New framework for volumetric constitutive behaviour of compacted unsaturated soils

2012 ◽  
Vol 49 (11) ◽  
pp. 1227-1243 ◽  
Author(s):  
Jayantha Kodikara
Keyword(s):  
Unsaturated Soils ◽  
Boundary Surface ◽  
Failure Surface ◽  
Constitutive Modelling ◽  
Tensile Failure ◽  
Compacted Soils ◽  
Compaction Curve ◽  
State Boundary ◽  
Observed Behaviour ◽  
New Framework

Volumetric behaviour is a fundamental consideration in unsaturated soil constitutive modelling. It is more complex than when the soil is saturated, as unsaturated soils exhibit a range of responses such as swelling and collapse under wetting and shrinkage and cracking during drying. While significant advances have been made, it is still difficult to generally explain all patterns of behaviour. This paper presents a new framework for modelling volumetric response of unsaturated soils with emphasis on compacted soils. The framework uses void ratio (e), moisture ratio (ew), and net stress (p) as the main constitutive variables and suction as a dependent variable. This choice of ew as a main constitutive variable is theoretically sound and is more attractive than the use of suction, which is relatively difficult to measure and displays significant hysteresis during drying and wetting. The framework incorporates the well-known compaction curve making it easily applicable to practical situations. Within the overall e–ew–p space, the operative space is constrained by three main surfaces; namely, loading–wetting state boundary surface, tensile failure surface, and the saturated plane. The conceptual basis for these state surfaces is described and the framework is qualitatively validated against observed behaviour of compacted soils.

Isotropic volumetric behaviour of compacted unsaturated soils within specific volume, specific water volume, mean net stress (v, vw, p) space

2019 ◽  
Vol 56 (12) ◽  
pp. 1756-1778 ◽  
Author(s):  
Arunodi Abeyrathne ◽  
Vinayagamoothy Sivakumar ◽  
Jayantha Kodikara
Keyword(s):  
Specific Volume ◽  
Unsaturated Soils ◽  
Boundary Surface ◽  
Degree Of Saturation ◽  
Water Volume ◽  
Compacted Soil ◽  
State Variable ◽  
Alternative Approach ◽  
State Boundary ◽  
Soil Behaviour

A detailed description of the volumetric behaviour of compacted unsaturated soils is essential for modelling compacted soil behaviour. It is more complex than when the soil is saturated, as unsaturated soils exhibit a range of responses, such as yielding under loading, swelling and collapse under wetting, and shrinkage and cracking during drying. In unsaturated modelling, (v, s, p) or (v, s, p′) is commonly used as the state space to describe volumetric behaviour, where v (= 1 + void ratio, e) is the specific volume; s is the soil suction; and p and p′ are the mean net and mean effective or skeleton stress, respectively. An alternative approach is to use (v, vw, p) space to describe volumetric behaviour, where vw is specific water volume. In either case, coupled water retention behaviour is needed to describe the overall macroscopic process more completely by including the fourth state variable (vw or degree of saturation, Sr, for the former and s for the latter). Following from work undertaken under one-dimensional conditions, the current paper presents the volumetric behaviour of compacted kaolin in (v, vw, p) space. A series of state path tests comprising various loading, unloading, and (or) wetting paths with nondecreasing degrees of saturation was carried out. The results show that a state boundary surface that is also the virgin compaction surface depicting the loosest state of soil takes control of the volumetric behaviour in (v, vw, p) space, which can be used as a more practical approach to modelling compacted soil behaviour, especially for analysing major wetting events.

scholarly journals A volumetric yield surface for compacted soils based on constant water content testing

2019 ◽  
Vol 92 ◽  
pp. 15008 ◽  
Author(s):  
C. Jayasundara ◽  
J. Kodikara ◽  
A. N. Zhou
Keyword(s):  
Water Content ◽  
Yield Surface ◽  
Unsaturated Soils ◽  
Boundary Surface ◽  
Degree Of Saturation ◽  
Water Retention Curve ◽  
Soil Water Retention Curve ◽  
Soil Water Retention ◽  
Engineering Structures ◽  
Compacted Soils

Unsaturated soils exhibit various complex behaviours compared to saturated soils, such as collapse upon wetting. Therefore, understanding the response of unsaturated soils under general field conditions is essential for the design and construction of safe and economical geotechnical engineering structures. This research is based on the Monash-Peradeniya-Kodikara (MPK) framework proposed by Kodikara [1] for unsaturated compacted soils, which provides a direct link to the traditional compaction loaded curves and constant water content loading experiments. Kodikara [1] named the loaded compaction surface the loading wetting state boundary surface (LWSBS) and validated the model for a combination of loading and wetting stress paths. However, the experimental validation of the yield surface after drying stress paths was not addressed in the original paper. This paper reports the results of drying stress path tests carried out within the specific volume (v),specific moisture ratio (vw) and mean net stress (p) space of the MPK model, and observations suggest that the yield surface is unique after drying stress paths. Mathematical equations for the volumetric behaviour of unsaturated soils are derived using the constant degree of saturation hyperlines derived from constant water content testing, as this enables direct coupling with the soil water retention curve. Finally, the volumetric equations are validated based on the available experimental data.

