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The stability problem of high fill slopes has always been a research hotspot. Its failure mechanism is complex and prominent, featuring strong concealment, a short occurrence time and great harmfulness. In this paper, the stability of a high fill slope under rainfall conditions will be studied by using indoor tests, numerical simulations, etc. The study is based on a high fill slope in Yichang City. The evolution law of high fill slope stability under the maximum rainfall condition is revealed. The results show the following: The influence of moisture content on stress–strain curves is reflected in both the curve’s shape and the peak value of deviatoric stress. Under the constraint of confining pressure, the curve decreases and the peak value of deviatoric stress decreases with the increase of moisture content at the same confining pressure. The safety factor obtained by a rigid body limit equilibrium analysis and numerical calculation indicates that the safety factor for a 30° slope meets the requirements for slope stability evaluation and remains in a fundamentally stable state. An on-site investigation suggests that surface failure and shallow failure may be primary failure modes for this slope; therefore, it is recommended to implement slope protection measures. This study provides valuable references for similar high fill slopes.

In order to study the changes in the mechanical properties of road subgrade in cold areas after the freezing and thawing of highways in cold areas, indoor mechanical tests were carried out to investigate the effects of the number of freeze–thaw cycles, freezing temperature, water content, and circumferential pressure on the mechanical properties of road subgrade soil in cold areas after thawing. The mechanical properties of road subgrade soil in cold areas after thawing were measured under different conditions. The test results show that, within the study range: (1) After 7 freeze–thaw cycles, the destructive stress of the subgrade soil decreased from 321.7 kPa to 289.9 kPa, a decrease of 9.9%, and the elastic modulus decayed by 19.9%. (2) When the freezing temperature was reduced from −5 °C to −15 °C, the destructive stress of the subgrade soil decreased from 303.9 kPa to 290.1 kPa, a decrease of 13.8 kPa, approximately 4.5%, and the decrease in modulus of elasticity was about 1.6%. (3) The water content increased from 6% to 12%, and the destructive stress decreased from 405.43 kPa to 288.4 kPa, a decrease of 29.1%, and the modulus of elasticity decreased approximately linearly, with an attenuation of 50.4%. (4) The peripheral pressure increased from 50 kPa to 150 kPa, and the destructive stress increased from 194.7 kPa to 367.7 kPa, a growth of 88.8%, and its modulus of elasticity increased with the increase in peripheral pressure, an increase of 154.1%. The results of this research can provide a reference for highway and engineering construction in the western silt–soil distribution area.

In this study, for triaxial compression testing in geotechnical engineering, large-scale triaxial shear tests of coarse-grained soil were performed under end-restraint and end-free (microfriction) conditions utilizing a large-scale triaxial shear apparatus and a self-developed microfriction load-transfer plate. Under end-restraint and end-free (microfriction) circumstances, the strength and deformation characteristics of the coarse-grained soil were investigated. Further, the effect of the end restraint on the stress–strain characteristics of the coarse-grained soil was analyzed. The findings showed that the coarse-grained soil’s stress–strain curves under the end-restraint and end-free (microfriction) conditions displayed both softening under low confining pressures and hardening under high confining pressures. However, the stress–strain curves’ tendency to soften under low confining pressures was more pronounced under the end-free (microfriction) condition. Due to the influence of the end constraint, the peak strength of the coarse-grained soil increased under the same confining pressure, although the increase was less than 10% when the specimen had the typical height-to-diameter ratio of 2 in the drained triaxial test. Meanwhile, the coarse-grained soil first displayed volumetric contraction under the low confining pressures, followed by volumetric dilation, and it displayed volumetric dilation under the high confining pressures. The volumetric contraction tendency of the coarse-grained soil was more pronounced in the first stages of shearing when the low confining pressures were present. As the shear increased, it became more obvious that the coarse-grained soil had a tendency to dilate under the end-free (microfriction) conditions. Throughout the shearing operation, the coarse-grained soil exhibited a high propensity toward shear contraction. The coarse-grained soil’s strength values were not greatly impacted by the end limitation, but the deformation parameters were. Under the end-restraint conditions, the deformation parameter increased significantly, while the strength parameter only changed slightly.

