Cyclic Shear Research Articles

Evolution of Reversible and Irreversible Deformations of Compact Sandstone Under Different Modes of Triaxial Loading

Abstract Uniaxial or standard triaxial tests, which are the most frequently used in geotechnical practice, do not always simulate in-situ conditions of rocks well. Therefore, the deformations of rocks are now investigated even along alternative loading paths in the stress space. However, these alternatives are mainly used to study the conditions of the ultimate failure of rocks. Their deformational behavior along the alternative paths in the anticipated quasi-elastic stress region and corresponding stiffness moduli are rarely analyzed. Our recent study of the Brenna sandstone therefore compared deformational responses to monotonic loading along selected alternative paths in this stress region. The present new study aimed to evaluate the role of irreversible processes in deformation behavior under the different triaxial loading modes. The experimental methods included the following tests: cyclic isotropic compression, cyclic triaxial pure shear, and cyclic conventional triaxial compression. Irreversible deformation processes representing gradual breakage of rock were confirmed throughout the hypothetical quasi-elastic region. These processes, which may include damage to inter-grain connections or permanent displacements at grain contacts in cracks, are dependent on the stress path. The results also indicate a slight material anisotropy associated with stratification. The reversible and irreversible strains along several alternative triaxial stress paths were estimated. The study’s results are significant for predicting the deformation response of sedimentary rocks to in situ stress. Identification of the extent of the irreversible processes is crucial for understanding the mechanical behavior of these rocks during different time evolutions of in-situ stress or conditions of repeated loading/unloading.

Investigation of morphological features and mechanical behavior of jointed limestone subjected to wet-dry cycles and cyclic shear in drawdown areas of the Three Gorges Reservoir

Investigation of morphological features and mechanical behavior of jointed limestone subjected to wet-dry cycles and cyclic shear in drawdown areas of the Three Gorges Reservoir

Cyclic Simple Shear Response of Coral Sand under the Dual Effects of Isotropic Confinement and Normal Stress

Cyclic Simple Shear Response of Coral Sand under the Dual Effects of Isotropic Confinement and Normal Stress

Analysis of Cyclic Shear Characteristics of Coarse-Grained Soil Reinforced with Geogrids

Analysis of Cyclic Shear Characteristics of Coarse-Grained Soil Reinforced with Geogrids

Experimental Study on Strength Characteristics of Overconsolidated Gassy Clay

Gassy clay, commonly encountered in coastal areas as overconsolidated deposits, demonstrates distinct mechanical properties posing risks for submarine geohazards and engineering stability. Consolidated undrained triaxial tests combined with cyclic simple shear tests were performed on specimens with varying overconsolidation ratios (OCRs) and initial pore pressures, supplemented by SEM microstructural analysis. Triaxial results indicate that OCR controls the transitions between shear contraction and dilatancy, which govern both stress–strain responses and excess pore pressure development. Higher OCR with lower initial pore pressure increases stress path slope, raises undrained shear strength (su), reduces pore pressure generation, and induces negative pore pressure at elevated OCR. These effects originate from compressed gas bubbles and limited bubble flooding under overconsolidation, intensifying dilatancy during shear. Cyclic tests reveal gassy clay’s superior cyclic strength, slower pore pressure accumulation, reduced stiffness softening, and enhanced deformation resistance relative to saturated soils. Cyclic pore pressure amplitude increases with OCR, while peak cyclic strength and anti-softening capacity occur at OCR = 2, implying gas bubble interactions.

