High Stress Conditions Research Articles

Correlation between one-dimensional consolidation coefficients and different basalt fiber lengths and RHA-cement contents in fiber-reinforced stabilized expansive soils

Recently, environmentally friendly soil reinforcement and stabilization techniques, used to reconstitute weak expansive soils, are on the rise, calling for an in-depth analysis of the consolidation projections on the engineering structures built on them. This study investigated one-dimensional consolidation coefficients by conducting a series of oedometer tests on expansive soils reinforced with basalt fibers of different lengths, stabilized with rice husk ash (RHA) as an environmentally friendly cement-reducing aggregate, and nominal dosages of cement in specified combinations. The correlation between the coefficients of consolidation (cv), volume change (mv), and permeability (k) and different basalt fiber lengths and RHA-cement contents in ultimate soil composite material was quantified using equations and graphical forms. Furthermore, scanning electron microscopic imagery (SEM) was conducted to examine the structural modifications within the reinforced and stabilized soil specimens upon one-dimensional consolidation. The results showed that basalt fiber-reinforced specimens, comprised of 5% RHA and 3% cement mixtures, showed the lowest one-dimensional consolidation coefficients with a notably greater reduction at high-stress states than the control specimen. Additionally, the coefficients of volume change (mv) and permeability (k) decreased with the increased compactive effort, with a clear and significant reduction in the basalt fiber-reinforced stabilized soil composites. This study also proposed the best material combination scheme and analytical equations for evaluating the cv, mv, and k considering basalt fiber lengths at different pressure levels. The ultimate soil composites had superior properties, and thus, can be used as fill or subbase material for such engineering structures as embankments, pavements, and foundations.

Cognitive inflexibility and suicidal ideation among adolescents following hospitalization: The moderating role of life stress

BackgroundCognitive inflexibility has recently been investigated as potential vulnerability factor for suicidal ideation (SI), but the context in which it may convey risk is unclear. Life stress has also been reliably associated with SI among adolescents, and following a stress-diathesis model, may be a factor that moderates the relationship between cognitive inflexibility and SI. MethodsPsychiatrically hospitalized adolescents (N = 259) at high risk for future SI were followed for 18 months after discharge. Interviews assessing life stress and SI and a neurocognitive task assessing cognitive inflexibility were conducted at six- and 12-months. SI was also assessed at 18-month post-discharge. Linear mixed models were used to determine the moderating effect of stress on the relationship between cognitive inflexibility and SI, accounting for relevant clinical and demographic covariates. ResultsChronic stress moderated the association between cognitive inflexibility and SI, with a stronger association found among youth with greater levels compared to lower levels of chronic stress. This finding was maintained after statistically adjusting for depressive symptoms and relevant demographic covariates. No prospective associations between cognitive inflexibility, life stress, and SI were found. LimitationsSI was measured at 6-month intervals, precluding evaluation of the relationship on a more proximal timescale. ConclusionsCognitively inflexible adolescents under conditions of high chronic stress are more likely to experience increased SI severity, supporting a cognitive inflexibility stress-diathesis model of SI in adolescents. The findings highlight the importance of assessing these modifiable factors among adolescents at a high risk for SI.

Compaction-deformation behaviors and breakage characteristics of loose broken coal under various stress–temperature coupling loads

This study probed the compaction-deformation and breakage characteristics of loose broken coal under stress–temperature coupling loads. The constitutive model of loose broken coal under stress–temperature coupling loads was first constructed. Then, we quantificationally investigated the particle size distribution (PSD) evolution for the compacted loose coal using the fractal and Weibull functions. In addition, the relative breakage rate, energy evolution, and particle breakage degree of the loose coal compacted were quantificationally evaluated. Results suggest that stress is the prominent factor leading to the breakage of loose broken coal, while increased temperature exacerbates the particle breakage process in combination with the axial stress. Changes in temperature have a distinctive influence on particle breakage for loose broken coal under low-stress conditions, whereas less conspicuous under high-stress conditions. Finally, the evolution of PSDs and related breakage parameters for the entire loose broken coal compaction process were mathematically predicted utilizing the grey model.

