Total Suction Research Articles

Measurement of soil suction using moist filter paper

Measurement of soil suction is important as soil suction is one of the two stress-state variables that control both the hydro and mechanical behaviour of unsaturated soils. One of the soil suction measurement techniques is the filter paper method. Even though the filter paper technique has been standardized, the experimental procedure can still be improved in order to reduce the inconsistencies that are often reported with the filter paper technique. This paper explores usage of both initially dry and initially moist Whatman No. 42 filter paper for matric and total suction measurements. Residual soils from the Bukit Timah Granite in Singapore were compacted at various water contents from dry to wet of optimum using standard Proctor energies and their suctions were measured using both contact and non-contact filter papers. Results of the suction measurements showed hysteresis between the initially dry and the initially moist filter papers for both the contact and non-contact methods. Suction measurement by the contact filter paper method is more consistent than suction measurement by the non-contact filter paper method. Condensation causes the non-contact filter papers to have higher water contents. The results showed that the non-contact initially dry filter paper follows the total suction curve but the non-contact initially moist filter paper may follow the matric suction curve instead.

Transient boundary conditions in the frame of THM-processes at nuclear waste repositories

In nuclear waste repositories, initially unsaturated buffer is subjected to constant heat emitted by waste canister in conjunction with peripheral hydration through water from host rock. The transient hydration process can be potraied as transformation of initial heterogeneity towards homogeneity as final stage. In this context, this paper addresses the key issue of hydro mechanical behaviour of compacted buffer in context of clay microstructure and its evolution under repository relevant loading paths and material heterogeneity. This paper also introduces a unique column experiment facility available at Ruhr Universitat Bochum, Germany. The facility has been designed as a forerunner of field scale testing program to simulate the transient hydration process of compacted buffer as per German reference disposal concept. The device is unique in terms of having proficiency to capture the transient material response under various possible repository relevant loading paths with higher precision level by monitor the key parameters like temperature, total suction, water content and axial & radial swelling pressure at three different sections along the length of compacted soil sample. In general, a larger spectrum of loading paths/scenarios, which may arise in the nuclear repository, can be covered precisely with existing device.

Soil water retention behaviour for an instrumented embankment

Measurement of soil suction is important as soil suction is one of the two stress-state variables that control both the hydro and mechanical behaviour of unsaturated soils. One of the soil suction measurement techniques is the filter paper method. Even though the filter paper technique has been standardized, the experimental procedure can still be improved in order to reduce the inconsistencies that are often reported with the filter paper technique. This paper explores usage of both initially dry and initially moist Whatman No. 42 filter paper for matric and total suction measurements. Residual soils from the Bukit Timah Granite in Singapore were compacted at various water contents from dry to wet of optimum using standard Proctor energies and their suctions were measured using both contact and non-contact filter papers. Results of the suction measurements showed hysteresis between the initially dry and the initially moist filter papers for both the contact and non-contact methods. Suction measurement by the contact filter paper method is more consistent than suction measurement by the non-contact filter paper method. Condensation causes the non-contact filter papers to have higher water contents. The results showed that the non-contact initially dry filter paper follows the total suction curve but the non-contact initially moist filter paper may follow the matric suction curve instead.

Gas migration through geomembrane/ geosynthetic clay liner composite liner with a defect in the geomembrane

(GMB)/geosynthetic clay liner (GCL) composite liner where the GMB contained a circular defect and the GCL was partially hydrated. The results indicate that gas leakage rate increased with increasing gas differential pressure and increase of the GCL total suction. It was also observed that gas leakage rate reduced with the increase of the gravimetric water content of the GCL.

The influence of saturation on the cracking process in compacted desiccating clays

Tensile failure in unsaturated cohesive soils during desiccation is important for the design of geotechnical applications such as capping systems of landfills and sealing material of dikes. This study presents the results of different initial parameters of compacted clay samples such as gravimetric water content, dry density and degree of saturation. These parameters are varied systematically for each test to find the correlation between those parameters and the tensile failure. The tensile failure for all tests occurred by a comparable constant change of the degree of saturation. The soil specific saturation ratio Sr,s is defined as the quotient of saturation changes ΔSr to initial saturation Sr,0 . This parameter related to the total suction shows an equal course for all results. All in all, the course of the soil specific saturation ratio Sr,s is independent of all initial parameters. These results provide a physical and hydraulic-mechanical description for modelling the desiccation process. To demonstrate the initiation and progress of tensile failure, the experimental results are modelled with a Discrete Element Method (DEM) approach.

