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Rectangular pipe jacking or box jacking has become more popular in municipal applications because of its better adaptability to shallow overburdens and its higher structural section utilization than the conventional circular pipe jacking. This case study presents a utility tunnel constructed by using rectangular box jacking in Suzhou, China. The utility tunnel, which has a cross section of 9.1 m in width and 5.5 m in height, was jacked 233.6 m, which is the longest known single jacking length of a rectangular box jacking project in China. The box jacking mainly passed through a silty sand layer with high groundwater levels with a minimum depth of cover of only 3.5 m underneath the Yuanhetang River. In this zone, the structures on the surface are sensitive to external disturbance, thus increasing the challenges of construction. A series of measures were taken during the jacking process, and the project was successfully completed. This paper provides an overview of this project and introduces key techniques in the construction of working shafts as well as in the installation and retrieval of the box jacking machine. In addition, the use of lubrication to reduce friction resistance, navigation and application of an anti-buoyancy slab under the Yuanhetang River, and analyses of soil deformation caused by box jacking are described.

Metro tunnels play a crucial role in urban transportation. However, with growing tunnel operation periods, defects, and large deformations appearing, these are influencing tunnel structural performance and threatening public safety. Three-dimensional (3D) tunnel reconstruction is an effective way to highlight tunnel conditions and provide a basis for engineering management and maintenance. However, the current methods of tunnel 3D reconstruction do not sufficiently combine the qualitative and quantitative characteristics of tunnel states. In this study, a novel method for metro tunnel 3D reconstruction based on structure from motion (SfM) and direct linear transformation (DLT) is proposed. The dimensionless 3D reconstruction point cloud acquired through the SfM method showcases the qualitative characteristics (such as leakage and pipelines) of the tunnel state. The close-range photogrammetry DLT method provides scale information missing from the SfM method and quantitative characteristics (such as profile deformation) of the tunnel state. The SfM-DLT method was tested in a Shanghai metro tunnel, and proved to be feasible and promising for future tunnel inspections.

With the rapid growth of automobile transport over the last century, conflicts between automobile and pedestrian transport have been viewed as a major concern in urban and transport planning. Elevated and underground pedestrian networks, which compensate for sidewalks at the street level and provide alternative options for pedestrians, have been developed in many cities. Elevated and underground pedestrian networks offer pedestrian–car separation in a vertical dimension and efficient connections between transit services and cities for subway passengers. This study aims to provide a balanced understanding of the development of underground pedestrian networks and propose supportive strategies for decision makers, planners, and designers concerned with the future implementation of underground pedestrian networks and the building of three-dimensional pedestrian networks in cities. The study applied textual analysis to examine the topic. The study indicated that three-dimensional pedestrian systems were developed based on historical precedents. It highlighted important considerations (such as dense cities, disaster mitigation and protection, and urban functions) in developing underground pedestrian networks in cities. Furthermore, it discussed significant aspects in planning and designing such networks, including safety, ease of orientation, and convenience. The paper also discussed policy implications in developing underground pedestrian networks and the building of three-dimensional pedestrian networks in cities.

Use of the longitudinal critical velocity in tunnel fires may destroy the stratification of smoke downstream, which is not conducive to the evacuation of downstream tunnel users. Reducing the longitudinal velocity can maintain stratification, but the appropriate longitudinal velocity range is unknown. Stratification of smoke under the longitudinal velocity is studied using Fire Dynamics Simulator (FDS). The aims of this paper are to explore the relationship between the longitudinal velocity and smoke stratification and to obtain a proper velocity range that can maintain clear downstream stratification. Based on Newman`s theory, the “stratification velocity” is proposed, which is the maximum velocity that maintains downstream smoke stratification. A good correspondence between the average Froude number within 200 m downstream and the longitudinal velocity and heat release rate (HRR) is found. The correlation between the temperature stratification and Froude number is obtained. Fr = 0.49 can be used to distinguish whether the stratification is clear. The relationship between the critical velocity and the stratification velocity is also discussed.

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.

