Suction Measurements Research Articles

Hysteretic soil water characteristics and cyclic swell–shrink paths of compacted expansive soils

The investigation of the hydromechanical behavior of unsaturated expansive soil depends on the determination of hysteretic soil water characteristic curves (HSWCCs). This research investigates the HSWCCs of two natural expansive soils initially compacted at optimum moisture content (OMC) and maximum dry density (MDD) and then saturated to their maximum expansion state to ensure identical capillary history. Filter paper, pressure plate and chilled mirror hygrometer suction measurement techniques were utilized, and corresponding measurements of three-dimensional volume change made. The cyclic swell–shrink paths were deduced in terms of volumetric strain versus either water content or suction. The cyclic three-dimensional volumetric measurements showed a much higher amount of swelling and shrinkage than those determined from one-dimensional measurements. Hydraulic hysteresis rapidly decreased with the swell–shrink cycles as a result of macro-structural stabilization. Under the no/low confining conditions, the swell–shrink cycles generally caused a decrease of global expansion and an increase of global shrinkage. Moreover, a special phenomenon showing a reduction of global shrinkage on significant drying was discovered in the less plastic soil sample.

Analysis and Assessment of Behavior of Compacted Soils

Abstract: Most of the natural soils above ground water table (or above capillary zone) and invariably all the compacted soils in their placement condition are in the state of partial saturation. Unsaturated soils exist all over the world where the weather conditions are such that the annual evaporation potential is in excess of the precipitation. Unsaturated soils in their natural condition are generally found in tropical regions with arid and semi arid conditions. In such regions the soils are formed under peculiar hot and humid climate conditions and the soils so formed are subjected to seasonal moisture deficits. Hence the soils are in the state of partial saturation. All compacted soils in their placement water content are in state of partial saturation. The mechanical behaviour of unsaturated soils is strongly influenced by the presence of both the pore air and the pore water. The mechanisms governing the behaviour of unsaturated soils are quite different and need to be analyzed carefully as these soils are frequently encountered in engineering practice for founding many structures involving infrastructure development. The present investigation considers different soils representing wide spectrum of properties present in this region for probing the compaction and stress-strain characteristics. The soils are tested in quasi saturated state to circumvent the problems associated with the suction measurement and developing a phenomenological model for easy use by practicing engineers.

An analysis of quantitative measurements of drainage exudate using negative suction in 96 microtia ear reconstructions

Negative suction drainage is commonly used for the prevention of seromas or hematomas in auricular reconstruction surgery; however, there are few reports regarding the quantitative measurement of negative suction and its relation to disposed time, patient age or microtia type. In the present study, the authors recorded the volume of suction exudate in microtia reconstruction and elaborate on the relevant details of controlling negative suction. A negative suction drainage system was applied in 96 microtia patients between 2007 and 2010. Two small polyethylene drains were inserted adjacent to the concha and the scapha, respectively. The volume of exudate was recorded for three days after surgery and was analyzed according to disposed time, patient age and microtia type. The drains were removed on the third postoperative day, when only a small amount of exudate remained. A significant change in drainage was observed over three days postoperatively, and the quantity decreased progressively on the third postoperative day. Comparison of age groups showed that the volume of drainage from adults was greater than that from children or adolescents in the first two postoperative days, regardless of whether the drains were inserted in the scapha or concha. No statistical differences were found on the third postoperative day. A comparison of drain types revealed no statistically significant differences between scapha and concha drains three days postoperatively. The analysis demonstrated that drainage quantity is related to disposed time and patient age, but not to microtia type. The authors recommend removal of suction drains on the third postoperative day. Moreover, individualized negative suction treatment according to age or microtia type provides a safe and consistent approach to achieving acceptable results and fewer complications.

Development of a Large-Scale Infiltration Column for Studying the Hydraulic Conductivity of Unsaturated Fouled Ballast

Abstract To study the hydraulic behavior of fouled ballast, an infiltration column 600 mm high and 300 mm in diameter was developed. Five time domain reflectometer (TDR) sensors and five tensiometers were installed at various levels, allowing the measurement of volumetric water content and matric suction, respectively. The material studied was fouled ballast that was formed in the railway track-bed by penetration of fine-grained soil into the ballast. This material is characterized by a high contrast of size between the largest and the smallest particles. During the test, three stages were followed: saturation, drainage, and evaporation. Based on the test results, the water-retention curve and the unsaturated hydraulic conductivity were determined. The quality of the results shows the capacity of this large-scale infiltration column in studying the unsaturated hydraulic properties of such fouled ballast.

