Measurement Of Matric Suction Research Articles

Laboratory Investigation of the Effect of Initial Dry Density and Grain Size Distribution on Soil–Water Characteristic Curves of Wide-Grading Gravelly Soil

Wide-grading gravelly soils are often encountered in debris flow source areas. To perform stability analyses under rainfall conditions the soil–water characteristic curves (SWCC) are significant. However the studies for SWCC of wide-grading gravelly soils are rare. In order to investigate the effects of initial dry density and grain size distribution on the SWCCs of wide-grading gravelly a large-scale osmotic column allowing the measurement of both volumetric water content and matric suction at various levels was fabricated for a series of osmotic column tests. The test data were best-fitted to Van Genuchten equation using a least-squares algorithm and found that both the initial dry density and grain size distribution had a greater effect on the SWCCs. An increase in the initial dry density resulted in an increase in water retention capacity. The air entry value and residual volumetric water content increased linearly with increases in the initial dry density whereas the maximum slope of SWCC decreased linearly with increases in the initial dry density. The air entry value and residual volumetric water content increased linearly with increases in the fine content (particle diameter 10. © 2017 Springer International Publishing AG.

Experimental investigation of matric suction in compacted fine-grained soils

ABSTRACTThis paper presents the results of laboratory tests performed to study the effect of compaction properties on the development of matric suction in four different soils (three soils were classified as silty clay and one was classified as silty sand). The soils were compacted at the optimum water content (OWC) and wet and dry of optimum according to the standard Proctor procedure (ASTM D698-12). For each sample, matric suction measurements were made using the filter paper technique. When the silty clay soils were compacted at a water content less than the OWC, a significant increase in matric suction was observed. For all the soils tested, matric suction values were very low when the compaction water contents were greater than the OWC. Plots of matric suction vs. compaction water content [ranging from (OWC-2%) to OWC] were developed for the compacted silty clays. The test results indicate that there is a direct relationship between the compaction properties (i.e. compacted dry unit weight and water content) and the matric suction values retained in compacted silty clays. Preliminary relationships were proposed between the matric suction of compacted silty clays and water content based on the data collected in this paper.

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.

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.

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.

Applicability and accuracy of the initially dry and initially wet contact filter paper tests for matric suction measurement of geosynthetic clay liners

An initially wet contact filter paper test (IW-CFPT) and an initially dry contact filter paper test (ID-CFPT) were used to examine the wetting paths of geosynthetic clay liners, including non-contact filter paper tests for comparative purposes. The CFPTs were applied to both geosynthetic clay liner faces to examine the effect of geotextile type on capillary contact. The non-woven geotextile face was found to be more likely to cause capillary breaks than the woven geotextile face. Both IW- and ID-CFPTs were found to be applicable to geosynthetic clay liners within their accurate upper matric suction measurement limits of 146 kPa and 66 kPa, respectively.

Matric suction measurements of compacted subgrade soils

The mechanical response of compacted subgrade soils is highly influenced by matric suction. This paper proposes a detailed procedure for matric suction determination, using the filter paper technique, in samples compacted in the laboratory using the standard Proctor procedure (ASTM D698-12). Special attention is paid to the quantification of errors associated with the measurement of matric suction in compacted soils using the filter paper technique. The procedure is illustrated through suction measurements made for two fine-grained soils obtained from Indiana road sites. Soil samples were compacted at the optimum water content (OWC) and also both wet and dry of optimum. Test results indicated that the matric suction was substantially different for soils compacted on the dry side of the OWC and at the OWC. Matric suction measurements approached zero for soils compacted at water contents greater than the OWC + 2%. At the OWC, the soil with the lowest plasticity index but highest clay content developed higher matric suction than the soil with the highest plasticity index. The proposed test procedure facilitates the estimation of matric suction of subgrade soils in the laboratory.

Modeling the Drying Shrinkage Cracking of Untreated Soils and Cementitiously Stabilized Soils

Shrinkage cracking is a major concern that greatly limits the use of local soils and their cementitious stabilization in geosystems. Few studies have addressed the fundamental mechanisms of shrinkage and the related cracking in soils and cementitiously stabilized soils. This study characterizes two untreated soils and two soils treated with cement. On the basis of the matric suction and free-shrinkage measurements, a relationship was established between moisture loss and the drying shrinkage potential of untreated and cementitiously stabilized soils. Thus, on the basis of moisture loss, the shrinkage potential of the soils could be predicted. In addition, stress–strain relationships of soils that were affected by matric suction and cement hydration were developed on the basis of indirect tensile testing. Models were input into finite element analysis to characterize the moisture loss, drying shrinkage potential, shrinkage stress under given restraint condition, and shrinkage cracking of untreated and cementitiously stabilized soils. A drying shrinkage cracking test was designed to verify the models and procedure in terms of cracking time, tensile strength, and tensile load due to shrinkage. This study provides an approach to predicting the shrinkage cracking to properly design a pavement.

