Pressure Generation Research Articles

Liquefaction behavior and shear strain-based pore pressure model of fiber reinforced calcareous sand

The generation mechanism of pore pressure plays an essential role in understanding the liquefaction behavior of sand under cyclic loading. Extensive undrained simple shear tests were undertaken to study the pore pressure and shear strain development characteristics of calcareous sand reinforced by fibers. The results show that the deformation patterns of the tested calcareous sand gradually shift from brittle to ductile failure as fiber content increases. The mechanism of pore pressure generation in calcareous sand subjected to cyclic loading is quite distinct from that of siliceous sand, exhibiting more pronounced accumulation in the initial stage of cyclic loading. Fiber reinforced calcareous sand exhibits reverse shear contraction behavior when liquefaction is imminent. A remarkable finding is the establishment of a unique correlation between pore pressure ratio and shear strain, irrespective of the fiber reinforcement. Consequently, a shear strain-based pore pressure generation model of reinforced calcareous sand is then developed to predict the pore pressure built-up trend under varying fiber content and length conditions. This model is also applicable to various testing conditions and soil types.

Dynamic Simulation of Rock‐Avalanche Fragmentation

AbstractFragmentation is a common phenomenon in complex rock‐avalanches. The fragmentation intensity and process determines exceptional spreading of such mass movements. However, studies focusing on the simulation of fragmentation are still limited and no operational dynamic simulation model of fragmentation has been proposed yet. By enhancing the mechanically controlled landslide deformation model (Pudasaini & Mergili, 2024, https://doi.org/10.1029/2023jf007466), we propose a novel, unified dynamic simulation method for rock‐avalanche fragmentation. The model includes three important aspects: mechanically controlled rock mass deformation, momentum loss while the rock mass fiercely impacts the ground, and the energy transfer during fragmentation resulting in the generation of dispersive lateral pressure. We reveal that the dynamic fragmentation, resulting from the overcoming of the tensile strength by the impact on the ground, leads to enhanced spreading, thinning, run‐out and hypermobility of rock‐avalanches. Thereby, the elastic strain energy release caused by fragmentation becomes an important process. Energy conversion between the front and rear parts caused by the fragmentation results in the enhanced forward movement of the front and hindered motion of the rear of the rock‐avalanche. The new model describes this by amplifying the lateral pressure gradient in the opposite direction: enhanced for the frontal particles and reduced for the rear particles after the fragmentation. The main principle is the switching between the compressional stress and the tensile stress, and therefore from the controlled deformation to substantial spreading of the frontal part in the flow direction while backward stretching of the rear part of the rock mass. Laboratory experiments and field events support our simulation results.

A Unified Model of Cyclic Shear–Volume Coupling and Excess Pore Water Pressure Generation for Sandy Soils under Various Cyclic Loading Patterns

A Unified Model of Cyclic Shear–Volume Coupling and Excess Pore Water Pressure Generation for Sandy Soils under Various Cyclic Loading Patterns

Ultrahigh Pressure Generation at High Temperatures in a Walker-Type Large-Volume Press and Multiple Applications

Ultrahigh pressure generation at high temperatures is technologically challenging for large sample volumes. In this study, we successfully generated pressures of 37.3–40.4 GPa at 1900–2100 K in a Walker-type large-volume press (LVP). Expansion of the pressure range at high temperatures was achieved by adapting newly designed ZK01F tungsten carbide (WC) anvils with tapered surfaces and using cell assemblies with an ∼1 mm3 sample volume and hard materials, as well as by applying certain adjustments to the apparatus. The pressure efficiencies of the different types of WC anvils and cell assemblies were also studied. Using the above-mentioned techniques, we successfully synthesized and characterized bulk samples of nearly pure sp3-hybridized ultrahard amorphous carbon, core–shell nanocrystals with high Néel temperatures, as well as large-sized single crystals of lower-mantle minerals. The developed LVP techniques presented here could enable the exploration of the chemical and physical properties of novel materials and Earth’s interior.

