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With the rising demand for hydropower energy, China has built numerous concrete‐faced rockfill dams (CFRDs) with considerable heights. The potential failure pattern of the concrete face slab is the key to the safety of the anti‐seepage system. However, engineers commonly employ an elastic relationship to model the concrete face slab for simplicity, which induces inaccurate estimation of the face slab's stresses, especially under seismic conditions. On the other hand, the existing elastoplastic models for concrete often require complex derivation of the necessary formula and thus are difficult to apply to finite element (FE) analysis. Under the comprehensive action of the upstream water, supporting rockfill, and surrounding mountains, the damage mode of the quasibrittle concrete slab is not a tensile mode but a compressive shearing mode. Therefore, it is urgent to establish an elastoplastic model that is adapted to the actual working environment of the slab and easy to apply. To this end, a generalized plasticity model is developed within the phenomenology modeling concept, which is validated at both the experimental level and application level. The results indicate that three‐dimensional stress‒strain behaviors, such as the strength nonlinearity, prepeak dilatancy, and postpeak softening, can be effectively captured. In addition, the seismic characteristics of a 200‐m high CFRD are numerically investigated. The findings show that the slab's stress accumulation can be reflected during the earthquake and that the final stress distribution conforms to the field observations. The conclusions of this paper provide a reliable reference for the seismic resistance design of CFRDs. [ABSTRACT FROM AUTHOR]

Marine soft clays are prevalent in coastal regions of China, giving rise to engineering challenges such as salt swelling, corrosion, and load bearing in foundations with soft soil. This study is dedicated to enhancing the mechanical properties of fiber-reinforced cement-stabilized soft clay (FCSSC) and revealing its strengthening mechanism. Uniaxial compression tests are performed to explore the impact of fiber length, fiber amount, and curing ages on mechanical behavior. The stabilization mechanisms of cement and glass fibers are explored through damage analyses and microscopy. Based on the experimental results, a damage constitutive model is formulated for FCSSC, and its validity is established by comparing fitting curves with testing curves. The results demonstrate a significant improvement in the mechanical properties of the stabilized soil, attributed to the synergistic effects of the cement and glass fibers. The growth rate of the unconfined compressive strength decreased with increasing curing ages. Notably, the fiber length significantly impacted the strength index, with short-chopped fibers playing a crucial role in strength enhancement. The compressive strength exhibited an initial increase followed by a decrease with rising fiber content, reaching a maximum between 0.3% and 0.4%. The bridging effect of the glass fibers proved effective in inhibiting compression crack expansion and mitigating structural damage of the soil sample. However, excessive fiber content or length led to improved local porosity, resulting in the deterioration of strength and deformation properties. The stress–strain curves fitted using the proposed damage constitutive model accurately reflected the stress–strain relationship and deformation characteristics of the FCSSC. [ABSTRACT FROM AUTHOR]

A combined support scheme was proposed to address the issue of large deformation in the deep soft rock roadway at the Tangkou coal mine in Shanxi Province, China. This support scheme includes high constant resistance, elongation, and prestressed negative Poisson's ratio (NPR) bolts as the core element, along with metal mesh, shotcrete, cable, and bottom angle grouting bolt. A numerical simulation test using Flac3D was conducted to verify the feasibility of the NPR bolt-anchored soft rock roadway. In addition, a constitutive model for a rock mass supported by NPR bolts was established. The model is based on a parallel model of a generalised Kelvin body and elastic–viscous sliding body, which was used to reveal the mechanical behaviour of an NPR bolt-anchored rock mass. The results showed that the stress–strain relationship of the NPR bolt-anchored rock mass was obtained as a piecewise function consisting of the initial, slipping, and sticking stages. The stress and strain of the NPR bolt-anchored rock mass exhibit distinct patterns under different stress conditions. Specifically, when the stress remains constant, the strain of the NPR bolt-anchored rock mass increases continuously while the stress decreases in a step-like manner. On the other hand, when the stress increases linearly with time, the strain of the anchored rock mass increases linearly, while the stress of the anchorage rock mass increases slowly in a sawtooth pattern. Furthermore, a field support test fully confirmed the effective control of the NPR bolt support on the large deformations of soft rock roadways. These findings can guide further theoretical research, engineering design, and field applications of NPR bolt-anchored rock masses. Highlights: A new combined support scheme is proposed using the NPR bolt as the core. The mechanical behaviour of an NPR bolt-anchored rock mass is revealed. Both numerical simulations and field tests demonstrated that the combined support scheme effectively controls the large deformations of soft rock roadways. [ABSTRACT FROM AUTHOR]