Influence of Initial Water Content and Specimen Thickness on the SWCC of Fine-Grained Soils

Earlier researchers have demonstrated that the compaction effort and water content, type of soil and mineralogy, void ratio, fabric, and stress history influence the soil-water characteristics curve (SWCC) of fine-grained soils to a great extent. However, it should be noted that compacting the soil and retrieving specimens from the compacted mass for suction measurements is a tedious task. Also, many times, identical soil specimens with similar compaction states may result in varied pore-size distribution characteristics. Hence, for establishing the SWCC, soil specimens in the form of slurry of adequate consistency would be quite handy, particularly for maintaining uniformity in specimen preparation. With this in view, the current study was carried out to understand the influence of initial water content on the SWCC and to recommend its best suited value for conducting experiments. It has also been noted that suction measurement devices, such as pressure membrane extractor and the dew point potentiameter WP4, have limitations associated with the thickness of the specimen, which may become an important and deciding parameter. Hence, in this study, SWCCs were established for commercially available kaolin and bentonite clays by varying the initial water contents and thickness of their specimens. Details of the methodologies adopted for these investigations are presented in this paper. These investigations reveal that the initial water content influences only the initial portion of the SWCC for soil suction less than 500 kPa, while the specimen thickness does not significantly influence the shape of the SWCC. It has also been demonstrated that specimens prepared from the initial slurried state facilitate uniformity in suction measurements.

Evaluating the In Situ Lateral Stress Coefficient (K0) of Soils via Paired Shear Wave Velocity Modes

AbstractThe utilization of shear wave velocities toward the evaluation of the in situ geostatic horizontal stress state in soils is validated, specifically the lateral stress coefficient K0. Field shear wave velocities from paired sets of different directional and polarization modes are compiled from 16 well-documented test sites involving a variety of geomaterials. Focus is particularly placed on shear wave velocities measured by downhole tests (VsVH), crosshole tests (VsHV), and special rotary-type crosshole tests (VsHH). At these sites, field K0 stress states have been quantified using one or more direct assessment techniques, including self-boring pressuremeter, total stress cells, and hydrofracture in field testing, as well as suction measurements, special consolidometers, and/or triaxial arrangements on undisturbed samples in the laboratory. Although the specific delineation of stress-induced versus inherent or fabric anisotropy may be difficult, it is shown that the ratio of horizontally polarized ...

On-sample water content measurement for a complete local monitoring in triaxial testing of unsaturated soils

To provide a complete local monitoring of the state of an unsaturated soil sample during triaxial testing, a local water content measurement device was adapted to a triaxial device comprising the measurement of local displacements (Hall effect transducers) and suction (high-capacity transducer). Water content was locally monitored by means of a resistivity probe. The water content/resistivity calibration curves of an intact, natural, unsaturated loess from northern France extracted by block sampling at two depths (1 and 3·3 m) were carefully determined, showing good accuracy and repeatability. The validity of two models giving the resistivity of unsaturated soils with respect to their water content was examined. The first triaxial tests carried out with this device in the range of in situ stresses gave satisfactory results, but with some effects of the applied cell stress on the water content measurements. Some preliminary behaviour characteristics of the natural unsaturated loess, a material rarely tested up to now in the literature, were evidenced. Also, the yield stresses appeared significantly higher than the in situ stresses, confirming the combined effect of partial saturation and bonding.