Tunnels buried in liquefiable deposits are vulnerable to liquefaction-induced uplift damage during earthquakes. This paper presents support vector machine (SVM) and artificial neural network (ANN) models to predict the liquefaction-induced uplift displacement of tunnels based on artificial databases generated by the finite difference method. The performance of the SVM and ANN models was assessed using statistical parameters, including the coefficient of determination R2, the mean absolute error, and the root mean squared error. Applications for the above-mentioned approaches are compared and discussed. A relative importance analysis was adopted to quantify the sensitivity of each input variable. The precision of the presented models is demonstrated using centrifuge test results from previous studies.

Jet grouting slabs are widely used in deep excavations owing to their effectiveness for reducing the deflection of the diaphragm wall and the prop forces acting on the struts and improving the basal-heave stability. In this paper, according to case histories in Singapore, a series of finite-element numerical simulations are performed to evaluate the effects of jet grouting slabs on responses to deep braced excavations. On the basis of a parametric sensitivity study, a reasonable thickness of jet grouting slabs is proposed. The effects of the wall depth, wall stiffness, soft-clay thickness, and stiffness on the performance of the jet grouting slabs are assessed by comparing and analyzing a series of simulation results. It is found that the soft-clay thickness significantly affects the wall deflection and basal heave in deep excavation. During the design of support structures, soil profiles should be considered first. The findings of this study provide a reference and guidance for the support system design of similar projects.

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.

An algorithm was developed to automate processing of large datasets of Earth remote sensing. The algorithm was developed and implemented in the form of an M-Processor program in the Python programming language using the modules of the ArcGIS Desktop 10.2 software, which allows complex calculations without spending additional time on programming and reduces the number of manipulations for calculating separate desired characteristics. The implementation of the developed algorithm is considered on the example of ice data processing for the Sea of Okhotsk according to the data of the Multisensor Analyzed Sea Ice Extent – Northern Hemisphere (MASIE-NH) with a spatial resolution of 1 and 4 km and an ice-cover zoning mask.

The paper presents the results of statistical processing of data on the thickness and size of the tephra fragments of andesidacite composition erupted as a result of a phreatic explosion in the caldera of Golovnin volcano about 1000 years ago. A petrochemical description of the products of volcanic activity of the crustal Golovnin volcano and its evolution process is presented based on geological and geophysical data. The relationship between the thickness of the tephra, the size of its fragments, and the distance to the eruption center was studied using the polynomial regressions of varying degrees and exponential distribution. The adequacy of the constructed models to the initial data is illustrated by determination coefficients. Tephra distribution models were constructed on the basis of a three-dimensional trend analysis. For the first time, a logarithmic model was used to describe the size of tephra fragments. The accuracy of the model used was estimated. A method for estimating the potential dispersion range of tephra fragments of a certain size was obtained. The work demonstrates the potential of mathematical statistics for describing the distribution of products of volcanic eruptions of a certain type. The results of this study are suitable for creating an information database of pyroclastite distribution across the Kuril-Kamchatka volcanic region.

The Kuril island arc is an important element of the Pacific transition zone, within which such modern geological processes as underwater gas-hydrothermal activity occur. The study of underwater gas-hydrothermal activity, which affects the natural environment and all life activities, has not only fundamental but also a great practical importance. The article provides a review of research studies into the underwater gas-hydrothermal activity of the Kuril island arc. New information on the manifestations of underwater gas-hydrothermal activity within this zone obtained as a result of processing, revision and analysis of materials of complex volcanological shipboard studies at the Volcanolog research vessel (1981–1991) is presented.

Heat exchange between the three media – water, ice and air – must be taken into account when predicting the ice dynamics, drift and redistribution. It is known that the components of the heat balance vary quite strongly depending on the boundary of which media they are considered. Evaporation and turbulent heat exchange with the atmosphere are great in the areas of pure water, while evaporation from the surface of ice and snow is much less pronounced. To study the appearance of ice, it is necessary to consider only those environments between which intense heat exchange takes place; these environments are water and the atmosphere. This article studies the thermodynamic processes occurring over the seawater area by the statistical method of correlation analysis using the data on air temperature collected at hydrometeorological stations and those on the ice area from open sources. A new predictor is proposed, indicating a high correlation of 0.90–0.95 between the sum of degrees of daily temperature difference at the hydrometeorological stations of Okha and Oymyakon and the data on the area of the sea ice in the northwestern region of the Sea of Okhotsk on the last day of the month.

