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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 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]

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]

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]

Turkey is in an active earthquake zone. Recently, Izmir city was shaken by a major earthquake in October 2020. The earthquake caused extensive structural damage and more than 100 casualties. Therefore, the analysis of the dynamic response of local soils in this region is of great importance. In this study, the shear modulus and damping ratio of natural silts obtained from Izmir province are determined. A total of 29 cyclic triaxial tests and 12 tests with pre-loading were performed to establish a general framework for understanding the behavior of local silt soils before and after an earthquake. Besides the effect of an earthquake, the characteristic behavior of Izmir silts of different levels of plasticity was also investigated and significant changes were observed. In addition, the effect of void ratio, effective confining pressure, plasticity, and shear stress amplitude of the pre-loading stage on the dynamic characteristics of the low plasticity silts were investigated. It is understood that after seismic action, changes in the small strain behavior of silts are remarkable. [ABSTRACT FROM AUTHOR]

An interlayer soil in ancient rail tracks was identified as a mixture of ballast grains and subgrade fines. As the permanent strain ε 1 p of such mixture was affected by water content, cyclic triaxial tests were performed, under varying water contents of fines wf and coarse grain contents fv. Comparison between present and previous studies showed the significant effect of sample preparation method on ε 1 p . In the present study, a constant fine dry density ρd-f was maintained, leading to an unchanged suction of mixture whatever the fv value. In this case, only the reinforcement effect of fv on ε 1 p was identified. By contrast, in previous studies, the global dry density of mixture ρd was kept constant, resulting in a decrease in ρd-f with increasing fv and consequently a decrease in suction. In this case, when the negative effect of decreasing suction prevailed on the positive reinforcement effect of increasing fv, the ε 1 p increased. [ABSTRACT FROM AUTHOR]

Liquefaction damage from earthquakes frequently indicates effects of sand aging on liquefaction resistance: Liquefaction damage in natural or aged reclaimed ground has been much less than that in young reclaimed ground. However, the mechanisms underlying aging effects remain unclear. Cementation and stress history of sand strongly influence aging effects: Cementation raises liquefaction resistance, whereas liquefaction history sometimes reduces liquefaction resistance. Small cyclic shear strain, from which the induced density change is almost negligible, was adopted as representing the stress history. To evaluate liquefaction resistance, initial shear modulus, and deformation characteristics of sand, we prepared specimens by adding cement and by applying a small cyclic shear strain. In cementitious sand, liquefaction resistance increased when cement contents exceeded 0.3% by mass. The initial shear modulus apparently increased at the same degree of cement addition as that which increased the liquefaction resistance. For sand with a small cyclic shear strain, the liquefaction resistance increased when the applied cyclic axial strain exceeded 0.01%. Application of small cyclic shear strain only slightly increased the initial shear modulus, but the linear elastic region tended to expand to greater shear strain. Shear properties of sand with small cyclic shear strain resembled those found for sand that had been consolidated for a long time. [ABSTRACT FROM AUTHOR]

Site-specific dynamic soil properties, such as nonlinear stiffness and damping of subsoil, play a crucial role in assessment of vulnerability of structures incorporating seismic soil structure interaction (SSSI). The present study aims at the evaluation of dynamic parameters of subsoil samples collected from a case study railway construction site at Agartala, capital of Tripura, a North Eastern (NE) state of India, which is situated in an active seismic zone. Soil samples extracted from the site were mainly constituted of peat clay and very soft clay at shallow depth followed by silty fine sand layer at moderate to higher depth below existing ground level (EGL). A series of small strain and large strain element tests were conducted using bender element (BE) and cyclic triaxial (CTX) apparatus to obtain the shear modulus and damping ratio. Then, implications of dynamic properties of soil are studied through one-dimensional ground response analysis (1D GRA) using site-specific synthetic ground motions attributing scenario earthquakes. This study provides valuable inputs on importance of consideration of local site effect while performing the seismic design of structures embedded in soft alluvial deposits. Besides, the stiffness contrast of subsoil layers and ground motion are found to be key influential parameters. Finally, a case study analysis on seismic response of railway embankment also validates the importance of local site effect. [ABSTRACT FROM AUTHOR]

