Search results

Filters

  • Journals
  • Authors
  • Contributor
  • Keywords
  • Date
  • Type

Search results

Number of results: 115
items per page: 25 50 75
Sort by:

Abstract

One of the main threats to constructions made from rammed earth is destruction due to exposure to water. The way to limit this dangerous phenomenon is to supplement the local soil mixtures with stabilizing agents. The main component used is Portland cement. This article analyses the results of research which focused on the resistance of rammed earth to water erosion. Because of the lack of national standards regarding the method of examining the durability of rammed earth, the research was based on the New Zealand standard NZS 4298: 1998. The results confirm the possibility of using rammed earth stabilized by cement in a temperate climate.
Go to article

Abstract

Hydraulic fracturing of rocks boosts the production rate by increasing the fracture-face surface area through the use of a pressurized liquid. Complex stress distribution and magnitude are the main factors that hinder the use of information gathered from in situ hydraulic fracturing in other locations. Laboratory tests are a good method for precisely determining the characteristics of these processes. One of the most important parameters is breakdown pressure, defined as the wellbore pressure necessary to induce a hydraulic fracture. Therefore, the main purpose of this investigation is to verify fracture resistance of rock samples fractured with the assistance of the most popular industry fluids. The experiments were carried out using a stand designed specifically for laboratory hydraulic fracturing. Repeatable results with a relative error within the range of 6-11% prove that the experimental methodology was correct. Moreover, the obtained results show that fracturing pressure depends significantly on fluid type. In the case of a water test, the fracturing pressure was 7.1±0.4 MPa. A similar result was achieved for slickwater, 7.5±0.7 MPa; however, a much lower value (4.7±0.5 MPa) was registered in the case of carbon dioxide.
Go to article

Abstract

Geomechnical model testing has been widely applied as a kind of research technique in underground engineering problems. However, during the practical application process, due to the influence of many factors, the desired results cannot be obtained. In order to solve this problem, based on the measurement requirements of the model test, combined with FBG(Fiber Bragg Grating) sensor technology and traditional measurement methods, an FBG monitoring system, Micro-multi-point displacement test system, resistance strain test system and surrounding rock pressure monitoring system are developed. Applying the systems to a model test of the tunnel construction process, the displacement in advance laws of tunnel face, radial displacement distribution laws and surrounding rock pressure laws are obtained. Test results show that a multivariate information monitoring system has the advantage of high precision, stability and strong anti-jamming capability. It lays a solid foundation for the real-time data monitoring of the tunnel construction process model test.
Go to article

Abstract

The analysis of changes in the mechanical properties of wooden mining cribs under the influence of different types of exploitation loads is the question for which deals with many domestic and abroad research centers deal with. High The high interest in this subject results from the increase of the conducted depth exploitation, which contributes to the increase in both the vertical pres-sure and the complexity of geological – mining conditions and in- the intensification of natural hazards. Another reason is the tendency of decreasing the thickness of the exploited ores deposits. Wooden crib support is used Both both in underground ore, hard coal and salt mining is used wooden crib support. Mining cribs with various configurations are especially useful for the reinforcement of excavations workings behind the front and for further strengthen of the crossings. In particular, additional reinforcement support in the form of wooden cribs (pile supporting), which shall be left empty or filled with waste rock is applied in the ore mining in places where found extended rooms or drifts are found or in places with degraded roof conditions, applies additional reinforcement support in the form of wooden cribs (pile supporting), which shall be left empty or filled with waste rock. During underground ex-ploitation is produced waste Waste rock, which comes from the access, prepar-atory excavations and from ongoing field of exploitation is produced during underground exploitation. In the case of the underground exploitation of cop-per ore, waste rock is used to fill voids after exploitation as rock stowing. It is also used for filling mining wooden cribs, as an artificial support and for harder transportation roads. This paper presents the results of the laboratory strength tests performed on models of four-point timber cribs, built with beams set horizontally, at the ge-ometrical scale of 1:10. In the laboratory research Research wooden cribs models with size 200 × 200 × 200 mm and 100 × 100 × 100 mm were used in the laboratory. The paper describes the maximum loading capacity of the cribs consisted consisting only of beams and filled with waste rocks. In addition, a vertical and appropriate strain of cribs at maximum force was shown. On the basis of laboratory research it was found that the use of the same number of timbers and the management of waste rocks, the filling of the four-point cribs with the waste rocks allowed several times to increase its support to be increased several times.
Go to article

