Dilatational Stress Research Articles

Correlating Differences in the Surface Activity to Interface-Induced Particle Formation in Different Protein Modalities: IgG mAb Versus Fc-Fusion Protein.

The propensity of protein-based biologics to form protein particles during bioprocessing can be related to their interfacial properties. In this study, we compare the surface activity and interfacial film properties of two structurally different biologics, an IgG and Fc-fusion, in the absence and presence of interfacial dilatational stresses, and correlate these differences to their tendency to form interface-induced protein particles. Our results show that interface-induced particle formation is protein-dependent, with the Fc-fusion demonstrating greater interfacial stability. This observation can be correlated with faster adsorption kinetics of the Fc-fusion protein, and formation of a less incompressible film at the air-liquid interface. The addition of polysorbate 80 (PS80), commonly added to mitigate protein particle formation, led to a surfactant-dominant interface for quiescent conditions and coadsorption of protein and surfactant for the Fc-fusion when exposed to interfacial stress. On the other hand, for the IgG molecule, the surface always remained surfactant dominant. Image analysis demonstrated that PS80 was more effective in mitigating particle formation for the IgG than Fc-fusion. This suggests that a surfactant-dominant interface is necessary to prevent interface-induced protein particle formation. Further, while PS80 is effective in mitigating particle formation in the IgG formulation, it may not be the best choice for other protein modalities.

Understanding the impact of combined hydrodynamic shear and interfacial dilatational stress, on interface-mediated particle formation for monoclonal antibody formulations

During biomanufacturing, several unit operations expose solutions of biologics to multiple stresses, such as hydrodynamic shear forces due to fluid flow and interfacial dilatational stresses due to mechanical agitation or bubble collapse. When these stresses individually act on proteins adsorbed to interfaces, it results in an increase in protein particles in the bulk solution, a phenomenon referred to as interface-induced protein particle formation. However, an understanding of the dominant cause, when multiple stresses are acting simultaneously or sequentially, on interface-induced protein particle formation is limited. In this work, we established a unique set-up using a peristaltic pump and a Langmuir-Pockels trough to study the impact of hydrodynamic shear stress due to pumping and interfacial dilatational stress, on protein particle formation. Our experimental results together demonstrate that for protein solutions subjected to various combinations of stress (i.e., interfacial and hydrodynamic stress in different sequences), surface pressure values during adsorption and when subjected to compression/dilatational stresses, showed no change, suggesting that the interfacial properties of the protein film are not impacted by pumping. The concentration of protein particles is an order of magnitude higher when interfacial dilatational stress is applied at the air-liquid interface, compared to solutions that are only subjected to pumping. Furthermore, the order in which these stresses are applied, have a significant impact on the concentration of protein particles measured in the bulk solution. Together, these studies conclude that for biologics exposed to multiple stresses throughout bioprocessing and manufacturing, exposure to air-liquid interfacial dilatational stress is the predominant mechanism impacting protein particle formation at the interface and in the bulk solution.

Multi-doping effect on the martensitic transformation behavior of shape memory alloys

Incorporating various elements into host shape memory alloys (SMAs) has proven to be an effective strategy for optimizing their functional properties. However, modeling the complex multi-doping effect is challenging. In the present study, we introduced a phenomenological model based on Ginzburg–Landau theory, wherein each doping element is conceptualized as an internal dilatational stress. This internal stress is represented as a spatial Gaussian distribution characterized by two influential parameters: potency (h) and range (σ). The interaction between doping elements arises from the superposition of these stresses. Utilizing a time-dependent Ginzburg–Landau simulation based on our proposed model, diverse combinations of h and σ replicate the varied experimental outcomes associated with multi-doping effects. This model offers insight into the understanding of the doping impact on martensitic transformation and may contribute to the development of SMAs with tailored properties.

