Strength Criterion Research Articles

An improved three-dimensional extension of Hoek–Brown criterion for rocks

The Hoek–Brown (H–B) criterion has found widespread application in numerous rock engineering projects. However, its efficacy is compromised by an underestimation of rock strength due to its neglect of the influence of the intermediate principal stress (σ2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sigma_{2}$$\\end{document}). Experimental evidence underscores the significant impact of σ2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sigma_{2}$$\\end{document}. Consequently, there exists an imperative to formulate a three-dimensional (3D) criterion. In this study, a new deviatoric function with two additional parameters (k\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$k$$\\end{document} and A\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$A$$\\end{document}) is developed firstly, which ensure compliance with the prerequisites of smoothness and convexity. In addition, the parameters k\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$k$$\\end{document} and A\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$A$$\\end{document} are bonded with the weakening effect of the Lode angle (θσ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ heta_{\\sigma }$$\\end{document}) and the strengthening effect of the mean stress (σm\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sigma_{m}$$\\end{document}), respectively. Then a new 3D strength criterion for rocks is proposed by combining this new deviatoric function and the triaxial compression meridian function of the original H–B criterion. Four distinct sets of test data encompassing various rock types are employed to validate the proposed criterion. The results demonstrate that the proposed criterion adeptly captures the strength characteristics of the four rock types, providing a good depiction of failure surfaces within the 3D principal stress space. Comparative analyses involve the utilization of several existing 3D H–B criteria for strength predictions. The proposed criterion exhibits superior fitting performance for all the selected rocks.

Determination of Residual Stresses in 3D-Printed Polymer Parts.

This paper presents the results of an investigation of the possibility of the reliable determination of the residual stress-strain state in polymers and composites using a combination of bridge curvature, optical scanning, and finite element methods. A three-factor experiment was conducted to determine the strength of printed PLA plastic products. The effect of the residual stresses on the strength of the printed products was evaluated. By comparing the values of the same strength stresses, a relationship between the nature of the stresses and the strength of the samples was found. A tendency of the negative influence of tensile stresses and the opposite strengthening effect of compressive stresses was obvious, so at the same values of tensile strength, the value of residual stress of 42.9 MPa is lower than that of the fibre compression at the value of 88.9 MPa. The proposed new methods of the residual stress determination allow obtaining a complete picture of the stressed state of the material in the investigated areas of the products. This may be necessary in confirming the calculated models of the residual stress-strain state, clarifying the strength criteria and assessing the quality of the selected technological modes of manufacturing the products.

Integrated approach of predicting rock stability in high mountain valley underground caverns

High mountain valleys are characterized by the development of intricate ground stress fields due to geological processes such as tectonic stress, river erosion, and rock weathering. These processes introduce considerable stability concerns in the surrounding rock formations for underground engineering projects in these regions, highlighting the imperative need for rigorous stability assessments during the design phase to ensure construction safety. This paper introduces an innovative approach for the pre-evaluation of the stability of surrounding rocks in underground caverns situated within high mountain valleys. The methodology comprises several pivotal steps. Initially, we conduct inverse calculations of the ground stress field in complex geological terrains, combining field monitoring and numerical simulations. Subsequently, we ascertain stress-strength ratios of the surrounding rocks using various rock strength criteria. To assess the stability characteristics of the surrounding rocks in the 1# spillway cave within our project area, we employ numerical simulations to compute stress-strength ratios based on different rock strength criteria. Furthermore, we undertake a comparative analysis, utilizing data from the 5# Underground Laboratory (Lab 5) of Jinping II Hydropower Station, aligning the chosen rock strength criterion with the damage characteristics of Lab 5′s surrounding rocks. This analysis serves as the cornerstone for evaluating other mechanical responses of the surrounding rocks, thereby validating the pre-evaluation methodology. Our pre-evaluation method takes into account the intricate geological evolution processes specific to high mountain valleys. It also considers the influence of the initial geostress field within the geological range of underground caverns. This comprehensive approach provides a robust foundation for the analysis and assessment of the stability of surrounding rocks, especially in high mountain valley areas, during the design phase of underground engineering projects. The insights derived from this analysis hold substantial practical significance for the effective guidance of such projects.

