Static Stress Changes Research Articles

Tectonophysical criteria for forecasting the locations of quartz crystal deposits (case of Subpolar Ural)

Spatial reconstruction of tectonic stresses within the Subpolar Ural quartz crystal-containing province was conducted by the kinematic method [Gushchenko, 1973, 1979] based on the main indicators of tectonic stresses on slickensides. Local stress states (LSS) and general stress fields for large blocks were reconstructed by the method described in [Sim, Marinin, 2015]. In the blocks with numerous occurrences of quartz crystal (Pelingichey and Omega-Shor blocks), the general stress fields is characterized by a stress state close to uniaxial tension, i.e. the Lode-Nadai coefficient µ=–1. In these blocks, thick quartz veins are perpendicular to the tension axis of the general stress field. In the block without quartz crystal (West Saled), the general stress field is characterized by a triaxial stress state or pure shear state (–1˂µσ˂+1). The LSS of the quartz crystal deposits show the following: the stress state of µ=–1 is typical of quartz veins without quartz crystal nests, and a special kind of stress state is reconstructed near the nests with piezoelectric material. It is named a variation of the type of stress state (VTSS), which means that within one tectonic stage, the type of stress state changes approximately as follows: µσ=+1 (40 %), µσ=–1 (40 %), and –1˂µσ˂+1. It means that in the piezoelectric mineral deposits, pulsating tectonic stresses provided for a fluid flow of hydrothermal solutions at the intersection of ore-bearing and ore-controling faults when tension (µ=–1) was replaced with compression (µ=+1), while the orientations of compression and tension axes remained unchanged. Apparently, such a regime was caused by alternating activation of the above-mentioned faults. The tectonic stress reconstructions were performed for 33 mineral deposits and occur­rences of quartz crystal. VTSS was determined in 32 deposits; one mineral occurrence is characterized by uniaxial tension. Therefore, we propose using VTSS (variation of the type of stress state) as a criterion for predicting the locations of quartz crystal deposits.

COMPOUND RUNS OF LOGS CALCULATION: ACCOUNTING OF LONGITUDINAL FORCES’ AND BENDING MOMENTS’ INTERACTION

Introduction. Studying the designing and constructing experience of beam bridges with composite log girders indicates the possibility of the load bearing capacity rising of the structures and their further usage in the IV and V categories bridges’ construction under A-11 and H-11 loads. The purpose of the research is to evaluate the effect on the magnitude and distribution of shear forces in shear bonds, considering the permissible pliability of fixation in wood and on the nature of the stress state change in the rods of the composite girders.Materials and methods. The authors presented the construction of the composite girder in the form of three rows united by means of tie bolts and gaskets of four-tier single-row composite girders and made of edged logs. The proposed studying method of a composite girder stress-strain state with discrete placement of concentrated shear bonds in the joints based on the classical method of forces for rod systems, taking into account the interaction of longitudinal forces and bending moments arising in the rods composing the girder of unknown forces in the shear bonds.Results. The determination of single displacements with joint account of bending and stretching-compression deformations haв a significant impact on the redistribution of shear forces in the direction of increasing them in the support zones and reducing them in the middle of the span, and, consequently, on the design of the connecting elements. The character of distribution of normal stresses on the stretching-compression indicated the rods’ girders between relationships under the eccentric compression (stretching).Discussion and conclusions. The proposed solutions demonstrate the most accurate assessment of the composite girders in the structures of spans wooden bridges and present the application possibility in modern conditions.Financial transparency: the authors have no financial interest in the presented materials or methods. There is no conflict of interest.

