Secondary Stress Field Research Articles

Method of Redevelopment of Underground Mining Facilities

Mining is a set of industrial branches engaged in exploration, extraction, primary processing and obtaining the initial semi-finished product of elements related to minerals. Deposits are ore, non-metallic and alluvial. These deposits are mined by open pit and closed pit methods. After the end of underground operations, empty mine fields remain, which on the surface are labeled as exclusion zones. The problem of cave-in zones, under which the waste mine fields of the mining industry are located, has been particularly acute for decades. These mines are located not only under the industrial zones of populated areas, but also under residential and public areas and cause irreversible transformation of the natural environment, which leads to catastrophic consequences. Transformation of underground space is the main task of redevelopment of industrial areas of this kind. It is possible to build underground structures for other purposes in worked-out mines. Due to the fact that these structures will be maintained and operated, the change in the secondary stress fields in the mountain massif will not have such catastrophic consequences as in the case of alienation-collapse zones. Besides, the reuse of worked-out workings is economically more favorable due to the fact that sinking will be minimal. In this paper only underground mining complexes and the possibility of their reuse will be considered.

Insight into the Mechanisms of Nitride Films with Excellent Hardness and Lubricating Performance: A Review.

Transition metal nitride (TMN) films with excellent hardness and lubricating performance are versatile low dimension materials, which are widely used in various fields including industries, transportation, aerospace, and so on. This paper introduces one film design strategy and provides a review of the mechanisms for strengthening and lubricating nitride films. The design strategy refers to two aspects which determine the structures, the performance, the components, and the chemical constitutions of nitride films The strengthening mechanisms of nitride films are then illuminated in detail, including the solid solution effect, the grain size effect, the secondary phase effect, the stress or stress field effect, the template effect, and the valence electron concentration effect. Five lubricating mechanisms are next summarized, including the easy-shear nature, the tribo-chemical reactions, the lubricious fluorides, the textured contact surface, and the synergistic effect. This paper aims to give a comprehensive introduction for understanding the mechanisms of strengthening and lubrication of nitride films for students and researchers, as well as to understand the current research progress in nitride films for exploring research gaps.

Numerical Study on Deformation and Failure Characteristics of Rectangular Roadway

In the practical processes of coal mines and tunnel, rectangular roadways are widely used in the underground environment. However, the stress distribution law of the rock mass around the rectangular roadways is relatively complicated that is influenced by different parameters, such as the in situ stress, geological structure, and properties of the surrounding rock mass. It is extremely significant to conduct systematic and in-depth research regarding the stress distribution and deformation failure mechanism of the rock mass around the rectangular roadways. Based on theoretical analysis, the stress distribution law of the surrounding rock of rectangular roadway under different rock mass strength grades is studied directly through rectangular roadway in this paper. This further reveals the distribution law of secondary stress field after excavation of rectangular roadway. A coal mine intends to excavate a roadway in rock mass, and then, the rectangular roadway is simulated by FLAC3D software. Then, the strain distribution and failure types of roadway surrounding rock under different rock mass properties are obtained. The results show that the failure of rectangular roadway is mainly shear failure and tensile failure. The roof and floor of roadway are mainly tensile failure, and the side of roadway is mainly shear failure. Moreover, the stress shifting and distribution of the rock mass around rectangular roadways is a complicated dynamic variation process. The damage degree of the floor and roof of the rectangular roadway is greater than that of the two sides of the roadway. Its variation is mainly related to the strength of surrounding rock mass.

Non-Newtonian Thermo-Elastohydrodynamics and Sub-Surface Stress Field of High-Performance Racing Spur Gears

Meshing teeth pairs of involute spur gears often form the final drive of high-performance motorsport transmissions. They are subject to high normal and shear loading. Under transient conditions pertaining to a meshing cycle, the contact conditions alter from the onset of teeth pair engagement through to maximum normal loading, followed by contact separation. Sliding motion only ceases instantaneously at the pitch point. The regime of lubrication remains mostly in non-Newtonian thermo-elastohydrodynamic conditions. The results show that a starved inlet boundary is attained throughout most of the meshing cycle which leads to the diminution of the pressure spike at the exit from the contact conjunction. The reversing sub-surface shear stresses are the main source of the onset of any inelastic deformation, which is dominated by the primary pressure peak in compliance with the Hertzian maximum pressure. The shear stress field is supplemented by an induced field due to the presence of the pressure spike. Under starved conditions this secondary stress field is diminished. The combined solution of elastohydrodynamics with a thermal network model, non-Newtonian lubricant traction, and sub-surface stress evaluation provides for a comprehensive solution not hitherto reported in the literature.