Tongue strength and swallowing-related masseter activity and oropharyngeal timing across the lifespan

Purpose: This study examined lifespan changes in maximum tongue strength, swallowing time, and masseter activity during swallowing. It provides normative data with which to compare clinical assessments of orofacial myofunctional disorders (OMD) and oropharyngeal dysphagia (OPD). Method: 409 healthy participants without identified OMD or OPD (ages 5 – 79 years) provided instrumental measures of tongue strength and electromyographic measurements for oropharyngeal transit time and masseter activity during swallows of four boluses. Participants were placed in three broad age groups (5 – 15, 16 – 59, 60 – 79) for crosssectional analysis. Results: Differences were found between age groups for tongue strength, such that the youngest group had significantly lower anterior tongue strength than the other groups, and lower posterior tongue strength than the 16 – 59 age group. Anterior tongue strength was significantly greater for males than females; posterior tongue strength did not differ significantly between the sexes. The youngest group had longer oropharyngeal transit times than either of the two older groups for most boluses. Swallowing transit time decreased in duration across the age groups, from youngest to oldest, for the 2.5 cc pudding bolus. Both right and left masseters differed in activation among tasks and age groups. The oldest age group had consistently greater levels of activation of the right masseter, and all groups had greater activation for the cracker bolus. Spearman rank-order correlations largely confirmed the inferential statistics and provided evidence of a relationship between tongue weakness and increased oropharyngeal transit time. Conclusion: Maximum tongue pressure generation and oropharyngeal timing measures support a developmental hypothesis, with lower tongue strength and longer swallowing transit times for children ages 5 through 15. The smaller pudding bolus provided the greatest differentiation among the age groups, which may prove to be a functional indicator for clinical evaluation. These results are largely consistent with existing data for tongue strength and oropharyngeal swallowing transit times.

Nonlinear seismic response analysis of liquefiable sites based on effective stress method

In this study, the one-dimensional nonlinear Matasovic model was extended to the two- and three- dimensional stress space by replacing the shear strain with the generalized shear strain. The extended Matasovic model was subsequently combined with Dobry’s excess pore water pressure generation model, and the reliability of the proposed loosely coupled effective stress analysis model was verified through undrained cyclic triaxial tests and a one-dimensional site response analysis. Finally, this method was applied to an engineering site in China to evaluate the nonlinear seismic response of liquefiable sites. The results show that the proposed effective stress analysis method can capture the dynamic behavior of the soil and the generation of pore water pressure during strong shaking. Moreover, there are differences between the proposed effective stress analysis method and the total stress analysis method for liquefiable sites, which indicates the need for careful selection in practical applications.

Influence of drainage conditions on piezocone penetration mechanism in offshore clays

ABSTRACT CPTu (piezocone penetration test) is widely used in engineering practice to determine various parameters of clays under partially drained conditions. However, most existing research is based on undrained or fully drained conditions for clays, leading to underestimation or overestimation of soil strength. By applying the Eulerian-Lagrangian large deformation finite element method to analyse the water-soil interaction, the CPTu driving mechanism in offshore saturated soft clays under different drainage conditions is revealed. An advanced hypoplastic constitutive model for clays is used to simulate the nonlinear behaviour of kaolin under different drainage conditions. The generation, accumulation, and dissipation of excess pore water pressure under different drainage conditions are analysed, as well as the influence of excess pore water pressure on cone tip resistance and the effective stress of the soil during the CPTu penetration process.

Plant infection by the necrotrophic fungus Botrytis requires actin-dependent generation of high invasive turgor pressure.

The devastating pathogen Botrytis cinerea infects a broad spectrum of host plants, causing great socio-economic losses. The necrotrophic fungus rapidly kills plant cells, nourishing their wall and cellular contents. To this end, necrotrophs secrete a cocktail of cell wall degrading enzymes, phytotoxic proteins and metabolites. Additionally, many fungi produce specialized invasion organs that generate high invasive pressures to force their way into the plant cell. However, for most necrotrophs, including Botrytis, the biomechanics of penetration and its contribution to virulence are poorly understood. Here, we use a combination of quantitative micromechanical imaging and CRISPR-Cas-guided mutagenesis to show that Botrytis uses substantial invasive pressure, in combination with strong surface adherence, for penetration. We found that the fungus establishes a unique mechanical geometry of penetration that develops over time during penetration events, and which is actin cytoskeleton dependent. Furthermore, interference of force generation by blocking actin polymerization was found to decrease Botrytis virulence, indicating that also for necrotrophs, mechanical pressure is important in host colonization. Our results demonstrate for the first time mechanistically how a necrotrophic fungus such as Botrytis employs this 'brute force' approach, in addition to the secretion of lytic proteins and phytotoxic metabolites, to overcome plant host resistance.

