Role Of Suction Research Articles

Suction effect-induced reduction in shotcrete thickness in tunnels

ABSTRACT The classical shotcrete design approaches often ignore the effect of suction, which enables higher strength and, accordingly, a cost-effective temporary support. This paper addresses a numerical approach to design an economic tunnel temporary support considering suction effect on the mechanical characteristics of a simulated soil and shotcrete. Various suction profiles at: fully saturated, high degrees of saturation, transition zone and residual saturated zone, at various shotcrete thicknesses (t), strength (cc) and cohesion values were analysed. Nonlinear stability–suction relationships were obtained. The role of suction on (t) for the simulated soil was more significant in the transition zone and then in the zone of high degrees of saturation. Reduction in (t) increased with suction increase until beyond the residual saturation. An increase of suction from 58.86 to 78.48 kPa (in the transition zone) at cc = 400 kPa was sufficient to cause a reduction of 61.4% in (t).

Numerical study of thermal radiation and suction effects on copper and silver water nanofluids past a vertical Riga plate

PurposeThe purpose of this paper is to explore the flow of Cu-water and Ag-water nanofluids past a vertical Riga plate. The plate is infinite in height and has zero normal wall flux through its surface. Influence of thermal radiation, slip, suction and chemical reaction on the flow characteristics are reported.Design/methodology/approachNon-dimensional forms of the flow governing equations are obtained by means of a set of similarity transformations. Numerical solution is obtained with the help of fourth-fifth-order Runge–Kutta–Fehlberg method with shooting procedure. Comparison of solution profiles of Cu-water and Ag-water nanofluids are presented graphically and with the help of tables. Influence of pertinent parameters on skin friction and heat transfer rate is also reported.FindingsResults reveal that the skin friction coefficient is more prominent in the case of Ag-water nanofluid for an increase in thermal radiation and volume fraction. The role of suction and slip is to increase velocity but decrease the temperature in both nanofluids. Temperature and velocity of both nanofluids increase as volume fraction and thermal radiation values are augmented. Heat transport increases with thermal radiation. Region near the plate experiences rise in nanoparticle concentration with an increase in chemical reaction parameter.Originality/valueA complete investigation of the modeled problem is addressed and the results of this paper are original.

Experimental study on the influence of saturation degree on unstable behavior within granular material

According to regulations and standards, risks of liquefaction are considered only if a soil is fully saturated. However, some authors have demonstrated that a soil can liquefy even with an initial degree of saturation under 100%. However, those studies remain descriptive and do not provide specific frameworks for evaluating the risk of liquefaction, taking the degree of saturation into account. This article presents an experimental study on the unstable behavior of sand as a function of its initial degree of saturation. Saturation states are defined and three saturation zones are investigated as a function of their pore fluid distribution patterns. Cyclic triaxial tests are performed on Fontainebleau sand to study the unstable behavior of each saturation zone. The results show that a soil can liquefy even if it is not initially fully saturated. They also provide new data on the role of suction and pore fluid compressibility in the unstable behavior of granular materials. The final aim of this article is to study the general unstable behavior of Fontainebleau sand under cyclic loading, and more specifically the influence of the degree of saturation on the triggering of these instabilities.

A thermomechanical constitutive model for unsaturated clays

A thermomechanical constitutive model for unsaturated clays is presented in this paper based on an existing model for saturated clays originally proposed by the authors. The saturated clay model was formulated in the framework of critical state soil mechanics and modified Cam-clay. The existing model has been generalised to simulate the experimentally observed behaviour of unsaturated clays by introducing Bishop’s stress and suction as independent stress parameters and modifying the hardening rule and yield criterion to take into account the role of suction. The number of modelling parameters was kept to a minimum, and they all have clear physical interpretations, to facilitate the usefulness of model for practical applications. A step‐by‐step procedure for parameter calibration is also described. The model was finally evaluated using a comprehensive set of experimental data for the thermomechanical behaviour of unsaturated soils. Based on the results, the model is able to simulate the principle aspects of thermomechanical behaviour of unsaturated clays in a good manner.

Influence of saturation degree and role of suction in unsaturated soils behaviour: application to liquefaction

The effect of the pore fluid compressibility on liquefaction has been studied by various authors. But few papers have been published about the role of suction in cyclic behavior of unsaturated soils. Most of these works use Skempton coefficient B as a reference in terms of saturation degree to analyze their results. The use of B in experimental conditions is convenient, but is not accurate when studying liquefaction behavior, since effects of suction are neglected. In this paper, the influence of saturation degree on mechanical behavior of a soil under dynamic loads is studied. Cyclic undrained triaxial tests were performed on sand samples, under various levels of saturation. Soil-water characteristic curve was used, in order to study influence of suction. The first results confirm that when the degree of saturation decreases, the resistance increases. Initial positive suction tends to stiffen the soil. It also appears that the presence of air delays the occurrence of liquefaction, but doesn’t prevent it. Indeed, liquefaction is observed, whether the soil is saturated or not.