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

This study numerically investigates the effect of material micro- and macro-parameters on the failure mechanisms and geometry of a wellbore breakout. The analysis of the borehole breakout is essential in addressing wellbore stability, well completion, and sand production problems. The three-dimensional discrete element method (DEM) was used in the simulations. The numerical tool was used in numerical model simulations of drilling through sandstone in cubic samples at the laboratory scale subjected to pre-existing far-field stresses. Besides, a series of triaxial testing simulations were performed to relate the micromechanical parameters to the macromechanical material properties. The results showed that the geometry of the breakout is affected, among the material micro-parameters, by the particle contact modulus, bond normal and shear strengths, particle crushing strength, and particle size distribution. Further, it was found that the macro-parameters including Young’s modulus, friction and dilation angles, and uniaxial compression strength (UCS) also affect the type of breakout.

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.

Micro steel pipe pile was used for existing foundation reinforcement and renovation. An energy micro pile-raft foundation equipped with heat exchange tube was constructed in silty clay. The diameter and the length of the energy micro pile are 160 mm and 13.0 m, respectively. A series of in situ thermal performance tests were carried out by controlling cycle heating, in which the inlet and outlet water temperatures, flow rate, and thermomechanical properties of the energy micro pile were measured. Combined with a numerical simulation method, the thermomechanical stresses and displacement of the raft were also analyzed and discussed. The energy micro pile-raft foundation was also analyzed for different combinations of energy piles and nonenergy piles in the group. Results show that the micro pile-raft foundation can provide sufficient heat exchange compared with other types of ground heat exchangers. Differential settlement at both the pile top and tip were observed for the groups that contained both energy piles and nonenergy piles.

Different methods of enhanced oil recovery have been used to produce trapped oil. One of these methods is carbonated water injection in which CO2 contained water is injected in reservoirs in order to decrease free CO2 injection mobility, increase water viscosity and store/remove produced greenhouse CO2 gas safely. Another enhanced oil recovery method is smart water injection at which the ions in brine are modified in order to make controlled reactions with distributed ions on the surface of rock to cause more hydrocarbon recovery. Therefore, combination of these two methods may also have a great effect on enhancing oil recovery or may result in recovery factor less than each method used alone. In this paper hybrid smart carbonated water injection method is investigated to study its applicability in oil recovery using core flooding setup. The experimental core flooding setup was designed to perform different types of EOR methods for the sake of recovery comparison with the new hybrid method. The effect of both brine content and volume of CO2 is determining in hybrid EOR assessment. The main findings of this work show that the hybrid smart carbonated water results in the highest recovery factor in comparison to the most well-known EOR methods for carbonate cores.

Based on stratigraphic variations of petrology, geochemistry (major, trace elements), and pyrite framboids, we study the sedimentary environment of siliceous rocks of the Wufeng Formation in Wuxi, Northeastern Chongqing, China. Coupled Al2O3/(Al2O3+Fe2O3), SiO2/Al2O3, with Al–Fe–Mn values indicate that Wufeng Formation are deposited in a continental margin and influenced by detrital input. UEF-MoEF and V/Cr–U/Th cross-plots suggest that the siliceous shale was formed in dysoxic to anoxic conditions. Redox proxies imply that the lower, the middle to upper, and the top part of the Wufeng sediments were deposited in an anoxic, dysoxic and oxic environment, respectively. Accordingly, the average size of pyrite framboids are gradually increased from bottom to top, showing that increased oxidisability. A complete vibratory third-order cycle of sea level fluctuations during the Wufeng deposition can be identified. During Wufeng to Longmaxi transition, the sedimentary environment exhibits a short-scale oscillatory pattern and was probably transformed from an outer shelf to inner shelf. Coupled multi-proxies are considered more reliable proxies for deciphering redox conditions in fine-grained sediment.