Complex function method considering rock strength for determining critical warning deformation of deep-buried complex cavern

Most existing deformation warning methods for the safety of surrounding rock rely on empirical index or complicated numerical simulation and are unable to accurately and quickly determine the critical warning deformation, so an accurate determination method of critical warning deformation based on rock strength was investigated by the complex function theory in this study. The complex function theory was used to demonstrate that the elastic deformation of surrounding rock at a point is linearly related to its circumferential stress. Based on this demonstration, the critical warning deformations for blue warning, yellow warning, and red alert can be theoretically determined according to the crack initiation stress, dilatancy stress, and uniaxial compressive strength of surrounding rock, respectively. In addition to these critical stresses, the cavern’s shape, the in-situ stress, the deformation properties, and the position of the surrounding rock were also considered in the determination. The accuracy of the proposed theoretical method was verified by a finite element simulation of an example tunnel. Subsequently, the method was applied to the underground powerhouse on the left bank of the Baihetan hydropower station. Compared with the on-site monitoring displacements of the surrounding rock, the resulting warning displacements could accurately indicate the safety status of all monitoring areas around the cavern after each layer of excavation. In addition, the resulting warning positions, warning times, and warning grades matched the on-site failures of the surrounding rock very well. Thus, the proposed method is highly reliable and can be used for real-time warning of underground engineering.

Study on the mesomechanical behavior and damage process of coal samples with hole defects under eccentric loading.

When using end shield shearer to recover end slope coal resources, the stability of the overlying rock slope of the end slope is controlled by leaving coal pillars. Due to the influence of the self weight of the overlying rock layer, the coal pillar will be subjected to eccentric loads, and the influence of eccentric loads needs to be considered in the design of the coal pillar size. With the help of PFC discrete element software, uniaxial compression tests were carried out on coal sample containing hole defects under different degrees of eccentric loads based on the calibration of micro mechanical parameters. The results show that the peak stress, cracking stress and dilatancy stress of coal sample decrease in a linear function law with the increase of load eccentricity coefficient. The evolution of the number of microscopic cracks during uniaxial compression under eccentric load can be divided into four stages: the calm stage before crack initiation I, the stable propagation stage II, the unstable propagation and penetration stage III, and the post failure stage IV. The distribution of macroscopic cracks is jointly influenced by the relative position of the loading area and the hole defect. When the hole defect is within the loading area, the hole plays a guiding role in the evolution of coal sample cracks, and the macroscopic crack runs through the edge of the loading area and the hole. When the hole defect is located outside the loading zone, the degree of eccentric load is large, weakening the guiding effect of the hole defect on the crack, and the macroscopic crack does not pass through the hole defect.

Vascular responses during handgrip exercise in healthy postmenopausal females and older males

Introduction: Aerobic exercise interventions improve peripheral endothelial function in healthy older males. However, this effect is not always observed in healthy postmenopausal females and possible mechanisms underlying this sex-related difference remain unknown. Greater vascular shear stress during acute exercise is a key stimulus mediating longer-term improvements in vascular function. It remains unknown if postmenopausal females display a reduced endothelial sensitivity to exercise-induced shear stress relative to males of similar age. Objective and hypothesis: The objective of this study is to test the hypothesis that healthy postmenopausal females exhibit a lower endothelial sensitivity to exercise-induced shear stress relative to males. Methods: Fourteen healthy postmenopausal females (67 ± 8 years) not under hormone replacement therapy and 9 males of similar age (65 ± 7 years) performed handgrip exercise for 4 minutes at 20%, 40%, 60%, and 80% of their maximal voluntary contraction. Each exercise bout was separated by a 10-min recovery period. Brachial artery diameter and blood velocity were continuously measured using high-resolution ultrasound and analyzed using edge-detection software. Endothelial sensitivity to shear rate was quantified as the slope of the linear regression between brachial artery dilation (% change from baseline) and shear stress and compared between groups with an independent t-test. Workload, vascular conductance, diameter dilation, and shear stress were analyzed with mixed-effects models. Results: Males exercised at greater workloads relative to females across all exercise bouts (M: 17 ± 11 vs. F: 9 ± 5 kg, p<0.01). Forearm vascular conductance was greater in males throughout each exercise intensity (M: 2.23 ± 1.70 vs. F: 1.03 ± 0.51 ml/min/mmHg, p=0.02). Despite these differences, arterial dilation (M: 5.32 ± 5.55 vs. F: 5.20 ± 4.80%, p=0.96) and shear stress (M: 142 ± 80 vs. F: 171 ± 86 s−1, p=0.27) did not differ between groups across exercise intensities. Endothelial sensitivity to exercise-induced shear stress did not differ between males (0.02 ± 0.05%/s−1) and females (0.03 ± 0.01%/s−1, p=0.67). Conclusion: These data suggest that a reduced endothelial sensitivity to exercise-induced shear stress may not explain why aerobic exercise interventions do not consistently improve peripheral endothelial function in healthy postmenopausal females. Montreal Heart Institute Foundation. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Experimental Study on Compression Failure of Type II Ballastless Track Slab Based on Optical Fiber Sensing

