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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]

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]

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]

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]

With the increasing number of vehicles plying on the roads, alarming volumes of the waste tires are generated every year throughout the globe. The disposal of these materials is of great concern. The most efficient way to reduce their volume is to reuse these materials for various applications. To investigate the behavior of the scrap tire derivatives under cyclic load, a series of cyclic triaxial tests were conducted. Seven different mixes of sand and tire crumbs (by weight) were tested under three different confining pressures (50 kPa, 75 kPa, and 100 kPa) and four different shear strain amplitudes (0.075%, 0.15%, 0.225%, 0.3%). All the tests were reported for 200 loading cycles. The result showed that the addition of tire crumbs reduced the shear modulus and increased the damping ratio. The addition of tire crumbs reduced the modulus degradation rate remarkably and makes the material useful for structures subjected to cyclic loading. The resistance toward liquefaction is also increased drastically upon the addition of tire crumbs, and the mixes showed high resistance toward the generation of excess pore water pressure. The detailed characterization of sand-tire crumbs mixes reported in the present study can be very helpful when choosing the mix for different applications. [ABSTRACT FROM AUTHOR]

For equivalent linear and nonlinear site response analysis, both shear modulus and damping ratio are critical input factors. The elastic modulus and damping ratio of saturated soft clay are usually determined using cyclic triaxial tests. However, the dynamic behaviors of saturated clay are affected by excess pore-water pressure induced under cyclic loading. Therefore, the evolutions of both elastic modulus and damping ratio, under cyclic triaxial tests with and without drainage, are the main focus of the investigation. Two types of cyclic triaxial tests were performed, in which the primary distinction is whether the excess pore-water pressure caused by the previous stage's cyclic loading is released prior to the application of the next stage's cyclic loading. The impacts of several parameters, such as effective confining pressure and excess pore-water pressure, were investigated. As the effective confining pressure increases, so does the maximum elastic modulus. Excess pore-water pressure has a significant effect on maximum elastic modulus. The maximum elastic modulus under the condition with drainage increases linearly with that obtained without drainage. Besides that, the variations of normalized elastic modulus with effective confining pressure are negligible under the condition without drainage, while the impact of effective confining pressure is more apparent in the condition of drainage. Nevertheless, the influence of effective confining pressure on the damping ratio can be ignored over the range of axial strain. The damping ratio without drainage is higher than that obtained under the condition with drainage. Based on that, the variation of normalized elastic modulus versus axial strain can be depicted by an empirical function, while the evolution of the damping ratio is represented by a hyperbolic model. [ABSTRACT FROM AUTHOR]

Site survey revealed that a liquefiable sand layer was often sandwiched by low-permeable layers with fine particles, which could hinder the dissipation of excess pore water pressure (EPWP) after earthquake excitation. However, the remaining EPWP within the liquefied sand layer may significantly reduce the reliquefaction resistance of the sand during an aftershock of the main earthquake. Many investigations on the liquefaction of stratified sand have been performed in model tests, e.g., 1 g shaking table tests and centrifuge tests as boundary value problems. However, few contributions on this topic from element tests are available in the literature. Investigations on the reliquefaction of sand sandwiched by low-permeable layers are even less available. Therefore, three groups of reliquefaction tests with different reconsolidation ratios, or different dissipation degrees of EPWP, were performed on Toyoura sand using a cyclic triaxial loading apparatus. In each group of tests, two key factors, stress-induced anisotropy formed in the first liquefaction process and the cyclic stress ratio in the second loading, were designed to investigate the reliquefaction resistance of incomplete reconsolidated sand that had already experienced liquefaction in the first loading. The test results indicated that the reliquefaction resistance decreased significantly if residual EPWP existed in the specimens. Furthermore, stress-induced anisotropy has a substantial influence on the reliquefaction resistance of both complete and incomplete reconsolidated sands. In an extreme case, even a small amplitude of aftershock could trigger reliquefaction of sand if the first liquefied sand maintains a high level of stress-induced anisotropy or has a large amount of residual EPWP. Finally, the relations among the cyclic stress ratio, stress-induced anisotropy, and reconsolidation ratio were proposed to predict the reliquefaction resistance of sand sandwiched by low-permeable layers. [ABSTRACT FROM AUTHOR]

