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The reliability of disc cutters has a significant influence on the safety and working efficiency of tunnel boring machines (TBMs). To investigate the reliability of disc cutters under different geological and operational conditions, we conducted a series of novel rolling cutting tests on intact and jointed sandstone blocks using different dip angles and interlayers. Different normal forces and rotational speeds of the cutterhead were also applied during the experiment. A novel reliability estimation method, based on a logistic regression model, was then proposed, and the influence of dip angle, strata, normal force, and rotational speed on the reliability of the disc cutter were analyzed. The reliability estimation method consisted of data acquisition regarding the normal force and cutter wear, feature extraction using wavelet packet transform and correlation analysis, and the estimation of the logistic regression model. To obtain the spectrum and normalized wavelet energy for each frequency band, we decomposed the time domain of the normal force by the wavelet packet transform. A correlation analysis was employed to determine the feature frequency bands that were sensitive to wear loss. On the basis of salient feature parameters and wear loss, the logistic regression model was established to evaluate the reliability of disc cutters. The analytical results indicated that the optimal dip angle for rock cutting was 30°. In the presence of mixed-face and single ground, the reliability of disc cutters was primarily affected by the difficulty of TBM excavation and wear loss, respectively. An increase in normal force and rotational speed aggravated wear on the cutter, thus reducing reliability. Furthermore, compared with Rabinowicz’s formula, the proposed method considers various geological and operational conditions, making the proposed method more applicable to estimate the reliability of disc cutters.

This paper presents a numerical investigation of hydraulic fracturing in oil sands during cold water injection by considering the aspects of both geomechanics and reservoir fluid flow. According to previous studies, the low shear strengths of unconsolidated or weakly consolidated sandstone reservoirs significantly influence the hydraulic fracturing process. Therefore, classical hydraulic fracture models cannot simulate the fracturing process in weak sandstone reservoirs. In the current numerical models, the direction of a tensile fracture is predetermined based on in situ stress conditions. Additionally, the potential transformation of a shear fracture into a tensile fracture and the potential reorientation of a tensile fracture owing to shear banding at the fracture tip have not yet been addressed in the literature. In this study, a smeared fracture technique is employed to simulate tensile and shear fractures in oil sands. The model used combines many important fracture features, which include the matrix flow, poroelasticity and plasticity modeling, saturation-dependent permeability, gradual degradation of the oil sands as a result of dilative shear deformation, and the tensile fracturing and shear failure that occur with the simultaneous enhancement of permeability. Furthermore, sensitivity analyses are also performed with respect to the reservoir and geomechanical parameters, including the apparent tensile strength and cohesion of the oil sands, magnitude of the minimum and maximum principal stress, absolute permeability and elastic modulus of the oil sands and ramp-up time. All these analyses are performed to clarify the influences of these parameters on the fracturing response of the oil sands.

Underground natural gas storage (UNGS) is an important part of the natural gas supply system to ensure a balanced energy supply. The surface system, as an important part of the gas storage, undertakes the functions of gas injection and gas production of the gas storage, and its investment economy is of vital importance. In fact, the UNGS surface pipeline network has two-way injection and production characteristics, which is different from the one-way production characteristics of conventional oil&gas gathering and transportation systems. This paper takes the minimum investment of the pipeline network as the objective function, considers the gas injection and gas withdrawal flow conditions and esablishes a mixed integer non-linear programming model (MINLP) for the surface pipeline network of the UNGS to optimize its pipeline layout and diameter parameters. Constraints including the well affiliation, the number of stations, the gathering radius, the processing capacity and the flow/pressure equilibrium equations, are also taken into consideration. Taking an UNGS in China as an example, the results of the optimal structure and diameter of the pipeline network, as well as the pipe flow, node pressure, and maximum/minimum flowrate during gas injection and gas withdrawal are obtained. Finally, the effects of constraints such as processing capacity and radius on the structure layout and investment of the UNGS are analyzed, verifying the reliability and effectiveness of the model.

A systematic model development for oil flow in quasi-3D (1D + 2D) is presented. Our approach provides a unified modeling scheme. Besides, additional terms are obtained, which allows for tubing area variation along the flow direction. The area variation can be modeled as analytic function or random fluctuation, as it could be the result of deposits or tubing internal surface roughness. The proposed approach can be used to obtain analytic solutions which provide physical insight into the phenomena under scrutiny, including the validation of software tools, sensor development and sensor placement. One starts from conservation laws as given by kinetic theory and applies the transverse averaging technique (TAT) to extract the one-dimensional approximation in formal grounds. To demonstrate its application, the steady-state Ramey's model, the Hasan's transient model and a simple two-phase model are generated from the obtained equations., Comment: 19 pages, 3 figures

The increasing demand for resources and depletion of near ground mineral resources caused deeper mining operations under high-stress rock mass conditions. As a result of this, strain burst, which is the sudden release of stored strain energy in the surrounding rock mass, has become more prevalent and created a considerable threat to workers and construction equipment. It is, therefore, imperative to understand how strain burst mechanism and stored excess strain energy are affected due to the high confinement in deep underground conditions. For this purpose, post-peak energy distributions for brittle rocks were investigated using a newly developed energy calculation method associated with acoustic emission (AE). A series of quasi-static uniaxial and triaxial compression tests controlled by the circumferential expansion was conducted. Snap-back behaviour known as Class-II behaviour associated with energy evolution and the material response under self-sustaining failure were analysed on granites under a wide range of confining pressures (0–60 MPa). The experimental results underline that the energy evolution characteristics are strongly linked to confinement. Stored elastic strain energy ( d U E ), energy consumed by dominating cohesion weakening ( d Φ C W ) and energy dissipated during mobilisation of frictional failure ( d Φ F M ) showed a rising trend as increasing the confining pressure. An intrinsic ejection velocity was proposed to express the propensity of strain burst that was purely determined by the excess strain energy released from Class II rock.

This paper focuses on the presence of nodules of insoluble materials within salt specimens, and their effect on the volumetric strain measurements and the dilatancy phenomenon. We analyzed experimental results of over 120 conventional triaxial compression tests, and found that in 20% of the cases, the volumetric strain measurements were atypical. We also noted that the natural variability of the specimens can lead to a non-negligible data scattering in the volumetric strain measurements when different specimens are subjected to the same test. This is expected given the small magnitude of those strains, but it occasionally implies that the corresponding specimens are not representative of the volumetric behavior of the studied rock. In order to understand these results, we numerically investigated salt specimens modeled as halite matrices with inclusions of impurities. Simulations of triaxial compression tests on these structures proved that such heterogeneities can induce dilatancy, and their presence can lead to the appearance of tensile zones which is physically translated into a micro-cracking activity. The modeling approach is validated as the patterns displayed in the numerical results are identical to that in the laboratory. It was then employed to explain the observed irregularities in experimental results. We studied the natural variability effect as well and proposed a methodology to overcome the issue of specimen representativity from both deviatoric and volumetric perspectives.