The 2019 Mw 6.4 and Mw 7.1 Ridgecrest earthquake sequence in Eastern California: rupture on a conjugate fault structure revealed by GPS and InSAR measurements

SUMMARYOn 4 and 6 July 2019, an Mw 6.4 foreshock and an Mw 7.1 main shock successively struck the city of Ridgecrest in eastern California. These two events are the most significant earthquake sequences to strike in this part of California for the past 20 yr. We used both continuous global positioning system (GPS) measurements and interferometric synthetic aperture radar (InSAR) images taken by the Sentinel-1 and ALOS-2 satellites in four different viewing geometries to fully map the coseismic surface displacements associated with these two earthquakes. Using these GPS and InSAR measurements both separately and jointly, we inverted data to find the coseismic slip distributions and fault dips caused by the two earthquakes. The GPS-constrained slip models indicate that the Mw 7.1 main shock was predominately controlled by right-lateral motions on a series of northwest-trending faults, while the Mw 6.4 foreshock involved both right-lateral slipping on a northwest-trending fault and left-lateral slipping on a northeast-trending fault. The two earthquakes both generate significant surface slip, with the maximum inferred slip of 5.54 m at the surface. We estimate the cumulative geodetic moment of the two earthquakes to have been 4.93 × 1019 Nm, equivalent to Mw 7.1. Furthermore, our calculations of the changes in static Coulomb stress suggest that the Mw 7.1 main shock was promoted significantly by the Mw 6.4 foreshock. This latest Ridgecrest earthquake sequence ruptured only the northern part of the seismic gap between the 1992 Mw 7.3 Landers earthquake and the 1872 M 7.4–7.9 Owens Valley earthquake. The earthquake risk in this area, therefore, remains very high, considering the significant accumulation of strain in the Eastern California Shear Zone, especially in the southern part of the seismic gap.

Numerical study on the progressive failure of heterogeneous geomaterials under varied confining stresses

The failure of geomaterials has been well recognized as a process of crack evolution due to heterogeneity. However, the influence of confining stresses on the progressive failure process has still not been fully understood. In this study, a series of numerical simulations were conducted to study the confinement effects after being calibrated by the existing experimental observations. A Gaussian distribution function and a plastic strain-dependent strength model were adopted to depict the heterogeneity and the variable mechanical parameters of the materials, respectively. The results reveal that the tensile cracks are dominant for experiments under low confining stresses, while shear cracks become more dominant as the confinement increases. The total acoustic emission (AE) events demonstrates a “U" shape, i.e. decrease firstly, and then keep nearly invariant, subquentently increase as confining stress increases. These investigations indicate that the dominant effects of confining stress on cracking mechanisms are constraint on tensile cracks under low confining stresses and promotion for shear damages under high confining stresses. The results of AE events intensity disclose that macro failure always occurs in the post-peak domain. The confining stress can advance the macro failure occurrence from the post-failure domain towards the pre-peak stress domain, and increase the uniformity of damages occurred in materials. The fitting analysis shows that the relation of crack initiation stresses to confining stresses can be well represented by a nonlinear equation. This study can improve our understanding of the failure features of geomaterials resulting from stress state changes in engineering.

Numerical investigations on the effect of ultra-high cutting speed on the cutting heat and rock-breaking performance of a single cutter

As a new drilling technology, the ultra-high-speed diamond drilling can exhibit great superiority in drilling deep hard rock, which can achieve high rates of penetration (ROP) with substantially lower energy and load. In order to better understand the removal mechanism, the effect of ultra-high cutting speed on the cutting heat and rock-breaking performance of a single cutter was investigated by using ABAQUS software. A thermal elastoplastic damage model has been established by using a finite element analysis system aiming at the linear cutting operations. The changes of stress state, strain accumulation, and heat migration in the tool unit were analyzed. The results show that when the cutting speed exceeds 8 m/s, the heat flux and mechanical specific energy (MSE) decrease as the rotary speed (RPM) increases. That is, when cutting at ultra-high linear speed (>8 m/s), more input energy was used to break rock. In addition, when the cutting speed is in the ultra-high-speed stage and continues to increase, the proportion of brittle failure of the rock will gradually increase, and a new balance will not be reached until the cutting speed reaches 12 m/s, which helps to improve the rock breaking efficiency.

