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In a recent work, the authors demonstrated the merits of the diametrical core deformation technique (DCDT) for stress determination at an excavation face. An analytical model was developed and verified with laboratory tests. This paper aims to validate the DCDT in the field using a well-documented case study from a Canadian underground mine. Rock cores are extracted from the floor of a footwall drive 1000 m below surface for the purpose of estimating stress magnitude and orientation. The DCDT is applied to the extracted cores and the state of stress in the drift floor is estimated. On the other hand, a mine wide FLAC3D model was developed using the geomechanical data and in situ stress regime obtained from a previous study. The model is a pared-down version of a comprehensive FLAC3D mine wide model that simulates past mine-and-fill sequence and was calibrated with various burst criteria and recorded mining-induced seismic events. A comparison of FLAC3D and DCDT in terms of floor stress estimates and orientation shows good agreement. The DCDT could be used as a ground control tool to help detect stress-related ground control issues. Highlights: Extraction of rock cores from a drift floor 1000 m below surface for the purpose of stress estimation. Application of diametrical core deformation technique (DCDT) to estimate the biaxial state of stress—magnitude and orientation—in the floor. Development of a mine-wide 3D numerical model using geomechanical data and in situ stress regime. Validation of DCDT by comparison of stress orientation and magnitude estimates with calibrated numerical model. The comparison shows good agreement. [ABSTRACT FROM AUTHOR]

Hydrogen silsesquioxane (HSQ) and Medusa are spin-on-glasses used for several applications and more specifically for electron-beam lithography. To characterize the thermal densification of these resists on silicon, the mean resist film stress was measured in situ as function of temperature up to 600 °C in a vacuum chamber by the curvature method. The curvature was evaluated from 3D profiles of uncoated and coated dies measured by full field phase shifting interferometry. Three resists were investigated: FOx-15, FOx-25 and Medusa-82. The initial resist stress at room temperature after spin coating and baking is slightly tensile and becomes highly tensile above a certain temperature dependent on the resist. This variation is mainly attributed to resists densification. FOx-15 and FOx-25 start densifying at 500 °C, and FOx-25 densifies more than FOx-15. Medusa-82 is densifying around 300 °C and has the highest tensile stress but the film relaxes beyond 405 °C. In the case of FOx-15, it was found that vacuum annealing prevents densification. Finally, we evaluated the in-plane average coefficient of thermal expansion of the resists from stress measurements during cooling to room temperature. For FOx-15, a CTE equal to 1.5 ppm/K is found, while it is close to 0.0±0.2 ppm/K for FOx-25 and 1.3 ppm/K for Medusa-82.

The in situ stress conditions of reservoirs are the fundamental parameters for determining the arrangements of horizontal boreholes and assessing borehole stability, especially for the exploration and exploitation of unconventional oil and gas. The borehole wall stress relief method (BWSRM) is a new technique that can directly measure three-dimensional (3D) stress without any assumptions regarding the stress field. In deep vertical borehole situations, a new experiment is proposed to prevent electronic components from becoming damp while simultaneously maintaining borehole stability. The effect of drilling fluid pressure on the strain measurement of the stress relief processes is studied. The finite-element model (FEM) simulates the stress relief process and verifies the theoretical solutions under different testing depths. The results show that complete stress relief is impossible under deep vertical borehole conditions, and the wall drilling process changes the stress conditions of the measured points from modified plane strain to triaxial compression. Therefore, the data measured by the strain gauges cannot be directly imported into the original relationships between the measured strains and far-field stress. The comparisons between the original theoretical solutions and FEM results indicate that if the confining pressure is ignored, then the maximum error between the measured and real in situ stress components is over 35%. After correcting the estimated strain data using the proposed methods, the stress tensors obtained from theoretical equations are consistent with the natural stress tensors. [ABSTRACT FROM AUTHOR]

Reliable and low-cost in situ stress measurement is important for design and operation of underground excavations. Deformation rate analysis (DRA) is a rock memory stress determination method based on carrying out cyclic, non-destructive uniaxial compression tests on rock cores in the laboratory. The DRA method may not be applicable to rock cores with low uniaxial compressive strength as fractures or failure may be induced during loading. A triaxial DRA test was proposed with the intention of increasing rock strength by confining stresses in the course of DRA testing. However, triaxial DRA tests overestimate the pre-stress (the maximum previous stress), with the error increasing as the confining stress increases. To solve this problem, we develop a simple DRA model and propose linear triaxial deformation rate analysis (LDRA) based on performing triaxial DRA tests with different confining stresses and reconstruction of the pre-stress using linear regression. The LDRA method is demonstrated to work well on determining the maximum previous stresses memorized in rocks. Highlights: We conduct deformation rate analysis (DRA) in uniaxial compression and triaxial compression. We find that triaxial DRA tests overestimate the pre-stress, the stronger the higher the confining stress. We propose linear triaxial deformation rate analysis based on performing triaxial DRA tests with different confining stresses and reconstruction of the pre-stress using linear regression. [ABSTRACT FROM AUTHOR]