Granite is the main host rock for the underground storage of nuclear waste in Beishan, China. Heat is continuously generated during the long-term disposal of nuclear waste; therefore, it is important to investigate the influence of high temperature on the physical and mechanical properties and the constitutive relation of Beishan granite. In this study, laboratory experiments on heat-treated (25 ∘ C, 200 ∘ C, 400 ∘ C, 600 ∘ C and 800 ∘ C) Beishan granite samples were performed in combination with nuclear magnetic resonance (NMR) analysis and regular physical-mechanical tests. The results show that the elastic modulus tends to decline faster at the temperature ranges of 25–200 ∘ C and 600–800 ∘ C by approximately 26.767% and 66.996%, respectively. Compared with the results at 25 ∘ C, the peak stress decreases by 72.664% at 800 ∘ C. The peak strain increases gradually from 25 ∘ C to 600 ∘ C and abruptly from 600 ∘ C to 800 ∘ C. The peak strain at 800 ∘ C is 2.303× greater than that at 25 ∘ C. Based on the damage theory, the Weibull distribution, the rock damage threshold point, and the residual strength, this study corrected the Drucker–Prager (D–P) criterion to consider the damage stress and then to establish the constitutive model of thermally damaged Beishan granite. The parameters required for the model are conventional mechanical parameters that can be calculated from the uniaxial test results, thus making the model convenient to apply. Meanwhile, the mechanical behavior of thermally damaged Beishan granite under uniaxial compression was simulated using the Particle Flow Code (PFC) to explore the development of cracks from the microscopic scale. The research results can provide theoretical support for the calculation and numerical simulation related to the mechanics of high-temperature treated rocks. [ABSTRACT FROM AUTHOR]

Using undrained triaxial shear tests, this study investigates the mechanical properties of fine-grained materials (silty clay and sand) which are extensively used for China's Qinghai–Tibet Railway (QTR) under different confining pressures (σ3) and freezing temperatures (T). The results show that a reduction in T causes an increase in the shear strength and elastic modulus of all the materials tested in the present study. In addition, the freezing of the silty clay has no significant effect on the type of soil behaviour (strain-hardening), whereas the freezing of the sand changes its strain-hardening behaviour to strain-softening. Supposing that the deviatoric stress–strain curves of the silty clay and sand can be divided into two segments due to a reverse bending point, it was assumed that the first segment follows a hyperbolic function. Meanwhile, the second segment is also a hyperbola, with the reverse bending point as the origin and the residual strength as the asymptote. Accordingly, a nonlinear relation constitutive model that considers σ3 and T is derived. All model parameters are identified. The reasonability of the new model was verified using the test results of the materials. A comparison of the predicted and test results shows that this model can well simulate the deviatoric stress–strain response in the failure process of the tested materials. In particular, it can reflect the residual deviatoric stress after the materials' failure. [ABSTRACT FROM AUTHOR]

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The deep resources within existing gold mines have great potential to prolong the life of mines such as the Jiaojia gold mine in Shandong province in China. However, with the increase of mining depth in the Jiaojia gold mine, the overburden stress is increasing and the spatial and temporal distribution of the mining stress field is becoming more complex. This in turn is causing the spatial structure of the overlying strata to be seriously damaged, which often leads to mine water disasters. In this paper, based on the analysis of borehole data and a profile map, a three-dimensional geological model was established to predict the height of the water-conducting fracture zone near a regionally significant fault. The effects of mining show that the maximum height of the water-conducting fractured zone is about 21.2 m during mining at the − 700 level. The shape of the fractures that are developed varies from nearly horizontal to micro arch-shaped. The failure range of the plastic area near the fault was found to be larger near the fault than that at a distance from the fault. The stress distribution on both sides of the fault was found to be not continuous, and to be larger in the hanging wall than that in the footwall. A stress concentration zone was found to be formed in the front and back of the stope during the mining process and to increase with mining depth. This method can restore the original state of the underground stress field to the greatest extent and make up for the lack of empirical formula theory and the limitation of the similar material methods for deep mining, which is relatively more accurate and reliable. [ABSTRACT FROM AUTHOR]

The mechanical behavior of basalt is critical to the stability and safety of large structures erected on basalt. In this paper, a series of tests (hydrostatic compression test, triaxial compression tests, and triaxial cyclic loading test) are conducted on basalt specimens from the Baihetan hydropower station in southwest China. The test results show that the crack closure (σcc), crack initiation (σci), and crack damage (σcd) stresses are approximately 39%–43%, 54%–68%, and 74%–96% of the peak strength (σp), respectively. Based on the experimental results, a coupled elastoplastic damage model is proposed for basalt within a thermodynamic framework. In this model, elastic stiffness is affected by induced damage. Linear yield function and nonassociated flow rule are used to control inelastic dilatancy. Model parameters are determined from the triaxial compression tests and triaxial loading tests performed in this study. Comparison between numerical results and test results shows that the proposed model can accurately simulate the mechanical behavior of basalt under triaxial compression conditions. [ABSTRACT FROM AUTHOR]

