Cyclic Shear Strain Amplitude Research Articles

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.

Dynamic Properties of a Compacted Residual Soil from the West Indies

This paper presents a laboratory investigation of the strain-dependent cyclic properties of a compacted tropical residual soil as measured in a resonant column and cyclic triaxial testing program. The mechanical properties were evaluated with respect to cyclic shear strain amplitude, initial void ratio, and confining pressure. It was shown that the existing models for the prediction of shear modulus reduction and damping ratio curves were not pertinent in the case of the compacted residual soil studied. Empirical equations were developed for the small-strain shear modulus and the normalized shear modulus, damping ratio, and pore water pressure ratio curves for void ratios between e = 1.00 and e = 1.50 and mean effective pressures of p′ = 50−300 kPa. The comparison of the models to the measured values suggest that the uncertainties associated with each of these models are lower than 20% of the predicted values. The results were established as part of a project for the construction of an embankment dam in the West Indies. However, the methodology as well as the model formulation framework presented in the article can be generalized to other residual soils and applied in all fields of geotechnical engineering.

Dynamic behavior of geocell-reinforced rubber sand mixtures under cyclic simple shear loading

Due to the attributes of low shear modulus and high initial damping, rubber sand mixtures (RSM) can be used as a soil alternative to reduce ground motions when seismic loads are of great concern. However, when RSM is used as a vibration isolation material for geotechnical seismic isolation systems, it suffers from a lack of load-bearing capacity. To overcome this, a three-dimensional interconnected geocell (one type of geosynthetics) is placed within RSM to increase the vertical confinement of the system. In this technical note, to investigate the shear modulus and damping ratio of geocell-reinforced RSM, large-scale cyclic triaxial tests were conducted on specimens prepared with four granulated rubber contents (by weight) and sheared under different cyclic shear strain amplitudes. The results show that Geocell reinforcement can restrict the development of local shear bands in the specimen, weaken the anti-S-shaped characteristics of hysteresis loops and enhance the damping ratio of RSM at large strain amplitudes. The tuck net effect causes an increase in the normal stress of both contact particles, and then leads to the degradation rate of the maximum shear modulus of RSM varying with the rubber content and vertical pressure. The normalized shear modulus degradation curves show the influence range of geocell reinforcement, and demonstrate that a rubber content of 20% for reinforced specimen may be an optimal value from the perspective of the stability of dynamic properties. Additionally, the quantitative analysis of the effect of geocell reinforcement on the mechanical behavior of RSM can provide a reference for subsequent theoretical research and engineering applications.

Cyclic porewater pressure generation in intact silty soils

The results of cyclic strain-controlled, constant volume direct simple shear (CDSS) tests and field shaking tests have been evaluated for intact, natural, low-plastic silts from six different fine-grained soils with 54%–100% fines content, 47%–83% silt content, and plasticity indices (PI) ranging from nonplastic to 16. These tests constitute a subset of a larger archive of CDSS tests performed on silt deposits from the Pacific Northwest, British Columbia, and Alaska collected and analyzed by the co-authors. The cyclic data are presented in this paper for two objectives: (a) to characterize cyclically-induced excess pore pressure generation in intermediate soils with various soil index properties and stress histories, and (b) to provide calibrated Vucetic and Dobry model parameters for simulating excess pore pressure generation in the silt soils based on the data and trends presented in the first objective. The CDSS test results showed that excess pore pressure ratios decrease with PI over the narrow range of PI evaluated and decrease with overconsolidation ratio. The cyclic threshold shear strain amplitude for pore pressure generation extracted from field shaking tests on silts were within the range proposed in the literature, confirming that the cyclic threshold shear strain amplitude is a fundamental soil property. Calibrated Vucetic and Dobry model parameters for these intermediate, fine-grained silts were significantly different than those reported for sands in the literature and were heavily influenced by the overconsolidation ratio. The calibrated parameters obtained in this study can be used as a benchmark in selecting model parameters for silts.

