Mechanical Behavior Evolution Research Articles

Mechanical behavior evolution and failure characteristics of saturated and dry rocks under different water pressure environments

A complex and changeable water environment is a key factor for safe rock engineering. Variations in water distribution and pressure pose serious challenges in evaluating rock properties and failure modes. To investigate the effect of real water‒rock interactions on rock mechanical behavior, the self-developed hydraulic loading test equipment was designed. A series of mechanical experiments (unjacketed) were carried out on three representative types of rocks under different water pressure environments, and the jacketed test was also performed for the saturated rocks. The experimental results showed that with increasing water confining pressure, the stress‒strain curve of the saturated rocks increased, while that of the dry rocks first decreased and then increased, and that of the sandstone became more obvious. Furthermore, when the water confining pressure increased, the peak stress and elastic modulus of the saturated rocks increased linearly, and those of the dry rocks first decreased and then increased more sharply. Interestingly, the water confining pressure weakened the local tensile failure and aggravated the shear failure. The relationship between the water confining pressure and strength also indicated that the change of saturated rocks more slowly when in contact with the water confining pressure. From the above results, the pore water pressure correction coefficients (μ) of sandstone, marble and granite were 0.98, 0.96 and 0.93, respectively, in the water pressure environment and rock connection. The failure mechanism of saturated rocks is similar to that of rocks without confining pressure due to the balance of the water confining pressure and pore water pressure, and pore water pressure mainly acts as piestic water. For dry rocks, the penetration of pore water firstly weakens the mechanical properties of rocks when pore water pressure is smaller. A greater confining pressure enhances the role of traditional confining pressure for granite and dry rocks.

Effect of SiC particle content on the mechanical behavior and deformation mechanism of SiCp/Al composite under high-frequency dynamic loading

SiCp/Al composites exhibit excellent structural properties but suffer from inherent brittleness, which has brought rigorous challenges on the materials processing. Ultrasonic-vibration-assisted approach offers a promising solution to improve the processability. However, the underlying mechanisms of mechanical response and defect suppression under ultrasonic action have been rarely studied for SiCp/Al composites, hindering the development of high-efficiency processing. This work aims to investigate the mechanical behavior and microstructural evolution in this class of composites with varying SiC volume fractions up to 45% under high-frequency dynamic load induced by ultrasonic vibration. The results showed that the deformation stress of SiCp/Al composites under ultrasonic compression was significantly reduced to only about 1/10 of that under conventional quasi-static loading. Moreover, as the SiC fractions increasing, this ultrasonic softening effect of SiCp/Al became more pronounced. The plastic limit of SiCp/Al with 45% SiC fraction nearly doubled under ultrasonic compression without any macroscopic cracks. The subsequent nanoindentation tests revealed a transition in work-hardening behavior of SiCp/Al with different SiC fractions under ultrasonic loading. Microstructure characterization was conducted to analyze the grain refinement, recrystallization, and deformation textures within the deformed areas, revealing the deformation mechanism of SiCp/Al under different loading mode. TEM observations confirmed the distribution of dislocations in Al matrix and dense stacking faults in SiC particles after ultrasonic compression, indicating that the plastic behaviors were enhanced in both Al matrix and SiC phase under the high-frequency cyclic stress. This research revealed the distinct deformation mechanisms of SiCp/Al composites under high-frequency dynamic loading, exhibiting extremely low deformation stress accompanied with significantly enhanced plasticity. The results provide theoretical insights for the high-efficiency processing and rapid property regulation of particle-reinforced-composites based on ultrasonic-vibration-assisted technologies.

Mechanical behavior and microstructure evolution of slag-fly ash based geopolymer stabilized sand

Geopolymers made from ground granulated blast-furnace slag and fly ash could effectively address the issues of high energy consumption and emissions associated with Portland cement, which is commonly used as a soil curing agent. In this study, the unconfined compressive strength and microstructure of geopolymer-solidified sand were presented and analyzed. The study focused on effect of the type and ratio of activator, the ratio of slag to fly ash, and the ratio of water to (activator and cementitious materials) (W/(A + C)) on the behavior of geopolymer stabilized sand. The results of computed tomography (CT), and scanning electron microscope (SEM) indicate that the variation in initial water content significantly affects the porosity of the specimen, which increased as initial water content increased. The cracks were mainly found at the joints between the individual aggregates and at the edges of the individual aggregates. The pore size distribution of the specimens was concentrated in the range 0.0761–5 μm, while the polymer particle distribution was concentrated in the range 0.0761–10 μm, with a concentration of over 90 %. A significant amount of cementing material was densely distributed around both the aggregates and the pores. CT and SEM testing techniques enable a thorough analysis and mutual verification of the self-compacting process, pore distribution, and size, as well as the distribution of cementing material within the specimens. The optimum ratio for B-S19 has been determined.