Hydro-mechanical behavior of polypropylene fiber reinforced expansive soils

This paper presents a series of laboratory tests and evaluates the effect of polypropylene fiber inclusion on volume change behavior and soil-water characteristics of expansive soils. Specimens were statically compacted at maximum Proctor dry density and optimum moisture content with 0%, 0.5% and 1% polypropylene fiber inclusions by dry weight of the soil, and their volume change behavior was studied through swell-shrinkage and consolidation tests. The soil-water characteristic behavior, which is the most significant aspect of soils, was also obtained by a series of matric suction measurements using filter paper technique. It was concluded that polypropylene fiber inclusion is very effective in reducing the compression and swell indices and swell pressures as well as one-dimensional swell amount in saturated condition. Upon desiccation, shrinkage of reinforced soil reduced considerably, as the shrinkage limit increased by more than 50%. Therefore, fiber reinforcement can effectively reduce swell-shrink movement of expansive soils.

In situ monitoring of the groundwater field in an unsaturated pyroclastic slope for slope stability evaluation

In the last 15 years, a series of catastrophic flowslides involving pyroclastic unsaturated soils has caused severe damage and a number of fatalities in the Campania region (southern Italy), where flowslides occur within the pyroclastic cover resting on the limestone massif. Rainwater infiltration is considered to be the triggering mechanism that leads to slope failure by reducing matric suction in unsaturated soils, hence reducing its shear strength. Therefore, knowledge of the groundwater regime is an important factor for slope stability evaluation as well as for predicting slope conditions prone to landslides triggered by water infiltration. The quality of prediction can be greatly improved if observations from in situ monitoring are available. This paper describes the results of an ongoing experimental research project on flowslides based on monitoring a test site in a typical geological environment in western Campania. The site was selected to carry out extensive laboratory and in situ testing. The test programme consisted of field monitoring of climatic conditions, matric suction and volumetric water content. The instrumentation and measuring techniques used in this research are systematically described to provide an example of good practice for use at other sites with similar features. With the use of the collected data, the seasonal fluctuations of the hydraulic regime in the subsoil may be observed and the critical periods for flowslide triggering identified. Measurements of matric suction from the test site are interpreted and directions of groundwater flow vectors in the subsoil are shown. Moreover, once the current state of the subsoil is known, slope stability conditions can be calculated using a simple infinite slope model that would provide continuously updated information on the current slope safety level.

Modelling of unsaturated ground behaviour influenced by vegetation transpiration

Vegetation contributes to weak soil stabilisation through reinforcement of the soil, dissipation of excess pore pressure and increasing the shear strength by induced matric suction. This paper describes the way vegetation influences soil matric suction, shrinkage and ground settlement in the vadose zone through transpiration. A mathematical model for the rate of root water uptake, including the root growth rate considering ground conditions, type of vegetation and climatic parameters, has been developed. A finite element approach is employed to solve the transient coupled flow-deformation equations. The finite element mesh is built using partially saturated soil elements capable of representing the salient aspects of unsaturated permeability and the soil water characteristic curve. The model formulation is based on the effective stress theory of unsaturated soils. Based on this proposed model, the distribution of the ground matric suction profile adjacent to the tree is numerically analysed. Current field measurements of soil matric suction and moisture content collected from Miram site located in Victoria State, Australia by the authors are compared with the numerical predictions. The results indicate that the proposed root water uptake model incorporated in the numerical analysis can be used for prediction of ground properties influenced by tree roots.

Evaluation of the Hydraulic Hysteresis of Unsaturated Pyroclastic Soils by in Situ Measurements

The triggering mechanism of debris flows and mudflows involving unsaturated soils has been extensively covered in the literature. It is associated with heavy rainfalls occurring during wet periods, when the pore water pressure regime is critical for landsliding. Having said this, full understanding of slope failure conditions needs a fair analysis of groundwater flow and, therefore, a proper hydraulic soil characterization as fundamental basis of the analysis. At this regard, laboratory characterization could be not sufficient: the soil water retention curve (SWRC) is hysteretic and the paths followed in situ, in terms of water content and matric suction, depend on the preceding hydraulic history. This aspect has to be accurately taken into account for analysis and prediction. In order to explore the hydraulic hysteretic behaviour of pyroclastic soils, in this paper pairs of water content and matric suction measurements registered at the same depth in an instrumented unsaturated pyroclastic slope are compared to a number of retention curves obtained in the laboratory.

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

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.

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.

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.

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.

