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Sustainable underground mining operation at deep levels requires a clear understanding of in situ stress conditions to ensure safety of personnel and equipment for continuous exaction of natural resources. Obtaining representative three-dimensional (3D) stress data at depth remains a significant challenge due to the operational complexities, high costs and time demands. Despite various methods proposed, core-based in situ stress estimation stands out as a cost-effective and reliable approach. Yet, these techniques come with inherent complexities within the laboratory environment, introducing considerable uncertainties and subjectivity in reliable stress estimation. The diametrical core deformation analysis (DCDA) was introduced to address these challenges, providing improved measurement repeatability and mitigating uncertainties. However, DCDA is limited to two-dimensional (2D) stress state estimation, leaving the determination of the full 3D stress tensor as an unresolved challenge. Therefore, this study presents a novel integrated methodology that combines DCDA with ultrasonic mapping to determine the full 3D stress state from core samples including the azimuth and dip angle of stress components. Both techniques leverage the expansion of core samples under various directions following the release from in situ stress, with greater expansion expected along the axis with the highest principal stress. Stress magnitudes were then calculated using a new analytical technique and the robustness and reliability of the proposed methodology were validated through analysing eight core samples from two vertical boreholes in an Australian underground metalliferous mine. The results were compared with the on-site overcoring stress measurements, having core-based measurements providing reliable predictions of the three principal stresses’ magnitude, azimuth, and dip angle. The current study contributes to sustainable mining by providing a more accurate and less invasive technique for 3D in situ stress estimation. Such an advancement helps to reduce uncertainties in geotechnical assessments, enabling efficient and sustainable mine planning and operation.

In real-life applications, electroencephalogram (EEG) signals for mental stress recognition require a conventional wearable device. This, in turn, requires an efficient number of EEG channels and an optimal feature set. This study aims to identify an optimal feature subset that can discriminate mental stress states while enhancing the overall classification performance. We extracted multi-domain features within the time domain, frequency domain, time-frequency domain, and network connectivity features to form a prominent feature vector space for stress. We then proposed a hybrid feature selection (FS) method using minimum redundancy maximum relevance with particle swarm optimization and support vector machines (mRMR-PSO-SVM) to select the optimal feature subset. The performance of the proposed method is evaluated and verified using four datasets, namely EDMSS, DEAP, SEED, and EDPMSC. To further consolidate, the effectiveness of the proposed method is compared with that of the state-of-the-art metaheuristic methods. The proposed model significantly reduced the features vector space by an average of 70% compared with the state-of-the-art methods while significantly increasing overall detection performance.

It is important to accurately characterize the plane-stress state of pipe walls for evaluating the bearing capacity of the pipe and ensuring the structural safety. This paper describes a novel ultrasonic technique for evaluating anisotropic pipe-wall plane stresses using three-directional longitudinal critical refracted (LCR) wave time-of-flight (TOF) measurements. The connection between plane stress and ultrasonic TOF is confirmed by examining how the anisotropy of rolled steel plates affects the speed of ultrasonic wave propagation, which is a finding not previously documented in spiral-welded pipes. Then based on this relationship, an ultrasonic stress coefficient calibration experiment for spiral-welded pipes is designed. The results show that the principal stress obtained by the ultrasonic method is closer to the engineering stress than that obtained from the coercivity method. And, as a nondestructive testing technique, the ultrasonic method is more suitable for in-service pipelines. It also elucidates the effects of probe pressure and steel plate surface roughness on the ultrasonic TOF, obtains a threshold for probe pressure, and reveals a linear relationship between roughness and TOF. This study provides a feasible technique for nondestructive measurement of plane stress in anisotropic spiral-welded pipelines, which has potential application prospects in the health monitoring of in-service pipelines.

