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Cyclic triaxial tests with intermittent cyclic loading are usually used to investigate the deformation behaviors of soil; however, both deviator stress and confining pressure vary cyclically under traffic loading. Moreover, the pore water in soil can be dissipated throughout the test, affecting the mechanical behaviors of soils. Therefore, in this study, three test modes were applied to saturated soft clay to analyze the deformation behaviors, in which different cyclic confining pressures were used during cyclic loading periods, and different drained conditions during cyclic loading and intermittent periods were considered. The variations in strain increment were similar in all cases: as the loading stages progressed, the strain increment gradually diminished. The distinct variation in strain increment became evident in the initial loading stage, but it became negligible in subsequent loading stages. Furthermore, the change in strain increment with respect to cyclic confining pressure was influenced by drained conditions during the cyclic loading period: it increases as the cyclic confining pressure increased under partially drained conditions and decreases under undrained conditions. Moreover, the strain increased under partially drained conditions during intermittent periods, companying with the discharge of pore water, while it decreased for the recovery of specimen deformation under undrained conditions. The greater strain increment was caused under partially drained conditions during cyclic loading periods compared with the corresponding strain increment under undrained conditions. Besides, an empirical model was developed to forecast accumulated axial strain of soil subjected to intermittent cyclic loading, and the variations of parameters under different drained conditions were studied. [ABSTRACT FROM AUTHOR]

Red mudstone is a problematic soil that is easily subjected to weathering, disintegrating, and swelling. In this study, a series of large-scale cyclic triaxial tests were performed to investigate the cumulative deformation behavior of red mudstone clay mixed with weathered red mudstone gravel as an improved coarse-grained red mudstone soil (IRMS). The influences of compaction moisture content and confining pressure were investigated. The cyclic loading was applied from 25 to 225 kPa with an increment of 25 kPa and 1,000 or 2,000 cycles for each stage at a frequency of 2 Hz. The experimental results indicate that the strains at the onset of failure are approximately 1% for the optimal moisture content (OMC) with the number of cycles N = 14,000–16,000, and the strains are approximately 1% for the moisture content 2% dry of OMC with N = 12,000–14,000, while the strains exceed 10% for the moisture content 2% wet of OMC with N = 3,000–4,000. The cumulative strain decreases with increasing confining pressure from 20 to 50 kPa, but the influence becomes more significant under higher dynamic stress. A prediction model is proposed for the evolution of cumulative strain under cyclic loading. The IRMS could be used as a construction material for railway subgrade with proper control of field compaction moisture content. [ABSTRACT FROM AUTHOR]

The cyclic hardening characteristics of soil hold significant importance for understanding its performance, and the evolution of the deformation modulus serves as a crucial indicator of the hardening properties. Deformations can be classified into elastic and plastic deformations and expressed in terms of modulus; however, their roles in the cyclic hardening process remain unclear. In this study, the elastic and plastic moduli were separated using the hyperbolic evolutionary model, which characterized the evolutionary properties of both to reflect the cyclic hardening process. A series of cyclic triaxial shear tests was conducted utilizing ISO sand and emery as test materials. A hyperbolic evolution model relating the equivalent modulus to the number of cycles was established, and the effect of various test conditions on the elastic modulus is discussed. The results indicate that: (1) the relationship between the equivalent modulus and the number of cycles is hyperbolic; and (2) the parameters k and b of the hyperbolic evolution model correspond to the elastic and plastic moduli, allowing for the separation of the evolution of both from that of the deformation modulus. The hyperbolic evolution model of the equivalent modulus proposed in this paper offers new insight into the cyclic hardening properties of sand. [ABSTRACT FROM AUTHOR]

In this article, a numerical calibration procedure for undrained cyclic triaxial tests is presented to evaluate the liquefaction potential in sand and silt samples from mining tailings in northern Chile. The numerical modeling of an axisymmetric specimen involved two stages: isotropic consolidation using the Hardening Soil Small (HSS) model and a cycling phase employing the UBC3D-PLM model to simulate the onset of liquefaction using the criterion that the excess pore pressure ratio R u should exceed 0.8. The results demonstrate that the UBC3D-PLM modeling calibrated with experimental data from cyclic triaxial tests effectively represents the excess pore pressure in both sandy and silty soils from mining tailings. The accuracy of the modeling decreases when a single set of parameters is applied to the same soil at different cyclic stress ratios (CSR), highlighting the need for specific calibrations for each loading. [ABSTRACT FROM AUTHOR]

Liquefaction assessment based on strain energy is significantly superior to conventional stress-based methods. The main purpose of the present study is to investigate the correlation between shear wave velocity and strain energy capacity of silty sands. The dissipated energy until liquefaction occurs was calculated by analyzing the results of three series of comprehensive cyclic direct simple shear and triaxial tests on Ottawa F65, Nevada, and Firoozkuh sands with varying silt content by weight and relative densities. Additionally, the shear wave velocity of each series was obtained using bender element or resonant column tests. Consequently, for the first time, a liquefaction triggering criterion, relating to effective overburden normalized liquefaction capacity energy (WL/σc’) to effective overburden stress-corrected shear wave velocity (Vs1) has been introduced. The accuracy of the proposed criteria was evaluated using in situ data. The results confirm the ability of shear wave velocity as a distinguishing parameter for separating liquefied and non-liquefied soils when it is calculated against liquefaction capacity energy (WL/σc’). However, the proposed WL/σc’-Vs1 curve, similar to previously proposed cyclic resistance ratio (CRR)-Vs1 relationships, should be used conservatively for fields vulnerable to liquefaction-induced lateral spreading.

Accurately predicting pore-water pressure is essential for comprehending soil behavior under seismic loads and for estimating effective stresses. In recent years, various models have been proposed to estimate pore pressure development for clean sands, silts, and clays. However, in nature, soils often consist of mixed formations. Considering the nature of soil formations, in this study the pore pressure development of clayey sand was investigated. The excess pore water pressure development of clayey sand under dynamic loads using three different models from the literature is analyzed. For this purpose, stress-controlled dynamic triaxial test were performed on specimens prepared poorly graded sands with three different kaolin clay contents (FC=5-15) to measure excess pore water pressure generation at four cyclic stress ratios. Specimens were prepared by using wet tamping method to be ensure homogeneity. The tests were conducted under an effective confining pressure of 100 kPa. The results were used to obtain excess pore water pressure development of clayey sands under undrained dynamic conditions. Then, the results were compared with three different pore water pressure generation models. The model coefficients of three models were updated for clayey sand. Although it was proposed for clean sands, the model presented by Seed et al. [23] has also proven to be quite suitable for clayey sands. [ABSTRACT FROM AUTHOR]