Growth, oil and physiological parameters of three mint species grown under saline stress levels.

Salinity stress is known to have a detrimental effect on mint plants. The aim of the present work was to investigate the possible effects of salinity stress on Menthaspicata, Mentha piperita and Mentha arvensis. Plants were exposed to salinity stress using different concentrations of NaCl (0, 50, 100, 150 mM). Under salinity stress, plant growth, oil yield, content and composition, as well as physiological parameters were adversely affected. Among the studied species, M. arvensis experienced the maximum loss in terms of oil percentage. Physiological characteristics and oil composition were significantly affected with intensification of salt stress. For instance, in M. spicata, with increasing salinity stress, piperitone oxide was decreased from 78.4% in control to 38.0% in 150 mM NaCl, whereas menthol was increased from 1.0 to 37.1%. Moreover, in M. piperita, menthone, isomenthone and limonene were all increased in low stress and then were decreased in high stress conditions. In M. arvensis, the major compound; menthol was not affected but the content of menthone increased. It could be concluded that the salinity stress is detrimental but might be useful and may be recommended as an appropriate approach in improving the oil quality or to producing specific compounds under mild or moderate stress.

Evolution Laws of Stress–Energy and Progressive Damage Mechanisms of Surrounding Rock Induced by Mining Disturbance

The rock burst induced by the mutual disturbance of mining and excavation is significantly influenced by high static load stress and external dynamic load disturbance. In this paper, the evolution characteristics and progressive damage mechanism of surrounding rock in the process of mutual disturbance of mining and excavation are systematically studied. The results show that the evolution of surrounding rock stress can be roughly divided into three stages: rapid rise in the early stage, continuous rise and step-like decline in the middle stage, and slow rise in the late stage. In the process of parallel mining, the overlying rock movement above the goaf shows the sequence of horizontal penetration of tiny fissures—fracture intensification transition to stratification—non-coordinated caving of middle–low overlying rock—obvious horizontal cracks in the upper key layer. Only under the quasi-static loading mining action does the upper key layer not reach the breaking condition. The wave side of the heading face which is close to the focal point is affected by the dynamic load disturbance, the acceleration duration is short, and the attenuation is relatively fast, so it is the area prone to the earliest impact failure in the face of mining disturbance. The conclusion is helpful to deepen the understanding of the coal burst mechanism of mutual disturbance of mining and excavation.

Analysis of an improved Nishihara creep model considering plastic strain accumulation

Rock-engineering structures, particularly subway excavation rock-engineering structures, are subjected to the long-term effects of external loading that may gradually damage and cause creep and severe plastic deformations or even progressive failure. The traditional Nishihara creep model cannot accurately describe the accelerated creep stage of rock with particularly obvious nonlinear characteristics. Based on this model, a damage variable that can consider the plastic strain accumulation is introduced in this study to replace the viscoplastic body in the traditional model with a damaged viscoplastic body and establish an improved Nishihara creep model. Using the superposition principle, the creep equations of the improved model in the one- and three-dimensional stress states are derived. The accuracy and rationality of the improved model are verified using uniaxial and conventional triaxial creep tests of mudstone and sandstone under different confining pressures. The improved model can not only accurately reflect the nonlinear characteristics of the creep curve in the decay and constant velocity stages but also describe the accelerated creep characteristics of mudstone and sandstone in a high-stress state. Its applicability and accuracy are superior to those of the traditional model. This study can provide a theoretical reference for subway tunnel excavation and stability analysis of deep roadway surrounding rocks.