Investigation of the Mechanical Strength of Artificial Metallic Mandibles with Lattice Structure for Mandibular Reconstruction.

Mandibular reconstructive surgery is necessary for large bone defects. Although various reconstruction methods have been performed clinically, there is no mandibular reconstruction method that meets both sufficient strength criteria and the patient's specific morphology. In this study, the material strength of the cylindrical lattice structures formed by electron-beam melting additive manufacturing using titanium alloy powder was investigated for mandibular reconstruction. The virtual strengths of 28 lattice structures were compared using numerical material tests with finite element method software. Subsequently, to compare the material properties of the selected structures from the preliminary tests, compression test, static bending test and fatigue test were conducted. The results showed that there were correlations with relative density and significant differences among the various structures when comparing internal stress with deformation, although there was a possibility of localized stress concentration and non-uniform stress distribution based on the lattice structure characteristics. These results suggest that the lattice structure of body diagonals with nodes and a cell size of 3.0 mm is a potential candidate for metallic artificial mandibles in mandibular reconstruction surgery.

Mechanical Properties of Rock Salt from the Kłodawa Salt Dome-A Statistical Analysis of Geomechanical Data.

Rock salt is a potential medium for underground storage of energy resources and radioactive substances due to its physical and mechanical properties, distinguishing it from other rock media. Designing storage facilities that ensure stability, tightness, and safety requires understanding the geomechanical properties of rock salt. Despite numerous research efforts on the behaviour of rock salt mass, many cases still show unfavourable phenomena occurring within it. Therefore, the formulation of strength criteria in a three-dimensional stress state and the prediction of deformation processes significantly impact the functionality of storage in salt caverns. This article presents rock salt's mechanical properties from the Kłodawa salt dome and a statistical analysis of the determined geomechanical data. The analysis is divided into individual mining fields (Fields 1-6). The analysis of numerical parameter values obtained in uniaxial compression tests for rock salt from mining Fields 1-6 indicates an average variation in their strength and deformation properties. Upon comparing the results of Young's modulus (E) with uniaxial compressive strength (UCS), its value was observed with a decrease in uniaxial compressive strength (E = 4.19968·UCS2, R-square = -0.61). The tensile strength of rock salt from mining Fields 1-6 also exhibits moderate variability. An increasing trend in tensile strength was observed with increased bulk density (σt = 0.0027697·ρ - 4.5892, r = 0.60). However, the results of triaxial tests indicated that within the entire range of normal stresses, the process of increasing maximum shear stresses occurs linearly ((σ1 - σ3)/2 = ((σ1 + σ3)/2)·0.610676 + 2.28335, r = 0.92). A linear relationship was also obtained for failure stresses as a function of radial stresses (σ1 = σ3·2.51861 + 32.9488, r = 0.73). Based on the results, the most homogeneous rock salt was from Field 2 and Field 6, while the most variable rock salt was from Field 3.

Knee flexor strength at 6 months after anterior cruciate ligament reconstruction using hamstring tendon can be predicted from that at 3 months.

This study aimed to identify factors influencing persistent muscle weakness in knee flexor strength after anterior cruciate ligament (ACL) reconstruction using the hamstring tendon and establish a clear cut-off value at 3 months postoperatively for the limb symmetry index (LSI) to exceed 90% at 6 months postoperatively. One hundred forty-eight patients undergoing ACL reconstruction were included and categorised into two groups based on knee flexor strength at 6 months postoperatively: patients with LSI of 90% or greater (achieved group: n = 114) and patients with LSI less than 85% (nonachieved group: n = 34). Items with significant differences between the two groups (preoperative waiting period, LSI to body weight ratio of knee flexor and extensor strength at 3 months postoperativelyand peak torque angle of knee flexor muscle) were included in the multiple logistic regression analysis. Additionally, a receiver operating characteristic curve was used to calculate the cut-off value of the LSI at 3 months postoperatively, which was required to achieve the LSI criteria for knee flexor strength 6 months postoperatively. Multiple logistic regression analysis extracted the preoperative waiting period and LSI for knee flexor strength at 3 months postoperatively. The cut-off value at 3 months postoperatively was 76.9% (area under the curve value, 0.82; sensitivity, 0.76; and specificity, 0.81) of the LSI. The LSI of at least 76.9% for knee flexor strength at 3 months after ACL reconstruction was an indicator for achieving the 6 months postoperatively. This is a criterion to aim for, considering the stress on the graft and the regeneration process of the semitendinosus tendon. Level III.

