At-rest Conditions Research Articles

Seismic response of braced excavation wall supporting deep sand layer using dynamic centrifuge tests

This paper presents the dynamic centrifuge model tests to investigate the seismic performance of a 24.8 m deep braced diaphragm wall supporting dry sand backfill soil at 40 g level acceleration. The model tests aim to determine the acceleration response of the backfill, seismic earth pressures acting on the wall, and the dynamic increment of the structure's inner force for sand backfills with different relative densities. Particularly, the horizontal seismic coefficient, earth pressure distribution, and dynamic thrust are analyzed in detail. Based on the experimental results, the dynamic thrust development is consistent for peak ground accelerations at bedrock less than 0.12 g and 0.10 g for relavitve densities of 78 % and 54 %, respectively. However, the dynamic thrust starts to increase when the bedrock acceleration exceeds this threshold. Moreover, the varying trend of dynamic thrusts under ground input motion employed during at the initial excitation differs from that of the succeeding input motions, likely due to the changes in relative density caused by backfill disturbance from sequential excitation. The increasing rate of increase on the dynamic thrusts among Northridge, Kobe, and artificial excitations was changed with the amplitude of the acceleration response. Lastly, the wall bending moment and strut axial force increase by up to 97.3 % and 12.9 % of the maximum value of member force on the at-rest condition due to earthquake loading.

Impact of Relief Shelves on Earth Pressure Reduction Under At-Rest Conditions: Physical Modeling Tests

Impact of Relief Shelves on Earth Pressure Reduction Under At-Rest Conditions: Physical Modeling Tests

Performance improvement of a biotechnology vaccine cleanroom for contamination control

Cleanrooms play an important role in various industries, such as pharmaceuticals, specifically for vaccine cleanrooms by strictly regulating contaminants, temperature, humidity, and pressure to ensure product reliability, particularly in critical areas. This study investigates a biotechnology vaccine cleanroom using a comprehensive field measurement test and numerical simulation analysis. Field measurements were conducted during the at-rest and operational occupancy states. As a result, it was discovered that the operational condition has a higher concentration than the at-rest condition. To mitigate this issue, the numerical simulation improvement strategy employed in this study aimed to reduce the concentration under operational conditions. The strategy proposed in this simulation is determining the ventilation rate and arranging the outlet air grilles. To assess and evaluate the performance of the cleanroom, we utilized ventilation and removal efficiency metrics. These indices served as important metrics for evaluating the cleanroom's efficiency in controlling contaminants. In at-rest conditions, ventilation and removal efficiency were 90.0 % and 86.2 %, respectively. However, under operational conditions, these metrics dropped to 81.3 % and 80.1 %, respectively, in the baseline case. After the proposed improvement design, the ventilation and removal efficiency in the operational condition could improve by up to 6.8 % and 5.2 %, respectively. A proper arrangement of outlet air grilles could control the decrease in concentration. In addition, a higher ventilation rate also could decrease the concentration. However, it caused high energy consumption. Therefore, the ventilation rate must be designed optimally to compromise contamination control and energy saving.

Measurement of stresses and strains around a pushed-in model pile or cone penetrometer

This paper describes the methods and outcomes of tests designed to simulate the penetration of a pushed-in model pile, or a field testing penetration element. The penetration element was a 25 mm dia. cylinder with a conical tip. The element was advanced into a sand profile subjected to vertical pressure under at-rest conditions. The unique aspect of the testing was the inclusion of in-soil measurement tools. Null soil pressure gauges were used to monitor radial pressures and in-soil linear strain devices were used to monitor radial strain at points within a measurement horizon as the penetration element was advanced into the profile. Testing revealed that radial pressures return to their ambient pre-penetration magnitudes once the element passes below a sensing horizon. In-soil radial strain measurements illustrated that the rapid drop in radial soil pressure coincides with a small, but consistent reversal in the increment of radial strain. As distance from the axis of penetration decreases this reversal is more significant. These observations have importance in considering the development of frictional resistance and axial capacity of pushed-in piles and at the same time have relevance to the analysis of cone penetration testing in the determination of rational material properties.