Brittleness is an important parameter controlling the mechanical behavior and failure characteristics of rocks under loading and unloading conditions, such as fracability, cutability, drillability and rockburst proneness. As such, it is of high practical value to correctly evaluate rock brittleness. However, the definition and measurement method of rock brittleness have been very diverse and not yet been standardized. In this paper, the definitions of rock brittleness are firstly reviewed, and several representative definitions of rock brittleness are identified and briefly discussed. The development and role of rock brittleness in different fields of rock engineering are also studied. Eighty brittleness indices publicly available in rock mechanics literature are compiled, and the measurement method, applicability and limitations of some indices are discussed. The results show that (1) the large number of brittleness indices and brittleness definitions is attributed to the different foci on the rock behavior when it breaks; (2) indices developed in one field usually are not directly applicable to other fields; and (3) the term “brittleness” is sometimes misused, and many empirically-obtained brittleness indices, which lack theoretical basis, fail to truly reflect rock brittleness. On the basis of this review, three measurement methods are identified, i.e. (1) elastic deformation before fracture, (2) shape of post-peak stress–strain curves, and (3) methods based on fracture mechanics theory, which have the potential to be further refined and unified to become the standard measurement methods of rock brittleness. It is highly beneficial for the rock mechanics community to develop a robust definition of rock brittleness. This study will undoubtedly provide a comprehensive timely reference for selecting an appropriate brittleness index for their applications, and will also pave the way for the development of a standard definition and measurement method of rock brittleness in the long term.

Micaceous soil is a problematic soil due to its low strength and poor ductility. In this context, the performances of micaceous soils were improved by applying a combination of granulated blast furnace slag, fiber and polymer additive. The dosages examined included 0%–30% mica, 3%–15% slag and 0.25%–1.25% fiber by weight, and 0.1–0.5 g/L polymer additive. Most of the combinations were found to increase the material strength and ductility, yet to be optimized. To refine the dosage, response surface method was used to conduct experimental design and develop predictive models for material strength. The developed models formulate the material strength as a nonlinear function of dosages and, by interrogating it, can optimize additive contents in terms of target requirements. The models were verified through trials and can be used to determine dosages to upscale micaceous soils to field conditions.

Sand production is, a challenging issue in petroleum industry, mainly associated with weak unconsolidated formations. A novel testing procedure and a new apparatus were developed to conduct an integrated experiment of diagenesis, perforation and sand production on a single large cylindrical artificial sandstone specimen, where solid and fluid pressures can be independently controlled such that realistic reservoir historical conditions can be well simulated in the laboratory. Fluid injection can be performed in both radial and vertical directions, where both single- and two-phase flows can be implemented for study of sand production behaviors at different reservoir's maturity stages. The equipment consists of an intensive instrumentation system to monitor pressures, displacements and material states continuously. The produced sand particles were filtered and monitored in real-time for the study of time-dependent phenomena. The experimental results showed similar patterns to that observed in the field and provided valuable insight for the development of prediction methods for sand production of similar materials.

Different artificial intelligence (AI) methods have been applied to various aspects of rock mechanics, but the fact that none of these methods have been used as a standard implies that doubt as to their generality and validity still exists. For this, a literature review of application of AI to the field of rock mechanics is presented. Comprehensive studies of the researches published in the top journals relative to the fields of rock mechanics, computer applications in engineering, and the textbooks were conducted. The performances of the AI methods that have been used in rock mechanics applications were evaluated. The literature review shows that AI methods have successfully been used to solve various problems in the rock mechanics field and they performed better than the traditional empirical, mathematical or statistical methods. However, their practical applicability is still an issue of concern as many of the existing AI models require some level of expertise before they can be used, because they are not in the form of tractable mathematical equations. Thus some advanced AI methods are still yet to be explored. The limited availability of dataset for the AI simulations is also identified as a major problem. The solutions to the identified problems and the possible future research focus were proposed in the study subsequently.

To understand the evolution of stress-induced elastic wave anisotropy, three triaxial experiments were performed on sandstone specimens with bedding orientations parallel, perpendicular, and oblique to the maximum principal stress. P-wave velocities along 64 different directions on each specimen were monitored frequently to understand the anisotropy change at various stress levels by fitting Thomsen's anisotropy equation. The results show that the elastic wave anisotropy is very sensitive to mechanical loading. Under hydrostatic loading, the magnitude of anisotropy is reduced in all three specimens. However, under deviatoric stress loading, the evolution of anisotropic characteristics (magnitude and orientation of the symmetry axis) is bedding orientation dependent. Anisotropy reversal occurs in specimens with bedding normal/oblique to the maximum principal stress. P-wave anisotropy e ′ is linearly related to volumetric strain Sv and dilatancy, indicating that stress-induced redistribution of microcracks has a significant effect on P-wave velocity anisotropy. The closure of initial cracks and pores aligned in the bedding direction contributes to the decrease of the anisotropy. However, opening of new cracks, aligned in the maximum principal direction, accounts for the increase of the anisotropy. The experimental results provide some insights into the microstructural behavior under loading and provide an experimental basis for seismic data interpretation and parameter selection in engineering applications.

Slope failures lead to catastrophic consequences in numerous countries and thus the stability assessment for slopes is of high interest in geotechnical and geological engineering researches. A hybrid stacking ensemble approach is proposed in this study for enhancing the prediction of slope stability. In the hybrid stacking ensemble approach, we used an artificial bee colony (ABC) algorithm to find out the best combination of base classifiers (level 0) and determined a suitable meta-classifier (level 1) from a pool of 11 individual optimized machine learning (OML) algorithms. Finite element analysis (FEA) was conducted in order to form the synthetic database for the training stage (150 cases) of the proposed model while 107 real field slope cases were used for the testing stage. The results by the hybrid stacking ensemble approach were then compared with that obtained by the 11 individual OML methods using confusion matrix, F1-score, and area under the curve, i.e. AUC-score. The comparisons showed that a significant improvement in the prediction ability of slope stability has been achieved by the hybrid stacking ensemble (AUC = 90.4%), which is 7% higher than the best of the 11 individual OML methods (AUC = 82.9%). Then, a further comparison was undertaken between the hybrid stacking ensemble method and basic ensemble classifier on slope stability prediction. The results showed a prominent performance of the hybrid stacking ensemble method over the basic ensemble method. Finally, the importance of the variables for slope stability was studied using linear vector quantization (LVQ) method.

Previous studies show that infrared radiation temperature (IRT) abnormalities are always accompanied by the crack development in rocks under external loads. In this context, experiments were conducted on preflawed sandstone to investigate the infrared radiation characteristics during failure process. Two indicators were defined herein, i.e. coefficient of variation of IRT (CVIRT) and skewness of IRT (SIRT). The regression analysis shows that the IRT probability distributions during loading process fit the Gaussian model. The variations in the CVIRT are characterized by four stages: primary stage, steady stage, accelerating stage and post-peak stage. Besides, the variations in the SIRT are divided into three stages: primary stage, steady stage and failure and post-peak stage. The precursor point for preflawed rock failure is identified based on the CVIRT–time curve, with average precursor point of 83% of the peak stress. Compared with other IRT indicators, the proposed two IRT indicators have higher sensitivity to IRT abnormalities during failure process. Furthermore, the connection between the IRT indicators and the rock fracturing was investigated to interpret the IRT indicator abnormalities. Based on the Verhulst inverse function, a new quantitative model was presented to describe the primary stage, steady stage and accelerating stage of the CVIRT–time curve. The results obtained in this study can provide early-warning information for rock failure prediction.