Compacted Gaomiaozi (GMZ) bentonite has been considered as the first choice of buffer materials in the deep geological disposal of high-level radioactive wastes (HLW) in China. During the long-term lifespan of the repository, the bentonite barriers will simultaneously undergo a coupled thermohydromechanical (T-H-M) process, which induces complex volume changes. In this study, the constitutive model of GMZ bentonite with consideration of THM coupling was established, using the framework of the BExM model along with a thermal volume change model for unsaturated soils. New formulations for the interaction between micro and macrostructures (fI and fD) and the thermal loading yield surface (TY curve) were adopted. Emphasis was placed on the identification and validation of the material parameters based on a series of experimental results. A comparison between the simulated and measured values show that the improved model with parameters calibrated successfully represents the main features of volume changes observed in the laboratory and during wetting-drying cycles, elastic thermal expansion, and plastic thermal contraction under various suctions and stresses, as well as compressibility under various suctions and temperatures. [ABSTRACT FROM AUTHOR]

The study of the mechanical properties of frozen saline soil is one of the key issues in addressing the design of infrastructure in cold regions. This research focuses on the supersulfated saline soil of the Ningxia Yellow River Irrigation Area in China, conducting triaxial tests under negative temperatures (−5, −10, −15 °C, and − 20 °C) with varying water contents (12%, 16%, 20%). Based on fractional calculus theory and incorporating an exponential decay factor, this study proposes a novel fractional-order constitutive model for a unified description of the softening and hardening behaviors in frozen saline soil. The model treats frozen saline soil as a composite blend of ideal solids and ideal fluids in varying proportions, taking into account the material's inherent time-dependency and non-linear stress-strain relationships. Finally, the validity of the model is verified by the calculated values of the model and the triaxial tests. The results indicate that, based on preliminary judgment, due to the presence of salt solutes, a large amount of liquid water remains in the supersulfated saline soil at temperatures ranging from 0 to −10 °C, forming an unstable state called "warm frozen saline soil". The mechanical properties of frozen saline soil depend on the relative content of unfrozen water, ice crystals, and salt crystals and the formation of ice and salt crystals significantly enhances the strength of frozen saline soil. The computational results of the improved fractional constitutive model align well with experimental results, effectively describing the stress-strain relationship of frozen supersulfate saline soil. In the model, the parameter κ functions analogously to an elastic modulus and exhibits a linear relationship with temperature, and the parameter α characterizes the strain hardening of saline soil, while β describes its softening behavior. The proposed fractional constitutive model, with only three parameters having clear physical significance, is convenient for practical engineering applications. • A fractional-order constitutive model of saline frozen soil is proposed. • The mechanical properties of supersulphate saline frozen soil are studied. • The fractional-order constitutive model can describe the process of strain softening and hardening uniformly. [ABSTRACT FROM AUTHOR]

Creep properties of loess are related with time-dependent deformation of loess slope. In particular, creep properties of loess at slope foot in the high stress state vary significantly when meeting water, which influence the long-term stability of slope significantly. Therefore, how do creep properties of aquiferous loess under a high confining pressure change is a problem that has to be solved urgently. In this study, creep properties of loess with different moisture contents at a slope foot in Liquan County, Xianyang City, Shaanxi Province, China under a high confining pressure were analyzed through a triaxial creep test. A new nonlinear viscous-plastic model was constructed based on the fitting analogy technology of accelerated creeping segment of loess with different moisture contents and used to improve the four-element model of loess. Results demonstrate that when the deviatoric stress is smaller than the critical stress threshold, axial strain of loess is manifested as the pattern of instantaneous deformation, decelerated creeping and deformation constant. When deviatoric stress is larger than critical stress threshold, axial strain of loess is manifested as the pattern of instantaneous deformation, decelerated creeping and steady creep or instantaneous deformation and accelerated deformation. With the increase of moisture content under a high confining pressure, the creep deformation ability of loess is enhanced. The elastic deformation and viscoelastic strain parameters of loess present negative exponential reduction with the increase of moisture content. The improved four-element model of loess can describe creep properties of aquiferous loess under a high confining pressure well. The study results can provide some theoretical references to analyze time-dependent deformation of loess slope when meeting water. [ABSTRACT FROM AUTHOR]