Ballastless track structures are widely employed in high-speed rail networks because of their superior safety and durability. Among the various types of ballastless track, the Type II slab is currently one of the most extensively used and mature technologies in practice. Over the course of its service life, the damage within the ballastless track structure gradually accumulates in response to increased external loads. Therefore, it is crucial to continuously monitor the health condition of the track structure. In this study, a quasi-distributed fiber optic sensing system is adopted to monitor the deformation capacity and force performance of a Type II ballastless track slab under vertical load. The investigation aims to analyze the damage mechanism of the track structure under vertical pressure by assessing the deformation differences among its different components. The findings reveal that the incorporation of vertical reinforcement can enhance the pressure bearing capacity of the cement asphalt mortar layer to a certain extent, subsequently affecting the stress dilation. The stress performance of the ballastless track slab can be effectively monitored using the quasi-distributed fiber optic sensing technology under pressure. The outcomes of this research offer valuable insights for controlling displacement and analyzing damage in ballastless railway systems subjected to compression.

Effect of aggregate sizes on dilation properties and stress−strain behavior of FRP-confined recycled aggregate concrete

Aggregate size plays a crucial role in determining the mesoscale uniformity and compactness of concrete, directly influencing its dilation characteristics. This dilation behavior, especially under axial load, has significant implications for the tri-axial stress conditions when the concrete undergoes passive confinement using Fiber-Reinforced Polymer (FRP). This study focuses on comprehensively investigating the stress−strain behavior and dilation properties of FRP-confined recycled aggregate concrete (RAC), with a specific emphasis on the effects of recycled aggregate (RA) sizes. A series of compression tests were conducted to examine the stress−strain response of FRP-confined RAC, shedding light on how the dilation properties are influenced by varying RA sizes. The results revealed notable differences in the physical properties (crushing index and water absorption ratio) of RA compared to natural aggregates, with these differences significantly impacting the unconfined concrete strength. Although, an increase in aggregate size demonstrated an improvement in FRP confinement efficiency, it did not bring about a change in the ultimate strength of FRP-confined concrete due to the interaction between the weakening of unconfined concrete strength and the increase in confinement efficiency. In addtion, the transition stress on the stress−strain curve proved highly dependent on both aggregate size and FRP confinement efficiency to RAC. Consequently, a new modified transition stress model, accounting for the effect of aggregate size and FRP confinement, was introduced. Incorporating this newly proposed transition stress model into the existing stress−strain expression yielded predicted stress−strain curves that closely matched the experimental results for FRP-confined RAC with varying RA sizes.