The stability of subway tunnel is mostly determined by the evolution of the physical and mechanical properties of the surrounding soft clay under the disturbance of cyclic loads. Mastering the evolution law of strain behavior of soft soil under cyclic load and obtaining the critical stress–strain index is of great significance to engineering design and construction safety. It is necessary to organically combine the methods of test and mathematical model simulation to obtain the key critical index and explore its change mechanism under different cyclic conditions. In this study, a series of cyclic triaxial tests were conducted to study the cyclic strain development characteristics of Shenzhen soft clay under traffic loads. The results show that both the amplitude of axial strain and the cumulative axial strain increase with increasing cyclic stress amplitude (CSA) until the critical cyclic stress amplitude is exceeded. As the cyclic stress ratio increases, the critical CSA value decreases and the failure cyclic numbers decreases. It shows that the increase in cell pressure causes the forces among the soft clay particles increase, which improves the cyclic resistance of soft clay to external energy. But improvement of this ability is limited, when the CSA is greater than the critical value, the structure of the soft clay begins to collapse immediately. The discussion result of the physical meaning of the parameters of the empirical mathematical model indicated that strong adjustment of soft clay particles mainly occurs during the initial hundreds of cycles. When the cyclic number is large enough, the final strain and values of critical CSA are mainly affected by the physical properties of the soft clay, the effect of stress path and stress state is insignificant. Therefore, the research on soft clay physical properties and monitoring of soft clay deformation in the initial stage of subway construction and operation should be enhanced. [ABSTRACT FROM AUTHOR]

The paper presents a numerical simulation of stress-controlled undrained cyclic tri-axial tests conducted on local sand at various relative densities and CSR values. Two constitutive models for liquefaction, namely, Finn-Byrne model and PM4 sand model are used for the simulation. The results from both the material models are compared with the cyclic test results in terms of the stress strain loops, excess pore pressure ratio, and effective stress path. The chosen models have shown good predicting capabilities for predicting cyclic responses of a sand in terms of stress path and pore water pressure generation but lacks in predicting the stress strain behavior. Also, in terms of simulating the behavior of sand in pre- and post-liquefaction regime, it is found that PM4 sand model is more efficient than Finn model for all the relative densities. Hence, it is recommended that Finn model may be only utilized when a sand fails due to flow liquefaction, whereas PM4 sand model can predict both, flow liquefaction and cyclic mobility, accurately. Finally, the liquefaction resistance curves for different relative densities are obtained using experimental values and PM4 sand model. These curves are thus proposed for any sand with index properties similar to the particular sand considered for the study. [ABSTRACT FROM AUTHOR]

Elasticity test of soil, which is based on small-strain deformation test, is a big challenge in geomechanical laboratory testing due to the limitation of current state-of-art laboratory deformation control and measurement technique. The hysteresis loop generated by un-/reload process of soil testing, which is regarded as the quasi-elastic process of soil, is conventionally believed to be unable representing the real elastic properties of soil unlike the ideal elastoplastic material. In this study, it is hypothesized that the quasi-elastic process of granular soil would evolve with cyclic loading and can represent the elastic properties of granular soil reasonably after sufficient number of cyclic loading and reaching steady state. Therefore, the cyclic triaxial test can be used as an alternative method to detect the elastic response of granular soil. Three-dimensional discrete element method (DEM) simulations of the cyclic triaxial test are conducted to illustrate the evolution of quasi-elastic response of soil and validate the hypothesis. Simulation results show that the elastic modulus detected through elastic probe test (small-strain deformation test) is insensitive to the structure change during cyclic shear and almost invariant at its corresponding stress level and the deformation modulus measured at the quasi-elastic process of granular soil asymptotically approaches the elastic modulus with the increase number of cyclic loading. Through the thermodynamic analysis of DEM, this evolution of quasi-elasticity of granular soil can be attributed to the energy dissipation due to the sliding events between particle contacts. When the energy dissipation of the quasi-elastic process reaches a steady-state level after sufficient number of cyclic loading, its value is comparable to the energy dissipation of the elastic probe test and thus the quasi-elastic process can be used to represent the elastic response of granular soil. This study provides a conceptual exploration of essential mechanism of elastic response of granular soil. More comprehensive laboratory tests and DEM simulations are expected for fully understanding of the hypothesized mechanism in the future study. [ABSTRACT FROM AUTHOR]

Due to the increasing pore water pressure in the saturated sandy soils under dynamic loads, soils turn from solid to a liquid state, and loss of bearing capacity is observed. Liquefaction causes different types of deformations in soils. As a result, deformations such as different settlement, tilting, and turning occur and cause great damage to the structure. Destruction occurring under dynamic loads should be minimized as a result of determining the areas where liquefaction is expected by taking necessary measures. Adapazari that experienced liquefaction during the earthquakes in 1999 is one of Turkey's active seismic regions consisting of sand soils that are susceptible to liquefy. For this reason, researchers have run dynamic experiments and conducted studies with samples obtained from the region. In this study, using a dynamic triaxial test system, silty sand samples taken from region were prepared at different void ratios and then dynamically loaded. Moreover, permeability tests of the samples were carried out under the same conditions. The results showed that concrete relations between the cyclic stress ratio and void ratio were constituted at different number of cycles and permeability is directly linked to the cyclic resistance. [ABSTRACT FROM AUTHOR]