The expected growth of urban areas requires the construction of underground infrastructures, especially for improving transportation and mobility. These new infrastructures are commonly constructed below the water table because they must be deeper than previous underground structures. In addition, many urban areas are located near surface water bodies (i.e., seas, rivers and/or lakes) that induce a shallow water table. The “cut and cover” method combined with dewatering wells is a frequently used procedure under these conditions for the construction of underground infrastructures. The main concerns of this procedure are related to the stability of the excavation bottom, the behavior of the retaining walls and/or the impacts induced by the dewatering actions. These issues must be evaluated, and new solutions must be proposed to improve its weak points. This paper compiles the main publications focused on the construction of underground infrastructures below the water table and in urban areas by using the cut and cover method combined with pumping. This review reveals that, despite many published studies, more research is needed to address some relevant issues such as: (1) the mitigation of dewatering impacts by using artificial recharge, (2) the adaptation of methods for characterizing retaining walls to be used under heterogeneous conditions, (3) the improvement of the prediction of surface settlements produced by pumping, and (4) the consideration of non-Darcy flows in the design of dewatering systems.

The 121 mining method of longwall mining first proposed in England has been widely used around the world. This method requires excavation of two mining roadways and reservation of one coal pillar to mine one working face. Due to considerable excavation of roadway, the mining roadway is generally destroyed during coal mining. The stress concentration in the coal pillar can cause large deformation of surrounding rocks, rockbursts and other disasters, and subsequently a large volume of coal pillar resources will be wasted. To improve the coal recovery rate and reduce excavation of the mining roadway, the 111 mining method of longwall mining was proposed in the former Soviet Union based on the 121 mining method. The 111 mining method requires excavation of one mining roadway and setting one filling body to replace the coal pillar while maintaining another mining roadway to mine one working face. However, because the stress transfer structure of roadway and working face roof has not changed, the problem of stress concentration in the surrounding rocks of roadway has not been well solved. To solve the above problems, the conventional concept utilizing high-strength support to resist the mining pressure for the 121 and 111 mining methods should be updated. The idea is to utilize mining pressure and expansion characteristics of the collapsed rock mass in the goaf to automatically form roadways, avoiding roadway excavation and waste of coal pillar. Based on the basic principles of mining rock mechanics, the “equilibrium mining” theory and the “short cantilever beam” mechanical model are proposed. Key technologies, such as roof directional presplitting technology, negative Poisson's ratio (NPR) high-prestress constant-resistance support technology, and gangue blocking support technology, are developed following the “equilibrium mining” theory. Accordingly, the 110 and N00 mining methods of an automatically formed roadway (AFR) by roof cutting and pressure releasing without pillars are proposed. The mining methods have been applied to a large number of coal mines with different overburdens, coal seam thicknesses, roof types and gases in China, realizing the integrated mode of coal mining and roadway retaining. On this basis, in view of the complex geological conditions and intelligent mining demand of coal mines, an intelligent and unmanned development direction of the “equilibrium mining” method is prospected.

Different techniques have been proposed to increase the bearing capacity of open-ended piles. Welding helices to the shaft and tapering the pile shaft could be used simultaneously to enhance the static and dynamic behaviors of these piles. This paper subjects the bearing capacity, stiffness, frictional behavior, and material efficiency of the tapered helical piles to scrutiny. Tapered helical piles are introduced herein as an alternative option to improve the material efficiency of hollow piles. Based on the Taguchi method, a series of experiments was designed and conducted. The axial responses of tapered helical piles are also investigated using finite element analyses. The results derived from load–displacement curves and strain gages are used to characterize the axial compression responses of tapered helical piles. The effects of tapered angle, helices diameter and helices distance are examined using dimensionless parameters, and the degree of contribution of these factors is calculated on each of the enumerated variables individually. Experimental results show that the shaft friction resistance of tapered helical piles increases continuously with the pile head settlement. Furthermore, the effect of tapered wall on the shaft friction resistance is more tangible at low stress levels. The results showed that the relative material efficiency factor of the optimum pile could be 2.5 times that of unoptimized pile with a similar quantity of material.

Evaluation of blocky or layered rock slopes against toppling failures has remained of great concern for engineers in various rock mechanics projects. Several step-by-step analytical solutions have been developed for analyzing these types of slope failures. However, manual application of these analytical solutions for real case studies can be time-consuming, complicated, and in certain cases even impossible. This study will first examine existing methods for toppling failure analyses that are reviewed, modified and generalized to consider the effects of a wide range of external and dead loads on slope stability. Next, based on the generalized presented formulae, a Windows form computer code is programmed using Visual C# for analysis of common types of toppling failures. Input parameters, including slope geometry, joint sets parameters, rock and soil properties, ground water level, dynamic loads, support anchor loads as well as magnitudes and forms of external forces, are first loaded into the code. The input data are then saved and used to graphically draw the slope model. This is followed by automatic identification of the toppling failure mode and a deterministic analysis of the slope stability against this failure mode. The results are presented using a graphical approach. The developed code allows probabilistic introduction of the input parameters via probability distribution functions (PDFs) and thus a probabilistic analysis of the toppling failure modes using Monte-Carlo simulation technique. This allows calculation of the probability of slope failure. Finally, several published case studies and typical examples are analyzed with the developed code. The outcomes are compared with those of the main references to assess the performance and robustness of the developed computer code. The comparisons demonstrate good agreement between the results.

It is generally accepted that the uniaxial compressive strength (UCS) and P-wave velocity of rocks tend to decrease simultaneously with increasing temperature. However, based on a great number of statistical data and systematic analysis of the microstructure variation of rocks with temperature rising and corresponding propagation mechanism of elastic wave, the results show that (1) There are three different trends for the changes of UCS and P-wave velocity of sandstone when heated from room temperature (20 °C or 25 °C) to 800 °C: (i) Both the UCS and P-wave velocity decrease simultaneously; (ii) The UCS increases initially and then decreases, while the P-wave velocity decreases continuously; and (iii) The UCS increases initially and then fluctuates, while the P-wave velocity continuously decreases. (2) The UCS changes at room temperature–400 °C, 400 °C–600 °C, and 600 °C–800 °C are mainly attributed to the discrepancy of microstructure characteristics and quartz content, the transformation plasticity of clay minerals, and the balance between the thermal cementation and thermal damage, respectively. (3) The inconsistency in the trends of UCS and P-wave velocity changes is caused by the change of quartz content, phase transition of water and certain minerals.

Asphaltene adsorption on reservoir rock minerals causes wettability alteration and pore plugging which subsequently reduces crude oil production. Also, it has a negative effect on the efficiency of production and enhanced oil recovery operations. In this study, the adsorption of extracted asphaltenes of two samples of Iranian oil fields on dolomite, quartz, and magnetite was investigated in two-and three-phase systems in both static and dynamic flow modes. Mineral adsorbents were analyzed by Brunauer–Emmett–Teller and X-ray fluorescence methods. Also, several laboratory tests including elemental analysis, field emission scanning electron microscopy, and Fourier transform infrared spectroscopy were carried out to characterize asphaltenes. The results showed that in addition to the effect of known parameters such as asphaltenes concentration and specific surface area of the solid phase, the water phase also affects the amount of asphaltenes adsorption. The adsorption amount of asphaltenes increases with increasing the specific surface area of adsorbent (decreasing particle size) and increasing the initial concentration of asphaltenes, and decreases with the addition of water to the two-phase system. The static adsorption amount of asphaltenes in a two-phase system can be up to 90% higher than the adsorption amount in a three-phase system. Doubling the fluid flow rate in dynamic adsorption significantly (by about 20%) reduces the asphaltenes adsorption, which could be a sign of physical adsorption of asphaltenes on adsorbents. The structure and elemental composition of asphaltenes also have a significant effect on asphaltenes adsorption. The asphaltene sample, which had a more aromatic nature and high nitrogen content, had higher adsorption on reservoir rock minerals. Finally, fitting the adsorption equilibrium models with experimental data reveals that the adsorption isotherm model depends on the type and particle size of the adsorbents and the concentration and type of asphaltenes. Cited as : Mohammadi, M.R., Bahmaninia, H., Ansari, S., Hemmati-Sarapardeh, A., Norouzi-Apourvari, S., Schaffie, M., Ranjbar, M. Evaluation of asphaltene adsorption on minerals of dolomite and sandstone formations in two and three-phase systems. Advances in Geo-Energy Research, 2021, 5(1), 39-52, doi: 10.46690/ager.2021.01.05