Drilling through active shale formations has been a challenging practice in the oil and gas industry for a long period of time, given the complexity of shale structure and its interaction with Water Based Muds (WBMs). Although there have been many additives and methodologies proposed for a safe drilling through shale formations using WBMs, little success has been reported to the application of these methods once tested under different field conditions. In this paper, a new WBM formulated by nanomaterials was proposed to stabilize active shale layers during drilling. A series of rheological, density, filtration loss, bentonite dispersion and shale recovery tests were conducted on the mud samples formulated by nanosilica and Nano Glass Flakes (NGFs). The results indicated that NGF, as a cheap but effective nanomaterial, is able to significantly reduce the flirtation loss without posing any significant impacts on the density and the rheology of WBMs. It also appeared that the bentonite molecules were incapable to either hydrate or disperse in the drilling fluid system in the presence of NGFs. It seems that NGFs can stabilize clay minerals and reduce the filtration loss as remarkably efficient additive, but caution must be taken to ensure that they are properly disperse in the WBMs.

In this paper, we study the state estimation of compressible single phase flow in compressible porous media. The initial pressure distribution is estimated according to discrete adjoint approach based on the collected well pressure data. The first-order Tykhonov regularization method is used to obtain reasonable estimation. By analyzing the optimality condition of estimation problem, the discrete adjoint state equation and discrete adjoint gradient are derived based on the numerical scheme of the continuous equations. A quasi-Newton numerical optimization method related to adjoint gradient is proposed to solve the estimation problem. The estimation results with different regularization coefficients are compared and analyzed by numerical experiments. The deviation between the estimated pressure obtained without regularization and the real pressure is large. Estimation result with smaller deviation and higher smoothness can be obtained through appropriate regularization coefficient. When the observation error is large, the observed values generated by the estimated pressure fit well with the real pressure.

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.

The deformation instability of surrounding rock and the collapse of rock blocks are two common failure modes observed during the construction of underground caverns. Therefore, a comprehensive safety evaluation method (CSEM) of surrounding rock for application during underground cavern construction is presented in this paper. The method can be used to evaluate the deformation stability of surrounding rock and predict the collapse of rock blocks, rapidly. First, a deformation stability prediction and evaluation method (DSPEM) for rock mass is established. It combines the safety evaluation method based on a deformation statistical analysis and an inverse deformation prediction method using measured deformation data of surrounding rock. This approach possesses the unique characteristics of complementary and mutual verification. In addition, a comprehensive early-warning index system (CWIS) for assessing the deformation stability of surrounding rock is presented. It consists of three types of warning indicators and three levels of warning values. The early-warning values can be adjusted reasonably by the prediction correction method according to the measured displacements. For the collapse of rock blocks controlled by structural surfaces, a rapid prediction method of rock block collapse (RPMBC) based on the block theory is then presented. Finally, combining the DSPEM, RPMBC, and CWIS, the CSEM of surrounding rock for assessing the safety of cavern construction is established. It can provide technical support for decision making on the safety of surrounding rock during the construction of underground caverns.

Current interest in deep, low-permeability formations (

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.

Spectral induced polarization (SIP) and bender element (BE) techniques show a high sensitivity to particle size, particle distribution and content of generated hydration products, which essentially govern the efficiency of ground improvement. In this context, both SIP and BE were integrated on a column setup to monitor the processes of lime and cement stabilization. A 5 mmol/L Na2CO3 solution was injected into the sand-lime mixture to produce CaCO3 precipitation, while deionized water was injected into the sand-cement mixture to induce the hydration of cement. The average diameters of the precipitated particles or clusters were calculated from the relaxation time, which was a significant parameter of SIP signals, via the Schwarz equation. Two pairs of BE were used to demonstrate the heterogeneity of the product precipitation, which was probably caused by the location of the inflow and outflow on the SIP-BE column. SIP and BE showed the capability of nondestructively monitoring the spatiotemporal chemical evolution processes, which could be helpful for engineering applications.

