Post-cyclic Shear Strength Research Articles

Large-Scale Triaxial Testing of Geogrid-Stabilized Field-Sourced Fouled Ballast Under Simulated Progressive Rainfall Wetting and Cyclic Loading Conditions

Railroad track ballast composed of uniformly graded crushed aggregate is susceptible to fouling from substances like ballast fines degraded during track service, coal dust, clay, and sand. Fouling reduces the drainage capacity of ballast, often leading to water accumulation and subsequent performance degradation. Fouled ballast with high moisture content experiences excessive settlement and could benefit from stabilization for safe operations. While previous studies have highlighted the efficacy of geogrids in stabilizing fouled ballast and minimizing the overall track settlement, the effect of geogrid on the performance of fouled ballast under progressive rainfall wetting and continuous cyclic loading conditions remains unexplored. This study examines the performance of geogrid-stabilized field-sourced fouled ballast through large-scale triaxial tests. The findings reveal that the inclusion of a single-layer geogrid can effectively reduce settlement and deformation rates under equivalent water content conditions. A layer of geogrid could prevent sample failure under saturated conditions, retaining approximately 1,000 kPa post-cyclic shear strength. Furthermore, the results indicate that geogrid stabilization enhances the resilience of fouled ballast and maintains the track geometry under progressive rainfall conditions. These findings offer crucial insights for geogrid applications in railroad maintenance.

Use of recycled ceramic beads to enhance mechanical behavior of low-plastic clays

Due to the huge amount of annual non-renewable ceramic waste disposal, it is in favor of eco-system to reuse the ceramic waste in earthwork structures. Thus, among several different applications of ceramic components, they can also be used to replace aggregates in the core of embankment dams, waste disposal projects and to form subgrade of roads and railways. The main issues addressed in this study are the effect of the volumetric content and size of the ceramic inclusions on the mechanical properties of ceramic-clay mixtures. Using an experimental approach, strain-controlled monotonic, stress-controlled cyclic, and post-cyclic monotonic triaxial undrained tests were made. The innovation of this study is that sphere beads of ceramic with different diameters were added to low-plastic clay to explore the role of bead size on the mechanical properties of bead and clay mixtures under monotonic, cyclic and post-cyclic loadings. Thus, we tested four types of specimens consisting of merely pure clay, 80% clay–20% bead, 60% clay–40% bead, and 40% clay–60% bead. Scanning electron microscope (SEM) images were additionally used to investigate the fabric of the clay between the ceramic beads. Test results revealed, firstly, that effective friction angle and undrained shear strength increase with the bead content. Secondly, dilative behavior was captured in all the bead and clay mixtures. Further, both dynamic shear modulus and damping ratio increase with the bead content. Similarly, post-cyclic shear strength increases with the bead content. Finally, different bead diameters did not change the observed trend.

Strength characteristics of biomimetic carbonate precipitation (BCP) treated mortar under cyclic loading

L-Aspartic acid (L-Asp) has the potential to mediate the crystal form of calcium carbonate, and biomimetic carbonate precipitation (BCP) with L-Asp as the crystal modifier has been proposed for green mortar. However, the cyclic properties of BCP-treated mortar are rarely studied. In this study, the direct shear test was first performed to prove the ability of BCP treatment in improving the shear strength, friction angle, and cohesion of sand. It shows that higher normal stress can promote the pre-peak shear shrinkage of the specimen, while inhibiting the development of post-peak shear dilation. Then, the pre-peak cyclic shear test was conducted under different normal stresses, and the cyclic response of BCP-treated mortar with different number of loading cycles was investigated. The phenomenon of shear softening was observed, and the stress-strain behavior of the specimen was further studied. Finally, the specimens after cyclic loading were prepared for the direct shear test again to examine their post-cyclic properties. Results show that the specimen with more loading cycles has lower post-cyclic shear strength, while high normal stress can alleviate the decrease in shear strength after cyclic loading. With the increase in cyclic numbers, the cohesion of the specimen decreases, but the friction angle varies slightly. This study is expected to provide a deeper understanding on the shear response of BCP-treated mortar with cyclic loading.