Numerical study of effective parameters on true triaxial test results in rigid type apparatus

Operational parameters in true triaxial loading devices (TTA), such as the loading rod dimensions, friction between the loading platens and sample faces, loading gap, and one-side loading may affect the test results. Knowledge of the effect of each parameter is very important to correctly interpret rock behavior and to optimize these devices. Employing the Flac3D finite difference software, a rigid type true triaxial systemdesigned and builtat Amirkabir University of Iran (AUT-TTA) was simulated andinvestigated in this study. The results indicate that increasing the ratio of the rod cross-section to the loading platen area leads to an increase in the sample confinement, so, more uniform stress distribution occurs in the rock sample. The loading gap reduces strength of the rock specimen and leads to concentration of tensile stresses at the sample edges. The end effect leads to an increase in the stress level and a pseudo-hardening behavior in the samples. Also, the end effect is intensified under one-side loading condition compared to two-side loading. Comparison between results of AUT-TTA numerical simulation and analytical analysis (ideal conditions without considering operational parameters) indicates that the slope of the stress–strain diagram has low sensitivity to operational parameters. The most important operational factor affecting the stress level and dilatation stress is the end effect and other operational parameters have little effect. All parameters lead to an increase in the dilation strain. The clear edge and one-sided loading under low intermediate principal stresses and the end effect under high intermediate principal stresses have the greatest effect on the dilation strain.

Administration of USP7 inhibitor p22077 alleviates Angiotensin II (Ang II)-induced atrial fibrillation in Mice.

Atrial fibrillation (AF), the most common cardiac arrhythmia, is an important contributor to mortality and morbidity. Ubquitin-specific protease 7 (USP7), one of the most abundant ubiquitin-specific proteases (USP), participated in many cellular events, such as cell proliferation, apoptosis, and tumourigenesis. However, its role in AF remains unknown. Here, the mice were treated with Ang II infusion to induce the AF model. Echocardiography was used to measure the atrial diameter. Electrical stimulation was programmed to measure the induction and duration of AF. The changes in atrial remodeling were measured using routine histologic analysis. Here, a significant increase in USP7 expression was observed in Ang II-stimulated atrial cardiomyocytes and atrial tissues, as well as in atrial tissues from patients with AF. The administration of p22077, the inhibitor of USP7, attenuated Ang II-induced inducibility and duration of AF, atrial dilatation, connexin dysfunction, atrial fibrosis, atrial inflammation, and atrial oxidase stress, and then inhibited the progression of AF. Mechanistically, the administration of p22077 alleviated Ang II-induced activation of TGF-β/Smad2, NF-κB/NLRP3, NADPH oxidases (NOX2 and NOX4) signals, the up-regulation of CX43, ox-CaMKII, CaMKII, Kir2.1, and down-regulation of SERCA2a. Together, this study, for the first time, suggests that USP7 is a critical driver of AF and revealing USP7 may present a new target for atrial fibrillation therapeutic strategies.

Mechanical properties under triaxial compression of coal gangue-fly ash cemented backfill after cured at different temperatures

The triaxial mechanical properties of cemented backfill are the key indicators that affect the stability of cemented backfill in underground mining areas, and the high temperature environment in mines has become one of the main factors affecting the mechanical properties of cemented backfill. Understanding the triaxial mechanical properties of cemented backfill in high temperature environments is crucial for the stability of cemented backfill in mining areas. To investigate the effect of temperature on the mechanical characteristics of cemented backfill under triaxial compression, triaxial compression experiments were done on coal gangue-fly ash cemented backfill that had been cured at three temperatures (20 °C, 35 °C, and 50 °C). The deviatoric stress-strain curve of cemented backfill under triaxial compression was produced, its deformation parameters, dilatancy, and failure characteristics were investigated, and a more appropriate strength criteria was proposed. The research results indicate that, peak strength and dilatancy stress of cemented backfill under the same confining pressure decrease first and then increase as the curing temperature increases. The failure patterns of cemented backfill under triaxial compression will exhibit layered splitting failure except tension and shear failure since the curing temperature has increased. By comparing it with several other criteria, the Mogi-Coulomb strength criteria was found to be a good reflection of the failure strength properties of cemented backfill cured at different temperatures under triaxial compression. With curing temperature rises, internal friction angle of cemented backfill steadily lowers, while the cohesion first decreases and subsequently increases. The alteration in cohesion is consistent with the peak strength change rule, illustrating that the primary factor influencing peak strength of cemented backfill is cohesion. This study provides a good theoretical reference value for guiding the design of deep mine filling and optimizing the mixture ratio of cemented backfill.

