Suction Measurements Research Articles

Stabilization of expansive soils using ionic stabilizer

In many parts of the USA, expansive soils pose a significant hazard to infrastructures. These kinds of soils owe their characteristics to the presence of swelling clay minerals. As they get wet, they swell; conversely, as they dry, they shrink. Many stabilization methods have been developed to mitigate the adverse effects of expansive soil. One of them is the use of the ionic additive. In this research, a liquid ionic product is evaluated as a non-traditional stabilizer. Soil samples from a specific construction site in Texas and soil samples from Oklahoma were utilized. The evaluation tests involve the suction measurements, swelling, and plasticity index for treated and untreated soils. Cyclic swelling tests were also carried out on reconstituted specimens. From laboratory tests and analysis, it was found that this additive is effective in reducing swelling of both Texas and Oklahoma soils. It reduces swelling of Texas soils by 0.4–6% and Oklahoma soil by 2–7.4%. The results of swelling cycles reveal a permanent effect of this stabilizer on mitigating the swelling behavior. After the 3rd swelling cycle, the swelling for Oklahoma soils was 5.58% lower than the natural soil, and for Texas soils, it was reduced by 6.02–8.49% for different concentrations of the additive. However, no definitive trend was observed for reducing the shrinkage potential.

Influence of Water Retention Curves Model Fitting Parameters on Unsaturated Seepage Modeling of Fly Ashes and Pond Ashes

Water retention curves (WRC) and its fitting parameters are important inputs for conducting unsaturated seepage modeling study in any geotechnical and geo-environmental problems. This study investigated the effect of variation in WRC model fitting parameters on unsaturated seepage modeling behavior for different types of fly ashes and pond ash. A transient seepage analysis was carried out in a one-dimensional cylindrical column using a finite element method-based software SEEP/W, under a specified total head (H) boundary condition. The variation in pore water pressure (PWP) and volumetric water content (VWC) with time was studied for different conditions. It was found that both PWP and VWC variation with time got affected when WRC model fitting parameters of different fly ashes were used. The influence of suction measurement range on unsaturated seepage modeling result was also found to be considerable. It was established from this study that variation in PWP with time for different fly ashes was mainly due to the variation in the WRC model fitting parameters since the saturated hydraulic conductivity (ksat) value of all the fly ashes was comparable. Further, the sensitivity of Fredlund and Xing (Can Geotech J 31(3): 521–532, 1994) model parameters was studied in detail based on their standard deviations. The study showed that sensitivity on seepage modeling results drastically reduces beyond 20% variation from the reference mean value.

Analysis of WRCC of Fly Ash-Bentonite Mixes Based on Combined Shrinkage and Suction Measurement

Sand-Bentonite mixtures are used in landfill liner application in appropriate proportions. However, effort has been made to replace the sand by some waste materials like fly ash without compromising the required properties for liner construction. In recent years, many studies were carried out to determine the suitability of different fly ashes for using with bentonite based on different geotechnical parameters. On the other hand, limited studies were found in determining the unsaturated characteristics i.e. Water Retention Characteristics Curve (WRCC) of fly ash-bentonite mixes. The determination of WRCC in case of bentonite is very complexed compared to other types of clay soil due to its high shrinkage and swelling characteristics upon drying and wetting. In this study, a combined shrinkage and suction measurement was carried out in fly ash-bentonite mixes to accurately represent the WRCC under drying condition only. The shrinkage measurement was carried out using balloon method and suction measurement was carried out with the help of WP4 dew point potentiameter device. Both the shrinkage and suction results were finally used to obtain the WRCC for the different mixes. Further, the study on the variability of WRCCs for the different mixes indicates that WRCC can be represented by a generalized plot with 20% variation.