Post-cyclic undrained behavior of marine soft clay subjected to partially drained cyclic loading

Under long-term cyclic loading, marine soft clay in coastal areas is more likely to exhibit partially drained behavior than undrained behavior. The partially drained dynamic behavior of marine soft clay tends to exert a significant effect on the post-cyclic characteristics. Thus, this study conducted two series of monotonic shearing tests to investigate the mechanical behavior of marine soft clay after long-term (50,000 cycles) traffic loading in terms of variable confining pressure (VCP). The post-cyclic stress path, pore water pressure, and shear strength were discussed through comparison of the results with those of the standard monotonic shearing test (without cyclic loading history). Partially drained cyclic loading enhanced the post-cyclic shear strength and increased the brittleness of the specimen. The behavior of the pore water pressure and void ratio of post-cyclic soft clay were similar to those of clay during undrained cyclic loading to the reconsolidation process, that is, the specimen exhibited quasi-overconsolidation performance after partially drained cyclic loading. Subsequently, the relationships between the quasi-overconsolidation ratio (QOCR) and the total cyclic stress and strength ratios were developed, and the strength-dependent parameter of the latter relationship was determined through the standard undrained monotonic shearing test of overconsolidation soil.

A united hardening rule considering monotonic and cyclic strength degradation of clay

The strength degradation of clay subjected to monotonic or cyclic loading is a crucial factor causing nearshore or offshore marine structures instability. The monotonic shear strength softening or cyclic stiffness degradation is mainly discussed in previous degradation models, while the coupling of these two characteristics is rarely considered because of its complexity. Existing studies show that different from cyclic stiffness degradation, the post-cyclic shear strength will not eventually degenerate to zero but reach a residual shear strength, which is rarely accurately predicted by previous models. Therefore, in this paper, a united hardening rule is proposed within the bounding surface model framework, which can describe the monotonic shear strength softening, cyclic stiffness degradation, and post-cyclic strength degradation. The accuracy and validity of the proposed model are verified by experimental results.

Cyclic and post-cyclic characteristics of marine silty clay under the multistage cycling-reconsolidation conditions

Marine clay applied as the foundation of marine structures is constantly subjected to long-term cyclic loading, under which the drainage and reconsolidation of the clay are inevitable. However, in previous studies, the experimental method was to apply the completely undrained conditions. The clay's drainage effect during and after cyclic loading was considered in a few experimental studies, but the repeated effect of cycling and drainage which is a common condition for clay foundations in practical engineering was barely concerned. Therefore, a large number of triaxial tests were carried out considering the effects of confining pressure, cyclic stress ratio, degrees of reconsolidation, and the number of cycling-reconsolidation (C-R) cycles to clarify the cyclic and post-cyclic behavior of the marine silty clay. The test results show that the cyclic and post-cyclic characteristics of silty clay gradually stabilize after a given number of C-R cycles and are irrespective of continually increasing ones. The existence of residual cyclic pore pressure after the multistage C-R process can give rise to shear strength degradation. However, applying the C-R process can substantially enhance the clay's resistance to the shear, resulting in the lift of the post-cyclic shear strength. Besides, there is a consistent relationship between the post-cyclic shear strength and the reduction of water content caused by reconsolidation under different C-R conditions and a corresponding prediction formula has been obtained.