Effect of anisotropic consolidation and rubber content on dynamic parameters of granulated rubber-sand mixtures

To investigate the shear modulus and damping ratio of granulated rubber-sand mixtures, cyclic triaxial tests were conducted on specimens prepared with different granulated rubber content (by weight) and consolidated under different consolidation ratios. The specimens were then sheared under two cyclic shear strain amplitudes of 0.002 and 0.004 up to 300 cycles. The results show that adding granulated rubber has decreased shear modulus (G) and increased damping ratio (D) under both shear strain amplitudes, but rubber has been helpful in reducing the degradation rate of the shear modulus irrespective of the initial consolidation state. Overall, anisotropic consolidation has had little effects on the variations of shear modulus and damping ratio of granulated rubber-sand mixture (GRSM) compared to clean sand. The sand-rubber mixtures have become more isotropic by increasing the rubber percentage even under anisotropic consolidation. The point that the granulated rubber has significantly contributed to reducing the degradation potential of G with number of cycles makes it attractive in executing backfills and earth structures using rubber-sand mixtures in seismically active zones. The results of this study are also promising in efficient application of granulated rubber-sand mixtures as an isolation system under the foundation of buildings.

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.

Liquefaction and post-liquefaction of granular material under multi-directional cyclic loading

Soil liquefaction can be induced by natural events that entail complicated loading directions and magnitudes. To investigate the liquefaction behaviour of granular material under complex loading conditions, a series of strain-controlled cyclic simple shear tests are conducted on the uniform-sized glass beads. These tests include uni-directional and multi-directional loading paths. An energy-based method is used to assist the understanding of the cyclic behaviour of the specimens. After the first liquefaction happens, the specimens are re-consolidated and subjected to monotonic undrained shearing to investigate their post-liquefaction behaviour. The test results indicate that the specimens subjected to multi-directional cyclic shearing are more prone to liquefy than those under uni-directional loading. Furthermore, the cyclic shear strain amplitude and cyclic loading path have significant influences on the soil liquefaction resistance, re-consolidation volumetric strain and post-liquefaction shear strength. Nevertheless, the total energy that is dissipated for liquefying a specimen is only dependent on its relative density.

Methods for estimating the post-cyclic settlement of Hormuz Island calcareous sand: an experimental study

The surficial settlement due to the dissipation of excess pore water pressure after a cyclic loading, such as an earthquake, is important in structures located on soil materials. Many efforts have been made to calculate the post-cyclic settlement of siliceous soils. This study focused on different methods for estimating the post-cyclic volumetric strain of Hormuz Island soil as a marine calcareous soil. Calcareous soils cover about 40% of the ocean surface and are located in tropical and subtropical regions. The calcareous specimens were prepared in different relative densities and consolidated under an effective confining pressure of 150 kPa. Cyclic loading under stress-controlled and undrained conditions was applied to the samples using a hollow cylindrical torsional shear apparatus. The tests were terminated at different excess pore water pressure ratios and were then drained. The results showed that the physical properties of soil grains play a key role in mechanical behavior of this deposit. Estimation methods for calculating the post-cyclic volumetric settlement of Hormuz Island sand were introduced using the excess pore water pressure ratio, the maximum cyclic shear strain amplitude, the dissipated energy, the standard penetration number, the cone penetration resistance, the shear wave velocity and the liquefaction safety factor.

Assessment of Dynamic Response of Cohesionless Soil Using Strain-Controlled and Stress-Controlled Cyclic Triaxial Tests

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.

Application of Taguchi Method for Optimization of Various Factors in Improving the Shear Modulus of Enzyme Treated Soil

In this study, the effect of dosage of enzyme (50 to 400 ml/m3), curing period (7 to 28 days) and cyclic triaxial loading test parameters such as confining pressure (50 to 200 kPa), loading frequency (0.25 to 1 Hz) and loading rate (0.3 to 0.9%) on the shear modulus of enzyme stabilized soil is investigated. Taguchi method has been applied to the cyclic triaxial tests, and L16 orthogonal array with five factors and four levels was selected. Analysis of variance was carried out to study the significant factors affecting the response. Among the selected factors considered for the study, curing period is found to be the most effective parameter on the shear modulus of the enzyme treated soil. With the increase in dosage of the stabilizer, there is a significant improvement in the shear modulus of the treated soil. The increase in shear strain amplitude and loading frequency decreases the shear modulus. The higher value of shear modulus was obtained for the specimen with dosage of enzyme 400 ml/m3 after a curing period of 28 days under a confining pressure of 200 kPa, loading frequency of 0.25 Hz and cyclic shear strain amplitude of 0.3%.

