Suction Conditions Research Articles

Effect of wetting stress paths on mechanical behavior and instability of unsaturated soil in stress state space

In current study, a test program is designed to observe the influence of wetting stress paths on behavior and instability of unsaturated soil in stress state space. The mechanical behavior was studied by performing three test series in constant matric suction plane. In first series, water infiltration was performed together with shearing starting from zero (0 kPa) deviatoric stress. In second series, first water was infiltrated at zero (0 kPa) deviatoric stress then samples were sheared in drained pore water pressure conditions. In third series, water was first infiltrated at zero deviatoric stress then specimens were sheared in undrained pore water pressure conditions. Instability was studied in constant shear stress plane by first shearing soil up to predefined level of deviatoric stress then infiltrating water keeping deviatoric stress constant on the specimen. This research also describes how unsaturated soil behavior and instability is varied with variation in net confining stresses when suction is decreased from initial measured value to start water infiltration with different wetting stress paths and their effect on shear state and failure surface in stress state space. The test results revealed that the movement of stress paths was independent of net confining stress, matric suction and shearing conditions employed in the study.

Optimum operational conditions of surface suction leaching method for effective removal of partially accumulated salts from salt-damaged soil

Optimum operational conditions of surface suction leaching method for effective removal of partially accumulated salts from salt-damaged soil

Optimum operational conditions of surface suction leaching method for effective removal of partially accumulated salts from salt-damaged soil

Optimum operational conditions of surface suction leaching method for effective removal of partially accumulated salts from salt-damaged soil

극저온 냉각시스템용 스크롤 압축기 성능실험

This paper describes the performance test of a helium scroll compressor originally used for Gifford-McMahon (GM) cryocooler. This compressor can also be used for the reverse Brayton cryogenic refrigeration system. In this paper, the performance characteristics of a scroll compressor is experimentally investigated with helium and neon gas to obtain reference data for designing thermodynamic cycle of cryogenic refrigeration system. To maintain constant suction pressure during experiments, an experimental setup contains pressure regulation system which consists of three control valves and gas buffer. Pressures, mass flow rate and power consumption are measured for 400, 450, 500, 550 kPa of suction pressure condition. With experimental measurements, performance characteristics of a helium scroll compressor is investigated. The tested scroll compressor shows the higher isentropic efficiency with helium as a working gas than neon.

Analysis of Maxwell bioconvective nanofluids with surface suction and slip conditions in the presence of solar radiations

Several researchers have studied nanofluids over the past several decades and tried to identify potential agents that are added to nanofluids (nanoparticle suspensions) with tremendous thermal conductivity. In such suspensions, the Brownian motion of nanoparticles is the only means expected to be associated with the improved thermal conductivity of nanofluids, and the sections that may add to this are the subject of main conversation and discussion. In the current evaluation, the effect of Brownian motion has been investigated by injecting nanoparticles into the base fluid, and the existing fundamental information is available at creation. Propagation results show that this mixing effect can significantly increase the thermal conductivity of nanofluids. One of the interesting features of this model is that the temperature can be increased by the energy of sunlight, which is required for some industrial processes. The stretching property of the sheet is more conducive to the temperature rise. This model contains features that have not been previously studied, which is driving demand for this model in a variety of industries, now and in future generations.

The Duncan-Chang statistical damage correction model of unsaturated soil considering matric suction

In order to reflect the whole deformation process of unsaturated foundation soil, the consolidated drained triaxial compression test is carried out on the unsaturated soil of a foundation project. It is found that the partial stress-strain curve of unsaturated soil is similar to hyperbola, and the matrix suction has an obvious influence on the mechanical behavior of soil. The greater the matrix suction, the higher the partial stress of soil. According to the deformation characteristics and engineering characteristics of unsaturated soil, the Duncan-Chang hyperbolic model is selected as the basic model, and the statistical damage theory is introduced. Assuming that the micro element strength of unsaturated soil obeys the Weibull probability density distribution, the Duncan-Chang statistical damage model is established. By establishing the relationship between the initial tangent modulus and matrix suction, a new Duncan-Chang statistical damage model of the unsaturated soil considering matrix suction is established. The parameter analysis method is given, and the empirical expression of the Weibull distribution parameters is obtained, which is used to modify the model. The damage accumulation law of unsaturated soil under different matrix suction conditions is analyzed, and the partial stress-strain test curve of unsaturated soil is compared with the traditional Duncan-Chang model, which proves the feasibility and rationality of the model. The research results provide a certain reference for the study of mechanical properties and identification simulation of unsaturated soil.