Estimation of unsaturated hydraulic conductivity function: implication of low to high suction measurements

Establishment of the relationship between soil suction and water content, commonly termed as soil–water characteristic curve (SWCC), is of prime importance in the field of unsaturated soil mechanics. There are several instruments available that can be used to measure the SWCC of soil, but every suction measuring device has its own limitations in terms of its suction measurement range. Therefore, the preciseness of the estimated unsaturated soil properties largely depends on the range of suction measurements and the type of instruments used. The primary objective of this study is to quantify the error that can occur during the estimation of unsaturated hydraulic conductivity function (UHCF) from SWCC for low plastic soils. Experiments were performed to investigate the influence of different suction measurement devices on the estimated UHCF for four different soils with varying clay content. A dew point potentiometer (WP4) and a miniature tensiometer (T5) have been used in this study for the suction measurement. The SWCC of the selected soils were predicted mathematically using a commonly used pedo-transfer function (PTF). The experimental results clearly indicated that the sole use of WP4 overestimated the SWCC parameters, as well as UHCF (overestimation in the conductivity value is in order of 104 times). Rather, a combination of T5 and WP4 data, within their accurate range, provides a more precise estimation of UHCF. Further, the accuracy of the PTF was found very effective for low plastic soils with a relatively low percentage of clay (% clay < 10), in the absence of any experimental data.

Assessing crack initiation and propagation in flax fiber reinforced clay subjected to desiccation

Nowadays, raw earth construction is an area of growing interest, both for its eco-friendly characteristics and very interesting thermo-hygroscopic properties. Nevertheless, this type of construction exhibits a weakness related to cracking due to the shrinkage strains caused by desiccation. In this context, this paper presents an experimental study of restrained drying-shrinkage, carried out on a fine clayey soil. Several amounts of soil reinforcement with orderly layout patterns using vegetal flax fibers have been investigated in order to enhance soil properties. The new feature of this work is the analyzing of crack initiation and propagation by coupling the Digital Image Correlation (DIC) method with the Clay-Ring-Test (CRT) technique, using an innovative device called DIC-CRT. Suction measurements in clay samples are performed during desiccation using tensiometers. A good agreement is noticed between suction and strain evolution until cracking revealing the direct influence of suction on clay shrinkage. Through the two techniques, DIC and CRT, a relevant parameter to quantify crack intensity in materials is proposed. A significant decrease of crack ratio, by a factor of about 8, highlights the impact of soil reinforcement on the level of crack opening. Likewise, a significant decrease, by a factor of about 20, is observed in the analysis of DIC and CRT slopes, highlighting the impact of reinforcement on the kinetic of crack opening.

Evaluation of mine site reclamation performance using physical models: Case of Ity mine (Ivory coast)

The exploitation of the Ity gold mine in Ivory Coast will generate tailings that can be considered as potential generators of acid mine drainage (AMD). Various materials such as marble and clay are available around the mine site that could be used as components of an engineered cover for the reclamation of the reactive tailings impoundment. However, it is important to assess the properties of these potential cover materials and test different reclamation scenarios in the laboratory to select the best scenario for mine site reclamation. For this purpose, physical modeling was performed using experimental instrumented column tests simulating covers with capillary barrier effects (CCBEs) and monolayer covers. The columns were instrumented with sensors for measurement of volumetric water content (VWC) and suction. Leaching tests were performed over many cycles and physical and chemical analyses were carried out on the leachates. The observed hydrogeological behavior shows that either a CCBE or a monolayer cover with clayey silt materials can be used for the Ity mine site reclamation. However, hydrochemical results allow confirming that the monolayer cover made with clayey silt material can be considered as the best scenario for the Ity mine site reclamation.

Soil-water retention of highly expansive clay stabilized with a bio-polymer

The unpredictable expansiveness of clayey soils due to the change of water content can be responsible for significant pathologies on civil infrastructure. This behaviour depends mainly on the physical and chemical characteristics of the clayey soil and the stress-suction state of the soil. Extensive research has been carried out to control the swelling potential of clayey soils with traditional inorganic additives such as lime and cement. However, the use of these stabilizers presents adverse implications in terms of cost and environmental impact. Bio-products and waste by-products are an environmentally friendly alternative for geotechnical soil stabilization. In this article, we assess the effect of lignin on the hydro-mechanical behaviour of highly expansive clay. The research focuses on the behaviour upon wetting and the soil-water retention properties of clay and lignin-treated clay with different percentages. Suction measurements were made by using the filter paper technique. Particular emphasis on the mercury intrusion porosimetry analysis of the untreated and treated CR-Clay is done. Results of CR-Clay with lignin-based stabilizer show significant reduction of swelling upon wetting for the higher percentage of addition. Increase of the aggregation is observed with the growth of lignin percentage. An analysis of the soil-water retention properties with the van-Genutchen model is presented.