This paper develops a new method for calculating the passive earth pressure (PEP) on retaining walls under ultimate stress conditions. First, it is assumed that when the sliding wedge is in the limit equilibrium state, the soil elements on the slip surface, at the wall-soil interface, and within the wedge all reach the ultimate stress state obeying the Mohr–Coulomb criterion. The trajectory of principal stresses within the wedge takes the form of a circular arc. Subsequently, the PEP calculation equation for the retaining wall under ultimate stress conditions is derived based on the circular arc thin-layer unit method, with the unit obtained by layering along the principal stress trajectory. Furthermore, a formula for calculating the maximum friction angle ( δ max ) at the wall-soil interface is proposed under passive conditions. The influence of the wall-soil interface friction angle on the distribution form, magnitude, resultant force action point of PEP, and overturning moment at the base of the retaining wall is then analyzed. Additionally, the stress state of soil elements within the sliding wedge is determined according to the Mohr–Coulomb failure criterion. Finally, the proposed method was validated against numerical simulations and model test data. The PEP under ultimate stress conditions represents the plastic upper-bound solution, while Coulomb’s earth pressure serves as the plastic lower-bound solution, providing new insights for accurate assessment of PEP. The maximum wall-soil interface friction angle formulation established in this study offers a theoretical basis for determining the interface friction angle under passive conditions, particularly resolving the selection of interface friction angle when the backfill has a large internal friction angle ( φ  > 30°).

Information on the layer-specific residual deformations of aortic tissue and how these vary throughout the vessel is important for understanding the regionally-varying aortic functions and pathophysiology, but not so much can be found in the literature. Toward this end, porcine aortas were sectioned into eighteen rings, with one ring from each anatomical position radially cut to obtain the zero-stress state for the intact wall and the other ring dissected into intimal-medial and adventitial layers; these rings were then radially cut to reach the zero-stress state for the intima-media and adventitia. Peripheral variations in internal/external circumferences, thickness, and opening angle of the intact wall and its layers were measured through image analysis at the no-load and zero-stress states. Intact wall and layer circumferences at both states significantly declined along the aorta, as did intact wall and intimal-medial but not adventitial thickness. Adventitia exhibited the greatest opening angles, approaching 180 deg all over the aorta. The opening angles of the intima-media and intact wall were quite similar, with the highest values in the ascending aorta, the lowest at the diaphragm, and increasing subsequently. Bending-related residual stretches were released by radial cutting that were compressive internally and tensile externally, displaying distinct axial variation for the intima-media and intact wall, and non-significant variation for the adventitia. Evidence is provided for the release upon layer separation of compressive stretches in the intima-media and of tensile stretches in the adventitia, whose values were smallest in the descending thoracic aorta and highest near the iliac artery bifurcation.

Composite action between the components of the concrete-filled steel tube (CFT) is complex and it is difficult to accurately obtain the experimental relationship between the steel tube and the core concrete of CFT columns. The triaxially stressed core concrete has been studied by hydrostatic test in past research, while little research has been focused on the mechanical behavior of steel tube of CFT columns. It is difficult to obtain the experimental constitutive relationship of the steel tube of CFT columns to reflect the real-time influence of biaxial stress state and local buckling of steel plate on the steel tube. To clarify the mechanical behavior of the steel tube of CFT columns, this paper proposed an elastoplastic analytical method considering biaxial stress state and local buckling of steel tube to obtain the stress–strain curve of the steel tube. This method applied the Hook’s law and the plasticity theory to interpret the information conveyed by the measured vertical and hoop strain histories of the steel tube. To verify its effectiveness, 11 circular concrete-filled steel tube stub columns were fabricated and tested under axial compression. Superposition results of the axial load–strain of steel tube and core concrete were compared against the experimental curves. The widely used Sakino–Sun model of the confined concrete was adopted to calculate the axial load–strain curve of the core concrete. Satisfactory agreements between the calculated and experimental results confirmed the rationality of the proposed method in tracing the constitutive relation of the biaxially stressed steel tube even after the occurrence of the local buckling. The obtained stress–strain relationship is critical for establishment of mathematical constitutive model and finite element model of steel tube.