Post-cyclic mechanical behaviors of laterite clay with different cyclic confining pressures and degrees of reconsolidation

The post-cyclic mechanical behaviors of subgrade soil are usually assessed by conventional cyclic triaxial tests, however, the stress field induced by traffic loads consist of not only a cyclic deviator stress, but cyclic confining pressure and shear stress. Meanwhile, the pore water is allowed to be discharged under traffic loads. Furthermore, the traffic load-induced excess pore water pressure can be partially dissipated after load-cycling. Thus, different reconsolidation processes should be considered. Recognising this, cyclic loading with variable confining pressure was applied to remoulded laterite soils under partially drained conditions, and reconsolidation was allowed. The development of effective stress paths, excess pore water pressure, and undrained strength of post-cyclic shear process were analysed. Results show that the development of effective stress paths is similar and all stress paths cross the critical state line. Besides which, the remoulded laterite clay always has a positive excess pore water pressure and tend to dilate. The undrained strength will be increased under different conditions such that the greater the cyclic confining pressure, cyclic deviator stress, number of cycles, and degree of reconsolidation, the larger post-cyclic undrained strength. Moreover, the post-cyclic undrained strengths between cyclic loading with and without cyclic confining pressure were compared: the undrained strength ratio of cyclic confining pressure to that under constant confining pressure increases linearly with increasing slope of the stress path. Nevertheless, the post-cyclic undrained strength after reconsolidation can be obtained by the corresponding undrained strength without reconsolidation: the ratios of post-cyclic shear strength with and without reconsolidation increase with increasing degree of reconsolidation. At a certain slope of stress path, the undrained strength increases linearly with degree of reconsolidation.

Post-cyclic undrained shear behavior of soft marine clay under anisotropic consolidation stress paths

In offshore engineering, the soft marine clay beneath an embankment may be subjected to anisotropic consolidation stress paths, which greatly affect its monotonic and post-cyclic shear behavior. In this study, the post-cyclic undrained shear behavior of anisotropically consolidated soft marine clay was investigated by conducting a series of monotonic and post-cyclic shear triaxial tests. First, the post-cyclic undrained shear behaviors, including the stress–strain, pore water pressure, and effective stress paths, were investigated by comparing the results of the monotonic tests. Then, the degradation of the post-cyclic undrained shear strength was analyzed. Finally, an empirical prediction model of the post-cyclic anisotropy strength was proposed based on the definition of equivalent overconsolidation.

Laboratory Study on Dynamic Properties of Municipal Solid Waste in Saravan Landfill, Iran

Saravan landfill, located in northern Iran, has been an environmental cause of concern through its entire time of operation. As part of a project aimed at bringing the landfill conditions closer to standards, large-scale cyclic direct shear and bender element tests were carried out on reconstituted waste samples, obtained from different locations and depths at the landfill. Samples obtained at greater depths were found to have a higher fibre content which mostly consisted of nondegradable plastics that accumulated while a large part of the rest of the waste succumbed to biodegradation. Bender element tests showed an increase in the shear wave velocity and maximum shear modulus of the waste with ageing. This increase coincided with an increase in the sample unit weight. Normalized shear modulus reduction and damping ratio curves were obtained from the cyclic direct shear tests which were consistent with data available in literature. In addition, ageing was observed to shift the modulus reduction and damping curves to the left, decreasing the former while increasing the latter and resulting in a reduction in the shear strain corresponding to the onset of plastic behaviour. Ten cycles of direct shear loading at a 3.33% strain caused shear modulus and damping ratio to decrease by about 50% and 40%, respectively, most of which occurred within the first three or four cycles. Secant friction angle obtained from post-cyclic shear strength tests were found to vary between 32° and 55°, which was consistent with previous research.

The influence of roughness on cyclic and post-cyclic shear behavior of red clay-concrete interface subjected to up to 1000 cycles

Dynamic shear behavior of soil-structure interface is one of the most commonly problems in engineering practice, especially for the design and stability analysis of soil-structure interaction system subjected to cyclic loading. This paper presents the results of an experimental study on the interface between red clay and concrete that is subjected to a large number of cycles (up to 1000 cycles). Three concrete blocks with different surface roughnesses were fabricated and displacement-controlled cyclic tests were conducted by using a large-scale direct shear device under three different normal stresses (100 kPa, 200 kPa and 300 kPa). The effects of normal stress, roughness and number of cycles on cyclic and post-cyclic shear behavior of interface were then discussed in detail. The test results show that the red clay-concrete interface exhibits softening behavior under different normal stress levels. The mobilized shear stress decreases moderately with the number of cycles and subsequently remains constant after 500 cycles of loading. The response of interface subjected to cyclic loading shows apparent aeolotropy due to shear directions in every cycle. Interface shear stiffness and damping ratio decreases with increasing cycle numbers. The red clay-concrete interface represents an overall contraction behavior in cyclic and post-cyclic direct shear tests. The cyclic loading does not lead to degradation for post-cyclic shear strength.