Лаборатория геодинамики и горного давления Института горного дела УрО РАН: исследования массива горных пород

The activities of the Laboratory of Geodynamics and Formation Pressure of the Institute of Mining of the Ural Branch of the Russian Academy of Sciences are aimed at organizing and conducting fundamental research, training of highly qualified personnel, as well as solving applied tasks that contribute to successful development of the mining industry in the Russian Federation and the CIS countries. The laboratory conducts research in the following areas: 1) methodology of studies and control of the stress-and-strain state parameters of the rock mass, as well as forecasting their changes over time and in the course of mining operations; 2) theoretical justification of ensuring the stability of mine workings and structural elements of mining methods. The mission of the laboratory is to conduct fundamental research based on the principles of consistent, comprehensive, interdisciplinary and innovative approach in the field of geomechanical support of subsoil development in order to improve industrial and environmental safety, energy efficiency and resource conservation in the mining industry of the Ural region and Russia as a whole. Fundamental researches at the laboratory of Geodynamics and Formation Pressure are focused on studying regularities in formation of initial and secondary stress fields, development of methods to control the stress condition of rock mass and prevention of geodynamic phenomena to enhance the efficiency of subsoil development.

An new elastic\u2013plastic analytical solution of circular tunnel under non-axisymmetric conditions

The surrounding rock is in the initial stress state before the tunnel excavation, and it undergoes the stress redistribution to reach the secondary stress state after the tunnel excavation. The surrounding rock is not only the main load source but also is an important part of the load bearing structure. Once the stress of some zone in the surrounding rock exceeds the strength of the rock mass, the part surrounding rock will enter into a state of plasticity or failure. Analytical solution is the most powerful mean to analyze this kind of underground cavern engineering problems. However, the existing solutions can not directly or simultaneously obtain the secondary stress field and excavation disturbance displacement field that we are concerned about. The implicit approximate solution cannot be degenerated to an accurate axisymmetric expression for the most existing non-axisymmetric elastic–plastic solutions. Therefore, this paper derives the elastic solution of a circular tunnel under the condition of the non-axisymmetric external load with the radial and shear inner loads. On this basis, the new elastic–plastic solution and the plastic zone radius equation of the circular tunnel under the conditions of the non-axisymmetric external load with radial inner load are derived. It can directly obtain the secondary stress field and excavation disturbance displacement field, and can degenerate to an accurate axisymmetric expression. The distribution characteristics of the analytical solution are in good agreement with the numerical test results, indicating that the new solution can provide a relatively accurate theoretical basis for the analysis and research of tunnel engineering.

On the Modeling of Ship Stiffened Panels Subjected to Uniform Pressure Loads

Stiffened panels constitute structural assemblies of the entire ship hull, i.e., double bottom, side shell, deck areas, etc. Prescriptive dimensioning of the stiffeners (web thickness and height and flange thickness and breadth) is solely based on the application of beam bending theories. This work is divided into two parts. The first part involves the assessment of the structural response of one-way (single-bay) stiffened panels under uniform pressure. The objective is to evaluate the effectiveness of alternative approaches in obtaining accurate secondary stress fields. Both state-of-the-art analytical solutions (Paik, Schade, CSR, Miller) and numerical calculation tools (finite element analysis (FEA)) are employed and compared for this purpose. When it comes to cross-stiffened panels, numerical methods are usually used within the design process which is time demanding. The second part of this work focuses on the development of a fast, yet effective, prescriptive approach. This approach will allow the dimensioning of the longitudinal stiffeners by considering the secondary stress field. Combining finite element analysis and the Euler–Bernoulli bending theory, the effect of the transverse stiffeners to the longitudinal stiffeners is examined in order to estimate the type of support on the boundaries of the transverse stiffeners. Determining the type of support, will make it possible to apply the classical formula of bending stress instead of using finite element analysis, thus limiting the computational cost. Preliminary calculations show that most of the examined cases may be treated as fully clamped beams subjected to uniform pressure.