Cotton is one of the most important cash crops and textile materials in the world. The cotton production of China is also ranked at the top of the world, in terms of planting area and total yield. Specifically, the growing area of cotton is annually more than 3 million hectares. Packing storage and transportation of seed cotton have become two main determinants of production capacity in the cotton industry. However, the traditional storage and transportation of seed cotton cannot meet the high demand for the machine-picked cotton area in recent years. The packing facilities inevitably need to fit into the specific producing conditions in China, such as local topography, climate, and vegetation. Mechanical properties of seed cotton are thus fundamental, including compression and stress relaxation, to the optimal design of equipment for harvesting, stacking, and packing. Most previous researches were focused mainly on the mechanical properties of corn, wheat, and herbage straw in agricultural materials. Few studies were reported on the mechanical properties of seed cotton, particularly on compression and stress relaxation. Taking the seed cotton as the research object in this study, a systematic test of mechanical properties was performed on the compression and stress relaxation of seed cotton. An improved Nishihara model and a generalized Maxwell 5-element mechanical model were selected to represent the stress-strain curves of compression and stress relaxation. Various level factors were utilized to verify the constitutive models for the compression and stress relaxation of seed cotton. Relevant model parameters were obtained to determine the influence rules with different factors. The results showed that the determination coefficients of parameters in the constitutive model were beyond 0.9 using the curve-fitting in the compression and stress relaxation of seed cotton. An obvious regularity of coefficients indicated that two models were better suitable for the compression and stress relaxation of seed cotton. There was also a significant influence of water content and feeding quantity on the mechanical properties of seed cotton. Furthermore, the compression stress was positively correlated to the water content and feeding quantity. In addition, the viscosity coefficient and elastic modulus increased significantly at a higher level of water content, due mainly to the porosity of cotton fiber. The cell wall of fiber became stronger and tougher, because the hydrophilic groups on the cellulose macromolecule absorbed water from the external environment. The curl of cotton fiber also made the fiber shrink longitudinally and elastic elongation during the compression under the larger amount of feeding quantity, where there was a significant increase in the overall longitudinal deformability of seed cotton and the elastic modulus. The viscosity coefficient and packing height both rose up significantly, while the pressure transmission path was longer for the naturally stacked seed cotton in the same compression chamber, as the feeding quantity was larger. The main reason was that the bending deformation, contact and extrusion were induced to generate the greater local stress between the fiber bodies during the compressing process of seed cotton. Moreover, the water content was positively correlated to the elastic modulus and viscosity coefficient of seed cotton. This positive correlation was possible because the natural twist of cotton made the fibers entangled, linked, and adhered, difficult to disperse during the stress relaxation of seed cotton. Correspondingly, the elastic modulus and viscosity coefficient increased significantly, as the feeding quantity increased. This improvement was due mainly to a non-uniform attenuation rate of pressure during the stress relaxation of seed cotton. There were much more contact points of fiber curl subjected to the greater feeding amount of seed cotton. The elastic modulus increased, while the relaxation pressure was transferred from the bottom to the top of seed cotton. The adhesion force between fibers and the viscosity coefficient rapidly rose with the motion resistance increased. This finding can provide an insightful theoretical basis to simulate the compression of seed cotton in most machine-picked cotton areas. [ABSTRACT FROM AUTHOR]

Cracks will be introduced into mortar specimens and embedded copper sheets to simulate fractured concrete according to the designed 20 mm crack lengths and angles. By taking into consideration the actual environment of a hydro-fluctuation belt for a typical bank slope in the Three Gorges Reservoir Region of the Yangtze River, China, a dry–wet cycle testing program will be designed to study the mechanical properties of the fracture mortar specimens immersed in different sulfate solutions. The failure characteristics and modes of the fracture mortar specimens will be measured and analyzed. The tests results show that the strength initially decreased and then increased with an increasing crack angle from 0° to 90°, and this was the smallest for the specimens with a 45° angle. Deterioration occurred in the specimens subjected to dry–wet cycles in different sulfate solutions. The damage extent is expressed as the change in elasticity. A formula for damage evolution of the fracture specimens will be proposed and the relationship between the deformation properties and damage properties of the specimens will be developed for the combined action of dry–wet cycles and sulfate attack. Based on the proposed damage model, the damage evolution equation and elastic damage constitutive model will be derived under the combined action of dry–wet cycles and sulfate attack, and this damage constitutive relation could be used to the study damage evolution for the fracture mortar specimens under the combined effects of dry–wet cycles and sulfate attack. [ABSTRACT FROM AUTHOR]

In this study, the static tensile properties, activation recovery properties, and post-activation static tensile properties of the China-made iron-based shape memory alloys (Fe-SMA) were experimentally studied and theoretically analyzed. The material parameters of the Ramberg-Osgood curve are modified based on the static tensile tests of Fe-SMA plates, leading to the proposal of a static tensile constitutive model suitable for Fe-SMA. The applicability analysis of the theoretical model indicates that the calculated curve achieves an accuracy of R 2 ≥ 0.9. Subsequent activation tests revealed a locally optimal combination of pre-strain and activation temperature, which is concluded to be associated with the martensite content. Hot-rolled Fe-SMA plates demonstrate local maximum utilization when subjected to a 4% pre-strain and an activation temperature of 300 °C, resulting in a recovery stress of 314 MPa. Moreover, it has been determined that the two activation modes, namely single heating and multiple-cyclic heating, do not significantly impact the final recovery stress of hot-rolled Fe-SMA plates. Therefore, the multiple-cyclic activation of Fe-SMA can be utilized to compensate for prestress loss in practical applications. Furthermore, a comprehensive constitutive model for Fe-SMA is proposed based on the results of the post-activation static tensile tests. This model provides an accurate description of the static-tensile stress-strain relationship of Fe-SMA during pre-straining and after activation. This study focuses on investigating the constitutive relationship and activation recovery performance of Fe-SMA, providing an experimental basis, data support, and theoretical analysis for the practical application and further analysis of Fe-SMA in structural reinforcements. • A static tensile constitutive model for Fe-SMA is proposed. • A comprehensive constitutive model for Fe-SMA is worked out. • Comparison of single heating mode and multiple-cyclic heating mode is conducted. • Activation recovery performance through activation tests is studied. • Post-activation behavior of Fe-SMA is analyzed. [ABSTRACT FROM AUTHOR]