Thermal transport analysis in stagnation-point flow of Casson nanofluid over a shrinking surface with viscous dissipation

In arteries blood flow is the usual example for a Casson fluid flow among the other vital utilizations of this fluid model. Thus, it would be helpful to study the Brownian motion diffusion and thermophoresis diffusion in Casson fluid for biomedical applications. In this analysis, the electrically conducting Casson nanofluid, with suction and convective boundary condition, has been addressed in a shrinking surface. The mechanism of convective heat transfer has been elaborated with Ohmic heating and viscous dissipation effects. The numerical solutions to the governing equations have been obtained by applying the similarity transformation to the nonlinear partial differential equations. The present model is employed to examine the viscoplastic characteristics in the porous regime. This dimensionless ruling problem, along with physical boundary conditions, is handled numerically by using a Runge–Kutta Fehlberg scheme. The outcomes of the present study show that the rate of heat and mass transfer at the surface of the shrinking sheet enhances with the growth in Casson fluid parameter and magnetic parameter. Furthermore, it is observed that the shear stress at the wall rises with the increment in magnetic parameter. Moreover, unsteadiness parameter is the decreasing function of heat and mass transfer rates.

Four-Year Monitoring Study of Shallow Landslide Hazards Based on Hydrological Measurements in a Weathered Granite Soil Slope in South Korea

To build a comprehensive understanding of long-term hydro-mechanical processes that lead to shallow landslide hazards, this study explicitly monitored the volumetric water content (VWC) and rainfall amount for a weathered granite soil slope over a four year period. From the 12 operational landslide monitoring stations installed across South Korea, the Songnisan station was selected as the study site. VWC sensors were placed in the subsurface with a grid-like arrangement at depths of 0.5 and 1.0 m. Shallow landslide hazards were evaluated by applying an infinite slope stability model that adopted a previously proposed unified effective stress concept. By analyzing the variations in the monitored VWC values, the derived matric suctions and suction stresses, and the calculated factor of safety values, we were able to obtain numerous valuable insights. In particular, the seasonal effects of drainage and evapotranspiration on the slope moisture conditions and slope stability were addressed. Preliminary test results indicated that continuous rainfall successfully represented the derived matric suction conditions at a depth of 1.0 m in the lower slope, although this was not the case for the upper and middle slopes. The significance of a future study on cumulative field monitoring data from various sites in different geological conditions is highlighted.

Compressional wave velocity and effective stress in unsaturated soil: Potential application for monitoring moisture conditions in vadose zone sediments

AbstractCompressional seismic (P‐wave) velocities were measured experimentally at different matric suctions and confining pressure states using a variety of sediments collected from the USDOE Hanford Site in southeastern Washington State. The P‐wave velocity was measured in variably saturated sediments using ultrasonic piezoelectric transducers, and matric suction was measured with a heat dissipation sensor. Desaturation of the samples occurred by means of evaporative drying. We propose a model to relate changes in P‐wave velocity to soil stress conditions using an effective stress formulation that includes capillary stress as well as adsorptive stress. We show that compressional wave velocities can be related to matric suction and confining stress using a model with five fitted parameters. A single set of parameters describing the relationship between effective stress and P‐wave velocity provide an excellent fit to data acquired on Hanford Formation samples. The results presented here suggest the utility of seismic methods for establishing low matric suction and flow conditions within variably saturated Hanford formation sediments, which could be applied at the field scale for evaluating the performance of environmental remediation efforts, such as soil desiccation and surface infiltration barriers.

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.

용접 불티 포집기의 흡입 조건에 따른 포집효율 상관관계 분석

This research was conducted to analyze the collection efficiency of the welding spatter collecting device used for the reduction of fire accidents accompanied by welding work. The welding spatter collection device suggested in this study was mainly consisted of suction blower fan and collecting filter. The suction velocity and the mass of welding spatter collected by the device were measured for three types of filter porosity and three different blower powers. The relationship between collection efficiency and suction conditions was derived from the theoretical approach and the empirical model constants were determined by analysis of measuring data. The results showed that at the given blower power, the increase in pore size and rate of filter increased the suction force and the spatter collection efficiency.

New polymer composites improve silty clay soil microstructure: an evaluation using NMR

AbstractSoil erosion is a major environmental threat. The purpose of this study was to develop new polymer soil improvers that could mitigate the risk of soil erosion by modifying the microstructure of the soil and improving the ecological self‐repair ability. In particular, this study investigated new polymer composites (ADNB) based on different combination ratios of nano‐aqueous adhesive (NAB) and superabsorbent resin (SARn). The effects of different types of ADNB on soil water characteristics and pore size distribution were systematically investigated using nuclear magnetic resonance (NMR). In addition, an empirical model based on experimental data was developed to describe the effects of ADNB on the soil‐water characteristic curves. The results showed that in comparison to natural soil, the application of ADNB could significantly increase the peak signal strength of the relaxation time curve. In addition, ADNB can effectively reduce the number of pores with diameters of 1.11–8.3 μm, increase the number of pores with diameters of 0.5–1.8 μm, but had little effect on the number of pores with diameters of 0–0.5 μm. Through NMR imaging analysis, the effects of ADNB on soil moisture absorption and storage were quantified. The results showed that the ratio and content of ADNB have an obvious effect on the soil‐water characteristic curve under low suction but showed little effect under high suction conditions, indicating that the water‐holding capacity has been improved.

