19 research outputs found
Scaling Geological Fracture Network from a Micro to a Macro Scale
Characterizing fracture systems at various scales, modeling fracture distributions, and clarifying scale relations that correlate total fracture systems are of paramount importance in geology, mining, civil engineering, and petroleum engineering. In this paper, the conditions of fracture network geometry are investigated in a field scale (about 100 m) and a core sample scale (several centimeters). To achieve this purpose, field surveys and coring of rock outcrops were performed in the Asmari Formation of Iran. Fractures were manually sampled from rock outcrops on the field scale while micro-fractures were surveyed using CT-scan images of core samples on a small scale. To compare the fracture network geometry, two perspectives of fractal dimensions and orientation of fractures were used. The results showed that the fractal dimension has the same value in both field and core scales and the orientation of the fractures is similar in both scales. Therefore, it can be claimed that in the Asmari Formation of Iran the structure of the fracture network is similar in two studied scales
Geomechanical key parameters of the process of hydraulic fracturing propagation in fractured medium
International audienceHydraulic Fracturing (HF) is a well-stimulation technique that creates fractures in rock formations through the injection of hydraulically pressurized fluid. Because of the interaction between HF and Natural Fractures (NFs), this process in fractured reservoirs is different from conventional reservoirs. This paper focuses mainly on three effects including anisotropy in the reservoir, strength parameters of discontinuities, and fracture density on HF propagation process using a numerical simulation of Discrete Element Method (DEM). To achieve this aim, a comprehensive study was performed with considering different situations of in situ stress, the presence of a joint set, and different fracture network density in numerical models. The analysis results showed that these factors play a crucial role in HF propagation process. It also was indicated that HF propagation path is not always along the maximum principal stress direction. The results of the numerical models displayed that the affected area under HF treatment is decreased with increasing the strength parameters of natural fracture and decreasing fracture intensity
UTJECAJ RASLOJAVANJA ÄIMBENIKA OÅ TEÄENJA IZAZVANIH MINIRANJEM U HOEK-BROWNOVU KRITERIJU SLOMA NA PRAÄENJE OÅ TEÄENJA ETAŽA U KOPOVIMA
The process of creating a slope in a rock mass using the excavation and blasting methods consistently leads to stress release in the rock mass, resulting in a certain level of fracture and disturbance. Blast-induced vibrations can also influence the quality of the rock mass remaining after the blasting, as well as the stability and bench damage monitoring (BDM) of mines. A damage factor (D) is included in the HoekāBrown failure criterion to compute the disturbance of a rock mass in creating a slope. Choosing the value and thickness of the blast zone for the HoekāBrown criterion is crucial in the safety analysis and BDM of mines. However, the selection is still a crucial technical challenge in this criterion. Employing nonlinear layering, the present study divides the rock mass behind a blast hole into several layers with decreasing D values applied to each layer. The numerical simulation was conducted using the FLAC finite difference software for bench vibration assessment and damage monitoring by checking the peak particle velocity (PPV) in the bench face with different geometries. Behind the blast hole, five different layers of D were considered through which the HoekāBrown properties of the rock mass declined nonlinearly during the execution of the model. Since the disturbance threshold of PPV was assumed to be 120 mm/s, the toe and middle parts of the small benches were in the disturbance threshold, while for the medium and high benches, only the bench toe was within the disturbance threshold.Proces stvaranja kosina u stijenskoj masi metodama iskopa i miniranja dovodi do oslobaÄanja naprezanja u stijenskoj masi, Å”to rezultira odreÄenom razinom loma i oÅ”teÄenja. Vibracije izazvane miniranjem takoÄer mogu utjecati na kvalitetu minirane stijenske mase, kao i na stabilnost i praÄenje oÅ”teÄenja etaža (BDM) povrÅ”inskoga kopa. Koeficijent poremeÄenosti stijenske mase (D) ukljuÄen je u Hoek-Brownov kriterij sloma za izraÄunavanje oÅ”teÄenja stijenske mase pri izradi kosine. Odabir vrijednosti i Å”irine zone miniranja prema Hoek-Brownovu kriteriju kljuÄan je u analizi sigurnosti i BDM-a kopova. MeÄutim, odabir joÅ” uvijek predstavlja kljuÄni tehniÄki izazov. KoristeÄi se nelinearnom slojevitoÅ”Äu, ova analiza dijeli stijensku masu iza minske buÅ”otine u nekoliko slojeva sa smanjivanim vrijednostima D za pojedini sloj. NumeriÄka simulacija provedena je koriÅ”tenjem softvera FLAC za procjenu vibracija na etažama i praÄenje oÅ”teÄenja provjerom vrÅ”ne brzine Äestica (PPV) na etaži s razliÄitim geometrijama. Iza minske buÅ”otine razmatrano je pet razliÄitih nizova D kroz koje su Hoek-Brownova svojstva stijenske mase nelinearno mijenjana tijekom analize modela. BuduÄi da je graniÄna vrijednost PPV-a pretpostavljena na 120 mm/s, vrh i srediÅ”nji dijelovi malih etaža bili su na graniÄnoj vrijednosti oÅ”teÄenja, dok je za srednje i visoke etaže samo vrh etaže bio unutar graniÄne vrijednosti oÅ”teÄenja