Tension and Shear Behaviour of Basalt Fiber Bio-Composites with Digital Image Correlation and Acoustic Emission Monitoring.

This research investigates the mechanical behavior and damage evolution in cross-ply basalt fiber composites subjected to different loading modes. A modified Arcan rig for simultaneous acoustic emission (AE) monitoring was designed and manufactured to apply quasi-isotropic shear, combined tensile and shear loading, and pure tensile loading on specimens with a central notch. Digital image correlation (DIC) was applied for high-resolution strain measurements. The measured failure strengths of the bio-composite specimens under different loading angles are presented. The different competing failure mechanisms that contribute to the local reduction in stress concentration are described. Different damage mechanisms trigger elastic waves in the composite, with distinct AE signatures that closely follow the sequence of fracture mechanisms. AE monitoring is employed to capture signals associated with structural damage initiation and progression. The characteristic parameters of AE signals are correlated with crack modes and damage mechanisms. The evolution of AE parameters during the peak load transition is presented, which enables the timely AE detection of the maximum load transition. The combination of DIC and AE monitoring improves understanding of the mechanical response and failure mechanisms in cross-ply basalt fiber composites, offering valuable insights for possible performance monitoring and structural reliability in diverse engineering applications.

Numerical and experimental investigation of the dynamic mechanical behavior of precipitation-strengthed NiCoCrSi0.3C0.048 medium-entropy alloy

An extended crystal plasticity model and an optimized neural network are established to investigate the mechanical behavior of CoCrNiSi0.3C0.048 Medium entropy alloy (MEA) with a three-level hierarchical precipitation structure under dynamic compressive deformation at a variety of ranges of strain rates. The interaction between the matrix and first-level precipitates is described by a presented hybrid representative volume element RVE model, involving the effects of volume fraction (Vf), radius and geometric distribution on heterogeneous deformation. Effects of second- and third-level precipitates are realized through the extended crystal plasticity constitutive model, reflecting the motion mechanism of dislocations near the precipitates in the form of initial slip resistance. Meanwhile, this study investigates the influence of the presence of primary precipitates on the initiation of slip systems within special grains with Goss or S orientations in the matrix. Additionally, it provides a more in-depth explanation of the underlying principles behind the suppression of Goss texture formation by the precipitates from the perspective of slip systems analysis. The changing of volume fractions affects flow stress evolution. Avoiding suffering from expensive computational consumption by the crystal plasticity finite element method, an artificial neural network model optimized through a genetic algorithm, is presented to predict stress-strain responses and texture evolution results under varying compression strain rates. A reliable dataset derived from crystal plasticity finite element models and experimental results is utilized to train, test, and validate the genetic algorithm-based artificial neural network model. This model demonstrates good prediction capability in dynamic mechanical behavior and texture evolution, showcasing the feasibility and efficacy of the proposed neural network model. Compared to the CPFEM method, neural network models can greatly improve computational efficiency.

Mechanical behavior and performance evolution of railway ballast track under dynamic stabiliser based on the hybrid MBD-DEM simulation

The uncertainty in local structure and time-variable compaction of ballast aggregates poses challenges in selecting suitable stabilization methods and parameters for ballast tracks in practical engineering, often resulting in suboptimal operational outcomes. To address this issue comprehensively, the spatial hybrid model of the double dynamic stabilisers-ballast track (MBD-DEM) is proposed in this paper. Subsequent numerical simulations of stabilisation operations are conducted to elucidate ballast vibration, migration behavior and the evolution of ballast track resistance under varying initial conditions of the ballast bed. Initially, leveraging multibody dynamics theory (MBD) and discrete element method (DEM), a MBD model of double stabilisers and a DEM ballast track model containing 6 sleepers were established respectively. Using the coupling interface, the real-time hybrid calculation of these two models is achieved through 6 sleepers in the middle of the ballast bed. Subsequently, the model's accuracy was validated by comparing test data from stabilisation vehicle operations on a Kunming Railway Bureau test line with simulation data from the dynamic double stabilisers-ballast track spatial hybrid model. Finally, utilizing the proposed hybrid model, the dynamic behavior, contact states, and movement rules of ballast particles during stabilisation operations on both loose and initially stable ballast beds (LBB and ISBB) were investigated at the mesoscopic scale. Concurrently, an in-depth analysis of lateral resistance changes in the ballast bed before and after the stabilisation operation is presented. The relevant findings effectively unveil the evolution of dynamic behavior in the ballast bed during stabilisation operations, concluding with practical suggestions for on-site operations. Simulation results illustrate that the rotation of ballast particles in the XY plane beneath each sleeper is predominantly characterized by harmonic rotation. With an increase in the depth of the ballast bed, the range of the rotation axis for combined angular velocity diminishes, leading to the phenomenon of rotation axis deflection. To ensure operational safety and efficiency, a minimum of two-times stabilization operations is recommended for loose ballast beds (LBB), with three-times operations considered optimal. For initially stable ballast beds (ISBB), one-time stabilization operation is basically sufficient.