Formation damage caused by well drilling, completion, oil testing, oil recovery, and stimulation seriously affects oil and gas production, the evaluation of which plays an important role in the process of oilfield development. Thus, it is necessary to study formation damage mechanism from micro scale. In this study, two sets of displacement experiments were conducted using two sandstone samples and two chemical reagents. Each set was divided into three processes: first formation water injection, reverse chemical reagents injection and second formation water injection. According to the results of displacement experiments, the permeability changes of two sandstone samples were analyzed and the formation damage rates of different experimental processes were calculated respectively. In addition, we analyzed the formation damage of the two samples from the macroscopic aspect according to the changes of inlet pressure curves. We compared the pore structure changes of sandstone samples at different experiment processes by computed tomography (CT) images, and found the particle migration phenomenon. Based on the core sensitive regions observed by CT images, the pore network models of the sensitive regions were extracted to quantitatively characterize the change of pore structure parameters (pore radius, throat radius, coordination number and tortuosity). Finally, we designed a two-dimensional microscopic seepage channel model according to the real core structure. The flow rule of solid particles in fluid was simulated by finite element method, and the reason of reservoir clogging was analyzed. Through this study, we found that the injection of chemical reagents increased the inlet pressure and led to the decrease of core permeabilities. There was a negative correlation between the export rate of particle migration and matrix deformation degree. Cited as : Wang, Z., Li, H., Lan, X., Wang, K., Yang, Y., Lisitsa, V. Formation damage mechanism of a sandstone reservoir based on micro-computed tomography. Advances in Geo-Energy Research, 2021, 5(1): 25-38, doi: 10.46690/ager.2021.01.04

In the article by N.A. Sycheva and L.M. Bogomolov, the authors proposed to combine the interrelated data on the stress drop in the earthquake sources, ∆σ, and reduced seismic energy, ePR, to analyze the dependence of these parameters on earthquake scale along with expansion of the measurement statistics (assessments). The dependence of these parameters of a source on the seismic moment or on the earthquake magnitude within 2.2 ≤ М ≤ 4.0 magnitude range has been determined using the example of the Northern Tien Shan (Bishkek geodynamic polygon with the KNET network). The author of the letter to the editor notes the article conclusions to be limited, because such relationship is only manifested within the more or less narrow range of the magnitudes. Attention is also drawn to the semantic difference between the ∆σ and ePR parameters. It is the reduced seismic energy that reflects the mean strain in the source area, and its appliance to the analysis of scale dependences of earthquake sources is more informative.

This article describes the process and results of the development and testing of a cost-effective, portable, safe to move by air geophysical pulse voltage generator for seismic exploration of the subsurface. The generator is based on high-speed power electronic keys of a new generation consisting of an insulated gate bipolar transistor or a field-effect transistor based on silicon carbide, a compact power converter of alternating voltage from an autonomous generator or electric network to direct voltage using pulse-width modulation and current or voltage stabilization depending on the mode set by a researcher. Field tests were conducted to confirm the suitability of the developed design of the generator and the correctness of the chosen parameters of its elements. To this end, a detailed analysis of the effect of the developed geophysical generator on the parameters of the geoenvironment was carried out.

The work presents the results of a retrospective analysis of the seismicity of Sakhalin using the LURR method of mid-term earthquake prediction for 1997–2019. All previously performed computations are reduced to a single database of seismological data (catalogue) of the Sakhalin Branch of the Federal Research Center “United Geophysical Survey of RAS”. Similar to previous studies, the Sakhalin territory was scanned by applying computational areas in the form of circles with a radius of one degree; however, the resolution was increased. The entire territory was covered by such zones with a step of 0.5 degrees in latitude and longitude, with the grid being detailed down to 0.1 degrees in three most dangerous seismogenerating zones. As a result, the number of computational samples was increased, which allowed the omission of anomalies in the LURR parameter during computations to be avoided. Due to a reasonable binding of the lower bound of the magnitude for predicted events to the upper bound of the magnitude range of the computational sample (M = 5), the number of objects for the retrospective forecast was increased by 3 times for the study period. 323 computational samples (119 of which are basic and 204 ones are detailed) were processed on the territory of the island. 15 alarm periods were obtained, which geographically represent all zones of moderate and strong earthquake generation on Sakhalin Island. As a result, 17 out of 19 earthquakes with M ≥ 5 occurred in the areas with anomalies during the alarm periods not exceeding three years. Out of 15 periods, 4 turned to be false. Thus, 75 % of the alarms predicted 89 % of the earthquakes.

Underground research laboratory (URL) plays an important role in safe disposal of high-level radioactive waste (HLW). At present, the Xinchang site, located in Gansu Province of China, has been selected as the final site for China’s first URL, named Beishan URL. For this, a preliminary design of the Beishan URL has been proposed, including one spiral ramp, three shafts and two experimental levels. With advantages of fast advancing and limited disturbance to surrounding rock mass, the tunnel boring machine (TBM) method could be one of the excavation methods considered for the URL ramp. This paper introduces the feasibility study on using TBM to excavation of the Beishan URL ramp. The technical challenges for using TBM in Beishan URL are identified on the base of geological condition and specific layout of the spiral ramp. Then, the technical feasibility study on the specific issues, i.e. extremely hard rock mass, high abrasiveness, TBM operation, muck transportation, water drainage and material transportation, is investigated. This study demonstrates that TBM technology is a feasible method for the Beishan URL excavation. The results can also provide a reference for the design and construction of HLW disposal engineering in similar geological conditions. © 2020 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ).

Lost circulation is the most common problem encountered while drilling oil wells. Occurrence of such a problem can cause a lot of time and cost wastes. In order to drill oil wells, a fast and profitable way is necessary to predict and solve lost circulation problem. Expert system is a method used lately for problems that deal with uncertainty. In this paper, three approaches are carried out for prediction of lost circulation problem. These approaches include design of experiments (DOE), data mining, and adaptive neuro-fuzzy inference system (ANFIS). Data of 61 wells of Maroon oilfield are selected and sorted as the feed of the systems. Seventeen variables are used as inputs of the approaches and one variable is used as the output. First, DOE is conducted to observe the effects of variables. Plackett-Burman method is used to determine the effects of variables on lost circulation. After that, data mining is conducted to predict the amount of lost circulation. The class of regression is used to determine a function to model the data and the error of the model. Then, ANFIS is applied to predict the amount of lost circulation. The chosen data are used in order to train, test, and control the ANFIS. Furthermore, subtractive clustering is used to train the fuzzy inference system (FIS) of the model. The performance of the ANFIS model is assessed through the root mean squared error (RMSE). The results suggest that ANFIS method can be successfully applied to establish lost circulation prediction model. In addition, results of ANFIS and data mining are investigated through their prediction performances. The comparison of both methods reveals that ANFIS error is much lower than data mining.