Plant roots have been shown to improve the soil resistance to liquefaction upon cyclic loading. However, the effect of roots and their orientations on any changes in soil anisotropy and the mechanisms of dissipated energy involved at liquefaction state are not clear. This study applied the energy-based method to evaluate the liquefaction behavior of rooted soils of varying root volume ratios (RVRs). Results of 12 undrained cyclic triaxial tests on rooted soils published in the literature were reinterpreted under this energy framework. The assessment showed that the normalized cumulative dissipated energy (∑ΔW/σc′ , where σc′ is the effective confining pressure) of rooted soil at liquefaction state can be related to the cyclic resistance ratio at 15 cycles (CRR15). It was discovered that roots that were predominantly orientated in the direction perpendicular to the major principal stress of extension path reduced soil anisotropy. Additionally, the ∑ΔW/σc′ was linearly correlated with the normalized cumulative strain energy (∑4W/σc′) with a gradient of approximately 2, which implies that any recycling and recovering of strain energy was minimal in rooted soils. [ABSTRACT FROM AUTHOR]

Microbially induced calcite precipitation (MICP) is currently appraised to improve sandy soils, but only a few studies use it to solidify loess soil. MICP solidification tests and undrained cyclic triaxial tests were conducted to study the liquefaction resistance of MICP-solidified loess soil samples. The results showed that because calcium carbonate (CaCO3) cemented loess soil particles and filled voids in samples, the permeability coefficients of treated samples all decreased. However, the change pattern of the permeability coefficient of samples treated with various conditions was different. For the solidified samples, the liquefaction resistance was improved significantly, and increased treatment cycles resulted in the improvement of the liquefaction resistance. Adding bacterial suspension and the cementation solution together made the sample with initial density of 1.4 g/cm3 have higher liquefaction resistance. However, for samples of 1.5 and 1.6 g/cm3 , adding bacterial suspension and the cementation solution separately also achieved better liquefaction mitigation effects. Increasing total solution volume per treatment cycle improved the liquefaction resistance of the solidified samples. With the increase of CaCO3 content, the number of cycles before liquefaction (NL) and residual strength (τr) exponentially increased, while the damping ratio (D) exponentially decreased. Moreover, the linear corrections between specific gravity and CaCO3 content, NL , τr , and D can be established for MICP-solidified loess soil. In addition, significant corrections also existed between plasticity index and CaCO3 content, NL , τr , and D. Results in this work had a great significance and provided the foundation for the application of the MICP technique for liquefaction mitigation of loess soil. [ABSTRACT FROM AUTHOR]

Liquefied soils are considered as soils devoid of any strength or having only limited strength. Post-liquefaction shear behavior of soil before the drainage of excess pore pressure is important in predicting the immediate performance of foundation and soil structures subjected to liquefying loads. In the present study, the post-cyclic undrained behavior of weathered silty sand was examined under triaxial test conditions. The soil showed complete strength recovery after subjecting it to monotonic shearing up to large strains. The post-liquefaction shear behavior was mostly determined by the amount of excess pore pressures that developed during cyclic loading. The cyclic load amplitude and shear strain did not seem to have an effect on the post-cyclic shear behavior. Post-cyclic shearing showed that with sufficient strain the soil recovered its original strength even without dissipation of any excess pore pressure. [ABSTRACT FROM AUTHOR]

Once loose sand has liquefied, it becomes denser along with water drainage after liquefaction. Therefore, liquefied sand is regarded as more robust against liquefaction. Such sand after liquefaction is expected to liquefy again only slightly. Nevertheless, examples of repeated ground liquefaction have been reported during some earthquake events. Reliquefaction characteristics of saturated sandy ground must be estimated accurately with consideration of the liquefaction history related to past earthquakes. Moreover, the stress history affecting liquefaction strength must be considered. Cyclic triaxial tests were conducted to estimate the liquefaction strength ratio during and after liquefaction using specimens with a history of overconsolidation. The shear wave velocity, which is related strongly to the soil physical properties, was also measured in the same specimen. Results show that the stress history does not affect the specimen shear wave velocity despite increased liquefaction strength. The increased liquefaction strength induced by the stress history is eliminated by the liquefaction history. [ABSTRACT FROM AUTHOR]