Time-varying damage evolution of concrete under cyclic disturbance loading- an experimental observation utilizing AE and DIC

Cyclic disturbance loading affects the continuous operation of concrete structures. This study aims to better understand the failure behavior of concrete structures under cyclic disturbance loading. This study combined acoustic emission (AE) and digital image correlation (DIC) technologies to study mechanical failure behavior and damage evolution of concrete materials under cyclic disturbance loading and unloading. The AE event time-frequency characteristics, surface principal strain program, and damage parameters of samples with different cyclic disturbance amplitudes were obtained by theoretical calculation. The results reveal that when minor disturbance amplitudes are applied, the elastic modulus of concrete specimens tends to increase. When the disturbance amplitude is too large, the elastic modulus of the specimens drops, leading to faster specimen failure. The AE characteristic parameters exhibit a Felicity effect after the sample is subjected to a cyclic disturbance loading. Moreover, the larger the amplitude of the disturbance load, the more frequent the low-frequency and high-amplitude events generated during the final rupture, the higher the concentration of the principal strain on the sample's surface, and the wider the crack band distribution. AE energy and Effective crack are consistent in characterizing damage, and the changing trend of these two damage parameters can better reflect the deterioration process of concrete. The research results will provide practical and theoretical insights for safely operating and maintaining concrete structures.

Evolution and prediction of static and seismic properties in diatomite-incorporated concrete members exposed to freeze-thaw cycles

Freeze-thaw cycles induce substantial durability concerns for concrete infrastructures in cold regions. Traditional approaches to assess freeze-thaw degradation in concrete necessitate extensive environmental and mechanical testing, which are both resource-intensive and time-consuming. This paper introduces a concrete freeze-thaw damage constitutive model, designed for the accurate and efficient quantitative evaluation and prediction of the evolution in concrete's mechanical properties post freeze-thaw cycles. This model specifically considers the impact of supplementary cementitious materials, like diatomite. A numerical program was then developed to simulate the stress-strain responses of both diatomite-enhanced and ordinary concrete under freeze-thaw conditions. Based on these insights, the model was extended to structural members, creating a seismic and static finite element simulation methodology. The findings demonstrate the improvements in the mechanical performance of diatomite- incorporated concrete subjected to both static and seismic loads. This model offers theoretical support for predicting the mechanical behavior evolution of concrete materials and structures in cold climate regions.

Experimental Research on Anisotropy Characteristics of Shale under Triaxial Incremental Cyclic Loading and Unloading

Shale is a common rock type that is associated with underground engineering projects, and several important factors, such as bedding structure, confining pressure, and the loading and unloading path, significantly influence the anisotropy of shale. Triaxial monotonic loading tests and triaxial incremental cyclic loading and unloading tests of shale under three kinds of confining pressures and five types of bedding inclination angles (θ) were thus performed to investigate the anisotropy of shale in terms of mechanical behavior, acoustic emission (AE), and energy evolution, and reveal the mechanism by which shale anisotropy is weakened. The results show that (1) the compressive strength and elastic modulus of shale decrease and then increase as the θ increases, and that both σ3 and incremental cyclic loading and unloading reduce the anisotropy in terms of the compressive strength and elastic modulus of shale, with the ratio of plastic strain to total strain reaching its maximum at a θ of 60° during each loading and unloading cycle. (2) The failure modes of shale with θ of 0°, 30°, and 90° under triaxial monotonic loading are similar to the counterparts under triaxial incremental cyclic loading and unloading, while the failure modes of shale with θ of 45° and 60° differ significantly under the two loading conditions, and interestingly, the degree to which the bedding plane participates in shale crack evolution under incremental cyclic loading and unloading is considerably lower than that under triaxial monotonic loading. (3) The cumulative AE count and AE b-value of shale first decrease and then increase as the θ increases, while the Felicity ratio decreases as the number of cycles increases. (4) As the θ increases, the total energy density U0 and the parameter m, which reflects the accumulation rate of elastic energy, first decrease and then increase, with both reaching a minimum at a θ of 60°. (5) The mode by which cyclic loading and unloading leads to failure in shale with a θ of 60° is similar to that at a θ of 0° and is the main mechanism by which shale anisotropy weakening occurs as a result of cyclic loading and unloading. The results provide experimental support and a theoretical basis for safer and more efficient underground engineering projects that involve shale.