This study aims to explore the accumulated behavior of reinforced coarse-grained soils through cyclic triaxial tests and to develop a prediction model for the plastic shakedown limit. Cyclic triaxial test results illustrate that the reinforced specimens, especially those incorporating geocells, demonstrate the lowest accumulated axial strain and the highest plastic shakedown limit when compared to unreinforced ones under identical cyclic loading. Additionally, the accumulated axial strain at the plastic shakedown limit for reinforced specimens is determined. This strain is then used to determine the additional confining pressure exerted by geogrid or geocell, employing a function proposed by Yang and Han. By integrating the additional confining pressure into the plastic shakedown criterion for unreinforced specimens, a prediction model for the plastic shakedown limit in reinforced specimens is ultimately established. The model's applicability and the accuracy of computed additional confining pressure values are validated using experimental data. • Cyclic triaxial tests are conducted to investigate the coarse-grained soil. • The influence of reinforcement types on the accumulation behavior is analyzed. • The plastic shakedown limits of two types reinforced specimens are determined. • A prediction model is proposed to determine the soil's plastic shakedown limit. • The accuracy of the proposed model is validated using the experimental data. [ABSTRACT FROM AUTHOR]

Silty soil is a transitional soil between clay and sand and is widely distributed around the world. With the rapid urban development and associated infrastructure need, silty soil has become more widely used as the bearing soil for foundations and roads. The liquefaction of silty soil under the earthquake can cause serious damage to buildings and infrastructure resting on such soil. Correctly analyzing the dynamic characteristics of silty soil in earthquake areas plays a major role in the success or failure of infrastructure construction. Therefore, it is particularly important to study the various factors affecting the dynamic characteristics of silty soil and to analyze the changing trend and associated mechanism on the dynamic characteristics of silty soil. In this paper, a set of cycle triaxial tests were carried out using the orthogonal design method to study the effects of four factors, namely initial void ratio, load frequency, clay content and silt content, on the dynamic characteristics of saturated silty soil at different levels. The orthogonal design method is used to study the order of influence of four factors on the dynamic strength and excess pore water pressure of silty soil, and the significance level of each factor was also assessed. [ABSTRACT FROM AUTHOR]

The stable and safe operation of highway/railway lines is largely dependent on the dynamic behavior of subgrade fillings. Clay soils are widely used in subgrade construction and are compacted at different remolding water contents and compaction degrees, depending on the field conditions. As a result, their dynamic behaviors may vary, which have not been fully investigated until now. To clarify this aspect, a series of cyclic triaxial tests were carried out in this study with three typical remolding water contents (w = 19%, 24%, and 29%), corresponding to the optimum water content as well as its dry and wet sides, and two compaction degrees (Dc = 0.8 and 0.9), which were selected according to the field-testing data. Scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) tests were also conducted on typical samples to investigate the corresponding soil fabric variations. The findings indicate the following: (a) The soil fabric at the optimum remolding water content and its dry side was characterized by a clay aggregate assembly with a bimodal pore size distribution. In contrast, the soil fabric on the wet side of the optimum water content consisted of dispersed clay particles with a unimodal pore size distribution. (b) As the compaction degree increased, to ensure the optimum water content and its dry side, large pores were compressed to make them smaller, while small pores remained unchanged. Comparatively, all the pores on the wet side were compressed to make them smaller. (c) For each compaction degree, as the remolding water content increased, a non-monotonic changing pattern was identified for both the permanent strain and resilient modulus; the permanent strain first decreased and then increased, while, for the resilient modulus, an initial increasing trend and then a decreasing trend were identified. In addition, a larger changing rate of the permanent strain (resilient modulus) was observed on the dry side, indicating a larger effect of the remolding water content. (d) For each remolding water content, as the compaction degree increased, the permanent strain exhibited a decreasing trend, but an increasing trend was identified for the resilient modulus. Moreover, the rate of change in the permanent strain (resilient modulus) on the dry side of the optimum water content was larger than that on the wet side. In contrast, the minimum rate of change was identified at the optimum water content. The obtained results allowed for the effects of the remolding water content and compaction degree on the dynamic behavior to be analyzed, and they helped guide the construction and maintenance of the subgrade. [ABSTRACT FROM AUTHOR]

Numerical modeling serves as a widely utilized method for addressing geotechnical concerns. A pivotal aspect of this modeling process is the accurate characterization of material behavior. The connection between stress and strain tensors within soil is explicated by the soil constitutive equation, which is reliant on factors like soil type and deformation circumstances. One notable model is hypoplasticity, which has been in use for more than three decades. This research aims to calibrate the hypoplastic parameters for Danube sand using the SoilTest Module of PLAXIS. The constitutive hypoplastic model for Danube sand was fine-tuned through a series of numerical simulations. The parameter calibration occurred twice: initially according to 5 cycles of hysteresis loop of stress-strain diagram of cyclic triaxial testing, and then subsequently in accordance with strain trends observed after ten thousand cycles. A comparison was drawn between parameters determined from the overall strain trends and those calibrated based on the five cycles. The findings indicate that while the model calibrated during a specific segment of testing can accurately predict strain values during compression and extension, it falls short in forecasting the accumulated settlement following prolonged cyclic loading. This suggests the model's limited capability in anticipating long-term cyclic load effects on settlement behavior. [ABSTRACT FROM AUTHOR]

After the 1995 Hyogo-ken Nanbu Earthquake in Japan, rock structures, including rock slopes and underground cavities, were required to be evaluated for seismic resistance. Understanding the dynamic deformation properties of hard rock is essential for performing dynamic response analysis of large deformations of rock structures. This paper discusses the effect of confining pressure on the strain level dependence of the Young’s modulus and damping ratio of water-saturated sandstone based on the results of cyclic triaxial tests. The relationship between the axial strain and equivalent Young’s modulus ratio is different for quasi-elastic deformation below 2,000 με and elastoplastic deformation above 2,000 με and hence can be approximated by two logarithmic functions. The relationship at the quasi-elastic strain level can be approximated by the same function regardless of the confining pressure. However, at the elastoplastic strain level, the slope of the logarithmic function decreases with increasing confining pressure. Furthermore, the relationship between the axial strain and damping ratio is distributed on the same curve regardless of the confining pressure in the axial strain range below 4,000 με. However, when the axial strain exceeds 4,000 με, this relationship deviates from the curve and the damping ratio rapidly increases with decreasing confining pressure. The experimental results for water-saturated sandstone were compared with those for dry sandstone presented in a previous paper. At the quasi-elastic strain level, the relationship between the axial strain and equivalent Young’s modulus ratio can be approximated by the same function regardless of the water content. However, at the elastoplastic strain level, the slope of the logarithmic function is greater for water-saturated sandstone than for dry sandstone. Meanwhile, the relationship between the axial strain and damping ratio, regardless of the water content, is distributed on the same curve in the range from quasi-elastic to elastoplastic strain.