To efficiently link the continuum mechanics for rocks with the structural statistics of rock masses, a theoretical and methodological system called the statistical mechanics of rock masses (SMRM) was developed in the past three decades. In SMRM, equivalent continuum models of stress–strain relationship, strength and failure probability for jointed rock masses were established, which were based on the geometric probability models characterising the rock mass structure. This follows the statistical physics, the continuum mechanics, the fracture mechanics and the weakest link hypothesis. A general constitutive model and complete stress–strain models under compressive and shear conditions were also developed as the derivatives of the SMRM theory. An SMRM calculation system was then developed to provide fast and precise solutions for parameter estimations of rock masses, such as full-direction rock quality designation (RQD), elastic modulus, Coulomb compressive strength, rock mass quality rating, and Poisson’s ratio and shear strength. The constitutive equations involved in SMRM were integrated into a FLAC3D based numerical module to apply for engineering rock masses. It is also capable of analysing the complete deformation of rock masses and active reinforcement of engineering rock masses. Examples of engineering applications of SMRM were presented, including a rock mass at QBT hydropower station in northwestern China, a dam slope of Zongo II hydropower station in D.R. Congo, an open-pit mine in Dexing, China, an underground powerhouse of Jinping I hydropower station in southwestern China, and a typical circular tunnel in Lanzhou-Chongqing railway, China. These applications verified the reliability of the SMRM and demonstrated its applicability to broad engineering issues associated with jointed rock masses.

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.

The uniaxial compressive strength (UCS) of intact rock is one of the most important parameters required and determined for rock mechanics studies in engineering projects. The limitations and difficulty of conducting tests on rocks, specifically on thinly bedded, highly fractured, highly porous and weak rocks, as well as the fact that these tests are destructive, expensive and time-consuming, lead to development of soft computing-based techniques. Application of artificial neural networks (ANNs) for predicting UCS has become an attractive alternative for geotechnical engineering scientists. In this study, an ANN was designed with the aim of indirectly predicting UCS through the serpentinization percentage, and physical, dynamic and mechanical characteristics of serpentinites. For this purpose, data obtained in earlier experimental work from central Greece were used. The ANN-based results were compared with the experimental ones and those obtained from previous analysis. The proposed ANN-based formula was found to be very efficient in predicting UCS values and the samples could be classified with simple physical, dynamic and mechanical tests, thus the expensive, difficult, time-consuming and destructive mechanical tests could be avoided.

The objective of this paper is to develop a methodology for calibration of a discrete element grain-based model (GBM) to replicate the hydro-mechanical properties of a brittle rock measured in the laboratory, and to apply the calibrated model to simulating the formation of excavation damage zone (EDZ) around underground excavations. Firstly, a new cohesive crack model is implemented into the universal distinct element code (UDEC) to control the fracturing behaviour of materials under various loading modes. Next, a methodology for calibration of the components of the UDEC-Voronoi model is discussed. The role of connectivity of induced microcracks on increasing the permeability of laboratory-scale samples is investigated. The calibrated samples are used to investigate the influence of pore fluid pressure on weakening the drained strength of the laboratory-scale rock. The validity of the Terzaghi's effective stress law for the drained peak strength of low-porosity rock is tested by performing a series of biaxial compression test simulations. Finally, the evolution of damage and pore pressure around two unsupported circular tunnels in crystalline granitic rock is studied.

Determining the saturated vapor pressure (SVP) of LNG requires detailed thermodynamic calculations based on compositional data. Yet LNG compositions and SVPs evolve constantly for LNG stored in tanks. Moreover, the SVP of the LNG in a tank influences boil-off rates and tank pressure trends. In order to make improved tank pressure control decisions it would be beneficial for LNG tank operators to be made more constantly aware of the SVP of the LNG in a tank. Machine learning models that accurately estimate LNG SVP from density and temperature inputs offer the potential to provide such information. A dataset of five distinct, internationally traded LNG cargoes is compiled with 305 data records representing a range of temperature and density conditions. This can be used graphically to interpolate LNG SVP. However, two machine learning methods are applied to this dataset to automate the SVP predictions. A simple multi-layer perceptron artificial neural network (MLP-ANN) predicts SVP of the dataset with root mean square error (RMSE) = 6.34 kPaA and R2 = 0.975. The transparent open-box learning network (TOB), a regression-free optimized data matching algorithm predicts SVP of the dataset with RMSE = 0.59 kPaA and R2 = 0.999. When applied to infill unknown LNG compositions the superior TOB method achieves prediction accuracy of RMSE ∼3kPaA and R2 = 0.996. Predicting LNG SVP to this level of accuracy is beneficial for tank-pressure management decision making.