Mach reflection and pressure/heating loads on V-shaped blunt leading edges with variable cross-sections and crotches

The primary Mach Reflection (MR) and pressure/heating loads on V-shaped Blunt Leading Edges (VBLEs) with variable elliptic cross-sections and conic crotches are theoretically investigated in this study. The simplified continuity method is used to forecast the shock configurations. The theoretical predictions and the numerical simulations for the Mach stem and the triple point as well as the curved shock accord well. Based on the theoretical model, an analysis of the impact of the axial ratio a/b of the cross-sectional shape and the eccentricity e of the crotch sweep path on shock structures is carried out. The shock configurations obtained from the theoretical model enable the derivation of the transition boundaries between the primary MR and the same family Regular Reflection (sRR). It is found that the increase of a/b and e can both facilitate the primary MR to sRR transition. The resulting transition and the corresponding generation of the wall pressure and heat flux are then investigated. The results indicate that higher values of the ratio a/b can significantly reduce the wall pressure and heating loads by inducing the primary MR to sRR transition. Conversely, the increase in the eccentricity e results in increased loads, despite causing the same transition.

Post-failure deformation mode switching in volcanic rock.

Beyond a threshold applied compressive stress, porous rocks typically undergo either dilatant or compactant inelastic deformation and the response of their physical properties to deformation mode is key to mass transport, heat transport and pressure evolution in crustal systems. Transitions in failure modes-involving switches between dilatancy and compaction-have also been observed, but to date have received little attention. Here, we perform a series of targeted mechanical deformation experiments on porous andesites, designed to elucidate complex post-failure deformation behaviour. By investigating a sample suite and effective pressure range that straddles the transition between positive and negative volumetric responses to compression, we show two post-failure critical stress states: a transition from compaction to dilation ( ), and a transition from dilation to compaction, which we term . We demonstrate that multiple switches in deformation mode can be driven by stress application under conditions relevant to the shallow crust. While the effect on fluid flow properties of compaction-to-dilation switching may be masked by a net reduction in sample porosity, samples that underwent dilatant-to-compactant failure mode switching exhibited an increase in permeability of approximately two orders of magnitude, despite only slight net volumetric change. Such a substantial permeability enhancement underscores the importance of post-failure deformation in influencing solute and heat transfer in the crust, and the generation of supra-hydrostatic fluid pressures in volcanic environments.

Wave-induced liquefaction analysis of mildly sloping sandy seabed

Marine structures are commonly situated near the mildly sloping sandy seabed characterized by the slope angles (α) not exceeding 10°. The seabed liquefaction can be triggered due to the generation of the excess pore water pressure (EPWP), posing a threat to the stability of marine structures. This study focuses on the analysis of wave-induced liquefaction in the mildly sloping (MS) sandy seabed. A dynamic poro-elasto-plastic seabed model is developed to simulate the behavior of the MS sandy seabed under wave loading. The results indicates that the loading cycle required to trigger the initial liquefaction decreased as the position moved from the toe towards the crest of the MS sandy seabed. The amplitude of shear stress increases with the loading cycle and tends to increase with growing α before liquefaction, resulting in a slower accumulation of EPWP with larger α. Both the horizontal and vertical displacements induced by wave action reach the maximum at the crest of the sloping seabed. Notably, the horizontal displacement is much greater than the vertical displacement in the seabed under wave action. The displacement of the MS sandy seabed depends on not only the shear stress amplitude developed in the soils but also the accumulation of EPWP required to trigger the liquefaction in the seabed.

Swelling characteristics of montmorillonite mineral particles in Gaomiaozi bentonite

Highly compacted bentonite is an ideal back-filling (buffer) material for the deep geological disposal of high-level radioactive waste. Montmorillonite is the main constituent mineral of it. The nanoscopic swelling characteristic of montmorillonite mineral particles greatly influences the macroscopic buffering performance of highly compacted bentonite blocks. Firstly, the montmorillonite suspension liquid was exfoliated by freeze-thaw cycles, the appropriate mineral particles were selected by atomic force microscope (AFM) for making colloidal probes. Then, the swelling pressure between mineral particles was measured by AFM, investigating the effects of interlayer distance, layer number, temperature, and interlayer cation type on the nanoscale swelling pressure. The experimental results showed that the swelling pressure of montmorillonite mineral particles peaks at about 0.7–0.8 nm interlayer distance. The swelling pressure of mineral particles with more layers is smaller. The higher the ambient temperature, the greater the swelling pressure. The swelling pressure of Ca-montmorillonite is significantly larger than that of Na-montmorillonite. The Laird model has a relatively good applicability with the interlayer distance of 0.6–1.2 nm; the DLVO theory has a good applicability with the interlayer distance greater than 1.5 nm. Finally, a predictive model was developed for the swelling pressure of nanoscopic mineral particles considering the effect of layer number. The research results provide data support and theoretical support for swelling pressure generation and cross-scale transmission mechanism of highly compacted bentonite hydration.

Note on hydrostatic skeletons: muscles operating within a pressurized environment.