Experimental study on mechanical behavior and permeability evolution of weakly cemented sandstone under unloading conditions

Experimental study on mechanical behavior and permeability evolution of weakly cemented sandstone under unloading conditions

Experimental Study on Dynamic Tensile Mechanical Behavior and Fracture Mechanical Characteristics of Sandstone with a Single Prefabricated Fissure

The structural stability of engineering rock mass under dynamic disturbance is directly associated with the fracture mechanics properties in engineering practice. Fully understanding the rock’s fracture mechanical behavior and crack evolution caused by stress concentration at the crack tip in engineering rock mass under dynamic load can offer useful insight into the rock’s dynamic fracture mechanism. A dynamic test using split-Hopkinson pressure bar (SHPB) test system was performed on a single prefabricated fissure sandstone centrally cracked Brazilian disk (CCBD) specimens. Based on the theory of fracture mechanics and one-dimensional stress wave theory, the dynamic crack initiation criterion of CCBD specimen is proposed, and the regression model of sandstone’s dynamic fracture toughness under the coupling effect of fissure angle and strain rate is established by using response surface methodology (RSM). The influence of strain rate and fissure angle on stress wave characteristics, dynamic tensile mechanical behavior, and fracture mechanics characteristic was investigated in this study. The findings demonstrate that: (1) The fissure angle plays a pivotal role in determining the failure mode of sandstone. As the fissure angle increases, three distinct failure modes emerge in the sandstone specimens, while variations in strain rate have minimal impact on the fracture mode of these specimens. (2) Alterations in the fissure angle result in changes to the waveform of transmitted waves. When the fissure angle is below 30°, the transmitted wave exhibits “double peak” characteristics; when it exceeds 30°, a “single peak” waveform is observed. This phenomenon can be attributed to diffraction principles governing incident waves. (3) When the impact pressure is 0.2 MPa, the peak load initially exhibits an increase followed by a decrease, with the peak load reaching its maximum at a fracture angle of 60°; when the impact pressures are 0.3 and 0.5 MPa, there exists a negative correlation between the peak load and the fissure angle. (4) The influence of strain rate on sandstone’s fracture resistance is predominant, with alterations in fissure angle exerting an auxiliary effect on this property. The research results can provide a theoretical and experimental basis for dynamic disaster prevention in urban underground space.

Immature porcine cortical bone mechanical properties and composition change with maturation and displacement rate

Computational models of mature bone have been used to predict fracture; however, analogous study of immature diaphyseal fracture has not been conducted due to sparse experimental mechanical data. A model of immature bone fracture may be used to aid in the differentiation of accidental and non-accidental trauma fractures in young, newly ambulatory children (0–3 years). The objective of this study was to characterize the evolution of tissue-level mechanical behavior, composition, and microstructure of maturing cortical porcine bone with uniaxial tension, Raman spectroscopy, and light microscopy as a function of maturation. We asked: 1) How do the monotonic uniaxial tensile properties change with maturation and displacement rate; 2) How does the composition and microstructure change with maturation; and 3) Is there a correlation between composition and tensile properties with maturation? Elastic modulus (p < 0.001), fracture stress (p < 0.001), and energy absorption (p < 0.014) increased as a function of maturation at the quasistatic rate by 110%, 86%, and 96%, respectively. Fracture stress also increased by 90% with maturation at the faster rate (p = 0.001). Fracture stress increased as a function of increasing displacement rate by 28% (newborn p = 0.048; 1-month p = 0.004; 3-month p= < 0.001), and fracture strain decreased by 68% with increasing displacement rate (newborn p = 0.002; 1-month p = 0.036; 3-month p < 0.001). Carbonate-to-phosphate ratio was positively linearly related to elastic modulus, and fracture stress was positively related to carbonate-to-phosphate ratio and matrix maturation ratio. The results of this study support that immature bone is strain-rate dependent and becomes more brittle at faster rates, contributing to the foundation upon which a computational model can be built to evaluate immature bone fracture.