Thermal effects on tensile behavior and failure characteristics of granite-concrete bi-materials with different loading directions

The mechanical performance of the rock-concrete interface is greatly affected by high temperature and stress states in many geotechnical projects. It is significant to study the failure mode of the bi-materials subjected to different loading directions and temperature conditions to improve the bearing capacity of the rock or concrete engineering projects. The natural rough surface is obtained through a splitting test, and a surface close to the true roughness of the tunnel is selected from it. The 3D engraving technique is used to ensure that each specimen has the same rough surface. Then, the granite-concrete bi-material discs with a natural rough surface are heated to 100℃, 200℃, 300℃ and 400℃, respectively. A series of Brazilian splitting tests were carried out with an inclination angle between 0° and 90° to study the tensile properties and failure mechanism of the specimens. The results showed that high temperature would significantly reduce the nominal tensile strength (NTS) of the granite-concrete bi-material. The high temperature had the most apparent reduction in peak load at θ = 0°, and the reduction range was between 25% and 85%. The improvement was between 15% and 60% at θ = 90°. The NTS increased rapidly at first and then slowly with the boundary of θ = 45°. The digital image correlation (DIC) technology was also used to analyze the failure propagation process at the surface. Finally, the stress state on the interface and acoustic emission (AE) signals are analyzed to study the crack types in the failure process. The proportion of shear cracks increases first and then decreases with the increase of inclination angles, with the lowest proportion of 20% at 0° and the highest proportion of 38% at 15°. With the increase in temperature, the proportion of shear cracks increases.

The Role of Stress States on the Hysteric Behavior of Expansive Soil under Multiple Drying-Wetting Cycles

Expansive soils in the field are typically exposed to cyclic wetting and drying due to climatic fluctuations and subjected to a variety of stress conditions in nature or when used as compacted layers for the construction of hydraulic barriers or waste disposal facilities. The hysteric behavior of the soil-water characteristic curve (SWCC) is a key parameter for understanding, modeling, and interpreting the unsaturated behavior of these soils under such conditions. This study investigates the effect of stress states on the hysteresis behavior of soil-water characteristic curves (SWCCs) for compacted highly expansive clay over a range of matric suction between 0 and 1500 kPa. Two test series were performed, the first test series investigated the effect of stress states on the hysteresis of SWCCs during a single drying-wetting (DW) cycle. The second test series studied the combined effect of stress applied and multiple drying-wetting cycles on the SWCC hysteresis. For the sake of comparison, the overall SWCC hysteresis due to drying-wetting cycles was quantified using the average degree of hysteresis in terms of volumetric water content (ADHθ). Furthermore, contributors to the observed hysteresis were defined using two newly proposed measures; namely, average degree hysteresis in terms of gravimetric water content (ADHw) and in terms of volume change (ADHe*). The outcomes of this study indicate that consideration of stress states on the hysteresis of SWCC for expansive clay is of great importance. The results show a dual trend for the variation of ADHθ with applied vertical stress. Furthermore, multiple DW cycles induced a significant reduction in the hysteresis (ADHθ) under low- and high-stress states up to a certain level of DW cycles, then, no further changes in the hysteresis trend were detected. It was also found that hysteresis loops under a low-stress state were concentric in shape while hysteresis loops for specimens under a high-stress state were non-concentric, with a downward shift in hysteresis loops with the increase in DW cycles.

P-571 Endometrial cortisol and estradiol levels as indicators of pregnancy prognosis and their association with State-Trait Anxiety Inventory (STAI) psychological questionnaire punctuations in IVF patients