Muscles and muscle fibers are volume-constant constructs that deform when contracted and develop internal pressures. However, muscles embedded in hydrostatic skeletons are also exposed to external pressures generated by their activity. For two examples, the pressure generation in spiders and in annelids, we used simplified biomechanical models to demonstrate that high intracellular pressures diminishing the resulting tensile stress of the muscle fibers are avoided in the hydrostatic skeleton. The findings are relevant for a better understanding of the design and functionality of biological hydrostatic skeletons.

Mitigating Liquid Loading in Gas Wells Using Thermochemical Fluid Injection: An Experimental and Simulation Study.

Liquid loading significantly hinders gas production in unconventional shale wells, restricting flow and causing productivity decline. This study presents a novel approach to address this challenge, utilizing thermochemical fluids to generate in situ pressure and heat and effectively mitigating liquid loading issues. Laboratory experiments were conducted using a specially designed flow loop system to evaluate the performance of thermochemical fluids in alleviating liquid loading. The key treatment parameters such as thermochemical volumes, injection rate, number of cycles, and optimum injection time were optimized to improve the removal efficiency. In addition, PIPESIM software (pipe simulation program) was used to validate the effectiveness of the thermochemical approach for removing the liquid loading issue. Both laboratory results and PIPESIM outcomes confirmed the efficiency of thermochemical fluids in handling liquid loading. Removal efficiency of more than 90% can be achieved using thermochemical injection. The liquid removal efficiency increases with the number of cycles due to the generation of more pressure and heat at later injection cycles. Increasing injection cycles from 1 to 3 resulted in liquid removal efficiency rising from 17 to 95%. Also, PIPESIM results indicated that the gas production rate can be improved by around 74% after applying thermochemical treatment. Overall, this study introduces an effective treatment for liquid loading mitigation with significant potential to enhance gas production. The proposed method offers several advantages, including ease of application and extended well life.

Positive pressure in bamboo is generated in stems and rhizomes, not in roots.

Bamboos stand out among other tall plants in being able to generate positive pressure in the xylem at night, pushing water up to the leaves and causing drops to fall from leaf tips as guttation that can amount to a steady nocturnal 'bamboo rain'. The location and mechanism of nocturnal pressure generation in bamboos are unknown, as are the benefits for the plants. We conducted a study on the tall tropical bamboo species Bambusa oldhamii (giant timber bamboo) growing outdoors in southern California under full irrigation to determine where in the plant the nocturnal pressure is generated, when it rises in the evening, and when it dissipates in the morning. We hypothesized that the build-up of positive pressure would be triggered by the cessation of transpiration-driven sap flow and that resumption of sap flow in the morning would cause the pressure to dissipate. Nocturnal pressure was observed in mature stems and rhizomes, but never in roots. The pressure was episodic and associated with stem swelling and was usually, but not always, higher in rhizomes and basal stems than in stems at greater height. Time series analyses revealed that dry atmospheric conditions were followed by lower nocturnal pressure and rainfall events by higher stem pressure. Nocturnal pressure was unrelated to sap flow and even was generated for a short time in isolated stem pieces placed in water. We conclude that nocturnal pressure in bamboo is not 'root pressure' but is generated in the pseudo-woody rhizomes and stems. It is unrelated to the presence or absence of sap flow and therefore must be created outside of vessels, such as in phloem, parenchyma, or fibres. It is unlikely to be a drought adaptation and may benefit the plants by maximizing stem water storage for daytime transpiration or by transporting nutrients to the leaves.

Study of the Pore Water Pressure Development Characteristics of PHC Pipe Piles in Soft Soil Foundations

When constructing hollow prestressed high-strength concrete (PHC) pipe piles in soft soil foundations, the generation and dissipation of pore water pressure can induce negative friction on the pile. This phenomenon increases the settlement of the pile foundation and, in severe cases, can lead to pile deflection and flotation. To further investigate the development characteristics of pore water pressure during PHC hollow pipe pile driving in soft soil, this study combined existing theories and numerical models to analyze the generation and influence areas of pore water pressure. Field tests were conducted at three different sites: an untreated site, a surcharge preloading site, and a site treated with cement mixing piles and well dewatering. These tests monitored and analyzed the horizontal and vertical development and behavior of pore water pressure during pile driving at each site. The results indicate that during the pile driving process, when the horizontal distance from the pile center is 3d and 9d, the peak values of the excess pore water pressure in the site treated with cement mixing piles and well dewatering are 117 kPa and 100 kPa. After pile driving is completed, they decrease to 50 kPa and 48 kPa, respectively. The peak values of excess pore water pressure in the surcharge preloading site are 122 kPa and 97 kPa, and after pile driving, they decreased to 80 kPa and 21 kPa, respectively. The peak values of excess pore water pressure in untreated sites are 140 kPa and 121 kPa; after pile driving, they decreased to 82 kPa and 60 kPa, respectively. Pore water pressure increases with the depth of pile driving and decreases with distance from the pile driving location. The peak pore water pressure and dissipation rate during construction were found to be higher at the untreated site compared to the other two sites. Therefore, during pile sinking in soft soil foundations, dewatering and driving drainage boards are effective methods for reducing pore water pressure and accelerating its dissipation. These findings provide a theoretical basis and technical support for ensuring the safety of engineering constructions.