Effect of pore fluid osmotic suction on matric and total suctions of compacted clay

The experimental results of the present study on compacted expansive clay illustrate that matric suction increases with the increase in pore fluid osmotic suction due to changes in soil structure. Scanning electron micrographs show that particle stacking (aggregations) increases with increase in pore fluid osmotic suction and cation valence due to reduction in diffuse double layer thickness, and thus results in a reduction in micro pore size with a corresponding increase in macro pore size. At a given water content, the macro pore degree of saturation reduces with the increase in osmotic suction owing to the increase in macro pore size and leads to an increase in matric suction, as the matric suction is characteristic of the macro pore and the degree of saturation of the macro pore. The matric, osmotic and total suction measurements using the filter paper method also confirm that the matric and osmotic suction components are additive. This demonstrates that the method of obtaining matric suction from the difference between total suction and pore fluid osmotic suction determined using non-contact filter papers is reliable.

SOIL WATER CHARACTERISTIC CURVES OF COMPACTED KAOLIN FOR VARIOUS INITIAL MOISTURE CONTENT

The soil water characteristic curve (SWCC), also known as soil water retention curve (SWRC), describes the relationship between water content and soil suction in unsaturated soils. The importance of SWCC can be seen, as the relationship affects geotechnical properties such as shear strength, volume change, permeability and deformability of unsaturated soils. This paper presented a preliminary study on the effect of initial water content and the density on SWCC on unsaturated compacted kaolin. Filter paper technique was used for suction measurement on the unsaturated compacted kaolin soil. Filter paper was used to determine total suction and matric suction through contact and noncontact technique. The calibration curve was used to relate with the gravimetric water content obtained in filter paper with corresponding suction. A comparison on SWCC established through filter paper was also compared with that of the axis translation technique (pressure plate extractor). The study found that the initial water content and the density respectively, have great influence on the SWCC of compacted kaolin. However, the combined effect could be seen significantly at lower suction

Analysis of laminar film condensation over vertical permeable hollow short fins

Laminar falling film condensation over vertical short fin is analyzed. The fin is considered to be hollow and permeable in order to account for condensate suction towards its inner core. The present work accounts for the shear stress at the interface caused by the large velocity of the saturated vapor. The continuity, momentum, and energy equations for the film condensate are solved using an iterative and implicit finite-difference method. The condensate flow rate inside the fin is obtained using the conservation of mass principle and the Poiseuille flow equations. The one-dimensional fin equation model is used to relate the fin temperature to the condensate flow convection heat transfer coefficient. Various computational and numerical methods techniques such as advanced linearization and generations of best-fit correlations are implemented. This is to reduce significantly the number of iterations required for solution convergence as all of the aforementioned equations are coupled. It is found that the dimensionless total mass transfer rate increases slightly as vapor Reynolds number increases. It increases apparently as both suction Reynolds number and dimensionless suction length increase. For both large suction Reynolds number and large dimensionless suction length, the flow rate of the condensate in the falling film can be neglected compared to the total suction condensate flow rate. The fin thermal length increases as Reynolds number, dimensionless suction length, and Grashof number increase. This study shows that significant condensation mass flow rate enhancement ratios are obtainable (can be 18 folds) due to suction through a hollow super conductive fin.