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.

This paper presents the principles of rock support for rockburst control and three rockburst support systems used in deep metal mines. Before the principles of rock support are presented, rock fracture related to strain burst is first discussed with the help of photos taken on site, and the energy sources and transformations during bursting are illustrated through conceptual models. Surface parallel extension fracture usually occurs in the ejected and surrounding rocks in a strain burst event, while the ejected rock in a fault-slip rockburst is often already pre-fractured before the event. There must be excessive release energy available for rock ejection. The excessive release energy comes from both the ejected rock itself and the surrounding rock. To prevent rock ejection in a rockburst, the support system must be able to dissipate the excessive release energy. All support devices in a support system for rockburst control must be able to dissipate energy, be firmly linked, and be compatible in deformability. A support system for rockburst control comprises surface-retaining devices and yield rockbolts as well as yield cablebolts when needed. Laying mesh on the top of shotcrete liner is a good practice to enhance the surface-retaining capacity of the support system. Energy-absorbing yield rockbolts dissipate energy either by stretching of the bolt shank or by sliding of the inner anchor in the borehole. Mesh, mesh strap and shotcrete are the surface-retaining devices widely used in the current rock support systems. The three types of rock support used for rockburst control at present are soft support system using Split Set bolts, hybrid support system using rebar and two-point anchored yield bolts, and entirely yieldable support system using strong yield bolts.

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 acoustic response characteristics of shales were investigated by the acoustic transmission experiment, which is the basis of solving geological and engineering problems using the seismic or logging information during the process of the exploration and development of shale gas reservoirs. Based on the theory of acoustic wave and the background of acoustic transmission experiment, the initial condition, vibration source condition, boundary condition and stability condition were constructed, and the numerical simulation of acoustic transmission experiment of shales were completed through Matlab programming. The results show that under the same bedding angle, the acoustic time and attenuation coefficient of shales shown positive correlation with the bedding density; whereas under the same bedding density, the variation laws of the acoustic time and the attenuation coefficient of shales were more complex with the change of the bedding angle, that is, the acoustic time and attenuation coefficient of shales increased first, then decreased and then increased again with the increase of the bedding angle.

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.

This paper presents a case study on groundwater control and environmental protection during a deep excavation of the foundation pit for the Liyang Road Station of Metro Line 10 in Shanghai. A three-dimensional finite element simulation model was constructed to quantify the effects of a dewatering process on the environment around the excavation pit. To understand the decrease in the groundwater level around the foundation pit, the ground settlement and groundwater level were studied. During the excavation, environmental protection methods were used in the design of the optimal watering system to check its detrimental environmental effects. The effects of the diaphragm wall and horizontal barrier system were analyzed by varying their insertion depths and the resulting changes in the ground settlement and groundwater level were studied. It was found that increasing the insertion depth of the diaphragm wall reduced settlement near the excavation site but increased the construction costs. The diaphragm wall used in combination with a horizontal barrier was found to be effective in arresting the decrease in groundwater level and reducing settlement around the excavation site.

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

The relevance of the study is caused by the need to develop the effective technologies to ensure the preservation of the design position of the main pipeline sections in the areas with permafrost distribution. The workis of particular relevance, taking into account active development of the northern and Arctic gas and oil regions of Russia. The main aim of the research is to develop a design solution and the construction of underground supports for fixing non-heat-insulated sections of the pipeline in seasonally thawing and insular permafrost. Objects: main pipeline fixed in frozen soils. Results. The paper considers the existing types of supports and suspensions of pipelines in the context of their applicability for the fixing underground sections of oil and gas pipelines in permafrost and seasonally thawing soils, including at the intersection of insular permafrost, ice lenses and pingos. Based on the results of the analysis of the possible loads and limitations of existing supporting structures of pipelines with the risks of emersion and sagging of underground sections in the melted trench, the design of underground anchor supports is proposed and conclusions are made about the advantages of their use. To calculate the loads and determine the required dimensions and number of anchors, cross-sections of stretch ropes and a mounting clamp, a finite-element model was developed. Its effectiveness was confirmed analytically and experimentally on the developed test bench.

