Measurement of the coefficient of permeability for a deformable unsaturated soil using a triaxial permeameter

1998 ◽  
Vol 35 (3) ◽  
pp. 426-432 ◽  
Author(s):  
Shangyan Huang ◽  
D G Fredlund ◽  
S L Barbour
Keyword(s):  
Volume Change ◽  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Matric Suction ◽  
Soil Specimen ◽  
Normal Stresses ◽  
Permeability Measurement ◽  
Coefficient Of Permeability

The development of a specially designed triaxial permeameter for the measurement of the coefficient of permeability of deformable unsaturated soils is presented in this paper. The triaxial permeameter makes it possible to directly measure the coefficient of permeability at various combinations of net normal stresses and matric suction values. The volume change of the soil specimen during the permeability measurement can also be monitored. The performance of the permeameter is demonstrated for a group of tests conducted on slurried specimens of a silty sand.Key words: unsaturated soil, coefficient of permeability, triaxial permeameter, volume change.

Testing Study on the Permeability Characteristics of Unsaturated Soils

2011 ◽  
Vol 261-263 ◽  
pp. 1773-1777
Author(s):  
Ying Cui ◽  
Lin Chang Miao
Keyword(s):  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Matric Suction ◽  
Normal Stresses ◽  
Moisture Migration ◽  
Permeability Characteristics ◽  
Coefficient Of Permeability

The coefficient of permeability of unsaturated soil is an important parameter which is used to analyze moisture migration. For complexity and diversity of unsaturated soil behaviors, it is difficult to perform test of unsaturated soil because of many factors. With GDS system, the permeability characteristics of unsaturated soil are tested and studied in this paper which makes it possible to directly measure the coefficient of permeability at various combinations of net normal stresses and matric suction values. The research shows the coefficient of permeability of unsaturated soil is the function of suction and cell pressure.

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.

Settlement rate of foundations on unsaturated soils

1999 ◽  
Vol 36 (5) ◽  
pp. 940-946 ◽  
Author(s):  
Ernesto Ausilio ◽  
Enrico Conte
Keyword(s):  
Volume Change ◽  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Shallow Foundations ◽  
Settlement Rate ◽  
One Dimensional ◽  
Consolidation Rate ◽  
Degree Of Consolidation ◽  
The One ◽  
External Loads

This paper deals with the one-dimensional consolidation of unsaturated soils due to the application of external loads. A simple equation is derived that enables one to predict the rate of settlement of shallow foundations with time. This equation uses the constitutive relationships proposed by Fredlund and Morgenstern to define the volume change of unsaturated soils, and relates the settlement rate to the average degree of consolidation for both the water and air phases. A series of examples is shown to demonstrate the feasibility and usefulness of the derived equation. Key words: one-dimensional consolidation, unsaturated soil, degree of consolidation, rate of settlement.

Modeling the unsaturated soil zone in slope stability analysis

2014 ◽  
Vol 51 (12) ◽  
pp. 1384-1398 ◽  
Author(s):  
L. L. Zhang ◽  
Delwyn G. Fredlund ◽  
Murray D. Fredlund ◽  
G. Ward Wilson
Keyword(s):  
Shear Strength ◽  
Stability Analysis ◽  
Slope Stability ◽  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Matric Suction ◽  
Slope Stability Analysis ◽  
Engineering Practice ◽  
Rate Of Increase ◽  
Nonlinear Shear

The linear form of the extended Mohr–Coulomb shear strength equation uses a [Formula: see text] parameter to quantify the rate of increase in shear strength relative to matric suction. When the [Formula: see text] value is unknown, a [Formula: see text] equal to 15° is sometimes used in the slope stability study to assess the influence of matric suction on the stability of a slope. In many cases, however, a [Formula: see text] value of zero is used, signifying that the effect of matric suction is ignored. Experiment results have shown that the relationship between the shear strength of an unsaturated soil and matric suction is nonlinear. Several semi-empirical estimation equations have been proposed relating the unsaturated shear strength to the soil-water characteristic curve. In this paper, the results of a study using two-dimensional slope stability analysis along with an estimated nonlinear shear strength equations is presented. The effects of using an estimated nonlinear shear strength equation for the unsaturated soils are illustrated using three example problems. Several recommendations are made for engineering practice based on the results of the example problems. If the air-entry value (AEV) of a soil is smaller than 1 kPa, the effect of matric suction on the calculated factor of safety is trivial and the [Formula: see text] value can be assumed to be zero. If the AEV of a soil is between 1 and 20 kPa, the nonlinear equations of unsaturated shear strength should be adopted. For soils with an AEV value between 20 and 200 kPa, an assumed [Formula: see text] value of 15° provides a reasonable estimation of the effects of unsaturated shear strength in most cases. For soils with an AEV greater than 200 kPa, [Formula: see text] can generally be assumed to be equal to the effective angle of internal friction, [Formula: see text], in applications where geotechnical structures have matric suctions around 100 kPa.

