Wyniki wyszukiwania - BazTech

1

Kotwy iniekcyjne w gruntach i skałach

Roguska Emilia

Materiały Budowlane

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2024

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nr 2

61--65

2

Reductıon of thermal tensıons and temperatures formed ın the trıbonodes and surfaces of the equıpment and tools used ın well workover and restoratıon works

Mustafayev Amir G., Nasirov Chingiz R.

Nafta-Gaz

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2023

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R. 79, nr 10

661--669

EN

The maintenance of equipment and tools used in the workover of oil and gas wells depends on keeping them in good working condition, maintaining the reliability, strength, and temperature endurance of the tool. To restore wells after an accident and bring them back into operation, it is necessary to speed up the drilling and repair work by choosing the right repair equipment and following the existing rules and regulatory documents. The cutting elements of tools working under high pressure and loads are deformed, a tense situation is created in the cutting – a destruction zone and high temperatures (1000–1200°C) occur because of corrosion in the triboknots. The stress-deformation state in the cutting-destruction zone causes the formation of microcracks in the working area of the tool. Microcracks grow after a certain period. Cutting elements are quickly worn, in some cases break and fail quickly. Such cases affect the structural composition of the cutting elements, an increase in temperatures; as a result, riveting occurs. In order to keep the equipment and tools used in the repair in normal working condition, adjusting the mode parameters is one of the important requirements, in addition to taking special care of them. Optimum results obtained in repair and restoration depend on the efficiency of the cutting-destructive tool, longevity, material selection, construction manufacturing technologies, tools that meet modern requirements, dimensions, weight, and internal condition of the well being restored. It is necessary to keep the heat generated in the moving parts of the tool at the required level for the safe performance of restoration work. The thermal regime of cutting and rock-destroying tools depends on the physical-mechanical properties of the objects subjected to destruction, and the effect of thermomechanical stresses generated on the contact surfaces of the tool and the amount of heat released from the working surface. Studying the problems related to heat issues will ensure the temperature tolerance of not only the repair equipment, but also the equipment and tools used in other areas of the oil-field industry.

PL

Utrzymanie urządzeń i narzędzi używanych w rekonstrukcjach odwiertów ropy i gazu zależy od zachowania ich w stanie gotowości do pracy, niezawodności, wytrzymałości oraz trwałości temperaturowej narzędzia. Aby przywrócić odpowiedni stan odwiertów po awarii oraz ponownie rozpocząć ich eksploatację trzeba przyspieszyć prace wiertnicze i naprawy poprzez wybranie właściwych urządzeń naprawczych oraz przestrzeganie istniejących przepisów i dokumentów regulacyjnych. Elementy tnące narzędzi pracujących pod wysokim ciśnieniem i obciążeniami ulegają deformacji, wytwarza się sytuacja naprężenia w strefie tnąco-niszczącej i występują wysokie temperatury (1000–1200°C) w wyniku korozji w węzłach tarcia. Stan naprężenie-odkształcenie w strefie tnąco- -niszczącej powoduje tworzenie mikropęknięć w obszarze roboczym narzędzia. Mikropęknięcia propagują po pewnym czasie. Elementy tnące szybko się zużywają, w niektórych przypadkach szybko pękają i ulegają awarii. Takie przypadki wpływają na skład strukturalny elementów tnących, wzrost temperatury i w rezultacie następuje unieruchomienie. Aby utrzymywać urządzenia i narzędzia używane przy naprawie w normalnych warunkach roboczych, jednym z najważniejszych wymogów jest dostosowanie parametrów trybu pracy, oprócz objęcia ich specjalną uwagą. Dobre wyniki uzyskane w robotach naprawczych i renowacyjnych zależą od sprawności narzędzia tnąco-niszczącego, trwałości, doboru materiałów, technologii produkcji konstrukcji, narzędzia spełniającego nowoczesne wymagania, jego wymiarów, wagi oraz stanu wewnętrznego odwiertu podlegającego renowacji. Dla bezpiecznego wykonania prac renowacyjnych konieczne jest utrzymanie ciepła generowanego w częściach ruchomych narzędzia na wymaganym poziomie. Reżim cieplny narzędzi tnących i niszczących skałę zależy od właściwości fizyko-mechanicznych obiektów podlegających niszczeniu i efektu naprężeń termomechanicznych generowanych na powierzchniach kontaktowych narzędzia oraz od ilości ciepła uwolnionej z powierzchni roboczej. Badanie problemów związanych z zagadnieniami ciepła pozwoli na zapewnienie tolerancji temperaturowej nie tylko urządzenia naprawczego, ale również urządzeń i narzędzi używanych w innych dziedzinach przemysłu złóż ropy.

3

Rock transport after an outburst and the fluidisation phenomenon – can it occur during a dolomite and gas outburst?