This article presents a case study concerning a seismic characterization project. Full-wave sonic logging was used to characterize the shallow compressional wave and shear wave velocity profiles in the site. Anomalous values of the Poisson’s ratio derived from the velocity profiles suggested that the boreholes might have traversed slow formations (i.e. with shear wave velocity smaller than the borehole fluid compressional wave velocity or “mud-wave speed”) and that conventional processing of the sonic logs might have misinterpreted the direct arrivals of fluid acoustic waves as arrivals caused by shear wave propagation in the rock. Consequently, the shear wave velocity profiles provided by the contractor were considered to be unreliable by the project team. To address these problems, a non-conventional determination of the shear wave velocity was implemented, based on the relationship between the Poisson’s ratio of the rock formation and the shape of the first train of sonic waves which arrived to the receivers in the sonic probe. The relationship was determined based on several hundreds of finite element simulations of the acoustic wave propagation in boreholes with the same diameter as used in the perforations. The present article describes how this non-conventional approach was developed and implemented to obtain the shear wave velocity profiles from the raw sonic logs. The approach allows an extension of the range of applicability of full-wave sonic logging to determination of shear wave velocity profiles in formations with low compressional wave velocities. The method could be used to obtain shear wave velocity profiles where compressional wave velocity is as low as slightly larger than the mud-wave speed. A sample sonic log in Log ASCII Standard (LAS) format is provided as supplementary material to this paper via Mendeley Data, together with the FORTRAN source code used to process the log following the approach described in this study.

Crack dynamic propagation and arrest behaviors have received extensive attention over the years. However, there still remain many questions, e.g. under what conditions will a running crack come to arrest? In this paper, drop weight impact (DWI) tests were conducted to investigate crack arrest mechanism using single cleavage triangle (SCT) rock specimens. Green sandstone was selected to prepare the SCT specimens. Dynamic stress intensity factors (DSIFs) were calculated by ABAQUS code, and the critical DSIFs were determined by crack propagation speeds and fracture time measured by crack propagation gauges (CPGs). The test results show that the critical DSIF at propagation decreases with crack propagation speed. Numerical simulation for SCT specimens under different loading waves was performed using AUTODYN code. The reflected compressive wave from the incident and transmitted plates can induce crack arrests during propagation, and the number of arrest times increases with the wave length. In order to eliminate the effect of the incident and transmitted plates, models consisting of only one SCT specimen without incident and transmitted plates were established, and the same trapezoid-shaped loading wave was applied to the SCT specimen. The results show that for the SCT specimen with transmitted boundary (analogous to an infinite plate), the trapezoid-shaped loading wave cannot induce crack arrest anymore. The numerical results can well describe the occurrence of crack arrest in the experiments.

With rapid development of infrastructures like tunnels and open excavations in Shanghai, investigations on deeper soils have become critically important. Most of the existing laboratory works were focused on the clayey strata up to Layer 6 in Shanghai, i.e. at depth of up to 40 m. In this paper, Layers 7, 9, and 11, which were mostly formed of sandy soils at depth of up to 150 m, were experimentally investigated with respect to physico-mechanical behaviors. The stress–strain behaviors were analyzed by the consolidated drained/undrained (CD/CU) triaxial tests under monotonic loading. One-dimensional (1D) oedometer tests were performed to investigate the consolidation properties of the sandy soils. Specimens were prepared at three different relative densities for each layer. Also, the micro-images and particle size analyzers were used to analyze the shape and size of the sand grains. The influences of grain size, density, and angularity on the stress–strain behaviors and compressibility were also studied. Compared to the other layers, Layer 11 had the smallest mean grain size (D50), highest compressibility, and lowest shear strength. In contrast, Layer 9 had the largest mean grain size, lowest compressibility, and highest shear strength. Layer 7 was of intermediate mean grain size, exhibiting more compressibility and less shear strength than that of Layer 9. Also, the critical state parameters and maximum dilatancy rate of different layers were discussed.

As the price of oil decreases, it is becoming increasingly important for oil companies to operate in the most cost-effective manner. This problem is especially apparent in Western Canada, where most oil production is dependent on costly enhanced oil recovery (EOR) techniques such as steam-assisted gravity drainage (SAGD). Therefore, the goal of this study is to create an artificial neural network (ANN) that is capable of accurately predicting the ultimate recovery factor of oil reservoirs by steam-assisted gravity drainage (SAGD). The developed ANN model featured over 250 unique entries for oil viscosity, steam injection rate, horizontal permeability, permeability ratio, porosity, reservoir thickness, and steam injection pressure collected from literature. The collected data set was entered through a feed-forward back-propagation neural network to train, validate, and test the model to predict the recovery factor of SAGD method as accurate as possible. Results from this study revealed that the neural network was able to accurately predict recovery factors of selected projects with less than 10% error. When the neural network was exposed to a new simulation data set of 64 points, the predictions were found to have an accuracy of 82% as measured by linear regression. Finally, the feasibility of ANN to predict the recovery performance of one of the most complicated enhanced heavy oil recovery techniques with reasonable accuracy was confirmed.

Acidizing treatment is considered as a significant process in the oil well stimulations to form wormholes in carbonate formation in order to enhance the reservoir fluid production. Obtaining the number of pore volumes to breakthrough is an important objective in matrix acidizing, for it contributes to determining the wormhole characteristics such as type, shape, and size. Finding this number in experimental works requires a considerable amount of time, energy and cost. Therefore, this study aimed to establish an analytical method in which a reasonable result is achieved for the number of pore volumes to breakthrough. This purpose is accomplished by solely implementing acid and formation properties without performing any experimental works. The process of wormhole creation is done through developing a numerical model by utilizing the conservation of mass law method in which the carbonate core is considered as a closed system and the overall mass in the system as constant during the acid injection process. Furthermore, a constant number is added to the mathematical part of the model in order to eliminate the dimensionless Damkohler number which is supposed to be calculated experimentally. The results of the numerical procedure of the model are further compared to four other experimental works, which led to calculating the average accuracy of this model that is shown to be 95.98%. This study puts forward a comprehensive numerical model to estimate the number of pore volumes to breakthrough with an acceptable accuracy rate merely through implementing known acid and core properties.

This study aims to examine the influence of pre-existing discontinuities on the strengths of four natural rocks of different origins. A series of unconfined compression tests was performed on specimens of two types of sandstones, argillite and basalt that contain open and filled cracks. It was found that the presence of cracks tends to decrease the overall strength for all studied rocks; however, the magnitude of strength reduction is related to the property of rock. The larger strength decrease was observed for the relatively harder argillite and basalt, compared to the softer sandstone. It was also found that the infill material could increase the strength of rock specimens, while the obtained strength depended on the characteristics of the fill material.

Underground structures are normally located in highly-confined and congested spaces, which may lead to severe gas explosion accidents, with significant human and economic losses. For accurately evaluating the consequences of these explosions, a variety of influencing factors need to be considered, including concentrations of gas mixtures, vent conditions, obstacles, and ignition features. Moreover, a good review on these influencing factors is important for a better understanding of explosion behavior, e.g., the deflagration to detonation phenomenon. In this study, some critical influencing factors for gas explosions in underground or confined spaces are investigated, and the effects of the factors on such gas explosions are examined. The results are discussed, along with findings from literature. The present study provides a reference for future studies on safety management and consequence mitigation for underground gas explosions.