Joint Inversion of GPS, Leveling, and InSAR Data for The 2013 Lushan (China) Earthquake and Its Seismic Hazard Implications

On 20 April 2013, a moment magnitude (Mw) 6.6 earthquake occurred in the Lushan region of southwestern China and caused more than 190 fatalities. In this study, we use geodetic data from nearly 30 continuously operating global positioning system (GPS) stations, two periods of leveling data, and interferometric synthetic aperture radar (InSAR) observations to image the coseismic deformation of the Lushan earthquake. By using the Helmert variance component estimation method, a joint inversion is performed to estimate source parameters by using these GPS, leveling, and InSAR data sets. The results indicate that the 2013 Lushan earthquake occurred on a blind thrust fault. The event was dominated by thrust faulting with a minor left-lateral strike–slip component. The dip angle of the seismogenic fault was approximately 45.0°, and the fault strike was 208°, which is similar to the strike of the southern Longmenshan fault. Our finite fault model reveals that the peak slip of 0.71 m occurred at a depth of ~12 km, with substantial slip at depths of 6–20 km. The estimated magnitude was approximately Mw 6.6, consistent with seismological results. Furthermore, the calculated static Coulomb stress changes indicate that the 2013 Lushan earthquake may have been statically triggered by the 2008 Wenchuan earthquake.

Modeling Clam-inspired Burrowing in Dry Sand using Cavity Expansion Theory and DEM

The Atlantic razor clam exhibits exceptional penetration performance in wet sands by periodically expanding and contracting its shell and foot during burrowing. Essentially, this periodic penetration movement can be simplified as a cyclic alternation of cylinder expansion and cone penetration, which are analogous to the geotechnical pressuremeter test and the cone penetration test. The dynamic penetration movement of the razor clam was simplified as four major connective steps—cylinder expansion, cone penetration, cylinder contraction, and cylinder retraction—and the kinematics was parameterized based on the biological data. Using a simplified and idealized synthetic dry sand sample, we attempted to model the clam-inspired penetration process using two common geomechanics tools, an analytical model based on cavity expansion theory and a numerical discrete element method (DEM), and to showcase the advantages and limitations of these two approaches in the dynamic penetration modeling. In the analytical model, the four consecutive steps were assumed to be independent. The penetration resistance and energy consumption for each step were therefore roughly estimated using cavity expansion theory; in parallel, the independent cylinder expansion and cone penetration process as well as the clam-inspired coupled dynamic penetration process were also modeled using the DEM method. When the results were compared, it was found that the adopted cavity expansion theory solutions can predict the independent cylinder expansion and cone penetration behaviors, given that the parameters were carefully chosen and calibrated. However, it cannot capture the interference effect in a coupled dynamic penetration process. Specifically, the analytical model overestimates the cone penetration resistance of the coupled dynamic penetration process; the cylindrical shaft expansion causes stress release around the cone, leading to a reduction in the tip resistance as the cone continues to penetrate. The analytical model also underestimates the expansion pressure in the dynamic penetration process, which is attributed to the change in stress and fabric state caused by the cyclic expansion/contraction movement. Moreover, the clam-inspired dynamic penetration was found to reduce the energetic cost on the penetration of cone and shaft for about 36% and still maintain a slightly lower energy consumption with additional cost on the cyclic shaft expansion, compared with the pure cone penetration strategy. With a better future understanding of the highly effective and efficient self-burrowing behavior of natural burrowers, it is envisioned to develop self-burrowing robots for a spectrum of geotechnical applications.