Dietary Intake, Menopausal Symptoms, and Body Composition Associated with Possible Sarcopenia Among Vietnamese Middle-Aged Women: A Cross-Sectional Study.

Background: This study aims to investigate the prevalence of possible sarcopenia and its associated factors among middle-aged Vietnamese women. Methods: A cross-sectional study was conducted on 205 women aged 40-55 years who were admitted to the Can Tho Obstetrics and Gynecology Hospital between February and December 2023. The presence of possible sarcopenia was determined according to the AWGS 2019 criteria. Associated factors were dietary intake (total energy, protein, lipid, and carbohydrate intake), the severity of menopausal symptoms by using the Kupperman index, and body composition by using the bioelectrical impedance analysis device, Inbody S10. Logistic regressions were built to analyze the association between possible sarcopenia and its associated factors. Results: The prevalence of possible sarcopenia was 29.8%, with a mean age of 47.2. Possible sarcopenia was detected in 23% of the participants based on the criterion of low handgrip strength, whereas 83.6% of the participants when considered low performance in the chair stand test. Adjusted logistic regression analysis showed that living in a rural area (adjusted odds ratio [AOR]: 2.16, 95% confidence interval [95% CI]: 1.22-4.72), energy intake <25 kcal/body weight, (AOR: 1.94, 95% CI: 1.75-5.06), protein intake <0.91 g/body weight (AOR: 2.42, 95% CI: 1.51-5.76), skipping breakfast (AOR: 2.03, 95% CI: 0.91-4.54), mild menopausal symptoms (AOR: 2.68, 95% CI: 1.61-5.36), and obesity (AOR: 1.59, 95%CI: 1.29-3.67) were significantly associated with higher risk of possible sarcopenia. Conversely, higher muscle mass and higher upper limb mass were associated with a decreased risk of possible sarcopenia (total muscle mass AOR: 0.20, 95% CI: 0.07-0.59). Conclusions: These findings would provide a basis for enhancing management and prevention strategies to reduce the risk of sarcopenia in Vietnam. In particular, attention to nutrient intake and the management of menopausal symptoms may reduce the risk of sarcopenia.

Machine Learning-Based Identification of Diagnostic Biomarkers for Korean Male Sarcopenia Through Integrative DNA Methylation and Methylation Risk Score: From the Korean Genomic Epidemiology Study (KoGES).

Sarcopenia, characterized by a progressive decline in muscle mass, strength, and function, is primarily attributable to aging. DNA methylation, influenced by both genetic predispositions and environmental exposures, plays a significant role in sarcopenia occurrence. This study employed machine learning (ML) methods to identify differentially methylated probes (DMPs) capable of diagnosing sarcopenia in middle-aged individuals. We also investigated the relationship between muscle strength, muscle mass, age, and sarcopenia risk as reflected in methylation profiles. Data from 509 male participants in the urban cohort of the Korean Genome Epidemiology Study_Health Examinee study were categorized into quartile groups based on the sarcopenia criteria for appendicular skeletal muscle index (ASMI) and handgrip strength (HG). To identify diagnostic biomarkers for sarcopenia, we used recursive feature elimination with cross validation (RFECV), to pinpoint DMPs significantly associated with sarcopenia. An ensemble model, leveraging majority voting, was utilized for evaluation. Furthermore, a methylation risk score (MRS) was calculated, and its correlation with muscle strength, function, and age was assessed using likelihood ratio analysis and multinomial logistic regression. Participants were classified into two groups based on quartile thresholds: sarcopenia (n = 37) with ASMI and HG in the lowest quartile, and normal ranges (n = 48) in the highest. In total, 238 DMPs were identified and eight probes were selected using RFECV. These DMPs were used to build an ensemble model with robust diagnostic capabilities for sarcopenia, as evidenced by an area under the receiver operating characteristic curve of 0.94. Based on eight probes, the MRS was calculated and then validated by analyzing age, HG, and ASMI among the control group (n = 424). Age was positively correlated with high MRS (coefficient, 1.2494; odds ratio [OR], 3.4882), whereas ASMI and HG were negatively correlated with high MRS (ASMI coefficient, -0.4275; OR, 0.6521; HG coefficient, -0.3116; OR, 0.7323). Overall, this study identified key epigenetic markers of sarcopenia in Korean males and developed a ML model with high diagnostic accuracy for sarcopenia. The MRS also revealed significant correlations between these markers and age, HG, and ASMI. These findings suggest that both diagnostic models and the MRS can play an important role in managing sarcopenia in middle-aged populations.

