Pressure Generation Research Articles

Liquefaction characteristics of saturated marine coral sand with different non-plastic fines content subjected to complex cyclic stress paths

Coral reefs thrive in complex marine geological environments and are likely to suffer from dynamic marine disasters. The liquefaction characteristics of saturated marine coral sand subjected to dynamic loading, such as ocean waves, submarine earthquakes, storm tides, volcanic activities, and hurricanes, are key factors affecting the safety of coral reefs. A systematic study is conducted through a series of hollow-cylinder torsional shear experiments on the undrained response of saturated marine coral sand with different non-plastic fines contents (FCs) under cyclic linear stress paths with various cyclic loading direction angles (αd). An interesting discovery is that the cyclic linear stress paths with angles αd and 90°−αd have the same stress effect on liquefaction characteristics under isotropic consolidation condition. The test results show that if the near-zero effective stress state is defined as the criterion for initial liquefaction, then the liquefaction resistance of saturated coral sand decreases with increasing αd or FC. The generation of excess pore water pressure (EPWP) presents three modes: (1) “rapid–stable–fast,” (2) “rapid–stable,” and (3) “fast linear-like.” Moreover, an energy-based EPWP prediction method is established. A novel discovery is that the generalized shear strain amplitude (γga) is uniquely related to the EPWP ratio of coral sand for a given relative density and FC. In addition, by introducing unit cyclic stress ratio (USR) as a new index of liquefaction resistance, a common correlation between equivalent skeleton void ratio esk* and USR15 (required for initial liquefaction in 15 cycles) is established for all test cases considered. This is confirmed by the experimental data of five types of terrestrial siliceous sands reported in the literature.

Integrated effects of inherent and induced anisotropy on reliquefaction resistance of Toyoura sand with different strain histories

Recent earthquakes in New Zealand and Japan showed that pre-shaking histories significantly affected the reliquefaction resistance of soils. In this study, a series of experimental tests was conducted to elucidate the coupled effects of inherent and induced anisotropy on reliquefaction resistance of Toyoura sand, which have not been studied before. Accordingly, loose and dense Toyoura sands were prepared with two different methods: dry deposition and moist tamping. The specimens were sheared cyclically using a hollow cylinder torsional shear apparatus under various cyclic stress ratios up to different residual shear strains (γres) and reconsolidated at different states. The experimental results were assessed from various perspectives, including stress–strain relationships, failure mechanisms, liquefaction/reliquefaction resistance, excess pore water pressure (EPWP) generation and compressibility in conjunction with micromechanical interpretations. It was shown that fabric evolution affects the reliquefaction characteristics of Toyoura sand substantially. Interestingly, a unique correlation exists between EPWP and shear strain accumulation for all tests. An energy-based model was developed to uniquely correlate the dissipated energy with the cyclic resistance based only on residual shear strains; this model shows great promise to develop a unified, energy-based criterion for quantifying the liquefaction/reliquefaction resistance of soils with different fabrics.

Effects of Device-Facilitated Lingual Strengthening Therapy on Dysphagia Related Outcomes in Patients Post-Stroke: A Randomized Controlled Trial.

Swallowing impairments resulting from stroke have few rehabilitative options. Prior evidence suggests lingual strengthening exercise may provide some benefit, but more randomized controlled trials are required. The purpose of this study was to examine efficacy of progressive lingual resistance training on lingual pressure generative capacity and swallowing outcomesforindividuals with dysphagia after stroke. Participants with dysphagia within 6months of acute stroke were randomly assigned to: (1) treatment: progressive resistance tongue exercise using pressure sensors for 12weeks with usual care; or (2) control: usual care only. Outcomes were measured at baseline, 8 and 12weeks to assess group differences in lingual pressure generation, swallow safety, efficiency, oral intake, and swallowing quality of life. Final sample included 19 participants [treatment (N = 9) and control (N = 10)] with 16 males and 3 females (mean age = 69.33). Functional Oral Intake Scale (FOIS) scores improved significantly (p = 0.04) in the treatment group from baseline to 8weeks compared to usual care (control). No significant differences between treatment groups were identified for other outcomes; large effect sizes were detected for group differences in lingual pressure generative capacity from baseline to 8weeks at the anterior sensor (d = .95) and posterior sensor (d = 0.96), and vallecular residue of liquids (baseline to 8-week d = 1.2). Lingual strengthening exercise resulted in significant improvements in functional oral intake for patients with post-stroke dysphagia as compared to usual care after 8weeks. Future studies should include a larger sample size and address treatment impact on specific aspects of swallow physiology.

