High Suction Research Articles

Theoretical method for the estimation of vapour conductivity for unsaturated soil

The liquid water movement is commonly considered in the seepage analysis related to the unsaturated soil (e.g, residual soil above the ground water table). The hydraulic conductivity of unsaturated soil is commonly considered to decrease with the increase in soil suction (or decrease in the degree of saturation). As a result, the estimated hydraulic conductivity of unsaturated soil from the conventional method is very low in the high suction range (i.e., beyond the residual suction). However, the experimental results from recent studies indicate that in the high suction zone, the hydraulic conductivity of unsaturated soil may increase with an increase in soil suction. In addition, recent studies also indicate that in the high suction zone (i.e., greater than 3100 kPa), water in soil moves mainly in the vapour form. As a result, the estimation of the hydraulic conductivity of unsaturated soil due to vapour flow in soil is crucial for engineers in the estimation of water transmission through a relative dry soil. In this note, the theoretical method is proposed for the estimation of vapour conductivity from the soil-water characteristic curve. The proposed method is rational and it has the theoretical basis without any empirical parameter. It is observed that the estimated results from the proposed method agree well with the results reported in the published literature.

The Spread of Droplets and Aerosols of Surgical Motor Handpiece Irrigation Using Different Suction Systems

Objective: This study aimed to compare the effectiveness of various combinations of dental suction devices in reducing the amount and distance of spread of aerosols and droplets using an electrical surgical motor model with a self-irrigation system.Materials and Methods: In a standard single-chaired air-conditioned ventilated dental clinic, an electrical dental surgical motor with a high-speed handpiece (Implantmed) cooled with 0.2% fluorescein containing normal saline was used to drill a gypsum block mounted on a phantom head in a supine position. A single operator performed thrice each of the following suction settings: (a) no suction, (b) low-volume suction, (c) low-volume + high-volume suctions, and (d) low-volume + external oral suctions. Aerosols (0.1–5 μm) were measured with a particle counter at the mouth opening of the phantom head, and droplet sizes and distances were analyzed via a machine learning algorithm by identifying fluorescence droplets on pre-loaded pieces of paper on the floor for each group.Results: The different suction systems have different performances in terms of droplet distance (p = 0.007), whereas using (c) high volume suctions (41.1 ± 22.9 cm) and (d) external oral suction unit (39 ± 18.2 cm) had significantly reduced the spread of droplets when compared with (a) without suction (58.9 ± 17.1 cm). Using (d) external oral suction or (c) high volume suction could reduce the number for all droplet sizes. The use of (c) high volume suction was most effective in reducing aerosol count of 0.3–1 μm, while (d) external oral suction was most effective in reducing aerosol count of 3–5 μm.Conclusions: Both external oral suction and high-volume suction were effective in reducing aerosols and droplets generated by the irrigation of a surgical high-speed motor handpiece. External oral suction could be an effective alternative to high volume suction in dental surgical procedures to reduce the spread of aerosols and droplets.Clinical Relevance: External oral suction or high-volume suction should be used in conjunction with low-volume suction in surgical procedure to reduce the spread of aerosols and droplets in a dental clinic environment.

Experimental study on mitigating extreme roof suctions by passive vortex generators

High wind suction always occurs at the edges and corners of large-span low-rise flat roofs, which can lead to severe damage to roof elements and even to the overall destruction of the roof. The passive vortex generator (PVG), a new device which can generate streamwise vortices, is proposed to mitigate the extreme wind suction on a low-rise large-span flat roof. Wind tunnel tests were conducted to investigate the control effect of PVGs, and parametric analysis was performed, with parameters including the height, length, opening angle, tilt angle and interval of PVGs. The maximum reduction of peak wind pressure under the worst wind incident angle with PVGs reaches 74%, and they show excellent control effects at all wind incident angles. The recommended parameters of PVGs are also provided for engineering practice. Spectrum analysis and the structure of the conical vortices show that the streamwise vortices generated by PVGs which mixed into the conical vortices and can distort or destroy the conical vortices, and then alter the position of conical vortices axis and reduce the reattachment range. Meanwhile, the high frequency fluctuation is increased and the low frequency fluctuation is reduced accordingly.