In this paper, cyclic triaxial tests are performed by using discrete element method (DEM) to investigate the dynamic behaviors of QH-E lunar soil simulant. The influences of number of cycles, loading frequency, waveform, cyclic stress ratio (CSR) and confining pressure on the dynamic behaviors of lunar soil simulant are discussed. The results indicate that the axial strain and dynamic modulus first increase and then tend to be stable with increasing number of cycles. The dynamic modulus increases with increasing the loading frequency, while the axial strain decreases. The damping ratio is not particularly sensitive to the confining pressure and CSR, it only decreases slightly with increasing confining pressure or decreasing CSR. Under the same conditions, rectangular wave dynamic load can produce a larger axial strain and a smaller dynamic modulus than those of sine and triangular waves, and a higher loading frequency will lead to a higher dynamic modulus and a lower axial strain, these characteristics are consistent with other lunar soil simulants and sandy soils tested in the experiment. However, the effect of confining pressure on the dynamic modulus depends on the magnitude of the CSR. For the lower CSR (CSR<0.6), the dynamic modulus increases with increasing confining pressure. While for the higher CSR(CSR>0.6), the dynamic modulus decreases significantly with increasing confining pressure, which demonstrates the unique dynamic characteristics that differs from other lunar soil simulants and sandy soils, and shows the importance of considering the magnitude of the CSR under cyclic triaxial tests. • Dynamic characteristics of QH-E lunar soil simulant under cyclic triaxial tests are studied by DEM. • Dynamic modulus and axial strain first increase and then gradually tend to be stable with increasing number of cycles. • The damping ratio is not particularly sensitive to the confining pressure and CSR. • Effect of confining pressure on the dynamic modulus depends on the magnitude of CSR. [ABSTRACT FROM AUTHOR]

The present study provides insight into the cyclic behavior of unreinforced and geogrid-reinforced coral sand. To achieve these goals, stress-controlled undrained cyclic triaxial tests were conducted on medium-dense coral sand with and without geogrid reinforcements. The influence of geogrid reinforcement, cyclic stress ratios, and confining pressure on the deformation, pore pressure, liquefaction resistance, stiffness degradation, and particle breakage characteristics of saturated coral sand was investigated. The results indicated that coral sand reinforced with geogrid increased the liquefaction resistance and decreased the rate of pore pressure accumulation. The effectiveness of the geogrid inclusion on coral sand's liquefaction resistance was found to be more pronounced under large effective confining pressure and a smaller cyclic stress ratio. Increasing the effective confining pressure increases the liquefaction resistance for both unreinforced and geogrid-reinforced coral sand, whereas increasing the cyclic stress ratios decreases the liquefaction resistance of the unreinforced and reinforced coral sand. The particle breakage was observed to be increased with increasing the effective confining pressure and cyclic stress ratio, and the breakage was more in the reinforced coral sand than the unreinforced coral sand. [ABSTRACT FROM AUTHOR]

After the 1995 Hyogo-ken Nanbu Earthquake in Japan, rock structures, including rock slopes and underground cavities, were required to be evaluated for seismic resistance. Understanding the dynamic deformation properties of hard rock is essential for performing dynamic response analysis of large deformations of rock structures. This paper discusses the effect of confining pressure on the strain level dependence of the Young's modulus and damping ratio of water-saturated sandstone based on the results of cyclic triaxial tests. The relationship between the axial strain and equivalent Young's modulus ratio is different for quasi-elastic deformation below 2,000 and elastoplastic deformation above 2,000 p,E and hence can be approximated by two logarithmic functions. The relationship at the quasi-elastic strain level can be approximated by the same function regardless of the confining pressure. However, at the elastoplastic strain level, the slope of the logarithmic function decreases with increasing confining pressure. Furthermore, the relationship between the axial strain and damping ratio is distributed on the same curve regardless of the confining pressure in the axial strain range below 4,000 p,e. However, when the axial strain exceeds 4,000 re, this relationship deviates from the curve and the damping ratio rapidly increases with decreasing confining pressure. The experimental results for water-saturated sandstone were compared with those for dry sandstone presented in a previous paper. At the quasi-elastic strain level, the relationship between the axial strain and equivalent Young's modulus ratio can be approximated by the same function regardless of the water content. However, at the elastoplastic strain level, the slope of the logarithmic function is greater for water-saturated sandstone than for dry sandstone. Meanwhile, the relationship between the axial strain and damping ratio, regardless of the water content, is distributed on the same curve in the range from quasi-elastic to elastoplastic strain. [ABSTRACT FROM AUTHOR]

The relationship between stress and strain tensors in soil is described by the soil constitutive equation, which depends on the soil type and deformation conditions. The development of various constitutive models has enabled a better understanding of the macromechanical properties of soil. One such model is hypoplasticity, which was discovered more than three decades ago. The purpose of this study is to determine whether hypoplasticity could accurately represent the behavior of Danube sand, a specific type of sand. The researchers conducted laboratory measurements to obtain the eight basic hypoplastic parameters of Danube sand and employed the intergranular strain concept as an extension of hypoplasticity to achieve a more precise material behavior. All the parameters were then utilized to simulate the cyclic triaxial test using the SoilTest Module of PLAXIS. The results showed that the hypoplastic constitutive simulation model for Danube sand was capable of making relatively accurate predictions for accumulative settlement.

Liquefaction is considered one of the most common phenomena resulting in serious damage during earthquakes. Appropriate estimation of liquefaction potential, damping characteristics and shear modulus of soil under dynamic loading is crucial for precise dynamic response analysis and soil modelling problems. The present paper emphasises the influence of relative density, confining pressure, and shear strain on the cyclic response of sand specimens. A parametric study comprising varying relative densities (35–65%), confining pressures (100–150 kPa), and shear strain (0.015–1.3%) under 1 Hz loading frequency was conducted in the laboratory. The sand samples were subjected to a series of consolidated undrained cyclic triaxial tests. It is observed that with an increase in confining pressure and relative density, the pore pressure ratio reduced; whereas an increase in pore pressure ratio was witnessed with an increase in shear strain. The influence of cement inclusion on the cyclic response of the specimens is evaluated for varying cement contents (1–4%). The addition of 4% cement considerably enhanced the strength of sand and arrested the liquefaction instigation. [ABSTRACT FROM AUTHOR]