Abstract

Prof. Mirosław Wielgoś, MD, Rector at the Medical University of Warsaw, talks about why women of all ages should undergo prenatal testing and where they can turn for help.
Go to article

Abstract

This paper concerns an approach to model the ledger-stand joints of modular scaffolds. Based on the analysis of the working range of the ledger (represented by a linear relationship between load and displacement), two models of the ledger-stand joint are analysed: first – with flexibility joints and second – with rigid joints and with a transition part of lower stiffness. Parameters are selected based on displacement measurements and numerical analyses of joints, then they are verified. On the basis of performed research, it can be stated that both methods of joint modelling recommended in this paper, can be applied in engineering practices.
Go to article

Abstract

Having increasingly tightened geological and mining conditions in which the extraction of copper ore deposits in Poland is conducted, ensuring effective and safe mining is presently becoming a key task and a significant challenge for mine operators, mainly in the field of ground support systems being the equivalent for the new geological/mining conditions. As one may expect, these conditions shall be characterized by higher values of the primary stress tensor elements as well as the lower deformability and higher strength of the rock mass surrounding the copper ore body. T his means that in the near future, the rock bursts problem will become one of the most important issues deciding on the economy and safety within the newly developed mining areas. T herefore developing a novel effective ductile ground support systems which could be able to control the rock mass movement in squeezing and burst-prone rock conditions is recommended. T his type of requirement may fulfil only ductile or, in other words, the kinetic energy-absorbing systems, which permit slowing down a movement of violently ejected rock blocks. T his paper’s objective is to present the idea of the development of a new type of an effective and low cost ductile resin anchored rockbolt system with smooth and of the square cross-section steel rod is formed in coil shape of different pitch. T he developed bolt prototypes have been tested underground in the G-11 section of the Rudna mine. Results of the pull-out tests, involving different bolts’ shapes and different sliding materials set on the rockbolts’ rods, have proved those bolts’ efficiency as an element of the ductile support system.
Go to article

Abstract

The strength of conveyor belts splices made in mines rarely reaches full belt strength. It consists of a number of factors. The primary is the method of their construction and proper selection of ingredients. The significant impact has also has splice quality covering both keeping proper geometry matched to the belt construction and belts working conditions and adherence to the best practices in the field of technologies of their construction.Difficult conditions in underground mines and pressure on reducing conveyor downtime (avoiding production losses) is reflected by a drop in static and dynamic splices strength. This is confirmed by numerous studies of belt splices strength and fatigue life conducted in the Laboratory of Belt Conveying (LTT) within the framework of research and expert opinions commissioned by belt manufacturers and their users. The consequence of too insufficiently low belt splices strength is their low durability, decreasing reliability and, consequently, higher mining transportation costs. Belt splices are in fact the weakest link in the serial structure which form closed loops of interconnected belt sections working in series of conveyors transporting excavated material in the mine. The article presents the results of simulation analyzes analyses investigating how the increase of belt splices durability may contribute to the reduction of transportation costs in the underground mines.
Go to article