FRACTAL-BASED MODELS STUDY OF THE RELATIVE HYDRAULIC CONDUCTIVITY AND SWCC OF BENTONITE BY SYNCHROTRON RADIATION SAXS AND X-RAY COMPUTED TOMOGRAPHY

Fractal-based approaches have become popular for describing the hydraulic functions. The SWCC and relative hydraulic conductivity were calculated and compared based on fractal models by the fractal dimension ([Formula: see text] determined by small angle X-ray scattering (SAXS) and X-ray computed tomography (CT). Pore structure parameters including pore size, [Formula: see text], tortuosity and tortuosity fractal dimension, porosity, characteristic length were investigated. The SWCC and relative hydraulic conductivity were predicted, compared and verified. The results indicated that the [Formula: see text] of GMZ01 calculated by SAXS and CT were 2.60 and 2.72, respectively, and the difference was small. The [Formula: see text] of GMZ01 calculated by CT was 2.62. [Formula: see text] calculated by SAXS and CT has a large difference. Nitrogen adsorption revealed the effectiveness of SAXS in predicting porosity in the nanoscale self-similar interval. A SWCC fractal model considering the tortuosity fractal dimension was improved. The tortuosity of GMZ01, CaGMZ, GMZ07 and SY are calculated as 1.53, 1.47, 1.60 and 1.29, respectively. When the tortuosity was considered, the hydraulic conductivity became lower. For GMZ01, the SWCC predicted by the fractal dimension measured by SAXS was closer to the experimental data than the SWCC predicted by the fractal dimension measured by CT. The fractal model was difficult to describe SWCC under low matric suction, while the predicted SWCC had a good correlation with the experimental value in high matric suction. The relative hydraulic conductivity calculated by Xu and Yu model was larger than that calculated by Xu model.

Fighting Airborne Spread of COVID-19: An Innovative, Economical and Effective High Vacuum Extra Oral Dental Suction System (HVEDS) for Dental Practices

Introduction: The COVID-19 pandemic has led to a great deal of commentary about the airborne spread of the disease. It is of special concern for dentists as most dental procedures generate a significant amount of aerosols and droplets. Given such high risk and inevitable aerosol production in dentistry, special precautions and protective measures to ensure the safe delivery of dental treatment are directed. To ensure negligence-free dental practice, in addition to the standard protective procedures and measures, a high vacuum extra oral dental suction system is a mandated dental armamentarium. Aims and Objectives: Most commercially available vacuum aspirators are pricey and require special units with which they can work. In a country like Pakistan, where an expensive armamentarium is neither available nor easily affordable, we present an economical yet effective, high volume extra oral dental suction system for the dental offices which does not require a heavy monetary investment. Equipment: An in-house alternate to the commercially available extra oral aspirator is introduced here. We devised a make-shift extra oral aerosol aspirator that can be effortlessly assembled with the materials easily available around dental offices. Result: When tried in use, the aerosol and spatter were eliminated through the cone-shaped oil key and collected into the collection bin as observed visually. The equipment, due to its high vacuum suction capability, sucks the aerosol and splatter from the working area to the collection cone. Conclusion: Post COVID-19, we can expect a lot of changes in the infection control practices and guidelines. The use of extra oral vacuum aspiration along with the conventional protocol has been recommended to protect both the dental staff and the patients as the high vacuum extra oral aspirator may offer a way to reduce the generated aerosol particulate

Invention and Pilot Study of the Efficacy and Safety of the SUPRAtube Device in Continuous Supraglottic Aspiration for Intubated and Mechanically Ventilated Patients.

BackgroundBronchoaspiration of content that accumulates in the supraglottic area (eg, saliva, gastroesophageal reflux) is a risk factor for ventilator-associated pneumonia. A continuous supraglottic suction system may decrease the risk of bronchoaspiration in these patients.Objective(1) Constructing a conceptual model and functional prototype of a continuous supraglottic suction device for use in humans; (2) defining functional characteristics in ex vivo swine head models; and (3) evaluating its efficacy and safety in mechanically ventilated patients.MethodsStudy conducted in three phases. First phase: definition of distances and diameters of the triangle determined by dental arch, posterior oropharynx and vallecula, and diameter of the oropharynx in axial projection; and identification of the declining area of supraglottic suction. Second phase: design engineering and functional prototype evaluated in ex vivo models. Third phase: evaluation of device use in terms of safety and efficacy in ventilated patients.ResultsWe obtained a final functional model of the SUPRAtube device injected into PVC for medical use. Device effectiveness in in vitro simulation showed a high and fast suction capacity of liquid and thick volumes. Study of swine heads allowed to validate the shape, size and functional fenestration of the device. Study in intubated and mechanically ventilated patients showed a high supraglottic suction capacity and the absence of local adverse events during 72 (7–240) hours of continuous operation.ConclusionOur study describes the process of conceptualization, design and production of a practical, safe, low-cost continuous supraglottic suction device without representing antibiotic pressure, which appears to be a new complementary preventive strategy for the standard management of intubated and mechanically ventilated patients.