Numerical Evaluation of the Relief Shelves for Lateral Thrust Reduction on Wall under At-Rest Condition

Numerical Evaluation of the Relief Shelves for Lateral Thrust Reduction on Wall under At-Rest Condition

The full state of stress in monotonic simple shear tests on sand

The simple shear test has been an important tool in practical geotechnical engineering and the study of soil behaviour. The attractiveness of the simple shear test is founded in its relative ease of specimen preparation, similarity to at-rest conditions during consolidation and rotation of principal stresses during shear. Despite this test's attractive qualities, there are significant deficiencies in the interpretation of standard test results: horizontal normal stresses are not known and excess pore pressures are often interpreted from assumptions about constant-volume tests without saturation. To address this problem, a set of monotonic tests were performed on a sand, during which horizontal normal stresses were measured in the central portion of specimens. Based on the measurements, the full state of stress was defined, stress paths were drawn and directions of the principal stresses were determined. Outcomes showed that the conventional approach of estimating excess pore pressures as the change in vertical pressure to maintain constant volume in response to shear is problematic, and friction angles interpreted from conventionally measured shear and vertical stresses may be grossly underestimated in some cases.

Investigation of Airflow Distribution and Contamination Control with Different Schemes in an Operating Room

Controlling contamination via proper airflow distribution in an operating room becomes vital to ensure the reliable surgery process. The heating, ventilation, and air conditioning (HVAC) systems significantly influence the operating room environment, including temperature, relative humidity, pressurization, particle counts, filtration, and ventilation rate. A full-scale operating room has been investigated extensively through field measurements and numerical analyses. Computational fluid dynamics (CFD) simulation was conducted and verified with the field measurement data. The simulation was analyzed with three different operating room schemes, including at-rest conditions (case 1), normal operational conditions with personnel (case 2), and actual conditions with personnel inside and some medical equipment blocking the return air (case 3). The concentration decay method was used to evaluate this study. The results revealed that the contamination concentration in case 1 could be diluted quickly with the average value of 404 ppm, whereas the concentration in case 2 slightly increased while performing a surgery with the average value of 420 ppm. The return air grilles in case 3, blocked by obstacles from some medical equipment, resulted in the average concentration value of 474 ppm. Other than that, the contaminant dilution could be obstructed dramatically, which revealed that proper and smooth airflow distribution is essential for contamination control. The ventilation efficiency of case 2 and case 3 dropped around 6% and 17.91% compared to case 1 in the unoccupied and ideal condition. Ventilation efficiency also decreased along with decreasing the air change rate per hour (ACH), while with increasing ACH, the ventilation efficiency in case 3 actually increased, approaching case 2 in the ideal condition.

Field test of pharmaceutical cleanroom cleanliness subject to multiple disturbance factors

Biopharmaceutical cleanrooms have high cleanliness requirements to supervise and manage processes and ensure the quality of production. However, on-site data, including real-time particle concentrations and differential pressure in biopharmaceutical cleanrooms, are scarce for both operational and at-rest conditions. In this study, a field experimental investigation of multiple disturbance factors in a cleanroom environment was performed in a newly built cleanroom. The impact of the number of personnel, entry of personnel, and air change rate on the cleanliness level was measured and analyzed. It was concluded that: (1) a notable over-specification of cleanliness was observed in the operational state. The particle concentrations with size larger than 0.5 μm were 1041 pc/m3 and 2901 pc/m3 in the temporary storage room and configuration room, respectively, which was considerably lower than the required Class B specification; (2) An increase in the number of people entering the room and extension of the door opening time may cause the invasion of more particles to the cleanroom with higher cleanliness. The particle concentrations increased by approximately 2000 pc/m3 with the addition of one person. (3) In the at-rest state, the particle concentration was two orders of magnitude lower than the standards. Therefore, the supply air volume in the at-rest state can be reduced when other disturbance factors are under control. The active power of the supply air fan was reduced by 41.7% in this stage, indicating great potential for energy saving. The field measurement provides evidence of the effect of disturbance factors on the cleanliness.