Justification of functional organization and contents of modeling cluster concept for geomechanical research of convergent mining technologies

The new scientific school on the nature-like convergent mining technologies, which assume preventive negotiation of geomechanical consequences of mining-induced damage in the lithosphere, requires adjustment of the conventional modeling methods using the factor of time. In the framework of the main theories of similarity, the comparative studies of different model material composition are carried out, and the formula of solidifying mixtures is justified for equivalent materials for modeling joint loading of manmade and natural components of geotechnical systems. An original procedure is proposed for the construction of block models by means of gluing, such that the unit block sizes are determined in terms of sizes blocks generated by joint systems, and the number and location of gluing points are selected as function of condition of healed joints. The new procedure efficiency is checked by the method of calibration and comparison of the modeling data with the quantitative assessments of the real-life rock masses. For different mining systems, the interpolating functions of the influence factor are plotted to image the rock mass stability categories. The new instrumentation is created for the integrated test workbenches, which provides integrated patterns of strength, deformation and acoustic characteristics of physical models of the proposed convergent geotechnical systems, the obtained values of the strength and deformation characteristics of the physical models made it possible to calibrated the relevant numerical models based on the retrospective analysis of deformation process evolution. It has been proved for the first time that the values of microstrains can be used as the indicators of the secondary stress field in the structure of anthropogenically altered subsoil as an independent object in the lithosphere.The study was supported by the Russian Science Foundation, Project No. 19-17-00034.

The Study of the Dependence of Optimal Structure of Composite Materials Containing Hollow Aluminosilicate Microspheres on Humidity

Background: Experimental data on the conditions for the formation of gravel materials containing hollow aluminosilicate microspheres with a possibility to receive optimum structure and properties depending on humidity with the use of various binders are presented in this article. This article focuses on the scientific study of the possibility to optimize the physical and mechanical properties of composite materials. Objective: The main goal of this research is an exploration of energy-efficient building materials to be used to replace natural materials with industrial wastes and development of the theory and practice of how to obtain light and ultra-light gravel materials based on mineral binders and waste dump ash and slag mixtures of hydraulic removal. The objective of this research is to study the composite material containing hollow aluminosilicate microspheres. Method: The study is based on the application of the separation method for power and heat engineering functions. The method is based on the use of the structure optimality factor that takes the primary and secondary stress fields of the structural gravel material into account. It shows the possibility to obtain gravel material with the most uniform distribution of nano - and microparticles in the gravel material and to form stable matrices with minimization of stress concentrations. Experiments show that the thickness of the cement shell that performs power functions is directly related to the size of the raw granules. At the same time, the cement crust thickness regardless of the binder type has a higher formation rate for larger diameter granules when the moisture content increases. Results: The conditions of formation for gravel composite materials containing hollow aluminosilicate microspheres were studied. The optimal structure and properties of the gravel composite material were obtained. The dependence of the strength function on humidity and the binder type was investigated. The optimal size and shape of gravel material containing aluminosilicate hollow microspheres with a minimum thickness of a cement shell and a maximum strength function were obtained. Conclusion.: The obtained structure enables us to separate power and heat engineering functions in the material and to minimize the content of the aggressive environment centers.

Evolution of secondary stress field during underground mining of thick ore bodies

Rapidly evolving economic crisis generated by the unbalanced confrontation between the technosphere and biosphere dictates finding and implementation of a drastically new technology paradigm of development in the mineral mining sector based on the novel models and ideas about transition to nature-like geotechnologies. Regarding anthropogenic change in subsoil in the course of mineral mining, it is necessary to study the evolution of the secondary stress field in space and time as the structure of this field exerts a dominant influence on parameters of promising mining technologies. The study was supported by the Russian Science Foundation, Project No. 19-17-00034.