A study of the soil-water reliability model in the whole matric suction range

Soil–water characteristic curves (SWCCs) are considered as a basis for analyzing fluid–solid coupling of unsaturated soil. How to estimate the SWCC over the whole region with matric suction based on the limited local datasets is challenging. Laboratory test is separately carried out on the ranges with low and high matric suctions of the undisturbed residual soil widely distributed in southeast China. With the test data, a model for SWCCs of soil in the whole range with matric suction is established by applying the reliability analysis method. Through analysis and verification based on the test data and data of 52 samples of three types of soil (sand, silt-loam and clay) obtained from UNSODA, it is found that the model parameters involved in the model show significant physics meaning. The model can be used to estimate the SWCC of soil within the whole range with matric suction according to part of the data (in the low or high matric suction part). Compared with the other models, the model is robust and is applicable for acquiring SWCCs of different types of soil within the whole range matric suction with R2>0.98. In addition, the model provides an important method to obtain SWCCs of soils with different texture, and is of the reference significance to the geotechnical AI analysis.

Non-isothermal water retention curve model for adsorption

Non-isothermal water retention curve (WRC) in high suction range is a fundamental and interpretative tool to describe the behavior of bentonite and is crucial to ensure the safety and effective operation of high-level nuclear waste repository. In this study, an adsorption equation at given water content is proposed according to Kelvin equation, Clausius-Clapeyron equation and the adsorption enthalpy equation. Then, the proposed adsorption equation is incorporated into van Genuchten-Mualem model to establish a non-isothermal WRC model for adsorption. Four series of non-isothermal WRC data in a temperature range (293∼353 K) and high suction range (>1 MPa) from four different soils are employed to illustrate the application and performances of the proposed model. The proposed WRC model provides good agreement between the calibrated/predicted and measured non-isothermal WRCs.

Influence of soil and hydraulic conditions on the processes of internal erosion, cavity formation and collapse behind coastal structures

Collapse of cavities formed by internal erosion has occurred at the back sides of seawalls and quaywalls all over the world. Here, the process of internal erosion was investigated by conducting prototype-scale experiments. A series of processes of cavity formation and collapse were reproduced considering different grain size distributions and water level conditions. Suction, that is, negative pore water pressure relative to atmospheric air pressure, affected the formation of cavities and the timing and scale of their collapse. The scale of the collapse was large under high suction. The types of hydraulic force also affected the cavity formation. A symmetrical cavity was formed under one-dimensional water level fluctuations, whereas the cavity expanded in size toward the wave-incident boundary under incident waves. Cavity collapse was found to be caused by a decrease in suction accompanied by a rise in groundwater level. The collapse occurred within the area where ground surface displacement was observed, and the maximum ground surface displacement (dmax) was correlated with the ratio of the maximum width of the cavity and its depth (B/L) regardless of the ground height and water level fluctuation range. Countermeasure against the internal erosion using a two-layer filter was systematically studied in a series of sand filtration tests and prototype-scale hydraulic experiments. The filter maintained a sufficient deterrent effect under various hydraulic and dynamic forcing when the uniformity coefficient of the filter (DF60/DF10) was higher than 3.0, and the median particle diameter ratio (DF50/DS50) was less than or equal to 20.