Endoscopic Ultrasound-Guided Fine-Needle Aspiration of Pancreatic Lesions: A Systematic Review of Technical and Procedural Variables.

Endoscopic ultrasound (EUS)-guided tissue acquisition has emerged over the last decade as an invaluable diagnostic tool in approaching the different pancreatic lesions. Given the safety and minimal invasiveness of this approach combined with the high diagnostic yield, it became the standard of care when dealing with different pancreatic pathologies. However, some variables regarding this procedure remain not fully understood. These can influence the diagnostic yield of the procedure and include the presence of the on-site cytopathologist, the type and size of the needle used as well as obtaining aspiration versus core biopsy, the number of passes and the sampling technique, and the role of suction and stylet use among others. We performed a comprehensive literature search using PubMed, Google Scholar, and Embase for studies that assessed these variables. Eligible studies were analyzed using several parameters such as technique and procedure, with the aim of reviewing results from an evidence-based standpoint.

The role of suction and degree of saturation on the hydro-mechanical response of a dual porosity silt–bentonite mixture

To better understand the hydro-mechanical behavior of dual porosity expansive clays, three groups of tests were carried out. First, isotropic free drying and free wetting tests were performed to determine both branches of the soil water retention curve of a silt–bentonite mixture and its parameters. Next, constant suction oedometer tests at different matric suctions were employed using osmotic method. Finally, wetting–drying cycles were imposed on the samples in oedometric condition. At the end of wetting–drying tests, different suction values were enforced on the specimens and consolidation tests were performed, while the suction values were regulated through the samples using the osmotic method.Cross-examination of results indicates good consistency between the observed behaviors from different tests: Results of constant suction oedometer tests confirm the hardening phenomenon at low suctions indicated by the free drying test. Besides, all tests show that the amount of the suction hardening is negligible at suctions between the air entry of macropores and that of the micropores.However, the results contradict the physical models of hydro-mechanical behavior of expansive clays which do not take into account the suction induced hardening in the range of suctions less than the air entry value. Moreover, while most of the models assume that the shrinkage limit and air entry suction are coincident; results of the free drying test show the coincidence of the shrinkage limit and the air entry value of micropores.

Role of suction in sandy beach habitats and the distributions of three amphipod and isopod species

Sandy beach ecology has progressed rapidly with the emergence of several theories developed on the basis of understanding of hydrodynamic and morphodynamic processes on sandy beach habitats. However, the possible role of dynamic geophysical processes in the sediments remains poorly understood. The present study aims to explore the role of such geophysical processes in the sediments in forming the habitat environment and how they influence the species distributions. We conducted sets of integrated observations and surveys on intertidal and supratidal geophysical environments and the distributions of three amphipod and isopod species at four exposed sandy beaches located on the Japan Sea coast of Niigata Prefecture, Japan. The field results combined with a series of laboratory soil tests demonstrate that suction governed the variability of habitat environments observed, involving the degree of saturation, density, and hardness of the cross-shore intertidal and supratidal sediments, depending on the severity of the suction-dynamics-induced sediment compaction. While the observed species abundances were consistent with existing theories relating to intertidal and supratidal species, the observed magnitudes of suction were responsible for the distribution limits of the amphipods Haustorioides japonicus and Talorchestia brito and the isopod Excirolana chiltoni manifested consistently throughout the different beaches. The results of controlled laboratory experiments and field tests further revealed three distinctive suction-induced mechanisms, associated with their burrowing and physiology and the stability of the burrows. The novel role of such suction-induced geophysical processes in forming the habitat environment and influencing the species distributions may advance our understanding of sandy beach ecology in intertidal and supratidal zones.

Suction component in adhesion of mushroom-shaped microstructure

To shed light on the role of suction in adhesion of microstructure with mushroom-shaped terminal elements, we compared pull-off forces measured at different retraction velocities on structured and smooth surfaces under different pressure conditions. The results obtained allow us to suggest that suction may contribute up to 10 per cent of the pull-off force measured on the structured surfaces at high velocities. We therefore conclude that the attachment ability of this biomimetic adhesive must not be solely based on van der Waals forces. Our experiments also suggest a change in visco-elastic properties of the structured surfaces compared with the bulk material. Based on the results obtained, it is assumed that this adhesive may be suitable in dynamic pick-and-drop processes even under vacuum conditions at which sufficiently high adhesive capability is maintained.

