Search Results (41)

The dynamic response and failure of rubber-coated sandwich composite structures with buoyancy material core (RC-BMC-SCS) subjected to high-energy low-velocity impacts were experimentally and numerically investigated. Six types of BMC-SCSs were designed and manufactured, and high-energy low-velocity impact experiments were performed. Based on the Mohr-Coulomb theory and the Ogden hyperelasticity constitutive model, a low-velocity impact finite element analysis model was developed. The results indicate that BMC-SCS damage stages could be divided into: (1) matrix damage, (2) core cracks, (3) debonding and fiber breakage. Three distinct damage stages of the RC-BMC-SCS were revealed: (1) rubber layer energy absorption, (2) core cracks, (3) debonding. The rubber layer can enhance the damage threshold by approximately 100% compared to BMC-SCS. However, rubber energy absorption capacity has an upper limit. Additionally, the larger the curvature of the BMC-SCS, the higher the initial stiffness of the structure and the larger the impact damage area. The results of this study provide valuable insights for the multifunctional design of composite deep-sea marine structures. Full article

In order to reveal the intrinsic mechanism of the mechanical properties of lime-treated sandy soil from a microscopic perspective, triaxial tests were conducted to analyze the macroscopic mechanical characteristics of sandy soil with different lime contents (0%, 5%, 8%, and 12%). The changes in the microstructure of the lime-treated sandy soil were studied through scanning electron microscopy, energy-dispersive spectroscopy, and mercury intrusion tests, combined with fractal theory for quantitative characterization. The results indicate that the stress–strain curve of lime-treated sandy soil can be divided into four stages: linear elastic, non-linear, failure, and residual strength. With the increase in lime content, the peak stress and cohesion first increase and then decrease, while the internal friction angle first decreases and then increases, suggesting the presence of an optimal threshold for lime content between 5% and 12%. The failure mode transitions from diagonal shear failure to bulging failure, significantly enhancing stability; both the fitted Mohr–Coulomb and Drucker–Prager failure criteria effectively reflect the failure patterns of the specimens in principal stress space. The results based on the three fractal dimensions demonstrate that lime-treated sandy soil exhibits clear fractal characteristics, with the highest fractal dimension value at a lime content of 8%, corresponding to the highest overall strength. In addition, the fractal dimension shows a binomial relationship with pore characteristic parameters and shear strength parameters; it can effectively characterize the complexity of the microstructure and accurately predict changes in shear strength parameters. Full article

The drain pipe wrapped in steel wire mesh serves a dual purpose of drainage and reinforcement in tailings pond projects. The self-filtering layer that develops upstream of the steel wire mesh influences the reinforcement characteristics of the drainage pipe. This study first conducts interfacial shearing experiments to explore the impact of the self-filtering layer on the shearing properties between tailings and the steel wire mesh. An exponential interface constitutive model is then proposed to delineate the shear stress–displacement relationship. Finally, through finite element simulations, the study assesses the effect of the self-filtering layer on the load-bearing behavior of the drain pipe, considering the interactive dynamics between the tailings and the steel wire mesh. The results reveal that the interfacial shear strength, across varying median particle sizes of the self-filtering layer, adheres to Mohr–Coulomb strength theory. Specifically, as the median particle size of the self-filtering layer increases, interfacial cohesion diminishes while the friction coefficient rises. The initial shear stiffness demonstrates a linear increase with the median particle size. With the presence of the self-filtering layer, the pull-out resistance of the drainage pipe can be enhanced by up to 26%. Moreover, the self-filtering layer significantly affects the distribution of negative skin friction. This research enhances the safety assessment of tailings ponds by providing crucial insights and solutions, emphasizing the influence of the self-filtering layer on the bearing behavior of the drain pipe. Full article

Rock materials failures are accompanied by the co-existence of various failure mechanisms, including rock fracturing, shearing, and compaction yield. These mechanisms manifest macroscopically as multiple failure modes and nonlinear strength characteristics related to stress levels. Considering the limitations of current rock mechanics strength theories, which are primarily derived from single failure mechanisms, this study evaluates the applicability of alternative strength theories. Based on the extensional-strain criterion and the PMC (Paul-Mohr-Coulomb) model, a piecewise linear strength model was proposed that is suitable for analyzing multiple failure mechanisms in rocks, revealing the intrinsic mechanisms of multi-mechanism rock material failure. A multiple failure mechanism strength model in the form of inequalities was proposed, using the generalized shear stress, mean stress, and stress Lode angle as parameters. Strength tests conducted on sandstone and granite rock material samples under different stress conditions revealed distinct piecewise linear strength characteristics for both rock types, validating the rationality and applicability of the multiple failure mechanism model. The findings construct a multi-mechanism failure model for rocks, providing enhanced predictive capabilities and aiding in the prevention of rock structural failures. Full article