Effects of myocardial sheetlet sliding on left ventricular function

Left ventricle myocardium has a complex micro-architecture, which was revealed to consist of myocyte bundles arranged in a series of laminar sheetlets. Recent imaging studies demonstrated that these sheetlets re-orientated and likely slided over each other during the deformations between systole and diastole, and that sheetlet dynamics were altered during cardiomyopathy. However, the biomechanical effect of sheetlet sliding is not well-understood, which is the focus here. We conducted finite element simulations of the left ventricle (LV) coupled with a windkessel lumped parameter model to study sheetlet sliding, based on cardiac MRI of a healthy human subject, and modifications to account for hypertrophic and dilated geometric changes during cardiomyopathy remodeling. We modeled sheetlet sliding as a reduced shear stiffness in the sheet-normal direction and observed that (1) the diastolic sheetlet orientations must depart from alignment with the LV wall plane in order for sheetlet sliding to have an effect on cardiac function, that (2) sheetlet sliding modestly aided cardiac function of the healthy and dilated hearts, in terms of ejection fraction, stroke volume, and systolic pressure generation, but its effects were amplified during hypertrophic cardiomyopathy and diminished during dilated cardiomyopathy due to both sheetlet angle configuration and geometry, and that (3) where sheetlet sliding aided cardiac function, it increased tissue stresses, particularly in the myofibre direction. We speculate that sheetlet sliding is a tissue architectural adaptation to allow easier deformations of the LV walls so that LV wall stiffness will not hinder function, and to provide a balance between function and tissue stresses. A limitation here is that sheetlet sliding is modeled as a simple reduction in shear stiffness, without consideration of micro-scale sheetlet mechanics and dynamics.

Energy-based approach to study liquefaction triggering in homogeneous and stratified soils under consolidated undrained cyclic loading

Pore water pressure development through seismic effect is one of the key reasons for liquefaction failures in the foundations, dams, bridges, slopes and other vulnerable geotechnical engineering structures. The energy dissipation theories have provided a remarkable understanding of the pore water pressure generation inside a soil skeleton. In the present study, a series of consolidated undrained cyclic triaxial tests have been performed to evaluate the normalized dissipated energy (Wn) required for triggering liquefaction in both homogeneous and stratified soil specimens (prepared using silt interlayer) to replicate the site conditions nearby marine or alluvial deposits. The generated hysteresis loops using cyclic loading facilitate the calculation of dissipated energy. Also, the test results indicated a significant variation in the dissipated energy of homogeneous specimens at different magnitudes of cyclic stress ratios (CSR) and relative densities (Dr). With an increase in the cyclic stress ratio from 0.14 to 0.20, the trend of dissipated energy was observed to be different when relative densitie of sand varied from 30% to 65%. In the stratified specimens, thickness (t) and location of the silt layer (d) in the given soil specimen were the major influencing factors for estimating the liquefaction potential in loose conditions. Additionally, the highest value of Wn,max was obtained as 0.51 for the stratified specimen with topt = 28 mm at a cyclic stress ratio of 0.14. Based on the trendline variations, empirical models have been developed to estimate the normalized dissipated energy (Wn) for both homogeneous and stratified conditions. The developed models for homogeneous specimens are functions of CSR and Dr, whereas, in the case of stratified specimens, t, d and σd/σ'c (σd = deviator stress, σ'c = effective confining stress) have been utilized to predict the Wn with an satisfactory R2 value above 0.90. From the analysis of liquefaction resistance curves, the energy-based approach used in this study has been observed to provide more realistic results than the pore pressure ratio and strain-based failure criteria.