A New Technique to Calculate Earthquake Stress Transfer and to Probe the Physics of Aftershocks

ABSTRACTCoseismic stress changes have been the primary physical principle used to explain aftershocks and triggered earthquakes. However, this method does not adequately forecast earthquake rates and diverse rupture populations when subjected to formal testing. We show that earthquake forecasts can be impaired by assumptions made in physics-based models such as the existence of hypothetical optimal faults and regional scale invariability of the stress field. We compare calculations made under these assumptions along with different realizations of a new conceptual triggering model that features a complete assay of all possible ruptures. In this concept, there always exists a set of theoretical planes that has positive failure stress conditions under a combination of background and coseismic static stress change. In the Earth, all of these theoretical planes may not exist, and if they do, they may not be ready to fail. Thus, the actual aftershock plane may not correspond to the plane with the maximum stress change value. This is consistent with observations that mainshocks commonly activate faults with exotic orientations and rakes. Our testing ground is the M 7.2, 2010 El Mayor–Cucapah earthquake sequence that activated multiple diverse fault populations across the United States–Mexico border in California and Baja California. We carry out a retrospective test involving 748 M≥3.0 triggered earthquakes that occurred during a 3 yr period after the mainshock. We find that a probabilistic expression of possible aftershock planes constrained by premainshock rupture patterns is strongly favored (89% of aftershocks consistent with static stress triggering) versus an optimal fault implementation (35% consistent). Results show that coseismic stress change magnitudes do not necessarily control earthquake triggering, instead we find that the summed background stress and coseismic stress change promotes diverse ruptures. Our model can thus explain earthquake triggering in regions where optimal plane mapping shows coseismic stress reduction.

A constitutive model of concrete based on Ottosen yield criterion

The development of a constitutive model of concrete materials under multiaxial forces is an important problem in engineering science, and such a model is the theoretical basis for studying various mechanical behaviors. Based on the Ottosen yield criterion, a cap model parameter is proposed in this paper to describe the yielding behavior of concrete under high hydrostatic pressure; in addition, hardening and softening parameters are considered to reflect the hardening and softening of concrete during the stress state change, thus completely representing the yielding behavior according to the Ottosen criterion. A nonassociative flow rule for the Ottosen yield criterion is established to accurately calculate the strain change of concrete specimens and describe the expansion of concrete. The calculation is performed based on the established constitutive model, and the calculated results are compared with the results of uniaxial, biaxial, triaxial compression and uniaxial tension experiments on normal- and high-strength concrete. The comparison results show that the calculated stress–strain curves are in agreement with the experimental data. Hence, the proposed model can explain the stress–strain relationship and strength characteristics of concrete at different strengths.

Numerical Investigation of the Strengthening Method by Circumferential Prestressing to Improve the Fatigue Life of Embedded-Ring Concrete Foundation for Onshore Wind Turbine Tower

An embedded-ring foundation connected to the steel tower above it by inserting the steel ring into the concrete foundation is a traditional and widely used form for wind turbine towers. An insufficiently embedded depth of the steel ring leads to stress concentration on the corner of the concrete above the windward-side T-shaped plate. A damage zone of concrete develops, leading to gaps between the steel ring and the foundation concrete and a decline in the restrain stiffness of the foundation pier, which induces a larger horizontal displacement of the steel tower and a decrease in the natural frequency for the wind turbine system. To improve the fatigue life of the concrete around the steel ring under the precondition of not destroying the original foundation, a strengthening method using a circumferential prestressing technique is proposed in this paper. A series of numerical analyses were carried out to analyze the stress state change in the foundation concrete before and after strengthening. The fatigue life of the concrete above the T-shaped plate was evaluated according to CEB-FIP model code (fib Model Code for Concrete Structures 2010). The results show that the strengthening method can effectively decrease the fatigue stress amplitude and improve the fatigue life of the concrete above the T-shaped plate.