Effect of the soil–pile–structure interaction in seismic analysis: case of liquefiable soils

The design of earthquake-resistant structures depends greatly on the soil–foundation–structure interaction. This interaction is more complex in the presence of liquefiable soils. Pile and rigid inclusion systems represent a useful practice to support structures in the presence of liquefiable soils in seismic zones. Both systems increase the bearing capacity of soil and allow reducing the settlements in the structure. Numerical models with a 3-storey reinforced concrete frame founded on inclusions systems (soil–inclusion–platform–structure) and pile systems (soil–pile–structure) were analyzed. Finite difference numerical models were developed using Flac 3D. Two different soil profiles were considered. A simple constitutive model for liquefaction analysis that relates the volumetric strain increment to the cyclic shear strain amplitude was utilized to represent the behavior of the sand, and the linear elastic perfectly plastic constitutive model with a Mohr–Coulomb failure criterion was used to represent the behavior of the earth platform. Two earthquakes were used to study the influence of the different frequency of excitation in the systems. The results were presented in terms of maximum shear forces distribution in the superstructure and spectrum response of each system. The efforts and displacements in the rigid elements (piles or rigid inclusions) were compared for the different systems. The bending and buckling failure modes of the pile were examined. The results show that the pile system, the soil profile and the frequency of excitation have a great influence on the magnitude and location of efforts and displacements in the rigid elements.

Shear Strength Degradation Behavior of Offshore Clay Under Cyclic Loading

Deformation characteristics of Malaysian offshore clay subjected to undrained cyclic constant-volume direct simple shear loading were investigated at different over-consolidation ratios and strain levels. Cyclic strain-controlled tests were undertaken with cyclic shear strain amplitudes ranging from 0.6% to 5%. As the number of cycles increased, it was observed that the cyclic stress amplitude reduced, indicating cyclic degradation, while the pore water pressure increased.

High Strain Dynamic Properties of Perfectly Dry and Saturated Cohesionless Soil

Behaviors of sandy soils under dry and saturated conditions significantly differ from each other, especially under cyclic loading conditions. This paper highlights the behavior of dry and saturated Brahmaputra sand (DBS and SBS) subjected to constant strain monotonic and cyclic triaxial tests. Monotonic tests were conducted on specimens prepared at 60% relative density at a constant deformation rate 1.2 mm/min and varying confining pressures (50, 100, and 150 kPa), while the cyclic tests were conducted with varying cyclic shear strain amplitudes (0.015–7%). Monotonic tests reveal a phase transformation for SBS from contractive to dilative, while DBS shows an ever dilative response. An progressive asymmetric hysteresis behavior was observed under higher cyclic strains, based on which a modified methodology is developed to evaluate the dynamic properties of soil. Beyond 1% shear strain, damping ratio for dry sand was found to follow an asymptotic trend, while the saturated sand exhibited a significant reduction in magnitude. Comparison of the present findings with the standard dynamic models exhibits the importance of conducting site-specific dynamic soil characterization.

Effect of organic content and frequency on degradation and pore pressure in marine organic soils

ABSTRACTThe effects of organic content and the frequency of cyclic shear straining on the cyclic degradation and the normalized pore water pressure in 27 fibrous marine organic soil specimens were investigated with the two-way cyclic strain-controlled dynamic triaxial testing system. The testing program included three cyclic shear strain amplitudes, γc = 0.25, 0.5, and 1%, three ranges of the organic contents, OC = 13.3–18.4%, 23.3–27.9%, and 36.9–45.3%, and three loading frequencies, f = 0.05, 0.25, and 1 Hz. The results clearly exhibit that the degradation parameter, t, which means the rate of the cyclic degradation with the number of loading cycles, N, decreases with the OC and increases with the f. At the γc = 0.25–1%, if the OC decreases from 40.8 to 13.3%, the degradation parameter t may increase by 82.9–221.1%. If f is increased 20 times, from 0.05 to 1 Hz, then t may increases by 34.7–117.9%. The cyclic pore water pressure normalized by the effective consolidation pressure, , increases with the OC and decreases with the f was also observed.

A model for multi-directional cyclic shear-induced pore water pressure and settlement on clays

An estimation method for earthquake-induced pore water pressure and the post-earthquake settlement of soft clay was developed by focusing on its Atterberg’s limits and the direction of cyclic shearing. To clarify the fundamental characteristics of clays with different Atterberg’s limits under multi-directional cyclic shear, normally consolidated specimens of Kaolinite clay, Tokyo bay clay and Kitakyushu clay were subjected to cyclic simple shear under the undrained condition with various cyclic shear directions and shear strain amplitudes, followed by the dissipation of cyclic shear-induced pore water pressure. The effects of undrained cyclic shear on the pore water pressure accumulation and post-cyclic settlement were observed, and relationships with Atterberg’s limits were then investigated. In conclusion, the pore water pressure accumulation and post-cyclic settlement induced by multi-directional cyclic shear increase considerably to a higher level compared with those generated by the uni-directional one and such a tendency is evident for clays with a wide range of Atterberg’s limits. Comparisons of the results indicate that the soil with higher plasticity index shows the lower pore water pressure accumulation and post-cyclic settlement, irrespective of number of strain cycles and shear strain amplitude. Based on these results, a model for earthquake-induced pore water pressure and post-earthquake settlement was developed by incorporating the Atterberg’s limits as a function of experimental constants and the practical applicability was confirmed.