Kozieł Katarzyna, Skoczylas Norbert

Archives of Mining Sciences

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2023

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Vol. 68, no. 4

621--638

EN

Rock and gas outburst is a phenomenon in which fragmented rock material is transported deep into a pit. The transport of rock material by gas is a two-phase process. The article deals with the fluidisation of rock material. Considerations on the fluidisation phenomenon were carried out, and experiments were performed to help clarify whether the fluidisation of dolomite is possible. In the last chapter, a discussion was carried out, and the results obtained were analysed regarding the possibility of occurrence in mine conditions.

4

Landslide survey at Cam Mountain (An Giang, Vietnam) by seismic refraction and GPR methods

Nguyen Giang Van, Nguyen Dung Quang, Le Thanh Ngoc

Archives of Mining Sciences

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2023

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Vol. 68, no. 4

603--620

EN

Cam Mountain in An Giang Province, Vietnam, is a granite peak that is severely fractured and eroded on its slopes and summit. Trees cover the top of the mountain and around the side of the mountain. The roads are the primary means of transportation for indigenous people and tourists daily. Recently, there has been a phenomenon of large-sized boulders rolling down from the top of the mountain, causing an accident and killing tourists. To investigate the internal causes of landslides on a 2.3 km road stretch, geophysical profiles using GPR and seismic refraction methods were conducted to clarify the current status of geological structures beneath the road surface. The refractive seismic data analysis revealed four distinct layers based on elastic wave propagation velocity. Velocity values range from 1000 to 3000 m/s for the 2 upper layers corresponding to the weathered, broken, and highly fractured rock layers and in the lower 2 layers from 3000 to more than 4500 m/s, respectively corresponding to less fractured rock on the depth of more than 50 m. According to GPR data, the structural cross-section to an average depth of 30 m is a more complex picture. Detected 6 layers with different degrees of fracture cracking and showing different structural zones. In a few places are the drainage creeks from the mountain. These places need to be monitored regularly to have a basis for predicting landslides and rockfalls in the area of Cam Mountain. Landslides occur in geological rocks which are of different ages: claystone, mudstone, siltstone, shale, or marlstone. The rock-falls occur in more compact rocks: metamorphic or igneous rocks.

5

On the resistance of concrete hollow thin-walled high piers to rock collisions

Huang Yao

Archives of Civil Engineering

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2023

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Vol. 69, nr 3

187--197

EN

Concrete hollow thin-walled high piers (CHTWHPs) located in mountainous areas may be destroyed by the huge impact force of accidental rocks. The study focuses on analyzing the effects of rock impact on the pier, including its impact force, pier damage, dynamic response, and energy dissipation characteristics. The results show that: (1) Increasing the impact height led to a decrease in the peak impact force. Specifically, 15.5% decrease in the peak collision force is induced when the height of rock collision rises from 10 m to 40 m. (2) The damage mode of the pier’s collision surface is mainly oval damage with symmetrical center, radial damage on the side surface, and corner shear failure on the cross section. (3) The peak displacement of bridge pier increases with the increase of collision height. As the collision height increased from 10 m to 40 m, the bridge pier’s peak displacement also increased, rising by 104.2%. (4) The concrete internal energy gradually decreased with increasing collision height, dropping by 36.9% when the height of rock collision rises from 10 m to 40 m. The reinforcement internal energy showed an increase of 78%. The results of this study may provide reference for the rock collision resistance design of CHTWHPs.

6

An evaluation method of rock pore volume compressibility determination using a computed tomography scanned based finite element model

Moosavi Seyed Amin, Goshtasbi Kamran, Kazemzadeh Ezzatollah

Acta Geophysica

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2023

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Vol. 71, no. 1

147--159

EN

This paper has proposed a new perspective of studying internal structure-based tests, the results of which will improve the present experimental methods and enrich our understanding of rock structure-based modeling without any core preparations, with low cost in a short time. Pore volume compressibility (PVC) is an important feature of rock and is related to mechanical and structural behavior of porous rock sample. An accurate evaluation of pore volume compressibility depends on experimental test which is time-consuming and costly. This paper outlines new method for evaluation of PVC of rock cores using a computed tomography (CT) scan-based finite element method (FEM). The verification studies were performed on a series of porous rock cores which were extracted from deep oil reservoirs in Iran. In order to construct a finite element model, a relationship between spatial elastic properties of samples and CT-scanned data images was derived. The samples were scanned by a conic beam computed tomography (CBCT) machine, and the scanned data were converted into a model to simulate PVC tests. The pore volumetric strains were obtained from a linear elastic analysis for each stress and pore pressure step. To validate the finite element analysis (FEA) results, a series of experimental PVC tests were conducted on the pre-scanned samples and PVC curves were extracted. As a result, the predictions calculated from the CT scan-based numerical models have shown a good correlation with the results obtained from laboratory experiments. The results revealed that it is possible to simulate PVC tests using this numerical proposed evaluation method in such a way that the cost and time of the tests were lowered.

