Use of thermal conductivity sensors to measure matric suction in the laboratory

1989 ◽  
Vol 26 (3) ◽  
pp. 491-498 ◽  
Author(s):  
Pamela Sattler ◽  
D. G. Fredlund
Keyword(s):  
Thermal Conductivity ◽  
Unsaturated Soils ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Test Procedure ◽  
Matric Suction ◽  
Engineering Practice ◽  
Equilibration Time ◽  
Overburden Pressure ◽  
Conductivity Sensor

The measurement of soil suction is pivotal to the application of soil mechanics principles in geotechnical engineering practice related to unsaturated soils. Volume change, shear strength, and seepage analyses all require an understanding of the matric suction in the soil. This note summarizes the use of thermal conductivity sensors to measure matric suction in the laboratory. The thermal conductivity sensor is described along with its mode of operation. A brief description is given of the procedure for calibrating thermal conductivity sensors using a pressure plate apparatus. The measurement of matric suction can be performed in the laboratory on Shelby tube samples. The laboratory measurements of matric suction can be adjusted for the effect of overburden pressure in the field. The required equilibration time for suction measurements is discussed along with details of the test procedure. The applications of the measured suction values to design are briefly discussed.Key words: matric suction, negative pore-water pressure, thermal conductivity sensor, laboratory, undisturbed samples.

Mini suction probe for matric suction measurements

2002 ◽  
Vol 39 (6) ◽  
pp. 1427-1432 ◽  
Author(s):  
Inge Meilani ◽  
Harianto Rahardjo ◽  
Eng-Choon Leong ◽  
Delwyn G Fredlund
Keyword(s):  
Pore Water ◽  
Unsaturated Soils ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Matric Suction ◽  
Lateral Direction ◽  
Triaxial Apparatus ◽  
Specimen Height ◽  
Pressure Changes ◽  
Accurate Reading

A modified triaxial apparatus with mini suction probes was fabricated to study the matric suction along the specimen height during unsaturated triaxial testing. Three mini suction probes were placed at 3/4, 1/2, and 1/4 height of the specimen, each at 120° apart in the lateral direction. This paper presents the development of the mini probe for matric suction measurements. Evaluation of the performance shows that the fabricated mini probe provides a rapid response and accurate reading under negative and positive pore-water pressure changes. Matric suctions as high as 400 kPa were successfully measured on soil specimens over a time span of 15 h. On the other hand, the mini suction probes were also found to be able to measure a matric suction of 200 kPa for a longer period of 155 h.Key words: matric suction, mini suction probe, triaxial, unsaturated soils, mid-height pore-water pressure measurement.

Experimental verification of the theory of consolidation for unsaturated soils

1995 ◽  
Vol 32 (5) ◽  
pp. 749-766 ◽  
Author(s):  
Harianto Rahardjo ◽  
Delwyn G. Fredlund
Keyword(s):  
Water Content ◽  
Pore Pressure ◽  
Pore Water ◽  
Unsaturated Soils ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Matric Suction ◽  
Water Volume ◽  
Loading Tests ◽  
Undrained Loading

An experimental program was designed to study the behavior of unsaturated soils during undrained loading and consolidation. A Ko cylinder was designed and built for the testing program. Simultaneous measurements of pore-air and pore-water pressures could be made throughout a soil specimen using this Ko cylinder. Four types of tests were performed on a silty sand. These are (1) undrained loading tests where both the air and water are not allowed to drain, (2) constant water content tests where only the water phase is not allowed to drain, (3) consolidation tests where both the air and water phases are allowed to drain, and (4) increasing matric suction tests. Undrained loading tests or constant water content loading tests were conducted for measuring the pore pressure parameters for the unsaturated soil. Drained tests consisting of either consolidation tests or increasing matric suction tests were conducted to study the pore pressure distribution and volume change behavior throughout an unsaturated soil during a transient process. The experimental pore pressure parameters obtained from the undrained loadings and constant water content leadings agreed reasonably well with theory. The pore-air pressure was found to dissipate instantaneously when the air phase is continuous. The pore-water pressure dissipation during the consolidation test was found to be faster than the pore-water pressure decrease during the increasing matric suction test. The differing rates of dissipation were attributed to the different coefficients of water volume change for each of the tests. The water volume changes during the consolidation test were considerably smaller than the water volume changes during the increasing matric suction tests for the same increment of pressure change. Key words : consolidation, Ko loading, matric suction, pore-air pressures, pore-water pressures, unsaturated soils