Abstract Study question How anxiety and stress questionnaires punctuations and endometrial steroid biosynthesis metabolites levels are associated with embryo implantation and pregnancy outcomes in IVF patients? Summary answer Those patients with high cortisol and low estradiol endometrial levels, were stressed according to STAI State punctuations and showed lower rates of implantation and pregnancy. What is known already Although IVF treatments are known to be a source of stress, its relevance in reproductive success remains controversial, mainly due to the lack of accurate biomarkers. Steroid hormones, such as progesterone and estrogens, are essential for reproductive physiology, and directly related to common stress biomarkers such as cortisol. Nowadays, clinical stress evaluation is exclusively performed via highly subjective psychological questionnaires, not being standardized in the clinical setting. In this study, we measured endometrial levels of main steroid hormones -including cortisol-, stress psychological questionnaires, and reproductive outcomes for determining the relationship among potential stress biomarkers and their influence on fertility. Study design, size, duration In this prospective cohort study, a total of 55 IVF patients were included (<45 years old, no uterine or systemic pathologies and good quality embryos). All endometrial biopsies were collected in mid-secretory phase for metabolites measurement between 2019 and 2021. Also, these patients were psychologically evaluated by stress related questionnaires the same day of biopsy collection or days later in the same cycle. Reproductive outcomes were compared between groups established according to stress biomarkers thresholds. Participants/materials, setting, methods Concentration of eleven selected steroid metabolites was measured by ultra-performance liquid chromatography-tandem mass spectrometry. A psychological questionnaire was also assessed to measure patients’ stress and anxiety (STAI). According to metabolites’ concentration distribution, Barnard’s test was applied to compare the proportion of patients with successful and unsuccessful treatments at different thresholds. A Wilcoxon test was performed for mean metabolites’ levels comparison between stressed and unstressed patients. A p-value of 0.05 was stablished as significant. Main results and the role of chance All patients with high endometrial cortisol levels (>12.5 ng/g; n = 3) failed to implant (100% vs 45.8% non-implanted in > 12.5 ng/g and <12.5 ng/g patients respectively, p-value=0.047), while the totality of patients with high endometrial estradiol levels (>0.9 ng/g; n = 5) achieved embryo implantation and on-going pregnancy (100% vs 50% implanted in > 0.9 ng/g and <0.9 ng/g patients respectively, p-value=0.038). Those patients with high cortisol levels, all not pregnant, had also low estradiol levels and high stress state punctuation (STAI State punctuations ≥ 60). Conversely, patients with high estradiol levels, all pregnant, had also low cortisol levels and were not stressed (STAI State punctuations < 60). Stratification of patients into stressed (STAI State>60) and unstressed (STAI State<60) independently of their implantation results, revealed that 27% of stressed women presented high cortisol levels, while 100% of unstressed patients had low cortisol levels. In the same way, 42% of unstressed patients had high estradiol levels, while 100% of stressed patients presented low estradiol values. Hence, mean values differences of cortisol (10.54 vs 3.05 ng/g) and estradiol (0.55 vs 4.10 ng/g) between stressed and unstressed patients were not significant (p-value=0.08862 and p-value=0.2327, respectively). No relevant associations were observed with stress as a trait. Limitations, reasons for caution Due to the heterogeneous and non-normal metabolites’ concentration distribution among patients, this study would need a largest sample size for having a representative population in the different subgroups. Although we have used molecular and psychological validated stress biomarkers, a causal relationship between stress and reproductive outcomes should be further explored. Wider implications of the findings This study highlighted cortisol and estradiol as potential endometrial biomarkers that better reflect pregnancy prognosis. Further investigation is needed to find if other psychological questionnaires molecularly recognize stressed patients as a noninvasive diagnosis associated to reproductive outcomes. These patients would benefit from psychological counseling to improve their reproductive success. Trial registration number Not applicable

Impact of dark septate endophytes on salt stress alleviation of tomato plants.

Fungal endophytes can improve plant tolerance to abiotic stress conditions. Dark septate endophytes (DSEs) belong to phylogenetically non-related groups of root colonizing fungi among the Ascomycota with high melanin-producing activities. They can be isolated from roots of more than 600 plant species in diverse ecosystems. Still the knowledge about their interaction with host plants and their contribution to stress alleviation is limited. The current work aimed to test the abilities of three DSEs (Periconia macrospinosa, Cadophora sp., Leptodontidium sp.) to alleviate moderate and high salt stress in tomato plants. By including an albino mutant, the role of melanin for the interaction with plants and salt stress alleviation could also be tested. P. macrospinosa and Cadophora sp. improved shoot and root growth 6 weeks after inoculation under moderate and high salt stress conditions. No matter how much salt stress was applied, macroelement (P, N, and C) contents were unaffected by DSE inoculation. The four tested DSE strains successfully colonized the roots of tomato, but the colonization level was clearly reduced in the albino mutant of Leptodontidium sp. Any difference in the effects on plant growth between the Leptodontidium sp. wild type strain and the albino mutant could, however, not be observed. These results show that particular DSEs are able to increase salt tolerance as they promote plant growth specifically under stress condition. Increased plant biomasses combined with stable nutrient contents resulted in higher P uptake in shoots of inoculated plants at moderate and high salt conditions and higher N uptake in the absence of salt stress in all inoculated plants, in P. macrospinosa-inoculated plants at moderate salt condition and in all inoculated plants except the albino mutants at high salt condition. In summary, melanin in DSEs seems to be important for the colonization process, but does not influence growth, nutrient uptake or salt tolerance of plants.