In this paper, the possibility of using fine scrap tyre rubber to improve the mechanical properties of soil subjected to cyclic loading is addressed. Ground rubber (0.1–0.8 mm) in various proportions (0, 9, 33% and 100% by weight) was mixed with a uniform river sand and a lean clay. Cyclic triaxial tests with bender elements were executed to observe the behaviour of the materials and also to determine damping and shear stiffness parameters. The results have shown that the addition of rubber has significantly decreased the density and shear stiffness of both types of soils, which favours mitigation of vibrations. The shear stiffness degradation at shear strains higher than 10−3 was lower in specimens containing more rubber. Within this strain range, addition of rubber decreased the damping ratio, but increased the normalized accumulated absolute strain energy absorbed by the material. Higher rubber content in sandy specimens resulted in more elastic behaviour, with lower strain accumulation in each loading cycle, eventually resulting in a higher number of loading cycles before failure. The positive effect of rubber presence was not observed in compacted clay–rubber mixture, which sustained less loading cycles than clay alone. The influence of rubber addition in the p′-q stress space was expressed in the form of lower pore pressure generation which shifted the stress path further from the failure envelope. [ABSTRACT FROM AUTHOR]

The long-term loading of the trains on the subgrade in service is the cyclic loading when the train passes and the intermittent stage when there is no train passing. However, in most studies, continuous loading was used to investigate the dynamic characteristics of a subgrade soil, which ignores the effect of loading intermittence. The aims of this research were first to study the cumulative permanent deformation behaviors under intermittent cyclic loading of trains, then to establish the classification criterion for cumulative permanent strain behaviors, and finally to propose a practical method for estimating the critical dynamic stress in the intermittent loading mode. For this purpose, according to the actual conditions of the subgrade of Shuo-Huang Heavy-Haul Railway, the monotonic triaxial test and the cyclic triaxial test with intermittent loading were performed. Based on the shakedown theory, the cumulative permanent strain behaviors under intermittent loading can be classified into three categories of plastic shakedown, plastic creep, and incremental collapse. Then, the classification criterion was established based on the permanent strain rate. Finally, an empirical formula of critical dynamic stress for intermittent loading, which could also consider the varying moisture content, was proposed. [ABSTRACT FROM AUTHOR]

Polyurethane foam adhesive (PFA) has been introduced as an alternative stabilizer in geotechnical applications because PFA can improve the engineering characteristics of soil by filling the pore space and generating adhesive bonding among the particles. However, the dynamic properties of PFA-reinforced soils are not well understood. To analyze the dynamic characteristics of PFA-reinforced gravels, a series of cyclic triaxial tests were carried out to investigate the shear modulus and damping ratio of PFA-reinforced gravels, and to determine the corresponding effects of the PFA content, confining pressure, consolidation stress ratio and loading frequency. The results showed that the shear modulus increased, and the damping ratio decreased as the PFA content, confining pressure and consolidation stress ratio increased. In contrast, the effect of the loading frequency, which ranged from 0.05 to 1 Hz, was negligible. A modified hyperbolic empirical model can consider the effect of the PFA content on the maximum shear modulus and predict the relationship between the normalized shear modulus and the normalized shear strain was proposed. Moreover, the upper and lower bounds of the damping ratio were also proposed. [ABSTRACT FROM AUTHOR]

Stress controlled cyclic triaxial tests have been carried out on coastal sand of Digha, West Bengal, India at different frequencies, confining pressures, relative densities and number of loading cycles for determination of influence of these parameters on cyclic strength (expressed in terms of cyclic stress ratio) and initial liquefaction of Digha sand. The test results provide evidence that increasing density of sand increases liquefaction potential, though it has been found that increase in effective confining pressure reduces cyclic strength of sand. Cyclic strength of sand decreases with increase of number of loading cycles at a specific density and a particular confining pressure. It has been observed that frequency of loading cycles does have any significant influence on the number of cycles for initial liquefaction of Digha sand. An empirical correlation has been developed on cyclic strength of sand based on these parameters and it has been found that this correlation fits quite well with the observed experimental results. [ABSTRACT FROM AUTHOR]

During marine transport of coal commodities, cargo slip or liquefaction failure scenarios within the hold may occur under cyclic ship motions. The resulting cargo shift affects the vessel stability, and subsequently endangers goods and crews on board the vessel. This study aims to investigate the coal cargo stability under marine transport conditions. A suite of six coal samples was selected to undertake a series of undrained cyclic triaxial tests to investigate their liquefaction resistance. Results were subsequently compared to the liquefaction threshold advised by International Maritime Organisation. It was suggested that finer coals were observed to be more susceptible to liquefaction. In addition, discrete element modelling of the coal cargoes was conducted to study the cargo slip susceptibility. Calibration was performed to ensure materials modelled in the numerical program reflected the physical behaviours. Results indicated coarser coal samples with lower moisture contents exhibited cargo slip failures under nominated rolling ship motion. Nevertheless, resulting centre of gravity shift from cargo slip exhibited negligible effect on the cargo stability. Outcomes of this study provided important safety guidelines on marine transportation of coal commodities. [ABSTRACT FROM AUTHOR]