A novel unified model for volumetric hardening and water retention in unsaturated soils

This paper presents a novel unified model coupling soil volumetric hardening and water retention. The volumetric hardening law is formulated using the effective stress concept and can be applied to various soil types with unified formulations. This law also considers the influence of stress-induced anisotropy, and provides an enhanced prediction of soil response under elevated stress levels and loading–unloading cycles. Furthermore, this law is coupled with a new Soil Water Retention Curve (SWRC) model by considering the dependency of SWRC on the volume change. The new SWRC model captures the hysteretic nature of the water retention, and offers an improved prediction of the hydraulic path for high suction levels. The SWRC model also allows capturing the experimentally observed reduction in the degree of saturation which may occur during the early compression stage under constant suction. With the coupling of the volumetric hardening law and the SWRC model, the unified model is finally developed. The unified model is validated with reasonable accuracy against a wide range of experimental data reported in the literature on clay, silt and sand.

Coupled hydro-mechanical analysis of compacted bentonite behaviour during hydration

This study analyses the response of compacted bentonites upon hydration based on a coupled hydro-mechanical elasto-plastic framework. As an alternative to multi-porosity interpretation, the framework was selected based on the experimental evidence of adsorbed water behaviour in bentonites and the volumetric response at saturated states, apparently independent of its initial state. Based on these premises, a water retention model was formulated using an explicit distinction between adsorbed water and free water, enabling the postulation of the water properties and behaviour depending on its state. In order to effectively account for the transition between unsaturated to saturated state, that can occur in a wide range of suctions, the stress–strain constitutive equations are written in terms of an effective stress and degree of saturation framework. The mathematical formulation was implemented in a finite element code and used to simulate and interpret the behaviour of MX-80 bentonite compacted in different forms during hydration for several stress paths, including loading and unloading cycles after saturation. A good agreement of the model with experimental results was obtained using a consistent set of parameters describing the saturated state behaviour. The typical non-linear swelling pressure development was interpreted through the two-way coupling between the water retention behaviour and elasto-plastic compressibility. The possible high suctions at saturated states explain the swelling potential after full hydration. Overall, this study offers new perspectives on the role of hydro-mechanical interactions in bentonite behaviour upon hydration.

Numerical Analysis of Treatment of Highly Expansive Soil by Partial Replacement with Crushed Concrete

The major goal of this research work is to treat one type of the known problematic soil (expansive soil) by partial replacement with crushed concrete material which is found in large quantities and distributed on large area of Mosul city. Numerical analysis using Geo-Studio program 2007 is utilized to analyze this problem. Several parameters are considered in this study such as; thickness of the crushed concrete layer of (20, 30, 40, 50, 60, and 70) cm, width of crushed concrete layer is equal to width of footing B, 1.5B and 2B, soil with low and high suction and the time required to complete swelling are studied. All the mentioned parameters were studied with and without presence of footing. The main results of the analysis showed decreasing in vertical swelling upon increasing the thickness and width of the crushed concrete layers. The use of crushed concrete layers is more active in lowering the vertical swelling of high suction soil than that of low suction soil. Finally, the increase in thickness of the crushed concrete layers reduces the increase in vertical swelling with time.

Gastrointestinal Residue Removal Using a Balloon Overtube under Ultrathin Endoscopic Navigation: Ex Vivo and In Vivo Experimental Studies.

Pooled gastric residues involving blood clots and food interrupt appropriate endoscopic intervention, leading to poor outcomes in endoscopic hemostasis and lifesaving. However, procedures and devices that enable the effective removal of gastrointestinal residues remain unsatisfactory. This study aimed to evaluate the efficacy and safety of our developed suction method in ex vivo and in vivo studies. We created a hand-made device with a large suction diameter, consisting of a balloon overtube and an ultrathin endoscope for navigation. In the ex vivo study, we compared the success rate and the suctioning time for four types of simulated residue between a standard endoscope and our device. Our device had s significantly higher suction ability and a shorter procedure time than the standard endoscope. The subsequent in vivo animal study involved five beagle dogs that were administered with food jelly to mimic gastric residue. Suction was performed twice for five dogs (ten attempts). The outcome measure was the successful procedure rate; secondary outcomes were procedure-associated complications and procedure time. The procedure was successful in all attempts, without any complications. The mean procedure time was 5 min. This novel method enabled the efficient and safe removal of gastric residue, and our findings will likely lead to the development of the instrument.