7

Interakcja wodoru ze skałą zbiornikową

Cicha-Szot Renata, Leśniak Grzegorz

Nafta-Gaz

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2022

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R. 78, nr 8

580--588

PL

Istnieje szereg metod magazynowania wodoru, do których zaliczyć można stosowanie zbiorników napowierzchniowych, wiązanie w wodorkach metali, nanorurkach węglowych, sieciach metaloorganicznych, ciekłych organicznych nośnikach wodoru czy adsorbentach. Jednak to podziemne magazynowanie wodoru w strukturach geologicznych (PMW) wydaje się kluczowe dla rozwiązania problemu długoterminowego magazynowania dużych ilości energii oraz zwiększenia stabilności sieci energetycznej i poprawy wydajności systemów energetycznych. Kryteria wyboru struktury do magazynowania wodoru obejmują szereg czynników technicznych, ekonomicznych, ekologicznych i społecznych. Jednym z najmniej rozpoznanych obszarów badawczych dotyczących PMW jest utrata wodoru in situ wywołana reakcjami geochemicznymi, które mogą wpływać na parametry petrofizyczne oraz wytrzymałość skał uszczelniających. W artykule przeanalizowano reakcje, jakie mogą wystąpić podczas magazynowania wodoru w strukturach geologicznych. Na podstawie studium literaturowego wskazano grupy minerałów, które mogą wpływać na zmiany pojemności magazynowej oraz na czystość gazu. Należą do nich w szczególności węglany, anhydryt, ankeryt i piryt, które stanowiąc skład matrycy skalnej lub cementu, mogą znacząco wpływać na potencjał magazynowy analizowanej struktury. Podczas kontaktu z wodorem minerały te ulegają rozpuszczeniu, w wyniku czego uwalniane są m.in. jony Fe2+, Mg2+, Ca2+, SO4 2−, HCO3 − , CO3 2−, HS− . Jony te wchodzą nie tylko w skład minerałów wtórnych, ale również na skutek dalszych reakcji z wodorem zanieczyszczają magazynowany nośnik energii domieszkami CH4, H2S i CO2, co ogranicza możliwości dalszego wykorzystania wodoru. Zwrócono również uwagę na możliwość wystąpienia rozpuszczania kwarcu, którego szybkość zależy od stężenia jonów Na+ w solance złożowej oraz pH. Ponadto pH wpływa na reaktywność wodoru i zależy w dużej mierze od temperatury i ciśnienia, które w trakcie pracy magazynu będzie podlegało częstym cyklicznym zmianom. W artykule omówiono wpływ warunków termobarycznych na analizowany proces, co powinno stanowić podstawę do szczegółowej analizy oddziaływania skała–wodór– solanka dla potencjalnej podziemnej struktury magazynowej.

EN

There are several hydrogen storage methods, including surface tanks, metal hydrides, carbon nanotubes, organometallic networks, liquid organic hydrogen carriers, or adsorbents. However, underground hydrogen storage (UHS) appears to be crucial in solving the problem of long-term storage of large amounts of energy, increasing the power grid's stability and improving energy systems' efficiency. The criteria for selecting a hydrogen storage structure include a number of technical, economic, ecological, and social factors. One of the least recognized research areas concerning UHS is the in situ loss of hydrogen caused by geochemical reactions that may affect sealing rocks' petrophysical parameters and strength. The article presents the reactions that may occur during hydrogen storage in geological structures. Based on a literature study, groups of minerals that may affect changes in storage capacity and gas purity have been indicated. These include, in particular, carbonates, anhydrite, ankerite, and pyrite in both the rock matrix and the cement. Upon contact with hydrogen, these minerals dissolve, releasing, among others, Fe2+, Mg2+, Ca2+, SO4 2– , HCO3 – , CO3 2– , HS– ions. These ions are not only components of secondary minerals but also, as a result of further reactions with hydrogen, pollute the stored energy carrier with admixtures of CH4, H2S and CO2, which limits the possibilities of further hydrogen use. The possibility of quartz dissolution, the rate of which depends on the concentration of Na+ ions in the reservoir brine and the pH, was also noted. Moreover, pH influences the reactivity of hydrogen and depends mainly on temperature and pressure, which will be subject to frequent cyclical changes during the operation of the storage. This review paper discusses the influence of thermobaric conditions on the analyzed process, what should be a base for detailed analysis of the rock-hydrogen-brine interaction for the potential underground storage structure.