Experimental investigation on mechanical behavior of natural soft clay by true triaxial tests

Laboratory tests on undisturbed and remolded Shanghai clay were conducted with a novel mixed boundary true triaxial apparatus. The strength and deformation behaviors of the structured soft clay at different Lode angles were carefully investigated. The relationship between the shear stress ratio and the dilatancy ratio of the clay in three different stress spaces, that is p–q space, TS stress space and tij modified stress space, are discussed in detail. In particular, the influences of the stress path and the structure of non–disturbed clay on the strength, deformation and failure criterion of Shanghai clay were quantitatively evaluated. The shear strength and dilatancy of undisturbed /remolded clay decreases with the increase of the Lode angle. It is also found that the shear strength and dilatancy of the undisturbed clay are larger than those of the remolded clay; while the influence of the structure on the dilatancy decreases with an increase in the Lode angle. In the π–plane, the maximum strength of Shanghai clay under different stress paths generally obeys the SMP failure criterion. The coincidence of the stress–dilatancy relationship given by the TS and tij stress spaces with the test results is much better than that given by p–q stress space. Furthermore, the linearity of the plastic potential curves of the undisturbed/remolded clay is more evident in tij stress space.

Multi‐material topology optimization considering arbitrary strength and yield criteria constraints with single‐variable interpolation

AbstractMaterial heterogeneity gives composite constructions unique mechanical and physical qualities. Combining multiple materials takes full use of these features in stress‐constrained topology optimization. Traditional research in this field often assumes a consistent yield criterion for all possible materials but adapts their stiffness and strengths accordingly. To cope with this challenge, an innovative single‐variable interpolation approach is proposed to enable the simultaneous inclusion of distinct yield criteria and material strengths. A stress‐constrained topology optimization formulation is presented based on this yield function interpolation method, which can independently support various materials with different elastic characteristics, material strengths, and yield criteria. Then, the large‐scale problem of local stress constraints can be effectively solved by the Augmented Lagrangian (AL) method. Several two‐dimensional (2D) and three‐dimensional (3D) design scenarios are investigated to reduce the overall mass of the structure while considering stress constraints. The optimal composite designs exhibit several crucial benefits resulting from material heterogeneity, including the enlargement of the design possibilities, the dispersion of stress, and the utilization of asymmetry in tension‐compression strength.

Study on the differences between Hoek–Brown parameters and equivalent Mohr–Coulomb parameters in the calculation slope critical acceleration and permanent displacement