In this study, the damping responses of uniform soil, equi-proportional fly ash, and local soil as a single unit were investigated. The large-strain cyclic triaxial tests were performed for the specimen compacted at the desired density (95%–99% of maximum dry density). The compacted specimens were tested under the loading frequency of 0.3–1 Hz with medium confinement of 70–100 kPa. Also, the unsymmetrical behavior of the hysteresis loop was analyzed using three different damping estimation approaches, i.e. symmetric hysteresis loop (SHL), asymmetric hysteresis loop (ASHL), and the modified American Society for Testing and Materials (ASTM) method. The outcome of the study shows for fly ash, local soil, and layered soil-ash, the ASHL technique has the highest damping value, followed by ASTM and then the SHL approach. The specimens prepared under high density and subjected to high confinement show low damping values. However, the specimens tested at high frequency exhibits high damping behavior. Similarly, the damping value of fly ash determined using the SHL and ASHL methods has a similar profile and reaches a maximum at 1% shear strain value before decreasing. The composite stratified deposit exhibits more dependency on relative compaction, confining pressure, and less on loading frequency. Based on the results, it is highly recommended to use the ASHL approach, especially under large strain conditions irrespective of soil type. The maximum damping ratio of stratified deposits is always in between the damping ratio of local soil and fly ash. The damping ratio of stratified soil and local soil is slightly larger than that of the other soils, although the damping ratio of fly ash is equivalent to that of the sand and clayey soil. These results may be helpful in the accurate determination of the damping properties of the layered soil-ash system that is required in the seismic response analysis.

The stable and safe operation of highway/railway lines is largely dependent on the dynamic behavior of subgrade fillings. Clay soils are widely used in subgrade construction and are compacted at different remolding water contents and compaction degrees, depending on the field conditions. As a result, their dynamic behaviors may vary, which have not been fully investigated until now. To clarify this aspect, a series of cyclic triaxial tests were carried out in this study with three typical remolding water contents (w = 19%, 24%, and 29%), corresponding to the optimum water content as well as its dry and wet sides, and two compaction degrees (Dc = 0.8 and 0.9), which were selected according to the field-testing data. Scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) tests were also conducted on typical samples to investigate the corresponding soil fabric variations. The findings indicate the following: (a) The soil fabric at the optimum remolding water content and its dry side was characterized by a clay aggregate assembly with a bimodal pore size distribution. In contrast, the soil fabric on the wet side of the optimum water content consisted of dispersed clay particles with a unimodal pore size distribution. (b) As the compaction degree increased, to ensure the optimum water content and its dry side, large pores were compressed to make them smaller, while small pores remained unchanged. Comparatively, all the pores on the wet side were compressed to make them smaller. (c) For each compaction degree, as the remolding water content increased, a non-monotonic changing pattern was identified for both the permanent strain and resilient modulus; the permanent strain first decreased and then increased, while, for the resilient modulus, an initial increasing trend and then a decreasing trend were identified. In addition, a larger changing rate of the permanent strain (resilient modulus) was observed on the dry side, indicating a larger effect of the remolding water content. (d) For each remolding water content, as the compaction degree increased, the permanent strain exhibited a decreasing trend, but an increasing trend was identified for the resilient modulus. Moreover, the rate of change in the permanent strain (resilient modulus) on the dry side of the optimum water content was larger than that on the wet side. In contrast, the minimum rate of change was identified at the optimum water content. The obtained results allowed for the effects of the remolding water content and compaction degree on the dynamic behavior to be analyzed, and they helped guide the construction and maintenance of the subgrade.

Contamination of soils and groundwater resources has become one of the most serious global environmental problems in recent years. The use of natural and inexpensive adsorbents such as zeolite is one of the appropriate methods to prevent the spread of contaminants and increase the adsorption capacity of the soil. In this research, the behaviour of the mixture of sand with 15% kaolinite clay is investigated at first, in both conditions of non-contaminated and contaminated with lead nitrate. Due to the limited adsorption capacity of the sand containing kaolinite, different percentages of zeolite adsorbent were added to this mixture to investigate the adsorption capacity and changes in strength parameters of the soil and adsorbent mixture. According to the results of the atomic adsorption test, zeolite has a favorable effect on increasing the adsorption capacity of heavy metals in soils such that by adding 5% zeolite, the amount of lead adsorption capacity increases by about 70%. The dynamic behaviour of these compounds in both conditions of non-contaminated and contaminated with lead nitrate was studied. Dynamic behaviour shows that in the combination of soil with both types of adsorbents, by increasing the concentration of heavy metal, the cycles corresponding to Ru decreases. [ABSTRACT FROM AUTHOR]

The rational evaluation on the performance evolution of liquefiable soil subjected to the earthquake is essential to solve the problem of large deformation. The undrained cyclic triaxial tests are conducted on the saturated Nanjing fine sand to study the relationship of shear stress–strain, the development of excess pore water pressure, and the evolution of the fluidity including apparent viscosity and average flowing coefficient during the liquefaction process. An obvious stage characteristic is observed in the process of soil liquefaction, which can be divided into four stages including the solid stage, solid–fluid transition stage, thixotropic fluid stage, and stable fluid stage depending on the growth rate of excess pore water pressure ratio, which is related to the residual shear strain of soil. A higher cyclic stress ratio and lower confining pressure lead to a lower number of cycles and excess pore water pressure ratio for triggering the stage transformation. Moreover, a linear relationship between the required number of cycles and the corresponding pore pressure ratio for stage separation is demonstrated. Furtherly, the modified state equation describing the connection between shear stress and shear strain rate is obtained by introducing Gompertz growth function to express the relationship between the apparent viscosity and excess pore water pressure ratio. Consequently, a modified thixotropic-induced excess pore pressure (MTEPP) model is established by considering the stage characteristics of soil liquefaction by adapting varying destruction parameters c. At last, the flow chart using MTEPP model to calculate the excess pore pressure ratio and shear strain of liquefiable soil is proposed and implemented. Compared with the experimental results, the proposed MTEPP model can well describe the behaviors of soil liquefaction during the stage transition process. [ABSTRACT FROM AUTHOR]

This study investigated the capillary rise potential and dynamic behavior of rubber particles-silty sand mixtures. A series of capillary rise tests and undrained cyclic triaxial tests were designed and performed on pure silty sand and rubber soil mixtures. The impact of rubber particles content (RC) and mean grain size ratio ( D 50 , r / D 50 , s ) of the mixtures was investigated. The results showed that the increase of RC and D 50 , r / D 50 , s decreased the capillary rise behavior. Compared with pure silty sand, the total capillary water mass increment of mixtures with 30% rubber particles with 41.3 and 7.9 D 50 , r / D 50 , s decreased by 52.7% and 35.1%, respectively. An increase in D 50 , r / D 50 , s resulted in a harder performance for the mixtures, whereas an increase in RC resulted in softer performance for the mixtures. Compared with pure silty sand, the maximum Young's modulus of mixtures with 30% rubber particles (at 200 kPa confining pressure) for 41.3 and 7.9 D 50 , r / D 50 , s decreased by 52.7% and 35.1%, respectively. An increase in the normalized Young's modulus was associated with a decrease in RC and increase in D 50 , r / D 50 , s . An increase in RC and decrease in D 50 , r / D 50 , s resulted in an increase in damping ratio. A set of empirical equations was proposed to describe the normalized Young's modulus and damping ratio. The results presented here provide new ideas for the use of rubber soil mixtures in geotechnical engineering. [ABSTRACT FROM AUTHOR]

