Post-cyclic Shear Research Articles

Experimental Study on the Temperature-Dependent Static, Dynamic, and Post-Dynamic Mechanical Characteristics of Municipal Solid Waste.

Municipal solid waste (MSW) has huge potential to be recycled as construction material, which would have significant benefits for environmental conservation. However, the cornerstone of this undertaking is a solid comprehension of the mechanical response of MSW in real-world engineering locations, taking into account the effects of stress levels and temperature. In this paper, well-mixed MSW samples were sieved and crushed to produce standardized specimens in cylindrical molds. A series of static, dynamic, and post-cyclic shear tests were conducted on the MSW at temperatures ranging from 5 °C to 80 °C with normal stresses of 50 kPa, 100 kPa, and 150 kPa. The experimental findings demonstrate that the static, dynamic, and post-cyclic mechanical response of MSW presents temperature range-dependency; temperature variation between 5 °C and 20 °C affects MSW's mechanical reaction more than variation in temperature between 40 °C and 80 °C under various stress settings; at 5 °C~80 °C, the static peak shear strength of MSW is the highest, being followed by the post-cyclic peak shear strength, while the dynamic peak shear strength is the lowest; the sensitivity of the dynamic shear strength of MSW to temperature variation is the largest, being followed by the post-cyclic peak shear strength, and the static peak shear strength is the lowest.

Post-cyclic behavior of Haikou marine clay and their predictions using back-propagation neural network model

The evaluation of post-cyclic behavior of soft clay is critical for the lifetime safety and performance assessment of various infrastructures built on/in it. In this study, by employing the marine clays collected from Haikou, China, a series of both conventional shear tests and post-cyclic shear tests under undrained condition were performed using triaxial setup to investigate the post-cyclic behavior of the clay, with the investigation foci placed on the post-cyclic shear stress and secant modulus. Some important factors, namely confining pressure, loading frequency, cyclic shear strain amplitude and post-cyclic shear strain, were taken into consideration. From both the results from the tests and the parameter sensitivity analysis using random forest method, the confining pressure and cyclic shear strain amplitude were found to be evidently influential on the post-cyclic behavior of the clay, while the influence of loading frequency was relatively insignificant. In addition, an intelligent model was established based on the back-propagation neural network method to predict the post-cyclic behavior of Haikou marine clay, which was proven to be more favorable as compared to other two prediction methods developed based on multi-variate regression analysis and random forest algorithm.

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.

Post-cyclic Loading Relationship Effects to the Shear Stress and Cyclic Shear Strain of Peat Soil

Peats originate from plants and denote the various stages in the humification process. This condition renders the peat extremely soft and can be considered problematic soil. Thus, this study is conducted to examine and comprehend the particularities of peat engineering behaviour in respect to the relationship effects to the shear stress and cyclic shear strain of peat soil various characteristics to establish suitable correlation. This study carried out by using triaxial testing described by geotechnical test standards BS-1377: Part 8: 1990. Methods of Testing Soils for Civil Engineering Purposes: Shear Strength Tests (Effective Stress) that required for consolidated undrained and consist of five main stages: saturation, consolidation, static, dynamic, and post-cyclic loading using the GDS Enterprise Level Dynamic Triaxial Testing System (ELDYN). The parameters of shear strength were obtained in the peak deviator stress at a maximum of 20% of axial strain by using an undisturbed sample with an effective pressure imposed of 25, 50, and 100 kPa. In this study, all specimens are subjected to cyclic loading up to 100 cycles based on a one-way loading system with strain-controlled conditions. Based on the analysis conveyed, the post-cyclic shear stress decreased compared to its initial value of about 65.56 kPa (PNpt-100 kPa) in static and decreased to 14.9616 kPa in post-cyclic (PNpt-25 kPa-1 Hz). The principal stress ratio (σ'1/σ'3) shows the maximum values of this ratio that are located in the narrow zone of 1.61 to 1.12. Doi: 10.28991/CEJ-2022-08-12-08 Full Text: PDF

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.

A post-cyclic strength degradation model for saturated soft clay

The pore pressure of coastal marine soft clay will accumulate under cyclic loading, resulting in the reduction of the effective stress and hence the post-cyclic strength degrades. Such characteristic of clay would affect the stability of the structures on the clay ground. Most of the previous post-cyclic strength degradation models are semi-empirical ones. A few researchers developed elastic-plastic models by introducing the parameter of accumulated deviatoric plastic strain into the hardening rule. These models considered the complete strength loss of clay in the state of cyclic failure but cannot take into account strength degradation in the state of cyclic stability. Therefore, a cyclic memory parameter was introduced to develop a post-cyclic strength degradation bounding-surface model. This model was proposed based on the classical bounding-surface model with a vanishing elastic region. The post-cyclic strength degradation was achieved by the shrinkage of the bounding-surface during cyclic loading, and the degradation is not unlimited under the control of the cyclic memory parameter. The accuracy and validity of the proposed model were verified by comparing the predicted and the triaxial experimental results. Moreover, the effectiveness of the model for predicting the cyclic and post-cyclic shear characteristics of clay under various loading conditions was further demonstrated.

Cyclic and post-cyclic shear behaviours of natural fibre reinforced soil

ABSTRACT Soil behaviour under cyclic loading is a key component in assessing potential effects of earthquakes on infrastructure and the response of earth structures to dynamic loading. In this study, cyclic and post-cyclic shear behaviours of fibre reinforced and unreinforced soil were investigated. Series of undrained cyclic triaxial tests were performed to study effects of sisal fibres of 25 mm length and contents of 0.25%, 0.5% and 1% on the shear modulus, damping ratio, permanent strain, cumulative strain and liquefaction potential. The post- cyclic shear tests were conducted to study effects of fibre inclusion on the post cyclic energy absorbing capacity, toughness and static energy ratio. The results showed that fibre inclusions caused an increase in shear modulus to a limiting fibre content of 0.5% beyond which modulus reduced. The reduction was attributed to the loss of stiffness of soil composite due to high amount of voids. Fibre inclusions increased damping ratio due to enhanced resistance to deformation. Both permanent and cumulative strains reduced with fibre inclusions as a result of an increase in the resilience of soil composites to deformation. Both reinforced and unreinforced soil types exhibited high resistance to liquefaction. Increasing fibre content caused an increase in the post cyclic energy absorbing capacity, toughness and static energy ratio of the soil composite.