Effect of healthy aging on left ventricular relaxation and diastolic suction

Doppler ultrasound measures of left ventricular (LV) active relaxation and diastolic suction are slowed with healthy aging. It is unclear to what extent these changes are related to alterations in intrinsic LV properties and/or cardiovascular loading conditions. Seventy carefully screened individuals (38 female, 32 male) aged 21-77 were recruited into four age groups (young: <35; early middle age: 35-49; late middle age: 50-64 and seniors: ≥65 yr). Pulmonary capillary wedge pressure (PCWP), stroke volume, LV end-diastolic volume, and Doppler measures of LV diastolic filling were collected at multiple loading conditions, including supine baseline, lower body negative pressure to reduce LV filling, and saline infusion to increase LV filling. LV mass, supine PCWP, and heart rate were not affected significantly by aging. Measures of LV relaxation, including isovolumic relaxation time and the time constant of isovolumic pressure decay increased progressively, whereas peak early mitral annular longitudinal velocity decreased with advancing age (P < 0.001). The propagation velocity of early mitral inflow, a noninvasive measure of LV suction, decreased with aging with the greatest reduction in seniors (P < 0.001). Age-related differences in LV relaxation and diastolic suction were not attenuated significantly when PCWP was increased in older subjects or reduced in the younger subjects. There is an early slowing of LV relaxation and diastolic suction beginning in early middle age, with the greatest reduction observed in seniors. Because age-related differences in LV dynamic diastolic filling parameters were not diminished significantly with significant changes in LV loading conditions, a decline in ventricular relaxation is likely responsible for the alterations in LV diastolic filling with senescence.

Advances in suction measurements using high suction tensiometers

Significant advances in unsaturated soils testing have been gained through the development of high suction tensiometers allowing direct measurement of suction beyond 100kPa. This has allowed the implementation of techniques that measure and control suction directly, where the soil is tested in the same conditions as in nature. Previously, much reliance had been placed on indirect measurements of suction and on control of suction using the axis translation technique. It is argued that this technique should be avoided as the use of an elevated air pressure does not replicate natural conditions. This paper presents advances resulting from the use of high suction tensiometers for laboratory testing and field measurements. It also describes an automated suction control system using the air circulation method that can impose controlled cycles of drying and wetting.

Influence of Drying and Wetting Cycles on SWCCs of Fine-Grained Soils

AbstractThe soil-water characteristics curve (SWCC) is greatly influenced by the path that is followed for suction measurement (i.e., drying or wetting path) and the number of cycles of these paths to which the soil is exposed. To evaluate the influence of these parameters, drying- and wetting-path SWCCs of three fine-grained soils were developed for single and multiple cycles by employing the Aquasorp® Isotherm generator. This device has been primarily employed for food products, powders, and amorphous materials for determination of their moisture sorption isotherm, which relates moisture content to water activity. As water activity can be mathematically related to soil suction, the Aquasorp® can be used for developing the SWCC. Hence, demonstrating the potential of the Aquasorp® for characterizing fine-grained soils becomes essential. The present study has been focused at highlighting the possible uncertainties associated with establishment of the SWCCs (both during drying and wetting paths) and the benefits and limitations of the Aquasorp® in achieving these objectives. Furthermore, by employing mercury intrusion porosimetry (MIP), the significance of capillarity on soil suction, which in turn governs the SWCC, has been demonstrated.

Thermo-hydro-mechanical modelling of soil settlements induced by soil-vegetation-atmosphere interactions

The effect of soil-vegetation-atmosphere interactions on the soil water content variations and the induced settlements are studied using a numerical approach. A two dimensional model of soil-vegetation-atmosphere interaction is developed in θ-STOCK finite element program. The soil heat, the infiltration and the evaporation from the soil surface are calculated using water balance and energy balance equations. The model parameters are standard meteorological data, soil characteristics and canopy parameters. The main advantage of this approach is the settlement prediction using only the soil physical properties, e.g. soil water retention and shrinkage curves, with no need to continuous in-situ measurements of water content or suction. An instrumented site is modelled to verify the model capacities. The results show a good accordance between calculation and measurements.