In the quest for interpretable models, two versions of a neural network rule extraction algorithm were proposed and compared. The two algorithms are called the Piece-Wise Linear Artificial Neural Network (PWL-ANN) and enhanced Piece-Wise Linear Artificial Neural Network (enhanced PWL-ANN) algorithms. The PWL-ANN algorithm is a decomposition artificial neural network (ANN) rule extraction algorithm, and the enhanced PWL-ANN algorithm improves upon the PWL-ANN algorithm and extracts multiple linear regression equations from a trained ANN model by approximating the hidden sigmoid activation functions using N-piece linear equations. In doing so, the algorithm provides interpretable models from the originally trained opaque ANN models. A detailed application case study illustrates how the generated enhanced-PWL-ANN models can provide understandable IF-THEN rules about a problem domain. Comparison of the results generated by the two versions of the PWL-ANN algorithm showed that in comparison to the PWL-ANN models, the enhanced-PWL-ANN models support improved fidelities to the originally trained ANN models. The results also showed that more concise rule sets could be generated using the enhanced-PWL-ANN algorithm. If a more simplified set of rules is desired, the enhanced-PWL-ANN algorithm can be combined with the decision tree approach. Potential application of the algorithms to domains related to petroleum engineering can help enhance understanding of the problems.

Soft clays are usually classified according to their undrained shear strength, Su. Values of Su less than 12.5 kPa are associated with very soft clays. In addition to their low shear strength, soft clays exhibit high compressibility upon loading. Therefore, soft clays are considered to be problematic for foundation purposes. Geo-foam is an industrial material that is characterized by a very low unit weight (20 kg/m 3 on average) compared to that of the soil. The density of expanded polystyrene (EPS) ranges from 1.0% to 2.5%, which results in a compressive strength ranging between 70 kPa and 140 kPa and an elastic modulus ranging between 5 MPa and 12 MPa. EPS geo-foam blocks are used in a wide range of geotechnical applications as a lightweight fill material. The main objective of this study was to investigate the geotechnical properties of soft clays containing geo-foam beads and cement bypass dust (CBPD). We also investigated the viability of preparing low-strength excavatable fill mixtures. To study the effect of (geo-foam beads + CBPD) / soft clay on the fluid-state and hardened properties of new fill, we conducted experiments on two groups of mixtures (A&B). Each mixture contained different ratios of geo-foam beads and CBPD so that we could study the effect of the additive on the flow consistency, dry unit weight, unconfined compressive strength, and shear strength of the mixture. The test results showed that the unconfined compressive strength of the studied mixtures without geo-foam ranged from 271.8 kPa to 1405.14 kPa at CBPD concentrations between 3.88% and 18.63%. The cohesion values for the group containing geo-foam ranged from 50 kPa to 20 kPa at geo-foam percentages between 0.32% and 1.35%. The friction angle of the group containing geo-foam ranged from 10 kPa to 22 kPa at CBPD percentages between 0.32% and 1.35%. Cement bypass dust can be successfully used to process self-compacting, self-leveling, excavatable and flowable fill material.

Minimum miscibility pressure (MMP) is a key parameter in the successful design of miscible gases injection such as CO2 flooding for enhanced oil recovery process (EOR). MMP is generally determined through experimental tests such as slim tube and rising bubble apparatus (RBA). As these tests are time-consuming and their cost is very expensive, several correlations have been developed. However, and although the simplicity of these correlations, they suffer from inaccuracies and bad generalization due to the limitation of their ranges of application. This paper aims to establish a global model to predict MMP in both pure and impure CO2-crude oil in EOR process by combining support vector regression (SVR) with artificial bee colony (ABC). ABC is used to find best SVR hyper-parameters. 201 data collected from authenticated published literature and covering a wide range of variables are considered to develop SVR-ABC pure/impure CO2-crude oil MMP model with following inputs: reservoir temperature (TR), critical temperature of the injection gas (Tc), molecular weight of pentane plus fraction of crude oil (MWC5+) and the ratio of volatile components to intermediate components in crude oil ( x v o l / x i n t ). Statistical indicators and graphical error analyses show that SVR-ABC MMP model yields excellent results with a low mean absolute percentage error (3.24%) and root mean square error (0.79) and a high coefficient of determination (0.9868). Furthermore, the results reveal that SVR-ABC outperforms either ordinary SVR with trial and error approach or all existing methods considered in this work in the prediction of pure and impure CO2-crude oil MMP. Finally, the Leverage approach (Williams plot) is done to investigate the realm of prediction capability of the new model and to detect any probable erroneous data points.

The importance of soil water retention characteristics in modelling the hydro-mechanical response of unsaturated soils has been well recognised by many investigators in recent years. Determination of strain-dependent soil water retention curve (SWRC) is likely to be extraordinarily difficult. The first two authors have recently shown that SWRC can be computed from the gradation curve and the calculation result is consistent with the experimental results obtained from pressure plate tests. In this paper, based on a hypothesis related to change in the pore size distribution (POSD) due to volumetric strain of soil skeleton, a method to compute strain-dependent SWRC is presented. It is found that at initial degrees of saturation higher than 0.8, the influence of volumetric strain may be marginal whilst at initial degrees of saturation lower than 0.8, its influence is likely to be substantial. In all cases, the gradation curve of the soil affects the SWRC.

This study first reviews the numerical manifold method (NMM) which possesses some advantages over the traditional limit equilibrium methods (LEMs) in calculating the factors of safety (Fs) of the slopes. Then, with regard to a trial slip surface (TSS), associated stress fields reproduced by NMM as well as the enhanced limit equilibrium method are combined to compute Fs. In order to search for the potential critical slip surface (CSS), the MAX-MIN ant colony optimization algorithm (MMACOA), one of the best performing algorithms for some optimization problems, is adopted. Procedures to obtain Fs in conjunction with the potential CSS are described. Finally, the proposed numerical model and traditional methods are compared with stability analysis of three typical slopes. The numerical results show that Fs and CSSs of the slopes can be accurately calculated with the proposed model.

Fluid-flow measurements of petroleum can be performed using a variety of equipment such as orifice meters and wellhead chokes. It is useful to understand the relationship between flow rate through orifice meters (Qv) and the five fluid-flow influencing input variables: pressure (P), temperature (T), viscosity (μ), square root of differential pressure (ΔP^0.5), and oil specific gravity (SG). Here we evaluate these relationships using a range of machine-learning algorithms applied to orifice meter data from a pipeline flowing from the Cheshmeh Khosh Iranian oil field. Correlation coefficients indicate that (Qv) has weak to moderate positive correlations with T, P, and μ, a strong positive correlation with the ΔP^0.5, and a weak negative correlation with oil specific gravity. In order to predict the flow rate with reliable accuracy, five machine-learning algorithms are applied to a dataset of 1037 data records (830 used for algorithm training; 207 used for testing) with the full input variable values for the data set provided. The algorithms evaluated are: Adaptive Neuro Fuzzy Inference System (ANFIS), Least Squares Support Vector Machine (LSSVM), Radial Basis Function (RBF), Multilayer Perceptron (MLP), and Gene expression programming (GEP). The prediction performance analysis reveals that all of the applied methods provide predictions at acceptable levels of accuracy. The MLP algorithm achieves the most accurate predictions of orifice meter flow rates for the dataset studied. GEP and RBF also achieve high levels of accuracy. ANFIS and LSSVM perform less well, particularly in the lower flow rate range (i.e.