8

Badania laboratoryjne przyczepności stwardniałych zaczynów cementowych z dodatkiem nanotlenku glinu do wybranych formacji skalnych

Rzepka Marcin, Kędzierski Miłosz

Nafta-Gaz

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2022

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R. 78, nr 1

22--30

PL

Artykuł przedstawia wyniki badań laboratoryjnych przyczepności zaczynów cementowych do trzech formacji skalnych, tj. rdzeni powstałych z piaskowca, mułowca oraz węgla kamiennego. Przygotowane rdzenie skalne (przed zalaniem zaczynem cementowym) poddawane były procesowi przemywania w różnych cieczach (prowadzono też badania dla tzw. rdzeni suchych). Do badań przyczepności wytypowano recepturę zaczynu cementowego zawierającą 1% nanotlenku glinu (n-Al2O3) oraz recepturę konwencjonalną (porównawczą, tj. bez udziału nanokomponentu). Badane zaczyny cementowe miały dobre parametry technologiczne, umożliwiające ich zastosowanie do uszczelniania kolumn rur okładzinowych w otworach wiertniczych o temperaturze dynamicznej około 35°C oraz ciśnieniu około 15 MPa. Po wykonaniu szeregu badań laboratoryjnych stwierdzono, że zaczyn zawierający dodatek 1% n-Al2O3 w wyraźny sposób podnosił przyczepność kamienia cementowego do formacji skalnej. Uzyskane wartości przyczepności dla zaczynu z n-Al2O3 w porównaniu z wartościami otrzymanymi dla zaczynu konwencjonalnego są około 30–40% wyższe. Analizując przyczepność kamienia cementowego (z dodatkiem i bez dodatku nanokomponentu) do różnego rodzaju formacji skalnych, należy zaznaczyć, że: najwyższą przyczepność zanotowano w przypadku piaskowca, nieco niższą – mułowca (około 80–85% wartości przyczepności uzyskanej dla piaskowca), a najniższą – węgla (około 70–75% wartości przyczepności uzyskanej dla piaskowca). Zależność ta zachodzi w podobny sposób w przypadku rdzeni „suchych”, jak i przemytych płuczką, buforem oraz cieczą przemywającą. Należy podkreślić niezwykle istotną rolę odpowiedniego procesu przemywania otworu wiertniczego przed wykonaniem zabiegu cementowania rur okładzinowych. Zastosowanie samego buforu może okazać się niewystarczające. Dodatkowe użycie odpowiednio dobranej cieczy przemywającej pozwala skutecznie usunąć resztki osadu filtracyjnego pozostającego na powierzchni formacji skalnej po jej przewierceniu, co powinno znacznie poprawić stan zacementowania otworu wiertniczego.

EN

The article presents the results of laboratory tests of adhesion of cement slurries to three rock formations, i.e. sandstone, mudstone and hard coal cores. The prepared rock cores (before being poured over with cement slurry) were washed in various fluids (tests were also conducted for the so-called “dry” cores). The adhesion tests were carried out for two selected cement slurries recipes: cement slurry containing 1% aluminum nanoxide (n-Al2O3) and conventional cement slurry (comparative, i.e. without the addition of nanocomponents). The tested cement slurries had good technological parameters, enabling their use for sealing casing columns in boreholes with a dynamic temperature of approx. 35°C and a pressure of approx. 15 MPa. After a series of laboratory tests, it was found that the slurry containing the addition of 1% n-Al2O3 significantly increased the adhesion of the cement stone to the rock formation. The obtained values of adhesion for the n-Al2O3 slurry, compared to the values obtained for the conventional slurry, are about 30–40% higher. When analyzing the results of adhesion of cement stone (with and without the addition of a nanocomponent) to various types of rock formations, it is stated that the highest values of adhesion was obtained for sandstone, slightly lower for mudstone (about 80–85% of the adhesion value obtained for sandstone) and the lowest for coal (about 70–75% of the adhesion value obtained for sandstone). This dependence is similar in the case of “dry” cores and those washed with mud, spacer fluid and washing fluid. It should be emphasized that the proper process of washing the borehole is very important prior to cementing the casing. The use of a spacer fluid alone may not be sufficient. The additional use of a properly selected washing liquid increases the mud-cake removal efficiency, which should significantly improve the quality of borehole cementing.

9

Significance of a new preliminary treatment method of the Pen206_18 borehole penetrometer’s pressure readouts for a reliable analysis of rock stress-strain parameters