Cyclic threshold shear strain for pore water pressure generation and stiffness degradation in marine clays at Yangtze estuary

Cyclic threshold shear strain is a fundamental property of saturated soils under cyclic loading. To investigate the cyclic threshold shear strain for pore water pressure generation (γtp) and stiffness degradation (γtd), a series of strain-controlled multistage undrained cyclic triaxial tests were carried out on in-situ saturated marine clay in the Yangtze estuary with different plasticity index Ip. The test results show that both γtp and γtd increase with increasing Ip, and γtp is larger than γtd for the same marine clay tested under the same conditions, with γtp = 0.017 ~ 0.019%, γtd = 0.008 ~ 0.012% for Ip of 17, γtp = 0.033 ~ 0.039%, γtd = 0.020 ~ 0.025% for Ip of 32, and γtp = 0.040 ~ 0.048%, γtd = 0.031 ~ 0.036% for Ip of 40. Moreover, the development of stiffness degradation may not necessarily require the generation of pore water pressure but can be aggravated by it. Furthermore, the γtp and γtd of marine clay are compared with terrestrial soils and marine clays cited from the published literature, the results indicate that the special marine sedimentary environment and the combined action of flow and tidal wave system cause the γtp and γtd of marine clay in the Yangtze estuary to be smaller than that of the terrestrial clays and marine clays in other sea areas.

Development of an automatic sphygmomanometer simulator based on small volume displacement pressure generation

In general use of an automatic sphygmomanometer is essential to generate small and stable pressure during the rapid pressure expansion of the bladder cuff. The pressure generated by the sphygmomanometer simulator should simulate human blood pressure such as simulation for infant, neonatal and adult human or blood pressure conditions normal, hypertension, and hypotension. The simulator pressure system consists of three combinations of pressure generation, a dc motor for rough pressure generation, a small air cylinder for maintaining pressure stabilization, and brass bellows for simulation of small changes in volume or pressure. For air cylinder and brass bellows, two linear stages equipped with ball screew and the stepper motor are used to obtain a small change of linear displacement. The result for the simulator system contains these three combinations of pressure generation comply with the accuracy-test less than 3 mmHg and repeatable tests of less than 1 mmHg for automatic sphygmomanometer simulator based on ISO 81060-5:2020.

How to choose between high-flow nasal cannula, continuous positive airway pressure, and bilevel positive airway pressure in children with acute respiratory illness

In pediatric patients with acute respiratory illnesses, the widespread availability of heated humidified high-flow nasal cannula (HHHFNC) devices, ease of use, and increased compliance have increased their use in conditions such as pneumonia, acute respiratory failure, asthma, and acute respiratory distress syndrome. Due to the patient comfort and ease of use of HHHFNC, there are widely used. Similarly, the use of NIV is increasing due to the availability of better interfaces and non-invasive ventilators (NIV) for use in infants The conundrum has been regarding the generation of positive end-expiratory pressure in these open circuits of the HHHFNC devices versus the pressures delivered by the closed circuits in the NIV devices. This article reviewed the latest literature based on the clinical conditions and the rationale for selecting respiratory support in common acute respiratory illnesses.

Redesign of a closed-loop high-speed facility to test distortion generators

Aircraft engine architectures are currently in the phase of a change to meet future market demands. Certain such novel architectures force engines to operate under distorted inflow conditions, which are undesirable during flight. It is important to characterize the effect of such inflow distortions in order to understand the impact on the performance of engine components. This paper discusses the design and development of a novel test-facility that has the capability to test combined total pressure and swirl distortion generators under desired flow conditions. The return duct of the high-speed closed-loop compressor rig R4 at the von Karman Institute for Fluid Dynamics (VKI) has been redesigned to incorporate a test-section where distortion generators can be tested and characterized. Thus, a compressor test-rig is modified to act also as a wind tunnel capable of testing distortion generators at engine-like conditions.