Oil viscosity is an important factor in every project of the petroleum industry. These processes can range from gas injection to oil reservoirs to comprehensive reservoir simulation studies. Different experimental approaches have been proposed for measuring oil viscosity. However, these methods are often time taking, cumbersome and at some physical conditions, impossible. Therefore, development of predictive models for estimating this parameter is crucial. In this study, three new machine learning based models are developed to estimate the oil viscosity. These approaches are genetic programing, k-nearest neighbor (KNN) and linear discriminant analysis. Oil gravity and temperature were the input parameters of the models. Various graphical and statistical error analyses were used to measure the performance of the developed models. Also, comparison study between the developed models and the well-known previously published models was conducted. Moreover, trend analysis was performed to compare the predictions of the models with the trend of experimental data. The results indicated that the developed models outperform all of the previously published models by showing negligible prediction errors. Among the developed models, the KNN model has the highest accuracy by showing an overall mean absolute error of 8.54%. The results show that the new developed models in this study can be potentially utilized in reservoir simulation packages of the petroleum industry. Cited as : Mahdiani, M.R., Khamehchi, E., Hajirezaie, S., Hemmati-Sarapardeh, A. Modeling viscosity of crude oil using k-nearest neighbor algorithm. Advances in Geo-Energy Research, 2020, 4(4): 435-447, doi: 10.46690/ager.2020.04.08

In-situ stresses are highly important for wellbore stability studies during drilling, completion and production. Different methods are available to estimate the horizontal stresses especially maximum horizontal stress. Typically, Circumferential Borehole Image Logs can be run to determine the direction and width of breakouts and then stresses at different depths based on the equation developed by Barton et al. (1988). This research focuses on image logs from Harvey-1 well located in the Southern Perth basin to compare the maximum horizontal stresses obtained by various methods. The magnitudes of stresses from the breakout width approach (Barton’s method) exhibit a considerable offset in comparison with elastic methods. Further investigations show that the likely reason for the offset relates to the fundamental assumption of the breakout width approach in which shear failures are considered to be constrained to horizontal planes. Failures within the wellbore are not necessarily horizontal and can be developed in different non-planar trajectories with various angles to the horizontal plane. Furthermore, the possible in-situ stresses from regional studies are constrained by means of stress polygons against which the reliability of results from breakout methods can be checked. Results indicate that due diligence and special care must be exercised for determination of maximum stresses from breakouts and more reliable methods are required than those currently used. Cited as : Faraji, M., Rezagholilou, A., Ghanavati, M., Kadkhodaie, A., Wood, D. A. Breakouts derived from image logs aid the estimation of maximum horizontal stress: A case study from Perth Basin, Western Australia. Advances in Geo-Energy Research, 2021, 5(1): 8-24, doi: 10.46690/ager.2021.01.03

Different from the conventional oil reservoirs, the primary storage space of shale is micro/nano pore networks. Moreover, the multiscale and multi-minerals characteristics of shale also attract increasing attentions from researchers. In this work, the advances and challenges in the development of shale oil are summarized from following aspects: phase behavior, flow mechanisms, reservoir numerical simulation and production optimization. The phase behavior of fluids confined in shale nanopores are discussed on the basis of theoretical calculations, experiments, and molecular simulations. The fluid transport mechanisms through shale matrix are analyzed in terms of molecular dynamics, pore scale simulations, and experimental studies. The methods employed in fracture propagation simulation and production optimization of shale oil are also introduced. Clarifying the problems of current research and the need for future studies are conducive to promoting the scientific and effective development of shale oil resources. Cited as : Feng, Q., Xu, S., Xing, X., Zhang, W., Wang, S. Advances and challenges in shale oil development: A critical review. Advances in Geo-Energy Research, 2020, 4(4), 406-418, doi: 10.46690/ager.2020.04.06

Research subject. This article focuses on the geological structure of the northern part of the Pai-Khoi carbonate parautochthone.Materials and methods. The study was based on the data obtained on the key sections of the North-Western Pai-Khoi. Research methods included lithological and facies analysis, subsidence curves, reconstruction of the thermal maturity of deposits based on conodont alteration indexes, X-ray microtomography for determining porosity values.Results. The Upper Devonian–Carboniferous succession (ca. 900 m thick) is composed of the terrigenous and carbonate Pyrkov Fm. (Frasnian), carbonate Lymbadyakha Fm. (Famennian-Tournaisian), Bolvanskii Fm. (Visean-Bashkirian), and Hoiponganase Fm. and Reef Chaika (Moskovian-Kasimovian). The early Frasnian part of the succession was deposited in a shallow-water environment. In the Middle–Late Frasnian, the Korotaikha paleodepression and an isolated carbonate platform was formed on the shelf edge. Filling of the paleodepression was completed at the end of the Early Visean. In the Late Visean–Late Carboniferous, a carbonate platform (ramp) formed. A Middle Paleozoic paleogeothermal gradient reconstructed on the basis of conodont alteration indexes is much higher in the Pai-Khoi carbonate parautochthone than in the most of Pechora Plate regions. This is likely to have been caused by the tectonic activity of the plate border in the Late Carboniferous–Mesozoic. A downward decrease in open porosity (from 6% to 0.1%) is likely to have been associated with increased compaction and recrystallization of the carbonates.Conclusions. Famennian-Tournaisian carbonate formations of the Pai-Khoi carbonate parautochthone were deposited under the conditions of isolated platform environment; however, the Visean–Late Carboniferous deposits were formed in the outer ramp environment. The Late Devonian–Middle Carboniferous carbonate deposits of the Pai-Khoi parautochthone demonstrate an extremely low open porosity and a high thermal maturity. These properties, along with the pronounced faulting and folding of the rocks, significantly decrease petroleum-bearing prospects of these deposits.

Research subject. The Karabash ore district is a unique structural zone in the Ural folded system, formed at the joint of the Magnitogorsk and Tagil depressions. The uniqueness of this zone is associated with its specific formation conditions: a Paleozoic copper pyrite belt with a width of about 8 km was squeezed between two blocks of ancient metamorphic rocks. This zone features a classic copper-pyrite deposit represented by steeply dipping ore bodies, which were initially characterized by a gentle dip. Elucidation of the primary geological structure and tectonic evolution of the district presents a relevant research task.Materials and methods. A geological cross section of the Karabash district was studied. Particular attention was paid to interactions between Paleozoic volcanic and sedimentary rocks and ultramafic bodies, whose age was determined by the method of zircon U–Pb dating.Results. The age of ultramafic bodies in the Karabash district was found to be 430–440 million years. Serpentinite blend (mélange) zones having a width of 60m were discovered in the sites of contact between ultramafites and host rocks. Regularities in the location of these zones in the eastern and western parts of the district make them suitable horizon markers for constructing a geological cross section of the Karabash ore district.Conclusions. It is established that the Karabash district is represented by a monocline synclinal fold formed by contraction of primary horizontal layers in the direction from east to west. The formation of the Zolotaya Gora golden deposit located in the eastern limb of the synclinal fold was associated with tectonic contraction processes.