The relevance of the research consists in obtaining data on the geochemistry of springs and groundwater of the Sevastopol area as sources of drinking water supply and assessing their quality using modern analytical methods. The aim of the research is to reveal the role of interaction in the «water–rock» system, processes of continental salinization and anthropogenic pollution in formation of drinking water composition in the Sevastopol urban agglomeration. Methods. Sampling was carried out in accordance with generally accepted techniques. The laboratory study of the chemical composition by methods of titrimetry, ion chromatography, mass spectrometry with inductively coupled plasma, was carried out at the Problem Research Laboratory of Hydrogeochemistry of the Engineering School of Natural Resources of the Tomsk Polytechnic University. The theoretical foundations for solving the assigned tasks in this study were developed by professor S.L. Shvartsev at the Siberian Hydrogeochemical School. Results. During 2018–2019, field work was carried out on the territory of the Sevastopol city agglomeration to study the geochemistry of natural waters in order to assess the prospects for their use for drinking water supply. The studied waters are predominantly slightly alkaline (pH from 7,52 to 8,39), characterized by significant geochemical diversity in mineralization (from ultra-fresh 207,4 to brackish 1268,8 mg/dm3) and chemical composition. The application of the coefficients (Ca/Si, Mg/Si, Na/Si, Ca/Na, Ca/Mg, Si/Na, rNa/rCl and SO4/Cl) made it possible to identify homogeneous geochemical groups according to the formation of drinking water composition. The formation of their composition is influenced not only by the «water–rock» system, but also by the processes of continental salinization and anthropogenic pollution. The formation of the chemical composition from the perspective of the geological evolution of the water-rock system is in the initial stages. The equilibrium state of waters with carbonate minerals is achieved already in low-mineralized surface waters and the saturation of natural waters increases with the time of interaction with carbonate and carbonate-terrigenous formations. The composition of equilibrium minerals varies from calcite and dolomite in surface waters to their saturation in fissure-vein waters. For the waters of the regional fracture zone of carbonate and carbonate-terrigenous formations, the composition of the equilibrium minerals includes dolomite, calcite, siderite, rhodochrosite and magnesite. The equilibrium of waters with sulfate minerals can be traced only in some water points (the southern well in Kolkhoznoe, the Varnaly Fountain source, Stranny spring) and in waters with anthropogenic effect (Kolkhoznoe, Inkermansky and Orlovskii water intakes).

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.

The relevance of the research. In recent years, there have been significant changes in the territorial distribution of oil and gas reserves and resources in Perm region. At present, all large and medium-sized oil and gas deposits have been explored in the territory of the platform part of Perm region. At the same time within the Solikamsk petroleum district of the Volga-Ural petroleum province the possibility of opening such deposits actually exists, especially in pool outline of the Verkhnekamsky field of potassium and magnesium salts. Selection of objects and determination of their order of entry into prospecting and appraisal drilling play an important role for successful geological exploration works. The main aim of the article is to identify the priority objects for setting up prospecting and appraisal drilling based on statistical models of oil and gas forecasts. Object: lead and prepared oil and gas structures of the Solikamsk petroleum district of the Volga-Ural petroleum province located in pool outline of the Verkhnekamsky field of potassium and magnesium salts. Methods: development of multidimensional models by the method of recursive regression analysis. Results. For a comprehensive ranking of all available structures located on the territory of the Verkhnekamsky field of potassium and magnesium salts, a complex zonal-local criterion of oil and gas content – RnKOMP – was calculated. The impact of morphological (Pukvmorf), migration (Pkm), geochemical (Pukvgh) parameters and gas events data criterion (PnMNX) on the integrated PnKOMP indicator was evaluated. From the analysis of the constructed models, it follows that the criteria of Pukvmorf, Pukvgh are more universal, while Pkm, PnMNX are manifested only for the choice, which includes the structures with the highest values ​​of the complex indicator PnKOMP. The most perspective objects were selected for input into prospecting and appraisal drilling.