Effects of acute intermittent hypoxia on P0.1 in humans with spinal cord injury

Spinal cord injury (SCI) disrupts neural pathways to respiratory motor neurons, diminishing respiratory drive and breathing function. Breathing impairment remains a leading cause of illness and death after SCI. Therapeutic acute intermittent hypoxia (tAIH; 15, 1-minute episodes of 9% inspired O 2 , 1.5 min normoxic intervals), a promising strategy to restore breathing function after SCI, promotes spinal neuroplasticity in rodent models. However, in humans, respiratory drive is unchanged after a single tAIH session; thus we tested the hypothesis that tAIH on five successive days increases neuromechanical respiratory drive in humans living with chronic SCI. Sixteen participants with chronic SCI (1 female; 33.5 + 15.3 years of age; 1-28 years post-SCI; 11 cervical, 5 thoracic; C1-T6 AIS A-D) were studied; their respiratory function was 52% ± 19% of age predicted expiratory pressure generation, and 123% ± 32% for inspiratory pressure. Five days of tAIH or Sham treatment were delivered in a randomized, cross-over design (minimum 3 weeks apart). Airway occlusion pressure in the first 0.1s of inspiration (P0.1), a surrogate for neuromechanical respiratory drive prior to within-breath sensory feedback, was collected at baseline and at 1, 3, and 7-days post-treatment. Repeated measures ANOVA revealed no significant effect of time (F(3)=.49; P=.69) or group (F(3)=1.33; P=.27). Despite the lack of significant differences in this preliminary analysis, P0.1 increased by 25% on day 3 versus 0.8% after Sham. Because of this change, pairwise comparisons were conducted, revealing a near significant increase in P0.1, 3 days post tAIH (MD=-.17; P =.06). Thus, although P0.1, a surrogate for neuromechanical respiratory drive, did not significantly increase after 5 days of AIH in people with SCI, the marginally significant change at day 3 suggests further investigation is warranted. Next steps include assessment in a larger sample, investigation of biomarkers for treatment effects, and examination of combinatorial interventions including task specific training and/or mild CO 2 elevations to enhance AIH-induced neuroplasticity in the drive to breathe. DoD SCIRP Clinical Trial Award W81XWH-17-SCIRP-CTA; The Craig H. Neilsen Foundation (JW); NIH T32 HL134621 (MM); and the UF McKnight Brain Institute. This is the full abstract presented at the American Physiology Summit 2023 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.

PO-02-206 A MECHANISM FOR PACING-INDUCED REGIONAL CONTRACTILE DYSFUNCTION MEDIATED BY RELEASED CATECHOLAMINES

We have previously shown that non-excitatory epicardial stimulation (NES) increases measures of cardiac function mediated by local release of norepinephrine. In this further investigation we focused on the effects of NES on the local myocardial contractile pattern. Farm pigs were anesthetized and instrumented with a LV high-fidelity pressure/volume conductance transducer, thoracic aortic pressure transducer, left atrial (LA)/ LV epicardial electrodes, and sonomicrometer segment length (SL) gauges placed proximal (lateral base) and distal (posterior mid LV) to the LV stimulation site. During constant LA pacing, LV pulses (0.8ms, 2-3x threshold volts) were applied during the absolute refractory period before and after β-receptor blockade (BB, metoprolol). Regional contractile function was analyzed by constructing LVP vs. SL loops in a beat-by-beat fashion thus allowing characterization of local cardiac function in relation to LV pressure over the entire cardiac cycle. NES resulted in a local contractile dysfunction characterized by an early shortening, subsequent lengthening, and re-shortening pattern during the cardiac cycle in the SL gauge proximal (middle tracing), but not remote to the stimulation site (bottom tracing). The onset of early lengthening in the proximal SL coincided with peak pressure generation, followed by re-shortening as LV pressure fell. The LVP vs. SL loop was markedly altered. This contractile effect rapidly waned within 10-15 seconds after cessation of electrical stimulation and was abolished by BB. The NES induced dysfunction developed within an average of 5-10 seconds of stimulation onset and was accompanied by increases in several global indices of cardiac function (dP/dt, peak LVP, early aortic valve opening) which were also abrogated by B-blockade. These findings demonstrate that pacing elicits local catecholamine release that may cause dyssynergy and mimic the regional pacing-induced contractile dysfunction seen at pacing sites in man.