Quantitative prediction of multiperiod fracture distributions in the Cambrian-Ordovician buried hill within the Futai Oilfield, Jiyang Depression, East China

In the Futai carbonate oilfield of the Jiyang Depression, Bohai Bay Basin, oil enrichment is significantly related to fracture development during the oil production process. In this research, by methods of core observation and image logging interpretation, the tectonic fractures’ characteristics were distinguished. Numerically, through the elastoplastic mechanics method of finite element (FE) simulation, the three-dimensional (3-D) paleotectonic stress field (two key fracture-generating periods) and the current stress field in the Futai buried hill were quantitatively simulated. The equations between fracture parameters and tectonic stresses were deduced to predict the fracture distribution and development in various periods. Simultaneously, through the mechanical superposition algorithm, the fracture parameters under the present conditions were simulated by modifying the current stress field from preexisting fractures. The results indicated that: (1) The Yanshanian maximum principal stress ranged from −85 MPa to −435 MPa in the NWN-SES (344°) (343°–164°) direction. (2) The Himalayan minimum principal stress ranged from 5 to 30 MPa in the NWN–SES direction. (3) The fracture formation during the Yanshanian and Himalayan orogeny was primarily influenced by the regional stress field in the Jiyang Depression or the secondary stress field derived from the Tanlu fault zone, followed by the lithology. The current fracture porosity was primarily controlled by fold, followed by the large faults oriented by N–S direction and then by the secondary faults oriented by E-W direction. With successful calculations, the developed 3-D FE geomechanical modeling and fracture parameter calculation method holds great promise for characterizing fractures in other carbonate reservoirs.

The Influence of Time-Varying Stresses in the Rock Mass on the Stress State of Mine Workings

The stress state of the concrete walling of mine shafts is formed as a function of the structural parameters of the shaft, the total stress tensor, which includes gravitational-tectonic and time-varying stresses acting in the rock mass at the baseline, taking into account the physical and mechanical properties of the rock mass, the elastic modulus of concrete, which depends on the rate of advance and additional stresses caused by a subsequent change in the stress field, determined outside the zone of influence of mining by a cyclic change in natural stresses, and in the zone of influence of the mined-out space - by a change in the secondary stress field. The paper has presented the results of the research, which significantly increase the degree of geomechanical study of the Gaiskoye deposit’s rock mass. The main purpose of the research was to determine the parameters of the initial stresses acting in the concrete walling of the shafts at different depths. The parameters of stresses acting in the shaft walling at deep mine horizons were determined under field conditions, and the stress-deformed state of the shaft walling at various horizons was monitored throughout the depth of the shaft in the period 2013 - 2020.

Damage zones induced by in situ stress unloading during excavation of diversion tunnels for the Jinping II hydropower project

During the excavation of deep tunnels with high in situ stress, the stress unloading path caused by the rock mass excavation has important influences on the formation of the EDZ (excavation damage zone). In this study, the project background of the Jinping II diversion tunnels was firstly introduced. Then, the influences of stress unloading path induced by blasting excavation and tunnel boring machine (TBM) excavation on the EDZ were analyzed based on the acoustic data. Finally, the effects for different unloading paths of in situ stress induced by different excavation methods on the EDZ were studied by theoretical calculation and numerical simulation. The results show that compared with the quasi-static unloading, the transient unloading amplifies the effects of radial stress unloading and the tangential stress loading in surrounding rock masses. The EDZ depths of the blasting excavation tunnel are about 1.0 m greater than those of the TBM excavation tunnel. Moreover, the depths of the low-velocity band of the blasting excavation tunnel account for more than 50% of the total EDZ depths, while the depths of the low-velocity band of the TBM excavation tunnel account for about 30% of the total EDZ depths. The distribution of the low-velocity band along the excavation contour is closely related to the secondary stress field, indicating that the transient unloading of in situ stress is one of the important causes of the low-velocity band. After considering the post-peak mechanical properties of marble, the EDZ extents induced by different excavation methods can be estimated through numerical simulation.