Sandbars are commonly encountered in coastal environments, acting as natural protections during storm events. However, the sandbar response to waves and possible shear failure is poorly understood. In this research, a two–dimensional numerical model is settled to simulate the wave-induced sandbar soil dynamics and instability mechanism. The model, which is based upon the Reynolds-averaged Navier–Stokes (RANS) equations and Biot’s consolidation theory, is validated using available experiments. Parametric studies are then conducted to appraise the impact of the wave parameters and soil properties on soil dynamics. Results indicate that the vertical distribution of the maximum vertical effective stress in the sandbar is different from that in the flat seabed, which decreases rapidly along the soil depth and then increases gradually. The impact of soil permeability and saturation on the vertical effective stress distribution around the sandbar also differ from that in the flat seabed. Unlike the flat seabed, the vertical distribution of shear stress in the sandbar increases with an increasing wave period. The sandbar soil shear failure potential is discussed based upon the Mohr–Coulomb criterion. Results show that the range of shear failure around the sandbar is wider and the depth is deeper when the wave trough arrives. Full article

Earthquakes are one of the main causes of bedding slope instability, and scientifically and quantitively evaluating seismic stability is of great significance for preventing landslide disasters. This study aims to assess the bedding slope stability under seismic loading and the influences of various parameters on stability using a pseudo-dynamic method. Based on the limit equilibrium theory, a general solution for the dynamic safety factor of bedding slope is proposed. The effects of parameters such as slope height, slope angle, cohesion, internal friction angle, vibration time, shear wave velocity, seismic acceleration coefficient, and amplification factor on stability are discussed in detail. To evaluate the validity of the pseudo-dynamic solution, the safety factors are compared with those given by early cases, and the results show that the safety factors calculated by the present formulation coincide better with those of previous methods. Moreover, a two-dimensional numerical solution of bedding slope based on Mohr–Coulomb’s elastic–plastic failure criterion is also performed by using the finite element procedure, and the minimum safety factor is essentially consistent with the result of the pseudo-dynamic method. It is proved that the pseudo-dynamic method is effective for bedding slope stability analyses during earthquakes, and it can overcome the limitations of the pseudo-static method. Full article

Under the background of climate warming in the Qinghai-Tibetan Plateau (QTP), frequent freeze–thaw cycling (FTC) brings about great geological disasters such as subgrade failure, landslides, and mudslides, which is closely related to the strength reduction caused by the structural damage of soils. In this study, to explore the association between macro shear strength and microstructure evolution of soils subjected to FTC, the red clay distributed widely in the QTP was chosen and used to conduct a series of triaxial shear and nuclear magnetic resonance (NMR) tests in the range of 1 to 7 FTCs. Triaxial shear test results reveal that the shear strength reduction of specimens mainly occurs within five FTCs, and the trend of peak deviator stress with increasing FTCs can be described in three stages: rapid descent (FTCs less than three), slow descent (FTCs between three and five), and stabilization (FTCs greater than five). NMR tests show that the T₂ spectrum curves exhibit a distinct bimodal distribution characteristic, corresponding to macropores and micropores. Part of the micropores gradually develop into macropores with increasing FTCs, especially within five FTCs. The increase in macropores proportion leads to a loose soil structure, which is consistent with the deterioration of the shear strength of specimens. Finally, based on the experimental results and classical Mohr–Coulomb theory, a new shear strength model with structural damage for red clay has been proposed by introducing a damage factor expressed by T₂ spectral area. Full article