Analysis of Energy Piles Under Cyclic Axial Loads and Impact of Loading Amplitudes

This paper presents a study on model tests of single energy piles subjected to cyclic axial loads in sand and the development and validation of a 3D thermo-mechanical finite element model. The model accurately simulated the behavior of the pile-soil interface under cyclic shear loads. A subsequent parametric analysis examined the effects of the number of loading cycles and the loading amplitude on the vertical dynamic response characteristics of energy piles. The results showed that under heating conditions, the maximum variation in compressive thermal stress in the energy pile gradually decreased, with its location shifting upward along the pile shaft. A critical cyclic amplitude ratio was identified: below this threshold, the rate of increase in pile tip resistance continuously increased while the average pile side resistance weakened progressively. The presence of a static load accelerated the weakening of the average pile side resistance to some extent. As the number of loading cycles increased, the settlement rate of the energy pile gradually degraded. The cumulative settlement rate at the pile top increased with the cyclic amplitude ratio, peaking before slightly declining. In comparison, the static load ratio had a relatively minor influence on cumulative settlement.

Characteristics of the Damping Ratio of Undisturbed Offshore Silty Clay in Eastern Guangdong, China

Soil–pile interaction damping plays a crucial role in reducing wind turbine loads and fatigue damage in monopile foundations, thus aiding in the optimized design of offshore wind structures and lowering construction and installation costs. Investigating the damping properties at the element level is essential for studying monopole–soil damping. Given the widespread distribution of silty clay in China’s seas, it is vital to conduct targeted studies on its damping characteristics. The damping ratio across the entire strain range is measured using a combination of resonant column and cyclic simple shear tests, with the results compared to predictions from widely used empirical models. The results indicate that the damping ratio–strain curve for silty clay remains “S”-shaped, with similar properties observed between overconsolidated and normally consolidated silty clay. While empirical models accurately predict the damping ratio at low strain levels, they tend to overestimate it at medium-to-high strain levels. This discrepancy should be considered when using empirical models in the absence of experimental data for engineering applications. The results in this study are significant for offshore wind earthquake engineering and structural optimization.

Simulation study on the response characteristics of rock joints to cyclic shear load under constant normal stiffness boundary

Under cyclic loading, rock joints underwent continuous slipping and closure, resulting in fatigue damage to the joints and thereby affecting the stability of rock engineering projects. To investigate the fatigue shear characteristics of joints under cyclic stress, numerical simulations of rough joints under cyclic shear stress, involving variations in normal stiffness, loading amplitudes, and loading frequencies, were performed using a cyclic shear loading method based on the FISH language. The results indicated that there was a hysteretic effect in the shear stress–shear displacement curves of joints. During cyclic shear stress, the shear velocity of the joint fluctuated from positive to negative, with the maximum shear velocity changing by approximately 10 times, increasing from 0.012 × 10–2 to 0.15 × 10–2 mm/s before and after joint instability. As normal stiffness increased to the same shear displacement, more cracks developed in the joint. When the normal stiffness exceeded 3 GPa/m, a conspicuous failure zone was evident. Loading amplitude showed an inverse proportionality to the number of cycles required to achieve the target shear displacement. Loading frequency exhibited a linear proportionality to the number of cycles needed to reach the target shear displacement The fatigue damage degree of joints during cyclic shear could be represented by two indices: the Felicity ratio (FR) and the damage variable (D). Under different conditions, the critical D value ranged from 0.037 to 0.097, while the corresponding critical FR value varied between 0.700 and 0.822, reflecting the impact of normal stiffness, amplitude, and frequency on joint fatigue failure.

Cyclic behavior of glulam connections with inclined self-tapping screws

ABSTRACT Glued laminated timber (glulam) structures are attracting increased attention in seismic applications due to their sustainability and high strength-to-weight ratio. This study investigates the cyclic and static shear performance of glulam joints connected with inclined self-tapping screws (STS), aiming to identify optimal connection configurations for improved seismic resilience. Four types of inclined STS configurations were experimentally assessed under low-cycle repeated loading, simulating seismic stress conditions. Key mechanical properties such as energy dissipation, stiffness, ductility, and load-bearing capacity were analyzed in detail. Results show that under cyclic loading, all joint configurations exhibited stable hysteretic behavior. The ordinary screw joint with shear loading (OSJ-S) demonstrated the highest energy dissipation during the initial loading cycles, while the inclined screw joint under compression-shear loading (ISJ-C) exhibited superior energy retention at the yield stage. The inclined screw joint under tension-shear loading (ISJ-T) and the inclined screw joint under X-shear loading (ISJ-X) effectively mitigated stiffness degradation over multiple cycles, improving joint stability. Additionally, inclined screws – particularly at a 45° angle – significantly enhanced initial joint stiffness, with the highest stiffness observed in tension-shear connections. This study provides critical insights into the mechanical behavior of inclined STS in glulam joints, establishing a foundation for optimizing timber connection design in seismic applications.