The aim of this paper is to provide an insight into the effect of fine content (FC) on the artificially cemented gravel-silty clay mixed soils (CMS) in terms of strength, deformation, effective stress path and pore pressure response by undrained cyclic triaxial tests. In addition, some cyclic triaxial tests were also conducted on remolded gravel-silty clay mixed soils (RMS) under the same test conditions in order to evaluate the effect of cementation provided by the cementitious material. The corresponding cyclic responses, such as the generation and accumulation of axial strain, pore pressure and effective stress path, are compared across a range of CMS and RMS. A constant 5% percentage (by weight) of calcium oxide in mixed soils with four different ratios of fine content (13%, 30%, 50% and 70%) are tested under four types of confining pressures, 50 kPa, 100 kPa, 200 kPa and 300 kPa respectively. The results demonstrate that: an increase in fine content leads to decrease in both strength and liquefaction resistance, but accelerate the strain accumulation and pore pressure development. The cyclic responses of CMS exhibit "hysteresis" significantly compared with those of RMS due to the bonding strength between soil particles. [ABSTRACT FROM AUTHOR]

The soils are often distributed in a stratified structure. When an earthquake occurs, there are always risks of liquefaction for stratified soils which can cause serious consequences. The research aims to investigate the liquefaction and post-liquefaction deformation of saturated sand with stratified structure. The influences of liquefaction and post-liquefaction deformation were analyzed by varying the thickness, position, and layers of powdery sands. The findings showed that the correlations between the times taken to reach liquefaction for cyclic loading and the thicknesses of the powdery sandy interlayer are non-linear. With the optimal thickness, the powdery sand interlayer can effectively prevent the transfer of power water pressure. And two-layer powdery interlayer in the sample was more favorable to resist pore water pressure than that with single layer. The strength of post-liquefaction deformation and failure patterns are closely related to the distribution of powdery layer. The work provides new research evidence on the liquefaction and failure mechanism of saturated sands with stratified structure under cyclic loading which often happen during earthquakes. [ABSTRACT FROM AUTHOR]

Soils subjected to earthquake motions undergo random variations in stress, strain and frequency during the entire period of shaking. The spatial and temporal complexity of the strong motions is commonly addressed through simplistic strain-controlled or stress-controlled cyclic loading tests as a part of laboratory investigations. Such a methodology is utilized and reported in the present study for assessing the dynamic response of cohesionless sand obtained from River Brahmaputra, India. In order to assess the dynamic response and liquefaction potential of the cohesionless Brahmaputra sand, both stress-controlled and strain-controlled cyclic triaxial tests were performed on reconstituted cylindrical specimens prepared at different relative densities (Dr) ranging from 30 to 90%. The specimens were subjected to varying effective confining pressures (σ′c: 50–200 kPa), shear strain amplitudes (γ: 0.015–4.5%) and cyclic stress ratios (CSR: 0.05–0.3). For all the tests, the frequency of the applied harmonic loading was maintained at 1 Hz. The magnitude of excess pore-water pressure (PWP) generated during successive loading cycles of the strain-controlled tests was found to be considerably lower than that generated in a stress-controlled test. The strain-controlled test reveals a reduction in the development of excess PWP with the increase in confining pressure and relative density, thereby indicating a decrease in liquefaction potential with increasing confining pressure. The stress-controlled test highlighted that based on a particular CSR, an increase in confining pressure results in the requirement of higher deviatoric stress and smaller numbers of cycles are required to initiate liquefaction. Although apparently misleading, it is imperative that during earthquake, same deviatoric stress is applied on the entire soil deposit. Thus, for specimens at larger depths having higher confining pressure, the CSR value is smaller, and thereby successive deeper layers require more number of stress cycles to liquefy. Hence, the study revealed that both stress-controlled and strain-controlled tests can be successfully used to assess the dynamic properties and liquefaction potential of cohesionless specimens. Based on the findings, the developed cyclic shear stress ratio (CSR) = 0.5 and cyclic shear strain amplitude (γ) = 0.5% are considered as the limiting conditions to achieve the onset of liquefaction through strain-controlled and stress-controlled approaches, respectively. [ABSTRACT FROM AUTHOR]