Pierszalik Rafał

Archives of Mining Sciences

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2022

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Vol. 67, no. 1

159--178

EN

This article describes some selected aspects of a preliminary treatment of measurement cycle results obtained by a new Pen206_18 type hydraulic borehole penetrometer (a borehole jack type), a tool of an in situ determining of mechanical properties of rocks. The pre-treatment of the measurement cycle results is a necessary step to prepare the data for a following appropriate analysis of stress-strain parameters of rocks. Aforementioned aspects are focused mainly on a pre-treatment of hydraulic pressure readouts. The Pen206_18 type penetrometer is a modified version of a standard Pen206 type penetrometer. The standard version, based on a digital measurement of a critical hydraulic pressure, has been in use in polish hard coal mines for almost 15 years to determine various rock strength parameters. In contrary, the Pen206_18 type penetrometer now provides simultaneous recording of two main measurement cycle parameters (hydraulic pressure and a head pin stroke) during the whole measurement cycle duration. A recent modification of the penetrometer has given an opportunity to look closer at various factors having an influence on the measurement cycle data readouts and, as a consequence, to lay a foundation for a development a new penetrometric method of determining stress-strain parameters of rocks. In this article it was shown that just before a main stage of the measurement cycle, a transitional stage could occur. It complicates a determination of the beginning of an useful set of measurement cycle data. This problem is widely known also in other static in situ methods of determining stress-strain parameters. Unfortunately, none of various known workouts of this problem were sufficiently adequate to the pre-treatment of the penetrometric measurement cycle results. Hence, a new method of determining the beginning of the useful set of pressure readouts has been developed. The proposed method takes into account an influence of an operational characteristics of the measuring device. This method is an essential part of a new pre-treatment procedure of the Pen206_18 measurement cycle’s pressure readouts.

10

Overlying sand-inrushing mechanism and associated control technology for longwall mining in shallow buried coal seams with the soft surrounding rock

Wang Fangtian, Shao Dongliang, Zhang Cun, Zhang Chenkai, Song Ziyu

Archives of Mining Sciences

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2022

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Vol. 67, no. 4

681--697

EN

Taking the sand-inrushing accident of the Selian No. 1 coal mine in the Ordos of inner Mongolia as the research background, four main factors of sand-inrushing, including sand source, channel, sand-breaking power, and flowing space, were analysed. The disaster formation process (SCPS) illustrated that sand-inrushing disasters in shallowly buried coal seams with soft surrounding rock have the characteristics of being significantly influenced by mining, the development of vertical overburden channels, and sufficient space for water-sand mixed particles to flow. Universal Distinct Element Code (UDEC) software has been used to reveal that the vertical cracks in the overburden between the coal wall and support undergo a process of development and expansion along with the cumulative stress of mining. This showed that the vertical fissure through the overburden is the main pathway for the disaster. Combined with the site conditions, disaster occurrence mechanism, and numerical simulation results, a comprehensive prevention and control technology based on the working face and roadway grouting to block the channel was proposed. It contains reasonable mining height and optimisation of advancing speed, so that safe and efficient mining of coal seams in shallow-buried soft surrounding rocks could be achieved.

11

The role of water content in rate dependence of tensile strength of a fine-grained sandstone

Cai Xin, Cheng Chuanqing, Zhao Yuan, Zhou Zilong, Wang Shaofeng

Archives of Civil and Mechanical Engineering

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2022

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Vol. 22, no. 1

art. no. e58, 2022

EN

Rocks in nature are commonly in partially saturated conditions and exposed to dynamic loads. In this study, to explore the coupled effects of water content and loading rate, dynamic Brazilian disc experiments were conducted on Yunnan sandstone samples with four levels of water content (from air-dried to water-saturated) under various loading rates (from 100 to 600 GPa/s) using a split Hopkinson pressure bar. The test results show that for each water content, the dynamic tensile strength of sandstone is positively sensitive to loading rate. The rate dependence of tensile strength increases as the rise of water content. The change trends of tensile strength against water content depend on loading rate: as water content rises, the tensile strength displays the manner of “no change followed by fast drop” at loading rates of 10–4 and 100 GPa/s. However, when the loading rate is above 200 GPa/s, the tensile strength increases first and then declines. The turning point occurs at water content between 1.0 and 2.0%. These observations can be interpreted with the competition between water weakening and enhancing effects under different loading conditions.

12

Experimental and numerical study on the indentation behavior of TBM disc cutter on hard-rock precutting kerfs by high-pressure abrasive water jet

Cheng Jian‑Long, Yang Sheng‑Qi, Han Wei-Feng, Zhang Zuo-Ru, Jiang Zi-Hao, Lu Jun-Fu

Archives of Civil and Mechanical Engineering

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2022

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Vol. 22, no. 1

art. no. e37, 2022

EN

Tunnel boring machine (TBM) excavation of high strength or highly abrasive rock strata has some limitations, such as slow advance speed, low rock-breaking efficiency, and significant increase in the disc cutter changes and construction cost. To improve the rock boreability, a novel breakage method for hard rocks using a TBM disc cutter penetrating into kerfs precut by a high-pressure abrasive water jet is explored. With a confining pressure of 5 MPa, a series of cutter indentation tests and particle flow simulations of granite with two precutting kerfs are carried out to investigate the indentation behavior and the breaking efficiency. The effects of the kerf depth and the kerf spacing on the normal indentation force, rock chip volume, and specific energy are studied. The initiation, propagation, and coalescence modes of the surface and internal cracks and the failure mechanism are analyzed. The results show that the average peak force decreases significantly with the increase of the kerf depth, and the maximum rock chip volume and minimum specific energy are obtained at a kerf depth of 18.14 mm. The failure mode of kerf specimens after two indentations could be divided into the flat and slow shallow failure, one-sided inclined failure, and two-sided inclined failure. The micro-crack distribution of a single shallow kerf under low confining pressure is similar to that of intact rocks, while it is oblate and semi-elliptical under high confining pressure. However, for a single deep kerf, the breakage consists of a wedge-shaped crushed zone, a failure zone, and a damage zone around the kerf boundary and the bilateral inclined cracks, which are almost not affected by the confining pressure.