Prediction of pore water pressure generation of liquefiable clean sands under cyclic shear loading through deep learning

ABSTRACT In this study, a novel data-driven approach is carried out to predict the pore pressure generation of liquefiable clean sands during cyclic loading. An extensive and comprehensive database of actual stress-controlled cyclic simple shear test results in terms of pore pressure time histories is gathered from a large number of experiments. While the classical machine learning (ML) algorithms help predict the number of liquefaction cycles in a few models, the desired level of accuracy in predicting the actual trend and robustness in pore pressure build-up is only achieved in deep learning (DL) methods. Results indicate that the Long-Short Term Memory (LSTM) working model, employed with Stacked LSTM and the Windowing data processing method, is necessary for making fairly good cyclic pore pressure build-up predictions. This study proposes a model that can ultimately be utilised to predict the pore pressure response of in-situ liquefiable sandy soil layers without resorting to plasticity-based complex theoretical models, which has been the current practice. The robustness achieved in the model reassures the reliability of the study, raising confidence in developing data-driven constitutive models for soils that have the potential to replace conventional plasticity-based theories.

Shear characteristics and damage mechanisms of the bolt–grout interface under cyclic shear loading

Shear characteristics and damage mechanisms of the bolt–grout interface under cyclic shear loading

Unified equivalent intergranular void ratio for biotreated binary soils in characterising liquefaction resistance

Both calcareous silt and calcium carbonate (CaCO3) precipitation crystals generated by microbially induced calcium carbonate precipitation (MICP) are fine-grained but exhibit distinct properties. The combined effect of these two components on the liquefaction resistance of biotreated binary soils is rarely reported. In this study, systematic undrained cyclic triaxial tests and bender element tests were conducted on reconstituted calcareous sand specimens, varying in two density parameters, four levels of fines content and three biotreatment levels. The results reveal that packing density, fines content and biotreatment levels significantly affect the cyclic behaviour, liquefaction resistance and shear wave velocity of biotreated soils. In addition, low-boundary curves were established to improve the accuracy of liquefaction assessments at sites with high shear wave velocity. Furthermore, the relative contributions of fines and calcium carbonate crystals were incorporated using the concept of the unified equivalent intergranular void ratio (EIVR). The utility of this approach in characterising the liquefaction resistance of biotreated binary soils was validated through the data from both this study and previous research. The new unified EIVR concept can be used to estimate the complex liquefaction resistance of cemented binary soils, which further enhances the theoretical framework for dynamic liquefaction of non-cemented or cemented sandy soils.

Anomalous Softness in Amorphous Matter in the Reversible Plastic Regime.

We study an elastoplastic model of an amorphous solid subject to athermal quasistatic cyclic shear strain. We focus on cycling amplitudes in the so-called reversible-plastic regime where, after a transient, the system locks into a hysteretic limit cycle and returns to the same microscopic configuration after one or more strain cycles. We show that the ground state energy of the terminal limit cycle decreases with increasing cycling amplitude. In analogy to an annealed alloy or an aged colloidal glass, one would expect the states with lower energy to be mechanically harder and to require larger stresses and strains to trigger microscopic rearrangements. However, we show the opposite result: the systems with lower energy cycled at higher strain amplitude are mechanically softer and begin to exhibit plastic rearrangements at smaller stresses and strains within the cycle. We explain this anomaly quantitatively in terms of Eshelby inclusion theory where an inclusion is subjected to a particular negative stress value after it undergoes a yielding event. These results point the way toward measurements to be conducted in experiments and particle-based computer simulations on cyclically sheared amorphous solids.