Mechanism of the post-suffusion mechanical response of gap-graded soils from the perspective of force-chain evolution

The discrete element method (DEM) coupled with the pore-scale finite volume (PFV) method was used to simulate the suffusion and post-suffusion behavior of gap-graded soil with different initial fines content (fc). A series of drained triaxial tests were performed on the non-eroded, eroded and reconstituted samples. The results indicate that the erosion ratio (Er) increases as the fc of the sample increases. The mechanical response of the sample with an initial fc of 15 % is almost unaffected by suffusion. The dilatancy and peak deviatoric stress ratios of sample with initial fc of 25 % and 35 % are significantly lower with increasing erosion ratio. When the Er is greater than 8.2, eroded samples with an initial fc of 35 % collapse during shearing, and the eroded and reconstituted samples behave as dilation and contraction, respectively. As the initial fc increases, the mechanical response of the reconstituted samples differs more and more from that of the corresponding eroded samples. The force chain analysis indicates more force chains in the eroded sample than in the reconstituted sample, resulting in higher dilatancy of the eroded sample with fc of 25 % and 35 % during shearing.

Patients with Chronic Coronary Syndrome Can Benefit from Consumption of Enriched Chicken Eggs: The Effects on Microvascular Function, Inflammatory Biomarkers, and Oxidative Status—Randomized Clinical Study

The aim of this clinical study was to determine the impact of the consumption of chicken eggs enriched with n-3 polyunsaturated fatty acids, selenium, vitamin E, and lutein on micro- and macrovascular endothelium-dependent dilation, inflammation biomarkers, and oxidative stress levels in participants with chronic coronary syndrome (CCS). This was a double-blind, placebo-controlled clinical study that included 30 CCS participants (9 women, 21 men) randomized into the control group (N = 15), who ate ordinary chicken eggs (three per day), and the Nutri4 group (N = 15), who ate enriched eggs (three per day) for 21 days. Microvascular and macrovascular endothelium-dependent vasodilation was evaluated by measuring forearm skin post-occlusive reactive hyperemia (PORH) and acetylcholine-induced dilation (AChID) and the flow-mediated dilation (FMD) of the brachial artery, respectively. The serum lipid profile, anti- and proinflammatory cytokine levels, serum concentration of nitric oxide synthase (NOS) isoforms, and oxidative stress biomarkers were measured before and after the diet protocols. Enriched, but not regular, chicken eggs significantly improved microvascular PORH and AChID and macrovascular FMD, increased the serum concentration of inducible NOS, decreased serum triglyceride levels, and decreased proinflammatory cytokine IL-17A and TGF-1β levels compared to initial measurements. Patients with CCS can benefit from the consumption of enriched chicken eggs due to improved lipid biomarkers, a more favorable anti-inflammatory milieu, and improved vascular relaxation at micro- and macrovascular levels.

Secondary Bubble Entrainment via Primary Bubble Bursting at a Viscoelastic Surface.

Bubble bursting at liquid surfaces is ubiquitous and plays a key role for the mass transfer across interfaces, impacting global climate and human health. Here, we document an unexpected phenomenon that when a bubble bursts at a viscoelastic surface of a bovine serum albumin solution, a secondary (daughter) bubble is entrapped with no subsequent jet drop ejection, contrary to the counterpart experimentally observed at a Newtonian surface. We show that the strong surface dilatational elastic stress from the viscoelastic surface retards the cavity collapse and efficiently damps out the precursor waves, thus facilitating the dominant wave focusing above the cavity nadir. The onset of daughter bubble entrainment is well predicted by an interfacial elastocapillary number comparing the effects of surface dilatational elasticity and surface tension. Our Letter highlights the important role of surface rheology on free surface flows and may find important implications in bubble dynamics with a contaminated interface exhibiting complex surface rheology.

Experimental Study on the Dilatancy and Energy Evolution Behaviors of Red-Bed Rocks under Unloading Conditions.