Effects of freezing and thawing on retaining wall with changes in groundwater level

Freezing and thawing of pore water within backfill can affect the stability of retaining wall as the phase change of pore water causes changes in the mechanical characteristics of backfill material. In this study, the effects of freezing and thawing on the mechanical performance of retaining wall with granular backfill were investigated for various temperature and groundwater level (GWL) conditions. The thermal and mechanical finite element analyses were performed by assigning the coefficient of lateral earth pressure according to phase change of soil for at-rest, active and passive stress states. For the at-rest condition, the mobilized lateral stress and overturning moment changed markedly during freezing and thawing. Active-state displacements for the thawed condition were larger than for the unfrozen condition whereas the effect of freezing and thawing was small for the passive condition. GWL affected significantly the lateral force and overturning moment (Mo) acting on the wall during freezing and thawing, indicating that the reduction of safety margin and wall collapse due to freezing and thawing can occur in sudden, unexpected patterns. The beneficial effect of an insulation layer between the retaining wall and the backfill in reducing the heat conduction from the wall face was also investigated and presented.

Analysis of students’ foot pressure distribution on the ground, as well as their body balance before and after exercise

Background and Study Aim: The article presents the results of analyses of students’ foot pressure distribution on the ground, as well as their body balance before and after exercise (Harvard Step Test). The aim of the paper was to carry out a comparative analysis of foot pressure distribution on the ground, as well as assess the degree of body balance before and after exercise. With that purpose in view, the following research hypothesis was formulated: in the students participating in the study, the distribution of foot pressure on the ground and the degree of body balance differ significantly after physical effort compared with the at-rest conditions.
 Material and Methods: The study encompassed n=48 students, including 37 women and 11 men. The tests were carried out using such tools as: an EPS/R1 podobarographic mat and the impedance methods – i.e. the InBody 270 body composition analyser. An analysis was performed for the parameters concerning body composition, the distribution of foot pressure on the ground, and the level of body balance.
 Results: The results obtained revealed statistically significant differences in the physiological parameters of foot arching and the functional efficiency of the body balance system under different measurement conditions that reflected the impact of effort stimuli.
 Conclusions: Significant differences reflecting the impact of the effort stimuli were expected to be achieved during the mathematical analysis of the results of podobarographic tests that allow for the assessment of the physiological parameters of foot arching and the functional efficiency of the body balance system under different measurement conditions. The authors’ assumption was mathematically and statistically confirmed by significant differences foe most of the parameters arising out of the possibilities offered by the research method applied. Comparative assessment unquestionably revealed a negative change in foot arching, as well as lower body posture stability in the female and male subjects, resulting from the physical exercise applied.

K0determination using improved experimental technique

Lateral soil pressures under at-rest conditions are commonly estimated as K0times vertical normal pressure, where K0is obtained from generally accepted empirical formulae, related to the soil's friction angle and the stress history. Results of a programme of laterally, rigidly confined, vertical compression and unloading tests on sand and clay are presented, in which two significant experimental techniques were employed: (a) lateral pressures were measured using null pressure gauges, preventing gauge diaphragm deflection; (b) side-wall friction was measured, and minimised using special friction reduction measures. Comparative tests in which one or both of these measures were not employed indicate the significant errors induced in both the vertical and the horizontal pressures used for K0determination. The bank of experimental data, which formed the basis for the commonly accepted empirical formulae, did not take account of these issues, and they are shown to be inconsistent with values measured in the present study.

Microbiological evaluation of environmental cleanliness in haematopoietic cell transplant patient rooms: implementing JACIE standards

Environmental hygiene is one of the most important strategies to prevent hospital-acquired infections by reducing pathogens in haematopoietic cell transplant (HCT) patient rooms. This study was designed in response to JACIE requirements for microbiological monitoring, and aimed to assess environmental hygiene in protective isolation rooms. Environmental cleanliness was assessed by measuring microbial loads in at-rest and operational conditions sampled from target surfaces, and in passive and active air from rooms occupied by patients with different grades of neutropenia. The study also evaluated whether microbial loads were influenced by isolation precautions. The failure rate of cleanliness on target surfaces in at-rest conditions was 0% compared with 37% for surfaces and 13% for passive and active air samples in operational conditions. Differences in failure rates were observed in the rooms of patients with different levels of neutropenia (P=0.036 for surfaces, 0.028% for passive air). No relationship was found between infections and microbial loads. Microbiological assessment integrated with an enhanced monitoring programme for hospital hygiene provides invaluable information to drive infection control policies in HCT patients. These results highlight the need to set and validate strict standards for the assessment of cleanliness in a clinical setting.