The seismic response analysis of a tailing dam is studied using a fully coupled effective stress approach in conjunction with an advanced multi yield surface plastic constitutive model for tailing material. Strain controlled static and cyclic triaxial tests were carried out to obtain the constitutive model for the tailing material. The tailing materials were collected from the Rampura Agucha tailing dam (Rajasthan State, India). A 2D nonlinear finite element (FE) model was then developed using different boundary conditions from the tailing embankment constructed using the downstream and upstream method of rising using OpenSees software. In first case, the model boundary was fixed in both the X and Y directions, and in the second case, viscous dashpots were introduced for both side and horizontal boundaries. The model was validated with experimental results on tailing material. Analyses were carried out considering five different earthquake motions, which were applied at the base. Comparisons of the different boundary conditions in terms of displacement flow vectors, pore pressure and stress-strain curves during shaking are presented. From the analysis, it was observed that the viscous boundary condition replicates the actual field conditions more accurately than the fixed boundary condition. In addition, it was found that the tailing embankment constructed by the downstream and upstream method of rising is not susceptible to liquefaction and lateral spreading for earthquake motions, even for a magnitude > 5.5. [ABSTRACT FROM AUTHOR]

Jointed rock specimens with a natural replicated joint surface oriented at a mean dip angle of 60° were prepared, and a series of cyclic triaxial tests was performed at different confining pressures and cyclic deviatoric stress amplitudes. The samples were subjected to 10,000 loading-unloading cycles with a frequency of 8 Hz. At each level of confining pressure, the applied cyclic deviatoric stress amplitude was increased incrementally until excessive deformation of the jointed rock specimen was observed. Analysis of the test results indicated that there existed a critical cyclic deviatoric stress amplitude (i.e. critical dynamic deviatoric stress) beyond which the jointed rock specimens yielded. The measured critical dynamic deviatoric stress was less than the corresponding static deviatoric stress. At cyclic deviatoric stress amplitudes less than the critical dynamic deviatoric stress, minor cumulative residual axial strains were observed, resulting in hysteretic damping. However, for cyclic deviatoric stresses beyond the critical dynamic deviatoric stress, the plastic strains increased promptly, and the resilient moduli degraded rapidly during the initial loading cycles. Cyclic triaxial test results showed that at higher confining pressures, the ultimate residual axial strain attained by the jointed rock specimen decreased, the steady-state dissipated energy density and steady-state damping ratio per load cycle decreased, while steady-state resilient moduli increased.

Studying the unsaturated gypseous soils behavior may lead to more understanding of the gypseous soil problems associated with unsaturation under the effect of the vertical vibrations. The purpose of this paper is to assess the suitability of unsaturated gypseous soil as a machine foundation soil. Moreover, such a purpose is considered beneficial in assessing appropriate methods for studying the characteristics and the behavior of unsaturated gypseous soils such as soil elastic modulus parameters, compressibility parameter, waves velocities, and amplitude axial strain for cyclic loading parameters under different with degree of saturation. The tests were performed for conditions 35% and 70% relative density of natural gypseous soil under 1.0 Hz and 2.0 Hz cyclic frequency at degrees of saturation (30%, 60%, and 80%), and fully saturated gypseous soil to investigate the gypseous soil behavior. It was found the values of the elastic modulus and wave velocities at degree of saturation 60% for different number of cycles and frequency increased with decrease of the strain and compressibility. Then, it began to decrease gradually at the saturation degree 80% and 100%, respectively. The best results based on strength consideration were obtained at 60% saturation, and the lowest strength was found when the soil was 100% saturated, for both load frequencies 1, and 2 Hz. The load frequency 1 Hz gave higher values than cyclic frequency 2 Hz of elastic modulus and wave velocities, while the number of cycles was less at the same time and for different degrees of saturation.

Brittle failures were observed in pile foundations during past earthquakes due to seasonally frozen ground. This paper introduces a new geosynthetic material derived from waste tires, i.e., polyurethane-bonded rubber particles and sand, termed PolyBRuS, for application around deep foundations to improve their seismic performance in cold regions. Cyclic triaxial tests were carried out at various temperatures, confining pressures, and freeze–thaw cycles to assess the cold-weather dynamic characteristics of PolyBRuS. The results show that the material behaves as a nonlinear viscoelastic material at an axial strain of less than 1%. Its dynamic elastic modulus rises after freezing and continues to increase as temperature drops, but it is much less sensitive to confining pressures and freeze–thaw cycles; its damping ratio rises significantly with increasing axial strains and decreasing subfreezing temperatures and declines moderately with increasing freeze–thaw cycles. Compared with natural soils, its dynamic elastic modulus is similar to those of unfrozen fine-grained soils and is much less sensitive to subfreezing temperatures; its damping ratio is comparable to that of fine-grained unfrozen soils and is substantially higher than frozen soils at subfreezing temperatures. These characteristics make this material an excellent candidate to replace local soil around deep foundations for vibration reduction and seismic hazard mitigation in cold regions. [ABSTRACT FROM AUTHOR]

The Yellow River alluvial silt has unique engineering properties and is unstable when encountering moisture. The mechanical properties of silt subgrade can be impaired by the increase in moisture content due to rainwater infiltration, which has a negative effect on traffic safety. To further reveal the influence of moisture content on the deformation characteristics of silt, a series of monotonic and cyclic triaxial tests were conducted on the alluvial silt with different moisture contents. The development law of cyclic accumulative permanent strain and the effects of moisture content, cyclic deviator stress and confining pressure on the axial permanent strain of silt were explored. The study shows that the static strength of silt decreases with the increase in moisture content, and the attenuation of static strength is mainly caused by the decrease in cohesion due to the reduction in matric suction. The permanent strain rises linearly with the increase in moisture content and cyclic deviator stress, and decreases with the increase in confining pressure. An empirical model for predicting the permanent strain of silt under long-term cyclic loading considering the effect of moisture content was established. Compared with the test data and other existing models, the established model has easier obtained parameters, higher prediction accuracy and better applicability. [ABSTRACT FROM AUTHOR]