Effect of flywheels in pump stations for reducing the volume of air chambers

ABSTRACT The most common and destructive event of unsteady flow in pipes is water hammer. This phenomenon is caused by a sudden change in boundary conditions in pressurized pipes. Unsteady flow in pipelines can lead to a significant increase or decrease in pressure. This pressure generation may cause cavitation, bursting of pipes, and failure of the whole system. One type of equipment that can control both positive and negative pressure phases is a pressurized tank. Implementing such a pressure tank can impose increased costs. In order to reduce the design costs, the combination of a flywheel with the pressure tank can be used. In this study, a transmission pipeline from Zarineh River to Tabriz city is numerically simulated, and the effect of increasing the inertia of the flywheel on the reduction of the pressurized tank volume is investigated. The results show that increasing the flywheel inertia from 125 to 165 Nm2 can reduce the pressurized tank volume from 90 to 75 m3.

Influence of biocementation treatment extent on dynamic system performance: A centrifuge liquefaction study

Previous centrifuge experiments have shown Microbially Induced Calcite Precipitation (MICP) is a viable ground improvement technique to mitigate liquefaction. However, in these past experiments the entire sample in the model container was MICP treated. This study is an investigation of the effect of treatment extent on the system seismic performance by varying the depth of improvement, while maintaining the same cross-sectional area. Specifically, MICP treated zones (10 cm × 10 cm in model scale in plan view) were varied in depth to 100%, 75%, and 37% of the liquefiable sand layer depth. As a comparison, two additional models were constructed, an untreated and fully treated model. The treated models were initially prepared to a relative density of less than 40% and MICP treatment applied until a change of shear wave velocity (Vs) of 300 m/s was measured. All models were instrumented with accelerometers and pore pressure transducers to capture the dynamic responses during the same sequence of eight shaking events. Cone penetration resistance was measured to verify the uniformity of the untreated zones in the models and track the evolution of penetration resistances at three different times during the shaking sequence. Vs was measured after each shaking event to assess the cementation integrity of the MICP treated zones. Linear potentiometer and pre- and post-surface measurements were obtained to track seismic-induced settlements. Pore pressure generation and settlements were reduced in the MICP treated zones compared to untreated zones, showing the increased liquefaction resistance and system performance of MICP. Amplification of the strong ground motions in the models with treatment through the full liquefiable layer lead to significant degradation of the MICP. While a base isolation effect was observed in the models not treated to the full depth of the liquefiable layer, reducing seismic demands to the MICP treated zoned, and leading to minimal changes in cementation integrity. These findings suggest that there may be a benefit to not improving the entire liquefiable depth for maintaining cementation integrity of MICPtreated soils.

Quantifying near-fault motion effects on soil liquefaction through effective stress site response analysis

Near-fault (NF) pulse-like ground motions have a significant impact on the performance of structures, but their effects on soil liquefaction potential have been relatively understudied. This paper uses 1D effective stress site response analysis capable of modeling porewater pressure (PWP) generation to investigate the seismic site response under NF and general ground motions. The aim is to assess the effects of NF motions on soil liquefaction by considering different soil models and PWP generation models. The results show that NF ground motions generally induce larger ground responses in terms of PWP generation, especially when the durations of the motions are short. This is due to the higher cumulative absolute velocity associated with NF ground motions compared with general ground motions due to a high-velocity pulse under the same peak ground acceleration. However, this effect diminishes as the duration of motion increases. To avoid underestimating seismic demand, especially for small to moderate earthquakes, a preliminary magnitude scale factor modified for the NF effect is suggested for use in conventional soil liquefaction triggering analysis.

Prediction of Excess Pore Water Pressure Generation in Sand–Silt Mixtures During Cyclic Loading: A Dissipated Energy-Based Model

Prediction of Excess Pore Water Pressure Generation in Sand–Silt Mixtures During Cyclic Loading: A Dissipated Energy-Based Model