A novel methodology for measuring the tensile strength of expansive clays

Several experimental techniques (viz., triaxial tests, direct tensile tests or suction measurements) have been developed and employed by earlier researchers to measure the tensile strength of fine-grained soils. However, these studies yield results that are soil specific and dependent on the methodology adopted. Apart from this, due to the bulk form of the sample, the sample heterogeneity (i.e., both in terms of the density and the moisture content) influences test results to a great extent. Under this situation, and in the absence of guidelines regarding sample thickness, determination of the tensile strength of expansive clays by employing their thin samples (1 mm to 5 mm) appears to be an excellent alternative. With this in view, efforts were made to determine the tensile strength of expansive clays by resorting to techniques that deal with measurement of (a) the deflection undergone by a silicon wafer, due to air-drying of a thin film of these clays, with the help of a laser beam and (b) the suction by employing a dewpoint potentiameter, WP4. Results obtained from these techniques were critically evaluated vis-à-vis those obtained from triaxial tests and empirical relationships reported in the literature. It has been observed that there is a unique relationship between the results of the thin and thick samples and hence thin samples of expansive clays can be employed for determining their tensile strength. This shows the usefulness of the proposed techniques for measuring the tensile strength of expansive soils.

Measurement of Total Soil Suction Using Filter Paper: Investigation of Common Filter Papers, Alternative Media, and Corresponding Confidence

Abstract The small range of moisture contents measured with typical filter paper media in test method ASTM D5298 Measurement of Soil Potential (Suction) Using Filter Paper, require that the mass of the paper be measured to 0.0001 g. The accuracy and resolution of several readily available filter papers was investigated, along with investigating a polymer material as a possible alternative media. The importance of calibrating the filter paper was supported by the study, and suggested that because the slope of the calibration curve varies from paper to paper, the filter papers with the capability of measuring a broad range of water contents (low slope of the water content suction calibration curve) provide increased measurement resolution. The polymer media strips were found to have a much greater range of the moisture content than any of the filter papers, providing even greater resolution in the prediction of suction. The polymer strips performed just as well as the filter papers and showed repeatability in the measured suction values. The primary limitation in using polymer material is the lack of mass production of the material in a form suitable for suction measurements.

The water retention properties of a natural unsaturated loess from northern France

The water retention properties of a natural loess from northern France were investigated on intact block samples that were excavated along a high-speed train line (TGV) that experienced stability problems during heavy rain episodes. Suction measurements were made by using the filter paper method and an in-house constructed high-capacity tensiometer (HCT) so as to determine the water retention curve of the loess. The results showed that an alternative approach using a previously wetted filter paper could fruitfully be used with suction values reasonably compatible with the HCT measurements. The water retention curve obtained exhibited a peculiar form, with no hysteresis observed around the natural water content (14·4%) and two hysteresis loops on both the wet and dry sides of the curve. It is hypothesised that this zone with no hysteresis corresponds to the natural variations of the water content under seasonal changes, providing a range of natural suction between 20 and 80 kPa, and it is suggested that this should be checked by in situ measurements. The loess microstructure was investigated by using scanning electron microscopy and mercury intrusion porosimetry. It appeared that the clay fraction (16%) was not uniformly distributed, with some areas composed of clean grains and a well-graded corresponding intergrain pore population. Conversely, the clay aggregations define a smaller-sized porosity. The calculation of a water retention curve derived from the pore size distribution curve showed that water retention is governed by capillarity in the largest pores between clean grains, whereas clay adsorption becomes dominant in the smallest pores, a zone where the microstructure is sensitive to change in water content.

A study of the correlation between electrical resistivity and matric suction for unsaturated ash-fall pyroclastic soils in the Campania region (southern Italy)

In the territory of the Campania region (southern Italy), critical rainfall events periodically trigger dangerous fast slope movements involving ashy and pyroclastic soils originated by the explosive phases of the Mt. Somma-Vesuvius volcano and deposited along the surrounding mountain ranges. In this paper, an integration of engineering-geological and geophysical measurements is presented to characterize unsaturated pyroclastic samples collected in a test area on the Sarno Mountains (Salerno and Avellino provinces, Campania region). The laboratory analyses were aimed at defining both soil water retention and electrical resistivity curves versus water content. From the matching of the experimental data, a direct relationship between electrical resistivity and matric suction is retrieved for the investigated soil horizons typical of an ash-fall pyroclastic succession. The obtained relation turns out to be helpful in characterizing soils up to close saturation, which is a critical condition for the trigger of slope failure. In such a regime, the water content and the matric suction have small variations, while electrical resistivity variations can be appreciated in a larger range of values. For this reason, besides suction measurements on very small soil volumes through classical tensiometers, our analyses suggest the direct monitoring of in situ electrical resistivity values as an effective tool to recognise the hydrological state of larger and more representative soil volumes and to improve early warning of dangerous slope movements.