Artificial ground freezing (AGF) technology is sometimes adopted to reinforce the surrounding soil to ensure the safety of subway tunnels during construction in the eastern coastal areas of China. The mechanical characteristics of frozen soil are subjected to change due to the incorporation of chlorine salt, and the soil strength decreases significantly with an increase of salt content. The mechanical properties of frozen silty clay have been rarely investigated due to the coupling effect of temperature, strain rate, and salt content. In this study, before the application of AGF, a series of unconfined compressive strength (UCS) tests and the consolidated-undrained static triaxial compression tests were conducted on frozen silty clay to investigate the influence of salt content, temperature, and strain rate on the mechanical properties of frozen soil. From the stress-strain curves of the UCS test, strain-hardening and strain-softening behavior were identified as a result of the influence of different temperatures and salt contents. Regression analysis was performed to discriminate the effect of each individual factor and their coupling effect. The results reveal that soil UCS logarithmically increased with a decrease in relative temperature and strain rate. Both UCS and static triaxial strength linearly decreased with an increase in salt content. The influence of salt content on the strength of frozen soil was discussed and compared with previous researches. Furthermore, an elastic-plastic constitutive model was proposed to characterize the stress-strain behavior in which the effects of strain rate and salt content were included. At last, with consideration of salt content, a modified constitutive model was proposed to describe the strength and deformation behavior of frozen silty clay. • UCS was extracted and constitutive model was established with consideration of temperature, strain rate, and salt content • The frozen chloride soil strength is predicted by superimposing the coupling effect of salt content and confining pressure • The sensitivities of the strength and deformation behavior of NaCl saline soils to salt content are characterized [ABSTRACT FROM AUTHOR]

GJ steel is a high-performance steel manufactured in China, and its thick plates are widely used in building structures. The first companion study examined the material properties of the thick GJ steel plates (t ≥ 60 mm). This study focuses on the mechanical properties of butt welds in thick GJ steel plates (t ≥ 60 mm). Monotonic and cyclic tests were conducted on butt-weld specimens made of 60-mm and 100-mm thick Q345GJ steel plates in the longitudinal and transverse directions. In addition, the layered specimens obtained from five different thickness locations were tested. Based on the cyclic test results, the Chaboche constitutive parameters were calibrated and verified via the finite element analysis (FEA). Moreover, the differences in the static and cyclic mechanical properties of the base metal and butt welds were analysed. Compared with the base metal, the static tensile strength and hysteretic energy dissipation under the same cyclic loading protocol were better in the weld specimens; however, their ductility was significantly lower. Furthermore, the distribution of the mechanical properties along the thickness direction was more uniform in the weld specimens. Moreover, the weld specimens had higher yield surface reduction ratios. However, their initial and final yield surface sizes were larger than those of the base metals. [Display omitted] • The mechanical properties of butt welds in 60-mm and 100-mm thick Q345GJ steel plates were tested using layered specimens. • Totally 160 weld specimens were tested under monotonic and five different cyclic loading protocols. • The static and hysteretic properties of the butt welds and base metals were compared. • The constitutive parameters of the Chaboche model were calibrated and validated against test results. [ABSTRACT FROM AUTHOR]

The mechanical properties of the viscoelastic damper made of high damping rubber produced in China are investigated in order to provide the basis for its application. At first, the test on material properties of high damping rubber is conducted. The Mooney–Rivlin model, the Yeoh model and the Prony series are applied for simulating the nonlinear behavior of the high damping rubber with the aid of software ABAQUS. Then, three viscoelastic dampers with different sizes are tested under cyclic loading. The effects of strain amplitude and loading frequency on hysteretic behavior of dampers are analyzed. Viscoelastic dampers possess large deformation capability, stable energy-dissipation capacity and good fatigue-resisting property. The effect of strain amplitude is much more significant than loading frequency. The hysteretic behavior of the dampers is simulated by the Bouc–Wen model and the model of the equivalent stiffness and damping, respectively. The prediction results by using the Bouc–Wen model are in good agreement with the experimental results, which indicates that the Bouc–Wen model is applicable to simulate the mechanical properties of high damping viscoelastic dampers with a wide range of shear strain. As to the model of equivalent stiffness and damping, it has the advantages of clear concept and simple calculation. However, the good accuracy of prediction can be obtained only when the shear strain is not greater than 60%. [ABSTRACT FROM AUTHOR]

