Shape Effect of Fractures on Intensity and Density of Discreet Fracture Networks

Fractures are amongst the most important factors determining the behavior of rock masses. The lack of direct access to the real fractures’ distribution leads to the use of indirect methods for their study. The generation of the discrete fracture network is one of the most common indirect methods. Fractures’ shape is one of the most important properties that the simulation of which is of great help in studying the fracture network. A wide range of shapes which include from infinite plates to elliptical shape have been suggested for the simulation of fractures. The present paper makes use of the data collected from the pumped-storage power plant and dam project in Roudbar, Lorestan Province, to provide circular and elliptical network of discrete fractures; moreover, the parameters as density, intensity and the real mean value of the length of the fracture traces have been used to evaluate the effect and accuracy of the selected shapes. Following the implementation of the proposed method, it was made clear that the elliptical discrete fracture network, with a mean error value of 13.5 %, outperforms the circular disk discrete fracture network, with a mean error value of 27.5 %; hence, it was found providing more accurate results for the description of the fractures network in the aforementioned region

Optimized Fuzzy Cmeans – Fuzzy Covariance – Fuzzy Maximum Likelihood Estimation Clustering Method Based on Deferential Evolutionary Optimization Algorithm for Identification of Rock Mass Discontinuities Sets

Detecting of joint sets (clusters) is one of the most important processes in determining properties of fractures. Joints clustering and consequently, determination of the mean value representing each cluster is applicable to most rock mass studies. It is clear that the accuracy of the clustering process plays a key role in analyzing stability of infrastructures such as dams and tunnels and so on. Hence, in this paper, by reviewing several methods proposed for clustering fractures and considering their advantages and disadvantages, a three-stage hybrid method is developed which contains Fuzzy c-means, Fuzzy covariance and Fuzzy maximum likelihood estimation that by utilizing the modified orientation matrix had been optimized. This method is optimized by the Differential Evolutionary algorithm using a new and strong cost function which is defined as the computation core. In addition, using three clustering quality comparing criteria, the new developed method of differential evolutionary optimized of fuzzy cmeans - fuzzy covariance - fuzzy maximum likelihood estimation clustering method (DEF3) is compared with other base and common methods using field data. After doing the calculations, the developed method by giving the best values for all the criteria provided the best results and good stability in meeting different criteria. The DEF3 method was validated using actual field data which mapped in Rudbar Lorestan dam site. The results revealed that DEF3 acquired the best rank among the other method by getting the value of 0.5721 of Davis-Bouldin criterion, 1403.1 of Calinski-Harabasz criterion, and 0.83482 of Silihotte as comparing criteria of clustering methods

An approach towards ascertaining open-pit to underground transition depth

In this study, in order to determine OP to Ug mining TD of tabulate deposits, through various states some formulas were concluded. These formulas resulted based on the allowable and overall stripping ratios. For this objective, an analytical procedure was served. The contemplated states are variously combined from the deposits with outcrops or overburden and including maximum or minimum possible pit floor width

Determination of the Optimum Crown Pillar Thickness Between Open Pit and Block Caving

In this paper, a relationship between dependant parameters and the crown pillar thickness is first introduced. This relationship defines geotechnical problems caused by thin pillars and economic considerations created by pillars that are thicker than the optimum size. For this purpose, a dimensional analysis as an effective physico-mathematical tool was used. This technique restructures the original dimensional variables of a problem into a set of dimensionless products using the constraints imposed upon them by their dimensions. A model is hence introduced that calculates the optimum pillar thickness. The relationship introduced here and the method applied can be used by mining engineers in all situations where a combined open-pit and block caving method is deemed to be the most appropriate mining method

PREDVIĐANJE VISINE SLOMA PRIMJENOM PROGRAMIRANJA GENSKE EKSPRESIJE U AUSTRALSKIM ŠIROKOČELNIM OTKOPIMA, KOMPARATIVNA STUDIJA

