Protocol for the assessment of unsaturated soil properties in geotechnical engineering practice

2009 ◽  
Vol 46 (6) ◽  
pp. 694-707 ◽  
Author(s):  
Delwyn G. Fredlund ◽  
Sandra L. Houston
Keyword(s):  
Soil Properties ◽  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Soil Property ◽  
Unsaturated Flow ◽  
Soil Mechanics ◽  
Geotechnical Engineering ◽  
Engineering Practice ◽  
Engineering Project ◽  
Estimation Procedures

The implementation of unsaturated soil mechanics into routine geotechnical engineering practice requires an evaluation of methodologies that may be used for the assessment of “unsaturated soil property functions.” Guidelines and recommendations need to be provided to practicing engineers. The guidelines need to take the form of “engineering protocols” that define acceptable standards for engineering practice. “Engineering protocols” for unsaturated soils engineering practice can be divided into “preliminary design” protocols and “final design” protocols. Both design levels involve the use of a variety of estimation procedures that have been proposed for various classes of geotechnical problems (e.g., unsaturated flow, shear strength, volume change, and distortion). The hierarchy in methodologies is based mainly on the costs and risks associated with a particular engineering project. In this paper, “hierarchical levels” are suggested that take into consideration the cost of various direct and indirect methodologies for the determination of unsaturated soil properties. Recommendations and suggestions are provided for methods for the determination and use of the soil-water characteristic curves (SWCC) and consequently, for the computation of unsaturated soil property functions (USPFs). Primary attention is given to estimation procedures best known to the authors and most appropriate for geotechnical engineering practice.

The 1999 R.M. Hardy Lecture: The implementation of unsaturated soil mechanics into geotechnical engineering

2000 ◽  
Vol 37 (5) ◽  
pp. 963-986 ◽  
Author(s):  
Delwyn G Fredlund
Keyword(s):  
Soil Water ◽  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Soil Property ◽  
Soil Mechanics ◽  
Geotechnical Engineering ◽  
Characteristic Curve ◽  
Engineering Practice ◽  
Soil Water Characteristic Curve ◽  
Unsaturated Soil Mechanics

The implementation of unsaturated soil mechanics into geotechnical engineering practice requires that there be a paradigm shift from classical soil mechanics methodology. The primary drawback to implementation has been the excessive costs required to experimentally measure unsaturated soil properties. The use of the soil-water characteristic curve has been shown to be the key to the implementation of unsaturated soil mechanics. Numerous techniques have been proposed and studied for the assessment of the soil-water characteristic curves. These techniques range from direct laboratory measurement to indirect estimation from grain-size curves and knowledge-based database systems. The soil-water characteristic curve can then be used for the estimation of unsaturated soil property functions. Theoretically based techniques have been proposed for the estimation of soil property functions such as (i) coefficient of permeability, (ii) water storage modulus, and (iii) shear strength. Gradually these estimations are producing acceptable procedures for geotechnical engineering practices for unsaturated soils. The moisture flux ground surface boundary condition is likewise becoming a part of the solution of most problems involving unsaturated soils. The implementation process for unsaturated soils will still require years of collaboration between researchers and practicing geotechnical engineers.Key words: unsaturated soil mechanics, soil suction, unsaturated soil property functions, negative pore-water pressure, matric suction, soil-water characteristic curve.

scholarly journals Application of ‘Estimation Procedures’ in Unsaturated Soil Mechanics

Geosciences ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 364
Author(s):  
Delwyn G. Fredlund ◽  
Murray D. Fredlund
Keyword(s):  
Soil Properties ◽  
Water Content ◽  
Unsaturated Soil ◽  
Soil Mechanics ◽  
Geotechnical Engineering ◽  
Full Range ◽  
New Paradigm ◽  
Engineering Applications ◽  
Estimation Procedures ◽  
Unsaturated Soil Mechanics

The application of unsaturated soil mechanics in routine geotechnical engineering applications requires the determination of unsaturated soil properties. Unfortunately, the cost of direct measurement of unsaturated soil properties goes beyond the financial budget of most clients. A solution has arisen, however, that involves the measurement of two less costly soil properties functions that can be used in conjunction with a series of assumptions and estimation methodologies. The two laboratory tests involve measurement of the: (i) gravimetric water content versus soil suction, referred to as the soil-water characteristic curve (w-SWCC) and (ii) water content versus void ratio, referred to as the shrinkage curve (SC). These two unsaturated soil property relationships can be used along with saturated soil properties to extend unsaturated soil properties over the full range of soil suctions. “Estimation procedures” have been developed and verified for all physical properties of interest in unsaturated soil mechanics. The use of estimation procedures has meant that the geotechnical engineer must operate within a new paradigm. The new paradigm provides sufficient accuracy for most geotechnical engineering applications. The net result is an increased decision-making capability for geotechnical engineers.

scholarly journals State of practice for use of the soil-water characteristic curve (SWCC) in geotechnical engineering

2019 ◽  
Vol 56 (8) ◽  
pp. 1059-1069 ◽  
Author(s):  
Delwyn G. Fredlund
Keyword(s):  
Soil Water ◽  
Unsaturated Soil ◽  
Soil Mechanics ◽  
Geotechnical Engineering ◽  
Characteristic Curve ◽  
Laboratory Measurement ◽  
Engineering Practice ◽  
Soil Water Characteristic Curve ◽  
Unsaturated Soil Mechanics ◽  
State Of Practice