In order to investigate the mechanical properties and permeability characteristics of sandstone during damage evolution under hydromechanical condition, a series of coupled hydro-mechanical triaxial tests on sandstone specimens were conducted based on the Rock Top 50HT full-stress multi-field coupling triaxial test system. Variations in permeability as a function of confining pressure, seepage pressure gradient, and volumetric strain during damage evolution were obtained. The results show that: (1) When the confining pressure is constant and the specimen is gradually changed from a dry to a saturated state, the failure mode of sandstone changes from shear failure to single-slope shear failure. (2) There are four distinctive stages in the permeability evolution of sandstone: gradual decrease, steady development, gradual increase, and rapid growth. These stages correspond to the complete stress–strain curve under the respective working conditions. (3) Employing the Weibull distribution formula, this study investigates the evolution of fracture damage under varying working conditions and determines the permeability evolution relationships associated with damage variables. This exploration reveals an intrinsic link between permeability and damage variables. These findings enhance our understanding of the interplay between stress, deformation, permeability, and damage evolution in seepage-stress coupled sandstone. The results contribute valuable insights to the field of rock mechanics and hold implications for diverse geotechnical and engineering applications.

This research paper presents an investigation into the shear behavior of binary mixtures composed of cubic and spherical particles, employing the discrete element method (DEM) through triaxial tests simulations. A range of binary particle samples with varying volume fractions of cubic and spherical particles is generated for analysis. The study primarily focuses on examining the contracting-dilatancy relationship of binary granular material samples by scrutinizing deviatoric stress and volumetric strain curves, while considering the influence of confining pressure, initial porosity, and particle size ratio. Furthermore, the paper sheds light on the evolution of microstructures during the shearing process by presenting coordination numbers and rotational velocity fields for different particle types (overall particles, cubic particles, spherical particles), as well as between cubic-spherical particles. The findings demonstrate the substantial impact of both the volume fraction of cubic particles and the particle size ratio on the shear behavior of binary particles at both macroscopic and microscopic scales. Additionally, a comprehensive investigation reveals the dependence of anisotropy in normal contact forces, tangent contact forces, and contact orientations on the volume fraction of cubic particles.

Mining is a primary sector for the national economy of many countries, but exploiting these natural resources causes negative impacts on the environment. Tailings produced during mining, called mine tailings, have to be disposed of, and for that purpose, they are often mixed with Portland cement to control environmental toxicity and improve their mechanical properties. However, the high environmental impacts of producing Portland cement are well known. In this sense, sustainable binders based on the alkaline activation of industrial wastes have been studied as an alternative to using Portland cement. This study focused on applying a sustainable binder based on the alkaline activation of fly ash to improve the mechanical performance of a mine tailing from a mine located in Portugal. Geotechnical tests and chemical analysis were conducted to characterize the mine tailing and fly ash used in the alkaline activation process. In addition, triaxial tests were performed to evaluate the mechanical performance of the specimens, with both natural and stabilized tailings. The developed study proved that stabilized tailing with activated fly ash shows promising mechanical performance showing that this approach can be an excellent alternative to using Portland cement.

As a special road-building material widely distributed in desert areas, critical state soil mechanics is used to study the mechanical properties of sand and make up for the lack of research on its engineering characteristics. A series of drained and undrained triaxial compression tests with a loading rate of 0.12 mm/min medium-density aeolian sands taken from Tengger Desert in the northwest of China was carried out to obtain the three-dimensional state boundary surface. The test results reveal that the strength gained from drained and undrained tests increased, respectively, linearly and non-linearly with the increase of the effective confining pressure. Affected by the variation of pore pressure and shear rate, the undrained strength was higher than the drained strength at low effective confining pressures, and the two types of strengths tend to be consistent when the effective confining pressure becomes greater than 800 kPa. The volumetric changes of the aeolian specimens transition from dilatation to contraction when the effective confining pressures increase. The investigation of the strength, deformation and failure characteristics gives rise to the shape parameters of its state boundary surface, which provides not only a basis for the constitutive modelling of the aeolian sand, but also a reference for roadbed construction and other foundation engineering in desert areas.

The necessary application of sustainable engineering methodologies has been increasing as the number of environmental hazards caused by global warming is on the rise. Cement as a traditional common additive for soil improvement has several negative impacts on the environment. This led to an urge for alternative sustainable solutions. The use of biopolymers as environmentally friendly materials is one of the potential options. This study aims to investigate the effect of xanthan gum biopolymer as a sustainable solution for soil properties enhancement. The Atterberg limits, unconfined compression, CU and UU triaxial tests were performed to examine the effect of xanthan gum on the soil strength and plasticity. Additionally, the durability of biopolymer-treated and untreated soils under wetting and drying cycles and moisture susceptibility were assessed. The results showed that the compressive strength of soil increased by increasing the xanthan gum concentration and curing time and reached its peak value after a specific curing time. The addition of xanthan gum resulted in significant improvement in soil cohesion and caused a reduction in the internal friction angle of the soil. While increasing the number of wetting/drying cycles decreased the soil strength, the biopolymer-treated soil exhibited higher soil strength than the untreated soil. This study provides valuable experiences in the use of xanthan gum biopolymer in practical engineering applications.