Soil-moisture Retention Characteristics of Earth Materials in the Weathering Profile over a Porphyritic Biotite Granite

Problem statement: Three broad morphological zones and several sub-zones were differentiated within the weathering profile based on variations in earth materials and the degree of preservation of original bedrock minerals, textures and structures. Approach: The topmost Zone I (Grade 6) is some 12 m thick and comprises completely weathered bedrock materials (mainly a stiff, clayey sand) with indistinct relict bedrock textures. Results: The intermediate Zone II (Grades 3, 4 and 5) is some 30 m thick and consists of in situ, moderately to highly weathered bedrock materials (mostly friable, gravelly silty sands and coreboulders) that indistinctly to distinctly preserve the original bedrock minerals, textures and structures; the degree of preservation increasing with depth. The bottom Zone III (Grade 2) consists of continuous bedrock with effects of weathering only along and between structural discontinuity planes; the earth materials of zones I and II thus representing the residual soil over bedrock. Constant volume samples show a general increase in porosity, silt and clay fractions up the weathering profile, but a corresponding decrease in the sand and gravel fractions with sub-zone IC having the highest density and lowest porosity. Soil-moisture retention curves, determined with the pressure plate method, show increasing suctions from 0-4.19 pF (0 to -1,500 kPa) with decreasing moisture contents of 35-18% for sub-zone IC samples, 32-7% for sub-zone IIB samples and some 25-4% for sub-zone IID samples. Conclusion/Recommendations: These soil-moisture retention variations reflect textural differences and point to the inherent role of suction in the unsaturated earth materials. Differences in the volumes of calculated drainage and storage pores indicate that the earth materials of sub-zone IC will have the lowest rates of infiltration and percolation, whilst those of sub- zone IID will have the fastest rates and those from sub-zone IIB, intermediate rates.

Manipulating the Flow over Spherical Protuberance in a Turbulent Boundary Layer

Means of controlling the flow over a large spherical protuberance were examined. The role of suction around the base of the protuberance in reducing or even eliminating the necklace vortex created by the protuberance was considered. In the absence of suction, this vortex was lifted by the low base pressure existing behind the protuberance into the wake, thus affecting the turbulence level along its path. Large vortex generators placed upstream of the protuberance were able to delay local separation of the flow over the protuberance, thus affecting the symmetry of the wake and the level of turbulence on one side or the other. Observations made using flow visualization were supplemented by hot-wire measurements. The experiments were carried out at low speed at Reynolds numbers that did not exceed 3 x 105.

Effects of suction/blowing on the lower branch modes of the incompressible boundary layer flow due to a rotating-disk

In this study a theoretical approach is pursued to investigate the effects of suction and blowing on the structure of the lower branch neutral stability modes of three-dimensional small disturbances imposed on the incompressible von Karman’s boundary layer flow induced by a rotating-disk. Particular interest is placed upon the short-wavelength, non-linear and nonstationary crossflow vortex modes developing within the presence of suction/blowing at sufficiently high Reynolds numbers with reasonably small scaled frequencies. Following closely the asymptotic framework introduced in [1], the role of suction on the non-linear disturbances of the lower branch described first in [2] for the stationary modes only, is extended in order to obtain an understanding of the behavior of non-stationary perturbations. The analysis using the rational asymptotic technique based on the triple-deck theory enables us to derive initially an eigenrelation which describes the evolution of linear modes. The asymptotic linear modes calculated at high Reynolds number limit are found to be destabilizing as far as the non-parallelism accounted by the approach is concerned, and they compare fairly well with the numerical results generated directly by solving the linearized system with the usual parallel flow approximation. An amplitude equation is derived next to account for the effects of non-linearity. Even though the form of this equation is the same as that of found in [2] for no suction, it is under the strong influence of suction and blowing. This amplitude equation is shown to be adjusted by a balance between viscous and Coriolis forces, and it describes the evolution of not only the stationary but also the non-stationary modes for both suction and injection applied at the disk surface. A close investigation of the amplitude equation shows that the non-linearity is highly destabilizing for both positive and negative frequency waves, though finite amplitude growth of a disturbance having positive frequency close to the neutral location is more effective at destabilization of the flow under consideration. Finally, a smaller initial amplitude of a disturbance is found to be sufficient for the non-linear amplification of the modes in the case of suction, whereas a larger amplitude is required if injection is active on the surface of the disk.