Traditional analysis of embedded earth-retaining walls relies on simplistic lateral earth pressure theory methods, which do not allow for direct computation of wall displacements. Contemporary numerical models rely on the Mohr–Coulomb model, which generally falls short of accurate wall displacement prediction. The advanced constitutive small-strain hardening soil model (SS-HSM), effectively captures complex nonlinear soil behavior. However, its application is currently limited, as SS-HSM requires multiple input parameters, rendering numerical modeling a challenging and time-consuming task. This study presents an extensive numerical investigation, where wall displacements from numerical models are compared to empirical findings from a large and reliable database. A novel automated computational scheme is created for model generation and advanced data analysis is undertaken for this objective. The main findings indicate that the SS-HSM can provide realistic predictions of wall displacements. Ultimately, a range of input parameters for the utilization of SS-HSM in earth-retaining wall analysis is established, providing a good starting point for engineers and researchers seeking to model more complex scenarios of embedded walls with the SS-HSM. Full article

Bulk ideal flows constitute a wide class of solutions in plasticity theory. Ideal flow solutions concern inverse problems. In particular, the solution determines part of the boundary of a region where it is valid. Bulk planar ideal flows exist in the case of (i) isotropic rigid/plastic material obeying an arbitrary pressure-independent yield criterion and its associated flow rule and (ii) the double sliding and rotation model based on the Mohr–Coulomb yield criterion. In the latter case, the intrinsic spin must vanish. Both models are perfectly plastic, and the complete equation systems are hyperbolic. All available specific solutions for both models describe flows with a symmetry axis. The present paper aims at general solutions for flows with no symmetry axis. The general structure of the solutions consists of two rigid regions connected by a plastic region. The characteristic lines between the plastic and rigid regions must be straight, which partly dictates the general structure of the characteristic nets. The solutions employ Riemann’s method in regions where the characteristics of both families are curvilinear. Special solutions that do not have such regions are considered separately. In any case, the solutions are practically analytical. A numerical technique is only necessary to evaluate ordinary integrals. The solutions found determine the tool shapes that produce ideal flows. In addition, the distribution of pressure over the tool’s surface is calculated, which is important for predicting the wear of tools. Full article

Fiber-reinforced polymer (FRP) has been used for seismic retrofitting and structural reinforcement over recent decades. Numerous researchers have created stress–strain models based on experimental data to predict the mechanical properties of FRP-confined concrete. In this study, circular and square cross-section specimens with different design concrete strength were prepared, and the compressive strength of the specimens confined with different layers of aramid FRP (AFRP) were measured in compressive tests. A constitutive model was proposed to simulate the uniaxial compressive stress–strain relationship of the AFRP-confined concrete, which was derived from the Mohr–Coulomb failure envelope theory, and the corresponding axial strain was determined from the regression analysis. The internal friction angle of the proposed constitutive model was determined for the cylindrical concrete specimens confined with one and two layers of AFRP. The compressive strength of one and two layers of AFRP-confined concrete specimens were used to obtain the parameters of the constitutive model; the absolute average error between experimental and predicted compressive strength was 7.01%. Then, the constitutive model was used to predict the strength of a three-layer AFRP-confined concrete specimen, and the absolute average error was 4.95%. The cross-sectional shape coefficient of the square concrete specimen was obtained analytically. Substituting the cross-sectional shape coefficient into the proposed constitutive model, the average absolute error of the square cross-section concrete specimen was about 3.84%. The results indicated that the proposed constitutive model can predict the compressive strength of circular and square cross-section concrete specimens confined with AFRP. Full article

This paper develops the ideal plastic flow theory for the stationary planar flow of pressure-dependent materials. Two rigid plastic material models are considered. One of these models is the double-shearing model, and the other is the double slip and rotation model. Both are based on the Mohr–Coulomb yield criterion. It is shown that the general ideal plastic flow theory is only possible for the double slip and rotation model if the intrinsic spin vanishes. The theory applies to calculating the shape of optimal extrusion and drawing dies of minimum length. The latter condition requires a singular characteristic field. The solution is facilitated using the extended R–S method, commonly employed in the classical plasticity of pressure-independent materials. In particular, Riemann’s method is used in a region where all characteristics are curved. It is advantageous since determining the optimal shape does not require the characteristic field inside the region. The solution is semi-analytical. A numerical procedure is only required to evaluate ordinary integrals. It is shown that the optimal shape depends on the angle of internal friction involved in the yield criterion. Full article