The response of saturated soil during earthquakes is governed by many factors such as frequency content, strain, stress, excess pore-water pressure and strength variations within the soil mass. This paper highlights the effect of strains on the stiffness modulus and its degradation at the liquefied condition of cohesionless soil. Cyclic triaxial (CT) tests, in stress-controlled manner, were carried out on saturated sandy soil specimens made at different relative density (Dr = 30%–90%) and effective stress (σ′c = 50–200 kPa). The reconstituted specimens were subjected to regular and irregular stress histories. Representative strong motions with varying PGA were chosen, and the corresponding irregular stress histories were used. Additionally, regular stress histories constituted from different cyclic stress amplitudes were also used. The responses of the saturated specimen were obtained in terms of the excess pore-water pressure generation and strain accumulation with elapsed time. In comparison to the standard frequency and duration parameters (namely the predominant period and significant durations), it is observed that the responses are more influenced by Arias intensity and specific energy density of the strong motion. Based on the increase in pore-water pressure, reduction in shear modulus and increase in shear strain within the specimens, the complete manifestation of liquefaction is divided in four zones, namely the no liquefaction zone, quasi-liquefaction zone, zone marking the onset of liquefaction and the completely liquefied zone. The criteria for the onset of liquefaction of Brahmaputra sand involving shear strain, peak ground acceleration and cyclic stress ratio are provided. [ABSTRACT FROM AUTHOR]

Considering that the foundation soil (calcareous sand) of offshore platforms is subjected to wave loadings of different heights in a long time, cyclic triaxial tests are conducted on the Nanhai Sea calcareous sand under different loading conditions, i.e., amplitude, initial effective confining pressure, frequency, and waveform. Test results indicate that the failure of Nanhai Sea calcareous sand under cyclic loading is not only governed by the gradual development of excess pore water pressure but also by the accumulation of axial strain. There is a dilative tendency in loose or dense Nanhai Sea calcareous sand inhibiting the full liquefaction, which leads to the failure type of cyclic liquefaction. The effect of loading conditions on the excess pore water pressure, the axial strain, the secant modulus, and the cycle numbers to failure was investigated. The effect of loading amplitude, effective confining pressure, and waveform is profound, while the effect of frequency is not obvious. The cycle numbers to failure at different cyclic stress ratios demonstrated that the liquefaction resistance of Nanhai Sea calcareous sand is larger than that of calcareous sand in other sea areas. [ABSTRACT FROM AUTHOR]

Liquefaction has caused many catastrophes during earthquakes in the past. The strain energy-based method is one of the modern methods used to estimate liquefaction potential. In this study, wide-ranging experimental data were gathered from cyclic tests and centrifuge modeling of liquefaction. A model was then developed based on the strain energy needed for liquefaction to occur using the group method of data handling and the gravitational search algorithm. Contributions of the effective variables were evaluated through a sensitivity analysis. To check the accuracy of the developed strain energy model, cyclic triaxial tests were conducted on sandy soil and silty sand specimens. Comparison of the energy required to initiate liquefaction in the tested soil specimens with values predicted by the developed model indicated high accuracy of the energy-based model. Subsequently, the accuracy of the energy model was assessed in field conditions using the amount of strain energy released by real earthquakes in various sites. The ability of the model to distinguish liquefied areas from non-liquefied ones confirms its accuracy in field conditions. Finally, the developed model was compared with some available relationships to estimate the strain energy required for liquefaction to occur. [ABSTRACT FROM AUTHOR]

Irregular stress waves generated during an earthquake induce irregular shear stresses in the soil, which affect the dynamic behaviour of soil significantly. Laboratory investigations on the response of soils during real earthquake scenario are very limited. This paper reports about the response of saturated sandy soils subjected to irregular cyclic stress histories using stress-controlled cyclic triaxial tests. Tests were conducted at different relative densities (30-90%) and confining stresses (50-150 kPa) representing varying compactness of soil obtained from different confining depths. Cyclic loading was applied as per the three different earthquake motions considered having different peak ground accelerations (PGAs). The responses are presented in terms of stress-strain variations, excess pore-water pressure ratio and shear strain accumulation in the soil specimen. The results indicated that the accumulated shear strains and excess pore-water pressures get significantly affected by the increase in confining stress and simultaneous changes in the relative density. Further, the study emphasized that the strong motions scaled to the same PGA levels produce substantially differing soil responses due to the variation in the associated strong-motion parameters. [ABSTRACT FROM AUTHOR]