In the literature, the effect of different factors on the liquefaction resistance of sand has been widely investigated using the cyclic simple shear test or cyclic triaxial test. In which, the effect of CSR on liquefaction resistance significantly depends on the type of sand. In Vietnam, the sandy soils are widely distributed in coastal areas where many wind power farms are built and planned to build. Thus, the liquefaction resistance of sandy soil in these areas should be evaluated. In this study, the effect of cyclic stress ratio (CSR) on the liquefaction resistance of sand distributed in the coastal area of Soc Trang province, Vietnam will be evaluated for the first time using cyclic triaxial apparatus (Wykeham Farrance). The sand samples were prepared using the dry pluviation method with a relative density of about 56%. The stress-controlled method with CSR from approximately 0.1 to 0.35, the effective confining stress of 50 kPa, and the frequency of 1 Hz were applied. The research results showed that the axial strain and build-up of pore water pressure significantly depended on the range of CSR. In particular, this research has indicated the threshold of CSR for the liquefaction of sandy soil in this study area. Accordingly, under the testing conditions, sand samples were not liquefied with a CSR of less than 0.25. [ABSTRACT FROM AUTHOR]

Shear modulus and damping are of the most important dynamic characteristics of soil in seismic geotechnical engineering. Improving the dynamic properties of soils by adding cement content, and then replacing a part of cement, which its production is one of the most important sources of carbon dioxide emissions in the world, with natural materials such as nanoclay is of particular importance. In the present study, the cyclic behavior of silty sand was compared with the cyclic behavior of cemented sand containing cement and nanoclay additives. The soil used in this research was Firuzkooh mountain sand and silt, classified as ML type based on the unified classification system. All the samples were made by wet complaction method and cyclic triaxial tests were performed with three different confining pressures of 50, 100 and 150 kPa in the medium shear strain range. The results showed that the values of the shear modulus of cemented sand samples with a water to cement ratio of 1 are greater than the values of the shear modulus of the silty sand samples in all ranges of shear strains. The values of shear modulus increased by substituting nanoclay instead of cement in the cemented samples, and vice versa, the damping of the samples decreased with the addition of cement. By substituting part of the cement with nanoclay, the damping decreased with a lower rate. On the other hand, with the increase of confining pressure, the shear modulus values of all the considered soils increased and their damping decreased. [ABSTRACT FROM AUTHOR]

To investigate the effects of the properties of plastic fines on the pore water pressure generation characteristics of fine-grained soils during cyclic loadings, we used 29 sets of test data from the literature and prepared another 21 reconstituted specimens with different types of fines and fine contents (FCs) for cyclic triaxial testing. Two types of undisturbed soil specimens and three types of reconstituted soil specimens were also included for testing. The results indicated that under cyclic loading, the pore water pressure (PWP) ratios of clean sands increased slowly, stagnated, then finally accelerated until initial liquefaction, whereas those of the plastic soils containing fines with a plastic index (PI) value of >5 increased sharply in the initial stage. In addition, the cyclic stress ratio of specimens containing mudstone (PI = 12.4) and kaolinite (PI = 32.0) fines increased by 1.5–3.0 times more than non-plastic fines if the cyclic number chosen was 100. The range of the upper and lower limits of the PWP curves of the specimens with an FC of 30% were smaller that of the limits of the PWP curves of the specimens with an FC of 15%. The above results were further analyzed using a mathematical model. This paper systematically uses both the literature and laboratory test data to demonstrate that plastic fines and non-plastic fines have significantly different effects on water pressure generation under cyclic loading conditions, and a mathematical model also demonstrated the same trends. These findings are able to clarify previous unclear arguments. Thus, the model results developed in this study could also provide the field of engineering with a complete advanced calculation, requiring analysis only via software. [ABSTRACT FROM AUTHOR]

Shear modulus (SM) and damping ratio (DR) are significant in seismic design and the performance of geotechnical systems. The evaluation of soil reactions to dynamic loads, such as earthquakes, blasts, train, and traffic vibrations, necessitates the estimation of dynamic SM and DR. The aim of this research is to determine the cyclic parameters of unsaturated soils in and around Peshawar, and how these properties depend upon the varied confining pressures and shear strains. Undisturbed samples were collected using Shelby tubes from five boreholes at different locations along Jamrud Road, Peshawar. The index properties (grain size distribution, plasticity index, and specific gravity) and dynamic properties of these samples were determined. Three samples of 100 mm in height and 50 mm in diameter were obtained from each Shelby tube. After preparing and mounting the sample in the triaxial cell, the sample is first saturated by increasing the cell and back pressures in increments of 50 kPa until the value of Skempton's pore pressure parameter (B) reaches ≥ 0.96. Samples were consolidated at confining pressures of 150, 200, and 300 kPa, then subjected to cyclic shear strains of 0.2, 1, 2, 2.5, and 5%. Shear stress–strain hysteresis loops were plotted, and the values of SM and DR were calculated for each cycle. Generally, at shear strains of 0.2 and 1%, the slope of the loops is steep, and gradually becomes gentler at higher strains of 2, 2.5, and 5%. It is found that, with an increasing number of cycles, the SM and DR decrease. The SM decreases with increasing shear strain, whereas the DR increases at shear strains of 0.2–1%, then decreases for strains of 2, 2.5, and 5%. The confining pressure has more influence at a shear strain of 0.2–1%, while little effect has been observed at a shear strain of 2.2–5%. The values of SM are higher at higher confining pressures at a given shear strain. The results show higher stress values during the initial cycles because of the greater effective stress that developed in response to shear strain while, with an increase in the number of cycles, the pore water pressure gradually increases, thereby reducing the effective stress and weakening the bonds between soil particles. In dynamics, when the confining pressure increases, particles are closer to contact, so the travel paths of waves increase. The energy loss will increase, so DR will decrease. [ABSTRACT FROM AUTHOR]

Among other reasons, studies of the liquefaction potential of gravelly soils are limited because of the difficulties involved in preparing uniform specimens, without particle segregation, especially for a well-graded gravelly soil in a dry state for simple shear testing. Errors and difficulties are also involved in compensating for membrane penetration to a gravelly soil specimen in triaxial testing to get reliable data. Thus, innovative approaches for preparing triaxial and simple shear specimens for gravelly soils are introduced and implemented in this study to overcome experimental problems in acquiring accurate test results. In addition to the aim of obtaining reliable testing data on the liquefaction of gravelly soils under initial static shear stress for simulating sloping ground conditions, a study of the effect of various stress paths on the liquefaction resistance of gravelly soils was another goal of this research. In this regard, two sets of cyclic tests using medium-size triaxial and simple shear devices are conducted on a unique soil to compare the liquefaction potential of the tested gravelly soil using these two devices. Results of simple shear tests indicate that as the value of initial static shear stress increases, the cyclic resistance of the tested gravelly soil decreases. However, the results of the triaxial tests show that the variation of cyclic resistance for the tested soil depends on the initial static shear stress level and associated stress reversal conditions. Furthermore, the observed value of the pore water pressure ratio at failure using the strain-based liquefaction criteria for the tested gravelly soil was about 0.85, regardless of the type of testing. In addition, the relationship between the liquefaction resistance of gravelly soils using cyclic triaxial and simple shear devices was obtained. There is a common belief among practitioners that gravels have a far lower potential for liquefaction than sands. Results of experimental tests in this study reveal that gravels containing sands, known as gravelly soils, may have a high potential for liquefaction as well. However, the condition of zero effective stress, typically linked to liquefaction triggering in sandy soils, might not occur in gravelly soils. Rather, it is observed that the condition of excessive soil deformation leads to liquefaction triggering in gravelly soils. In addition, there are several observations on liquefaction triggering in sloping ground conditions. In this condition, initial static shear stress is present in the liquefiable soil; investigating the effects of such initial static shear stress on the liquefaction triggering of gravelly soils is strongly recommended, to ensure careful attention in design processes. [ABSTRACT FROM AUTHOR]

