inner gas pressures, cavern depths, cavern diameters and cavern wall thickness. As a result, geomechanical constraints are approximated and put into the optimization model OPTUGS. This way, the optimization enables not only the obtaining of an optimal solution but also that the rock mass achieves sufficient strength stability and safety. The optimization is proposed to be performed for the phase of preliminary design. The numerical example at the end of the paper demonstrates the efficiency of the introduced optimization approach.
COBISS.SI-ID: 15161366
In soil mechanics, the plasticity of fine-grained soils is expressed using the plasticity index. This represents the difference between the water content at the liquid and plastic limits, which are often collectively referred to as the Atterberg (or consistency) limits. They are of key importance in soil mechanics because they determine, in a simple way, the interaction between the solid and liquid phases in soils, and thus provide the possibility to classify soils into groups with similar mechanical properties. As the Atterberg limits are the most distinctive and the easiest property of fine-grained soils to measure, several researchers have tried to use them to predict various mechanical properties, such as the normalized, undrained shear strength of fine-grained soils. The most widely used expression for predicting this value from the plasticity index was suggested by Skempton. Since then, there have been several studies to examine the validity of his relation. A lot of the data agree with this relation; however, there is an equally large volume of data that contradicts it. The present study shows that the correlation between the normalized undrained shear strength of cohesive soils and the plasticity index really exists, but it is not as simple as was suggested by previous studies. By considering the mineralogical properties of clay minerals and their impact on the quantity and state of water in soils, it was found that there is no uniform criterion to determine the normalized undrained shear strength from the plasticity index for all fine-grained soils.
COBISS.SI-ID: 13823254
This paper presents the results of the 5th FP project AISUWRS (Assessing and Improving the Sustainability of Urban Water Resources and Systems) which aimed to assess the impact of the urban water infrastructure to underlying or nearby aquifers with the urban water balance modelling approach – a chain of different models that handle with contaminant fluxes and the movement of contaminants from the urban infrastructure into the underlying aquifer. An existing urban water management model UVQ was linked to a model for sewer infiltration and exfiltration (NEIMO), as well as unsaturated zone models (SLeakI/POSI, UL_FLOW) with existing numerical groundwater models. The linked process models offer the prospect of better quantification of urban water balance and contaminant loads, including improved estimates of total recharge and its components in urban areas. Once the model framework has been set up for a selected city, it can easily be updated in the future and it can be used for other purposes like planning of local remediation measures in the vicinity of individual contaminant spillages. This paper describes the application and results of the urban water model chain for the city of Ljubljana, which is the capital of Slovenia. The results from this study suggest that residential land-uses in urban areas with thick unsaturated zone may have significantly smaller impact on the groundwater than agriculture or industry. This can be seen as a speculative understanding of the groundwater pollutions problems. In this respect, use of sustainable urban development systems like on-site infiltration of roof runoff and improved sewer control and standards could result in better groundwater quality.
COBISS.SI-ID: 788062