The validity of the cubic law for laminar flow of fluids through open fractures consisting of parallel planar plates has been established by others over a wide range of conditions with apertures ranging down to a minimum of 0.2 µm. The law may be given in simplified form by Q/Δh = C(2b)3, where Q is the flow rate, Δh is the difference in hydraulic head, C is a constant that depends on the flow geometry and fluid properties, and 2b is the fracture aperture. The validity of this law for flow in a closed fracture where the surfaces are in contact and the aperture is being decreased under stress has been investigated at room temperature by using homogeneous samples of granite, basalt, and marble. Tension fractures were artificially induced, and the laboratory setup used radial as well as straight flow geometries. Apertures ranged from 250 down to 4µm, which was the minimum size that could be attained under a normal stress of 20 MPa. The cubic law was found to be valid whether the fracture surfaces were held open or were being closed under stress, and the results are not dependent on rock type. Permeability was uniquely defined by fracture aperture and was independent of the stress history used in these investigations. The effects of deviations from the ideal parallel plate concept only cause an apparent reduction in flow and may be incorporated into the cubic law by replacing C by C/ƒ. The factor ƒ varied from 1.04 to 1.65 in these investigations. The model of a fracture that is being closed under normal stress is visualized as being controlled by the strength of the asperities that are in contact. These contact areas are able to withstand significant stresses while maintaining space for fluids to continue to flow as the fracture aperture decreases. The controlling factor is the magnitude of the aperture, and since flow depends on (2b)3, a slight change in aperture evidently can easily dominate any other change in the geometry of the flow field. Thus one does not see any noticeable shift in the correlations of our experimental results in passing from a condition where the fracture surfaces were held open to one where the surfaces were being closed under stress.

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VALIDITY OF CUBIC LAW FOR FLUID FLOW IN A DEFORMABLE ROCK FRACTURE - eScholarship

The effect of scale on the shear behaviour of joints is studied by performing direct shear tests on different sized replicas cast from various natural joint surfaces. The result show significant scale effects on both the shear strength and deformation characteristics. Scale effects are more pronounced in the case of rough, undulating joint types, whereas they are virtually absent for planar joints. The key factor is the involvement of different asperity sizes in controlling the peak behaviour of different lengths of joints. It is shown that as a results both the joint roughness coefficient (JRC) and the joint compression strength (JCS) reduce with increasing scale. The behaviour of multiple jointed masses with different joint spacing is also considered. It is found that despite unchanged roughness, jointed masses consisting of many small blocks have higher peak shear strength than jointed masses with larger joint spacing. These scale effects are related to the changing stiffness of a rock mass as the block size or joint spacing increases or decreases. Economic methods for obtaining scale-free estimates of shear strength are described.

Experimental studies of scale effects on the shear behaviour of rock joints

Boundary element methods in solid mechanics

A bibliometric based survey on AHP and TOPSIS methods has been conducted.Scopus database was employed to retrieve the required data for this analysis.Assessment of quantitative and qualitative bibliometric indicators was obtainable.Efficacy of these methods promotes the development of related research.More scientific research interests will be devoted to these methods in the future. In recent years, the employment of multiple criteria decision analysis (MCDA) techniques in solving complex real-world problems has increased exponentially. The willingness to build advanced decision models, with higher capabilities to support decision making in a wide range of applications, promotes the integration of MCDA techniques with efficient systems such as intelligence and expert systems, geographic information systems, etc. Amongst the most applied MCDA techniques are Analytic Hierarchy Process (AHP) and Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS). The development of a comprehensive perspective on research activities associated with the applications of these methods provides insights into the contributions of countries, institutes, authors and journals towards the advancements of these methods. Furthermore, it helps in identifying the status and trends of research. This in turn will help researchers in shaping up and improving future research activities and investments. To meet these aims, a bibliometric analysis based on data harvested from Scopus database was carried out to identify a set of bibliometric performance indicators (i.e. quantitative indicators such as productivity, and qualitative indicators such as citations and Hirsch index (h-index)). Additionally, bibliometric visualization maps were employed to identify the hot spots of research. The total research output was 10,188 documents for AHP and 2412 documents for TOPSIS. China took a leading position in AHP research (3513 documents; 34.5%). It was also the leading country in TOPSIS research (846 documents; 35.1%). The most collaborated country in AHP research was the United States, while in case of TOPSIS it was China. The United States had gained the highest h-index (78) in AHP research, while in TOPSIS it was Taiwan with h-index of 46. Expert Systems with Applications journal was the most productive journal in AHP (204; 2.0%) and TOPSIS research (125; 5.2%), simultaneously. University of Tehran, Iran and Islamic Azad University, Iran were the most productive institutions in AHP (173; 1.7%) and TOPSIS (115; 4.8%) research, simultaneously. The major hot topics that utilized AHP and will continue to be active include different applications of geographic information systems, risk modeling and supply chain management. While for TOPSIS, they are supply chain management and sustainability research. Overall, this analysis has shown increasing recognition of powerful of MCDA techniques to support strategic decisions. The efficacy of these methods in the previous context promotes their progress and advancements.

https://scholar.ptuk.edu.ps/bitstream/123456789/349/1/TOPSIS.pdf

A bibliometric-based survey on AHP and TOPSIS techniques

Soft computing techniques are becoming even more popular and particularly amenable to model the complex behaviors of most geotechnical engineering systems since they have demonstrated superior predictive capacity, compared to the traditional methods. This paper presents an overview of some soft computing techniques as well as their applications in underground excavations. A case study is adopted to compare the predictive performances of soft computing techniques including eXtreme Gradient Boosting (XGBoost), Multivariate Adaptive Regression Splines (MARS), Artificial Neural Networks (ANN), and Support Vector Machine (SVM) in estimating the maximum lateral wall deflection induced by braced excavation. This study also discusses the merits and the limitations of some soft computing techniques, compared with the conventional approaches available.