The caving and subsidence developments above a longwall panel usually result in fractures of the overburden, which decrease the strength of the rock mass and its function. The height of fracturing (HoF) includes the caved and continuous fractured zones affected by a high degree of bending. Among the various empirical models, Ditton’s geometry and geology models are widely used in Australian coalfields. The application of genetic programming (GP) and gene expression programming (GEP) in longwall mining is entirely new and original. This work uses a GEP method in order to predict HoF. The model variables, including the panel width (W), cover depth (H), mining height (T), unit thickness (t), and its distance from the extracted seam (y), are selected via the dimensional analysis and Buckingham’s P-theorem. A dataset involving 31 longwall panels is used to present a new nonlinear regression function. The statistical estimators, including the coefficient of determination (R2), the average error (AE), the mean absolute percentage error (MAPE), and the root mean square error (RMSE), are used to compare the performance of the discussed models. The R2 value for the GEP model (99%) is considerably higher than the corresponding values of Ditton’s geometry (61%) and geology (81%) models. Moreover, the maximum values of the statistical error estimators (AE, MAPE, and RMSE) for the GEP model are 12%, 14%, and 16%, respectively, of the corresponding values of Ditton’s models.Razvoj kaverni i slijeganja iznad otkopa širokoga čela obično rezultira slomovima jalovinskih slojeva, što smanjuje čvrstoću stijenske mase. Visina sloma (HoF) uključuje udubljene i kontinuirane zone sloma zahvaćene visokim stupnjem savijanja. Među raznim empirijskim modelima Dittonovi geometrijski i geološki modeli široko se koriste u australskim ugljenokopima. Primjena genetskoga programiranja (GP) i programiranja ekspresije gena (GEP) u širokočelnim metodama posve je nova i originalna. U ovome radu primjenjuje se GEP metoda kako bi se predvidio HoF. Varijable modela, uključujući širinu čela (W), debljinu nadsloja (H), visinu čela (T), debljinu sloja (t) i njegovu udaljenost od otkopanoga sloja (y), odabiru se dimenzionalnom analizom i Buckinghamovim P teoremom. Skup podataka koji uključuje 31 širokočelni otkop koristi se za predstavljanje nove funkcije nelinearne regresije. Statistički procjenitelji, uključujući koeficijent determinacije (R2), prosječnu pogrešku (AE), srednju apsolutnu postotnu pogrešku (MAPE) i srednju kvadratnu pogrešku (RMSE), koriste se za usporedbu učinkovitosti razmatranih modela. Vrijednost (R2) za GEP model (99 %) znatno je veća od odgovarajućih vrijednosti Dittonove geometrije (= 61 %) i geologije (= 81 %). Štoviše, maksimalne vrijednosti procjenitelja statističkih pogrešaka (AE, MAPE i RMSE) za GEP model iznose 12 %, 14 % odnosno 16 % odgovarajućih vrijednosti Dittonovih modela

VARIJACIJA INTRINISTIČKIH SVOJSTAVA STIJENE U OVISNOSTI O HOEK-BROWNOVIM PARAMETRIMA KRITERIJA LOMA

The Hoek-Brown (H-B) criterion is one of the most commonly used rock failure criteria in recent years. This criterion includes a constant parameter called mi which is a fundamental parameter for estimating rock strength. Due to the importance of the mi parameter in the H-B criterion, it is necessary to conduct comprehensive studies on various aspects of the effect of this parameter on the behavior of rocks. Therefore, in this study, using numerical simulation of the Triaxial Compressive Strength (TCS) tests in PFC-2D code, the effects of microscopic properties of different rocks on the H-B parameter mi have been studied. Based on the results of this study, it was found that the effects of micro-parameters on the H-B parameter mi can be different depending on the type of rock, however this parameter has an inverse relationship to the micro-parameters of bond tensile strength and bond fraction of the rocks. Also, the mi parameter increases with an increase in the micro-parameters of the friction coefficient, the friction angle, the particle contact modulus, and the contact stiffness ratio of rocks.Hoek-Brownov kriterij (HB) jedan je od najčešće korištenih kriterija loma stijena posljednjih godina. Ovaj kriterij uključuje konstantni parametar zvan mi koji je temeljni parametar za procjenu čvrstoće stijene. Zbog važnosti parametra mi u Hoek-Brownovu kriteriju potrebno je provesti sveobuhvatne studije o različitim aspektima učinka ovoga parametra na ponašanje stijena. Stoga su u ovoj studiji, korištenjem numeričke simulacije ispitivanja troosne tlačne čvrstoće (TCS) u PFC-2D kodu, proučavani učinci mikroskopskih svojstava različitih stijena na Hoek-Brownov parametar mi . Na temelju rezultata ove studije utvrđeno je da učinci mikroparametara na Hoek-Brownov parametar mi mogu biti različiti, ovisno o vrsti stijene, međutim ovaj parametar ima obrnut odnos prema mikroparametrima vlačne čvrstoće veze i veza frakcija stijena. Također, parametar mi raste s povećanjem mikroparametara koeficijenta trenja, kuta trenja, modula kontakta čestica i odnosa krutosti stijena

Mining method selection and transition depth determination problems - which one is in priority of consideration?