Effect of pore fluid osmotic suction on matric and total suctions of compacted clay

Effect of pore fluid osmotic suction on matric and total suctions of compacted clay

Simplified compound suction schemes of an aspirated highly loaded compressor cascade

Active flow control should be adopted at more than one critical position in highly loaded aspirated compressors due to the severe flow separation and obvious three-dimensional characteristics of the flow field. A deep insight into the mechanism of the simplified compound boundary layer suction in a highly loaded compressor cascade was experimentally and numerically revealed in this paper. Locations of the two suction slots in the studied compound suction schemes were determined through previous experimental investigations on the single-slot suction schemes. Base on the one-side suction manner and the shared suction recycle system, the suction flow distribution over the suction surface slot (SS4) presented to be C-type along the spanwise both in single-slot cases and the compound suction schemes. On the other hand, the flow distribution over the endwall slot (EW1) was no longer that even along the axial direction after it cooperates with the SS4 slot, especially under the small total suction flow rate. The studied compound suction scheme owns obvious advantages in improving aerodynamic performance of the compressor cascade, when the total suction flow rate is big enough for both slots. About one-sixth loss reduction was achieved in the compound suction scheme with 1.5% suction flow rate. Therefore, the simplification of suction equipment via sharing one set of suction system and employing one-side suction manner is proved to be feasible and as effective in the studied multi-slot suction schemes.

Assessment of Molding Moisture and Suction on Resilient Modulus of Lime Stabilized Clayey Subgrade Soils

A comprehensive laboratory study was undertaken to evaluate the effects of molding moisture and suction on the resilient modulus (MR) and unconfined compressive strength (UCS) of lime stabilized clayey subgrade soils. Two subgrade soils, AASHTO class A-6 and A-7-6, are stabilized with three percentages (0, 5, and 7 %) of lime on the basis of pH test and used to prepare cylindrical MR samples at three moisture contents: optimum moisture content (OMC), dry state (OMC-2 %), and wet state (OMC +2 %). MR tests on lime stabilized soils are conducted with a modified stress sequence incorporated in the AASHTO T307 procedure based on past literature and laboratory experience gained in this study. Test results revealed that the effects of moisture on MR and UCS values of lime stabilized soils were less than those on untreated soils. MR and UCS values increased due to lime treatment, but improvement varied with soil type and lime dose. A filter paper method was used to determine the total and matric suctions at different moisture states in this study. It was observed that osmotic suction increased to 15 % of the total suction due to lime treatment. Finally, an existing MR constitutive model was revised by incorporating total suction. The revised model was shown to have better predictive capability over existing MR models.

Water Use Efficiency in Saline Soils under Cotton Cultivation in the Tarim River Basin

The Tarim River Basin, the largest area of Chinese cotton production, is receiving increased attention because of serious environmental problems. At two experimental stations (Korla and Aksu), we studied the influence of salinity on cotton yield. Soil chemical and physical properties, soil water content, soil total suction and matric suction, cotton yield and water use efficiency under plastic mulched drip irrigation in different saline soils was measured during cotton growth season. The salinity (mS·cm−1) were 17–25 (low) at Aksu and Korla, 29–50 (middle) at Aksu and 52–62 (high) at Aksu for ECe (Electrical conductivity measured in saturation-paste extract of soil) over the 100 cm soil profile. The soil water characteristic curves in different saline soils showed that the soil water content (15%–23%) at top 40 cm soil, lower total suction power (below 3500 kPa) and lower matric suction (below 30 kPa) in low saline soil at Korla had the highest water use efficiency (10 kg·ha−1·mm−1) and highest irrigation water use efficiency (12 kg·ha−1·mm−1) and highest yield (6.64 t·ha−1). Higher water content below 30 cm in high saline soil increased the salinity risk and led to lower yield (2.39 t·ha−1). Compared to low saline soils at Aksu, the low saline soil at Korla saved 110 mm irrigation and 103 mm total water to reach 1 t·ha−1 yield and increased water use efficiency by 5 kg·ha−1·mm−1 and 7 kg·ha−1·mm−1 for water use efficiency (WUE) and irrigation water use efficiency (IWUE) respectively.