Substantiation of the optimal mining sequence of an ore deposit under conditions of high stress and low rock mass strength

Introduction. When choosing the mining sequences of an ore deposit, technological and organizational factors are mostly taken into account. However, when using systems with caving which involve considerable mined-out spaces, the geomechanical factor, which determines stability of mine workings, plays a determining role. The research objective is to reveal the dependence between the stability of the development and face-entry headings within the mined-out space influence zone and the excavation sequence of the isolated ore block under conditions of high stress and low ore and rock mass strength. Methods of research. Numerical modeling of the enclosing ore and rock mass secondary stressstrain state formation was carried out by the finite element method in the Rocscience RS3 program together with the original FEM software package. Modeling was performed for two variants of block excavation – from the center to the flanks and from one flank to the other along the strike. For the analysis, we proposed a coefficient representing the product of compressive stress concentration zones length by their existence duration. Results. Based on the analysis of the maximum stress concentration areas distribution in the marginal rock mass, as well as the time of their influence, the optimal sequence of actual mining was substantiated according to the factor of influence on bottom workings stress-strain state – from flank to flank along the strike. Conclusions. The obtained result confirms the model representations about the mechanism of rock mass stressed redistribution in the process of lens-shaped deposit excavation. The representations suggest that during mined-out space development along the strike, compressive stresses concentrate at its ends. However, the intensity of end sections expansion in the flank to flank variant is two times as high as in the center to flank variant. The duration of the stress concentration zones impact on the bottom workings is therefore less, which is indicated by the proposed coefficient.

Impact of Foliar Spraying by Using Some Stimulative Substances on Growth, Green Pods, Dry Seed Yield, Its Components and Some Chemical Constituents of Pea Plants (Pisum sativum L.) under High Temperature Stress Conditions

This experiment was carried out during the two winter seasons of 2020/2021 and 2021/2022 at Qaha Vegetable Research Farm (Qalubia Governorate), Horticulture Research Institute, Agriculture Research Center (A. R. C.), Egypt. The objectives of this study were to investigate the effect of foliar spraying with some stimulative substances i.e. Green Miracle at the rate of 3 cm3 / L, Kaolin (Aluminum silicate) at the rate of 20 g/ L, Selenium element at the rate of 12 mg /L, Megacal Hort at the rate of 2.5 cm3/L, Super Grow Hortic at the rate of 0.75 cm3 /L and High Harvest at the rate of 0.75 cm3/L beside the control treatment (spraying with tap water) on vegetative growth, green pods, dry seed yield and its components as well as seed quality of pea Master B cv. under high temperature stress conditions. The experimental design was a randomized complete block containing seven treatments with three replicates. Seeds of peas were sown in the 2nd week of September during the two winter growing seasons.
 The results showed that, the most estimated parameters were significantly affected with all tested treatments as foliar applications; the superiority effect of the treatments was recorded by using kaolin (Aluminum silicate) followed by selenium element and green miracle which led to obtain the highest significant increase in all the previous studied traits i.e. the vegetative growth, green pods yield, dry seed yield and its components as well as seed quality under high temperature stress conditions. The superior treatment; kaolin at the rate of 20 g/ L increased green pod yield by 36.8 and 33.6 % and enhanced dry seed yield /fed by 34.2 and 32.3 % over the control treatment (the untreated plants) in the two winter seasons, respectively.