Response to Discussion of ‘Modified Null Pressure Plate Apparatus for Measurement of Matric Suction' by Power, K. C. and Vanapalli, S. K.REFERENCE: Geotechnical Testing Journal, Vol. 33, No. 4, 2010 pp. 335–341

Response to Discussion of ‘Modified Null Pressure Plate Apparatus for Measurement of Matric Suction' by Power, K. C. and Vanapalli, S. K.REFERENCE: Geotechnical Testing Journal, Vol. 33, No. 4, 2010 pp. 335–341

Real-time unsaturated slope reliability assessment considering variations in monitored matric suction

A reliability-based slope stability assessment method considering fluctuations in the monitored matric suction was proposed for real-time identification of slope risk. The assessment model was based on the limit equilibrium model for infinite slope failure. The first-order reliability method (FORM) was adopted to calculate the probability of slope failure, and results of the model were compared with Monte-Carlo Simulation (MCS) results to validate the accuracy and efficiency of the model. The analysis shows that a model based on Advanced First-Order Reliability Method (AFORM) generates results that are in relatively good agreement with those of the MCS, using a relatively small number of function calls. The contribution of random variables to the slope reliability index was also examined using sensitivity analysis. The results of sensitivity analysis indicate that the effective cohesion c\' is a significant variable at low values of mean matric suction, whereasmatric suction (ua-uw) is the most influential factor at high mean suction values. Finally, the reliability indices of an unsaturated model soil slope, which was monitored by a wireless matric suction measurement system, were illustrated as 2D images using the suggested probabilistic model.

Reply to discussion by Haghighi et al. on “Measurements of suction versus water content for bentonite–sand mixtures”Appears in the Canadian Geotechnical Journal 48(2): 336–337 (2011)

The discussers presented filter paper calibration data measured using the vapour equilibrium technique using a salt solution for suctions greater than 300 kPa and through a pressure plate apparatus, in which the filter papers sandwiched between two soil samples were equilibrated to the induced suction values. The data presented agree well with those obtained by the authors for the matric suction (or the in-contact) filter paper calibration up to about 800 kPa and for the total suction greater than 8000 kPa. It should be noted that the accuracy of the total suction measurement using the noncontact technique reduces as total suction decreases. In contrast, the error of the matric suction measurement using the in-contact filter paper increases with increasing matric suction. The total suction (or the noncontact filter paper) calibration data presented by the authors were obtained for total suctions greater than 4000 kPa. It is thought that the errors associated with the measurement of total suction lower than this value are high and are not only caused by the possible temperature gradient during calibration, but also by the error in preparation of the salt solution involving a small amount of salt. No attempt was made by the authors to induce total suction less than 4000 kPa due to the above-mentioned reasons. However, the data presented in Agus (2005) suggest that an extrapolation to total suction values between 2000 and 4000 kPa is possible, but with a maximum possible error of 860 kPa. The use of this technique for measuring total suction of less than 2000 kPa is not recommended. The discussers have shown that in the suction range from 4000 to 8000 kPa the measured filter paper water contents are lower than those presented by the authors for the same total suction values. Filter papers equilibrated to total suctions within this range will normally undergo a wetting process due to the initially relatively dry filter paper used. The amount of water absorbed by the filter paper during the equilibration period is a function of the equilibration time allowed. Equilibrium is thought to be attained after a relatively long equilibration time and is affected by the temperature fluctuation in the calibration system, or more importantly by the temperature gradient between the salt solution, vapor space, and filter paper. The discussers used a 2 week equilibration time as opposed to a 5 week equilibration time adopted by the authors. It is thought that the discussers’ data would be closer to those obtained by the authors if the same equilibration time had been used. The resulting total suction calibration curve will consequently be different from that obtained for the matric suction measurement. Similarly, the equibration time at high matric suctions (i.e., close to 1500 kPa) is thought to be long as water may transfer in vapor form without good contact between the ceramic disk and the filter paper during the matric suction measurement. At high matric suctions, filter paper tends to absorb a smaller amount of absorbed water than it should had a sufficiently long equilibration time not been allowed. Hence, although theoretically the technique can be used to measure matric suction as high as 1500 kPa, the calibration data for matric suctions ranging from 1000 to 1500 kPa are difficult to obtain with sufficient accuracy. In conclusion, reasonable measurement accuracy will be obtained when the filter paper technique is used to measure matric suctions of less than 1000 kPa, or total suctions of greater than 4000 kPa.

Discussion of “Modified Null Pressure Plate Apparatus for Measurement of Matric Suction” by Power, K. C. and Vanapalli, S. K., Geotechnical Testing Journal, Vol. 33, No. 4, Paper ID GTJ102478

Discussion of “Modified Null Pressure Plate Apparatus for Measurement of Matric Suction” by Power, K. C. and Vanapalli, S. K., Geotechnical Testing Journal, Vol. 33, No. 4, Paper ID GTJ102478