Surrounding rock deformation and consequent support failure are the most prominent issues in red-bed rock tunnel engineering and are mainly caused by the effects of unloading, rheology, and swelling. This study investigated the mechanical responses of two kinds of red-bed mudstone and sandstone under unloading conditions via laboratory observation. Volume dilation was observed on the rocks during unloading, and the dilatancy stress was linear with the initial confining pressure. However, the ratios of dilatancy stress to peak stress of the two rocks kept at a range from 0.8 to 0.9, regardless of confining pressures. Both the elastic strain energy and the dissipated energy evolved synchronously with the stress-strain curve and exhibited conspicuous confining pressure dependence. Special attention was paid to the evolution behavior of the dilatancy angle. The dilatancy angle changed linearly during unloading. When the confining pressure was 10 MPa, the dilatancy angle of mudstone decreased from 26.8° to 12.5° whereas the dilatancy angle of sandstone increased from 34.6° to 51.1°; when the confining pressure rose to 25 MPa, the dilatancy angle of mudstone and sandstone decreased from 45.8° to 17.4° and increased from 21.7° to 39.5°, respectively. To further understand the evolution of the dilatancy angle, we discussed the links between the variable dilatancy angle and the processes of rock deformation and energy dissipation.

Significance of dynamic thickness changes and compression effects of commercial lithium-ion spring-braced cells

Lithium-ion battery (LIB) cells undergo thickness changes during cycling that can be reversible and irreversible. According to the literature, cell compression can prevent various defects, such as volume-change-induced contact losses. Moreover, densely packed cells represent the battery electric vehicle (BEV) use case, where volumetric energy density can still be optimized. In this study, a uniaxial compression test bench is developed to evaluate the dynamic dilation behavior and stress susceptibility of commercial LIB pouch cells. Using a spring-compression approach, the active material can expand and contract under moderate normal stress variations while keeping the inner cell layers in permanent contact. After applying stress to the cell, the cycling behavior and thickness changes are monitored under the variation of several parameters. A rig-integrated force measurement mat is used to monitor stress distribution, providing additional insight. Our results show that varying the charging rate leads to significant differences in the thickness change of a mildly compressed cell. In this particular case, both reversible and irreversible dilation fractions are present and electro-mechanical effects were identified. As a result, gained insights can serve battery system manufacturers with information to optimize their battery pack regarding operating efficiency, sustainability and mechanical safety.

Numerical simulations on shear behaviour of rock joint network under constant normal stiffness conditions.

In this study, the numerical direct shear tests were conducted to investigate the shear mechanical properties of joint networks under constant normal stiffness (CNS) boundary conditions. The influence of random joint number on shear stress (τ), dilation (normal displacement, δv) and normal stress (σn) of rock mass were studied quantitatively with fixed main slip surface. At the same time, the internal stress evolution process and failure process were analyzed. The results reveal that the number of random joints (γ) has little effect on the shear and normal stresses. The normal displacement of the sample generally decreases as the number of random joints increases. In addition, the normal displacement of the specimen is absorbed by the random joints when the number of random joints in the specimen increases to a certain level: when γ is greater than 6 and the shear displacement (μ) reaching 10 mm, the specimen exhibits shear contraction. Therefore, the internal random joints mainly control the failure mode and dilatancy performance of the specimen, while the main joint of the rock controls the shear stress of the specimen.

Comparison of Protein Particle Formation in IgG1 mAbs Formulated with PS20 Vs. PS80 When Subjected to Interfacial Dilatational Stress.