Semi-Empirical Model for Predicting the Swelling Stress of Compacted, Unsaturated Expansive Soils

Heaving soils are the most problematic worldwide. These soils develop swelling stress that produces uplift forces detrimental to the foundations. In engineering practice, swelling stress is not considered in general. Considering the swelling stress in foundation design enhances the service life of construction. The oedometer swelling test is the technique ordinarily used to assess the swelling stress. Nonetheless, the oedometer swelling test is cumbersome, time-consuming, making the test unattractive, and not cost-effective for the low-cost housing project. The objective of this research work is to propose a model to predict swelling stress as an alternative to oedometer testing. Geotechnical studies such as Atterberg limits, particle size distribution, free swell ratio, specific gravity, linear shrinkage, suction measurement, Proctor compaction test, and zero-swell test are performed to estimate the soil properties. Multivariate regression analysis is performed using NCSS.11 Program to develop the predictive model. The model is assessed base on the following: determining coefficient value, comparing predicted values with experimental values, comparing the proposed model with other existing models found in the literature. Besides, the Box-cox transformation function is used to improve the accuracy of the model. The developed model can be utilized to assess the swelling stress of compacted heaving soils, and it is much more accurate than other existing models.

Investigation to Quantify Suction Characteristics of Marine Soil during Drying and Wetting Cycles

Abstract The water retention characteristics of soil play a significant role in controlling its behavior (viz., strength, volume change, and cracking characteristics) during drying and wetting. In the case of marine soils, the water retention characteristics during drying and wetting cycles depend on both matric suction and osmotic suction. Studies by earlier researchers have mainly focused on soils with low osmotic suction and are applicable to higher degrees of saturation. Furthermore, there is a lack of studies that quantify the hysteresis associated with drying and wetting cycles for marine soils. In this context, the present work attempts the estimation of osmotic suction for marine soil by the experimental measurement of total and matric suction at different stages of drying and wetting by employing Dewpoint PotentiaMeter (WP4C). The study also evaluates hysteresis associated with matric, osmotic, and total suction. It has been observed from the study that osmotic suction has a significant influence on water retention characteristics of marine soils and attains a threshold value for a relatively dry state of the specimen. Furthermore, the hysteresis associated with matric suction is observed to be quite reproducible for different specimens, whereas for osmotic suction, some deviation is observed. The study presents the methodology for experimental quantification of osmotic suction, which would be quite useful in understanding the water retention behavior of marine soils in a more scientific way. It is opined that the findings of the study would be useful for understanding the influence of osmotic suction on marine soil behavior with respect to desiccation cracking during drying and time rate of settlement.

Investigation of the Influencing Soil Parameters on the Air Entry Values in Soil-Water Characteristic Curve of Compacted Heaving Soils

The air-entry value (AEV) is a fundamental parameter of the soil-water characteristic curve (SWCC). AEV is the minimum matric suction value required for entry of air into soil voids. The primary objective of this research work is to assess the impact of geotechnical index properties, swelling properties, mineral composition on AEV of compacted heaving soils, and discuss how they affect AEV. Soil properties were investigated through lab tests such as grain size distribution (GSD), specific gravity, Atterberg limits, linear shrinkage, free swell index, free swell ratio, X-ray diffraction, compaction test, and soil suction measurement. SWRC Fit program was used to perform non-linear fitting of the SWCC based on models VG, DB, FX, LN, and BL. Surface plot of data was used to characterize the impact of soil properties on AEV. It was observed that AEV is ranging from 10 kPa to 20.20 kPa, models DB and BL gives the best fitting SWCC. The percent of smectite mineral exhibits a significant impact on AEV. Swelling properties such as free swell index and free swell ratio influence the AEV with a respective determination coefficient of 85.72%, 88.68%. The plasticity index, linear shrinkage, specific gravity, and dry unit weight impact the AEV with a respective determination coefficient of 95%, 95.45%, 90.43%, 94.29%. The fine-grained content, clay fraction, void ratio, and water content influence the AEV with a respective determination coefficient of 97.95%, 84.89%, 80%, 94.31%. The finer the soil, the higher the AEV. The activity of clay and percent of illite mineral exhibit a marginal effect on the AEV.