The in-situ stress state in the shallow crust of the coastal region of Southeastern China (CRSC) remains poorly understood. We conducted anelastic strain recovery measurements in a 2 km deep geothermal borehole to investigate the in-situ stress state. Four high-quality granite core samples were employed to successfully estimate the full stress tensors. The results show that the maximum principal stress σ1 is nearly vertical, implying an extensional shallow crust that is controlled by normal faulting. From ~1865 to ~1959 m in depth, the maximum and minimum horizontal principal stresses (SHmax and Shmin) are 36.1–48.7 MPa and 34.0–38.5 MPa, respectively. Based on the paleomagnetic analysis, the orientation of the maximum horizontal compressive stress SHmax is determined as N43° ± 19°W and aligned with the subduction direction of the Philippine Sea plate. According to the compiled stress data, the SHmax orientations in the CRSC rotate counterclockwise towards the Chinese mainland, which are consistent with those of the earthquake focal mechanisms and regardless of earthquake type, indicating a heterogeneous stress field dominancy in the CRSC. Our findings manifest that there is a lower horizontal compressive stress state in the upper crust in the study region. We also discussed the possible influence of in-situ stress on wellbore stability and fracture propagation in hot dry rock exploration and further quantitatively analyzed the reactivation possibility of natural fractures under different injection pressures. This study will provide scientific data for geodynamic research, fault seismicity, and geothermal development in the region in the future.HighlightsWe used the anelastic strain recovery (ASR) method to obtain the in-situ stress state at 2 km depth in Xiamen, Fujian, China, indicating that Xiamen is controlled by normal-faulting stress.In ASR experiments, rock mechanics and rock compliance experiments were conducted to help better constrain the in-situ stress state.The collision of the Eurasian and Philippine Sea plates controls shallow crustal stress pattern and shows a relatively low horizontal compressive stress state in the coastal region of Southeastern China.Implications of in-situ stresses on geothermal resource development were discussed and quantitatively analyzed.

The image-based arterial geometries used in patient-specific arterial fluid–structure interaction (FSI) computations, such as aorta FSI computations, do not come from the zero-stress state (ZSS) of the artery. We propose a method for estimating the ZSS required in the computations. Our estimate is based on T-spline discretization of the arterial wall and is in the form of integration-point-based ZSS (IPBZSS). The method has two main components. (1) An iterative method, which starts with a calculated initial guess, is used for computing the IPBZSS such that when a given pressure load is applied, the image-based target shape is matched. (2) A method, which is based on the shell model of the artery, is used for calculating the initial guess. The T-spline discretization enables dealing with complex arterial geometries, such as an aorta model with branches, while retaining the desirable features of isogeometric discretization. With higher-order basis functions of the isogeometric discretization, we may be able to achieve a similar level of accuracy as with the linear basis functions, but using larger-size and much fewer elements. In addition, the higher-order basis functions allow representation of more complex shapes within an element. The IPBZSS is a convenient representation of the ZSS because with isogeometric discretization, especially with T-spline discretization, specifying conditions at integration points is more straightforward than imposing conditions on control points. Calculating the initial guess based on the shell model of the artery results in a more realistic initial guess. To show how the new ZSS estimation method performs, we first present 3D test computations with a Y-shaped tube. Then we show a 3D computation where the target geometry is coming from medical image of a human aorta, and we include the branches in our model.

This study investigated the twinning behavior with increasing compressive strain in rolled AZ31 alloy. With that purpose, a polycrystalline structure with an average grain size of 30 μm was utilized to perform the uniaxial compression tests. Microstructure evolution was traced by in situ electron backscattered diffraction (EBSD). Multiple primary twin variants and extension double twins were observed in the same grain. A comprehensive analysis of kernel average misorientation (KAM) and Schmid factor (SF) revealed that the nucleation of twins in one special grain is not only based on the SF criterion, but that it is also strongly influenced by surrounding grains. Moreover, the existing primary twins modified the inner and outer strain distribution close to the twin boundaries. With continued compression, the strain inside the primary twins stimulated the nucleation of double twins, while the strain in the matrixes facilitated twin growth. Therefore, the primary twin growth and the new nucleation of secondary twins could take place simultaneously in the same twinning system to meet the requirements of strain accommodation. Twinning behaviors are controlled by the combined effect of the Schmid factor, strain accommodation between surrounding grains, and variation in the local stress state. The local stress exceeded the critical resolved shear stress (CRSS), implying that twin nucleation is possible. Hence, the twinning process tends to be a response of the local stress rather than the applied stress.

Mathematical model is developed to study the elastoplastic stress-strain state with the assessment of the strength of compound spatial bodies and shells of revolution which simulate the structural members of rocket and space technology under thermo-mechanical loading. Constitutive equations are used that take into account the dependence of material properties on temperature, type of the stress state, and deformation history. The equations include two nonlinear dependencies between invariants of the stress-strain state and angle of the type of the stress state. For convenience of constructing the algorithm, the stress-strain tensors components relation is presented in the generalized Hooke’s law with additional terms that are considered known from the previous approximation. The procedure of successive approximations is described. Numerical results are presented.