The engineering properties of tailings are important for the safety evaluation and engineering design of tailing dams. In the present study, laboratory experiments were performed to investigate the geotechnical properties of four different tailings, including two iron tailings (coarse and fine) and two copper tailings (coarse and fine). Compared to the copper tailings, the iron tailings showed higher compressibility, lower permeability, lower strength, and lower cyclic resistance. With the decrease in void ratio, the coefficient of consolidation almost kept constant for the fine iron tailings, whereas for the fine copper tailings, the coefficient of consolidation gradually increased. Under cyclic loading, the accumulation of pore water pressure was faster in the fine tailings than that in the coarse tailings. The cyclic resistance ratios (CRR) of the four tailings were found to be comparable with previous report data on other metal tailings, and the consolidation stress showed little impact on CRR. The laboratory tests provided useful information to understand the geotechnical behaviors of mine tailings including seepage, deformation, strength, as well as seismic responses. [ABSTRACT FROM AUTHOR]

Due to the ever-increasing demand for electricity, generation of fly ash in large quantities has become a problem throughout the world. The utilization of fly ash in rail and road embankments in earthquake-prone areas requires thorough understanding of its dynamic strength characteristics. A series of resonant column and cyclic triaxial tests have been carried out on fly ash to investigate the influence of various factors on its maximum dynamic shear modulus (Gmax) and dynamic damping (Ds). Correlations for predicting Gmax and Ds for fly ash have been proposed. The fly ash is found to be far more liquefiable than sand. The particle-size distribution and low unit weight play a vital role in the determination of cyclic strengths. The dynamic shear damping is found to be very much influenced by the confining pressure and induced strain, but independent of the relative density of the fly ash. The damping of sand is found to be always more than the damping of the fly ash irrespective of the confining pressure. [ABSTRACT FROM AUTHOR]

In this study, cyclic behavior and dynamic properties of Renusagar pond ash samples reinforced with geotextiles have been studied. Pond ash samples were collected from the upstream side of the pond ash embankment. Laboratory tests have been carried out to obtain the material properties of the pond ash. Strain-controlled cyclic triaxial tests have been carried out on reconstituted pond ash samples with and without geotextiles, at varying confining pressures (70, 100, and 150 kPa), loading frequencies (1 and 0.5 Hz), and cyclic shear-strain amplitudes (0.5, 0.8, and 1.05%). The woven geotextiles were used as reinforcing materials, which were placed in the pond ash samples in one and three layers. Results show that the pond ash samples reinforced with geotextiles exhibit better friction angle, drainage properties, and liquefaction resistance. It may be concluded that pond ash reinforced with geotextiles can be used effectively as embankment construction material. [ABSTRACT FROM AUTHOR]

Because of the large grainsizes typical of railroad ballast, large triaxial samples are required to assess the reactions of these materials. The parallel gradation modeling technique was originally developed by John Lowe in 1964 to allow assessment of large grain-size geomaterial properties in smaller, more typical testing facilities. Emphasis has focused on monotonic loading, in which the material is progressively loaded to failure. Cyclic testing of this model has been absent. This paper presents an investigation of the possibility of using the parallel gradation modeling technique in a cyclic triaxial testing framework. Three separate gradations of ballast material were used in this research. The largest gradation contains a top particle size of 63.5 mm (2.5 in.) and is marketed as #3 modified railroad ballast. The second two gradations contained a top size of 38 mm (1.5 in.) and 19 mm (.), respectively. Up to 10,000 load cycles were applied for each test. Resilient modulus, permanent axial, volumetric strain, and particle shape were determined from the test results. It is concluded that applying parallel gradation technique to cyclic behavior characterization should be cautious. If particle shape is not consistent throughout the particle sizes used in the parallel gradation model, the model is invalid in the cyclic triaxial framework. [ABSTRACT FROM AUTHOR]

The estimation of strength and stiffness of reinforced aggregates is very important for the design and construction of reinforced unpaved/paved road sections. This paper presents the experimental results from static and cyclic triaxial tests carried out on granular subbase samples reinforced with multiple layers of geogrid reinforcement. Aggregates of different size ranges were mixed in calculated proportions by weight to obtain the gradation specified for rural roads. Triaxial samples of 300 mm diameter and 600 mm height were prepared using this sampled aggregate. The strength and stiffness characteristics of this aggregate reinforced with geogrids at different elevations were determined from static and cyclic triaxial tests. Triaxial tests were also carried out on geocell encased aggregates, and the results are compared. From the experimental results it is observed that reinforced systems carried more stresses than unreinforced systems at the same strain level. The beneficial effect increased with increase in the quantity of reinforcement, whereas for geocell reinforcement, the advantage was evident only at higher strains. [ABSTRACT FROM AUTHOR]