Application of Mathematical Function to Estimate the Compaction Characteristics of Unsaturated Soils

The study aims to propose a mathematical approach to determine the optimum moisture content (<img src=image/14820636_01.gif>) and the corresponding maximum dry unit weight (<img src=image/14820636_02.gif>) of unsaturated fine-grained clay soils with accuracy. Laboratory tests such as grain size distribution, Atterberg limits, specific gravity, Proctor compaction test, and soil suction measurement are conducted to assess soil properties. The WOP and <img src=image/14820636_02.gif> are determined using the mathematical approach based on differential function (∂) and the graphical method. The differences in optimum moisture content values between the mathematical approach and the graphical method (<img src=image/14820636_03.gif>) values are 0.43 %, 0.36 %, 0.42 %, 0.24 %, respectively for soils PES, BFS, WIS, BES, and induced differences in total suction of 179.17 kPa, 144.00 kPa, 175.00 kPa, 96.00 kPa, respectively for soils PES, BFS, WIS, BES. Moreover, the differences in matric suction are 148.27 kPa, 116.13 kPa, 144.83 kPa, 80.00 kPa, respectively for soils PES, BFS, WIS, BES. <img src=image/14820636_02.gif> and <img src=image/14820636_03.gif> values are smaller than 0.5 % and marginal in the context of saturated soil mechanics. However, the total suction and matric suction values induced by <img src=image/14820636_02.gif> values are significant for unsaturated soils. An accurate estimation of <img src=image/14820636_03.gif> and <img src=image/14820636_01.gif> can be performed on unsaturated compacted soils using the mathematical approach.

Evaluation of time response of GMS for soil suction measurement

The Granular Matrix Sensor (GMS) is an indirect method for soil suction measurement. Since GMS is comparatively inexpensive, robust and usually provide continuous soil suction data, it is a natural candidate for civil engineering practice. The sensor has been used mainly for irrigation purposes, and also for some civil engineering activities. Questions about its effectiveness and reliability are still posed, making studies about this topic desirable. This study presents a laboratory comparison between Watermark and an ordinary tensiometer during an equilibrium period and for a wetting procedure performed in a compacted sandy silt soil (residual soil of gneiss). The results yielded that GMS may provide tensiometer equivalent suction values in a context of no significant water content variation. However, it takes a longer time to obtain stabilized suction values. During the wetting procedure, GMS presented a delay of about 2 h in detecting water while tensiometer detection was almost instantaneous.

Effects of compaction and suction on the hydromechanical properties of a dam core clay

The paper presents an experimental study of the hydromechanical behavior of a compacted clay used in the design of the core of the Boughrara dam (western Algeria). The influence of compaction energy level (CEL) is explored using three different energies: Standard Proctor energy (SP), reduced Proctor energy (SP-20 blows) and enhanced Proctor energy (SP+ 20 blows). The resulting compaction curves are supplemented by measurements of suction, which is a very important parameter in the behavior of compacted unsaturated soils. In addition to the compaction curves, elastic modulus and immediate bearing capacity ratio (IBCR) are measured, and related to suction and compaction energy level (CEL). Mechanical compaction paths following the SP curve and drying-wetting paths starting from SPO are compared. Mechanical properties such as E-modulus and IBCR are related to the two independent major parameters γd and Sr. Measuring these mechanical properties in the field allows to evaluate the compaction state regardless of the CEL. The results are compared with those of the literature.