Abstract

The paper presents the statical research tests of rod bolt made of plastic with a length of 5.5 m, which were performed in a modern laboratory test facility at the Department of Underground Mining of the University of Science and Technology. Innovative The Self-excited Acoustic System (SAS) used to measure stress changes in the bolt support was characterized. The system can be used for the non-destructive evaluation of the strain of the bolt around the excavations as well as in tunnels. The aim of the study was to compare the re-sults recorded by two different measuring systems, thanks to which it will be possible to assess the load of long bolt support by means of the non-destructive method. The speed and simplicity of measurement, access to the sensors, accuracy of measurement and reading should be kept in mind in determining the load of rock bolt support . In addition, the possibility of damage to the sensor as a re-sult of technological or natural hazards should also be taken into account. In economic conditions, the „technical - balance laws of production”, which ex-cludes the use of load sensors on each bolt must be preserved. The use of indi-vidual load sensors of rock bolt support for the boundary state, allows appro-priate protection actions of the mining crew against sudden loss of excavation stability to be taken. The paper presents two basic effects used in the ultrasonic measurement sys-tem. The first result was the existence of stable limit cycle oscillations for posi-tive feedback. This effect is called the self-excited effect. The second effect is called the elasto-acoustic effect. It means that with the change of elastic stress-es in the material bring the change of the speed of propagation of the wave. In this connection, the propagation time between measuring heads is also changed. This effect manifests itself in the change in the oscillation frequency of the self-excited system. For this reason, by measuring the frequency of self-excited oscillation, it is possible to indirectly determine the level of effort of the tested material.
Go to article

Abstract

Hundred years ago education aimed mainly at memorizing as much information as possible. Such an approach lost its sense in the digital age of today since we are overwhelmed by an easily accessible ocean of true information mixed with “fake news”. Hence, the role of the teachers nowadays must be to guide and organize the learning process rather than provide knowledge. The students must no longer be passive recipients but active participants in the process of acquiring knowledge. A new approach of “phenomenon-based learning” introduced in schools in Finland, Norway and other countries agrees also with the holistic process of human cognition rather than absorbing information in a way sliced into traditional disciplines. In the future, say, fifty years from now, the role of teachers may be partly modified by the use of robots, which however could not replace creative thinking of human beings.
Go to article

Abstract

In this paper, flysch is presented as a representative material of a wide section of the Carpathian Mountains, with some areas in Poland highlighted. The geological structure of this area is complex due to the alternating layers of blocky rock masses and soil (Vessia et al., 2017). Such a complex pattern is seen in some Alpine flysch slopes, such as the Ingelsberg landslide area (Romeo et al., 2015). Many authors are monitored, predicted landslides (Allasia et al., 2013; Bertacchini et al., 2009; Casagli et al., 2010) by sophisticated sensors. The rock-soil flysch successions have become intensively fissured as a result of their geological history, weathering (precipitation and snowmelt), and long-term water retention, especially on the surface layers. These complex materials are characterised by heterogeneous lithologies, whose mechanical properties are largely uncertain. These geological structures have also been confirmed by monitoring and control studies performed on a large number of landslides (Bednarczyk, 2014). One of the most striking phenomena is the sudden decrease in the strength parameters in the studied rocks in the direction parallel to the layers due to watering. The process is made possible by heterogeneous fractured strong rock layers with high permeability coefficients for water. This study precisely describes the phenomena occurring at the contact area between the component layers of flysch under the wet conditions of a weak plane. An elastic-plastic analysis method that considers the developed strength model at the surfaces of the contact areas (Biernatowski & Pula, 1988; Pula, 1997) has been used to estimate the load capacity for piles working under a horizontal load. The piles are part of a reliability chain (Pula, 1997) in a given construction and are the first element of concern for monitoring (Muszynski & Rybak, 2017). A particular device intended to study the dependence of the shear stress on a fixed failure surface in a controlled consolidation condition was utilized. The study was conducted for a wide range of displacements and for different values of stabilized vertical stresses of consolidation. The complexity of the processes occurring in the shear zone, presented as a detailed study of the material crack mechanics, is highlighted. The laboratory results were used to construct the mechanical model of the slip surface between the soil and rock with the description supported by a neural network (NN) approximation. The artificial NN was created as a multi-layered, easy to use approach for interpreting results and for quick reconstruction of approximated values useful for the calculations presented in laterally loaded piles. For the calculations, long, sheared strips of material were considered in a semi-analytical procedure to solve a differential equation of stability. The calculations are intended to reveal the safety indexes for a wide range of boundary tasks as the most significant indicator for design decisions.
Go to article

