Use of instantaneous profile and statistical methods to determine permeability functions of unsaturated soils

2009 ◽  
Vol 46 (7) ◽  
pp. 869-874 ◽  
Author(s):  
Henry Krisdani ◽  
Harianto Rahardjo ◽  
Eng-Choon Leong
Keyword(s):  
Statistical Method ◽  
Unsaturated Soils ◽  
Pore Water Pressure ◽  
Direct Method ◽  
Water Pressure ◽  
Residual Soils ◽  
Profile Method ◽  
Permeability Function ◽  
Direct And Indirect Methods

This paper presents the determination of permeability functions by direct and indirect methods. The direct method used in this study was the instantaneous profile method, while the indirect method used was the statistical method. The instantaneous profile method was adopted to calculate permeability functions of residual soils used in laboratory slope models. Pore-water pressure measured using tensiometers along the slope models and independently measured soil-water characteristic curves (SWCCs) were used for the instantaneous profile calculation. To obtain a continuous permeability function, the instantaneous profile results were then fitted using the statistical method.

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 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.

Aspects of the behaviour of compacted clayey soils on drying and wetting paths

2002 ◽  
Vol 39 (6) ◽  
pp. 1341-1357 ◽  
Author(s):  
Jean-Marie Fleureau ◽  
Jean-Claude Verbrugge ◽  
Pedro J Huergo ◽  
António Gomes Correia ◽  
Siba Kheirbek-Saoud
Keyword(s):  
Water Content ◽  
Pore Water ◽  
Unsaturated Soils ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Dry Density ◽  
Clayey Soils ◽  
Maximum Dry Density ◽  
Optimum Water Content ◽  
Optimum Water

A relatively large number of drying and wetting tests have been performed on clayey soils compacted at the standard or modified Proctor optimum water content and maximum density and compared with tests on normally consolidated or overconsolidated soils. The results show that drying and wetting paths on compacted soils are fairly linear and reversible in the void ratio or water content versus negative pore-water pressure planes. On the wet side of the optimum, the wetting paths are independent of the compaction water content and can be approached by compaction tests with measurement of the negative pore-water pressure. Correlations have been established between the liquid limit of the soils and such properties as the optimum water content and negative pore-water pressure, the maximum dry density, and the swelling or drying index. Although based on a limited number of tests, these correlations provide a fairly good basis to model the drying–wetting paths when all the necessary data are not available.Key words: compaction, unsaturated soils, clays, drying, wetting, Proctor conditions.

A Flexible Wall Permeameter for the Determination of the Water Permeability Function in Unsaturated Soils

2011 ◽  
Vol 34 (5) ◽  
pp. 103595
Author(s):  
L. D. Suits ◽  
T. C. Sheahan ◽  
M. P. H. Moncada ◽  
T. M. P. de Campos ◽  
G. Steger
Keyword(s):  
Water Permeability ◽  
Unsaturated Soils ◽  
Permeability Function ◽  
Flexible Wall

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

Simplified Computation of 1D Consolidation for Unsaturated Soil when Air Phase Neglected

2010 ◽  
Vol 168-170 ◽  
pp. 298-302
Author(s):  
Hao Feng Xu ◽  
Kang he Xie
Keyword(s):  
Unsaturated Soils ◽  
Laboratory Tests ◽  
Continuity Equation ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Soil Mass ◽  
Excess Pore Water Pressure ◽  
One Dimensional ◽  
Consolidation Model ◽  
Consolidation Analysis

It is a complicated problem for consolidation analysis of unsaturated soils. Nowadays’ theories are very theoretical, and the parameters in them are so many that it is difficult to solve the equations, i.e., they are not excellently fit for application in engineering. So it is significant to get a simplified theory for consolidation analysis of unsaturated soils. In this paper, according to the phenomena observed in consolidation’s experiments for unsaturated soils, it is assumed that pore-air pressure undergoes an instantaneous dissipation and the consolidation of unsaturated soils can be described as the process of dissipation of excess pore-water pressure. Then a simplified consolidation model is put forward. And based on the principle of the whole soil mass conversation, the continuity equation is founded. Subsequently one- dimensional consolidation equation is derived, which is similar to Terzaghi’s equation for consolidation of saturated soils. Finally, the numerical results from the derived equation are compared with the experimental results from laboratory tests reported in the literature, and the agreement is good. It can be concluded that the hypothesis is rational and the simplified computation is practical in engineering.

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.

Development of a new calibration chamber for conducting cone penetration tests in unsaturated soils

2011 ◽  
Vol 48 (2) ◽  
pp. 314-321 ◽  
Author(s):  
Mohammad Pournaghiazar ◽  
Adrian R. Russell ◽  
Nasser Khalili
Keyword(s):  
Unsaturated Soils ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Bottom Plate ◽  
Cone Penetration ◽  
Rubber Membrane ◽  
Cone Penetration Tests ◽  
Horizontal Pressure ◽  
Calibration Chamber ◽  
Penetration Tests

A calibration chamber has been developed to conduct laboratory-controlled cone penetration tests in unsaturated soils. The chamber allows independent application of lateral and vertical pressures to an unsaturated soil specimen. Horizontal pressure is applied by cell water pressure pushing on a rubber membrane enclosing the specimen, while vertical pressure is maintained by a hydraulic loading ram at the base of the specimen. Suction is controlled using the axis-translation technique. Air pressure is applied to the top of the chamber where it spreads uniformly across the top of the specimen. Pore-water pressure is applied through eight high air-entry value porous disks embedded in the bottom plate. A particularly original aspect of the chamber design is the specimen formation system comprising four moveable cylinder quarters, which enables the creation of specimens of repeatable properties from a variety of soil types. The results of typical cone penetration tests conducted on dry, saturated, and unsaturated sand specimens are presented and highlight the contribution of suction to cone penetration resistance.

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