COMBINED EFFECTS OF TEMPERATURE AND MOISTURE CONTENT ON SOIL SUCTION OF COMPACTED BENTONITE

Based on experimental determination of soil suctions of two clayey soils, this study investigated the combined effects of temperature and moisture content on soil suction. First, two clayey soils were statically compacted at target moisture contents ranging from 5% to 20%, such that a broad spectrum of compaction conditions can be evaluated. Then, filter paper method and thermocouple psychrometer were adopted to measure soil suction, including total and matric suctions, at temperatures ranging from 10℃ to 60℃. It was found that soil suctions of expansive soils vary with compaction parameters such as compaction moisture content and compaction effort, and that temperature is influential on soil suction also. As moisture content increases, the effects of compaction effort and temperature on suction become less significant. Formulations developed using multiple regression were established for predicting the soil suction of as-compacted expansive soils.

Coupled Behavior of Cemented Paste Backfill at Early Ages

Once cemented paste backfill (CPB) is poured into a mine stope, it is subjected to strong coupled thermal (T), hydraulic (H), mechanical (M) and chemical (C) processes. A laboratory investigation is performed to understand the THMC behavior of CPB at early ages. An experimental setup is developed to study the THMC behavior of CPB. The testing and monitoring are conducted in undrained conditions, with and without pressure application, and take into consideration two types of tailings (artificial and natural). The evolutions of the total pressure, pore pressure, suction, temperature and electrical conductivity are monitored for a period of 7 days. Also, the CPB samples are tested or analyzed with regards to their shear strength properties, hydraulic conductivity, thermal conductivity, and physical and microstructural characteristics at 1, 3 and 7 days. The obtained results show that the THMC properties of CPB are strongly coupled due to several mechanisms, such as curing stress, heat of hydration, self-desiccation and pore fluid chemistry. The results presented in this paper will provide a better understanding of the THMC behavior of CPB at early ages and thus contribute to the better designing of CPB structures.

Mechanisms for Soil-Water Retention and Hysteresis at High Suction Range

AbstractConventional conceptual mechanisms for the hysteresis of soil-water retention are the ink-bottle pore neck and the solid–liquid–air-contact angle. However, these mechanisms fail to explain hydraulic hysteresis for matric suction greater than 10 MPa. A conceptual model, based on hydration-water retention, is provided in this paper. Two hydration mechanisms, namely, particle-surface hydration and crystalline cation hydration, are distinguished to explain hydraulic hysteresis. The former is mainly involved in water retention by anions of oxygen and/or hydroxyls on particle surface, leading to reversible water adsorption and desorption. By contrast, cation hydration is controlled by both exchangeable cations and the intermolecular forces such as Coulomb attraction and London dispersion, leading to hysteretic water-retention behavior. Based on this hysteresis model, the highest total suction for any soil can be identified. From the isotherms of various soils at 25°C, it is found that the highest total ...

Influence of Soil Cracking on the Soil-Water Characteristic Curve of Clay Soil

The hydraulic conductivity for unsaturated soil conditions is more difficult to estimate than for the saturated condition. In addition, as the soil transitions from intact to cracked, the difficulty in estimating the unsaturated hydraulic conductivity increases. One critical step in the determination of unsaturated flow hydraulic conductivity is the evaluation of the Soil-Water Characteristic Curve (SWCC). In this paper, a series of laboratory studies of direct measurements of cracked soil SWCCs is presented, including challenges associated with the control of very low suction levels associated with crack dewatering. An oedometer-type SWCC apparatus, capable of suction and net normal stress control, and volume change measurement, was used in these experimental studies. It is common that SWCCs are comprised of matric suction values below about 1500 kPa, and total suction values for suctions higher than about 1500 kPa (Fredlund et al., 2012). In this study, all measured or controlled suction values were less than 1500 kPa and obtained using the axis translation method, and the curve in the higher suction range was projected by forcing the SWCC through 106 kPa for completely dried conditions (Fredlund et al., 2012). Volume change corrections were made to the reported volumetric water contents, which is of particular importance when the soil under consideration undergoes volume change in response to wetting or drying. A technique for the determination of the SWCC for cracked clay soils is presented. Test results validated the fact that the SWCC of a cracked soil can be represented by a bimodal function due to the Air Entry Value (AEV) of the cracks being much lower than the AEV of the soil matrix. It was also found that differences between the SWCC for cracked and intact soil appears only in the very low suction range.