Polysorbates (PS) are nonionic surfactants that are commonly included in protein formulations to mitigate the formation of interfacial stress-induced protein particles and thus increase their long-term storage stability. Nonetheless, factors that dictate the efficiency of different polysorbates in mitigating protein particle formation, especially during the application of interfacial stresses, are often ill defined. Here, we used a Langmuir trough to determine the surface activity of two IgG1 monoclonal antibodies formulated with two different polysorbates (PS20 and PS80) when subjected to interfacial dilatational stress. Interfacial properties of these formulations were then correlated with characterization of subvisible protein particles measured by micro-flow imaging (MFI). Both mAbs, when formulated in PS20, demonstrate faster adsorption kinetics and higher surface activity compared to PS80 or surfactant-free formulations. Compression/expansion results suggest that when exposed to interfacial dilatational stresses, both mAb/PS20 formulations display interfacial properties of PS20 alone. In contrast, interfacial properties of both mAb/PS80 formulations suggest mAbs and PS80 are co-adsorbed to the air-water interface. Further, MFI analysis of the interface and the bulk solution confirms that PS20 is more effective than PS80 at mitigating the formation of larger particles in the bulk solution in both mAbs. Concomitantly, the efficiency of PS to prevent interface-induced protein particle formation also depended on the protein's inherent tendency to aggregate at a surfactant-free interface. Together, the studies presented here highlight the importance of determining the interfacial properties of mAbs, surfactants, and their combinations to make informed formulation decisions about the choice of surfactant.

Understanding the static rate dependence of early fracture behavior of cemented paste backfill using digital image correlation and acoustic emission techniques

In mining engineering practice, cemented paste backfill (CPB) are subjected to loads at different static rates, so it is crucial to clarify the mechanical evolution mechanism of CPBs at different static rates. This work aims to understand the early fracture evolution mechanism of the CPB at static rates. First, the CPB with different static rates were monitored in real-time using acoustic emission (AE) and digital image correlation (DIC) techniques, and the effects of static rates on the CPB compressive strength as well as failure characteristics were analyzed; then, the intrinsic relationship between AE rise time/amplitude (RA) and average frequency (AF) was used to classify the crack types, and AE b-values and RA fractal dimensions were discussed for the crack evolution of the scale; finally, the strain field, displacement field, and dilation characteristics of the CPB were investigated. The results show that the increase in static rate increases the compressive strength of the CPB increase first and then decreases, and there is a critical loading rate effect. The final failure form of the specimen is transformed from tensile failure to tensile-shear composite failure with the increase of static rate. In addition, the growth of the loading rate will inhibit the formation of tensile cracks and promote the development and expansion of shear cracks. The trend of the AE b-value and the RA fractal dimension have a synergistic feature, which can be used as a sudden drop before and after the peak intensity as the failure precursor information of the CPB. The increased static rate will make the CPB reach the dilatancy state in advance, and the changing pattern of dilatancy stress synergizes with the peak strength. The study results provide a theoretical basis for evaluating the structural safety of the CPB.

A State-Dependent Hypoplastic Bounding Surface Model for Gassy Sand

As a kind of partially saturated soil often containing dissolved gas with a high degree of saturation (S > 85%), gassy sand sediment widely exists in the marine environment all over the world. Due to the effect of gas dissolution and exsolution on the pore fluid compressibility, its stress–strain and pore pressure responses are quite different from those of common saturated and unsaturated soils when subjected to undrained loading. Since almost all the gas bubbles are occluded in the pore water of offshore gassy sand, the matric suction may be neglected, and an undrained constitutive model for gassy sand is developed based on the existing hypoplastic bounding surface model for saturated sand. Both Boyle’s and Henry’s laws are employed in the model to characterize the equilibrium behavior of the gas compressibility and solubility, and then the equivalent compressibility coefficient of the pore fluid is obtained. To avoid unrealistic volumetric expansion, the concepts of the critical state and state-dependent dilatancy stress ratio are incorporated to describe its ultimate shear strength and dilatancy characteristics, respectively. Finally, the triaxial undrained test results on gas-charged sand from Hangzhou Bay are analyzed at three initial saturation degrees of 85%, 90%, and 100%, and two effective confining pressures of 50 kPa and 200 kPa. Moreover, carbon dioxide (CO2) was selected in the test, and the samples were loose with a relative density of 30%. It is noted that a good agreement is achieved between the simulation results and the experimental data, including the influence of gas content and confining pressure on the shear dilatancy and the mean effective stress increase at the beginning of the effective stress path, among others.