Compared with other natural fibers, coir fiber has good strength characteristics and long-term anti-biodegradation ability. At present, most studies on randomly distributed coir fiber-reinforced soil have focused on cohesionless soil or granular soil. In this paper, the influence of randomly distributed coir fiber on the deviatoric stress and shear strength index of red clay with different fiber content was assessed by a consolidated undrained (CU) triaxial compression test. Since the hyperbolic variational character of the stress–strain relation of the samples conformed to the hyperbolic hypothesis of the Duncan–Chang model of nonlinear elastic model, the Duncan–Chang model was used to fit it, and the influences of fiber content and confining pressure on the parameters of the Duncan–Chang model were studied. The fiber content was determined by testing to be 0%, 0.2%, 0.25%, 0.3%, 0.35% and 0.4% of the dry soil mass. It has been found that coir fiber distributed in a random radial manner can significantly increase the deviatoric stress of red clay, and thus can be effectively used in the case of soil and fiber mixing. The cohesion of the red clay first increases and then decreases with the increase in fiber content, with an optimum content of 0.3%. The internal friction angle changes little with increasing fiber content.

To improve the poor characteristics of low strength and high compressibility of weak silty soil, a series of samples with different cement dosage, fiber content, and fiber length was prepared in this experiment, and unconfined compressive strength (UCS) tests, triaxial tests, and scanning electron microscopy (SEM) tests were carried out to explore the influence of polypropylene fiber on the strength of cement-stabilized soil and analyze the curing mechanism of fiber-reinforced cement soil. The test results show that the factors affecting the UCS of the sample from high to low were: cement dosage, fiber content, and fiber length. An orthogonal test found that the optimal ratio of the sample was cement dosage of 18%, fiber content of 0.4%, and fiber length of 3 mm, and the UCS of the sample can reach 1.63 MPa. The triaxial test shows that when the cement dosage is 15% and the fiber length is 9 mm, the incorporation of fiber can significantly improve the toughness and strength of soil. When the cement dosage is 15%, the UCS with 0.4% fiber content is 1.6 times that without fiber. With the increase of fiber content, the peak stress and axial strain of fiber-cured soil are increased, and the cohesion and internal friction angle are also increased. The failure mode and SEM test of fiber-reinforced cement soil show that when the cement dosage is 15% and the fiber length is 9 mm, the addition of fiber can improve the deformation ability of cement soil and slow down the development of cracks. With the increase in fiber content, the number and width of cracks are significantly reduced, and the failure mode changes from brittle failure to ductile failure.

Different from the other roadbed material, the unique mechanical properties of aeolian sand bring great difficulties to the construction and maintenance of desert highways. However, the main attention was usually paid to the engineering properties of aeolian sand, such as collapsibility, strong permeability, and poor gradation. To investigate the shear behaviour of aeolian sand under different engineering conditions, the drained and undrained tests were performed on aeolian sand with relatively large range of density and confining pressure. Under this condition, both the drained and undrained tests tend to the same critical state line, and the shear behaviour of aeolian sand is directly dependent on its density. Under the undrained condition, the q-ε1 curves and the effective stress paths in triaxial stress space exhibit four types of undrained shear behaviour, such as flow, limited flow, strain hardening, and strain softening. Meanwhile all the specimens exhibit three types of failure, such as flow slip, bulging failure, and shear bands. In the q-p’ plane, the analogous drained and undrained stress paths can be followed by aeolian sand with same initial relative density but different confining pressures, and there are two critical state lines due to the generation of shear bands for dense sand. In addition, the critical state lines in e-lnp’ plane decrease with increasing initial relative density Dr, that is, the material constant eᴦ decreases with increasing Dr, and the λ is also not constant but decreases with the increase in Dr. The results suggest that the strength behaviours of aeolian sand can be fitted by a straight line considering relative density and confining pressure and that two empirical formulas are established to describe this feature.

The discrete element method (DEM), a discontinuum-based method to simulate the interaction between neighbouring particles of granular materials, suffers from intensive computational workload caused by massive particle numbers, irregular particle shapes, and complicated interaction modes from the meso-scale representation of the macro information. To promote the efficiency of the DEM and enlarge the modelling scales with a higher realism of the particle shapes, parallel computing on the graphics processing unit (GPU) is developed in this paper. The potential data race between the computing cores in the parallelisation is tackled by establishing the contact pair list with a hybrid technique. All the computations in the DEM are made on the GPU cores. Three benchmark cases, a triaxial test of a sand specimen, cone penetration test and granular flow due to a dam break, are used to evaluate the performance of the GPU parallel strategy. Acceleration of the GPU parallel simulations over the conventional CPU sequential counterparts is quantified in terms of speedup. The average speedups with the GPU parallelisation are 84, 73, and 60 for the benchmark cases.