Using inverse analysis to estimate hydraulic properties for unsaturated layered sand

In order to better evaluate the applicability of the inverse analysis method for calculation and evaluation of hydraulic properties of unsaturated soil in more realistic conditions, a transient one – step outflow experiment for layered sands was applied in the desaturation process with the purpose to attain the profiles of suction, saturation and flow rate with time. In this study, the fine sand and medium sand were used with the same thickness of 40cm for each layer. The sand grains were mixed under water and scooped into the plexiglas column (H = 80cm, D = 28cm, wall thickness = 1cm) to prepare a fully saturated sample. For homogeneity within each sand layer, the density of two sands must be controlled during soil column construction. For numerical study, the inverse simulation and one straightforward calculation were carried out to determine the unsaturated hydraulic properties of sands. Unsaturated hydraulic parameters in the van Genuchten model were estimated using soil suction measurements at 10cm intervals and an outflow rate at the bottom of a layered sand column. To reduce the quantity of data for analysis and simulation but still keep enough typical information for the experiment, four data sets of soil suction and saturation at four locations (L2, L4, L5 and L8) were selected out of eight to compile the Soil Water Characteristic Curve. The comparison between predicted unsaturated hydraulic properties and the experimental unsaturated hydraulic properties shows good agreement in the case of the fine sand was overlaid with medium sand. The results concluded that besides the homogeneous sand, the inverse analysis based on the 1-D outflow experiment promises to be a useful method in determining the hydraulic properties for unsaturated heterogeneous sand.

On the Reliability of Suction Measurements for Skin Characterization.

in vivo skin characterization methods were shown to be useful in the detection of microstructural alterations of the dermis due to skin diseases. Specifically, the diagnostic potential of skin suction has been widely explored, yet measurement uncertainties prevented so far its application in clinical assessment. In this work, we analyze specific factors influencing the reliability of suction measurements. We recently proposed a novel suction device, called Nimble, addressing the limitations of existing instruments, and applied it in clinical trials quantifying mechanical differences between healthy skin and scars. Measurements were performed with the commercial device Cutometer and with the new device. A set of new suction measurements was carried out on scar tissue and healthy skin, and FE-based inverse analysis was applied to determine corresponding parameters of a hyperelastic-viscoelastic material model. FE simulations were used to rationalize differences between suction protocols and to analyze specific factors influencing the measurement procedure. Tissue stiffness obtained from Cutometer measurements was significantly higher compared to the one from Nimble measurements, which was shown to be associated with the higher deformation levels in the Cutometer and the nonlinear mechanical response of skin. The effect of the contact force exerted on skin during suction measurements was quantified, along with an analysis of the effectiveness of a corresponding correction procedure. Parametric studies demonstrated the inherently higher sensitivity of displacement- over load-controlled suction measurements, thus rationalizing the superior ability of the Nimble to distinguish between tissues.

VOLUME CHANGE AND COMPRESSIVE STRENGTH OF COMPACTED LATERITIC SOIL UNDER DRYING-WETTING CYCLE REPETITION

This study was conducted to investigate volume changes and compressive strength behavior of compacted high expansive soils from lateritic soils (60%) and bentonite (40%) mixture under drying-wetting cycle repetition as a construction materials alternatives. Lateritic soil obtained from waste Nickel mining site in East Halmahera, North Maluku, Indonesia. Laboratory tests of physical properties using ASTM standard test were conducted to lateritic soil, bentonite, and mixture soil, while SEM test for lateritic and mixture soil. The soil samples have optimum moisture content based on Proctor standard compaction test results (28%). Then, samples were treated drying-wetting cycle and repeating four cycles with 25, 50, 75, and 100% series path. The soil suction measurement used the Whatman #42 filter paper placed at the top, middle, and bottom of each sample, and after that, the unconfined compression strength test was performed based on the ASTM standard. The experimental results showed that the drying-wetting cycle repetition has a significant effect on volume change, suction, and compressive strength of the soil. The increasing number of cycle causing void ratio decrease and degree of saturation increase, and soil suction tend to decrease at the certain void ratio; likewise, soil compressive strength decreases at particular water content. Decreasing soil compressive strength causes a decrease in elastic modulus so that soil failure behavior is more brittle and work-softening. Therefore, the study results provide important geotechnical characteristics data of lateritic soil with high swell-shrink potential. Henceforth, some soil improvement innovations can perform to generate high-quality construction materials more effectively and efficiently.