Subgrade soils are often unsaturated and the resilient modulus (MR) of subgrade soils is usually subjected to the climate environment and traffic loading in the field. Therefore, the Matric Suction (MS) and traffic loading are considered to be two important parameters associated to the MR prediction model. To verify the MR prediction model, the MS of the typical subgrade soil were determined through the pressure plate test. In this study, the soil-water characteristic curves were also described using the Fredlund & Xing’s model. Then, the dynamic MR of the typical subgrade soil under various stresses and water contents was measured. After that, a new prediction model was proposed with the model variables including the minimum bulk stress, octahedral sheer stress and matric suction, and the validity of the new model was verified by previous research results. Finally, the correlations between the physical properties of subgrade soils including the percentage passing through the No. 200 sieve (0.075 mm), plasticity index, liquid limit, dry density and the regression coefficients of the new model were established. The results show that the new model can be used to predict the MR well, and it effectively solves the problem that the bulk stress is equal with a different combinations of the confining pressure and deviator stress. At the same time, the MR can be predicted much more easily with physical parameters of subgrade soils rather than conducting triaxial tests. [ABSTRACT FROM AUTHOR]

In order to analyze the stability of a landfill site, it should analyze some properties of waste introducing the main structural elements. Up to now, it has not been done much research on the properties of municipal solid waste. In addition, due to the differences in waste properties from one country to another and even from one to another landfill site, it is impossible to generalize the results. These conditions caused local research on the evaluation of static and dynamic parameters of municipal solid waste to be done. Because Iran is a seismic country, the short-term behavior of waste controls landfill sites stability during seismic loads; so it is necessary to know the dynamic behavior of these materials. In this paper, about 18 cyclic tests were performed, and in addition to determining the dynamic parameters of municipal solid waste of Tehran Kahrizak Disposal Site using cyclic triaxial test, the effect of confining stress and loading frequency on dynamic properties of these materials was evaluated. The results have shown that with increasing the confining stress and loading frequency, shear modulus and damping ratio was increased and decreased, respectively, and it is related to the composition of the municipal solid waste materials. [ABSTRACT FROM AUTHOR]

Cyclic triaxial test by means of the geotechnical digital system is conducted for the soil near the Guoquan Road Station of Metro Line 10 in Shanghai to analyze the strain characteristics and the variation law of saturated silty soil under subway loading. Orthogonal design method is used to arrange the experiment, considering the following factors: frequency ratio f , cyclic stress ratio σ , vibration time ratio N , and the interaction function among them. Results show that the cyclic stress ratio σ , the frequency ratio f , the vibration time ratio N , and the interaction between the cyclic stress ratio σ and the vibration time ratio N have a significant effect on the axial strain of the subway tunnel. The effect of the interaction between the cyclic stress ratio σ and the vibration time ratio N is also significant. From the analysis of variance and regression theory, the nonlinear regression equation of the cumulative plastic strain of silty soil under subway loading is established. Residual analysis proves that the equation is ideal and credible. The results have important value for the design of subway tunnels. [ABSTRACT FROM AUTHOR]

We present empirically derived liquefaction resistance curve from a large database of measurements from published literature and also simple shear tests that were performed in this study. The data measured from simple shear and triaxial tests are separately compiled. The data are fitted with two empirical models to develop representative liquefaction resistance curves. Comparisons illustrate that the slope of the widely used power law is highly dependent on the range of data it is fitted to and that the power law underestimates the resistance at high number of cycles (N). The alternative empirical model is demonstrated to provide favorable fit with the measurement over a wide range of data. The representative curves are normalized by the equivalent number of uniform cycles for a magnitude (M) 7.5 event (N) to reduce the wide scatter of the measurements and to make it usable with liquefaction triggering charts that relate in situ parameter with cyclic resistance ratio for a M = 7.5 event. Comparison with published liquefaction resistance curves show that the proposed curve is lower at N ≤ N and higher at N > N. A single-parameter empirical exponential function that closely fits the normalized liquefaction resistance curves and representative values for its parameter are presented. We also propose an empirical equation to correct the liquefaction resistance curve measured from a triaxial test to match that from a simple shear test. [ABSTRACT FROM AUTHOR]

Devastating ground failures at seismically active sites underlain by saturated fine-grained soils have led to a need for revealing liquefaction potential of fines and effects of the characteristics governing this potential. A cyclic pore pressure model is introduced to examine the effects of plasticity index, ratio of water content to liquid limit and cyclic stress ratio on liquefaction susceptibility of such soils. The model is developed using data of 68 cyclic triaxial tests compiled through a comprehensive literature review. By means of pore pressure behavior estimated by the model and strain tendencies observed during the tests, a critical assessment on liquefaction susceptibility criteria for fine-grained soils is provided. Beyond evaluation of the susceptible and non-susceptible fines, this assessment partially provides distinction between liquefaction-related phenomena one of which is induced by complete loss of strength, whereas the other is induced by high strain levels without complete loss of strength. [ABSTRACT FROM AUTHOR]

