Numerical Simulation of Fully Grouted Rock Bolts

This chapter describes the application of numerical modelling to civil and mining projects, particularly rock bolting, developing a Final Element (FE) model for the bolt, grout, rock, and two interfaces under axial and lateral loading, verifying the model, analysing the stress and strains developed in the bolt and surrounding materials. Numerical methods are the most versatile computational methods for various engineering disciplines because a structure is discritised into small elements and the constitutive equations that describe the individual elements and their interactions are constructed. Finally, these numerous equations are solved together simultaneously using computers. The results from this procedure include the stress distribution and displacement pattern within a structure. Numerical modelling includes analytical techniques such as finite elements, boundary elements, distinct elements, and other numerical approaches that depend upon the material. The finite element method FEM is considered to evaluate the behaviour of materials and their interactions in a fully grouted bolt which is installed in a jointed rock mass. The simulations were carried out by ANSYS code

Finite difference modelling in underground coal mine roadway

This paper presents stability analysis of roadways of the Tabas coal mine in Iran. Tabas Coal Mine is the first fully mechanised coal mine in Iran, producing 1.5 million tons of coal per year. The mine extracts coal by both longwall and room and pillar methods. The results gathered from field investigations and the geomechanical properties of rocks, were determined in the laboratory and indicate that the rock masses of this area are weak. So, the excavated roadways need to have suitable support. For this purpose, the roadways were modeled with FLAC-2D software. The Finite Difference Method (FDM) models were calibrated to study the interaction between rock mass and support. The use of V29 and V36 section arches are under consideration. After modelling these roadways in FLAC2D software the results achieved from this model show that; displacements of around the roadways are high and safety factors are very low, so roadways need to be support. The extracted results from this software show that; steel arch V36 with a spacing of 1m is the best support system for these roadways. With this type of support system, displacements around the roadway are low and safety factors are in suitable values. After installation it was observed that the critical strain values on roadway walls and roof were less than the permitted values, which demonstrated the roadway stability

ANALIZA RIZIKA OD PADA KROVINE I PREDVIĐANJE OŠTEĆENJA PODRUČJA PRI RUDARENJU UGLJENA POVLAČENJEM ŠIROKOGA ČELA

This study presents a model based on rock engineering systems (RES) to evaluate the risk of roof falls and determine damaged regions, using recorded roof falls, prior to mining with a retreat from a longwall face. In this regard, a case study was considered to examine the model. The results showed that the level of determined risk has an acceptable correlation with the special roof fall (SRF), with R-squared value (R2) equal to 0.792 for all estimated vulnerability indexes (VIs) in considered longwall panels. By investigating and comparing the evaluated values of VI in considered panels and their corresponding recorded roof falls, damaged regions were distinguished from undamaged regions. Based on these investigations, four classes including safe, moderate, danger, and critical regions were determined to identify the safe and damaged regions prior to the mining operation. The results of the research showed that the identification of damaged regions is feasible to provide a detailed operation plan to control roof falls in longwall mining faces through the developed approach. The RES-based model could be used for the same conditions and the presented methodology could be applied to other parts in underground coal mines.U ovome radu prikazan je model utemeljen na sustavima inženjerskih stijena za procjenu rizika od urušavanja (pada) krovine i određivanje oštećenih područja primjenom zabilježenih padova krovine, prije rudarenja metodom širokoga čela. Razmatrana je studija slučaja koja je ispitala model. Rezultati su pokazali da je razina utvrđenoga rizika imala relativno prihvatljivu korelaciju i kompatibilnost s posebnim padom krovine (PPK), s koeficijentom determinacije (R2) jednakim 0,792 za sve procijenjene indekse ranjivosti (IR) u razmatranim područjima rudarenja. Istražujući i uspoređujući procijenjene vrijednosti indeksa ranjivosti na razmatranim područjima i pripadajućim zabilježenim padovima krovine, otkrivena su oštećena područja unutar onih neoštećenih. Na temelju tih istraživanja izvedene su četiri klase: sigurno, umjereno, opasno i kritično područje, radi identificiranja sigurnih, umjereno opasnih i kritičnih područja prije rudarskih operacija. Rezultati istraživanja pokazali su da je identificiranje štetnih područja razvijenim pristupom prikladno za izradu detaljnoga operativnoga plana za kontrolu pada krovine na širokom čelu. Konačno, model temeljen na inženjerskim sustavima stijena može se koristiti i drugdje za iste uvjete, a predstavljena metodologija može se primijeniti i na ostale dijelove podzemnih rudnika ugljena

PROCJENA ČVRSTOĆE I PETROFIZIČKIH SVOJSTAVA ANHIDRITNE KROVINE NA TEMELJU PROMJENJIVIH OPTEREĆENJA I RAČUNALNE TOMOGRAFIJE