To probe into the time-dependent behaviour of the ballastless track–bridge structural system under train load, based on the import of the static and fatigue damage constitutive model of materials to simulate damage deterioration of the structural system and interface cohesive zone model to the interface layer, a three-dimensional nonlinear finite element model of the China Railway Track System Type II (CRTS II) ballastless track–bridge structural system was established using the equivalent static method. Then, using this model, we developed the numerical simulation analysis of the influence law of material damage deterioration on structural system performance under train load and revealed the fatigue evolution of the structural system. The results show that the beam remains in compressed status for the whole process, the track is in compression in the midspan and in tension at the beam end, and the tensile stress is larger near the shear groove under the double-track static load. Under the fatigue load, stiffness degradation of the structural system is not obvious, and integral rigidity of the structural system is dependent on the rigidity of the beam. Strength reduction of the materials caused stress redistribution of the structural system and had a larger effect on the stress of each layer of track structure than on the stress on the beam. The fatigue degradation of the cement-emulsified asphalt (CA) mortar layer material has a significant impact on the structural system, which directly affects structural layer stress variation with the fatigue loading cycle. [ABSTRACT FROM AUTHOR]

[Display omitted] • Material properties of 60-and 100-mm thick Q345GJ steel plates were investigated by layered specimens. • Eighty specimens were tested under monotonic and five different cyclic loading protocols. • The differences in the mechanical properties among the various thickness positions were compared and analysed. • The constitutive parameters of the Chaboche model were calibrated and validated against test results. The Q345GJ steel plate is a common Chinese product that has an increasingly wide usage in civil engineering. However, previous research on Q345GJ steel plates with thicknesses of no less than 60 mm is limited, especially the systematic cyclic loading tests, causing an inadequate understanding of the cyclic behaviour and corresponding constitutive parameters of thick steel plates. To further investigate the mechanical property of Q345GJ thick steel plates and fill the gap of test databases, layered specimens obtained from five different thickness positions of the 60-mm and 100-mm thick Q345GJ steel plates were tested under monotonic tension and five cyclic loading protocols. The mechanical properties of specimens in different thickness positions were compared and analysed. Moreover, parameters of the Chaboche cyclic constitutive model were calibrated and then validated by finite element analysis (FEA). Results indicated that the surface-layer specimens exhibited greater strength and lower ductility than the middle-layer specimens. Furthermore, the hysteretic curves of all the specimens were plump, where the energy dissipation of the surface-layer specimens was greater than that of the middle layer, particularly for the 100-mm thick plate. Based on the test results and calibrated parameters of the Chaboche constitutive model, significant isotropic softening characteristics were observed for all thickness positions. Following the tests and analysis, the cyclic constitutive model calibrated in this study was verified to support further numerical simulations. [ABSTRACT FROM AUTHOR]

This paper presents a finite element analysis for the behavior of the Lianghekou high earth-core rockfill dam, which was just completed in construction in China. An elastoplastic constitutive model that can account for the degradation of rockfills due to particle breakage (hhu-SH-breakage model) was applied to simulate the mechanical behavior of the rockfills. The earth-core wall was analyzed by using the modified Cam-clay model combined with the Biot's consolidation theory. Numerical results are in good agreement with in-situ measurements during construction, indicating the reasonability of the numerical analysis. Based on the breakage-packing concept, which is able to extract the breakage-induced deformation from the total deformation, numerical analysis showed that the breakage-induced settlement for the extra high rockfill dam is not negligible. Inspired by the sensitivity analysis using the hhu-SH-breakage model, engineering advices were proposed to reduce the settlement of high rockfill dams. [ABSTRACT FROM AUTHOR]

High strength structural steels (HSS) with a nominal yield strength f y ≥ 460 MPa have begun to be applied in many steel structures. This paper focuses on material properties of the HSS fabricated in China and calibration of partial factors for resistance based on the theory of structural reliability. An extensive range of material property data of 500 MPa, 550 MPa and 690 MPa steels produced by major steel manufacturers in China (over 10,000 samples) was collected. Besides, independent material tests were carried out. The statistical parameters of the material properties were then obtained with the influence of test machine types and strain rates being incorporated. Uncertainties of the resistance model of HSS were subsequently investigated through finite element (FE) analyses, including members under axial compression, flexural members and members under combined axial compression and bending. By combining the statistical parameters of both the material properties and the resistance model uncertainties as well as that of geometric properties investigated in the previous research, the statistical parameters of resistance uncertainties of HSS were gained. It may provide a significant statistical evidence for the following reliability analyses. Based on structural reliability theories, partial factors for resistance of HSS were eventually calibrated. As an important part of the Design Specification of High Strength Steel Structures in China, these partial factors for resistance developed herein are helpful for promoting the application of HSS in China. In addition, based on the massive material properties data, a constitutive model of HSS under monotonic loading was suggested. [ABSTRACT FROM AUTHOR]

To accurately describe the damage creep properties of marble, especially during the acceleration creep phase, creep testing was performed on the marble in the Jinping II hydropower station in China. Based on the experimental results, a time-dependent damage constitutive model was proposed in terms of fractional calculus theory and damage variables to describe these time-dependent damage characteristics. The time-dependent constitutive equations were derived for constant loading levels below and above the marble's long-term strength. The robustness and parameter sensitivity of the proposed model were analysed by utilizing data of creep testing. The results of the analysis showed that the proposed model could describe not only the attenuation and steady-state creep of marble but also the acceleration creep characteristics and negative exponential attenuation law of the yield strength over time when the constant loading was above the long-term strength. These are crucial to failure prevention during rock engineering construction and operating periods. [ABSTRACT FROM AUTHOR]