A possible elastic–plastic framework for unsaturated soils with high-plasticity

2002 ◽  
Vol 39 (4) ◽  
pp. 894-907 ◽  
Author(s):  
Gary X Tang ◽  
James Graham
Keyword(s):  
Stress State ◽  
Unsaturated Soils ◽  
Boundary Surface ◽  
Failure Criteria ◽  
Matric Suction ◽  
High Plasticity ◽  
Mean Stress ◽  
Elastic Plastic ◽  
State Boundary ◽  
State Boundary Surface

The paper proposes a new elastic–plastic framework for unsaturated, high-plasticity, clayey soils and sand–clay mixtures. The framework considers possible coupling of stress- and suction-induced hardening, leading to a yield surface that is closed or "capped" as suctions increase. This produces a stress state boundary surface in three-dimensional p–q–s stress space (where p is the net mean stress, q is the deviator stress, and s is the matric suction) which differs from that of other conceptual models of its kind. Yielding, a hardening law, and failure criteria for saturated soils are incorporated into the stress state boundary surface. Two parameters, equivalent pressure pe and stress ratio ηs, are introduced to form the basis of the proposed elastic–plastic framework for highly plastic soils with high suctions. This provides an alternative for the stress variables net mean stress and matric suction that are commonly used in modeling unsaturated soils with lower plasticity and lower suctions. This framework has allowed results of experiments on an unsaturated sand–bentonite mixture to be successfully described using elastoplasticity. Yield and failure envelopes associated with the proposed state boundary surface in p–q–s space can be normalized using pe and ηs in such a way that they agree with a comparable envelope for saturated specimens. Key words: unsaturated, elastic–plastic, triaxial, matric suction, state boundary surface, sand-bentonite.

scholarly journals Practical method to estimate parameters of elasto-plastic constitutive model for unsaturated soils from compaction curve

2020 ◽  
Vol 60 (5) ◽  
pp. 1287-1298
Author(s):  
Shinya Tachibana ◽  
Masayoshi Matsumoto ◽  
Atsushi Iizuka
Keyword(s):  
Constitutive Model ◽  
Unsaturated Soils ◽  
Practical Method ◽  
Compaction Curve

scholarly journals Modelling shear strength of compacted soils

2019 ◽  
Vol 92 ◽  
pp. 15007
Author(s):  
Sam Bulolo ◽  
Eng Choon Leong
Keyword(s):  
Shear Strength ◽  
Unsaturated Soils ◽  
Soil Mechanics ◽  
Published Data ◽  
State Variables ◽  
Compacted Soils ◽  
Earth Structures ◽  
Unsaturated Soil Mechanics ◽  
Coulomb Failure Criterion ◽  
Direct Shear Apparatus

Compacted soils constitute most engineering projects such as earth dams, embankments, pavements, and engineered slopes because of their high shear strength and low compressibility. The shear strength of compacted soils is a key soil parameter in the design of earth structures but it is seldom determined correctly due to their unsaturated state. The shear strength of compacted soils can be better evaluated under the framework of unsaturated soil mechanics. Saturated and unsaturated tests were conducted on compacted specimens using conventional direct shear apparatus under constant water content condition. Tests were conducted at different water contents and net normal stresses. The main objective of this study is to develop a shear strength model for compacted soils. Initial matric suction was measured before the test using the filter paper method. The two-stress state variables together with the extended Mohr-Coulomb failure criterion for unsaturated soils were used to obtain a lower bound model of the shear strength. The model was demonstrated using published data.

scholarly journals Interpretation of the loading–wetting behaviour of compacted soils within the “MPK” framework. Part I: Static compaction

2016 ◽  
Vol 53 (5) ◽  
pp. 783-805 ◽  
Author(s):  
Tanvirul Islam ◽  
Jayantha Kodikara
Keyword(s):  
Moisture Content ◽  
Unsaturated Soils ◽  
Void Ratio ◽  
Swelling Pressure ◽  
The State ◽  
Moisture Ratio ◽  
Parameter Determination ◽  
Compacted Soils ◽  
Pressure Development ◽  
State Path

Depending on the state paths, loading–wetting of compacted unsaturated soils can exhibit complex volumetric behaviour, such as swelling, collapse, collapse followed by swelling, swelling followed by collapse, and swelling pressure development. Microscopically, these behaviours arise from complex interactions among applied stresses, air–water pressure deficit or suction at the water menisci, moisture content or degree of saturation in the voids, and the nature of the micro- and macrosoil aggregates of compacted soils that depend on the level of suction. While significant advances have been made in modelling hydromechanical behaviour of compacted unsaturated soils taking these interactions into account, input parameter determination requires advanced testing equipment and the testing processes can be very time-consuming. In 2012, a relatively simple and practical framework within the void ratio – moisture ratio (water volume / solid volume) – net stress space (referred to as the MPK framework) has been proposed by Kodikara to explain–predict these state paths. A desirable feature of this framework is that it identifies a direct link between the well-known compaction curve and the compacted soil constitutive behaviour. This paper presents a comprehensive series of tests on statically compacted soils, the results of which are in close agreement with this framework. Two soil types, namely lightly reactive kaolin and more reactive clay (referred to as Merri Creek soil), were used in the testing. The soils were prepared with different moisture contents from the dry state and statically compacted at constant water content to obtain void ratio – moisture ratio – net stress constitutive surfaces, as well as soil specimens for state path tests. The state path test results of yielding under loading, collapse under wetting, swelling pressure development, and change in yield pressure due to wetting are explained within this framework. In addition, some published data on a silty soil mixture were also analysed, highlighting that the framework is valid, regardless of the degree of reactivity of the soil. Suction was not measured in the authors’ experiments, as it was not required to explain the above state paths according to this framework. However, it is recognised that suction is the conjugate state variable to the moisture content. Therefore, in future experiments, suction will be measured and its role will be fully explained within the framework, adding more generality.

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