Recycled waste tires when mixed with soil can play an important role as lightweight materials in retaining walls and embankments, machine foundations and railroad track beds in seismic zones. Having high damping characteristic, rubbers can be used as either soil alternative or mixed with soil to reduce vibration when seismic loads are of great concern. Therefore, the objective of this work was to evaluate the dynamic properties of such mixtures prior to practical applications. To this reason, torsional resonant column and dynamic triaxial experiments were carried out and the effect of the important parameters like rubber content and ratio of mean grain size of rubber solids versus soil solids ( D/ D) on dynamic response of mixtures in a range of low to high shearing strain amplitude from about 4×10% to 2.7% were investigated. Considering engineering applications, specimens were prepared almost at the maximum dry density and optimum moisture content to model a mixture layer above the ground water table and in low precipitation region. The results show that tire inclusion significantly reduces the shear modulus and increases the damping ratio of the mixtures. Also decrease in D/ D causes the mixture to exhibit more rubber-like behavior. Finally, normalized shear modulus versus shearing strain amplitude curve was proposed for engineering practice. [ABSTRACT FROM AUTHOR]

The liquefaction vulnerability of fine- to coarse-graded saturated sand and gravelly sand is evaluated by stress control cyclic triaxial laboratory tests. Cyclic triaxial test on reconstituted specimens is carried out with relative density of 45 %. Cyclic triaxial tests performed by sinusoidal wave form with 1-Hz frequency and with the effective consolidation pressure equal to 100 kPa. Cyclic stress ratio which caused initial liquefaction in 15 cycles recognized as the liquefaction resistance in cyclic triaxial test of present study. The result had been used to find a relationship between liquefaction resistance and the grading characteristics (e.g., coefficient of curvature and coefficient of uniformity) of various graded sands and gravelly sands. Then, it is realized that a relationship between liquefaction resistance and any of the sizes (i.e., D, D, D, D) appears to be more practical. [ABSTRACT FROM AUTHOR]

Shale mechanical properties are evaluated from laboratory tests after a complex workflow that covers tasks from sampling to testing. Due to the heterogeneous nature of shale, it is common to obtain inconsistent test results when evaluating the mechanical properties. In practice, this variation creates errors in numerical modeling when test results differ significantly, even when samples are from a similar core specimen. This is because the fundamental models are based on the supplied test data and a gap is, therefore, always observed during calibration. Thus, the overall goal of this study was to provide additional insight regarding the organization of the non-linear model input parameters in borehole simulations and to assist other researchers involved in the rock physics-related research fields. To achieve this goal, the following parallel activities were carried out: (1) perform triaxial testing with different sample orientations, i.e., 0°, 45°, 60°, and 90°, including the Brazilian test and CT scans, to obtain a reasonably accurate description of the anisotropic properties of shale; (2) apply an accurate interpretative method to evaluate the elastic moduli of shale; (3) evaluate and quantify the mechanical properties of shale by accounting for the beddings plane, variable confinement pressures, drained and undrained test mechanisms, and cyclic versus monotonic test effects. The experimental results indicate that shale has a significant level of heterogeneity. Postfailure analysis confirmed that the failure plane coincides nicely with the weak bedding plane. The drained Poisson's ratios were, on average, 40 % or lower than the undrained rates. The drained Young's modulus was approximately 48 % that of the undrained value. These mechanical properties were significantly impacted by the bedding plane orientation. Based on the Brazilian test, the predicted tensile strength perpendicular to the bedding plane was 12 % lower than the value obtained using the standard isotropic correlation test. The cyclic tests provided approximately 6 % higher rock strength than those predicted by the monotonic tests. [ABSTRACT FROM AUTHOR]

An equivalent visco-elastic model of saturated soft clay was studied under unconsolidated undrained (UU) condition, which can be used to evaluate the stability of ocean foundation. Cyclic triaxial compression and extension tests were conducted to study the parameters of the model. Results showed that the relationships of the damping ratio and the octahedral shear modulus with the octahedral cyclic shear strain were nearly unique, when the initial octahedral shear stress ratios of specimens were equal to 0.3, 0.5 and 0.7. The relationships of the damping ratio and the octahedral shear modulus with the octahedral cyclic shear strain determined from the cyclic triaxial compression tests were basically the same as those determined from the cyclic triaxial extension tests. Furthermore, the relationships were not related to the initial stress condition, the test stress state and the octahedral cyclic shear stress ratio. The relationships determined from the cyclic triaxial tests under no deviatoric stress were basically the same as those determined from the cyclic triaxial tests under deviatoric stress. The change of the octahedral cyclic accumulative strain with the number of cycles was unique under different tests stress states. An equivalent visco-elastic constitutive model of saturated soft clay under UU condition was initially established. [ABSTRACT FROM AUTHOR]