Dynamic stability evaluation of underground cavern sidewalls against flexural toppling considering excavation-induced damage

Flexural toppling is a crucial engineering issue for high sidewalls of underground powerhouse caverns in low stress regions, when a small angle between cavern axis and bedding planes is formed. In this study, a novel dynamic method is proposed for stability evaluation of a high sidewall subjected to flexural-toppling, by integrating our derived criterion, continuum modelling and microseismic (MS) data. First, by virtue of cantilever slab theory, a geo-mechanical model is defined for analysing the toppling rock strata exposed on the high sidewalls of underground caverns. The Rayleigh-Ritz method is then adopted to deduce the equation for potential energies of toppling rock strata. A criterion for assessing the stability of high sidewalls considering a secondary stress field can thus be derived from catastrophe theory. Subsequently, stresses acting on the bedding planes are numerically obtained by continuum modelling coupled with MS data. Finally, a quantitative stability evaluation methodology is presented for flexural-toppling in view of progressive failure, considering the influence of fractures along bedding planes. A practical case of flexural toppling failure is analysed to verify our proposed approach. Good agreements indicate that our proposed approach is reliable for quantitatively evaluating the stability of larger underground powerhouse caverns against flexural toppling.

An Elastic Solution for Twin Circular Tunnels’ Stress in Hydrostatic Stress Field

In order to present an elastic solution for twin circular tunnels’ stress distribution in hydrostatic stress field, based on the complex variable theory and the superposition principle, the stress field of twin tunnels under static hydraulic pressure is decomposed into two parts: the original stress field and the secondary stress field. According to the symmetry of the structural form and the load distribution, the secondary stress filed can be simplifyed into a half-plane model. Therefore, the stress filed can be analyzed with the complex variable theory conveniently. Finally, the elastic solution of the twin tunnels under static hydraulic pressure is demonstrated by the superposition of the original stress field and the secondary stress field. In order to verify the analytical solution, a finite element model is adopted as the comparative test.. The result of the finite element simulation shows that the stress concentration at the middle rock wall is most obvious. And the stress concentration factor keeps increasing when the twin tunnels’ spacing distance and supporting pressure are decreasing. Besides, the maximum tangential stress appears at the tunnel boundary. The farther away from the tunnel’s boundary, the tangential stress gets lower. Furthermore, the supporting pressure leads to the increasing of radial stress and the decreasing of tangential stress. The analytical results are highly consistent with the numerical results with finite element method.

Stope stability assessment by the Mathews–Potvin method: a case-study of open stoping in salt rock mass under conditions of secondary stress field

Predicting the stability of open stopes is a challenging task for underground mine engineers. The introductory part of this paper presents main issues related to stability and safety of soil and rock mass in course of large earthworks and underground works. On the basis of former studies, this paper reviews the research findings on stope stability by the methods of Mathews and Potvin in the stoping design for rock salt mines operating at depths greater than 1 km under conditions of secondary stress fields, as well as the rock mass quality assessment by Barton’s method. The conservative stope design has been performed for a few scenarios of design parameters. In conclusions, it is underlined by the stability graph at the given parameters, that in the first case-study scenario, HR is 4.5 m and the Mathews–Potvin stability number is 68 m. It is concluded that the stopes will be stable and preserve their shapes. On the basis of presented case study (stope stability assessment in the test halite–polyhalite–polymineral salt deposit was carried out for a few scenarios at maximal effective stresses and under conditions of jointing), the authors provide the general provisions on salt rock mass assessment at great depths.

Geomechanical justification of room-and-pillar dimensions for rock salt and polymineral salt mining

The key target of room-and-pillar planning for mining rock salt, polymineral salt and polyhalite at the minimized loss of minerals in pillars is optimization of the dimensions of rooms and rib pillars. The authors compare some variants of mining with rooms and rib pillars, as well as with honeycomb mine structure. The theoretical and experimental studies prove efficiency of room-and-pillar dimension optimization by combination of analytical estimation with numerical analysis and physical modeling of the stress–strain behavior of underground structures (honeycomb mine structures). It is found that the honeycomb mine structures feature higher resistability of structural components to external loads. The research into secondary stress field generation and influence on structural elements of the roomand- pillar mining systems made it possible to calculate stable parameters for the conventional and innovative mining systems. The study was supported by the Russian Science Foundation, Project No. 19-17-00034.