Mohr–Coulomb (MC) strength criterion has been widely used in many classical analytical expressions and numerical modeling due to its simple physical calculation, but the MC criterion is not suitable for describing the failure envelope of rock masses. In order to directly apply MC parameters to analytical expressions or numerical modeling in rock slope stability analysis, scholars established a criterion for converting Hoek–Brown (HB) parameters to equivalent MC parameters. However, the consistency of HB parameters and equivalent MC parameters in calculating critical acceleration of slope needs to be further explored and confirmed. Therefore, HB parameters are converted into equivalent MC parameters by considering the influence of slope angle (1# case and 2# case when slope angle is not considered and slope angle is considered respectively). Then, the lower-bound of finite element limit analysis is used for numerical modeling, and the results of calculating critical acceleration using HB parameters and equivalent MC parameters are compared, and the influence of related parameters on the calculation of critical acceleration is studied. Finally, the influence of different critical accelerations on the calculation of slope permanent displacement is further analyzed through numerical cases and engineering examples. The results show that: (1) In the 1# case, the critical acceleration obtained by the equivalent MC parameters are significantly larger than that obtained by the 2 #case and the HB parameters, and this difference becomes more obvious with the increase of slope angle. The critical acceleration obtained by the 2# case is very close to the HB parameters; (2) In the 1# case, slope height is inversely proportional to ΔAc (HB(Ac) − 1#(Ac)), and with the increase of slope height, ΔAc decreases, while in the 2# case, the difference of ΔAc (HB(Ac) − 2#(Ac)) is not significant; (3) In the 1# case, the sensitivity of the HB parameters to ΔAc is D > GSI > mi > σci, but in the 2# case, there is no sensitivity-related regularity; (4) The application of HB parameters and equivalent MC parameters in slope permanent displacement is studied through numerical cases and engineering examples, and the limitations of equivalent MC parameters in rock slope stability evaluation are revealed.

Study on the preparation of two-component structural acrylate adhesive with high performance and low odor

ABSTRACT This article describes the preparation of structural acrylic adhesives (SAA) with low odor and high strength. Isobornyl methacrylate and methacrylic acid were used as the main monomers. Cumene hydroperoxide was used as a radical polymerization initiator. The effects of tougheners, coupling agents, elastomers, monomers, and peroxide on the performance of acrylic adhesives were studied sequentially. The toughness of acrylic structural adhesives was discovered to be enhanced by the addition of carboxyl-terminated butadiene-acrylonitrile liquid rubber (CTBN) to the acrylic matrix. Coupling agents were added to improve SAA’s ability to adhere to steel. The results demonstrated that the SAA performs best when the methacrylic acid’s content is 7 wt%, cumene hydroperoxide’s content is about 1.5 wt%, CTBN’s content is 3 wt%, and the coupling agent’s content is 1 wt%. Adhesive modified using 2-hydroxyethylmethacrylate phosphate and CTBN as the toughener provided excellent adhesion to the steel substrate. Its lap shear strength was found to be above 24 MPa, its T-peel strength was up to 8.29 N/mm, and its impact strength was up to 12 kJ/m2. The resulting SAA is capable of meeting structural adhesive bonding strength criteria for steel-to-steel joints.

Partial Replacment of LDPE in Bituminous Pavement

Bituminous concrete mix is a composite material which is widely used for the construction of flexible pavements, surfacing of roads and airports, various parking lots etc. It generally consists of bitumen which works as a binder material, coarse aggregates, fine aggregates and filler materials which are generally mixed together in right proportion and laid down in layers followed by the compaction. In this present age of modernization and urbanization, construction is non stoppable and the construction by demolishing of old building has arisen a serious problem of treatment of demolished waste. Similarly, the use of plastic in our day-to-day life and its improper disposal is also creating serious environment pollution. So, there is big challenge in managing the demolished waste as well as the waste plastics. In this project i.e. partial replacement of LDPE in Bituminous concrete mix we have tried to replace LDPE (2%, 4%, 6% and 8% respectively) in bitumen content for the improvement of the pavement characteristics satisfying both the strength criteria and the economic aspects giving emphasize to less environment degradation and sustainability.

Numerical modelling of the pit wall stability while optimizing its boundaries to ensure the ore mining completeness

Purpose is to assess changes in the stress-strain state of walls along the whole periphery of a super-deep open pit while optimizing its current and final boundaries for the complete ore excavation. Methods. Finite element 3D analysis of stress-strain state (SSS) of the soil and rock mass relies upon the models varying in their scales. Macrolevel model includes the full pit helping perform initial evaluation of its stability depending upon changes in the general wall slope along the pit periphery. Then, the macromodel is separated into sectoral models with smaller scales oriented radially in such a way to include potentially unstable wall areas. The sectoral models make it possible to show the complex bench line in more detail after the peripheries were optimized in terms of economic factor and simulate layered structure of the rock mass. Elastoplastic model of the medium as well as Mohr-Coulomb strength criterion has been implemented using RS3 (Rocscience) program codes. Findings. An indicator of wall strength (safety factor) distribution along the pit periphery has been identified; potential sliding surfaces within each of the separated open pit sectors have been localized based upon the shear strength reduction (SSR) procedure. Influence by the general wall slope as well as by the indicator of the ore excavation completeness on the stripping ratio has been demonstrated. Originality. For the first time, two-level modelling has shown difference in a safety factor depending upon a model scale and a reflection degree of the soil-rock mass structure. In the context of the actual mining and geological conditions of Kacharsky open pit, changes in the safety factor along the pit periphery have been identified depending on the general slope of the wall. Practical implications. Based upon the pit wall stability along the whole periphery, the possibility has been substantiated to optimize its design boundaries for the excavation of those amenable ore reserves, occurred near them, inclusive of ore, occurring in a bottom, which mining is impossible due to inaccessibility.