In situ stress measurements have been widely used in various deposition processes for stress detection. The substrate size can affect the uniformity of curvature across the entire surface, which is a major cause of incorrect stress measurements. However, because of the inherent concept of measurement theory and the complexities of the influence of substrate size on measurement accuracy, the underlying nonlinear effects of the rectangular substrate are still not fully understood. We discovered that increasing the substrate size caused an increase in nonlinear effect (nonuniform distribution of curvature radii and stresses in the x and y directions) and surface defects on the rectangular substrate using in situ stress measurement. Furthermore, the bending stiffness of the substrate, which was influenced by the substrate size, was established to illustrate the effect of substrate size on the nonlinear effect. The total stress of the deposit was concentrated at the edge in both the x and y directions, and the deposit at the edge was prone to delamination and cracking. When the substrate size was reduced, the deposit surface did not show obvious defects, and the stress errors in the x and y directions were only 2.34% and 2.54%, respectively. These findings will be beneficial to improve the accuracy of in situ stress measurement and further understand the causes of nonlinear effects. [ABSTRACT FROM AUTHOR]

Adopting 47 sets of in situ stress measurements taken at depths ranging from 417 to 1123 m in a coal mining district in central China by the overcoring method, we characterize the magnitude and orientation of the current stress field and its relationship to tectonism in this district to determine the controls on in situ stress in underground coal energy exploration and seismogeology. The measurements reveal that this district is in a relatively high horizontal stress environment. The stress regimes are generally favorable for strike-slip faulting and reverse faulting and are characterized by σH> σv> σhand σH> σh> σv, revealing that the regional stress field is absolutely dominated by horizontal tectonic stress and reflects a typical tectonic stress field type. The maximum horizontal principal stress is predominantly oriented between the ENE–WSW and WNW–ESE directions and averages nearly E–W,​ which is closely related to the tectonic plate movement and crustal deformation and agrees well with the direction derived from focal mechanism solutions and other stress indicators in and around the region. The current stress field in this district generally inherited the characteristics of the tectonic stress field in the third stage and partially retained the traces generated by the tectonic stress field in the first and second stages. In addition, the frictional parameter μm, which is calculated using the derived stress data, is used as a strong predictor to reflect the capability of the level of crustal stress accumulation. This region is in a state of critical or subcritical equilibrium, and regional faults at shallow depths have a medium to slightly high frictional strength, indicating that some well-oriented faults may theoretically approach or reach frictional equilibrium and that frictional sliding may occur.

In situ stress measurement data was analyzed to estimate the temporal and spatial stress variations at shallow depths in the Longmenshan fault zone (LMSF), prior to and following the 2008 Wenchuan earthquake (WCEQ). Analysis of the stress field related to fault strength and behavior is useful for understanding geodynamic processes and conducting hazard assessments. The shallow stress changes after the WCEQ show clear along‐strike variations. Degrees of stress orientation rotations have a negative correlation with the horizontal principal stress ratios and the WCEQ apparently reduced the magnitude difference between horizontal principal stresses. Taking stress magnitudes and orientation distribution relative to the fault strike into account, we propose an intermediate‐strength of LMSF, with a friction coefficient generally constrained between 0.35 and 0.6. In addition, high‐pressure fluids in the fault zone reduce the effective normal stress and to a certain degree weaken the fault strength. The accumulated stress over a certain period following release of the WCEQ indicates the start of another earthquake cycle. The changing crustal stress field makes the LMSF stable or slipping optimally during geodynamic processes. The segmentation feature of the shallow crustal stress field in the LMSF may imply a different tectonic loading and seismic release processes along the fault. The southwestern section to the epicenter of the WCEQ favors the occurrence of future earthquakes, as high μm in a state of critical failure was present in this area, which indicates that the Wenchuan and Lushan earthquakes did not release the accumulated stress to a sufficient extent there. [ABSTRACT FROM AUTHOR]