Rice husk ash (RHA), owing to its pozzolanic properties and wide abundance, is an additive that can be used as an alternative to cement to improve a variety of soils. Damping and shear modulus are two important soil dynamic parameters used to predict soil behaviour under dynamic loading. Therefore, in this study, materials were prepared and their specifications were determined. A cyclic triaxial device was used to determine the dynamic parameters (stress control). Subsequently, the results related to shear modulus and damping calculated for pure sand before and after stabilisation were analysed according to different percentages of stabilisers for two frequencies of 0.5 and 1 Hz. The results revealed the effect of different frequencies on the damping of pure sand, which differed for stabilised sand. In all stabilised specimens, the shear modulus decreased with increasing frequency. Additionally, the damping decreased with increasing frequency in the stabilised samples. The shear modulus increases with the increase in the amount of stabilisers. The results also showed the positive effect of partially replacing cement with RHA. [ABSTRACT FROM AUTHOR]

Sand liquefaction triggered by earthquakes is a devastating geological disaster and has emerged as an engaging topic in earthquake engineering. With an enhanced understanding of pure sand liquefaction promoted by laboratory research, there is a growing concern, following filed investigations, over the influence of fine particles on the liquefaction potential of sand containing inclusions. Efforts have been devoted to clarifying the significance of certain physical indicators (e.g., plasticity index, particle shape and gradation characteristics), and fruitful conclusions can be found in the published literature. However, the relationship between the content of fine particles and the cyclic degradation in liquefaction process seems still unclear. To fill this knowledge gap, three sets of cyclic triaxial tests were performed on various sand–fines mixtures with the dry tamping method. The experimental results revealed that (i) fine particles provided a negative contribution to the global soil structure; (ii) however, the damping ratio measured from the obtained stress–strain loops manifested its independence from the fines content during cyclic degradation. In this paper, we propose a shearing mechanism on the microscopic scale to explain the above contrasting observations. For a given soil fabric, the fine particles around sand-to-sand contact points probably break strong force chains, intensifying the threat of liquefaction. By contrast, these fines play the same role in favouring relative sliding between sand grains during both the loading and unloading stages. As the maximum stored energy and the energy loss per cycle are amplified with the same scaling factor, the damping ratio, defined as the ratio between them, should display a macroscopic invariance in triaxial tests. [ABSTRACT FROM AUTHOR]

• The dynamic characteristics of MBT waste were investigated. • The dynamic shear modulus increases with increasing confining pressure. • The damping ratio increases with the increase in the strain amplitude. • The modified Devidenkov model considering the confining pressure was applied. • MBT waste exhibits a higher dynamic shear modulus but lower damping ratio. The dynamic characteristics of landfills under seismic loading and their stability strongly depend on the cyclic stress-strain characteristics of the waste. An accurate assessment of the dynamic characteristics of mechanically – biologically treated (MBT) waste is crucial to the construction and safe operation of landfills. Considering the effects of the confining pressure, strain amplitude, and loading frequency, 72 sets of consolidated undrained cyclic triaxial (CTX) tests were conducted on MBT waste. Our results showed that the dynamic stress amplitude of MBT waste increases with increasing strain amplitude and decreases with increasing number of cycles. Furthermore, the shear modulus of MBT waste increases with the increase in the confining pressure and decreases with the increase in the strain amplitude. By increasing the strain amplitude, the damping ratio of MBT waste increases. However, the shear modulus and damping ratio of MBT waste are less affected by the loading frequency. A modified Davidenkov model is presented, which describes the correlations among the normalized shear modulus of MBT waste, shear strain, and confining pressure. The fitting parameters are discussed, and the correlation between the normalized shear modulus and shear strain of MBT waste and that between the normalized shear modulus and shear strain of municipal solid waste were compared. The results of this study can be used as references for analyses of the dynamic stability of MBT landfills. [ABSTRACT FROM AUTHOR]

Drainage conditions and consolidation states can affect the deformation behaviour of clayey soil under cyclic loading. A series of cyclic triaxial tests were carried out on normally and over consolidated kaolin under both undrained (UD) and partially drained (PD) conditions. The effects of drainage conditions on the strain accumulation, excess pore water pressure (EPWP) and resilient modulus (Mr) of the soil are analysed under different over consolidation ratios and cyclic stress amplitudes. The results indicate that greater axial strain may accumulate under PD condition than under UD condition if the cyclic stress is small. With the increase of over consolidation ratio, lateral deformation in soils under PD condition is similar to those under UD condition. Meanwhile, a large axial strain could accumulate with a small amount accumulation in EPWP under UD condition or in volumetric strain under PD condition. The Mr of soil decreases as EPWP increases under UD condition or as volumetric strain increases under PD condition. For the over consolidated soil, Mr could degrade significantly with little accumulation in EPWP under UD condition or in volumetric strain under PD condition. For example, under an over consolidation ratio of 5 and UD condition, Mr degrades about 20–55% with EPWP accumulation of 2–13 kPa. [ABSTRACT FROM AUTHOR]

Case studies show that earthquake-induced soil liquefaction can cause large lateral deformation of piles, leading to bridge damage. In this study, an iron and steel manufacturing by-product, slag powder, was utilized for the first time to mitigate soil liquefaction, thereby reducing the lateral deformation of piles during earthquakes. First, the liquefaction resistance of soil improved by slag powder was analyzed by cyclic triaxial tests. The results indicate that as the slag powder content increased, the soil liquefaction resistance increased. When the cyclic stress ratio is 0.2, the number of liquefaction cycles of the reinforced soil increases by 30 compared with that of the unreinforced soil. Second, a numerical modeling method of slag powder reinforced sand was proposed and validated by the cyclic triaxial test results. Third, the seismic response of piles in liquefiable soils enhanced by slag powder was evaluated using finite element analyses, and slag powder was determined to be effective in decreasing the lateral deformation of piles in liquefiable soils, the maximum displacement of the pile was reduced by 45 %. Last, an empirical formula that can easily evaluate the mitigation effect of slag powder on the lateral deformation of piles is proposed and verified by the results of finite element analysis.