Underground gas storage (UGS) in depleted reservoirs affects caprock properties. The resemblance of Qom anhydrite outcrop with cutting obtained from a 2629 m depth was confirmed using X-ray diffraction (XRD) results and scanning electron microscope (SEM) tests. The anhydrite specimens unconfined compressive strength (UCS) changed under static cyclic loading conditions, and also petrophysical properties, such as porosity and permeability altered under 10, 20, and 30 cycles of loading. The magnitude of loading ranged from 30 to 43% of intact anhydrite UCS. The loading rate used for cyclic loading tests was 0.004 mm/s. The samples’ UCS decreased between 3.5 to 23.9% under cyclic loading conditions. The study of specimens computed tomography (CT) imaging with porosity and permeability indicated the growth of cracks, the cracks did not initiate in all lengths of specimens, hence the incremental increase in porosity did not increase the permeability of specimens. Even being under cyclic loads, the permeability of specimens stayed lower than 10-15 m2 (0.001 mD) but the trend of pressure versus time for measuring permeability shows a higher drop in pressure due to changes in permeability. The study indicated that the CT imaging results are in good accordance with petrophysical findings.Podzemno skladište plina smješteno u iscrpljenim ležištima utječe i na svojstva krovine. Sličnost između anhidrita Qom uzorkovanoga na površinskome izdanku te iz krhotina dobivenih s 2629 m dubine opisana je na temelju rezultata difrakcije x-zraka i skeniranja elektroničkim mikroskopom. Maksimalna jednoosna tlačna čvrstoća uzorka anhidrita mijenja se u uvjetima statičkih, promjenjivih, cikličkih opterećenja, pri čemu dolazi i do promjene petrofizičkih svojstava poput šupljikavosti i propusnosti, npr. tijekom 10, 20 i 30 ciklusa. Magnituda opterećenja bila je u rasponu od 30 do 43% maksimalne tlačne čvrstoće anhidrita, dok je intenzitet opterećenja kod cikličkih testova iznosio 0,004 mm/s. Kod ispitivanih uzoraka zamijećeno je smanjenje maksimalne tlačne čvrstoće u rasponu od 3,5 do 23,9% pri različitim uvjetima promjena opterećenja. Proučavanjem šupljikavosti i propusnosti uzoraka i snimki računalne tomografije vidljiv je porast broja pukotina u uzorku, pri čemu je uočeno da do stvaranja pukotina nije došlo uzduž cijeloga uzorka, kao što niti porastom šupljikavosti nije došlo do rasta propusnosti. Iako su uzorci bili izloženi cikličkim opterećenjima, propusnost uzoraka ostala je manja od 10-15 m2 (0,001 mD). Proučavanjem promjene tlaka u vremenu uočen je veći pad tlaka zbog promjene propusnosti uzorka. Rezultati istraživanja upućuju na dobro podudaranje podataka dobivenih snimkama računalne tomografije i rezultata petrofizičkih ispitivanja

Prediction of damaged zone in longwall working panels

In longwall mining, the instability of roadways can affect the mine safety, production rate and consequently the economic condition of mine. Therefore their stability analysis is one the most important technical problems in underground mining. The stability analysis and the design of support systems have to be investigated from two points of view; 1) the pressure and displacements of damaged zone around gate roadways due to the construction process and stress redistribution and 2) the working loading due to coal seam extraction and overburden caving that extends the damaged zone size. The aim of this research is the calculation of working effect on the damaged zone around gate roadway considering geomechincal properties of medium and the geometric characteristic of the roads and working. Therefore, a method has been obtained to calculate the total damaged zone area and working influence coefficient using geometric concepts and mathematical relations, then a design algorithm has been suggested based on the obtained method

A review on half a century of experience in rate of penetration management: Application of analytical, semi-analytical and empirical models

Rate of penetration management is a matter of importance in drilling operations and it has been used in some research studies. Although conventional approaches for rate of penetration management are mainly focused on analytical and semi-analytical models, several correlations have also been developed for this purpose. The history of rate of penetration management studies extends back more than half a century and ever since, research interest in this concept has never declined, making it a focus of industry and academic studies. In this article, some of these studies are reviewed to achieve a better understanding of rate of penetration management concept, its financial benefits and also its research capacities. This review reveals the most common rate of penetration management methods which applied analytical, semi-analytical and empirical correlations in different fields around the world. In other words, the main purpose of this study is to evaluate the research studies in which different models and correlations have been used as the main approach for rate of penetration management. Based on the results of this review, the best models for performing rate of penetration management studies and the best objective functions for optimization algorithms are introduced.Cited as: Najjarpour, M., Jalalifar, H., Norouzi-Apourvari, S. A review on half a century of experience in rate of penetration management: Application of analytical, semi-analytical and empirical models. Advances in Geo-Energy Research, 2021, 5(3): 252-273, doi: 10.46690/ager.2021.03.0

Effectiveness of Matched and Mismatched Natural Rock Joints Using Experimental Direct Shear Tests

In practice, the shear strength of joints is not only determined by the roughness, but also by the degree of joint matching. Due to alteration or movement, the joints with equal roughness might be mismatched. The matching degree of the joint is a significant factor that controls the normal closure, aperture, stiffness, hydraulic conductivity, and shear strength of the jointed rock mass. Studying the shear behavior of natural mismatched rock joints obtained from core drilling with different morphological characteristics, degrees of matching, and irregular shapes is an issue that has gained less attention due to the lack of samples and difficulty to obtain data. This study investigates the shear behavior of mismatched joints obtained from core drilling. Here, a new criterion is developed based on 35 series of direct shear tests, Barton and other classical theories, three-dimensional morphological characteristics, and matching condition of joints. To validate the proposed criterion, the estimation accuracy of the available classical models is compared with that of the new model. It is observed that the new criterion could achieve higher prediction accuracy for mismatched joints. Moreover, it is found that the average estimation error of the predicted values is reduced by considering the matching conditions

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

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