Ductile–brittle quantitative evaluation of rock based on post-peak properties under true triaxial stress

To quantitatively evaluate the influence of high true three-dimensional stresses on the ductile–brittle behaviours of rock in deep underground engineering, a series of true triaxial compression tests with different stress levels were carried out on marble and four kinds of granite. The influences of true triaxial stress states (σ2, σ3) on the post-peak characteristics were analysed, and a new normalized ductile–brittle evaluation index was proposed based on post-peak energy conversion characteristics of rock under true triaxial stresses. The ductile–brittle behaviours of rock were divided into four qualitative levels, namely, ductile-brittleness, transitional, brittleness and super-brittleness, and the influences of true triaxial stress states on the ductile–brittle behaviours of rock were quantitatively investigated. The research shows that as σ2 increases or σ3 decreases (that is, the differential stress between σ2 and σ3 increases), the brittleness of rock increases, and its increase rate gradually decreases and tends to be stable, transforming from ductile-brittleness to transitional, brittleness and super-brittleness and resulting in super-brittleness being easily induced by low-σ3 and high-σ2 conditions. When the differential stress between σ2 and σ3 is small, the intrinsic characteristics of rock itself have an obvious influence on ductile–brittle behaviours. When the differential stress between σ2 and σ3 is large, all kinds of rocks can exhibit super-brittle behaviour. The change of stress controls the evolution of rock ductile–brittle behaviours, and high-stress controls rock brittleness. The rock brittleness under true triaxial stress is significantly higher than that under conventional triaxial stress at the same σ3. σ2 induces an increase in rock brittleness and causes the decay rate of brittleness to decrease with increasing σ3, and σ2 increases the upper limit of σ3 for brittle failure of rock. The enhancement effect of σ2 on rock brittleness must be considered when evaluating the brittle failure of deep surrounding rock under high-stress conditions; otherwise, the risk of brittle failure may be underestimated.

Numerical simulation of geothermal energy production from hot dry rocks under the interplay between the heterogeneous fracture and stimulated reservoir volume

Efficient development of hot dry rock (HDR) relies on a thorough assessment of the extraction potential. Stimulated reservoir volumes (SRV) and hydraulic fractures are the primary sites for water circulation and heat exchange in the heat mining process, and thus are crucial to HDR development. The objective of this study is to investigate the heat extraction performance of HDR reservoir under the interplay between the heterogeneous fracture and SRV, which can enhance the thorough understanding of the heat extraction process of stochastic HDR reservoirs and contribute to optimizing the design of the HDR development. A series of 3D thermal-hydraulic-mechanical coupling models with different permeability distributions were established innovatively. Results indicated that the homogeneous reservoir with a 35-year operation time yields an outlet temperature ranging from 161 to 131.8 °C, a thermal breakthrough time of 18 years, a production thermal power between 14.5 and 10.5 MW, and a maximum heat extraction ratio of 32%. Spatial heterogeneity in the fracture permeability significantly impacted the reservoir productivity by creating preferential flow channels. Introducing heterogeneity with a variance of 1 and correlation length of 60 m resulted in a reduction of 4.4 °C in the outlet temperature, 1 year in thermal breakthrough time, 0.6 MW in production thermal power, and 1% in heat extraction ratio compared to homogeneous reservoirs. Moreover, the heterogeneous permeability in SRV further decreased heat mining capability, with a reduction of approximately 14.8 °C, 10 years, 1.9 MW, and 5.17% observed when incorporating SRV heterogeneity (variance of 2 and correlation length of 120 m) into the reservoir already subjected to heterogeneous fracture. This study also provided valuable insights into how stress conditions affect the performance of a reservoir with the heterogeneous fracture and SRV. The results pointed out that applying in situ stress lowered reservoir attenuation rate and allowed for greater heat extraction compared to the reservoir without in situ stress. This can be attributed to the less dispersed fracture permeability occurring under in-situ stress, which caused by the reduced sensitivity of permeability to stress under high-stress conditions. Results also demonstrated that the thermal breakthrough time is the most sensitive performance metric to the variations of the fracture and SRV permeability, followed by the output thermal power, heat extraction ratio, and finally the produced temperature.