A unified elasto-plastic constitutive model for sandy and clayey soils accounting for at-rest condition

ABSTRACT Taking advantages of some existing two-surface soil constitutive models in a critical state framework, a unified two-surface constitutive model was developed for rigorous simulation of elasto-plastic deformation of different soils such as loose and dense sands, normally and over-consolidated clayey soils subjected to any type of monotonic loadings. Employing the dilatancy parameter, the strain-softening and stress-dilatancy were described using non-associated flow rule to generalise the application of the model to different soils under various stress states. The applicability of the proposed model was validated comparing the numerical simulations with the existing experimental data for variety of soils subjected to different phases of monotonic loadings. The model was found to be capable of simulating drained and undrained behaviour of clayey and sandy soils under triaxial stress conditions as accurate as the constant stress-ratio loading state. The results also demonstrated the ability of the model to determine the at-rest earth pressure coefficient (K0 ) for variety of soils suitable to be applied to the geotechnical problems affected by this parameter such as piles groups and retaining earth structures. While the formulation of hardening parameter in the integration scheme is based on volumetric and deviatoric plastic strains, the simulation of dilatancy response especially in dense sands showed an excellent agreement with the experimental data.

Displacement-Dependent Earth Pressures on Rigid Retaining Walls with Compressible Geofoam Inclusions: Physical Modeling and Analytical Solutions

AbstractA rigid nonyielding retaining structure needs to be dimensioned to have adequate stiffness, such that it can resist mobilized lateral earth pressures. This corresponds to the at-rest condition, as there are, in general, negligible lateral deformations in the backfill. Measures that can mobilize higher soil shear strength and reduce lateral thrust are therefore sought to provide a more efficient design. The present study investigates the possibility of inserting compressible geofoam panels against rigid walls using physical model testing. Controlled yielding is allowed in the backfill with the occurrence of deformations in the geofoam. The mobilized earth pressures vary from the maximum at rest, to the intermediate, and finally to the minimum full active state depending on the magnitude of displacement. The effects of geofoam thickness and stiffness on lateral earth pressure reduction are explored. The measured pressure and displacement distributions form a comprehensive reference for use in calibr...

Verification of Rankine Earth Pressure Theory Using Finite Element Analysis with Elastic-Plastic Material

To simulate the Rankine earth pressure theory in the finite element analysis, a frictionless rigid wall and backfill system supported by rollers can be used. Beginning from the initial at-rest pressure conditions, the wall is moved towards or away from the backfill in a series of increments, until the passive or active earth pressure condition is reached. To obtain numerical solutions, twenty-five finite isoparametric elements are used to simulate the backfill and six linear bar elements to represent the rigid retaining wall. In order to simulate the incremental displacements, bar elements with a very high stiffness are used. The effect of wall displacement can be accomplished by applying a load equal to the value of the bar stiffness times the displacement to the nodal points that connect bars and soil elements. The elastic-plastic Drucker-Prager soil model is used in this study. Two earth pressure study cases have been analyzed. The first case deals with a cohesionless soil, while the second one a cohesive soil. The obtained load-displacement curves and stress-displacement curves are presented. It is found that the earth pressures behind the retaining wall at different heights based on the numerical solutions are identical with the calculations obtained from the Rankine earth pressure theory.

Investigation of EEG Alpha Rhythm of Artists and Nonartists During Visual Perception, Mental Imagery, and Rest

In this article, differences in alpha power between multichannel EEG signals of artists and nonartists were investigated. The two groups were compared during visual perception, mental imagery, and at-rest conditions. We found no significant differences between the two groups in absolute alpha power at rest. Both absolute and relative alpha power were found to be significantly lower in artists during the visual perception and the mental imagery tasks for some of the channels, suggesting that the cerebral efforts of artists were higher during these conditions. These results indicate that artists considered more features of a painting compared to nonartists. The two groups differed in relative alpha power during the visual perception task compared to the at-rest condition. Relative alpha power values decreased during the visual perception for both groups; however, their variation patterns were different. More significant decreases in relative upper alpha power (10-12Hz) during the visual perception task for ...