Experimental study on mechanical behavior, AE response and energy evolution of fissure-filled sandstone from mine roadway under conventional triaxial compression

Engineering reliability exhibit sophistication and unpredictability for mining from all the regions, largely due to the random combinatorial morphology of natural discontinuities associated with the ubiquitous fissures in the rock formation. This study determined the effects of intersecting fissure angle (none, 0°, 30°, 45°, 60°, and 90°) and confining pressures (4, 8, 12, and 16 MPa) on its mechanical behaviors by triaxial compression tests targeting in fissure-filled sandstones from Lu-Xi coal in Shandong Province, China. Mechanical and AE results indicated that fissure inclination and confining pressure were the origin of the variation in the mechanical behaviors and AE parameters of the sandstone specimens. With increase of pre-existing flaw angle, the peak strength, elastic modulus, peak strain and AE counts presented a U-shape trend. With rise of confining pressure, these parameters displayed a linearly upward trend. However, no significant correlation was found for the Poisson’s ratio. Besides, energy analysis showed that the energy values of the specimens at the peak stress reflected well the variation of the mechanical parameters of the fractured sandstone. This study provided implications for stability of surrounding rock in mine roadway.

Microstructure, mechanical properties and thermal shock behavior of 2.5D oxide fiber preform reinforced oxide matrix composites

The 2.5D oxide/oxide composites become attractive for their excellent integrity and mechanical properties. The thermal shock resistance performance of the material is very important in the actual high temperature application. In this work, the evolution of microstructure and mechanical behavior of the 2.5D oxide/oxide composites from thermal shock at different temperatures and cycles was investigated experimentally mainly by optical microscope, X-ray computed tomography and macro-mechanical tests. The thermal shock resistance mechanism of oxide/oxide composites was qualitatively explored. The results showed that cracks propagation was the main manifestation of thermal shock damage in composites. Compared with 2D composites, 2.5D composites exhibited the finite domain effect on crack propagation due to its reinforcement had certain fibers in Z-direction. This directly caused the critical thermal shock temperature difference of the 2.5D composites (∼900 °C) was more than twice that of the 2D oxide/oxide composites (∼400 °C). In addition, the finite domain effect also significantly reduced the damage growth rate of the 2.5D composites from cyclic thermal shock, highlighting its excellent thermal shock damage resistance.

Dual-scale 3DEC-GBM Discrete Element Simulation On Mechanical Behavior and Anisotropic Fracture Evolution Mechanism of Rock Induced by True Three-dimensional Stress

Dual-scale 3DEC-GBM Discrete Element Simulation On Mechanical Behavior and Anisotropic Fracture Evolution Mechanism of Rock Induced by True Three-dimensional Stress

Study on time effect and prediction model of shear strength of root-soil complex under dry-wet cycle

Triaxial compression tests were conducted on the alfalfa root-loess complex at different growthperiods obtained through artificial planting. The research focused on analyzing the time variation law of the shear strength index and deformation index of the alfalfa root-loess complex under dry-wet cycles. Additionally, the time effect of the shear strength index of the alfalfa root-loess complex under dry-wet cycles was analyzed and its prediction model was proposed. The results show that the PG-DWC (dry-wet cycle caused by plant water management during plant growth period) causes the peak strength of plain soil to change in a "V" shape with the increase of growth period, and the peak strength of alfalfa root-loess complex is higher than that of plain soil at the same growth period. The deterioration of the peak strength of alfalfa root-loess complex in the same growth period is aggravated with the increase of drying and wetting cycles. Compared with the 0 days growth period, the effective cohesion of alfalfa root-loess complex under different dry-wet cycles maximum increase rate is at the 180 days, which are 33.88%, 46.05%, 30.12% and 216.02%, respectively. When the number of dry-wet cycles is constant, the effective cohesion of the alfalfa root-loess complex overall increases with the growth period. However, it gradually decreases comparedwith the previous growth period, and the minimum increase rate are all at the 180 days. For the same growth period, the effective cohesion of the alfalfa root-loess complex decreases with the increase of the number of dry-wet cycles. This indicates that EC-DWC (the dry-wet cycles caused by extreme natural conditions such as continuous rain) have a detrimental effect on the time effect of the shear strength of the alfalfa root-loess complex. Finally, based on the formula of total deterioration, a prediction model for the shear strength of the alfalfa root-loess complex under dry-wet cycles was proposed, which exhibits high prediction accuracy. The research results provide useful guidance for the understanding of mechanical behavior and structural damage evolution of root-soil composite.