Discrete Element Modeling of Reliquefaction Behavior of Sand Under Undrained Cyclic Simple Shear Considering the Effects of Reconsolidation Degrees

Abstract Since the Niigata earthquake in 1964, a series of site surveys[4,5,13,14] have shown that sand liquefied during the mainshocks may reliquefy during the aftershocks. As there is an uncertain interval between the two consecutive earthquakes, the excess pore pressure built up during the mainshock dissipates partially or completely, which means the soil will be reconsolidated to different degrees prior to the aftershock. However, it has been reported that the damage of sand reliquefaction caused by aftershocks may exceed that caused by mainshocks[2,5,13,14] even if the sand was reconsolidated until the excess pore water pressure dissipated completely. To gain more micromechanical insights into the reliquefaction behaviors of sand, a series of discrete element simulations[1] of undrained cyclic simple shear tests were carried out on granular specimens[3,9] with different degrees of reconsolidation and liquefaction history.

Influence of Sand Fabric on Pore Water Pressure Build-Up

Abstract The sand fabric is created depending on the art of the grain deposition. A certain deposition method creates a specific type of soil fabric that can be linked to a particular soil density which, when related to the limit density states obtained from the standard index tests, can vary within a large range for different sands prepared by the same method. This paper aims to clarify the impact of varying the relative density in the case of one deposition method on the pore water pressure (PWP) accumulation in sands. A simplified cyclic shear test (PWP Tester) enabling a fast testing of the PWP accumulation during undrained cyclic shearing in granular soils is used for this purpose. The tested specimens are pluviated under water via a funnel and thus have a similar fabric. The results show a greatly comparable rate of PWP accumulation during undrained shearing, despite the fact that the relative densities following the same soil deposition vary greatly for different soils.

Do human brain white matter and brain stem structures show direction-dependent mechanical behavior?

Do human brain white matter and brain stem structures show direction-dependent mechanical behavior?

A DEM Investigation on the Effect of Gradation on the Liquefaction Response and Fabric Evolution of Soils

Abstract Assessment of liquefaction triggering potential is an important aspect in the design of critical infrastructure. This paper uses Discrete Element Modeling (DEM) simulations to explore the effect of gradation on the liquefaction triggering and deformation accumulation in coarse-grained soils. Cyclic direct simple shear (DSS) simulations indicate that the state parameter, as defined as the difference between the current and critical state void ratios at a the same mean effective stress (p’), is a more robust metric for relating the soil state to the liquefaction resistance of sands. At the same state parameter, more broadly graded soils have greater resistance to liquefaction and accumulate smaller post-liquefaction deformations. These trends are explained by the more broadly graded soils having more contacts per particle than the poorly-graded soils and developing greater anisotropy in the strong contact force network during shearing. This analysis sheds light on the effects of gradation on the micro and marco responses in sands, and how they relate to soil liquefaction.

Effect of static shear stress on cyclic behaviors of medium-dense sand under multi-directional cyclic simple shear loading

Effect of static shear stress on cyclic behaviors of medium-dense sand under multi-directional cyclic simple shear loading

Undrained cyclic and post-cyclic shear behaviour of sand with varying liquefaction degrees: insights from DEM

Undrained cyclic and post-cyclic shear behaviour of sand with varying liquefaction degrees: insights from DEM

Cyclic Resistance of Liquefiable Sand Improved by Biopolymer Soil Treatment

Abstract Various methodologies have been proposed in geotechnical engineering to address seismic liquefaction and mitigate earthquake-induced destruction. Cement, commonly used as a soil stabilizer, is applied through injection techniques to establish stable ground in numerous human endeavors. However, nowadays, biopolymer-based soil treatment (BPST) has emerged as a sustainable geotechnical engineering approach. This study investigates the enhancement of seismic resistance in loose sand prone to liquefaction through the application of polysaccharide biopolymers. Cyclic direct simple shear (CDSS) test was conducted to evaluate the effectiveness of BPST on liquefiable sand ground.