Abstract

This paper analyses the influence of the applied microwave power output on the intensification of drying in the context of process kinetics and product quality. The study involved testing samples of beech wood (Fagus sylvatica L.). Wood samples were dried in the microwave chamber at: 168 W, 210 W, 273 W, 336 W and 378 W power output level. For comparison, wood was dried convectively at 40 ◦C and 87% air relative humidity. The analysis of drying process kinetics involved nonlinear regression employing the Gompertz model. Dried samples were subjected to static bending tests in order to specify the influence of the applied microwave power on modulus of elasticity (MOE) and modulus of rapture (MOR). The obtained correlations of results were verified statistically. Analysis of drying kinetics, strength test results and Tukey’s test showed that the applied microwaves of a relatively low level significantly shortened the drying time, but did not cause a reduction in the final quality of dried wood, compared with conventional drying.
Go to article

Abstract

The methane hazard is one of the most dangerous phenomena in hard coal mining. In a certain range of concentrations, methane is flammable and explosive. Therefore, in order to maintain the continuity of the production process and the safety of work for the crew, various measures are taken to prevent these concentration levels from being exceeded. A significant role in this process is played by the forecasting of methane concentrations in mine headings. This very problem has been the focus of the present article. Based on discrete measurements of methane concentration in mine headings and ventilation parameters, the distribution of methane concentration levels in these headings was forecasted. This process was performed on the basis of model-based tests using the Computational Fluid Dynamics (CFD). The methodology adopted was used to develop a structural model of the region under analysis, for which boundary conditions were adopted on the basis of the measurements results in real-world conditions. The analyses conducted helped to specify the distributions of methane concentrations in the region at hand and determine the anticipated future values of these concentrations. The results obtained from model-based tests were compared with the results of the measurements in realworld conditions. The methodology using the CFD and the results of the tests offer extensive possibilities of their application for effective diagnosis and forecasting of the methane hazard in mine headings.
Go to article

Abstract

Work is being carried out on possibilities of limiting the content of mercury in hard coal products by gravity concentration of run-of-mine coal in the Branch of the Institute of Mechanized Construction and Rock Mining in Katowice and on the Faculty of Energy and Fuels of the AGH University of Science and Technology in Krakow. Under domestic industrial conditions, gravity concentration is carried out with heavy medium liquids and in jigs. Preliminary - pilot studies have shown the possibility of mercury removal also by using the dry deshaling method involving vibratory air separators. Mercury is mainly found in the pyrite and the rubble formed by the mineral carbon, but also in the organic carbon. Some of it is located in layers of coal roof fields, which in the course of their exploitation go to coal. The mercury removal efficiency during the gravity concentration process will depend on the decomposition of the listed components in the density fractions. The paper presents the results of investigations of total mercury and total sulphur content in the separated coal fractions from four mines. These contents were determined in fractions: –1.5 g/cm3 (conventionally clean coal – concentrate), 1.5–1.8 g/cm3 (conventionally middlings) and +1.8 g/cm3 (conventionally rock – waste). The results are summarized in Tables 3–5 and in Charts 1–4. Conversely, graphs 5-8 show the relationship between mercury content and total sulphur content in the tested coal samples. The study, which can be called a preliminary analysis of the susceptibility of the coals to gravity concentration, showed that the dry deshaling method on the vibratory air separators would allow significant amounts of mercury accumulated in the middlings and waste fractions to be removed.
Go to article