Second Canadian Geotechnical Colloquium: Appropriate concepts and technology for unsaturated soils

1979 ◽  
Vol 16 (1) ◽  
pp. 121-139 ◽  
Author(s):  
D. G. Fredlund
Keyword(s):  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Three Dimensional ◽  
Earth Pressure ◽  
Saturated Soil ◽  
Engineering Practice ◽  
The Matrix ◽  
Matrix Suction

A practical science has not been fully developed for unsaturated soils for two main reasons. First, there has been the lack of an appropriate science with a theoretical base. Second, there has been the lack of an appropriate technology to render engineering practice financially viable.This paper presents concepts that can be used to develop an appropriate engineering practice for unsaturated soils. The nature of an unsaturated soil is first described along with the accompanying stress conditions. The basic equations related to mechanical properties are then proposed. These are applied to practical problems such as earth pressure, limiting equilibrium, and volume change.An attempt is made to demonstrate the manner in which saturated soil mechanics must be extended when a soil is unsaturated. Two variables are required to describe the stress state of an unsaturated soil (e.g., (σ – ua) and (ua – uW). There is a smooth transition from the unsaturated case to the saturated case since the pore-air pressure becomes equal to the pore-water pressure as the degree of saturation approaches 100%. Therefore, the matrix suction (i.e., (ua – uW) goes to 0 and the pore-water pressure can be substituted for the pore-air pressure (i.e., (σ – uW)).The complete volumetric deformation of an unsaturated soil requires two three-dimensional constitutive surfaces. These converge to one two-dimensional relationship for a saturated soil. The shear strength for an unsaturated soil is a three-dimensional surface that reduces to the conventional Mohr–Coulomb envelope for a saturated soil.The manner of applying the volumetric deformation equations and the shear strength equation to practical problems is demonstrated. For earth pressure and limiting equilibrium problems, the unsaturated soil can be viewed as a saturated soil with an increased cohesion. The increase in cohesion is proportional to the matrix suction of the soil. For volume change problems it is necessary to have an indication of the relationship between the various soil moduli.There is a need for further experimental studies and case histories to substantiate the proposed concepts and theories.

scholarly journals Influence of Matric Suction on the Shear Strength Behaviour of Unsaturated Sand

10.14311/590 ◽  
2004 ◽  
Vol 44 (4) ◽  
Author(s):  
A. Farouk ◽  
L. Lamboj ◽  
J. Kos
Keyword(s):  
Shear Strength ◽  
Stress State ◽  
Unsaturated Soils ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Matric Suction ◽  
Test Method ◽  
State Variables ◽  
Unsaturated Sand

As a part of the effort made to understand the behaviour of unsaturated soils, this work studies the shear strength characteristics of a cohesionless unsaturated soil. Generally, the determination of the shear strength of unsaturated soils is a great challenge to geotechnical engineers, both in terms of understanding it and the effort necessary to determine it. Matric suction is one of the stress state variables that control the shear strength of unsaturated soils. Therefore, the main aim of this study is to investigate the effect of matric suction on the shear strength characteristic of sand known commercially as Sand PR33. The shear strength behaviour of unsaturated sand is studied in this work using the constant water content triaxial test method with measurements of matric suction during the shearing stage. The tests were performed using the axis translation technique in such a way that the pore-air pressure was controlled while the pore-water pressure was measured during all tests.

scholarly journals Evaluation on slope stability of unsaturated soils

2000 ◽  
Vol 22 ◽  
Author(s):  
L. J. Wang ◽  
M. Zhang
Keyword(s):  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Pore Water Pressure ◽  
Limit Equilibrium ◽  
Water Pressure ◽  
Matric Suction ◽  
Groundwater Table ◽  
Degree Of Saturation ◽  
Engineering Properties ◽  
Soil Slopes

In drought-prone and semiarid areas, the groundwater table is deep and the soils are at an unsaturated state because of evaporation or transpiration. The negative pore water pressure or matric suction (ua-uw) is an important property of unsaturated soils that are situated above the groundwater table. In the conditions of rainfall, ground seepage, or drainpipe leakage, the matric suction will decrease with the increase of the degree of saturation, and the soils will lose their part of shear strength, which is the main reason why many unsaturated soil slopes become unstable. This paper discusses the engineering properties of unsaturated soils. Following the limit equilibrium principle, the unsaturated soil slopes are evaluated by applying the slice method.