Large Scale Direct Shear Experiments to Study Monotonic and Cyclic Behavior of Sand Treated By Polyethylene Terephthalate Strips

The continuously increasing production of plastics in the last few decades has taken a heavy toll on the environment. Soil reinforcement with the use of randomly distributed fibers, plastics and glass has recently received a lot of attention. The use of polyethylene terephthalate (PET) strips as soil reinforcement has been observed to result in the increase in the shear strength. In this paper, the monotonic, cyclic, and post-cyclic properties of sand reinforced with different contents and aspect ratios of PET strips are investigated by carrying out a set of monotonic and cyclic direct shear tests. Accordingly, the influence of various parameters on the direct shear response of sand-PET mixture is examined. Results show that in the monotonic tests, for mixtures containing 0%, 0.5%, 0.75% and 1% PET with AR = 1, the peak friction angle is 37.5°, 41.8°, 42.7°, and 44.6°, repectively, while these values increase to 41.8°, 45.4°, 48.2°, and 50.4°, respectively, for post-cyclic monotonic tests. In addition, in the monotonic tests, for mixtures containing 0.5%, 0.75% and 1% PET with AR = 5, the peak friction angle is 48.8°, 52.2°, 54.0°, respectively, while these values increase to 50.9°, 54.8°, 55.9°, respectively, for post-cyclic monotonic tests. Results clearly imply that normal stress and cyclic shear strain amplitude contribute jointly to the contractive behavior of the reinforced mixtures. Moreover, the hardening behavior becomes less eminent when the sand is reinforced with PET strips due to the resistance mobilized against particle rearrangement. The post-cyclic shear strength of the PET-sand mixture is higher than their monotonic strength due to the densification occurring during the cyclic loading. In summary, the favorable impact of PET inclusion on the monotonic and cyclic performance of granular materials is deduced.

DETERMINATION OF THE POST-CYCLIC YIELD STRENGTH AND INITIAL STIFFNESS OF TWO PEAT SOILS

The post-cyclic yield shear strength and initial stiffness of a peat soil after subjecting to cyclic loading is a major topic in this study. Due to the effects of cyclic loading, post-cyclic shear strength decreases lower than its initial strength. A series laboratory static and cyclic triaxial test followed by post-cyclic monotonic tests carried out to determine the yielding parameters. Tests were carried out on the undisturbed samples taken from Parit Nipah, Johor and Lumadan, Sabah within west and east Malaysia peat soils. Postcyclic loading test conducted with effective stress 100 kPa with frequency 1.0Hz. The initial stiffness is the initial tangential modulus with yield shear strength was half of the deviator stress in which two tangential lines intersect. The post cyclic yield shear strength of undisturbed peat soil is considerably lower compared to static at the axial strain of only 1.4% and 1.5%. The Parit Nipah and Lumadan peat are classified as Hemic

Investigation of the mechanical behavior of soft clay under combined shield construction and ocean waves

This study aims to investigate the mechanical behavior of soft clay under both shield construction and long-term dynamic wave loading in the practical construction of breakwaters to protect coastal power plants. Continuous rotation of the principal stress axis due to cyclic wave loading is reproduced by altering the control loads (that is, axial load, torque, inner cell pressure, and outer cell pressure) in a hollow cylindrical shear apparatus (HCA). In the HCA, the confining pressure is progressively reduced to replicate the stress release induced by ground loss during shield construction. The HCA test results show that both long-term wave loading and shield construction significantly affected the dynamic stiffness of soft clay. Under the combined effects of wave loading and shield construction, the post-cyclic shear strength and stiffness of the soft clay are reduced more significantly compared to the isolated effect of wave loading, especially at lower confining pressure. The degradation of the dynamic secant modulus, Ed, and the initial tangential modulus, Ei, is indicated to be synchronous at the end of the cyclic loading test, which implies the unique disturbance of the combined action of shield construction and dynamic wave loading on the microstructure of soft clay considered in this study. Based on the experimental observations, a simple and effective constitutive model is also developed to reproduce the degradation of stiffness and shear strength of soft clay induced by shield construction and dynamic wave loading.