Abstract

The paper presents results of the field tests on membrane biogas enrichment performed with the application of mobile membrane installation (MMI) with the feed stream up to 10 Nm3/h. The mobile installation equipped with four hollow fibre modules with polyimide type membranes was tested at four different biogas plants. Two of them were using agricultural substrates. The third one was constructed at a municipal wastewater plant and sludge was fermented in a digester and finally in the fourth case biogas was extracted from municipal waste landfill site. Differences in the concentration of bio-methane in feed in all cases were observed and trace compounds were detected as well. High selectivity polyimide membranes, in proper module arrangements, can provide a product of high methane content in all cases. The content of other trace compounds, such as hydrogen sulphide, water vapour and oxygen on the product did not exceed the values stated by standard for a biogas as a vehicle fuel. The traces of hydrogen sulphide and water vapour penetrated faster to the waste stream enriched in carbon dioxide, which could lead to further purification of the product – methane being hold in the retentate (H2O > H2S > CO2 > O2 > CH4 > N2). In the investigated cases, when concentration of N2 was low and concentration of CH4 higher than 50%, it was possible to upgrade methane to concentration above 90% in a two-stage cascade. To performsimulation ofCH4 andCO2 permeation through polyimide membrane,MATLABwas used. Simulation program has included permeation gaseous mixture with methane contents as observed at field tests in the range of 50 and 60% vol. The mass transport process was estimated for a concurrent hollow fibre membrane module for given pressure and temperature conditions and different values of stage cut. The obtained results show good agreement with the experimental data. The highest degree of methane recovery was obtained with gas concentrating in a cascade with recycling of the retentate.
Go to article

Abstract

The arc suppression coil determines whether it can effectively extinguish the arc when it is grounded in the neutral non-effective grounding system. An artificial grounding test is an importantway to verify its performance. In this study, 13 substations with the 10 kV system in the Ningxia areawere selected and considered. Based on the artificial single-phase grounding test, the residual current, the compensation current and the off-resonance degree were measured in the arc suppression coil, and the performance of the arc suppression coil in the 10 kV system was verified. The experimental results show that the error of arc suppression coil automatic measurement is large, the off-resonance degree is large, the resistive component in the compensation current is excessive, the harmonic component exists in the compensating current and capacitive current. To solve these problems, this paper puts forward the corresponding countermeasures for reference.
Go to article

Abstract

An uniaxial compression mechanical model for the roof rock-coal (RRC) composite sample was established in order to study the effects of height ratio of roof rock to coal on the structural strength of composite sample. The composite sample strengths under different height ratios were established through stress and strain analysis of the sample extracted from the interface. The coal strength near the interface is enhanced and rock strength near the interface weakened. The structural strength of composite sample is synthetically determined by the strengths of rock and coal near and far away from the interface. The area with a low strength in composite sample is destroyed firstly. An analytical model was proposed and discussed by conducting uniaxial compression tests for sandstone-coal composite samples with different height ratios, and it was found that the structural strength and elastic modulus decrease with a decrease in height ratio. The coal strengths far away from the interface determine the structural strengths of composite sample under different height ratios, which are the main control factor for the structural strength in this test. Due to its lowest strength, the rock near the interface first experienced a tensile spalling failure at the height ratio of 9:1, without causing the structural failure of composite sample. The coal failure induces the final failure of composite sample.
Go to article

Abstract

This paper presents a new test method able to infer - in periods of less than 7 seconds - the refrigeration capacity of a compressor used in thermal machines, which represents a time reduction of approximately 99.95% related to the standardized traditional methods. The method was developed aiming at its application on compressor manufacture lines and on 100% of the units produced. Artificial neural networks (ANNs) were used to establish a model able to infer the refrigeration capacity based on the data collected directly on the production line. The proposed method does not make use of refrigeration systems and also does not require using the compressor oil.
Go to article

Abstract

The aim of this study was to estimate the measurement uncertainty for a material produced by additive manufacturing. The material investigated was FullCure 720 photocured resin, which was applied to fabricate tensile specimens with a Connex 350 3D printer based on PolyJet technology. The tensile strength of the specimens established through static tensile testing was used to determine the measurement uncertainty. There is a need for extensive research into the performance of model materials obtained via 3D printing as they have not been studied sufficiently like metal alloys or plastics, the most common structural materials. In this analysis, the measurement uncertainty was estimated using a larger number of samples than usual, i.e., thirty instead of typical ten. The results can be very useful to engineers who design models and finished products using this material. The investigations also show how wide the scatter of results is.
Go to article