The in situ stress measurement technique can be used in long-term monitoring of induced stress to obtain three-dimensional stress states in slope engineering. In the monitoring, the ambient temperature fluctuation, “zero” drift of the logging data, and stable power supply should be considered. A dual temperature compensation circuit and experimental calibration techniques are proposed to increase accuracy based on the principle of the CSIRO method and considering the effect of a long-term disturbance of temperature in slope engineering. In view of the characteristics of the stress field distribution of the slope rock, the strain gauge layout scheme for induced stress monitoring of slope rock is modified to achieve the acquisition of three parallel measurements at one measurement and a stress–strain relationship equation for multilayer elastic layers is derived. An in situ stress logging system with the function of transient logging and data-connection in power cut condition is introduced to achieve a continuous correlation of measurement data under power cut conditions. An online cloud platform is established for the slope engineering of Au Mountain Iron Mine in Maanshan City. The results show that the data deviation of logging system is ±14 με with 24 days’ power off, and errors with amount of 15% were corrected by the dual temperature compensation method. The remotely transmitted data reflect the effect of temperature changes and the evolution of strain (induced stress) in real time to satisfy the demand of long-term monitoring of slope engineering.

Deep borehole cores are an important material basis for understanding deep stress conditions and rockburst risk; however, the complex environment of deep boreholes poses many challenges to traditional core orientation techniques, thus limiting the application of cores in fields such as in situ stress measurement. A technical method of restoring the original spatial attitude of nonoriented geological cores on the ground was proposed based on the inherent "trajectory projection consistency" relationship between the borehole and the corresponding core. A prototype machine of core ground reorientation was developed. Using this method and machine, ground reorientation was performed on cores drilled from the deepest shaft in China. Subsequently, the reoriented core acoustic emission (AE) method was conducted to identify the in situ stress within the project area. Meanwhile, measurement accuracy was verified by the stress relief method. The results show that the in situ stress distributions, including the azimuth and the trends in principal stresses by the two methods, are in good agreement and indicate that the historical maximum principal stress in the case of the mine has little abrupt variability with that of the present day. The research results can be used as the design basis for the safe construction of the deepest shaft. [ABSTRACT FROM AUTHOR]

The hydraulic fracturing technique (also termed mini-frac test) is commonly used to estimate the in situ stress field. We recently conducted a mini-frac stress measurement campaign in the newly-established Bedretto Underground Laboratory (BedrettoLab) in the Swiss Alps. Four vertical boreholes, dedicated for stress characterization of the granitic rock mass, hosted a total of 19 mini-frac test intervals. Systematic pressure transient analysis was performed to carefully estimate the magnitude of the least principal stress ( S 3 ). We compared five different methods (inflection point, bilinear pressure decay rate, tangent, fracture compliance, and jacking pressure) to identify an adequate approach best suited for our test scale and the host rock mass. We found that the methods used to determine the fracture closure pressure underestimate the magnitude of S 3 , presumably due to the rapid closure of the hydraulic fracture after shut-in. The most consistent results were found using the inflection point and bilinear pressure decay rate method, which both determine the (instantaneous) shut-in pressure as the proxy for the S 3 magnitude. The determined shut-in pressure, or S 3 magnitude, is 14.6 ± 1.4 MPa from the inflection point method. This allowed us to further estimate the stress environment around the BedrettoLab, which is transitional between normal and strike-slip faulting. The measured local pore pressures from extended shut-in periods are between 2.0 and 5.6 MPa, significantly below hydrostatic. A combination of drainage, cooling, and the excavation damage zone of the tunnel may have significantly perturbed the in situ stress field in the vicinity of the BedrettoLab. [ABSTRACT FROM AUTHOR]

Knowledge of the crustal stress field is critical to understanding the driving forces and processes responsible for seismicity. The purpose of this article is to systematically comment on the interaction between the stress state and seismicity, as well as the potential application value and limitations of stress/strain observations in earthquake research. In situ stress measurements and stress/strain monitoring have been employed to detect the stress/strain anomalies and the corresponding earthquake precursors, and great progress has been made. There are some correlations between seismicity and the stress field from stress monitoring before and after an earthquake. However, the relationship between stress changes and the mechanism of earthquake genesis cannot be well explained because of a lack of strong evidence. Moreover, the extremely shallow depth of stress/strain measurements relative to the focal depth limits the efficacy and persuasiveness. Therefore, it is necessary to master the mechanical state and strain energy accumulation at the earthquake source during the adjustment of the regional stress field in earthquake prediction. In addition, emphasis should be placed on investigations of the genesis of abnormal stress/strain and action mode and scope of the stress/strain to study the mechanism of earthquake precursor anomalies and earthquake focal mechanisms. [ABSTRACT FROM AUTHOR]