Investigation of the hydraulic conductivity of an unsaturated compacted bentonite/claystone mixture

A pre-compacted MX80 bentonite/Callovo-Oxfordian (COx) claystone mixture has been proposed as a candidate sealing material in a French deep geological repository for high-level radioactive waste. An in-depth understanding of the hydraulic property of this material is essential for accessing the over-pack corrosion and nuclide migration along the gallery. In this study, water flow in the compacted bentonite/claystone mixture was investigated by carrying out infiltration and water retention tests under constant-volume conditions alongside detailed microstructure observation. The evolution of total water hydraulic conductivity with suction was experimentally determined based on the instantaneous profile method. It was observed that the measured total hydraulic conductivity increased slowly at high suctions, then quickly at low suctions and finally approached the saturated value. A new method was developed based on the evolving pore structure, accounting for both vapour and liquid-water hydraulic conductivities. The total hydraulic conductivity predicted by the proposed method agreed well with the measured value, indicating the reliability of the predictive method. The vapour hydraulic conductivity was larger than the liquid-water one at a suction larger than 15·2 MPa, while liquid-water hydraulic conductivity became dominant at a suction lower than 15·2 MPa. In addition, based on the predicted vapour and liquid-water hydraulic conductivities, a numerical model was set up to simulate the water infiltration process. Comparison between the simulation and the measurement showed close agreement, validating the two-phase water flow mechanism in the bentonite/claystone mixture.

Micro-scale analysis on shear characteristics of unsaturated soil by considering capillary suction and adsorption suction based on DDA

In this research, Discontinuous Deformation Analysis (DDA) is extended to analyze shear characteristics of unsaturated soil by separately considering capillary suction and adsorption suction at micro-scale. First, the developed matric suction model is validated by comparing simulation results with the analytical solution. Then, the shear characteristics of unsaturated cohesionless soil are simulated and compared with experimental results. The “peak effect” of the shear strength is reproduced, and it is quantitively explained by the proposed micro parameter CSN (number of the capillary bridge). Further, in the high suction range of cohesive soil, adsorption suction is the dominant factor for apparent cohesion. As the contact area of the clay layer decreases slightly in the high suction range, adsorption suction controls shear strength, therefore, there is seldom a “peak effect” of the shear strength for cohesive soil. The extended DDA provides an innovative approach to analyze the micro mechanism of matric suction in a wide suction range.

A bound water model for numerical simulation of SWCC in the wide suction range based on DDA

In this study, Discontinuous Deformation Analysis (DDA) method is extended to simulate Soil-Water Characteristic Curve (SWCC) by considering both capillary water and bound water at the micro-scale. First, a simple and practical bound water model is proposed and incorporated into DDA program to simulate SWCC in the high suction range. Then, to prove the availability of the developed program, the extended DDA is used to simulate the SWCCs of two types of fine sand with kaolin clay in a wide suction range. The simulation results agree with the experimental results, which demonstrate that the extended DDA is an alternative method for simulating and analyzing SWCC of both cohesionless soil and cohesive soil. Finally, one of the influential factors specific surface area is theoretically analyzed. This study provides an approach to simulate the matric suction of unsaturated soil, and the extended DDA could be a potential tool for unsaturated soil research.

Experimental investigation of wind pressure characteristics and aerodynamic optimization of a large-span cantilevered roof

Cantilevered roof is particularly vulnerable to wind because high suction loads often occur on the rooftop due to flow separation. However, wind load characteristics associated with cantilevered roof have not been fully understood. In this paper, a 1/100 scale model of a cantilevered roof, over a grandstand, has been tested in a turbulent boundary layer flow, with particular emphasis on characterizing the wind pressure distribution on the cantilevered roof, and assessing the performance of several aerodynamic optimization devices. The results indicate that large wind suction generally occurs near the windward edge on rooftop surface. The effect of approaching wind direction is evident, which can influence the distribution pattern and value of wind pressure. For the effect of roof inclination, the down-sloping roof is found to be more appropriate since it results in most significant reduction in mean wind pressure, as well as the net lifting and bending moment coefficients. Furthermore, it is shown that adding a vented leading edge slot can effectively reduce the rooftop wind suctions. The maximum reduction in mean and peak suction loads is respectively 30% and 45%.