Effect of Particle‐Size Gradation on Coarse Sand‐Geotextile Interface Response in Cyclic and Postcyclic Direct Shear Test

In order to investigate the influence of sand particle‐size gradation on cyclic and postcyclic shear strength behaviour on sand‐geotextile interfaces, a series of monotonic direct shear (MDS), cyclic direct shear (CDS), and postcyclic direct shear (PCDS) tests were performed using a large‐scale direct shear apparatus. The influence of cyclic shear history on the direct shear behaviour of the interface was studied. The results indicated that cyclic shear stress degradation occurred at the sand‐geotextile interface. Shear volumetric contraction induced by the cyclic direct shear increased with the increase in cycle number. The lowest final contraction value was observed in discontinuously graded sand. In the MDS tests, there were great differences in interface shear strength due to the different particle‐size gradations, whereas the differences between shear volumes were negligible. In the PCDS tests, the shear stress‐displacement curves exhibited postpeak stress hardening behaviour for different particle‐size gradations, and differences in shear volumes were detected. The well‐graded sand‐geotextile interface had a higher value of shear stiffness and a higher damping ratio relative to the other interfaces. Postcyclic shear stress degradation was observed for the discontinuously graded sand‐geotextile interface.

Cyclic and postcyclic behaviour of silts and silty sands from the Indo Gangetic Plain

The Indo Gangetic Plain (IGP) that lies on the verge of subduction zone of Indian and Eurasian plate is a seismically active, densely populated region with deep soil deposits. A number of critical structures such as rail and highway bridges and nuclear power plants are being built in the region to cater to the large population of the region, and hence the characterization of deep soil deposits in this region are important. In the present study undisturbed soil samples (UDS) from a site in the IGP plane are examined for static, cyclic, and post-cyclic behaviour. The soils tested have fines content varying from about 20% to 80%, and the fines are non-plastic in nature. The modulus reduction and damping ratio of soil at small, medium and large strain range is examined with the UDS by carrying out bender element, resonant column, and cyclic triaxial tests, respectively. Post cyclic behaviour of non-plastic silty soils is also examined with single stage and multistage cyclic triaxial testing. It is observed that the post-cyclic shear strength increases with increase in the non-plastic fines in the soil. The history of cyclic loading preceding the post cyclic tests is found to influence the tangent modulus observed in post cyclic tests. A site specific calibration parameter is proposed to predict pore pressure response using the energy based Green Mitchel Polito (GMP) pore pressure model.

Characterization of the Reduction in Undrained Shear Strength in Fine-Grained Soils due to Cyclic Loading

AbstractTo evaluate the effect of plasticity characteristics and mineralogical composition on postcyclic shear strength degradation, 18 soils, prepared as different proportions of kaolinite, montmo...

Post-cyclic shear behavior of reconstituted marine silty clay with different degrees of reconsolidation