13

Effect of loading characteristics and specimen size in split Hopkinson pressure bar test on high-rate behavior of phyllite

Mishra Sunita, Khetwal Anuradha, Chakraborty Tanusree, Basu Dipanjan

Archives of Civil and Mechanical Engineering

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2022

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Vol. 22, no. 4

art. no. e212, 2022

EN

Split Hopkinson pressure bar (SHPB) tests are performed on Himalayan phyllite rock with five different specimen sizes and with different gas gun pressures and striker bar lengths of the SHPB device. The high-strain-rate phyllite parameters investigated are the peak stress, strain at peak stress, dynamic increase factor (DIF), strain energy absorbed, and dynamic modulus. It is observed that the dimensions of the phyllite specimens and the SHPB loading characteristics (i.e., the gas gun pressure and striker bar length) have a strong impact on the phyllite response. Given that SHPB specimen dimensions are small compared to any field rock mechanics problem, the rate-dependent rock mass properties are also determined for each rock using Hoek–Brown criteria. Numerical simluations of the SHPB tests are performed using finite element (FE) analysis in conjunction with the strain rate-dependent Johnson–Holmquist (JH-2) constitutive model to calibrate the JH-2 model parameters for phyllite. The calibrated JH-2 model parameters are dependent on the phyllite specimen size and on the magnitudes of the gas gun pressure and striker bar length. The different calibrated parameters corresponding to different specimen sizes and different SHPB loading characteristics are used to perform FE analysis of a tunnel constructed in phyllite rock and subjected to a blast load. The FE results show that the tunnel responses can significantly differ with strain rate-dependent JH-2 model parameters with difference in the mean stress and vertical displacement at the crown of the tunnel in the phyllite rock as high as 126% and 250%, respectively.

14

Natural radionuclides in rocks and their association with the mineralogy of rocks in Dakshina Kannada region of southern India

Lokesh Narsha, Vinutha Pudiyaneravana Ramanand, Malleshi Kavasara, Narayana Yerol

Acta Geophysica

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2022

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Vol. 70, no 5

2149--2160

EN

The radioactivity levels of natural radionuclides 226Ra, 232Th, and 40K in the rocks of Dakshina Kannada region of southern India were measured by NaI (Tl) gamma-ray spectrometer. The specific activities of 226Ra, 232Th, and 40K ranged from 4.2±0.4 to 74.5±1.7 Bq kg−1, 14.5±0.7 to 83.5±1.6 Bq kg−1, and 172±3 to 964±7 Bq kg−1 with the mean of 25.1±1.0 Bq kg−1, 36.1±1.0 Bq kg−1, and 502±5.0 Bq kg−1, respectively. The normality of the frequency distribution curves of 226Ra, 232Th, and 40K was tested using the Kolmogorov–Smirnov test. The radiological hazard indices were computed from the measured activity concentration of natural radionuclides in rocks and these were found to be within acceptable levels. To investigate the sources of radioactivity, the minerals involved in the rocks were detected using XRD and FTIR. The mineralogical studies reveal that the principal sources of gamma radiation in the study area are 232Th-rich phosphates and 40K-bearing feldspars.

15

Experimental study on deformation and damage evolution of a mining roadway with weak layer rock under compression-shear load

Song Yimin, Ren He, Xu Hailiang, An Dong

Archives of Mining Sciences

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2021

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Vol. 66, no. 3

351--368

EN

The structure and load characteristics of the roadway are simplified, and the experimental model of the roadway deformation and damage under compression-shear load is established. The experimental data acquisition system is built with a CCD camera. The digital speckle correlation method is used to calculate the image data of the experimental model. The correspondence between the evolution law of the deformation field, the interlayer displacement and deformation evolution are analysed, including the dynamic characteristic of the roadway surrounding the rock. Research results indicate: (1) The damage peak load of the weak layer structure shows a decreasing trend as the interlayer shear stress increases. As the initially applied shear stress increases, the value of interlayer sliding displacement increases, and the dynamic characteristics become more apparent. (2) In the sub-instability phase of the loading curve, when the surrounding rock slides along the layers under compression-shear load, the stress is re-distributed and transmitted to the deep part of the surrounding rock. Then the surrounding rock of the roadway forms the characteristic of alternating change, between tension to compression. (3) According to the state of dynamic and static mechanics, the deformation evolution of the roadway before the peak load belongs to the static process. Zonal fracturing is part of the transition phase from the static process to the slow dynamic process, and the rockburst damage is a high-speed dynamic process. (4) Under the compression-shear load, due to the weak layer structure of the coal and rock mass, the local fracture, damage, instability and sliding of the surrounding rock of the roadway are the mechanical causes of rockburst. (5) Even if the coal and rock mass does not have the condition of impact tendency, under stress load of the horizontal direction, distribution of large shear stress is formed between layers, and the dynamic damage of the rockburst may occur.