The Results of Abdominoplasty by electrodissection and short term complications

Objective: To describe abdominoplasty by electrodissection technique for improving short-term complications.Design: A prospective controlled study consisting of 100 consecutive female candidates for abdominoplasty by electrodissection employing spray-coagulation was conducted . The technique and electrical current used are described in detail.Results: Intraoperative bleeding ranged from 25 to 160 ml, (median 85 ml). The short-term specific and general complication rates were very low, not exceeding the rates observed using cold scalpel. The frequency of seroma was 24% and the occurrence of seroma, total seroma volume, and total suction tube discharge were correlated to the area of dissection or depth of electrical tissue injury. Conclusion: Despite the relatively high frequency of seroma, we recommend the use of spray-coagulation for abdominoplasty because bleeding is minimized, visibility during dissection is highly increased and the rate of short-term complications is very low.

A New High-Pressure Triaxial Apparatus for Inducing and Tracking Hydro-Mechanical Degradation of Clayey Rocks

Abstract This paper presents the development of a new high-pressure triaxial apparatus specifically prepared for inducing and tracking the degradation of clayey rocks. Total suction—used to induce the hydraulic degradation—is applied with vapor transfer technique by controlling the relative humidity of air in contact with the material. The evolution of the degradation process along different hydro-mechanical stress paths is continuously tracked with bender elements, as well as with air or water permeability measurements on partially saturated or saturated states, respectively. Relevant test results on a low porosity clayey rock (Lilla claystone, Spain) are presented to evaluate the main capabilities of the new equipment. The results bring up the high sensitivity to water of the material, which is evidenced by the important reduction of shear wave velocity induced on first wetting and drying at low confining stress, as well as by the significant increase in the air permeability of the degraded material (around four orders of magnitude larger than the intact material). Test results also showed clear differences in the volume change and shear strength behavior of undisturbed, saturated, and degraded samples, highlighting the relevance of degradation on macroscopic behavioral features.

Influence of Seawater on the Suction and Swelling Behavior of Clayey Soils

The present study examines the suction characteristics and swelling behavior of clayey soils when exposed to natural seawater with respect to distilled water. The effects of saline waters on the engineering behavior of soils need to be determined since the salinity of the pore fluid of soils near coastal areas increases continuously. Six clayey soil samples with different mineralogy and characteristics were gathered and tested to determine the suction and swelling characteristics in the presence of natural seawater and distilled water. The results show that the total suction values of the samples are higher in the presence of seawater than in distilled water. The samples with high swelling potential have lower matric suction values than nonswelling soils. Moreover, in contrast to swelling-type soils, the matric suction values of the nonswelling soils remain similar in the presence both distilled water and seawater. The modified free swell index (MFSI) of the samples is well correlated with the liquid limit (LL), plasticity index (PI), and cation exchange capacity (CEC) in distilled water. However, coefficients of determination decreased in the presence of seawater. Also, there is no significant correlation existing between total and matric suction values and the MFSI values of the samples.

Effective Stress in Unsaturated Silt at Low Degrees of Saturation

This paper presents an evaluation of the effective stress concept in unsaturated, compacted silt at low degrees of saturation. A set of isothermal, consolidated‐drained triaxial tests was performed on silt specimens under different combinations of total suction and net normal stress. The total suction was controlled using an automated humidity system, and variables monitored during equilibration and shearing include anisotropic volume change, axial displacement, temperature, relative humidity at the top and bottom of the specimen, and the gas pressure difference across the specimen. The results from the triaxial tests were analyzed to examine the applicability of predicting the suction stress characteristic curve (SSCC) using parameters from soil water retention curve (SWRC) models fitted to experimental data obtained at low suction magnitudes. The SSCC predicted from the SWRC at low suctions was found to overpredict the suction stress values at high suctions obtained from back‐extrapolation of the failure envelope to define the tensile strength. However, small adjustments in the fitting of the SWRC were found to provide a better fit between the SSCC and experimental suction stress data. The suction stress defined using the adjusted SWRC was found to provide a good interpretation of the critical state line in terms of mean effective stress over both high and low suction ranges.