Neuromuscular coupling of obligatory respiratory muscles to inspiratory pressure is reduced in dystrophic (mdx) mice

Neuromuscular coupling (NMC) is a recognised clinical index of inspiratory muscle function which reflects the efficiency of conversion of neural activation to inspiratory pressure. Duchenne muscular dystrophy (DMD) is characterised by respiratory insufficiency culminating in respiratory failure. We investigated inspiratory pressure generating capacity and electrical activation of obligatory inspiratory muscles in X-linked muscular dystrophy ( mdx) mice, to evaluate NMC of diaphragm, external intercostal and parasternal intercostal to inspiratory pressure across a range of behaviours in early established to late progressive disease.In urethane anaesthetised mice (1.7 g/kg i.p.), inspiratory pressure was recorded via a pressure transducer positioned in the thoracic oesophagus. Diaphragm EMG activity was recorded using needle electrodes. Studies were performed in male wildtype (WT) and mdx mice at 4, 8, 12 and 16 months old. Recordings were made at baseline and during sustained tracheal occlusion to task failure, defined as an inability to sustain peak pressure. Peak pressure was determined from the average of five successive peak efforts at the maximum response. The corresponding peak inspiratory EMG activities were determined. Two factor (age x genotype) analysis of variance was performed.Obligatory muscle EMG activities were significantly lower in mdx mice from 4 months of age. Peak inspiratory pressure was significantly greater in mdx at 4 months of age. At 8 months, peak inspiratory pressure was equivalent between WT and mdx followed by a significant decrease in peak inspiratory pressure in 12- and 16-month-old mdx. NMC was lower in mdx mice across the ventilatory and non-ventilatory range, emerging early in dystrophic disease.Reduced NMC of obligatory muscles to inspiratory pressure in mdx mice reveals a greater reliance on accessory muscles to support respiratory performance in dystrophic disease. Remarkably, this burden is adequately accommodated in early disease with a preserved capacity to generate peak inspiratory pressure. We reason that the loss of compensation afforded by accessory muscles to peak inspiratory pressure generation underpins the emergence of respiratory compromise in advanced disease. Our results may have implications for the understanding and treatment of DMD. Funded by Science Foundation Ireland SFI/19/6628 INSPIRE DMD. This is the full abstract presented at the American Physiology Summit 2023 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.

Acute Intermittent Hypoxia and Respiratory Strength Training to Improve Respiratory Function in Individuals with Chronic Spinal Cord Injury: Preliminary Outcomes

Spinal cord injury (SCI) disrupts neural pathways to respiratory motor neurons, causing paralysis and breathing impairment, a major cause of illness and death in SCI. Acute intermittent hypoxia (AIH) is a promising therapeutic modality that elicits spinal synaptic plasticity, improving breathing in rodent models of SCI. AIH also elicits plasticity in limb motor systems in both rodent models and humans with chronic SCI, where functional gains are greatest when paired with task-specific training. The impact of similar combinatorial treatments on breathing ability is unknown. Here, we report preliminary breathing outcomes in seventeen adults with chronic SCI who received AIH and task-specific training (respiratory strength training; RST). Seventeen males with chronic SCI (33.7 ± 15 yrs of age; 1-28 yrs post-SCI; 12 cervical, 5 thoracic injuries; C1-T6 AIS A-D). Respiratory function was 52% ± 19% of the age-predicted normative function for expiratory pressure generation and 123% ± 32% of normative values for inspiratory function. Participants completed four random ordered 5-day protocols of AIH, Sham, RST, and AIH+RST, >3 weeks apart. AIH consisted of 15, 1-minute episodes of breathing a hypoxic gas mixture (9% oxygen), interspersed with 1.5-minute episodes of breathing room air (21% oxygen). Thirty minutes after AIH, RST involved both inspiratory and expiratory training; 4 sets of 6-12 breaths with the pressure threshold device set to 80% of each individual’s maximum. Sham treatments replicated AIH but used room air. A linear mixed model was used to test for differences in maximal inspiratory pressure (MIP), maximal expiratory pressure (MEP), and forced vital capacity (FVC) prior to and 1 day post-intervention. MIP increased 10±15.6% (pre 120±34cmH20, post 129±36 cmH20) 1 day after RST (p=0.001) and 6±10.5% (pre 123±34cmH20; post 131±34cmH20) 1 day after AIH+RST (p=0.04), but did not change after AIH or Sham. MIP increased by >10% in 5/17 participants following AIH+RST and 9/17 participants following RST. Neither MEP nor FVC changed following any block. Although there were no significant differences between AIH+RST and RST intervention blocks, there was a medium effect size (0.44). Since RST and AIH+RST preliminary outcomes suggest functional respiratory benefit, future steps will determine if the combinatorial treatment elicits greater gains. Examination of biomarkers associated with outcomes will provide insight into outcome variability. Department of Defense CDMRP W81XWH1810718 This is the full abstract presented at the American Physiology Summit 2023 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.