According to historical records, the soil in the Xinhua District of Tainan City, Taiwan, has been liquefied several times in 1946, 2010, and 2016. To assess the soil liquefaction resistance and understand the recurring liquefaction mechanism of this site, this study conducts a series of experimental tests, including the undrained dynamic triaxial tests on undisturbed and remolded soil samples retrieved from the site. Different fines contents, dry densities, and effective confining pressures are considered for the remolded samples during the test program to investigate their influence on the soil liquefaction resistance. A complete experimental soil liquefaction resistance curve of the site is constructed based on the test results. The liquefaction resistances of the undisturbed and remolded samples were found to be similar at the recurring liquefaction site in the present study. Besides, the experimental soil liquefaction resistance curve of the recurring liquefaction site was lower than the in situ empirical soil liquefaction resistance curve that is based on all site conditions, including the aging effect. This observation agrees with the other laboratory test and field investigation that the triggered liquefaction leads to the “reset” of the aging effect that lowers the liquefaction resistance. The finding of this study may explain why a recurring liquefaction site is more vulnerable to liquefaction in a seismic event. [ABSTRACT FROM AUTHOR]

This study aims to investigate the influence of dynamic properties of the ground soil on vibration properties of a rigid body placed on the sand ground surface to clarify the vibration behavior of a structure in terms of the interaction between the structure and the ground. A series of cyclic triaxial tests and three types of model vibration tests were performed. The dynamic properties of ground soil were clarified using cyclic triaxial tests. It was found that the equivalent shear modulus markedly depends on confining pressure and relative density, and that the hysteresis-damping ratio also depends on confining stress but not upon relative density. In model vibration tests, rigid body models with variable masses, inertial moment, base size and base shape were prepared and their vibration behaviors were observed. Vibration characteristics were estimated from the observed behavior, and the period and damping ratio were examined. It was found that the period depends on not only the mechanical properties of the rigid body and the relative density of ground, but also upon the magnitude of the vibration amplitude. A simple model of a spring and a dashpot was used to correlate period and damping ratio of ground soil in a model vibration test with equivalent shear modulus and hysteresis damping ratio by cyclic triaxial testing. The relationship between normalized inverse squares of the period and rotation amplitude was similar to the relationship between the normalized equivalent shear modulus and the shear strain amplitude. Normalized damping ratio also showed good agreement with the normalized hysteresis-damping ratio. The calculated equivalent shear modulus from the simple model linearly increased with increased average contact pressure, as the equivalent shear modulus of the cyclic triaxial test 1 inearly increased with effective confining pressure on a log-log scale. [ABSTRACT FROM AUTHOR]

According to the results of cyclic triaxial tests, a linear correlation is presented between liquefaction resistance and elastic shear modulus, which shows the relation of G max (kPa) with (σd/2)1/2(kPa)1/2. When applied to soils from different sites, the correlation can be normalized in reference to its minimum void ratio ( e min). Accordingly, an improved method is established to evaluate the liquefaction potential with shear-wave velocity. The critical shear-wave velocity of liquefaction is in linear relation with 1/4 power of depth and the maximum acceleration during earthquakes, which can be used to explain the phenomenon that the possibility of liquefaction decreases with the increment of the depth. Compared with previous methods this method turns out simple and effective, which is also verified by the results of cyclic triaxial tests. [ABSTRACT FROM AUTHOR]

Medium-coarse sands (CS) were dredged and exhausted in land reclamation. However, the remaining silty-fine sands (FS) were wasted. The liquefaction behavior of dredged silty-FS and the possibility of utilizing the remaining silty-FS as dredger fill source for land reclamation should be investigated. Cyclic consolidation-undrained triaxial tests were performed to investigate the liquefaction resistance of dredged silty-FS under different influencing factors. The cyclic stress ratio (CSR) of dredged silty-FS increased with the increase in initial relative density and consolidation stress ratio and decreased with the increase in silt content and consolidation stress. The CSR first decreased with the increase in clay content up to a threshold value and increased with the increase in clay content. A regression model was created to estimate the relationship between CSR and silt content, clay content, initial relative density, consolidation stress, consolidation stress ratio, and cyclic resistance ratio. Response surface methodology (RSM) was employed to investigate the mutual influence among the five independent variables. On the basis of cyclic triaxial tests, particle flow code models were introduced to investigate the microscopic internal fabric changes of dredged silty-FS and the influence of extended factors on liquefaction. The average microscopic contact force and coordination number between particles controlled the macroscopic mechanical behavior of sands. Sand liquefaction was due to the cumulative loss of coordination number under cyclic loading. The average contact force between particles was linearly decreased to 0 and the coordination number sharply decreased when the sample reached initial liquefaction. On the basis of numerical tests, CSR increased with the increase in D50 and vibration frequency. The influence of vibration frequency was relatively small. In addition, the CS-FS and CS-FS-CS combination layers showed greater liquefaction resistance than the FS layer. In the filling process, the interbed of FS and CS improved the liquefaction resistance of dredged silty-FS to a certain extent. [ABSTRACT FROM AUTHOR]