16

Experimental and theoretical study on the dynamic ejection process of a rock burst under a static load

Zheng Weiyu

Archives of Mining Sciences

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2021

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Vol. 66, no. 1

43--56

EN

As the duration of a rock burst is very short and the roadway is seriously damaged after the disaster, it is difficult to observe its characteristics. In order to obtain the dynamic characteristics of a rock burst, a modified uniaxial compression experiment, combined with a high-speed camera system is carried out and the process of a rock burst caused by a static load is simulated. Some significant results are obtained: 1) The velocity of ejected particles is between 2 m/s and 4 m/s. 2) The ratio of elastic energy to plastic energy is about five. 3) The duration from integrity to failure is between 20 ms and 40 ms. Furthermore, by analyzing the stress field in the sample with a numerical method and crack propagation model, the following conclusions can be made: 1) The kinetic energy of the ejected particles comes from the elastic energy released by itself. 2) The ratio of kinetic energy to elastic energy is between 6% and 15%. This can help understand the source and transfer of energy in a rock burst quantitatively.

17

Statistical damage constitutive model based on the Hoek-Brown criterion

Chen Yifan, Lin Hang, Wang Yixian, Xie Shijie, Zhao Yanlin, Yong Weixun

Archives of Civil and Mechanical Engineering

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2021

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Vol. 21, no. 3

556--564

EN

The constitutive models of rock are essentially the general depictions of the mechanical responses of rock mass under complex geological environments. Statistical distribution-based constitutive models are of great efficacy in reflecting the rock failure process and the stress–strain relation from the perspective of damage, while most of which were achieved by adopting Drucker–Prager criterion or Mohr–Coulomb criterion to characterize microelement failure. In this study, underpinned by Hoek–Brown strength criterion and damage theory, a new statistical damage constitutive model, which is simple in terms of model expression and capable of reflecting the strain softening characteristics of rock in post-peak stage, was established. First, the rock in the failure process was divided into infinite microelements including elastic part satisfying Hooke’s law and damaged part retaining residual strength. Based on strain equivalence hypothesis, the relation between rock microelement strength and damage variable was derived. By assuming the statistical law of microelement strength obeying Weibull distribution and the microelement failure conforming to Hoek–Brown criterion, the new statistical damage constitutive model based on Hoek–Brown criterion was, therefore, gained. The mathematical expressions of the corresponding model parameters were subsequently deduced in accordance with the geometric characteristics of the deviatoric stress–strain curve. Last, the existing conventional triaxial compression test data of representative rock samples under different confining stresses were employed to compare with the theoretical curves by proposed model, the consistency between which was quantified by utilizing the correlation factor evaluation method. The result indicated that the proposed model could well describe the entire stress–strain relationship of rock failure process and manifest the characteristics of rock residual strength. It is of great significance to the researches on rock damage and softening issues and rock reinforcement treatments.

18

Penetration behaviour of TBM disc cutter assisted by vertical precutting free surfaces at various depths and confining pressures

Cheng Jian‑Long, Wang Yong‑Xing, Wang Lian-Guo, Li Yuan-Hai, Hu Bo, Jiang Zi-Hao

Archives of Civil and Mechanical Engineering

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2021

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Vol. 21, no. 1

375--392

EN

The ability to improve rock-breaking efficiency of tunnel boring machines in hard rock stratum is significant to improve driving speed and reduce construction cost and time. The undercutting method has been used to improve the rock-breaking efficiency of disc cutters, including the design of curved and multistage cutterheads. The limited radian of curved cutterheads and the number of multistage cutterheads, however, are restricted by the current manufacturing level. We explored mechanical response and rock-breaking efficiency assisted by water jet kerfs as the vertical free surface. We conducted a quasi-static penetration test of the disc cutter considering four kerf depths and three groups of confining pressures. We analysed the surface crack propagation and fractures inside the sample using acoustic emission and computed tomography scanning. We studied the influence of confining pressure and cutting depth of the water jet on penetration force, rock chips, and specific energy. We analysed the failure evolution and stress field of kerf specimens using numerical simulation. The results showed that increasing cutting depth relieved restraint stress and the resulting influence of the confining pressure on removed rock volumes and specific energy was not remarkable. We recommended a kerf depth of greater than 18 mm to reduce penetration force and significantly improve rock-breaking efficiency.