Photoacoustic Imaging and Characterization of Bone in Medicine: Overview, Applications, and Outlook.

Photoacoustic techniques have shown promise in identifying molecular changes in bone tissue and visualizing tissue microstructure. This capability represents significant advantages over gold standards (i.e., dual-energy X-ray absorptiometry) for bone evaluation without requiring ionizing radiation. Instead, photoacoustic imaging uses light to penetrate through bone, followed by acoustic pressure generation, resulting in highly sensitive optical absorption contrast in deep biological tissues. This review covers multiple bone-related photoacoustic imaging contributions to clinical applications, spanning bone cancer, joint pathologies, spinal disorders, osteoporosis, bone-related surgical guidance, consolidation monitoring, and transsphenoidal and transcranial imaging. We also present a summary of photoacoustic-based techniques for characterizing biomechanical properties of bone, including temperature, guided waves, spectral parameters, and spectroscopy. We conclude with a future outlook based on the current state of technological developments, recent achievements, and possible new directions.

Hypocapnia as a predictor of the need for non-invasive mechanical ventilation in subjects with SARS-CoV-2 related pneumonia

Background: SARS-CoV-2 related pneumonia is characterized by moderate-to severe hypoxemia often associated with hypocapnia the prognostic role of which is poorely documented.
 Aims: evaluate if hypocapnia can predict the need for non-invasive mechanical ventilation (NIMV) in this setting.
 Materials and methods: we prospectively studied 52 subjects with moderate-severe SARS-CoV-2 related pneumonia. All the following data were collected at admission to the Emergency Department and processed by univariate and multivariate analysis: clinical and laboratory data, blood gas analysis in room air and lung ultrasound.
 Results: 33/52 subjects (63,4%) underwent NIMV. At univariate analysis PaCO2 was inversely associated to the need for NIMV (OR 0,82, CI 95% 0,689-0,976, p .025). At multivariate analysis PaCO2 predicted the need for NIMV independently from age, gender, number of comorbidities, d-dimer, CRP, PaO2 and LUS SCORE (OR 0,838, CI 95% 0,710-0,988, p .035).
 Conclusions: our data suggest that hypocapnia could be an early predictor of clinical worsening in these patients independently from other known predictors of unfavourable outcome, reflecting the occurrence of a deep and frequent respiratory pattern possibly related to the generation of excessive transpulmonary pressure swings leading to a self-induced lung injury (P-SILI). Further studies are needed for validating these data on greater populations.

New 2.5‐Dtwin screw extruder model for the feed section of a co‐rotating twin screw extruder with comparisons to data

AbstractMany polymers are processed and compounded in co‐rotating, fully intermeshing twin screw (TS) extruders. The typical compounding process consists of multiple unit operations including feed introduction, conveying solids away from the feed zone, transitioning from the conveying zone to the kneading block (KB) melting zone, melting, a downstream feed zone, a downstream mixing zone, a devolatilization region, and a pressure generating discharge section. This paper will focus on the first of these unit operations, the conveying of pellets in a partially filled screw leading to compaction and pressure generation in the full screw channel prior to the KB melting zone. Mechanisms for pellet conveying, for heating the polymer pellets, and for developing pressure at the end of the solids conveying screw elements are first presented for low‐density polyethylene (LDPE). The predictions of the model are also compared with a classical set of experiments on high‐density polyethylene (HDPE). The model is then tested using published characteristics of a polyamide‐type polymer. This paper focuses on the physics and engineering concepts that are inherent in the feed section of the TS extruder where the pressure is calculated using the friction of the polymer pellets. The effects of throughput,Q, at a constant rotation speed,N, are examined. Low and highQ/Nratios have significantly different axial pressure profiles.