The mechanical properties of rock can be weakened under the influence of high temperatures. To describe the mechanical behavior of rock under the action of high temperature more accurately, based on the Zienkiewicz–Pande yield criterion, the damage variable Dc which accounts for the coupling between high temperature and load is introduced. According to plastic potential theory and plastic flow law, the iterative incremental method for a high-temperature and load-coupled damage constitutive model in Flac^3D is deduced in detail and compiled into the corresponding dynamic link library file (.dll file). By modifying the shape function to degenerate into the Mohr–Coulomb constitutive model, an elastic–plastic analysis of an ideal circular tunnel is performed, and a comparison is made between calculation results obtained from the built-in Mohr–Coulomb constitutive model in Flac^3D, proving the correctness of the secondary development program. Finally, numerical simulations are conducted to study the effects of high-temperature damage using rock uniaxial compression tests, and the model’s validity is established by comparing it with previous experimental results. Full article

The evaluation of the bearing capacity of strip footings generally assumes that the soil is either dry or fully saturated, which contradicts the actual condition in nature where the soil is often in a partially saturated state. Furthermore, infiltration has a significant impact on the shear strength of the soil. Following the upper bound theory of the limit analysis, this article provides a theoretical framework for assessing the bearing capacity under transient flow with linear variation in infiltration intensity for the first time. Firstly, the closed form of suction stress under linear transient infiltration is derived using Laplace transform and introduced into the Mohr–Coulomb criterion. A discrete failure mechanism with fewer variables and higher accuracy is provided to ensure kinematic admissibility. The upper bound solution for bearing capacity is obtained by solving the power balance equation. The present results are compared with results from the published literature and the finite element, confirming the validity and superiority of the theoretical framework provided. A parametric analysis is also conducted on three hypothetical soil types (fine sand, silt, and clay), and the results show that unsaturated transient infiltration has a positive influence on increasing the foundation bearing capacity. The magnitude of the influence is comprehensively controlled by factors such as soil type, saturated hydraulic conductivity, infiltration intensity, infiltration time, and water table depth. The increase in bearing capacity due to unsaturated transient infiltration can be incorporated into Terzaghi’s equation as a separate component presented in tabular form for engineering design purposes. Full article

This study aimed to examine the shear strength characteristics of sand–granular rubber mixtures in direct shear tests. Two different sizes of rubber and one of sand were used in the experiment, with the sand being mixed with various percentages of rubber (0%, 10%, 20%, 30%, and 50%). The mixtures were prepared at three different densities (loose, slightly dense, and dense), and shear stress was tested at four normal stresses (30, 55, 105, and 200 kPa). The results of 80 direct shear tests were used to calculate the peak and residual internal friction angles of the mixtures, and it was found that the normal stress had a significant effect on the internal friction angle, with an increase in normal stress leading to a decrease in the internal friction angle. These results indicated that the Mohr–Coulomb theory, which applies to rigid particles only, is not applicable in sand–rubber mixtures, where stiff particles (sand) and soft particles (rubber) are mixed. The shear strength of the mixtures was also influenced by multiple factors, including particle morphology (size ratio, shape, and gradation), mixture density, and normal stress. For the first time in the literature, genetic programming, classification and regression random forests, and multiple linear regression were used to predict the peak and residual internal friction angles. The genetic programming resulted in the creation of two new equations based on mixture unit weight, normal stress, and rubber content. Both artificial intelligence models were found to be capable of accurately predicting the peak and residual internal friction angles of sand–rubber mixtures. Full article

Studying the stability of slopes is of great interest since it is associated to various geotechnical applications, e.g., access embankments and landslide mitigation. This paper describes the research conducted to determine the failure load applied at the top of excavations in sandy soils during the construction of deep digs without the use of retaining systems. An experimental program was performed to measure the failure load of ten laboratory-compacted sand slope models that were constructed using different slope angle values and different locations for the applied loading, which consisted of an imposed uniform rate of vertical displacement at the top of the slope. Then, a three-dimensional (3D) numerical model of the laboratory tests was developed to simulate the observed behavior during the experiments by the Plaxis 3D code. The Mohr–Coulomb (MC) and hardening soil (HS) models were used to describe the behavior of the compacted sand. The results showed that the 3D numerical simulations based on the MC model were able to predict the measured failure load within a relative difference of less than 11% for nine tested slope models, while the HS model was better in predicting the measured failure load (a relative difference of 3.5%) for only one experimental setup when the slope angle was equal to 35°. Furthermore, analytical prediction of the failure load using the yield design theory (YDT) permitted the validation of the log-spiral curve describing the observed failure surface for the tested sand slope models. Full article