This work presents the discussion of the results for an experimental study conducted to characterise the mechanical behaviour of ammonia-soda residue (ASR). The calcareous sludge is an alkaline waste formed during the production of soda ash and deposited at the area of the former Solvay Sodium Plant factory in Krakow, Poland. Isotropically consolidation drained (CID) triaxial tests and constant rate of strain (CRS) consolidation tests include the full saturation with water, completion of the consolidation, and the loading/strain rate choice. For this purpose, ASR undisturbed samples were collected from the ground and submitted to laboratory experiments. These samples show a distinct difference in the initial bulk density, the initial level of compaction, initial void ratio, and the natural water content. The CD triaxial tests were conducted under three different levels of confining pressure; in turn, CRS tests were run with two appropriate input strain rates. According to the physical state of ASR and the depth of sampling, two different evolutions of the critical state in the stress–strain space were observed. In the light of the assessed stress–strain–strength behaviour, key design engineering parameters of ASR were calculated.

Liquefaction risk assessment is critical for the safety and economics of structures. As the soil strata of Ramsar area in north Iran is mostly composed of poorly graded clean sand and the ground water table is found at shallow depths, it is highly susceptible to liquefaction. In this study, a series of isotropic and anisotropic consolidated undrained triaxial tests were performed on reconstituted specimens of Ramsar sand to identify the liquefaction potential of the area. The specimens are consolidated isotropically to simulate the level ground condition, and anisotropically to simulate the soil condition on a slope and/or under a structure. The various states of soil behavior are studied by preparing specimens at different initial relative densities and applying different levels of effective stress. The critical state soil mechanics approach for identifying the liquefaction susceptibility is adopted and the observed phenomena are further explained in relation to the micro-mechanical behavior. As only four among the 27 conducted tests did not exhibit liquefactive behavior, Ramsar sand can be qualified as strongly susceptible to liquefaction. Furthermore, it is observed that the pore pressure ratio is a good indication of the liquefaction susceptibility.

Numerous triaxial tests on sand and sand-like materials have been performed worldwide during the past several decades. Their results provided a development of the advanced soil constitutive models and laboratory testing devices, as well as the establishment of a worldwide database of different types of uniform sandy materials. From such research, the critical state and steady state theory has emerged as one of the most useful tool for the modelling of a soil behaviour. This paper presents the results of static drained tests performed on the uniform Drava River sand from the Osijek region in Croatia. The main aim was to determine the shear behaviour and critical state, given that these characteristics are mostly unknown for the tested sand material. A series of detail triaxial tests were performed in drained conditions for three different initial relative densities, DR, and two different loading directions; e.g., axial compression and axial extension. In total, 18 drained tests were performed. The study indicated that the value of 33.75∘ is the critical friction angle for the tested sand. The relative density of 57% is determined as the critical relative density. Additionally, the study confirmed the difference in critical state for compression and extension loading. In addition, the results indicate that the sample preparation procedure has an important impact on the critical state of loosely prepared sandy samples. These results give the first insights into the behaviour of the Drava River sand, which can generally contribute to the worldwide sand behaviour knowledge base.

Fissured expansive soils were widely distributed in the South-to-North Water Transfer Project. Most of the fissures were filled with clay, which controlled the stability of the slope. With the method of layered filling—bevel cutting—refilling and a modular design idea, the sample with a filled fissure preparation device for triaxial test was designed. After setting the filled fissures of gray-green clay in the expansive soil, triaxial tests were carried out for the samples with no filled fissures and with filled fissures with inclination angles of 15°, 30°, and 45°. Then, considering the spatial distribution and the strength of the filled fissures in the slope, the stability analysis method for the expansive soil slope with filled fissures was proposed. The stability of a typical slope in Nanyang was analyzed. The results show that the c of expansive soil with filled fissures was about 12 to 15 kPa and the φ was 3° to 6°. Filled fissures had an attenuation effect on the strength of the expansive soil. The larger the inclination of filled fissures, the more significant the effect of soil strength attenuation. The fissured slope stability was controlled by the filled fissures. The sliding surface was affected by the vertical fissures on the top of the slope and the slow-inclined long-large fissures in the slope, and the shape of the sliding surface was a broken line, which was basically consistent with the actual landslide.