Multistage carbon dioxide compressor efficiency enhancement using waste heat powered absorption chillers

AbstractThe performance of a multistage centrifugal compressor is highly influenced by the ambient conditions, especially during the summer seasons; their capacity shrinks and thus the power requirement for compression will increase. The prime cause of these constraints is the interstage cooling limitations. This study simulates various suction conditions of a multistage compressor on Aspen HYSYS® and suggests its debottlenecking by making the suction temperatures comparable to winter seasons. This is achieved by installing an additional exchanger at the downstream of each interstage cooler, cooling down the gas further by using absorption refrigeration chillers. These chillers are powered up by the waste heat recovered from the exhaust steam coming from the prime mover, steam turbine, of the same compressor. This modification will save a considerable amount of power (663 kW), net savings (Gross Savings – OPEX: 72 289 $/y), and reduce the carbon footprint (954 ton/y) of the overall process.

Weak alkali ASP flooding in the second type reservoir in the A OilfieldProfile control technology and effect

Profile control technology refers to the operation of plugging high permeability layers from injection wells, which can adjust the suction profile of injection layers and improve the ultimate recovery. In this paper, the heterogeneity of the weak alkali ternary compound block of the second kind of oil layer in the A area of the some Second Division is strong, the injection conditions between well groups are different, the injection pressure level of some wells is low, the suction conditions of each sedimentary unit are different, and the comprehensive water cut of the block is high. In order to alleviate the contradiction between in formation and in plane, improve the utilization rate of chemical agents, and improve the ultimate recovery rate of the block, the deep profile control is carried out according to the characteristics of the oil layer development of the well group. Ten profile control wells were selected to adopt the profile control system of one and two polymer gel, which is a water shutoff agent for oil production. The polymer solution was used to carry particles for deep profile control. In this paper, the characteristics of profile control technology and the method of well and layer selection are studied, and the change law of dynamic index after profile control is analyzed in detail.

Dual solutions for Casson hybrid nanofluid flow due to a stretching/shrinking sheet: A new combination of theoretical and experimental models

Using the experimental relations for approximating the effective thermophysical properties of a water/MgO-Ag hybrid nanofluid is the novelty of the present investigation in order to simulate the two dimensional MHD Casson flow past a linearly stretching/shrinking sheet with suction, radiation and convective boundary condition effects. The dual solutions along with its stability analysis are also taken into account. The Tiwari-Das mathematical formulation coupled with mass-based hybrid nanofluid model is implemented to write the governing PDEs which are then transferred to a complicated system of dimensionless ODEs with help of the similarity transformation technique. Then a well-known finite difference method with forth order accuracy in MATLAB is employed to solve them. It is proved that the selective experimental relations for effective thermophysical models must be considered more serious in the numerical modeling of hybrid nanofluids in the future. Moreover, results indicate that the range of the Casson fluid parameter for which the solution exists, enhances with radiation parameter, suction parameter and also second nanoparticle mass. Also it is shown that the magnetic field which is applied normal to the sheet results in boost up the similarity velocity profiles into the hydrodynamic boundary layer.

Mathematical Analysis of Radiating Viscoelastic Unsteady MHD Fluid Flow through an Absorbent Media between Upstanding Equidistant plates with Joule Heating Impact

Focus of the present study is to explore Joule heating effect on incompressible, radiating, electrically conducting viscoelastic unsteady magnetohydrodynamic fluid and heat transfer through an absorbent media between upstanding equidistant plates with constant suction and slip condition. Lorentz force and Joule heating is discussed by momentum and energy equation respectively. Electric conductivity and the electromagnetic force both are in very small case in fluid flow. A consistent magnetic field is taking to perpendicular to the plane of the plates. The oscillatory time-dependent coupled equations (non-linear) are simplified to provide result for the fluid velocity and heat transfer by using structured perturbation execution. It has been noticed that velocity and heat transfer rise due to rise in Grashof number, Eckert number, heat source parameter or slip parameter while decrease as permeability parameter, radiation parameter or wavelength rises. As Hartmann number rises the fluid velocity diminishes, while opposite behaviour is noted in case of heat transfer effect. The velocity and heat transfer impact of the fluid rise with cross flow Reynolds parameter or frequency of the oscillation. Numerical outcomes for the motion and heat transpose effect profiles for multiples physical numbers also the local skin friction coefficient and spot Nusselt number are argued numerically, presented graphically along with.