Routine geotechnical engineering practice has witnessed a significant increase in the usage of unsaturated soil mechanics principles. Laboratory measurement of the soil-water characteristic curve (SWCC) for a soil has been labelled as a primary reason for the improved understanding of unsaturated soil behaviour. Laboratory measurement of the “shrinkage curve” has yielded further insight into the estimation of unsaturated soil property functions (USPFs). The USPFs provide the necessary information for the simultaneous numerical modeling of the saturated and unsaturated portions of the soil profile. This paper presents a state-of-practice summary of the engineering protocols that have emerged amidst the numerous research studies reported over the past couple of decades. It also introduces issues related to hysteresis associated with the SWCC and suggests a pathway forward.

scholarly journals Numerical Modeling of Unsaturated Soils Problems

2016 ◽  
pp. 97-109
Author(s):  
Murray D. Fredlund
Keyword(s):  
Finite Element ◽  
Numerical Modeling ◽  
Numerical Solution ◽  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Soil Property ◽  
Characteristic Curve ◽  
Thermal Flux ◽  
Solution Technique ◽  
Estimation Procedures

Numerical modeling (finite element analyses) of saturated-unsaturated soils problems generally involves the solution of linear or nonlinear partial differential equations, PDEs. The soil properties for unsaturated soils usually take on a functional form that subsequently requires an iterative procedure to obtain a solution. Special numerical solution techniques are helpful (and in some cases necessary) in order to have confidence that the results of the numerical solution are accurate. The dynamic upgrade of the finite element mesh (and time steps) during the iterative solution process have proven to be of significant value in ensuring the proper convergence of the numerical solution. The unsaturated soil property functions are usually obtained through use of estimation procedures based on the measurement of the soil-water characteristic curve, SWCC. One or more estimation procedures have been proposed in the research literature for soil property functions for each physical process of interest in unsaturated soil mechanics. The numerical modeller must be aware of the relationship between the estimated soil property functions and the solution technique. Boundary conditions required when solving unsaturated soils problems often involve the assessment of moisture and thermal flux conditions computed from meteorological records. There are conditions and requirements that must be quantifiable when solving unsaturated soils problems. The estimation of the unsaturated soil property functions makes the solution of unsaturated soils problems more complex than those of saturated soils.

Method for Quick Prediction of Hydraulic Conductivity and Soil-Water Retention of Unsaturated Soils

2018 ◽  
Vol 2672 (52) ◽  
pp. 108-117 ◽  
Author(s):  
Shaoyang Dong ◽  
Yuan Guo ◽  
Xiong (Bill) Yu
Keyword(s):  
Finite Element ◽  
Hydraulic Conductivity ◽  
Soil Properties ◽  
Soil Water ◽  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Hydraulic Properties ◽  
Water Retention ◽  
Characteristic Curve ◽  
Soil Water Retention

Hydraulic conductivity and soil-water retention are two critical soil properties describing the fluid flow in unsaturated soils. Existing experimental procedures tend to be time consuming and labor intensive. This paper describes a heuristic approach that combines a limited number of experimental measurements with a computational model with random finite element to significantly accelerate the process. A microstructure-based model is established to describe unsaturated soils with distribution of phases based on their respective volumetric contents. The model is converted into a finite element model, in which the intrinsic hydraulic properties of each phase (soil particle, water, and air) are applied based on the microscopic structures. The bulk hydraulic properties are then determined based on discharge rate using Darcy’s law. The intrinsic permeability of each phase of soil is first calibrated from soil measured under dry and saturated conditions, which is then used to predict the hydraulic conductivities at different extents of saturation. The results match the experimental data closely. Mualem’s equation is applied to fit the pore size parameter based on the hydraulic conductivity. From these, the soil-water characteristic curve is predicted from van Genuchten’s equation. The simulation results are compared with the experimental results from documented studies, and excellent agreements were observed. Overall, this study provides a new modeling-based approach to predict the hydraulic conductivity function and soil-water characteristic curve of unsaturated soils based on measurement at complete dry or completely saturated conditions. An efficient way to measure these critical unsaturated soil properties will be of benefit in introducing unsaturated soil mechanics into engineering practice.

scholarly journals TERRE project: interplay between unsaturated soil mechanics and low-carbon geotechnical engineering

2020 ◽  
Vol 195 ◽  
pp. 01002 ◽  
Author(s):  
Alessandro Tarantino ◽  
Grainne El Mountassir ◽  
Simon Wheeler ◽  
Domenico Gallipoli ◽  
Giacomo Russo ◽  
...  
Keyword(s):  
Construction Industry ◽  
Unsaturated Soil ◽  
Soil Mechanics ◽  
Geotechnical Engineering ◽  
Infrastructure Development ◽  
Construction Sector ◽  
Low Carbon ◽  
Unsaturated Soil Mechanics ◽  
Low Carbon Technologies ◽  
Industry Sectors

The geotechnical construction industry is a major component of the overall construction sector and is strategically important in infrastructure development (transportation, flood and landslide protection, building foundations, waste disposal). Although industry and research in the overall construction sector have been investing significantly in recent years to produce innovative low-carbon technologies, little innovation has been created in geotechnical construction industry, which is lagging behind other construction industry sectors. This paper discusses the interplay between low-carbon geotechnical engineering and unsaturated soil mechanics based on the research carried out within the project TERRE (Marie Skłodowska-Curie Innovative Training Networks funded by the European Commission, 2015-2019,H2020-MSCA-ITN-2015-675762).

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.

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