In order to evaluate the improvement effect of fiber on the brittle failure of cement-treated subgrade soil, a series of triaxial unconsolidated undrained (UU) tests were carried out on samples of polypropylene fiber-cement-treated subgrade soil (PCS) with polypropylene fiber mass content of 0‱, 2‱, 4‱, 6‱, and 10‱. The results showed that, (1) the deviatoric stress-axial strain curve of PCS samples were all strain-softening curves. (2) For the same fiber mass content, the peak stress, residual stress, and strain at peak stress of PCS samples gradually increases with the increase in the confining pressure, while their brittleness index gradually decreases. (3) With the increase in confining pressure, compared with that of the 0‱ PCS sample, the increase in peak stress, residual stress, and strain at peak stress of 6‱ PCS sample were in the ranges of 24%−29%, 87%−110%, and 85%−120%, respectively. The decrease in the brittleness index and failure angle was 52%−79% and 16%, while the cohesion and internal friction angle increased by 25.9% and 7.4%, respectively. The results of this study indicate that it is feasible to modify cement subgrade soil with an appropriate amount of polypropylene fiber to mitigate its brittle failure.

Cohesive soils subjected to cyclic loading in undrained conditions respond with pore pressure generation and plastic strain accumulation. The article focus on the pore pressure development of soils tested in isotropic and anisotropic consolidation conditions. Due to the consolidation differences, soil response to cyclic loading is also different. Analysis of the cyclic triaxial test results in terms of pore pressure development produces some indication of the relevant mechanisms at the particulate level. Test results show that the greater susceptibility to accumulate the plastic strain of cohesive soil during cyclic loading is connected with the pore pressure generation pattern. The value of excess pore pressure required to soil sample failure differs as a consequence of different consolidation pressure and anisotropic stress state. Effective stresses and pore pressures are the main factors that govern the soil behavior in undrained conditions. Therefore, the pore pressure generated in the first few cycles plays a key role in the accumulation of plastic strains and constitutes the major amount of excess pore water pressure. Soil samples consolidated in the anisotropic and isotropic stress state behave differently responding differently to cyclic loading. This difference may impact on test results analysis and hence may change the view on soil behavior. The results of tests on isotropically and anisotropically consolidated soil samples are discussed in this paper in order to point out the main features of the cohesive soil behavior.

Knowing the deformation properties of cemented sand and gravel (CSG) material can help construct reasonable constitutive models for the material, which can be used to simulate the structural performance of various practical projects including CSG dams. In this study, to investigate the effect of cement content on the deformation properties of CSG material, we employ triaxial compressive tests for cement contents of 20, 40, 60, 80, and 100 kg/m3 with a confining pressure range of 0.3−1.2 MPa, and theoretically analyze the results by the regression analysis prediction method. Here, we show that both cement content and confining pressure influence the deformation properties of CSG material: for an increase in cement content, the failure strain decreases and brittleness of CSG material increases; the initial modulus of the CSG material increased exponentially with increasing cement content or confining pressure; the peak volumetric strain and its corresponding axial strain increase linearly with increasing confining pressures, which decrease with increasing cement content; the initial tangent volumetric ratio can also be determined by the peak volumetric strain and its corresponding axial strain.

In order to study the influences of confining pressure and temperature on the shear properties of asphalt mixtures, triaxial tests were conducted at 40 °C, 50 °C, and 60 °C, with the confining pressure ranges from 0 to 1 MPa for the widely used continuous-graded AC (Asphalt Concrete)-13, open-graded OGFC (Open-Graded Friction Course)-13, and gap-graded SMA (Stone Mastic Asphalt)-13 asphalt mixtures in China. A nonlinear regression/prediction model of triaxial strength for asphalt mixtures was proposed. The results show that confining pressure and temperature had a significant effect on the shear resistance of asphalt mixtures. With increasing temperature, the shear strength of the asphalt mixture gradually decreased due to the decreasing of cohesion strength; the shear strength of the asphalt mixture increased with the increase of confining pressure. Meanwhile, the cohesion strength increased and the friction angle decreased gradually with the increase of confining pressure. When the confining pressure was close to 0.6 MPa, the Mohr–Coulomb failure envelope bended down, so the linear Mohr–Coulomb criterion is not suitable to describe the failure behavior of asphalt mixtures. Therefore, a power function failure envelope was put forward to characterize the nonlinear shear properties of asphalt mixtures. The nonlinear evolutional laws of shear parameters, which includes cohesion strength and friction angle, were also proposed for asphalt pavement material and structure design. Among these asphalt mixtures, the gap-graded SMA-13 asphalt mixture exhibited better performance on the resistance to shear failure, and it was recommended as the upper layer material to improve the shear performance of asphalt pavement.