MEHANIZAM KAISEROVA EFEKTA U FILITU PRI VLAÄNOME OPTEREÄENJU NEIZRAVNIM MJERENJEM
Determination of in-situ stress serves as an important step in the design and construction of civil and mining projects, among others. Conventional methods of the in-situ stress measurement are time- and cost-intensive. Therefore, the application of low-cost yet rapid methodologies for in-situ stress evaluation has been increasingly regarded by researchers. The Kaiser effect-based acoustic emission method is one of such novel approaches to the in-situ stress evaluation. Not only the point at which the Kaiser effect occurs, but also the mechanism of the Kaiser effect is of paramount importance. In this research, acoustic emission tests were conducted on phyllite rock samples under Brazilian tensile loading to collect a variety of acoustic data, including the amplitude, rise time, count, duration, and energy. Then, the Kaiser effect point was determined using the collected data on acoustic parameters, with its occurrence mechanism investigated. In addition, mathematical transformations were adopted to transform the acoustic signal from the time domain to the frequency domain, where the peak frequency was analyzed. The results of the RA/AF ratio analysis showed that the acoustic emission was sourced from tensile micro-cracks. Moreover, the high level of energy indicated a high intensity of crack formation at the Kaiser effect point. The large number of received hits showed that the count of generated cracks increases abruptly within the range of the Kaiser effect. In addition, the obtained high value of the peak frequency implied that the crack growth rate is high at the Kaiser effect point.In situ odreÄivanje naprezanja, meÄu ostalim, služi kao važan korak u projektiranju i izradi graÄevinskih i rudarskih projekata. Konvencionalne in situ metode mjerenja naprezanja vremenski su i troÅ”kovno zahtjevne. Stoga istraživaÄi sve viÅ”e razmatraju primjenu jeftinih, ali brzih metodologija za procjenu in situ naprezanja. Metoda akustiÄne emisije koja se temelji na Kaiserovu efektu jedan je od takvih novih pristupa u procjeni in situ naprezanja. Ne samo toÄka u kojoj se Kaiserov efekt javlja, nego i mehanizam Kaiserova efekta od iznimne je važnosti. U ovome su istraživanju provedena ispitivanja akustiÄke emisije na uzorcima filitnih stijena pri ispitivanju vlaÄne ÄvrstoÄe stijena uporabom brazilskoga testa kako bi se prikupili razliÄiti akustiÄki podatci ukljuÄujuÄi amplitudu, vrijeme porasta, broj, trajanje i energiju. Potom je na temelju prikupljenih podataka o akustiÄkim parametrima odreÄena toÄka Kaiserova efekta te je ispitan mehanizam njezina nastanka. Osim toga, usvojene su matematiÄke transformacije za transformaciju akustiÄkoga signala iz vremenske domene u frekvencijsko podruÄje, gdje je analizirana vrÅ”na frekvencija. Rezultati analize omjera RA/AF pokazali su da je akustiÄka emisija nastala iz vlaÄnih mikropukotina. Å toviÅ”e, visoka razina energije upuÄuje na visok intenzitet stvaranja pukotina u toÄki Kaiserova efekta. Velik broj primljenih impulsa pokazao je da se broj novonastalih pukotina naglo poveÄava unutar raspona Kaiserova efekta. Osim toga, dobivena visoka vrijednost vrÅ”ne frekvencije implicira da je brzina Å”irenja pukotine visoka u toÄki Kaiserova efekta
PREGLED PRIMJENE KAISEROVA EFEKTA U MJERENJU IN SITU NAPREZANJA U STIJENAMA
Knowledge of in-situ rock stress is one of the significant issues in many engineering problems. There are various methods for determining in-situ stress. Most of the common methods used for the determination of in-situ stress are time and cost consuming, and in many cases need specific accessibility. Therefore, attention to core-based methods is increasing. One of these methods is the acoustic emission technique based on the Kaiser effect. This method is among the stress stressing-destressing methods and is based on observing rock behaviour without having any important impact on it. Knowledge of the acoustic emission principles and acoustic signal parameters is the first step to use the Kaiser effect method for in-situ stress determination. Also, using the Kaiser effect method requires knowledge on the mechanism and theory associated with the Kaiser effect. In this research, different methods for determining the Kaiser effect in parametric (tangent method and maximum slope, etc.) and signal processing (Fourier transform, wavelet transform, etc.) terms were reviewed. The results obtained from the Kaiser effect method were compared to other common methods used for in-situ stress measurement, like over-coring and hydraulic fracturing methods, and based on the results, there