In this paper, a series of dynamic triaxial tests have been carried out to study the post-cyclic shear behavior of the reconstituted marine silty clay. Most previous studies on the post-cyclic shear characteristics of clay considered no reconsolidation after cyclic loading, and a few studies investigated the influence of full reconsolidation. The actual marine clay after cyclic loading tends to be in a state between no reconsolidation and full reconsolidation after cycling. Therefore, different reconsolidation processes including no reconsolidation, full reconsolidation and different degrees of reconsolidation were conducted to investigate their effects on the post-cyclic shear characteristics. Various factors including confining pressure, initial consolidated deviator stress ratio, cyclic stress ratio and degree of reconsolidation were taken into account. Results show that the post-cyclic shear strength will be enhanced and weakened with the full and no reconsolidation, respectively. And a specific degree of reconsolidation is existed for the specimens, with which the post-cyclic shear strength equals to the corresponding static shear strength. During the post-cyclic monotonic shear process, the silty clay always have a positive pore pressure and show dilative tendency. Moreover, no significant effects of cyclic loading and reconsolidation history on the change of critical stress ratio in p′-q plane was observed for the reconstituted silty clay. The critical stress line for specimens in e-log p′ plane tends to be affected by the previous cyclic loading amplitude, irrespective of the reconsolidation process. Besides, a post-cyclic shear strength model which can consider different degrees of reconsolidation was obtained based on the Yasuhara equivalent overconsolidation model. The predicted results demonstrate a good agreement with the measured one.

Post-cyclic undrained shear behavior of marine silty clay under various loading conditions

The post-cyclic undrained shear characteristics of marine silty clay was investigated by conducting a series of cyclic triaxial tests on undisturbed specimens. The effects of confining pressure, initial undrained shear stress ratio (qs/p0), cyclic stress ratio (qcy/p0) and number of cycles (N) on the post-cyclic undrained shear behavior were investigated. Results show that the post-cyclic shear strength decreases with the increase in qs/p0, qcy/p0 and N. The confining pressure has no apparent effect on the normalized post-cyclic monotonic undrained shear strength for the silty clay. During the post-cyclic shear, the specimens with small qs/p0 and qcy/p0 contract, while the cases with large qs/p0 and qcy/p0 dilate. Also, the terminal value of normalized post-cyclic shear-induced excess pore pressure decreases with qs/p0 or qcy/p0 increasing. The Equivalent Hvorslev Line (EHL) was proposed to form a failure envelop for the post-cyclic silty clay and the slope of EHL increases with the increase in qcy/p0 or qs/p0, regardless of the number of cycles. Moreover, a post-cyclic strength model, which could consider the influence of initial shear stress and previous cyclic loading history was proposed on the basis of Yasuhara model. This model demonstrates a good agreement with the test results.

Effect of silt on post-cyclic shear strength of sand

Adding non-plastic fines to sand can greatly change its behavior. Size difference between sand and silt particles is the main reason which causes this change. While post-cyclic and post-liquefaction behavior of clay and clean sand has been widely studied, silty sand is wrongly considered to behave like clean sand and researches usually do not focus on it. In silty sand, through low cohesion, applying cyclic load can displace particles and result in heterogeneity within the mixture. Even if liquefaction does not occur, rearrangement of soil particles can affect monotonic ultimate strength. This study, with a series of post-cyclic monotonic triaxial tests, has shown that in sand with a considerable amount of silt, cyclic loading can change the ultimate state strength. In sand with 15% silt it decreases and in sand with 30% silt it increase the ultimate state strength. Changes are negligible in clean sand or sand with 5% silt.

Cyclic and post-cyclic monotonic behavior of Adapazari soils

The August 17, 1999 Kocaeli earthquake affected the city of Adapazari, which is located in the northwest of Turkey, with severe liquefaction and bearing capacity failures causing tilting of buildings, excessive settlements and lateral displacements. To understand the stress–strain behavior and pore pressure behavior of undisturbed soils during the earthquake, the cyclic and post-cyclic shear strength tests have been conducted on soil samples obtained from Adapazari in a cyclic triaxial test system within the scope of this research. Cyclic tests have been conducted under stress controlled and undrained conditions. Post-cyclic monotonic tests have been conducted following cyclic tests. The strength curves obtained in the experiments showed that the dynamic resistance of silty sand was found to be 45% lower than those of high plasticity soils (MH). The strength of clayey soils with the plasticity index of PI=15–16% was lower compared to the strength of high plasticity soils. Also, it was observed that silty sand soils had the lowest strength. The dynamic strength of the soils increased with the increase in plasticity.