Pore-water pressure and water volume change of an unsaturated soil under infiltration conditions

2005 ◽  
Vol 42 (6) ◽  
pp. 1509-1531 ◽  
Author(s):  
Inge Meilani ◽  
Harianto Rahardjo ◽  
Eng-Choon Leong
Keyword(s):  
Pore Water ◽  
Volume Change ◽  
Unsaturated Soils ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Volumetric Strain ◽  
Confining Pressure ◽  
Matric Suction ◽  
Water Volume ◽  
Infiltration Tests

Triaxial shearing–infiltration tests were conducted to study the pore-water pressure and volume change of unsaturated soils subjected to infiltration conditions. A modified triaxial apparatus with three Nanyang Technological University (NTU) mini suction probes along the specimen height was used for the experimental program. Elastic moduli were obtained for the soil structure with respect to changes in net confining pressure (E) and matric suction (H). Water volumetric moduli associated with changes in net confining pressure (Ew) and matric suction (Hw) were also obtained from the shearing–infiltration tests. Water volumetric strain and pore-water pressure during the shearing–infiltration tests were computed based on volume change theory. This paper presents the significance of obtaining the parameter Hw from an appropriate scanning curve of a soil-water characteristic curve (SWCC) for the computation of water volumetric strain and pore-water pressure changes during a shearing–infiltration test. The appropriate scanning curve should be obtained from the wetting curve of the SWCC at the matric suction where the infiltration test commences.Key words: infiltration, matric suction, triaxial, unsaturated soils, pore-water pressure, water volume change.

scholarly journals Seismic detection of transient changes beneath Black Rapids Glacier, Alaska, U.S.A.: II. Basal morphology and processes

1999 ◽  
Vol 45 (149) ◽  
pp. 132-146 ◽  
Author(s):  
Matt Nolan ◽  
Keith Echelmeyer
Keyword(s):  
Hydraulic System ◽  
Seismic Analysis ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Basal Layer ◽  
Thick Layer ◽  
Reflection Coefficients ◽  
Overburden Pressure ◽  
Arrival Times ◽  
Black Rapids Glacier

AbstractUsing changes observed in daily seismic reflections, we have investigated the basal morphology of Black Rapids Glacier, Alaska, U.S.A. The englacial drainage of ice-marginal lakes caused significant changes in the daily reflections, as well as dramatic increases in basal motion. Changes in reflection arrival times and amplitudes indicate that there is a basal till layer at least 5 m thick at some locations beneath this surge-type glacier. Rapid changes in the observed reflection coefficients during the drainage events indicate that changes in till properties must occur throughout the entire 5 m thick layer, they must last for several days following the lake drainages and they must be completely reversible over as little as 36 min. Our seismic analysis shows that changes in effective pressure of the till are unlikely to cause the required changes in the reflection coefficients, but that a decrease in till saturation is likely. We therefore interpret the cause of the seismic anomalies as being a temporary decrease in saturation as water is input to the subglacial hydraulic system, and propose that such a change may occur quickly and reversibly by a redistribution of overburden pressure. Higher water pressures within the hydraulic system cause that region to support more of the glacier’s weight, leaving the remaining areas to support less. Any till within these areas of decreased normal stress would experience a consequent decrease in pore-water pressure, causing gas to exolve, thus decreasing saturation. This decrease in saturation would cause a change in the strength of the basal layer and may affect basal dynamics.

Prediction of liquefaction potential and pore water pressure beneath machine foundations

2014 ◽  
Vol 4 (3) ◽  
Author(s):  
Mohammed Fattah ◽  
Mohammed Al-Neami ◽  
Nora Jajjawi
Keyword(s):  
Pore Water ◽  
Sandy Soil ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Soil Liquefaction ◽  
Elastic Model ◽  
Liquefaction Resistance ◽  
Overburden Pressure ◽  
Liquefaction Potential ◽  
Frequency Changes