Studies on support techniques for roadway bearing structure features under different geo-pressures

This study investigates the timely support and multi-echelon support in relation to the structure partition of the surrounding rock. The instability behavior of the roadway bearing structure for different working depths and ground pressures is studied and the impact of the supports on the stability of the roadway is analyzed. Considering the distribution of the secondary stress field and the degree of deterioration of the surrounding rock strength resulting from the excavation, a new division method is proposed that involves “deep-shallow-critical” coupling bearing strata. In a similar simulation experiment, we used a stress-loading device fabricated in-house and a support airbag to simulate the impact of ground pressure and timely support force on the stability of the bearing structure and the development of fracture in the surrounding rocks. The results indicate that, with the increase in the ground pressure, the deep and critical bearing strata will move farther away from the roadway wall, the shallow bearing stratum would expand, and hence, the difficulty and expense of providing support will also increase. Timely support can control the movement of the bearing structure and the expansion of the affected range. With the increase in the ground pressure, the bearing structure will become unstable easily, and the stress in the arch foot of the roadway will be considerably concentrated. The instability will lead to more serious damage to the surrounding rocks, which is necessary to reinforce the support in advance. According to the bearing structure of the naked roadway, a multi-echelon support method is proposed. The effective support area is designed based on the outer boundaries of the deep, shallow, and critical bearing strata. The improved multi-echelon support can impose limits on the unfavorable impacts exercised by burial depths on the stability maintenance of the roadway bearing structure and eliminate the adverse effects on the integrity of the surrounding rock. Finally, the relationship between the area of failure and the bearing stratum is established theoretically, and the polynomial interaction equation is fitted according to the results of the simulation.

Features of secondary stress field formation under anthropogenic change in subsoil during underground mineral mining

Features of secondary stress field formation under anthropogenic change in subsoil during underground mineral mining

Coupling of strike-slip faulting and lacustrine basin evolution: sequence stratigraphy, structure, and sedimentation in the North Yellow Sea Basin (West Bay Basin offshore North Korea), eastern China

The North Yellow Sea Basin in offshore areas of eastern China provides a unique opportunity to document the interaction between the paleo-Eurasian and circum-Pacific tectonic domains and the coupled relationship between Tanlu Fault strike-slip activity, intrabasinal tectonics and sedimentation. This study combines well data, three-dimensional (3-D), and two-dimensional (2-D) seismic data to make regional tectonics interpretations, and delineate the sequence stratigraphy, geological structure and sedimentary history of the basin's Eastern depression, particularly focusing on the influence of Tanlu Fault strike-slip activity on basin evolution. The Eastern depression data record the development of five second-order stratigraphic sequences, both the Mesozoic and the Cenozoic fault systems with basement F1, F2 and F3 faults, and the deposition of various deltaic, fan delta, lacustrine, and subaqueous fan facies associations. The F1 and F3 faults controlled the NW- and NE-trending secondary faults and associated Mesozoic sedimentation within the depression, while the F1 and F2 faults jointly controlled the development of NE- and near-E-W-trending secondary faults and associated Cenozoic sedimentation. The results indicate that the plate movements and Tanlu episodic, strike-slip faulting generated a left-lateral stress field in the Early Cretaceous, that switched to a right-lateral stress field during the middle Eocene to Oligocene. This transformation produced secondary shear stress fields in the North Yellow Sea Basin and generated NE-trending rifting superimposed on the previous NW-trending rift generation, and controlled the related structural geology and sedimentation in the Eastern depression of the basin. This proposed explanation of a tectonic regime transformation model, coupled with Tanlu strike-slip movements, could also provide new insights into the differences in gaps that occur in the stratigraphic record for the North Yellow Sea Basin and adjacent areas in eastern China.