Drawing in a Circle: Therapeutic Benefits on Anxiety in High and Low Stress Conditions

Prior research suggests that creating art can reduce mental health symptoms, such as anxiety. It has also been proposed that creating art within the geometric shape of a circle may confer additional therapeutic benefits. However, it remains unclear whether creating art within a circle or creating art with no restrictions reduces anxiety in both low and/or high stress conditions. A total of 158 students participated in an experimental 2 (high stress/low stress) x 3 (draw within a circle, draw freeform, and control) between-subjects design. Anxiety levels significantly decreased across all three conditions after a stressor, but only the drawing conditions decreased anxiety below baseline levels. Results suggest that drawing within a circle and drawing freeform both reduce anxiety following a stressor.

Failure Mechanism and Control Countermeasures for Argillaceous Surrounding Rock of Horsehead Roadway under High Stress.

The argillaceous surrounding rock of a horsehead roadway under high stress conditions is prone to deformation and failure, and the control of its long-term stability is difficult. Based on the engineering practices that control the argillaceous surrounding rock of a horsehead roadway in the return air shaft in the Libi Coal Mine in Shanxi Province, field measurements, laboratory experimentation, numerical simulation, and industrial tests are used to analyze the main influencing factors and mechanism of the deformation and failure of the surrounding rock of the horsehead roadway. We propose principles and countermeasures to control the stability of the horsehead roadway. The main factors of the surrounding rock failure of the horsehead roadway include the poor lithology of argillaceous surrounding rocks, horizontal tectonic stress, the superimposed influence of additional stress from the shaft and construction disturbance, the small thickness of the anchorage layer in the roof, and the insufficient depth of floor reinforcement. The results show that the shaft's presence increases the horizontal stress peak and stress concentration range in the roof, and the plastic zone range. The stress concentration and plastic zones and deformations of the surrounding rock increase significantly with the increase in horizontal tectonic stress. The control principles for the argillaceous surrounding rock of the horsehead roadway include increasing the thickness of the anchorage ring, the floor reinforcement exceeding the minimum depth, and reinforced support in key positions. The key control countermeasures include an innovative prestressed full-length anchorage for the mudstone roof, active and passive reinforcement technology with cables, and a reverse arch for floor reinforcement. The field measurements show that the control of the surrounding rock using the prestressed full-length anchorage of the innovative anchor-grouting device is remarkable.

Experiment on deformation and failure characteristics of sandstone at different unloading rates

The unloading effect is an important factor for the failure of surrounding rock in deep underground engineering projects, especially under high-stress conditions. To investigate the deformation and failure characteristics of sandstone at different unloading rates, the evolution law of the surrounding rock stress caused by excavation was clarified. Then, the single-side unloading test of surrounding rock at different unloading rates was conducted using a true triaxial rock mechanics test system. During the test, the acoustic emission (AE) signals were monitored using an AE monitoring system. The test results show that excavation disturbance leads to complete single-side unloading at the boundary of the surrounding rock, and partial single-side unloading occurs as the depth of the surrounding rock increases. The ultimate strength of the sandstone specimen decreases as a power function with the increasing unloading rate. The unloading rock mass is mainly subject to shear failure. However, the increasing unloading rate raises the proportion of tension cracks. The sudden high strain rate on the unloading side can be used as precursor information of rock fracture, which can effectively prevent accidents caused by loss of rock bearing capacity. The AE signal is active and releases less energy in the unloading stage. At this time, the internal fractures are in the development stage, and the energy is still mainly accumulated. The unloading and failure are not synchronized but suffer from the hysteresis effect. Additionally, the AE and the strain rate change on the unloading side are consistent. Due to the hysteresis effect of damage on unloading, anchor bolts (cables) should be installed to support the surrounding rock immediately to compensate for the stress loss caused by excavation in engineering practice.