Model for the prediction of shear strength with respect to soil suction

1996 ◽  
Vol 33 (3) ◽  
pp. 379-392 ◽  
Author(s):  
S K Vanapalli ◽  
D G Fredlund ◽  
D E Pufahl ◽  
A W Clifton
Keyword(s):  
Shear Strength ◽  
Soil Water ◽  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Characteristic Curve ◽  
Experimental Studies ◽  
Matric Suction ◽  
Glacial Till ◽  
Soil Suction ◽  
Soil Water Characteristic Curve

Experimental studies on unsaturated soils are generally costly, time-consuming, and difficult to conduct. Shear strength data from the research literature suggests that there is a nonlinear increase in strength as the soil desaturates as a result of an increase in matric suction. Since the shear strength of an unsaturated soil is strongly related to the amount of water in the voids of the soil, and therefore to matric suction, it is postulated that the shear strength of an unsaturated soil should also bear a relationship to the soil-water characteristic curve. This paper describes the relationship between the soil-water characteristic curve and the shear strength of an unsaturated soil with respect to matric suction. Am empirical, analytical model is developed to predict the shear strength in terms of soil suction. The formulation makes use of the soil-water characteristic curve and the saturated shear strength parameters. The results of the model developed for predicting the shear strength are compared with experimental results for a glacial till. The shear strength of statically compacted glacial till specimens was measured using a modified direct shear apparatus. Specimens were prepared at three different water contents and densities (i.e., corresponding to dry of optimum, and wet of optimum conditions). Various net normal stresses and matric suctions were applied to the specimens. There is a good correlation between the predicted and measured values of shear strength for the unsaturated soil. Key words: soil-water characteristic curve, shear strength, unsaturated soil, soil suction, matric suction.

Laboratory testing on an unsaturated soil: equipment, procedures, and first experimental results

1999 ◽  
Vol 36 (1) ◽  
pp. 1-12 ◽  
Author(s):  
C Rampino ◽  
C Mancuso ◽  
F Vinale
Keyword(s):  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Soil Mechanics ◽  
Stress Path ◽  
Matric Suction ◽  
Silty Sand ◽  
Compression Tests ◽  
Water Drainage ◽  
Triaxial Cell ◽  
Unsaturated Soil Mechanics

This paper describes two new apparatuses recently developed at the Università di Napoli Federico II (Italy) in order to test soils under unsaturated conditions. The related experimental procedures and the first results obtained on a dynamically compacted silty sand are also discussed. The devices mentioned are a Bishop and Wesley stress-path cell and a Wissa oedometer, modified to control matric suction and to measure all the stress-strain variables relevant to unsaturated soil mechanics. Specific experimental procedures were established to perform tests under general conditions and were carefully verified during several tests. Using the triaxial cell, isotropic and anisotropic compression stages were carried out under constant suction levels of 0, 100, 200, and 300 kPa. Furthermore, two deviator stages were performed following different stress paths and water drainage conditions. Using the oedometer, an additional suction level (400 kPa) was investigated during compression tests driven up to 5 MPa of vertical net stress (sigmav - ua). This research is a part of a major project in progress at the Dipartimento di Ingegneria Geotecnica of Naples; it is aimed at the experimental analysis of the behaviour of several dynamically compacted soils and at the numerical modelling of boundary problems related to earth structures.Key words: unsaturated soils, equipment layout, silty sand, matric suction.

Predicting the permeability function for unsaturated soils using the soil-water characteristic curve

1994 ◽  
Vol 31 (4) ◽  
pp. 533-546 ◽  
Author(s):  
D.G. Fredlund ◽  
Anqing Xing ◽  
Shangyan Huang
Keyword(s):  
Water Content ◽  
Soil Water ◽  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Characteristic Curve ◽  
Degree Of Saturation ◽  
Residual Water ◽  
Soil Water Characteristic Curve ◽  
Coefficient Of Permeability ◽  
Permeability Function

The coefficient of permeability for an unsaturated soil is primarily determined by the pore-size distribution of the soil and can be predicted from the soil-water characteristic curve. A general equation, which describes the soil-water characteristic curve over the entire suction range (i.e., from 0 to 106 kPa), was proposed by the first two authors in another paper. This equation is used to predict the coefficient of permeability for unsaturated soils. By using this equation, an evaluation of the residual water content is no longer required in the prediction of the coefficient of permeability. The proposed permeability function is an integration form of the suction versus water content relationship. The proposed equation has been best fit with example data from the literature where both the soil-water characteristic curve and the coefficient of permeability were measured. The fit between the data and the theory was excellent. It was found that the integration can be done from zero water content to the saturated water content. Therefore, it is possible to use the normalized water content (volumetric or gravimetric) or the degree of saturation data versus suction in the prediction of the permeability function. Key words : coefficient of permeability, soil-water characteristic curve, unsaturated soil, water content, soil suction.

scholarly journals Safety Factor of Unsaturated Soil Slopes considering the Intermediate Principal Stress Effect and Different Profiles of Matric Suction