The spatial response pattern of coseismic landslides induced by the 2008 Wenchuan earthquake to the surface deformation and Coulomb stress change revealed from InSAR observations

The 2008 Mw 7.9 Wenchuan earthquake triggered plenty of coseismic giant landslides, which resulted in almost one third of total fatalities and economic losses during the event. Previous studies investigated the spatial relations between landslide distribution and topographic and seismic factors such as elevation, slope aspect, distance from rupture trace and seismic intensity. However, few studies are performed exploring the effects of coseismic surface deformation and Coulomb stress change on triggering landslides due to lack of adequate deformation observation data and stress calculation model for slope failure. In this study, we develop an envelope method to map an entire coseismic deformation field in both near- and far-field areas of seismic faults through the data fusion from InSAR and pixel offset-tracking (POT) techniques. The change in static Coulomb stress (SCS) acting on coseismic landsliding surface caused by the event is determined using the faulting model derived from the joint inversion of InSAR and GPS data, and also with the use of the elastic half-space dislocation theory and the generalized Hook’s law. The analysis suggests the spatial response pattern of seismic landslides to the coseismic ground motion and stress change, especially in the vicinity of fault rupture trace. The landslide density dramatically rises with the stress increase within the range from Yingxiu to Beichuan areas along the major surface rupture. Moving further and eastward along the fault strike, most of large landslides are triggered as the zone of positive SCS change narrows. Moreover, the high-magnitude surface displacements are possibly responsible for the giant landsliding events in the easternmost section. From the analysis of the stress transfer, the occurrence of landslides in the study area is largely controlled by the Yingxiu-Beichuan fault with overwhelming rupture length and fault slip, yet the Pengguan fault indeed shows dominance in the area between the two faults. The results show that coseismic surface deformation (derived from InSAR data in this study) and static Coulomb stress change can serve as two significant controlling factors on seismic landslide distribution and that the stress factor seems more significant in the vicinity of surface rupture.

Evidence of Fault Immaturity from Shallow Slip Deficit and Lack of Postseismic Deformation of the 2017 Mw 6.5 Jiuzhaigou Earthquake

ABSTRACTThe Mw 6.5 Jiuzhaigou earthquake occurred on 8 August 2017 36 km west-southwest of Yongle, Sichuan, China. We use both ascending and descending Interferometric Synthetic Aperture Radar (InSAR) data from Sentinel-1 and coseismic offsets of four Global Positioning System sites to obtain the coseismic surface deformation field and invert for the fault geometry and slip distribution. Most slip of the left-lateral strike-slip earthquake occurred in the 3–10 km depth interval with a maximum slip of about 1 m and a large shallow slip deficit (SSD). An eight-month InSAR time-series analysis documents a lack of resolvable postseismic deformation, and inversions for the distribution of postseismic slip demonstrate the lack of shallow afterslip. We argue that the observations of a pronounced SSD and no early afterslip of the Jiuzhaigou earthquake are indicative of an immature fault and that all incipient young strike-slip faults likely feature a SSD. We would expect a complex rupture geometry with distributed coseismic failure in the uppermost part of the brittle crust during the fault-zone development. As faults mature, they straighten out, develop a localized fault-zone core, and the SSD diminishes. By calculating the static Coulomb stress change and nine-year viscoelastic stress change caused by the Wenchuan earthquake, we also show that the 2008 Wenchuan earthquake did not significantly affect the time of occurrence of the 2017 Jiuzhaigou earthquake.

Numerical and Experimental Analysis of Rotating Backward Extrusion as a New SPD Process

Rotating backward extrusion (RBE) as a new severe plastic deformation technique is a continuous process to produce cylindrical tubes with fine grains and superior properties. In this study, the RBE process with an open punch was applied to the AZ80 alloy at 653 K, and the deformation mechanisms and the microstructure evolution were examined by the finite element method (FEM) and thermal simulation experiment. The results showed that the effective strain of the RBE process was higher than that of the conventional backward extrusion (CBE) process, and the strain increased with revolutions increasing. The strain improvement of the RBE process was related to the large cumulative plastic deformation imposed by the continuous rotation of the open punch. Furthermore, the extrusion load was reduced significantly in the RBE process comparing with the CBE process, due to the change of friction stress and stress state of the materials. And the maximum load reduction of the FEM and experiment was 47.33% and 31.6%, respectively. The average grain size of the RBE sample could be reduced by up to 90% in the region A at 30 N compared with the CBE sample. The maximum increase in microhardness of the RBE sample relative to the CBE sample was 23% at 30 N in the region A. Therefore, the grain refinement and mechanical properties of the materials can be substantially improved by the RBE process.