was a good agreement between them. Also, the effective parameters on determining the Kaiser effect stress point were investigated. The important parameters were the testing procedure, confining pressure, physical properties of rock, delay time and retention time, direction and amount of loading, anisotropy angle and loading rate.Poznavanje in situ naprezanja u stijenskoj masi jedan je od važnijih aspekata u mnogim inženjerskim problemima. Postoje razliÄite metode za odreÄivanje in situ naprezanja. VeÄina uobiÄajenih metoda koje se koriste za odreÄivanje in situ naprezanja vremenski su i financijski zahtjevne te je u mnogim sluÄajevima potrebna posebna pristupaÄnost. Stoga se sve viÅ”e pažnje posveÄuje metodama temeljenim na ispitivanjima provedenim na jezgrama. Jedna je od tih metoda i metoda akustiÄke emisije koja se temelji na Kaiserovu efektu. Ubraja se u metode naprezanja postupcima optereÄenja i rastereÄenja, a temelji se na promatranju ponaÅ”anja stijena bez znatnoga utjecaja na nju. Poznavanje principa akustiÄke emisije i parametara akustiÄkoga signala prvi je korak u primjeni metode za odreÄivanje in situ naprezanja na temelju Kaiserova efekta. Nadalje, primjena metode Kaiserova efekta zahtijeva razumijevanje mehanizma i teorije povezane s Kaiserovim efektom. U ovome istraživanju razmatrane su razliÄite metode za odreÄivanje Kaiserova efekta u okviru parametara (metoda tangente i maksimalni nagib itd.) i obrade signala (Fourierova transformacija, valiÄna transformacija i sl.). Pored navedenog, rezultati dobiveni metodom Kaiserova efekta usporeÄeni su s drugim uobiÄajenim metodama koje se koriste za mjerenje in situ naprezanja, kao Å”to su overcoring metoda i metoda hidrauliÄkoga frakturiranja te je na temelju rezultata ustanovljena znatna podudarnost izmeÄu njih. TakoÄer su istraženi kljuÄni parametri za odreÄivanje toÄke naprezanja kod Kaiserova efekta. KljuÄni parametri bili su postupak ispitivanja, ograniÄavajuÄi tlak, fiziÄka svojstva stijene, vrijeme kaÅ”njenja i vrijeme zadržavanja, smjer i koliÄina optereÄenja, kut anizotropije i brzina optereÄenja
Tomografia pasywna pola prÄdkoÅci i symulacje geostatystyczne w obrÄbie pola Åcianowego
Generally, the accurate determination of the stress in surrounding rock mass of underground miningarea has an important role in stability and ground control. In this paper stress redistribution around thelongwall face has been studied using passive seismic velocity tomography based on Simultaneous IterativeReconstructive Technique (SIRT) and Sequential Gaussian Simulation (SGS). The mining-induced microseismicevents are used as a passive source. Since such sources are used, the ray coverage is insufficientand in order to resolve this deficiency, the wave velocity is estimated in a denser network and by the SGSmethod. Consequently the three-dimensional images of wave velocity are created and sliced into the coalseam. To analyze the variations of stress around the panel during the study period, these images are interpreted.Results show that the state of stress redistribution around the longwall panel can be deduced fromthese velocity images. In addition, movements of the stressed zones, including front and side abutmentsand the goaf area, along the longwall face are evident. The applied approach illustrated in this paper canbe used as a useful method to monitoring the stress changes around the longwall face continuously. Thiscan have significant safety implications and contribute to improvements in operational productivity
Calculation of periodic roof weighting interval in longwall mining using finite element method
Determination of the Fractal Dimension of the Fracture Network System Using Image Processing Technique
Fractal dimension (FD) is a critical parameter in the characterization of a rock fracture network system. This parameter represents the distribution pattern of fractures in rock media. Moreover, it can be used for the modeling of fracture networks when the spatial distribution of fractures is described by the distribution of power law. The main objective of this research is to propose an automatic method to determine the rock mass FD in MATLAB using digital image processing techniques. This method not only accelerates analysis and reduces human error, but also eliminates the access limitation to a rock face. In the proposed method, the intensity of image brightness is corrected using the histogram equalization process and applying smoothing filters to the image followed by revealing the edges using the Canny edge detection algorithm. In the next step, FD is calculated in the program using the box-counting method, which is applied randomly to the pixels detected as fractures. This algorithm was implemented in different geological images to calculate their FDs. The FD of the images was determined using a simple Canny edge detection algorithm, a manual calculation method, and an indirect approach based on spectral decay rate. The results showed that the proposed method is a reliable and fast approach for calculating FD in fractured geological media