2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Zhaoxin Li ◽  
Changguang Zhang ◽  
Jingyuan Zhao ◽  
Qing Yan
Keyword(s):  
Shear Strength ◽  
Principal Stress ◽  
Safety Factor ◽  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Matric Suction ◽  
Intermediate Principal Stress ◽  
Stress Effect ◽  
Soil Slopes ◽  
The Stability

Profiles of matric suction are critical for assessing the stability of unsaturated soil slopes, and the strength of unsaturated soils is affected by the intermediate principal stress. This study presents a theoretical formulation of safety factor for infinite unsaturated soil slopes under four different profiles of matric suction using the limit equilibrium method. The unified shear strength equation under plane strain conditions is adopted to capture the effect of intermediate principal stress on the strength of unsaturated soils. The proposed formulation of safety factor is found to have good comparability and broad applicability. The validity of the proposed formulation is demonstrated by comparing its predictions with the results of the extended shear strength method and the finite element method available in the literature. Parametric studies show that the effect of intermediate principal stress on the stability of unsaturated soil slopes is significant; the difference of safety factor among four suction profiles is pronounced, and the safety factor is highest for a linear suction profile. In addition, the safety factor changes with the infiltration depth in two stages, decreases with the slope angle, and increases with effective strength parameters. The results of this study are capable of providing beneficial guidance for optimization designs and disaster preventions of unsaturated soil slopes.

scholarly journals The, K.M. A Study on the Relationship Between Matric Suction and the Void Ratio and Moisture Content of a Compacted Unsaturated Soil

2018 ◽  
Author(s):  
Minh The Kieu ◽  
András Mahler
Keyword(s):  
Moisture Content ◽  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Void Ratio ◽  
Clayey Soil ◽  
Matric Suction ◽  
Moisture Ratio ◽  
Distinct Advantage ◽  
State Variables ◽  
Test Procedures

The volumetric behaviour of compacted unsaturated soils is particularly complex due to the co-existence of three different phases: solid, liquid and air. Matric suction has been perceived as a significant influence on the volumetric behaviour of unsaturated soils and has been used as one of the constitutive variables for most the constitutive models of unsaturated soils in the literature. However, suction-controlled works are complex in practice since they generally require special test procedures and advanced equipment, and usually are very time-consuming. Thus, some researchers have tried to seek alternative frameworks that use the traditional choice of state variables to simulate the behaviour of unsaturated soils. Recently, Kodikara [1] proposed the MPK framework to interpret the behaviour of compacted unsaturated soil in the void ratio (e) – net stress (p) – moisture ratio (ew ) space. The distinct advantage of the model is that it is based on traditional constant moisture content compaction testing which is more common and simple than constant suction loading. The MPK framework has been shown to be capable of presenting the volumetric behaviour of compacted unsaturated soils. However, this framework is expected to use not only for compacted soil but for the behaviour of unsaturated soil in general. The incorporation of soil suction within the MPK framework can be helpful for creating a correlation with previous models which used matric suction as a constitutive variable. This paper presents the development of LWSBS for one clayey soil in Hungary within the MPK framework and then suction is incorporated, which is related to void ratio and moisture ratio through SWCC.

scholarly journals Review of expansive and collapsible soil volume change models within a unified elastoplastic framework

2021 ◽  
Vol 44 (3) ◽  
pp. 1-30
Author(s):  
Sandra Houston ◽  
Xiong Zhang
Keyword(s):  
Volume Change ◽  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Constitutive Models ◽  
Change Models ◽  
Soil Response ◽  
Research And Practice ◽  
Collapsible Soils ◽  
Soil Volume ◽  
Change Response

Numerous laboratory tests on unsaturated soils revealed complex volume-change response to reduction of soil suction, resulting in early development of state surface approaches that incorporate soil expansion or collapse due to wetting under load. Nonetheless, expansive and collapsible soils are often viewed separately in research and practice, resulting in development of numerous constitutive models specific to the direction of volume change resulting from suction decrease. In addition, several elastoplastic models, developed primarily for collapse or expansion, are modified by add-on, such as multiple yield curves/surfaces, to accommodate a broader range of soil response. Current tendency to think of unsaturated soils as either expansive or collapsible (or, sometimes, stable), has likely contributed to lack of development of a unified approach to unsaturated soil volume change. In this paper, common research and practice approaches to volume change of unsaturated soils are reviewed within a simple macro-level elastoplastic framework, the Modified State Surface Approach (MSSA). The MSSA emerges as a unifying approach that accommodates complex volume change response of unsaturated soil, whether the soil exhibits collapse, expansion, or both. Suggestions are made for minor adjustments to existing constitutive models from this review, typically resulting in simplification and/or benefit to some of the most-used constitutive models for unsaturated soil volume change. In the review of practice-based approaches, the surrogate path method (SPM), an oedometer/suction-based approach, is demonstrated to be consistent with the MSSA framework, broadly applicable for use with expansive and collapsible soils, and yielding results consistent with measured field stress-path soil response.

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