A Study on Improving the Construction of Tunnel Steel Ribs Using High-Tensile Long Bolts

Steel ribs installed to enhance tunnel stability have consistently been criticized owing to their structural vulnerabilities and on-site construction inconvenience. Therefore, this study aims to address these issues and contribute to safer tunnel construction. To address the structural weaknesses resulting from the reduced steel section at the upper and lower junction parts of the tunnel steel ribs as well as the keystone junction parts, reinforcement was achieved by using long high-tensile bolts and steel bars. Test results on the bending strength of the junction revealed that the upper and lower junction parts exhibited a bending strength 1.38 times higher than those of the general sections of steel ribs, and the keystone junction parts showed a bending strength of 1.70 times higher, meeting or surpassing the equivalent strength criteria. Moreover, by utilizing high-tensile long bolts with adjustable heights, the constructability and construction speed were both enhanced. Consequently, it was determined that construction costs could be reduced by 2.42% and that the construction speed could be improved by approximately 333 h/km.

Stability assessment of jointed rock capturing roughness degradation under cyclic loading with special reference to railway formation

Repeated train loading on a jointed rock subgrade can cause excessive displacements of certain discontinuities leading to instability. Repeated shearing of discontinuities leads to a gradual reduction in joint roughness (i.e. wearing of asperities), which is quantified by the change in the joint roughness coefficient (JRC). This process reduces the joint shear strength over time. In this study, the classical shear strength criterion proposed by Barton and Choubey (1977) is extended to capture the influence of cyclic loading on joint degradation and the corresponding shear strength reduction, also considering the scale effect. This modified cyclic shear strength is implemented in FLAC-3D and validated with conventional cyclic triaxial data available from selected past studies. The model is applied to a simulated real-life track operating over a jointed sandstone formation commonly found towards the eastern coast of NSW. A modified limit equilibrium approach based on an Equivalent Factor of Safety (EFOS) is introduced and adopted to quantify the extent of instability, whereby an increase in the number of loading cycles affects a decrease in the EFOS of an unstable block. For a specific joint strike inclined to the track, the potential adversities are exacerbated when the joint dip angle is greater and when the initial JRC is smaller. In this paper, alternative geometrical combinations and different initial joint properties are considered to determine the worst combination of JRC and joint orientation upon cyclic train loading. As most past studies adhere to traditional static load analyses, the extended shear strength criterion described in this study is novel, and it offers significant practical benefit for railways that are subjected to prolonged cyclic loading.

Theoretical study on 3D elastic response and first layer failure strength of composite cylinders subjected to axisymmetric loadings

The traditional Lekhnitskii 3D elastic theory can obtain the exact stress and strain response of the composite cylinder under the axially symmetric loadings. However, when the cylinder contains 0° winding layers or isotropic layers, some calculation parameters corresponding to the two kinds of special layers will become singular. By analyzing the continuity of singular parameters and calculating their limits, the problem of singular parameters can be effectively solved and the Lekhnitskii theory can be extended to composite thick-walled cylinders with arbitrary winding angles. Furthermore, based on the Chang-Chang strength criterion of composite layers and the ideal elastic-plastic assumption of isotropic metal layers, the theoretical calculation method of first layer failure strength and the corresponding failure modes of the composite cylinders subjected to axisymmetric loadings was proposed. Then, the composite cylinder with metal liner was fabricated by fiber winding process. The experimental blasting pressure of the cylinder was 52.8 MPa with a major failure mode of fiber tensile fracture. Based on the proposed theoretical method, the cylinder's first layer failure strength of internal pressure was 44.1 MPa, and the initial failure mode was also fiber tensile fracture. The predicted result of the first layer failure strength was lower than the experimental results. The result proved the safety and economy of the proposed theoretical method for the initial design of the composite cylinder.