During this paper, in order to identify the priority of consideration between the problems of “mining method selection” and “determining transition depth from open-pit to underground mining” an accurate procedure is introduced step by step. First, it is essential to specify if an ore deposit that potentially will have mined by a combined method of open-pit and underground mining. In this case, optimal final open-pit limit and depth must be initially determined. After that, if the rest of deposit below open-pit limit is economically considerable, it is necessary to select the most adequate underground method with emphasis on the high production rate and low cost methods. Then, it is necessary to determine optimal transition depth from open-pit to underground mining considering a crown pillar immediately below open-pit mining. Finally, the procedure with its algorithm was used for an iron ore deposit with the combined mining potential

Tomografia pasywna pola prędkości i symulacje geostatystyczne w obrębie pola ścianowego

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

NUMERIČKA I EKSPERIMENTALNA ISTRAŽIVANJA MEHANIZMA LOMA STIJENE TE OVISNOSTI TOGA PROCESA O HOEK-BROWNOVU KRITERIJU LOMA mi

Rock failure mechanism is one of the most important issues in rock mechanics engineering which plays a key role in the stability analysis of various structures. Therefore, different failure criteria have been proposed to understand the failure mechanism of rocks. One of the most commonly used rock failure criteria is the Hoek-Brown criterion, in which there is a parameter called mi, which is very important to the response provided by this criterion. Due to the importance of conducting extensive studies on this parameter, in this current research, by performing a series of experimental triaxial compressive strength test and numerical simulating in PFC-2D code, the effect of the Hoek-Brown constant mi on the failure mechanism and crack growth of different rocks has been studied. Based on the results of this study, it was found that the effect of parameter mi on the failure mechanism of different rocks varied according to the type of rocks, and the greatest effect of this parameter was on the peak strength of rocks. In addition, it was found that under higher lateral pressures, there are less destructive cracks in rocks, and as a result, they show more ductile behaviour.Mehanizam loma stijene jedno je od najvažnijih pitanja u mehanici i inženjerstvu stijena te je ključno u analizi stabilnosti raznih struktura. Za različite kriterije loma predloženi su različiti mehanizmi odgovorni za takav proces. Jedan od najčešće korištenih kriterija kojim se opisuje lom stijena jest Hoek-Brownov kriterij, u kojemu postoji varijabla zvana mi, koja je vrlo važna kod ocjene tim kriterijem. Zbog važnosti provođenja opsežnih studija o prilagođavanju te varijable u prikazanim istraživanjima ona je određena izvođenjem serije eksperimentalnih ispitivanja troosne tlačne čvrstoće i numeričke simulacije u PFC-2D kodu. Time je istražen učinak vrijednosti mi na lom stijene i rast pukotina različitih stijena. Na temelju rezultata utvrđeno je kako je utjecaj varijable mi na lom različitih vrsta stijena varijabilan, a najveći je učinak na vršnu čvrstoću stijena. Također, utvrđeno je da su pod većim bočnim pritiscima razarajuće pukotine u stijenama manje (uspoređeno s prethodnim testom), a kao rezultat pokazuju više duktilno ponašanja

ISTRAŽIVANJE UTJECAJA MIKROPARAMETARA NA SVOJSTVA ČVRSTOĆE STIJENE

Rocks are formed from particles and the interaction between those particles controls the behaviour of a rock’s mechanical properties. Since it is very important to conduct extensive studies about the relationship between the micro-parameters and macro-parameters of rock, this paper investigates the effects of some micro-parameters on strength properties and the behaviour of cracks in rock. This is carried out by using numerical simulation of an extensive series of Uniaxial Compressive Strength (UCS) and Brazilian Tensile Strength (BTS) tests. The micro-parameters included the particles’ contact modulus, the contact stiff ness ratio, bond cohesion, bond tensile strength, the friction coefficient and the friction angle, and the mechanical properties of chromite rock have been considered as base values of the investigation. Based on the obtained results, it was found that the most important micro-parameters on the behaviour of rock in the compressive state are bond cohesion, bond tensile strength, and the friction coefficient. Also, the bond tensile strength showed the largest effect under tensile conditions. The micro-parameter of bond tensile strength increased the rock tensile strength (up to 5 times), minimized destructive cracks and increased the corresponding strain (almost 2.5 times) during critical stress.Svaka je stijena stvorena od čestica čijim se međudjelovanjem određuju njezina mehanička svojstva. Budući da je vrlo važno provesti opsežne studije o povezanosti mikroparametara i makroparametara stijene, u ovome su radu istraživani učinci nekih mikroparametara na svojstva čvrstoće i ponašanje pukotina stijene numeričkim simulacijama jednoosne tlačne čvrstoće (UCS) i brazilske vlačne čvrstoće (BTS). Ispitivani mikroparametri uključivali su kontakt čestica, omjer kontaktne krutosti, koheziju veze, vlačnu čvrstoću, koeficijent trenja i kut trenja, a mehanička svojstva stijene bogate kromitom bile su osnovne vrijednosti ispitivanih mikroparametara. Utvrđeno je kako su najvažniji mikroparametri na ponašanje stijene kod tlačenja kohezija veze, vlačna čvrstoća veze i koeficijent trenja. Također, vlačna čvrstoća ima najveći učinak u vlačnim uvjetima. Ovaj mikroparametar povećava vlačnu čvrstoću (do 5 puta), minimalizira destruktivne pukotine i povećava odgovarajuće naprezanje (gotovo 2,5 puta) pri kritičnome naprezanju