A large quantity of end-of-life tire (ELT) rubber is being blended with thermoplastic polyurethane to provide a durable and ecologically friendly material for flexible surfaces, while a significant quantity of thermoplastic elastomeric waste (left-over and cut-outs) is also generated. These waste materials can be used efficiently for seismic isolation and vibration damping at a minimal cost, a process known as frugal innovation. In this regard, waste thermoplastic elastomeric (TPE) material, which is also known as polyurethane-coated rubber (PUcR), obtained from the tire rubber recycling industry, is explored in this study. Herein, we targeted to evaluate the stiffness and energy dissipation capabilities of waste TPE or PU-coated rubber, which, to the best of our knowledge, has never been reported before. To that end, a series of cyclic triaxial tests were carried out on PU-coated rubber-soil mixtures. In comparison to untreated rubber-soil mixtures, the shear modulus of PU-coated rubber-soil mixtures reduces by 5.5–12.7%, while the damping ratio increases by up to 12.6%.

Since most natural deposits are a combination of sand and fine grains and as man-made geotechnical structures like tailing dams have a high percentage of cohesive and cohesionless fine grains, the study of cyclic and post cyclic behavior of these soils is essential. For saturated sands, the effect of non-plastic fine grains (silts) on their monotonic and cyclic behavior has been investigated. A majority of studies are related to monotonic and cyclic loading and post-cyclic loading has received less attention. In this paper, the effects of silt content and different Cyclic Stress Ratios on the cyclic and post-cyclic behavior of saturated loose sand are investigated. The sand used in this study is Firuzkuh silty crushing sand, which is abbreviated to sand . All samples were prepared so that their relative density was about after consolidating. The experiments were performed using the saturated cyclic triaxial apparatus. Suitable preparation of specimens was one of the most important factors in the accurate performance of triaxial tests. The cyclic and post cyclic tests on mixtures made of sand with silt were undertaken following the recommendation of D4254. Changes in pore pressure coefficient, liquefaction resistance, stress-strain curves, and stress path in clean and silty sand ( silt) were recorded. Results show that the tested samples become liquefied in a smaller number of cycles by increasing the until they show softening behavior at larger when effective stress rapidly drops to zero. In lower , the stress-strain curve is collapsible while in larger , loops expand and they indicate more damping of materials.

Nowadays, mass production of tires and construction operations adjacent to saturated soils have become a concern for engineers. The present study aimed to explore the potential of the combined effect of a waterproof polymer and rubber powder, confining pressure, and cyclic stress ratio on the static and dynamic properties of sand-rubber-polymer mixtures using a scanning electron microscope (SEM), attenuated total reflectance (ATR) analysis, unconfined compressive strength (UCS), and cyclic triaxial tests. The findings indicated that with the inclusion of 4% rubber, rough polymer chains are extended due to creating C─ CH3 bonds, uniform distribution of rubber particles between rigid materials, and interlocking rubbers in hydrocarbon chains. These chains increase adhesion with sand particles and prevent rubber flexibility, increasing UCS and shear modulus. In contrast, with the inclusion of 8% rubber, due to several mechanisms, including poor adhesion between particles because of the high surface area of the mixture and low polymer content (i.e., 2%), the dominance of weak rubber–polymer and rubber–rubber bonds over polymer–polymer and sand–polymer bonds, emerging free rubber particles (free CH2 groups), and creating the aromatic and double bond structures due to the nature of rubber flexibility, the trend is reversed. [ABSTRACT FROM AUTHOR]

Determining proper strain‐dependent shear modulus and damping ratio for soils is of utmost importance when investigating their response to cyclic loads. Experimental studies on the effect of the degree of saturation and suction on the shear modulus at large strain amplitudes are scarce due to the complexities involved in testing such soils. Furthermore, the previously presented micromechanical models for the cyclic behavior of unsaturated soils lack some of the required features of soil pore skeleton essential to model unsaturated soils' hydromechanical behavior. This paper is, thus, aimed at addressing this shortcoming by incorporating a pore‐scale numerical method that couples the discrete element simulation of the solid phase and the fluid pore network to capture the cyclic behavior of unsaturated sands. To this end, the model is first calibrated to determine the micro‐scale parameters using experimental results from static drained triaxial compression tests on dry and saturated sand samples. Next, the coupled model is employed to simulate the observed behavior during cyclic triaxial tests on unsaturated sands. A linear dependence of the plastic rolling coefficient and the interparticle friction angle on the degree of saturation is proposed from simulations of suction‐controlled cyclic triaxial tests. Variation of shear modulus with shear strain amplitude and degree of saturation indicates a continuous increase in the shear modulus with the decrease in saturation. In contrast, the trend for the damping ratio is the opposite. Finally, closed‐form relationships are proposed based on the simulation results for the shear modulus and damping ratio of unsaturated soils. [ABSTRACT FROM AUTHOR]

In this study, a series of cyclic triaxial tests were conducted to study the accumulated strain of coarse-grained soil reinforced with geogrids, and the effect of the number of geogrid layers, confining pressure and cyclic stress amplitude was investigated in detail. The test results show that the final accumulated axial strain of the soils reinforced with geogrids is less than that without reinforcement, and less accumulated axial strain is generated for the specimens with more geogrid layers under identical cyclic loading. The results also show that a higher confining pressure or a lower cyclic stress amplitude yields less accumulated axial strain for the reinforced soils. Furthermore, the plastic shakedown limits are determined by the criterion proposed by Chen et al. It indicates that the plastic shakedown limit increases significantly when one layer of geogrid is incorporated into the specimen and then tends to level off with a continuous increase in the number of geogrid layers. Moreover, a higher confining pressure yields a higher plastic shakedown limit for the soils reinforced with geogrid. The results demonstrated that the use of geogrid can be an effective method to reduce the accumulated deformation of subgrade filling materials under high-cycle traffic loading. • The accumulated behaviours of coarse-grained soil specimen with different geogrid layers were investigated. • The reinforcement effect induced by the added geogrid is milder for the coarse-grained soil specimens with more layers. • The reinforcement derived from confining pressure on the specimens decreases with an increasing number of geogrid layers. • Three types of accumulation curves for the identical specimens could be reached under different cyclic stress amplitudes. • The plastic shakedown limits of the coarse-grained soil specimens with different geogrid layers are determined. [ABSTRACT FROM AUTHOR]