Matric Suction Measurement of Unsaturated Soils With Null-Type Axis-Translation Technique

Abstract Matric suctions of several compacted soil specimens of a low-plastic soil were measured using null-type axis-translation technique. The study showed that in general, the dynamically compacted specimens reached equilibrium sooner than the statically compacted specimens and exhibited greater matric suctions. For a given compaction type (dynamic or static), the influence of an increase in the dry density due to an increase in the compaction effort had practically negligible influence on the measured matric suctions. Comparison of the null-type test results with the suction-water content soil-water characteristic curves of the soil showed some disagreements particularly for matric suctions greater than 20 to 30 kPa. Continuity in the water phase between the soil water, the water in the ceramic disk, and the water in the compartment below the ceramic disk, was verified soon after the measurements of matric suction were completed by increasing the chamber air pressure and monitoring the corresponding water pressure increase below the ceramic disk. The test results clearly showed a lack of continuity in the water phase during the suction measurements. Use of various interface materials (viz., a wet filter paper, slurries prepared from the tested soil and a kaolinite) significantly improved the water phase continuity; however, reduced the matric suctions of the soil specimens tested.

Calibration of a thermal conductivity sensor for field measurement of matric suction

This paper examines the calibration of a thermal conductivity sensor used for in situ matric suction measurement. A new calibration method is introduced. Performance of the thermal conductivity sensor in terms of salinity of pore water, heating power, hysteresis, response time and matric suction measurement range is also examined.

In Situ Matric Suction and Moisture Content Measurements in Expansive Clay during Seasonal Fluctuations

Abstract In the design of flexible pavements using the mechanistic-empirical pavement design guide (MEPDG), water flow analyses are used to predict changes in the mechanical behavior of unsaturated subgrade soils. However, the water flow analyses in the MEPDG are not well validated using field measurements of moisture content and matric suction with time. A research study was initiated to measure the variation in matric suction and moisture content in an expansive soil during seasonal fluctuations. Specifically, a thermal conductivity-based suction sensor was fully evaluated and calibrated in the laboratory and was later installed with moisture sensors at different sites in Texas. This paper presents a summary of field measurements of matric suctions and moisture contents from a site in Houston. Comparisons of field measurements of matric suctions are compared with those interpreted from the soil water characteristic curve using field moisture content measurements, and a decent match was obtained up to matric suctions close to 800 kPa.

Experimental Study of Suction-Monitored CBR Test on Sand-Kaolin Clay Mixture

Conventional laboratory CBR test has been widely used for predicting bearing capacity of subgrade layer for pavement design. In unsaturated soil, suction is one of the key parameters for understanding the soil behavior. The analysis of CBR is commonly presented in CBR-water content relation. The information of CBR based on soil suction is very rare and more study is still required. This paper presents a laboratory experiment of CBR test with direct suction measurement. Suction-monitored CBR test is introduced by attaching tensiometers on CBR mold and its surcharge. The standard compacted test on various proportions of sand-kaolin clay mixtures starting from 0% (pure sand), 5%, 10%, and 20% of clay were used. The tests were performed with different value of water content in both soaked and unsoaked conditions. The results indicated that the CBR versus matric suction forms a bi-linear curve. The discussion is presented in term of CBR-water content and CBR-matric suction relation.

Temperature Effects on Suction Measurement Using the Filter Paper Technique

Abstract This paper presents the results of an experimental study of thermal effects on filter paper calibration curves used to obtain the soil suction. When the temperature is significantly different from ambient values, it is essential to consider the influence of temperature on the filter paper calibration curves to obtain a reliable soil suction measurement. The calibration curve of Whatman No. 42 filter paper was determined at 10°C, 25°C, and 50°C using the vapor equilibrium technique with sodium chloride solutions at different concentrations and the axis translation technique. The experimental results showed a major influence of temperature on the filter paper calibration curves. Using the obtained experimental data a calibration equation was proposed, taking into account the effect of temperature. The obtained calibration curves were then used to determine the soil water retention curve of kaolin clay, which showed lower retention capacity at higher temperatures.