Mechanical behavior and microstructure evolution of different aluminum materials under shock loading

The mechanical behaviors and microstructure evolutions of different aluminum materials including high-purity aluminum, 7075 aluminum alloy and selective laser melted (SLM) AlSi10Mg alloy under shock loading were investigated through plate impact experiments and microstructure characterization. The results show that the Hugoniot elastic limit stress has nothing to do with impact velocity, but is related to material type; the peak shock stress significantly increases with increasing impact velocity and is somewhat affected by material type. The microstructure variation is highly dependent on the material type. In the 7075 aluminum alloy and selectively laser melted (SLM) AlSi10Mg alloy with relatively high strengths, the microstructure, including the grain size, grain shape and misorientation angle, is slightly influenced by the impact velocity. In high-purity aluminum with low strength, the microstructure is closely related to the impact velocity. As the impact velocity increases, dislocations, elongated subgrains, equiaxed subgrains and a fraction of low angle grain boundaries (LAGBs) first increase and then decrease, accompanied by the formation of numerous ultrafine equiaxed grains with sizes in the range of 1–5 μm. The limited adiabatic temperature rise during high-velocity impact cannot affect the microstructure. High rate loading was confirmed as an effective and promising method to refine grain structure for low strength materials.

Mechanical behavior, acoustic emission and principal strain field evolution properties of layered cemented paste backfill under unconfined compression

In order to save costs, the layered filling method is adopted by mine enterprise to fill the underground goafs. To understand the mechanical behavior, damage evolution and failure modes the layered cemented paste backfill (LCPB), this study investigated the strength properties, acoustic emission (AE) characteristics and principal strain field evolution of LCPB samples with cement-to-tailings (c/t) ratio of 1:4, 1:6, 1:8, 1:10, and the height (h) of middle layer of 30 mm, 35 mm, 40 mm, 45 mm, 50 mm. The obtained results indicate that: (1) UCS of LCPB decreases with the increases of h and with the decreases of c/t ratio. The influence of c/t ratio on UCS of LCPB is in a good agreement with logarithmic function, while the variation relationship between h and UCS of LCPB satisfies the exponential function. (2) The acoustic emission signals first appeared during the transition from the compression to the elastic stage, reaching a maximum approaching the peak stress, and AE ringing counts also appeared during the post-peak stage. Internal fracture type of LCPB under external loading is a tension-shear composite fracture dominated by shear fracture. (3) The damage of LCPB occurs mainly in the middle layer and then extends to the upper and lower layer with the formation of visible localized zones. The damage of LCPB developed from significant shear damage to tensile-shear damage with the decreased of the c/t ratio, and transitioned from tensile-shear damage to complex damage dominated by shear damage and supplemented by tensile damage as h increased. Ultimately, the findings of this work can provide a reference for the design of LCPB.

A new procedure for characterizing the critical intergranular contact state of non-plastic sand – fines mixed materials

A key and urgent scientific issue is how to characterize the complex intergranular contact state and mechanical behavior evolution of sand–fines mixed materials and then show how this state contributes to the static and dynamic properties of such materials. Both theoretical analyses and experimental data suggest that the mixes have different intergranular contact states as the fines content (FC) increases, and the mixed materials can be classified as sand-like, in-transition, or fines-like. The capability of the Rahman semi-empirical formula to predict the threshold fines content FCth—which distinguishes the regime of “fines in sand” (sand-dominated behavior) from that of “sand in fines” (fines-dominated behavior)—is verified using the basic material and mechanical properties of mixed materials from the literature. Developed from the method for determining the theoretical minimum void ratio, a new method that allows unified characterization of the critical intergranular contact state parameters FCin-min and FCin-max for in-transition soils is established based on the binary packing model, and FCin-min and FCin-max can be determined simply through explicit expressions that use some material physical indices of pure-sand and pure-fines materials. The proposed procedure offers significant advantages for evaluating the critical intergranular contact state and mechanical properties of sand–fines mixed materials in geotechnical engineering practice.

Mechanical behavior and microstructure evolution of Malan loess under dynamic compaction

Mechanical behavior and microstructure evolution of Malan loess under dynamic compaction