New seismic monitoring center in South America to assess the liquefaction risk posed by subduction earthquakes

The east of Cali is composed of loose sand deposits with high water table levels. This condition and the high seismic hazard of the city make cyclic liquefaction one of the main hazards in the city, which may affect more than 600,000 citizens and important infrastructures such as the city’s main drinking water treatment plants. Therefore, it was decided to design and implement a seismic monitoring center to study the behavior of liquefiable soils under local seismogenic conditions, in which subduction earthquakes predominate. First, more than 130 earthquakes from two seismic monitoring centers with liquefiable layers in the USA were studied to determine the requirements for the adequate design of the monitoring center. Then, a robust geotechnical and seismic characterization of the study area including SPT, CPTu, and seismic and ambient noise tests were carried out. From this information, the specifications and location of the instruments and, in general, the characteristics of the monitoring center were defined. The monitoring center has been planned to be established in two stages, and the first one has already been built and commissioned. The implementation of the first stage allowed to adequately record 35 earthquakes from different seismogenic sources, most of them from subduction earthquakes, and to verify that the potentially liquefiable layer remains saturated throughout the year. Subsequent ground motion sensors will allow to deeply study and understand large shear strains and excess pore pressures generation in the soil deposit, as well as their relationships with different intensity measures. The experience shared herein can benefit the design, construction, and operation of other seismic monitoring centers across the world.

Excess pore water pressure generation in fine granular materials under undrained cyclic triaxial loading

Understanding the mechanism of excess pore water pressure generation in subgrades is essential for not only designing but also further maintenance purposes. The primary goal of this research was to investigate excess pore water pressure generation in fine granular materials under cyclic loading. A series of undrained cyclic triaxial tests were performed to study the excess pore water pressure generation in two selected fine granular materials: (1) railway sand and (2) tailings. The excess pore water pressure response of these materials was evaluated in terms of density conditions, number of cycles, and applied cyclic stress ratios (CSR). As a result, excess pore water pressure accumulated over time due to cyclic loading. However, its accumulation was significantly dependent on the governing factors, i.e., densities, CSR values, and material types. The excess pore water pressure exhibited a slight increase at low CSR values, but a sharp increase was observed at higher CSR values, which ultimately led to a failure state after a certain number of cycles. In addition, under the same loading conditions, the samples that had higher relative compaction showed better resistance to cyclic loads as compared to those with lower relative compaction. Finally, a relationship between excess pore water pressure and cyclic axial strain of the fine granular materials was discovered.

Liquefaction assessment based on numerical simulations and simplified methods: A deep soil deposit case study in the Greater Lisbon

The accurate estimation of earthquake-induced liquefaction damage requires detailed ground response analysis, which does not generally consider liquefaction. This paper presents a well-documented pilot site where different approaches to estimate surface ground motion were compared. A simplified stress-based method and non-linear dynamic effective stress numerical analyses were used to identify liquefaction. HVSR curves were used to validate the numerical analyses and laboratory test results were employed to calibrate an advanced constitutive model capable of reproducing liquefaction stress-strain behaviour and pore water pressure generation.1D non-linear elastic numerical analysis evidenced high shear strains in weak soil layers where liquefaction may occur. When PM4sand model was used to simulate liquefaction behaviour in sandy layers, 1D and 2D model responses were rather similar, since liquefaction occurs predominantly at a sandy layer that extends across the valley. Therefore, 1D horizontally infinite layers seems to be a good approximation of the 2D response of this valley.

Generation of negative peak pressures under a separation bubble

This paper investigates the generation mechanism of negative peak pressures on a blunt plate under a separation bubble with Large Eddy Simulation (LES). Synchronized sampling of the wind pressures on and velocity fields around the plate is adopted to explore the relation between pressure fluctuations and vortex dynamics. The ordinary pressure fluctuation is found to be induced by high-frequency vortex convection. Formation of a negative peak pressure starts from the vortex head arriving at an observation point and ends up at the vortex tail leaving that location. A negative peak pressure occurs when the vortex core is right beneath/above the observation point. Spectral analysis of the wind pressures and Dynamic Modal Decomposition (DMD) for the velocity fields are combined to detect and visualize the low-frequency motion responsible for extreme pressure fluctuations. A counterpart of the low-frequency dominating component of the wind pressures is found in the velocity modal analysis, which is related to the shedding of an extreme large-scale vortical structure and demonstrates a flapping motion of the shear layer. The present study provides insights to the generation of negative peak pressures and the relation between vortex behaviors and the shear layer movement.