• The stress-strain curves and mesoscopic voids of shale were obtained their evolution exhibited staged characteristics. • The relationship between the damage variable and the axial strain follows the quadratic function. • The mesoscopic mechanism of the macroscopic response of shale was analysed. • A damage constitutive model of shale under uniaxial compression conditions was proposed. With the continuous development of shale gas engineering in China, an accurate and adequate understanding of shale damage mechanism has become a critical scientific problem addressed by rock mechanics. So far, many researchers have studied the fracturing process and mechanism of shale in multi-scales. The mesoscopic structural characteristics of shale during loading can be obtained using the in-situ X-ray computed tomography (CT) technology. Some scholars have observed the structure evolution of shale under in-situ uniaxial compression conditions, but the quantitative investigation of damage evolution and constitutive model of shale still requires further studies. Given this, the in-situ micro-CT device was adopted to study the macroscopic mechanical response and the mesoscopic structural evolution of Longmaxi shale under uniaxial compression conditions. The evolution law of the damage variable with the axial strain was analysed according to the characterisation of the damage variable based on the CT image grey variance. In combination with the macroscopic stress-strain curve shape, evolution stage of the mesoscopic void, evolution of the damage variable, mesoscopic mechanism of the macroscopic mechanical response was investigated, and a damage constitutive model of shale under the uniaxial compression test was proposed. The conclusion of this study can provide a foundation for further research into the multi-scale failure mechanism of shale and exert theoretical guidance significance on shale gas fracturing engineering practice. [ABSTRACT FROM AUTHOR]

Based on the unsaturated triaxial experiments for the intact fourth period Middle Pleistocene Epoch loess (Ql loess), the mechanical characteristic of Ql loess is studied. According to the continuum damage mechanics and elastic-plastic theory, the damage potential function and loading function were deduced. Besides, plastic deformation and irreversible damage deformation are supposed to obey Hyushin's postulate. The elastoplastic damage constitutive model and damage evolution law of the unsaturated intact Q loess are set up. Comparing the experiment curves with the computation result of this model, it is shown that the model can stimulate the mechanics characteristics of Q loess well. [ABSTRACT FROM AUTHOR]

According to the requirement of the West-East Gas Transmission Project in China, the solution-mined cavities located in the Jintan bedded salt formation of Jiangsu province will be utilized for natural gas storage. This task is more challenging than conventional salt dome cavern construction and operation due to the heterogeneous bedding layers of the bedded salt formation. A three-dimensional creep damage constitutive model combined with the generalized Hoek-Brown model is exclusively formulated and validated with a series of strength and creep tests for the bedded rock salt. The viscoplastic model, which takes the coupled creep damage and the failure behavior under various stress states into account, enables both the three creep phases and the deformation induced by vicious damage and plastic flow to be calculated. A further geomechanical analysis of the rapid gas withdrawal for the thin-bedded salt cavern was performed by implementing the proposed model in the finite difference software FLAC. The volume convergence, the damage and failure propagation of the cavern, as well as the strain rate of the salt around the cavern, were evaluated and discussed in detail. Finally, based on the simulation study, a 7-MPa minimum internal pressure is suggested to ensure the structural stability of the Jintan bedded salt cavern. The results obtained from these investigations provide the necessary input for the design and construction of the cavern project. [ABSTRACT FROM AUTHOR]

Laboratory tests on the large post-liquefaction deformation of saturated Nanjing fine sand were performed by using a hollow cylinder apparatus. The stress-strain responses and the characteristics of excess pore water pressure after liquefaction were studied. It was found that the relationship between deviatoric stress and axial strain presented a sigmoid curve, and there was a good linearity relationship between normalized pore water pressure and deviatoric stress. On this basis, a constitutive model of stress-strain responses and a dissipation model of excess pore water pressure were established. It was found that the results predicted by the two models were in good agreement with the experimental data. The influence of relative densities and confining pressure on the characteristics of liquefied soil were studied. The results showed the relative densities and initial effective confining pressure all had an important influence on the stress-strain responses of liquefied saturated Nanjing fine sand. However, the dissipation model of excess pore water pressure after liquefaction was only affected by the confining pressure. [ABSTRACT FROM AUTHOR]