https://dr.ntu.edu.sg/bitstream/10356/146887/2/1-s2.0-S1674987119302361-main.pdf

State-of-the-art review of soft computing applications in underground excavations

Shallow ore deposits are mined by surface methods but a depth is reached in the case of most deposits after which underground methods are applied for the extraction of the remaining ore. The determination of this depth and its analysis is the subject of this paper. In order to determine transition depth from open-pit to underground mining on the basis of the allowable and economically feasible overall stripping ratios, an economic-mathematical equation is first introduced. Using the achieved equation and an analytical procedure on a particular twodimensional hypothetical tabulate deposit, an effective formula is then established. The formula introduced here, together with the procedure adopted, could be used in all similar mining situations by the mining design engineer.

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Economico-mathematical analysis of transition from open-pit to underground mining

During the recent decades, the design and construction of underground spaces into rock salt have been particularly regarded for storing petroleum fluids, natural gas, and compressed air energy, and also for disposing nuclear and chemical wastes. The rock salt hosting such spaces will be subjected to various types of monotonic/cyclic, short-term/long-term stresses during the construction and/or operation phases. On this basis, it is necessary to investigate the mechanical behavior of the rock salt under the effects of various monotonic short-term/long-term stresses. Out of the most important factors affecting the creep behavior of rock salt are the composition of minerals and size of the crystals comprising the rock salt, humidity, temperature, time, loading scheme, loading rate, strain rate, and loading period. In the present research work, a loading scheme and a loading period were considered. On this basis, in order to achieve a true understanding of the creep behavior of rock salt, it is necessary to determine the creeping coefficients via laboratory tests. Thus, twenty cylindrical (length to diameter ratio > 2) specimens of rock salt were prepared for conducting the creep tests. Two stepwise short-term creep tests (each at three stress levels, namely 4.4, 10.1, and 11.9 MPa, and 7.5, 12, and 17 MPa, respectively) and eighteen long-term creep tests (at six stress levels, namely 5.5, 7.5, 10, 12, 14, and 18 MPa) were conducted. Then, first, the creep coefficients were determined according to the Lubby 2 constitutive model. These coefficients were adjusted using the results of the creep tests. Afterwards, a creep experimental model was presented using linear and nonlinear regression of the creep test data. For validation of the results obtained, both the adjusted Lubby 2 constitutive model and the proposed experimental model were compared with the results obtained for the creep tests. Both models had fairly good agreements with the data for the creep tests at a determination factor of about 93%.

http://jme.shahroodut.ac.ir/article_1179_0fd35c96914a52676df152941d6e1a35.pdf

Presenting an experimental creep model for rock salt

Experimental and discrete element methods were used to investigate the effects of distance between two preexisting cracks, bridge area (The length of the bridge area) and its angularities on the shear behaviour of bridge area. A punchthrough shear test was used to model the gypsum (concrete like) cracks under shear loading. Gypsum samples (concrete like) with dimension of 120 mm × 120 mm × 50 mm were prepared in the laboratory. Within the specimen model and near its four corners, four vertical notches were provided. Three different configuration systems were prepared for notches; i.e., paralell and in plane, inside echelon and outside echelon configuration systems, respectively. In these configurations, the length of cracks were taken as 2 cm, 4 cm and 6 cm based on the cracks configuration systems. Then, 9 specimens with different lengths of the bridge area and bridge area angles were prepared. Assuming a plane strain condition, special rectangular models were prepared with dimensions of 100 mm × 100 mm. similar to those for cracks configuration systems in the experimental tests i.e., 9 models with different lengths of the bridge area and bridge area angularities were prepared. The axial load was applied to the punch through the central portion of the model. This testing showed that the failure process was mostly governed by the lengths of the bridge area and bridge area angularities. The shear strengths of the specimens were related to the fracture pattern and failure mechanism of the discontinuities. It was shown that the shear behaviour of discontinuities is related to the number of the induced tensile cracks which are increased by increasing the lengths of the bridge area. The strength of samples decreases by increasing the crack length. Also, the outside echelon crack configuration system has the maximum value of strength while the inside echelon crack configuration system has the minimum value of specimen's tensile strength. The failure pattern and failure strength are similar in both methods i.e., the experimental testing and the numerical simulation methods.

Experimental and numerical investigation of the effect of bridge area and its angularities on the failure mechanism of non-persistent crack in concrete-like materials

Performance prediction of hard rock TBM using rock mass classification

This study provides an overview of the various issues influencing Out-of-Seam Dilution (OSD) in longwall mining method. The collected data has been statistically analyzed to examine the effect of the some factors causing OSD in front of the longwall mining face. Multiple parameter regression analysis was conducted on affecting parameters and the OSD. The SPSS (Statistics Package for Social Sciences) for Windows software package was used for the statistics analysis. Finally, a relationship between affecting parameters and the OSD is established by using the multiple parameter regression results. Results of this study have revealed that depth of seam, dip of seam, roof quality and variation in seam thickness are the most important influence factors for OSD. The proposed method may be utilized for the estimation of OSD for similar mines since, it was based on actual collected data from the coal mines.

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Kourosh Shahriar

Papers

Economico-mathematical analysis of transition from open-pit to underground mining

Presenting an experimental creep model for rock salt

Experimental and numerical investigation of the effect of bridge area and its angularities on the failure mechanism of non-persistent crack in concrete-like materials

Performance prediction of hard rock TBM using rock mass classification

A Method to Relate the Affecting Parameters and Estimate Dilution in Coal Mines