Validation of Semi-empirical Models for the Prediction of Swelling Stress for Compacted Unsaturated Expansive Soils

Unsaturated swelling soil behaviour is governed by the matric suction, thus the predetermination of swelling stress for expansive unsaturated soil requires rigorous procedures. However, some swelling stress equations assume full saturation of the soil, which leads to the over-design of infrastructure. This study focused on the validation of predictive swelling stress models that correlate suction with other soil properties. Three models were developed, and independent data were used for the validation of the developed models. The predicted swelling stress values were compared to the values predicted by the randomly selected predictive models from the literature. Series of initial studies include the determination of basic soil characterization and swelling stress along with soil mineralogical compositions were conducted to determine their geotechnical properties with their corresponding degree of expansiveness. The replicated expansive soils were also studied for suction, using filter paper techniques to obtain the soil's unsaturated parameters. Based on the obtained experimental results, three models were developed using a mathematical software package (NCSS11). Independent data obtained from a group of final year students working on the swelling stress response of expansive unsaturated soils at the geotechnical engineering Laboratory from the University of Johannesburg were used for the validation. The developed models showed good agreement with the independent data, having a coefficient of determination (R²) of 0.858, 0.931, and 0.890 for Eq. 4, 5, and 6, respectively. Compared to models selected from literature, which recorded R² values of 0.796 and 0.636 with an average variance of 0.097 and 0.257 respectively. The correlation variables showed that the degree of expansion represented by swelling stress demonstrated a proportionality with the moisture capacity along the drying and wetting path of the suction curves. Results suggest that the developed models can reasonably predict the swelling stress of compacted expansive soils at high suction values.

Rotationally symmetric flow of Reiner-Rivlin fluid over a heated porous wall using numerical approach

This research features one parameter family of solutions representing rotationally symmetric flow of non-Newtonian fluid obeying Reiner-Rivlin model. Such flows take place over a revolving plane permeable surface through origin such that fluid at infinity also undergoes uniform rotation about the vertical axis. Heat transfer accompanied with viscous heating effect is also analyzed. A similarity solution is proposed that results into a coupled non-linear system with four unknowns. Boundary layer structure is characterized by a parameter [Formula: see text] that compares angular velocity of external flow with that of the rotating surface. Solutions are developed by a well-known package bvp4c of MATLAB for full range of [Formula: see text]. Flow pattern for different choices of [Formula: see text] is scrutinized by computing both 2 D and 3 D streamlines. It is further noted that value of suction velocity is important with regards to the sign of axial velocity component. Boundary layer suppresses considerably whenever the surface is permeable. For sufficiently high suction velocity with [Formula: see text], entire fluid undergoes rigid body rotation. In no suction case, axially upward flow accelerates for increasing values of parameter [Formula: see text] in the range [Formula: see text], whereas opposite trend is apparent in the case [Formula: see text]. Results for normalized wall shear and Nusselt number are scrutinized for various choices of embedded parameters.

An effective stress constitutive framework for the prediction of desiccation crack in lime-treated soil: Experimental characterization and constitutive prediction

The present work investigates the desiccation effects on a lime-treated silty clay. Original experimental techniques have been developed to control suction conditions (with osmotic technique), to track volume variations and cracks occurrence upon drying. Free and constrained desiccations are performed to evaluate the shrinkage potential (for free drying) and the conditions of desiccation crack triggering (upon constrained drying). Also, indirect tensile tests and uniaxial compression tests are carried out to evaluate the strength and stiffness at various suctions. Those investigations have been performed on natural and lime-treated compacted silty clay in order to emphasize the benefits of the lime treatment in the triggering and/or mitigation of the cracking process. To simulate the field conditions of compaction and obtain specimens having geomechanical properties as close as possible of the real material on site, the particular kneading compaction process in a CBR mould was used, and the final specimens were cut at required sizes with a milling machine numerically controlled by computer (CNC). At the end, generalized effective stress framework with an effective stress parameter χ calibrated according to a power law is used to provide a constitutive interpretation of the occurrence of desiccation cracks in relation with the water retention properties, the soil stiffness, the tensile strength and the geometrical constraints of the soil specimens. It is observed that the cracks initiate under positive (compressive) effective stress. For the used compacted materials, it is demonstrated that the lime treatment postpones the occurrence of desiccation cracks, that are triggered at higher suctions. So, lime treatment plays a favourable role in the reduction of shrinkage and crack occurrence of soft soils subject to drying.