Numerical Modeling of Stress Disturbance Characteristics during Tunnel Excavation

The stress state and principal stress axis changes of the stress‐field tensor are analyzed during the advancement of a tunnel face on the basis of a given case study of the Jinping II Hydropower Station in China. First, the prevailing pole diagram in geology is used to illustrate the rotation of the stress axes as the tunnel face advances. The results show that the orientation adjustments of principal stresses in different positions near the tunnel boundary share common characteristics. The major and minor principal stress axes ahead of the tunnel face will rotate to intersect with the excavation surface at an angle, with the intermediate principal stress axis being almost parallel to the excavation surface. Furthermore, the stress triaxiality that is commonly used to indicate the deformation and damage of metal materials is introduced to describe the stress state change of the excavation‐induced stress. The stress triaxiality is found to represent the stress state change due to the variation in both the magnitude and orientation of the stress‐field tensor. According to the physical meaning and the change law of the stress triaxiality, stress disturbance during tunnel excavation can be divided into four stages, and the stress disturbance zone is divided into a strong disturbance zone and a weak disturbance zone. The disturbance characteristics of different stages and the distribution patterns of various zones are analyzed, which may be useful for practical application in the design and construction of rock tunnels.

Numerical Investigation and Analysis of Intermediate Principal Stress Effects on Rock Failure Behaviors

A series of numerical experiments have been conducted to investigate the intermediate principal stress effects on rock failure behaviors. The numerical results show that the strength and deformation of the rock samples are significantly affected by the intermediate principal stress. The effects are inconsistent in different intervals. As intermediate principal stress ratio b increases, the rock strength increases initially and finally decreases. When b is approximately equal to 0.5, the strength of the rock sample reaches the maximum. In the microlevel, the intermediate principal stress affects the number and distribution of microcracks. The increase of the intermediate principal stress makes the projection of the microcracks on the loading plane change from uniform to uneven. On the one hand, the intermediate principal stress restricts the propagation of microcracks in the normal direction along the intermediate principal stress (or with a component in this direction), which will lead to an increase in the strength of the rock samples. On the other hand, the propagation of microcracks along the normal direction with small principal stress (or with a component in this direction) is promoted, which leads to a decrease in the strength of the rock sample. End friction can make the intermediate principal stress effect more significant because the friction of the loading end to the rock sample can result in stress deviation between the actual value and experimental value. Inhomogeneity of stress field induced by the change of stress states or end friction forces is the external factor of the intermediate principal stress effect. Also, the inhomogeneity of rock material itself is the internal factor. Intermediate principal stress will promote or restrict the failure of certain directions, thus affecting the overall strength of the rock samples. The numerical results can be very meaningful for stability analysis of rock masses in practical engineering.

Influence of Initial Microstructure on Manufacturing Processes with Thermal Loads accompanied by Hardening

Abstract The presented investigation focuses on the correlation between concrete physical loads and resulting modifications. The physical and in a wider sense chemical loads are called internal material loads. The correlation between the generated internal material loads and the modifications is called Process Signature. This contribution presents some Process Signature components for thermal dominated processes with phase transformation and accompanying hardening. The selection of the Process Signature components considers the residual stress state at the surface and the positions of the zero crossings of the residual stress curve. Based on Finite Element simulation and experimental work the external thermal loading of both processes were characterized by the resulting maximal temperature and temperature gradient, which correlates with the change of the residual stress state. During the CIRP CSI conference 2018 in Tianjin the authors presented results for the mentioned Process Signature components for a ferrite/perlite state. The actual work focuses on the question, how the above described Process Signature components depend on the initial microstructure of the steel. For this purpose the phase kinetics of different initial quenched and tempered states are investigated for fast heating processes up to 5000 K/s. Additionally the mechanical materials properties of these material states will be presented.