Comparison and Correction of Modulus Reduction Models for Clays and Silts

AbstractPrediction models of normalized modulus reduction curves (G/Gmax) for clays and silts have been proposed by several researchers in the past decades. However, model uncertainties have been recognized in these studies. This study compares five prediction models of G/Gmax from previous studies, which use common predictor variables of cyclic shear strain amplitude, effective confining stress, and plasticity index. The relative differences between these models are described against these predictor variables. Then the model biases are evaluated through residual analyses using the modulus reduction database. Modulus reductions of G are also discussed by combining the prediction models of G/Gmax and Gmax to illustrate the importance of these combinations. Correlations among the residuals of ln(G) are calculated, and the correction factors of the G/Gmax model are presented conditioned on the Gmax and shear strength measurements.

Stress-Ratio-Based Interpretation of Modulus Reduction and Damping Curves

AbstractModulus reduction and damping values are commonly plotted against cyclic shear strain amplitude (γc), and the resulting curves are known to depend on mean effective stress (p′), plasticity characteristics, strain rate, and number of loading cycles. The dependence on p′ is potentially problematic for undrained effective stress analysis where excess pore pressure may develop during loading. This paper presents a new concept in which normalized modulus reduction (G/Gmax) and damping (D) values are plotted against stress ratio (η) rather than γc. Relations developed for sand, clay, and peat are found to be essentially pressure-independent when G/Gmax and D−Dmin are plotted versus η,whereas all three are pressure-dependent when plotted versus γc. This finding is potentially useful for undrained effective stress analysis where p′ may change during loading, and provides a new approach for interpreting laboratory tests in future development of G/Gmax and D curves.

Cyclic Behavior and Liquefaction Potential of Renusagar Pond Ash Reinforced with Geotextiles

AbstractIn 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.

Dynamic properties of polyurethane foam-sand mixtures using cyclic triaxial tests

Reducing the static and seismic earth pressures on geotechnical structures, such as retaining walls, bridges abutments and buried pipes, using compressible materials is a novel idea which has received increased consideration during recent years. Despite the high compressibility of injectable polyurethane (PU) foams, their performance as a compressible inclusion material has not yet been studied. This paper presents results from a series of cyclic triaxial tests to investigate the dynamic properties of PU foam and PU foam-sand mixtures at intermediate to large strains. Furthermore, the effect of various parameters including initial deviator stress, static confining stress and foam-sand mixing percentage, on damping ratio and shear modulus are identified. The laboratory test results indicated that in pure foam, the damping ratio attenuated in elastic strain amplitudes, which remained constant once the stress was increased to near the yield point. The results of the tests on the foam-sand mixture samples with various mixing ratios demonstrated that the variation in damping ratios is a function of foam mass. So that for specimens with 5% PU foam, after a relative decrease, the damping ratio increased in the cyclic shear strain amplitudes more than 0.03–0.05%. In addition, it was observed that the dynamic behavior of the mixture is significantly affected by the content of injected foam and also confining stresses (proportional to the depth of the treatment zone).

Strain-Controlled Cyclic Simple Shear Tests on Sand with Radial Strain Measurements

AbstractStrain-controlled cyclic simple-shear tests were performed on silica sand with radial strain measurements. The specimens were tested under a constant K0 condition and subjected to cyclic loading and postcyclic monotonic loading. Threshold cyclic shear strain, volumetric strain, secant shear modulus, and damping ratio are investigated. Generally, the volumetric strain behavior in this study agreed well with literature findings that were investigated using the conventional cyclic direct simple shear test (without radial constraints). Radial strain during monotonic simple shear (postcyclic loading) was found to be a good parameter in monitoring the onset of flow slide in cohesionless soil. The concept of threshold cyclic shear strain, γt, was adequately applied in assessing the specimen volume change. Dynamic engineering properties, including equivalent shear modulus and damping ratio, were also studied. The damping ratio was found to decrease when the cyclic shear strain amplitude was greater than 2...