Stress/Rest Circumferential Strain in Non-Ischemia, Ischemia, and Infarction

Adenosine triphosphate (ATP) induces relative hypoperfusion in significantly stenotic coronary arteries, but its effect on myocardial strain has not been used clinically for the detection of ischemia. The purpose of this study was to quantify ATP-stress-induced contractile impairment as altered myocardial strain in coronary artery disease (CAD) using tagged magnetic resonance (MR) and to evaluate its diagnostic capability in comparison with ATP-stress myocardial perfusion-MR. Tagged MR and perfusion-MR under ATP-stress and rest conditions and late gadolinium enhancement (LGE) MR imaging were performed in 22 patients with suspected CAD. The peak absolute value of the circumferential strain (C-strain) was measured in 12 segments. Myocardial segments were categorized as non-ischemic (n=201), ischemic (n=42), or infarcted (n=21) according to the perfusion-MR and LGE MR imaging results. The absolute C-strain was significantly greater under ATP-stress (19±13%) (mean±SD) than under at-rest (15±11%, P<0.001) conditions in non-ischemic segments. Conversely, the absolute C-strain was significantly lower under ATP-stress (10±13%) than under at-rest (16±6%, P<0.01) conditions in ischemic segments. Optimal cutoff values for stress C-strain (-17.5%) could successfully differentiate segments with ischemia or infarction from non-ischemic ones with a sensitivity of 86%, a specificity of 65%, and an area under the curve of 0.79. C-strain analysis using tagged MR could detect ATP-stress-induced contractile impairment in ischemic myocardium.

Amplification of Rocking Due to Horizontal Ground Motion

This paper addresses the fundamental behavior of rocking structures by investigating the rate of energy input due to horizontal ground motion. This perspective indicates that the assumption of initial at-rest conditions may be inappropriate, and identifies ground motions which cause ‘rocking resonance’ for various constraints. Furthermore, the ability of multiple impulses to either reduce or amplify the rocking response is demonstrated, and motivates the use of statistical assessment procedures to predict rocking stability during earthquakes. In this context, past earthquake data is used to generate an array of synthetic earthquakes of a given intensity which are applied to determine the overturning probability of the rocking block. The results emphasize the time dependence of the rocking response. Finally, simulation of the rocking response to real earthquake records confirms that multiple impulse rocking amplification may be significant.

Factors affecting kinked steel grid reinforcement in MSE structures

In order to investigate the factors affecting kinked steel grid reinforcement in Mechanically Stabilized Earth (MSE) structures, pullout tests were conducted to find out the new structure of steel grid reinforcement by making one or two triangular kinks on it to effect yielding in the steel grid. The pullout resistance is higher at larger pullout displacement when more kinks are made in the steel grid. Adding more kinks in the steel grid allowed sufficient lateral yielding with sufficient displacements to achieve the active condition as opposed to at-rest condition and thereby reduce the loading in the reinforcements.

Behavior of soil retaining walls on deformable foundations

Cost-effectiveness evaluations for soil retaining structures require better knowledge of the integrity and serviceability of these structures subjected to foundation settlements. As a preliminary study on the performance-based design of soil retaining structures that takes into account the influence of foundation settlements, the settlement-tolerating characteristics of cantilever soil retaining walls (CWs) placed on deformable foundations were explored using a 0.6 m-high model cantilever wall backfilled with rhombically stacked 1.96 mm uniform diameter steel rods used as two-dimensional backfills of the wall. Screw jacks were used to simulate a non-yielding foundation and three types of spring with various spring constants were used to simulate deformable foundations with maximum foundation settlements of approximately 2%, 5%, and 9% of the total wall height. It was found that the measured values of the lateral pressure coefficient ( K f) increased significantly with a decrease of subgrade stiffness, k v (or an increase of maximum foundation settlement, S max). The measured values of K f for the CWs placed on deformable ground may be greater than those for the at-rest ( K o) condition when S max is greater than 3% of the total height of the wall ( H t). For the tested cantilever wall with moderately high safety factors against sliding and overturning based on a commonly adopted assumption of an unyielding foundation, significant decreases in safety factors associated with the increase in S max were observed. Equations for additional margins of design lateral pressure coefficient and/or safety factors against sliding and overturning for the wall, expressed as a function of maximum foundation settlement, are proposed to substantiate the safety evaluation of soil retaining walls situated on a deformable foundation.