Treatment of primary spontaneous pneumothorax in Switzerland: results of a survey

Few trials to guide clinical management of primary spontaneous pneumothorax (PSP) exist. This study aims to reveal current practice in the management of PSP in Switzerland, to define the level of consensus and to provide evidence in guiding clinical practice. Questionnaires were sent to 355 departments of internal medicine and surgery in Switzerland and 114 (32.1%) were available for analysis. Recommendations based on the highest consensus are extracted. Good to very good consensus is reached in 63% of all management options. There is very good consensus for the management of clinically stable or unstable patients with small or large PSP, for the treatment of patients without chest tubes and the operative management of persistent air leaks and recurrence prevention. There is good consensus concerning the role of suction, the size of chest tubes, and the use of CT-scans. However, there is little consensus concerning chest tube removal and chemical pleurodesis. Good and very good consensus exists for most management options in the treatment of PSP in Switzerland. The given recommendations can be used as evidence in guiding clinical practice in circumstances where no evidence of higher levels exists.

Apoplasm hydrostatic pressure on growth of cylindrical cells

According to the model frequently used as reference, plant cell growth occurs only when turgor surpasses a threshold. This model was proposed considering a cylindrical cell of constant wall thickness immerged in a water solution, with viscoelastic behaviour, hydraulic conductivity, variable extensibility, and unidirectional elongation. The author, Lockhart (1965), did not consider the effects of apoplasm hydrostatic potential, a subject treated later by Calbo and Pessoa (1994) who argued that this component of cell potential would interfere with cell growth rate. To evaluate this effect, where possible the same deductive procedures as those employed by Lockhart were used here, which resulted in a set of equivalent equations for cell growth, turgor and water potential, developed with respect to physico-chemical variables. Relationships were derived from the conductivity equation, the definition of extensibility, Hook's law, and considering that the tension on cell wall transversal section is proportional to turgor and apoplasm hydrostatic potential. The numeric solutions for the equations showed that suction increased extension rate at the beginning of cell growth. Some experiments on plant growth and structural models of cell walls are discussed to point out the role of suction on wall tensioning and cell hydration during cell elongation.

Anisotropic bounding surface plasticity with rotational hardening for unsaturated frictional materials

A constitutive model for inelastic mechanical behaviour of inherently anisotropic soils is presented:An existing single surface model with isotropic hardening for empty and saturated cohesionless soils [1] and general bounding surface plasticity [2-3] form the basic framework to which rotational hardening is added. The concept of state parameter [4] is used to predict the response of soil to different densities, drainage and stress paths. Unsaturated behavior is described using net stress and suction as independent stress variables and modifying the basic constitutive surface parameters and hardening rules to consider the role of suction.

State Surfaces of Partially Saturated Soils: An Effective Pressure Approach

State surfaces may be given by interpolation of experimental data or may represent the integration of linear or nonlinear elastic constitutive equations. Anelastic behavior may also be considered if only loading is taken into account to ensure the uniqueness of the surface. State surfaces are usually defined in the (p, q, s) space, where p, q, and s represent, respectively, the excess of mean stress over air pressure, the deviatoric stresses, and suction. An alternative approach assumes similar constitutive equations but defined in the space (p′, q), where p′ represents the effective pressure. This latter approach is extended to the space (p′, q, s) and improved to carefully deal with the role of suction, in conjunction with the confining pressure, in controling soil expansion (swelling).

The Role of Suction in the Adhesion of Limpets

ABSTRACT Experiments were performed to determine the mechanism by which limpets attach to the substratum. Pressure measurements were made under the feet of three species of limpets as they were forcibly detached from the substratum. These measurements show that limpets actively decrease the pressure under their feet, and in almost every case this pressure decrease can account for all of their tenacity. The results are the same whether the pressure transducer is flush with the surface or connected to the surface via a tube. The tenacity of limpets is dependent on ambient pressure, as predicted for a suction mechanism. Leaks disrupt the attachment of limpets. Thus, for at least an hour after they have been moving, suction appears to be the primary attachment mechanism of limpets. Limpets using suction often have tenacities greater than 0.1 MN m−2, which corresponds to pressures under the foot lower than 0MPa. If limpets have more than a few hours to attach, approximately 30% of them form a different, stronger attachment that appears to be based on glue. These limpets remain stationary for extended periods. It is hypothesized that limpets in the field alternate between the use of suction and glue, depending on their need for mobility.

The Role of Suction in the Adhesion of Limpets

The Role of Suction in the Adhesion of Limpets

Magnetohydrodynamic Boundary Layer Flow with Suction or Injection past a Semi-Infinite Flat Plate

The steady two-dimensional magnetohydrodynamic boundary layer flow with a uniform suction or injection past a semi-infinite flat plate in the cross fields is studied on the assumption of small magnetic Reynolds number. The transformed boundary layer equation is found to be a non-similar one and an attempt is made to solve it numerically by a difference-differential method originated by Hartree and Womersley. Numerical results for various values of parameters are given for the velocity profile, coefficient of skin friction, displacement thickness and momentum thickness, and the effects of the magnetic field on a role of suction or injection are investigated.