Based on the consistency-viscoplastic constitutive model, the static William-Warnke model with threeparameters is modified and a consistency-viscoplastic William-Warnke model with three-parameters is developed that considers the effect of strain rates. Then, the tangent modulus of the consistency viscoplastic model is introduced and an implicit backward Elure iterative algorithm is developed. Comparisons between the numerical simulations and experimental data show that the consistency model properly provides the uniaxial and biaxial dynamic behaviors of concrete. To study the effect of strain rates on the dynamic response of concrete structures, the proposed model is used in the analysis of the dynamic response of a simply-supported beam and the results show that the strain rate has a significant effect on the displacement and stress magnitudes and distributions. Finally, the seismic responses of a 278 m high arch dam are obtained and compared by using the linear elastic model, as well as rate-independent and rate-dependent William-Warnke three-parameter models. The results indicate that the strain rate affects the first principal stresses, and the maximal equivalent viscoplastic strain rate of the arch dam. Numerical calculations and analyses reveal that considering the strain rate is important in the safety assessments of arch dams located in seismically active areas. [ABSTRACT FROM AUTHOR]

To prolong the life-span of crush hammers in the pyrite concentrate workplace of Ganbazi Coal Preparation Plant of Chongqing Nantong Mining Ltd., we used a progressive damage constitutive model based on the ductile and shear damage fracture energy to analyze the hammer wear failure caused by the impact and abrasion on the hammer surface by pyrite, and carried out simulation analysis with the explicit algorithm on hammer leftovers from the plant during the process of coarser pyrite comminution. The simulation results are consistent with hammer wear failure caused by pyrite impact. Then we proposed corrective measures to prolong hammer life-span. Results of the production test in the Ganbazi Coal Preparation Plant showed that non-clearance hammers can avoid wear erosion, and adding steel bonded tungsten carbides F3002 prolonged the hammer lifespan. The effect of austenitic manganese steel work-hardening was not prominent. Therefore, the hammer failure was mainly caused by superficial abrasion instead of fatigue cracks appearing when grains acted on the hardening layer. [ABSTRACT FROM AUTHOR]

The stress environments of rock masses are complex. To explore the mechanical properties of sandstone under earthquake or disturbance loads, laboratory triaxial creep tests under different disturbance loads were conducted on sandstone from Fuxin, Liaoning Province, China. Given the disturbance load, a creep deformation pattern for sandstone was analyzed, and the influence of the disturbance load on the mechanical properties of rock was considered. Thus, a constitutive model of rock under creep disturbance load was established. The results show that (1) the creep curve can be divided into four stages: attenuation creep, steady creep, disturbance creep, and acceleration creep; the increment of disturbance creep varies for different disturbance loads and the larger the disturbance load, the larger the disturbance creep deformation; (2) with increasing disturbance loads, the long-term strength, failure time, and elastic modulus of sandstone decreases linearly, while the peak strain increases; and (3) considering the influence of the disturbance load and introducing an acceleration element to modify the Nishihara model, a constitutive model describing the whole deformation process of sandstone under creep disturbance load was established. The accuracy of the model was verified by test data and provides a theoretical basis for rock mass stability analysis. [ABSTRACT FROM AUTHOR]

• The fineness modulus index was used to evaluate the crushing degree of concrete under impact load. • The steam-cured concrete shows the stronger strain rate sensitivity at higher curing temperature. • The influence of temperature on key parameters of damage constitutive models was analyzed. In order to clarify the influence of curing temperature on the dynamic properties of steam-cured concrete, series of SHPB tests were conducted to investigate the impact mechanical characteristics of a typical steam-cured concrete applied in prefabricated components of high-speed railway in China. The index of fineness modulus was proposed to evaluate the degree of concrete breakage under different strain rates. The results showed that the peak stress of steam cured concrete increased with increasing the strain rate, while the peak strain showed a decreasing trend, the fineness modulus of broken concrete particles decreased, and the degree of fracture increased obviously. As curing temperature increases, the peak stress of steam-cured concrete decreased significantly, and the concrete specimens showed a stronger strain rate sensitivity. A statistical damage constitutive model considering the strain rate was established and agreed well with the experimental stress–strain curves. Higher temperatures lead to an increase in internal defects of concrete, which makes the impact mechanical properties different from that of normal temperature cured concrete. [ABSTRACT FROM AUTHOR]

Tunnel Boring Machines (TBMs) are a cutting-edge excavating equipment, but are barely applied in underground coal mines. For TBM excavation projects involving the Zhangji coal mine, the surrounding rock properties, stress field, cross section geometry, as well as the excavation-induced stress path of TBM-excavated coal mine roadways are different from those of traditional tunnels or roadways. Consequently, traditional roadway supporting technologies and experiences cannot be relied on for this project. In order to research an appropriate supporting pattern for a TBM-excavated coal mine roadway, first of all, the constitutive model of roadway surrounding rocks was derived, and a rock failure criterion was proposed based on rock mechanical tests. Secondly, a three-dimension finite element model was established and computer simulations under three different supporting patterns were conducted. Stress redistribution, roadway convergence, and excavation damage zone ranges of surrounding rocks under three different support patterns were analyzed and an optimal support design of the TBM-excavated roadway was made based on simulation results. During roadway excavation, convergence gauge and rock bolt dynamometers were installed for monitoring roadway convergence and the axial forces of rock bolts. The in-situ monitoring results verified the validity of roadway supporting designs. [ABSTRACT FROM AUTHOR]