A constitutive model for hydromechanically coupled behavior of unsaturated soils with hydraulic hysteresis

There are several constitutive models developed for understanding coupled hydromechanical behavior of three phase medium of unsaturated soils as well as models for explaining hydraulic hysteresis in water retention. However, very few attempts that merge the two aspects of behavior are available. This study develops a one-way coupled model for understanding the hydromechanical behavior of unsaturated soils. In addition to the hysteresis between main drying and wetting retention curves, the model considers non-uniqueness of retention behavior resulting from void ratio changes due to compression under the stress application. As for the elastoplastic stress strain relationship of soil skeleton, the model is based on the formulation of classical plasticity relying on the critical state concept. Consequently, volumetric deformation due to wetting-drying cycles and its effect on elastoplastic behavior through simultaneously changing matric suction is modeled. Model results are calibrated with the results of isotropic compression stages of triaxial tests at both constant suction and constant water content conditions.

Loading rate effect on mechanical properties of an unsaturated silty sand

This paper presents the results of an experimental study on the effects of testing rate on stress-strain behavior and volumetric changes of soil. A series of suction-controlled triaxial tests has been performed on reconstituted specimens of a silty sand (SM), at different stress-rates and strain-rates, respectively. The stress-strain paths were applied by using a modified version of a Bishop and Wesley device (USPv2), capable of applying independently pore-water and air pressure at both ends of the soil sample. During the isotropic compression stages loading rates of 2 and 32 kPa/h have been applied under constant suction values of 15 and 45 kPa. The drained deviator stages were conducted at the same suction levels under strain rates of 0.25 and 2.50 %/h. Results are presented in terms of applied loading rates as a function of the specimens specific volume, preconsolidation pressure, soil compressibility and deviatoric stress against strain rate. A comparison of results was made to a former study, under similar testing conditions of suction and loading rates at University of Napoli Federico II. The effect of loading rate on the soil behavior seems to have an insignificant effect on the specific volume variations, for the imposed values during the testing campaign.

A semi-analytical solution to spherical cavity expansion in unsaturated soils

This paper presents a rigorous solution for spherical cavity expansion in unsaturated soils under constant suction condition. The hydraulic behavior that describes the saturation-suction relationship is modeled by a void ratio-dependent soil-water characteristic curve, which allows the hydraulic behavior to fully couple with the mechanical behavior that is described by an extended critical state soil model for unsaturated soil through the specific volume. Considering the boundary condition and introducing an auxiliary coordinate, the problem is formulated to a system of first-order differential equations with three principal stress components and suction as basic unknowns, which is solved as an initial value problem. Parameter analyses are conducted to investigate the effects of suction and the overconsolidation ratio on the overall expansion responses, including the pressure-expansion response, the distribution of the stress components around the cavity, and the stress path of the soil during cavity expansion. The results reveal that the expansion pressures and the distribution of the stress components in unsaturated soils are generally higher than those in saturated soils due to the existence of suction.

Analysis of Processes Mechanized Oil Mining with the Methods Theory of Electrical Circuits

The authors investigate the problems of the development of the oil and gas complex at the last stage of operation, when oil is extracted by lifting. The main methods of lifting employed in the Russian Federation and the USA are described. A particular focus is placed on large water cuts at this stage of oil production. Literature on the issue under investigation is reviewed and the problem is set to analyze and construct models of oil production processes at the stage of well operation by lifting methods using network analysis (electrical circuits) in order to rationally manage all processes comprehensively. A typical flow chart of the oil production process by lifting methods is described. Technological processes of oil production are compared to processes in electric circuits. Thus the process of pumping purified formation water into injection wells by means of block cluster pumping units is similar to the process of recharging a battery using an electric power generator. The process of filling a production well with gas-liquid mixture displaced from the formation under pressure of injection wells is similar to the process of charging a capacitor from a battery, the process of lifting liquid from production wells using production pumps — to the process of discharging a capacitor on an active load. The simplified electrical diagram of a typical flow chart of oil production processes at this stage is given. Based on the given equivalent electrical circuit of technological processes, according to the laws of theoretical electrical engineering, models of the battery charging, capacitor charging and discharging processes are built. The table of correspondence of the parameters of technological and electrical circuits is presented on the basis of which the authors propose simplified models of the processes of pumping purified formation water into injection wells using unit cluster pumping stations, of filling a production well under pressure of the injection well, lifting liquid from production wells by means of suction pumps and conditions under which various operating modes of lifting processes are achieved.