19

Analiza porównawcza metod badania zawartości siarki w rdzeniach wiertniczych, węglu i ropach naftowych

Matyasik Irena, Zapała Marek, Kierat Maria, Wciślak Agnieszka

Nafta-Gaz

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2020

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R. 76, nr 7

449--456

PL

Celem pracy było dobranie i zwalidowanie optymalnej metody analizy zawartości siarki w rdzeniach wiertniczych, w tym pochodzących z pokładów węgla. Ponadto badania zostały przeprowadzone dla rop naftowych. W ramach pracy porównano wyniki badań zawartości siarki metodą analizy elementarnej w dwóch analizatorach: w analizatorze elementarnym EA 1108, który daje możliwość spalania próbek w temperaturze do 1080°C, co nie zawsze jest wystarczające w przypadku próbek geologicznych, oraz w analizatorze Leco CR12 rozbudowanym o moduł do oznaczania siarki, który daje możliwość wykonania analizy w 1350°C. W toku analizy elementarnej następuje przekształcenie siarki wolnej i związanej w dwutlenek siarki SO2, którego zawartość jest mierzona za pomocą różnych detektorów: detektora cieplno-przewodnościowego (TCD) w analizatorze EA 1108 lub detektora podczerwieni w analizatorze Leco CR12. Przed badaniami porównawczymi zwalidowano metodę analizy siarki w analizatorze Leco CR12. Badania porównawcze wykonano dla próbek skalnych, dla węgli i dla rop naftowych oraz dla kerogenu. W ramach pracy przeprowadzono analizy elementarne zawartości siarki dla 23 próbek węgla, 22 próbek skał, 5 próbek kerogenu wydzielonego z tych skał oraz dla 9 rop naftowych. Badane próbki węgla i materiału skalnego pochodziły z rdzeni wiertniczych z otworów poszukiwawczych. Wykazano zgodność stosowanych metod dla kerogenu i dla węgli o zawartości siarki powyżej 0,75% w/w oraz dla rop powyżej 0,3% zawartości siarki. Dużo gorszą zgodność uzyskano dla materiału skalnego z rdzeni wiertniczych, charakteryzującego się dyspersją materii organicznej. Dla próbek o niskiej zawartości siarki bardziej wiarygodnych wyników dostarczają oznaczenia wykonane w analizatorze EA 1108. W przypadku ośrodków o dużej dyspersji substancji organicznej, takich jak warstwy istebniańskie, bardziej wiarygodne są wyniki oznaczeń w analizatorze Leco CR12, ze względu na wielkość próbki analitycznej.

EN

The purpose of the work was to select and validate the optimal method for analyzing sulfur content in drilling cores, including those from coal seams. In addition, research was done for petroleum. As part of the work, the results of sulfur content testing were compared by means of elemental analysis in 2 analyzers: in the EA 1108 elemental analyzer, which gives the possibility of burning samples at temperatures up to 1080°C, which is not always sufficient for geological samples, and in the Leco CR12 analyzer expanded with a module for determination of sulfur, which gives the opportunity to perform the analysis at 1350°C. In the course of elemental analysis, free and bound sulfur is transformed into sulfur dioxide SO2, the content of which is measured by means of various detectors: the thermal conductivity detector (TCD) in the EA 1108 analyzer, or the infrared detector in the Leco CR 12 analyzer. Before the comparative tests, the method of sulfur analysis in the Leco CR 12 analyzer was validated. Comparative studies were carried out for rock samples, for coals, for petroleum and for kerogen. As part of the work, elemental analyses of sulfur content were carried out for 23 coal samples, 22 rock samples, 5 kerogen samples separated from these rocks and for 9 petroleum samples. Tested coal and rock material samples came from drill cores from exploratory wells. The methods used for kerogen and for coals with sulfur content over 0.75 wt % have been shown to be compatible. For oils, compatibility was observed above 0.3% sulfur content. Much worse compliance was obtained for rock matter from drilling cores, characterized by dispersion of organic matter. For samples with low sulfur content, determinations in the EA 1108 analyzer provide more reliable results. For media with a high dispersion of organic matter, such as Istebna Beds, the results of determinations in the Leco CR12 analyzer are more reliable due to the size of the analytical sample.

20

A Pen206 borehole jack suitability assessment for rock mass deformability determination

Pierszalik Rafał, Rajwa Sylwester, Walentek Andrzej, Bier Krzysztof

Archives of Mining Sciences

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2020

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Vol. 65, no. 3

569--590

EN

Currently available field rock mass deformability determination methods are rather difficult to perform, due to their complexity and a time-consuming nature. This article shows results of a suitability assessment of a Pen206 borehole jack (a hydraulic penetrometer) for field rock mass deformability measurements. This type of the borehole jack is widely used in Polish hard coal mining industry. It was originally intended only for quick rock mass strength parameters determination. This article describes an analysis and scope of basic modifications performed mainly on a borehole jack head. It includes discussion of results with possible directions for future development of the device.