Research subject. The article sets out to investigate the change of the geodynamic regime from the island-arc type to the accretionary-collisional type in the Late Devonian–Early Carboniferous, which occurred as a result of 1) a collision between the Western part of the Magnitogorsk island arc and the Eastern margin of the East European continent and 2) its later coupling with the heterogeneous composite East Uralian terrain.Materials and methods. The content of petrogenic elements and microelements in the rocks of the Late Paleozoic island-arc complexes of the Magnitogorsk island arc were determined using XRF and ICP MS methods at the Laboratory of Physicochemical Research Methods of the Institute of Geology and Geochemistry, Ural Branch of the Russian Academy of Sciences. In addition, available publications on the composition and formation conditions of these complexes were reviewed.Results. It was found that, in the Late Devonian–Early Carboniferous period, the process of island-arc magmatism of the Magnitogorsk paleoarc was substituted with the formation of intraplate volcano-intrusive complexes. The island-arc magmageneration and its manifestations were controlled by a latitudinal linear zoning and different depths of formation of magmatic cameras, reflecting the self-consistency and spatial isolation of these events.Conclusion. Due to the intensifying collision, melts from different mantle sources were mixing, thus contaminating the island-arc rocks by intraplate (plume-dependent) magmas. According to the composition and concentrations of high-field strength and fluid-mobile chemical elements, suprasubductional fluids played an important role in the evolution of late-island arc magmatic series.

Research subject. This article is devoted to the formation features of the Ural-Timan-Paleo-Asian segment of Eurasia. Materials and methods. The research was based on the authors’ data and those obtained following a review of available publications on the geology of segmentation. The Timan region was investigated using the geological information obtained by V.G. Olovyanishnikov.Results. A geodynamic map of the Ural-Timan-Paleo-Asian segment with a scale of 1 : 2 500 000 was compiled, which allowed further research into the structure and formation of the north-western part of the Eurasian area. This part was found to be mostly composed of geodynamic associations of orogens, orogenic systems and orogenic belts of the Upper Proterozoic (Riphean) and Paleozoic time intervals, as well as by elements of the Mesozoic-Cenozoic neoplate. These processes were supplemented by the formation of tectonic systems of superimposed depressions and protoplate protrusions. The formation of orogens, orogenic systems and orogenic belts is associated with the development and subsequent transformation of paleooceanic basins under the conditions of accretion and collision. The terranes of the ancient continental crust also participated in the formation of the segment’s geodynamic elements, for which a typification scheme was proposed. The articles present new data on the formation conditions of the segment’s orogenic elements and the relationship of the orogeny with global reconstructions, including the problem of closing the surrounding oceanic space.

Displacement monitoring in open-pit mines is one of the important tasks for safe management of mining processes. Differential interferometric synthetic aperture radar (DInSAR), mounted on an artificial satellite, has the potential to be a cost-effective method for monitoring surface displacements over extensive areas, such as open-pit mines. DInSAR requires the ground surface elevation data in the process of its analysis as a digital elevation model (DEM). However, since the topography of the ground surface in open-pit mines changes largely due to excavations, measurement errors can occur due to insufficient information on the elevation of mining areas. In this paper, effect of different elevation models on the accuracy of the displacement monitoring results by DInSAR is investigated at a limestone quarry. In addition, validity of the DInSAR results using an appropriate DEM is examined by comparing them with the results obtained by global positioning system (GPS) monitoring conducted for three years at the same limestone quarry. It is found that the uncertainty of DEMs induces large errors in the displacement monitoring results if the baseline length of the satellites between the master and the slave data is longer than a few hundred meters. Comparing the monitoring results of DInSAR and GPS, the root mean square error (RMSE) of the discrepancy between the two sets of results is less than 10 mm if an appropriate DEM, considering the excavation processes, is used. It is proven that DInSAR can be applied for monitoring the displacements of mine slopes with centimeter-level accuracy.

Based on a great number of experimental data on various mechanical properties of rock in the literature, six empirical equations between the characteristic impedance (product of density and P-wave velocity) and mechanical properties of rock are proposed. These properties include uniaxial compressive strength, tensile strength, shear strength, mode I fracture toughness, Young's modulus, and Poisson's ratio. These empirical equations show that the values of the aforementioned properties increase with increase in characteristic impedance. It also implies that the characteristic impedance of rock may be considered as an index to represent the main properties of rock. In this sense, it is possible to consider using characteristic impedance to classify rock masses for studies in the future.

To investigate the post-liquefaction shearing behaviour of saturated gravelly soil, laboratory tests were conducted using a static-dynamic multi-purpose triaxial apparatus. In addition, numerical simulations using the discrete element method (DEM) were performed to preliminarily understand the micro-mechanism of gravelly soil in monotonic loading after liquefaction. The influences of dry density, initial confining stress and degree of liquefaction on the post-liquefaction shearing behaviour of gravelly soil were discussed, and the evolution of the micro-parameters of the granular system was also analysed. The results show that the stress-strain responses of gravelly soil after liquefaction can be divided into three stages: (1) low strength stage, (2) super-linear strength recovery stage, and (3) sublinear strength recovery stage, which are distinctly different from those of the general saturated gravelly soil without previous cyclic loading. The initial state and prior dynamic stress history have significant influences on the post-liquefaction shearing behaviour of gravelly soil. The DEM simulation revealed that the average coordination number sharply increases, the contact normal shows an obvious orientation distribution, and the destroyed force chain backbones are reconstructed in the monotonic reloading process after liquefaction. The evolution of the micro-parameters of the granular system clearly reflects the interior interaction process and micro-mechanisms in the particles during the three different stages of the macro-mechanical behaviour of gravelly soil.

In this study, servo-controlled biaxial compression tests were conducted on marble specimens to investigate their failure characteristics and fracturing process. The complete stress-strain curves were obtained, and the three-dimensional (3D) features of the failure surfaces were acquired by 3D laser scanning. Acoustic emission (AE) monitoring and moment tensor (MT) analysis were used in combination to better understand the fracturing mechanism of marble under biaxial compression. It was noted that a type of 3D stepwise cracking behaviour occurred on the fracturing surfaces of the examined specimens. The stress dropped multiple times, and a repeated fracturing mode corresponding to the repeated stress drops in the post-peak regime was observed. Three substages, i.e. stress stabilisation, stress decrease and stress increase, were identified for a single fracturing mode. Then quantitative and statistical analyses of the fracturing process at each substage were discussed. Based on the testing results, it was found that at the stress stabilisation substage, the proportion of mixed-mode fractures increased. At the stress decrease substage, the proportion of mixed-mode fractures decreased, and the tensile or shear fractures increased. At the stress increase substage, the proportion of mixed-mode or tensile fractures decreased, and the shear fractures increased. Finally, a conceptual model for the stepwise crack formation was proposed.

An inverse analysis procedure has been developed to interpret collected pore pressure data and observations during backward erosion piping (BEP) initiation and progression in sandy soils. The procedure has been applied to laboratory models designed to mimic the initiation and progression of BEP through a constricted vertical outlet. The inverse analysis uses three-dimensional (3D) finite element method (FEM) to successively produce models of the hydraulic head regime surrounding progressive stages of BEP based on observations at the sample surface and pore pressure measurements obtained from the laboratory models. The inverse analysis results in a series of 3D contour plots that represent the hydraulic-head regime at each stage of the BEP development, allowing for assessing the development of BEP mechanism as well as calculating the critical hydraulic conditions required for various BEP stages to initiate and progress. Interpretation of the results identified four significant stages of the piping process: (1) loosened zone initiation, (2) channel initiation and progression, (3) riser sand fluidization, and (4) loosened zone progression. Interpretation of the hydraulic head contour plots allows assessment of the critical hydraulic gradients needed to initiate and progress various components of the BEP development.