Development of a Methodology for Strain Field Analysis during Orthogonal Cutting

Functionality of all machined parts depends on their dimensional tolerance, surface condition and subsurface characteristics, which are often summarized as surface integrity. Key aspects of surface integrity are a change of the residual stress state and white layer formation. Reasons for any workpiece modification of the surface rim zone can be found in the occurring high thermo-mechanical loads during the cutting process. Over the last years, many researchers published simulation based approaches to determine both thermo-mechanical loads and changes in workpiece microstructure induced by machining. Nevertheless, the direct measurement of relevant state variables such as plastic strain and temperature fields at relevant cutting conditions is still a key challenge. Directly obtaining those state variable fields from the process will enable the development of fast computing analytical models to in-process estimate surface integrity features. As a basis for later modelling of dynamic recrystallization during cutting, a methodology to calculate the accumulated equivalent plastic strains alongside one particle movement path throughout the shear zone is developed in this paper. Therefore, an orthogonal cutting test bench has been used to obtain high resolution images when cutting AISI 4140 which were then analyzed using Digital Image Correlation (DIC).

Development of surface residual stress and surface state of 42CrMo4 in multistage grinding

Abstract In this study, cylindrical grinding of a 42CrMo4 (AISI 4140) steel with varied grinding sequence stages is analyzed regarding the effect of the different loads during multistage grinding up to the resulting final residual stress state and material structure. The grinding process was adjusted in a way to enhance the mechanical load with varying intensity and generate a pronounced compressive residual stress state in the final grinding step. Furthermore, consecutive multistage grinding processes were carried out and investigated. Using a mobile XRD system with a cos α method mounted on a robotic positioning arm, repetitive measurements of the ground surfaces were performed in the machine tool without sample removal, giving information about the surface residual stress development for each step of the process sequence. The information about the surface integrity development and possible effects of the grinding process during each step is relevant for the contact conditions and modification mechanisms which lead to the final surface integrity. It is shown that the final material state, normally accessible in post-process investigations, can also be achieved reliably by sequencing the process into several steps of a regular grinding process and depends strongly on the contact parameters in a non-linear way. It could be shown, that even the spark out step can lead to significant changes in the surface residual stress state.

Study on the Instability Mechanism and Grouting Reinforcement Repair of Large‐Scale Underground Stopes

The environmental conditions due to unreasonable mining in underground stopes, the slurry diffusion mechanism in the grouting reinforcement of a stope within its influence, the causes of large‐scale instability collapse, and the catastrophic stope process are analyzed, and limit upper line analysis theory and numerical analysis methods are comprehensively adopted, revealing the continuous catastrophic collapse mode of large‐scale underground stopes. The method of determining the stope instability collapse boundary and the slip surface within the range based on the theory of the maximum shear strain increment is proposed, and the diffusion radius and range of the grouting slurry during the reinforcement process, which considers the multifield coupling factors, are obtained. The results show that the U‐shaped hidden danger area formed after the collapse of the large‐scale underground stope. The influence range reaches six adjacent stopes, which are symmetrically distributed around the collapse; the mining instability is manifested as a catastrophic chain process of stress change, energy accumulation, state change, and instability collapse. The damage mode of instability collapse is a combination method of wedge collapse, circular arc rotation, triangular translation, and strip slip. According to the multiphysics coupling numerical calculation, the diffusion radius of the grouting slurry is 12 m, exhibiting an elliptical distribution. The research results can be used to comprehensively control the underground mining environment, thus effectively solving the safety problems faced by tunnel or roadway excavations above the goaf.

Improved phase stability of γ-CsPbI3 perovskite nanocrystals using the interface effect using iodine modified graphene oxide

The variation of the active element on rGO leads to the stress state change of γ-CsPbI3 NCs, improving their phase stability.