AbstractThe present research is concerned with predicting liquefaction potential and pore water pressure under the dynamic loading on fully saturated sandy soil using the finite element method by QUAKE/W computer program. As a case study, machine foundations on fully saturated sandy soil in different cases of soil densification (loose, medium and dense sand) are analyzed. Harmonic loading is used in a parametric study to investigate the effect of several parameters including: the amplitude frequency of the dynamic load. The equivalent linear elastic model is adopted to model the soil behaviour and eight node isoparametric elements are used to model the soil. Emphasis was made on zones at which liquefaction takes place, the pore water pressure and vertical displacements develop during liquefaction. The results showed that liquefaction and deformation develop fast with the increase of loading amplitude and frequency. Liquefaction zones increase with the increase of load frequency and amplitude. Tracing the propagation of liquefaction zones, one can notice that, liquefaction occurs first near the loading end and then develops faraway. The soil overburden pressure affects the soil liquefaction resistance at large depths. The liquefaction resistance and time for initial liquefaction increase with increasing depths. When the frequency changes from 5 to 10 rad/sec. (approximately from static to dynamic), the response in displacement and pore water pressure is very pronounced. This can be attributed to inertia effects. Further increase of frequency leads to smaller effect on displacement and pore water pressure. When the frequency is low; 5, 10 and 25 rad/sec., the oscillation of the displacement ends within the period of load application 60 sec., while when ω = 50 rad/sec., oscillation continues after this period.

scholarly journals Impact of the moisture content in medium sands on CPTU test results

2016 ◽  
Vol 48 (3) ◽  
pp. 221-231 ◽  
Author(s):  
Łukasz Zawadzki ◽  
Marek Bajda
Keyword(s):  
Moisture Content ◽  
Unsaturated Soils ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Degree Of Saturation ◽  
Test Results ◽  
Time Dynamic ◽  
Tip Resistance ◽  
The Impact ◽  
Resistance Value

Abstract Soils occurring in the soil “active zone” are in contact with the surface and are directly influenced by external factors (mainly climatic changes) that cause variation in their parameters over time. Dynamic and uncontrolled changes of soil properties e.g. due to rainfall and evapotranspiration processes may affect field test results leading to the misinterpretation of the obtained data. This paper presents investigations on the influence of moisture content changes in sandy soils on CPTU results. For this purpose, a field ground model has been constructed and five CPTU tests with a different moisture content of soil were carried out. During the investigations, the tip resistance (qc), friction on sleeve (fs), and pore water pressure (u2) were measured. Moreover, a TDR probe was applied to determine the distribution of the moisture content in the studied soil columns. Differences between CPT results obtained in saturated and unsaturated soils have been shown. Furthermore, a simple equation to correct the tip resistance value due to the impact of the degree of saturation has been proposed.

Soil-water characteristic curve and consolidation behavior for a compacted silt

2007 ◽  
Vol 44 (3) ◽  
pp. 266-275 ◽  
Author(s):  
Trinh Minh Thu ◽  
Harianto Rahardjo ◽  
Eng-Choon Leong
Keyword(s):  
Soil Water ◽  
Volume Change ◽  
Unsaturated Soils ◽  
Water Pressure ◽  
Characteristic Curve ◽  
Matric Suction ◽  
Confining Stress ◽  
Soil Water Characteristic Curve ◽  
Triaxial Cell ◽  
Isotropic Consolidation

Measurement of the soil-water characteristic curve (SWCC) in the laboratory is commonly conducted under zero confining pressure. However, in the field, the soil is under a confining stress. Therefore, it is important to study the effects of the confining stress on SWCC. In addition, the consolidation curve is normally generated under saturated conditions. However, the soil above the water table is usually unsaturated. Hence, it is also necessary to investigate the effects of matric suction on the characteristics of the consolidation curves. This paper presents the SWCCs under different net confining stresses and the isotropic consolidation curves under different matric suctions that describe the volume change characteristics of unsaturated soils with respect to stress state variables, net normal stress, and matric suction. A series of SWCCs was determined for statically compacted silt specimens in a triaxial cell apparatus under different net confining stresses. Isotropic consolidation tests under different matric suctions were also carried out. The results of the SWCC tests show that the air-entry value increased with increasing net confining stress. The yield points (i.e., yield suction, s0) obtained from the SWCC tests also increased with increasing net confining stress. The results of isotropic consolidation tests indicate the strong influence of matric suction on compressibility and stiffness of the compacted silt specimens.Key words: soil-water characteristic curve, isotropic consolidation, pore-water pressure, volume change, NTU mini suction probe, matric suction.

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