The contemporary stress field in and around a gold mine area (GMA) and its seismological implications were investigated based on overcoring stress measurements and focal mechanism solutions. The results indicate that the stress level of the GMA appears to be relatively high, and stress states are characterized by reverse and strike-slip faulting stress regimes, which vary somewhat with depth. The stress field is governed by the maximum horizontal stress, which is well oriented along the WNW–ESE or approximately E-W directions, revealing a uniform stress direction. This dominant stress orientation is identical to the regional tectonic stress field interpreted by various independent geological indicators, and the stress field is mainly caused by the combined actions of far-field, near-field, and local forces. The stress conditions suggest that this region is in the subcritical equilibrium state, so frictional sliding probably occurs along the pre-existing and cohesionless faults that are optimally oriented to the stress field. Moreover, the ratio of the maximum shear stress to the effective mean principal stress (μm) values of 0.3 to 0.5 can be used as the lower and upper critical bounds for future geodynamic-related prediction analysis in and around the GMA and other possible regions. [ABSTRACT FROM AUTHOR]

In this study, the thermal stress alterations generated in a tungsten fiber reinforced titanium composite (W/Ti composite) were evaluated by the neutron stress measurement method at cryogenic temperatures. The W/Ti composite thermal loads were repeated from room temperature to the cryogenic temperature (10 K), and alterations in thermal residual stress were evaluated using the neutron in situ stress measurement method. In this measurement, the stress alterations in the titanium matrix and the tungsten fibers were measured. This measurement was carried out by TAKUMI (MLF-BL19) of J-PARC, a neutron research facility in the Japan Atomic Agency. The measurement method of TAKUMI is the time-of-flight (TOF) method. Owing to this measurement method, the measurement time was significantly shortened compared to the angle-dispersion type measurement by a diffractometer. As a result of the measurement, large compressive stresses of about 1 GPa were generated in the tungsten fibers, and tensile stresses of about 100 MPa existed in the titanium matrix. The thermal stresses due to the temperature change between room temperature and cryogenic temperature is caused by the difference of thermal expansions between the tungsten fibers and the titanium matrix, and these stress values can be approximated by a simple elastic theory equation.

In situ stress is an essential parameter that directly affects all engineering construction and scientific research in deep rock masses. The shapes of deep borehole are often highly irregular, so that the traditional in situ stress measurement methods based on the assumption of circular or cylindrical boreholes are no longer applicable. We propose a stress relief correction method considering irregular borehole shape using the complex function method of elasticity. The conformal mapping function is introduced to project the irregular shape into a unit circle and the relationship between the strains at the borehole wall and the far-field in situ stress components are solved by the Cauchy integral methods. The results show the following: (1) The stress results from the stress relief correction method are consistent with the theoretical solutions and numerical simulation results for circular and square boreholes. (2) The irregular borehole shape significantly changes the distribution of stress magnitude and the direction of strain measurement on the borehole wall. The stress relief correction method considering irregular borehole shapes provides an essential theoretical basis for deep rock mass engineering construction and deep oil and gas field exploration. [ABSTRACT FROM AUTHOR]

Si is known for cracking and delamination during electrochemical cycling of a battery due to the large volume change associated with Li insertion and extraction. However, it has been found experimentally that patterned Si island electrodes that are 200 nm thick and less than 7 μm wide can deform in a purely elastic manner. Inspired by this, we performed in situ Raman stress characterization of model poly-crystalline Si island electrodes using an electrochemical cell coupled with an immersion objective lens and designed for a short working distance. A 5 μm wide Si island electrode showed a parabolic stress profile during lithiation, while for a 15 μm Si island electrode, a stress plateau in the center of the electrode was observed. A continuum model with coupled electro-chemo-mechanical (ECM) physics was established to understand the stress measurement. A qualitative agreement was reached between modeling and experimental data, and the critical size effect could be explained by the Li diffusive flux as governed by competition between the Li concentration and hydrostatic stress gradients. Below the critical size, the stress gradient drives Li toward the edges, where the electrode volume is free to expand, while above the critical size, the stress plateau inhibits Li diffusion to the edge and forces destructive stress relief by cracking. This work represents a promising methodology for in situ characterization of ECM coupling in battery electrodes, with suggestions provided for further improvement.