Abstract

To determine speech intelligibility using the test suggested by Ozimek et al. (2009), the subject composed sentences with the words presented on a computer screen. However, the number and the type of these words were chosen arbitrarily. The subject was always presented with 18, similarly sounding words. Therefore, the aim of this study was to determine whether the number and the type of alternative words used by Ozimek et al. (2009), had a significant influence on the speech intelligibility. The aim was also to determine an optimal number of alternative words: i.e., the number that did not affect the speech reception threshold (SRT) and not unduly lengthened the duration of the test. The study conducted using a group of 10 subjects with normal hearing showed that an increase in the number of words to choose from 12 to 30 increased the speech intelligibility by about 0.3 dB/6 words. The use of paronyms as alternative words as opposed to random words, leads to an increase in the speech intelligibility by about 0.6 dB, which is equivalent to a decrease in intelligibility by 15 percentage points. Enlarging the number of words to choose from, and switching alternative words to paronyms, led to an increase in response time from approximately 11 to 16 s. It seems that the use of paronyms as alternative words as well as using 12 or 18 words to choose from is the best choice when using the Polish Sentence Test (PST).
Go to article

Abstract

In this paper, an attempt was made to explain the causes of surface delamination in high carbon steel wires during the torsion test. For end wires with 1.7 mm diameter drawn at speeds of 5, 10, 15, 20, 25 m/s, technological tests were carried out. Then the susceptibility of the wire to plastic strain was determined. The microstructure analysis complemented the research. Analysis of the fracture torsion test showed that the wires drawn at speeds exceeding 15 m/s are delamination, which disqualify it as a material for a rope and a spring. The source of delamination in high carbon steel wires is their stronger strengthening, especially of the surface layer, which leads to a decrease in the orientation of the cementite laminaes and an increase in the degree of their fragmentation.
Go to article

Abstract

Hard bitumens are used in the construction industry primarily in it’s unmodified form, for instance for the production of the so-called traditional roofing felt. Due to the low price of these types of membranes, the use of a popular but expensive modifying agent, SBS copolymer, is not justified economically. Research carried out by the authors has shown that chemical organic compounds belonging to a group of imidazolines may potentially be used as much cheaper bitumen modifier. It was demonstrated that a new type of modifier based on oleic imidazoline, developed by the authors, has a significant impact on improving the physical properties of bitumen. The use of this modifier results in a significant increase in the bitumen plasticity range, both before and after laboratory ageing .In addition, there was a considerable increase of bitumen’s resistance to aging. Its use can help improve the quality and durability of popular waterproofing products manufactured with the use of hard bitumen.
Go to article

Abstract

The paper presents results of examination of material parameters of cast iron with structure obtained under rapid resolidification conditions carried out by means of the nanoindentation method.
Go to article

Abstract

In this paper the effect of soldering technique and thermal shock test were investigated on SAC 305 solder joints, produced by two different solder method. The solder joints were subjected to different cycle numbers up to 5000 thermal shock tests with two different thermal profiles of –30/+110°C and –40/+125°C. Microstructural properties of the tested joints were examined with the focus on intermetallic layer thickness and crack formation/propagation. Thickness of the scallop shaped Cu6Sn5 intermetallic layer was increased with increasing cycle number for both THRS and multiwave joints, but the thickening was more effective for the THRS joints. Cracks typically formed at the solder alloy/ PTH barrel and the solder alloy/pin interfaces and propagated along grain boundaries and precipitations of intermetallic compound.
Go to article

Abstract

The propagation of EEG activity during the Continuous Attention Test (CAT) was determined by means of Short-time Directed Transfer Function (SDTF). SDTF supplied the information on the direction, spectral content and time evolution of the propagating EEG activity. The differences in propagation for target and non-target conditions were found mainly in the frontal structures of the brain.
Go to article

This page uses 'cookies'. Learn more