Development of a Multifunctional Triaxial System for Unsaturated Soils: Addition of Permeameter Function

The details of a multifunctional triaxial system developed for unsaturated soils over the past ten years at The University of Tokyo are described. This study first briefly reviewed three functions of the triaxial system developed for the undrained cyclic loading test to evaluate liquefaction properties of unsaturated soils. In the triaxial system, accurate measurement of volumetric deformation was achieved with a linkage double cell system, application of the membrane filter technique gave prompt measurements of matric suction, and a p-constant control system well maintained a constant condition of total mean principal stress p. The article later described a newly developed permeameter function of which delicately designed local pin sensors (LPSs) and inflow/outflow measurement devices were introduced to the triaxial system for measurement of coefficient of permeability of unsaturated sandy specimens. The permeameter maintained constant water levels at inflow and outflow ends, and the flow rates were monitored by sensors. LPSs, as local sensors to directly measure water head difference, were manufactured with the membrane filter technique, a technique to measure or control suction. Typical permeability test results on saturated and unsaturated specimens were presented. For unsaturated specimens, constant hydraulic heads were supplied, and the same inflow and outflow rates were achieved. Meanwhile, local pore water pressures measured by LPSs well reflected specimen conditions. It was verified from this and past studies that the permeameter system can be applied to unsaturated specimens with coefficient of permeability in a range of 10−5 to 10−8 m/s.

Determining the soil-water retention curve using mercury intrusion porosimetry test in consideration of soil volume change

Abstract It is well-known that a close link exists between soil-water retention curve (SWRC) and pore size distribution (PSD). Theoretically, mercury intrusion porosimetry (MIP) test simulates a soil drying path and the test results can be used to deduce the SWRC (termed SWRCMIP). However, SWRCMIP does not include the effect of volume change, compared with the conventional SWRC that is directly determined by suction measurement or suction control techniques. For deformable soils, there is a significant difference between conventional SWRC and SWRCMIP. In this study, drying test was carried out on a reconstituted silty soil, and the volume change, suction, and PSD were measured on samples with different water contents. The change in the deduced SWRCMIP and its relationship with the conventional SWRC were analyzed. The results showed that the volume change of soil is the main reason accounting for the difference between conventional SWRC and SWRCMIP. Based on the test results, a transformation model was then proposed for conventional SWRC and SWRCMIP, for which the soil state with no volume change is taken as a reference. Comparison between the experimental and predicted SWRCs showed that the proposed model can well consider the influence of soil volume change on its water retention property.

Laboratory and Physical Prototype Tests for the Investigation of Hydraulic Hysteresis of Pyroclastic Soils

Proper soil water retention curves (SWRCs) are necessary for a fair analysis of groundwater flow in unsaturated slopes. The question is whether hydraulic parameters operating in situ can be reliably determined from laboratory tests or physical prototype models in order to interpret and predict soil water distributions in the field. In this paper, some results obtained by tests at different scales (testing on laboratory specimens and a physical prototype) are presented to explore the hydraulic behavior of pyroclastic soils. A theoretical interpretation of the observed behavior in the laboratory and using a physical prototype is proposed by adopting the hysteretic model of Lenhard and Parker. For each tested soil, the main hysteretic loop determined by interpreting experimental tests (at laboratory and prototype scales) overlaps with paths detected by coupling the field measurements of matric suction and water content collected at the site at the same depth. From these results, the physical prototype (medium scale) and the soil specimen (small scale) seem to be acceptable for determinations of SWRC, provided that the air entrapment value is well known.

Swelling Stress and Suction Correlation of Compacted, Heaving Soils

The behaviour of unsaturated soils is mainly influenced by suction. When unsaturated soils display swelling properties, it becomes fundamental to investigate the impact of soil suction on the swelling stress. A survey was done across Free State province in South Africa and samples were obtained from Bloemfontein, Winburg, and Welkom. Geotechnical studies were performed on particle size definition, free swell ratio, free swell index, Atterberg limits, X-ray diffraction, proctor compaction test, soil suction measurement, and constant volume swelling tests to determine the physical and hydro-mechanical properties of the soil samples. According to the findings, at the optimum water content, the swelling stress values are in the range of 177 kPa to 326 kPa which is more than the bearing limit (~ 40 kPa) applied for most lightweight footing. Smectite is identified as the predominant clay mineral in the study areas and has a key influence on the swelling properties. A solid relation is observed between the swelling stress and the soil suctions, with a correlation coefficient value greater than 80 %.