The psychological effects of sports disruptions in NCAA Division I and II athletes during the COVID-19 pandemic: a mixed methods analysis.

Improving mental health outcomes in college athletics requires better understanding of how student-athletes respond to stress-inducing events. Using a cross-sectional design, this study aimed to assess student-athletes' mental health status during the COVID-19 pandemic. Eligible participants (N.=489) included Division I and II student-athletes at least 18 years of age with plans to compete in the 2020-2021 sport season. Participants completed an online battery of psychological health surveys. Survey results suggested high psychological strain (APSQ: 20.58±8.08), mild symptoms of anxiety (GAD-7: 7.66±5.51) and depression (PHQ-9: 7.51±5.65), and burnout (ABQ: 2.37±0.96). A subset of student-athletes reported symptoms of psychological strain, depression, and anxiety warranting follow-up clinical evaluation and/or treatment according to scoring guidelines. Findings encourage psychological screening, particularly during sport-disrupting events, to better support athletes' mental health during high-stress conditions.

Effects of Hydrodynamic Environment on the Interaction of Shewanella oneidensis with Low Carbon Steel and the Impacts on Corrosion

Microbiologically influenced corrosion (MIC) impacts various industries such as oil/gas production and transmission, wastewater treatment, power generation, and chemical processing. In such settings, the combined impacts of microbiological activities and fluid flow dynamics could be primary controllers of metal corrosion. We examined the relative influences of fluid flow and the activities of the facultative Fe(III) reducing bacterium, Shewanella oneidensis MR-1, on the corrosion of carbon steel. Rotating cylinder electrode experiments were used to determine the shear stress and velocity at the surface of the metal coupon in a newly constructed flow system. The system was then used to study the impact of increasing fluid velocity and shear stress on the corrosion rate of coupons in O2-limited and O2-nonlimited incubations. Confocal scanning laser microscopy was used to monitor biofilm development on the metal surface at increasing shear stress. We found that the activities of S. oneidensis inhibited corrosion, even under conditions of high shear stress and limited attachment, indicating that the respiratory consumption of O2 by planktonic S. oneidensis protects the metal surface from enhanced corrosion.

Anisotropic time-dependent behaviors of shale under direct shearing and associated empirical creep models

Understanding the anisotropic creep behaviors of shale under direct shearing is a challenging issue. In this context, we conducted shear-creep and steady-creep tests on shale with five bedding orientations (i.e. 0°, 30°, 45°, 60°, and 90°), under multiple levels of direct shearing for the first time. The results show that the anisotropic creep of shale exhibits a significant stress-dependent behavior. Under a low shear stress, the creep compliance of shale increases linearly with the logarithm of time at all bedding orientations, and the increase depends on the bedding orientation and creep time. Under high shear stress conditions, the creep compliance of shale is minimal when the bedding orientation is 0°, and the steady-creep rate of shale increases significantly with increasing bedding orientations of 30°, 45°, 60°, and 90°. The stress-strain values corresponding to the inception of the accelerated creep stage show an increasing and then decreasing trend with the bedding orientation. A semilogarithmic model that could reflect the stress dependence of the steady-creep rate while considering the hardening and damage process is proposed. The model minimizes the deviation of the calculated steady-state creep rate from the observed value and reveals the behavior of the bedding orientation's influence on the steady-creep rate. The applicability of the five classical empirical creep models is quantitatively evaluated. It shows that the logarithmic model can well explain the experimental creep strain and creep rate, and it can accurately predict long-term shear creep deformation. Based on an improved logarithmic model, the variations in creep parameters with shear stress and bedding orientations are discussed. With abovementioned findings, a mathematical method for constructing an anisotropic shear creep model of shale is proposed, which can characterize the nonlinear dependence of the anisotropic shear creep behavior of shale on the bedding orientation.