Experimental Study on the Shear Strength of Different Interfaces of Fine-Grained-Tailing-Filled Geotextile Tubes

As damming material, fine-grained tailings present challenges such as low dam strength and poor stability. To address these issues, this study employs geotextile tube technology to mix water with fine-grained tailings, forming a tailing slurry with a concentration of 60%, which is filled into a geotextile bag to form a geotextile tube, so as to improve the stability of fine-grained tailings. The shear strength characteristics of each interface under different consolidation times and different filling degrees were studied via an indoor shear experiment, including the shear strength of tailing particles, that between tailings and geotextiles, and that within geotextile tubes themselves. The results show that the shear strength of each interface conforms to the Mohr–Coulomb strength criterion, and that the interface cohesion is greatly affected by the consolidation time, while the interface friction angle is mainly affected by the filling degree. Moreover, the shear strength comparison, based on the comprehensive friction angle concept, indicates a substantial increase in shear strength at the interfaces between geotextile tubes compared to both that of the tailings themselves and the interface between tailings and geotextiles, highlighting the reinforcing effect of the geotextile tube filling technology on tailings’ shear strength.

The relationship between asymmetrical grip strength criteria and fall incidence among middle-aged and older Chinese adults.

Current handgrip strength (HGS) protocols employ a variety of criteria, affecting the assessment of asymmetric HGS. The impact of these different criteria on fall prediction is understudied. This study was devised to compare the relative performance of average and maximum HGS asymmetry criteria as tools to predict fall incidence among middle-aged or older adults in China. 9627 Chinese adults 50 + years of age who were participants in the China Health and Retirement Longitudinal Study (2013-2015 waves) were evaluated. The measurement of HGS was achieved based on either the maximum recorded value (HGSmax) or the average (HGSave), and these values were employed for the calculation of HGS asymmetry. Fall incidence over a 2-year period was evaluated based on self-reported data. Logistic regression analyses were utilized to determine the predictive performance of HGSmax asymmetry or HGSave asymmetry when gaging 2-year fall risk. Significant differences in overall rates of HGS asymmetry and the rates of subdivisions thereof were observed when comparing the HGSmax and HGSave criteria, with moderate consistency (kappa = 0.599, p < 0.001). Over the 2-year follow-up period, 1743 fall incidents were recorded. Adjusted logistic regression models indicated that only HGSmax asymmetry > 30.0% was significantly related to fall risk (p = 0.034, odds ratio = 1.36, 95% confidence interval: 1.02-1.81). These findings highlight the importance of HGS criteria in detecting HGS asymmetry, and suggest that HGSmax is a more robust criterion for predicting fall risk among Chinese adults 50 + years of age.

Theoretical study on the water-induced weakening of rock based on microstructural mechanics approach

For rock structures exposed in the natural condition, water-induced weakening (including water softening and chemical weathering) is thought to be the main reason for its’ stiffness and strength degradation, thus it is of great significance to study the mechanical properties of rocks under the influence of water. In this study, a hexagonal close-packed particle assembly (2D) composed of bonded circular particles with same diameter is considered to approximate a typical soft rock, where the composite contact model for rock materials considering the water-induced wakening is adopted to define the microscopic mechanical reactions between particles. Based on homogenisation theory and lattice model, the stress-strain relationship and strength criteria for rock considering water-induced weakening, as well as the quantitative correlation between macroscopic elastic and strength parameters with microscopic parameters are obtained. The effects of water softening and chemical weathering respectively characterised by saturation and mass loss ratio on macroscopic mechanical behaviours of rock are analysed in detail. The long-term ageing effects of water-induced weakening are also analysed. All results are in good agreement with the laboratory test results, verifying the applicability of the theoretical solution for analysing the effect of water-induced weakening on mechanical behaviours of rock.