Constitutive relations for volume change in unsaturated soils

1976 ◽  
Vol 13 (3) ◽  
pp. 261-276 ◽  
Author(s):  
D. G. Fredlund ◽  
N. R. Morgenstern
Keyword(s):  
Volume Change ◽  
Unsaturated Soils ◽  
Soil Structure ◽  
Constitutive Relations ◽  
Water Volume ◽  
Engineering Practice ◽  
State Variables ◽  
Volume Changes ◽  
Stress Changes ◽  
Measured Volume

Volume change constitutive relations for unsaturated soils are proposed from a semi-empirical standpoint. One equation describes the deformation of the soil structure and a second equation defines the volume of water present in the element. Each equation can be viewed as a three-dimensional surface with two independent stress state variables forming the abscissas.Uniqueness is tested by measuring volume changes resulting from stress changes in two orthogonal directions and comparing predicted and measured volume changes resulting from a stress change in a third direction. Samples of undisturbed Regina Clay and compacted kaolin showed good agreement between the predicted and measured volume changes for monotonic deformation of the soil structure. The agreement was not as close for the water phase. The variation was attributed to difficulties in measuring water volume changes over a long period of time. The laboratory results indicate that the proposed constitutive equations are of the appropriate form for use in engineering practice.

Volume Change Associated to Carbon Partitioning from Martensite to Austenite

2012 ◽  
Vol 706-709 ◽  
pp. 2290-2295 ◽  
Author(s):  
M. J. Santofimia ◽  
Lie Zhao ◽  
Jilt Sietsma
Keyword(s):  
Volume Change ◽  
Chemical Potential ◽  
Theoretical Models ◽  
Carbon Partitioning ◽  
Volume Changes ◽  
Measured Volume

Annealing of martensite/austenite microstructures leads to the partitioning of carbon from martensite to austenite until the chemical potential of carbon equilibrates in both phases. This work calculates the volume change associated with this phenomenon using theoretical models for the carbon partitioning from martensite to austenite. Calculations are compared with experimentally determined volume changes. This comparison reveals that in the case of steels with higher contents of austenite-stabilizing elements, reported volume changes are satisfactory predicted assuming a low mobilily martensite/austenite interface. In the case of a steel with lower additions of austenite-stabilizing elements, experimentally measured expansions are considerably larger than predicted ones. The large measured volume expansions probably reflect the decomposition of the austenite.

A Diffused Air Volume Indicator for Unsaturated Soils

1975 ◽  
Vol 12 (4) ◽  
pp. 533-539 ◽  
Author(s):  
D. G. Fredlund
Keyword(s):  
Correction Factor ◽  
Volume Change ◽  
Unsaturated Soils ◽  
Effective Means ◽  
Computational Procedure ◽  
Technical Note ◽  
Water Volume ◽  
Volume Weight ◽  
Air Volume ◽  
Change Characteristics

The diffusion of air through saturated high air entry discs presents a serious problem in the testing of unsaturated soils. When determining either the strength (drained) or volume change characteristics of unsaturated soils, a technique must be available to measure the amount of diffused air in order for the appropriate corrections to be applied to the volume–weight relationships.The described diffused air volume indicator is a simple but effective means of measuring the quantity of diffused air. This technical note explains its construction and procedure of operation. Also outlined is the computational procedure for the correction factor that must be applied to the water volume change measurements. Numerous tests on the indicator show a reliability in the order of ±0.2 cc over a period of 2.5 weeks.

A new simple system for measuring volume changes in unsaturated soils

2002 ◽  
Vol 39 (3) ◽  
pp. 757-764 ◽  
Author(s):  
C W.W Ng ◽  
L T Zhan ◽  
Y J Cui
Keyword(s):  
Volume Change ◽  
Unsaturated Soils ◽  
Volumetric Strain ◽  
Apparent Volume ◽  
Differential Pressure ◽  
Simple System ◽  
Measuring System ◽  
Volume Changes ◽  
Ambient Temperatures ◽  
Triaxial Apparatus

A new simple system for accurately measuring overall total volume changes in unsaturated soil specimens with a triaxial apparatus is introduced in this paper. The basic principle of the measuring system is to record changes in the differential pressure due to changes in the water level inside an open-ended, bottle-shaped inner cell caused by volume change in the specimen and inside a reference tube using an accurate differential pressure transducer. Several important steps were taken to improve the accuracy and sensitivity of the measuring system. Detailed calibrations were carried out to account for apparent volume changes as a result of changes in cell pressure, fluctuation in the ambient temperatures, creep in the inner cell wall, and relative movement between the loading ram and the inner cell. The calibration results demonstrate that the measuring system is reasonably linear, reversible, and repeatable. The estimated accuracy of the measuring system is in the order of 32 mm3 (or 0.04% volumetric strain for a triaxial specimen 38 mm in diameter and 76 mm in height) once the system is properly calibrated.Key words: unsaturated soils, volume-change measurement, open-ended, bottle-shaped, inner cell, differential pressure, calibration.

Comparison of volume changes in the upper airway and thorax

1987 ◽  
Vol 62 (1) ◽  
pp. 284-290 ◽  
Author(s):  
J. P. Teeter ◽  
K. P. Strohl ◽  
J. M. Fouke
Keyword(s):  
Tidal Volume ◽  
Volume Change ◽  
Upper Airway ◽  
Inspiratory Effort ◽  
Mechanical Forces ◽  
Volume Changes ◽  
Percent Change ◽  
Anesthetized Dogs ◽  
Peak Increase ◽  
Measured Volume

To describe the mechanical cycles of the upper and lower portions of the respiratory system, we measured volume change in and out of the isolated upper airway in 13 anesthetized dogs and compared volume changes in the upper airway with tidal volume change during spontaneous respiratory efforts. During inspiration the onset and peak increase in volume into the upper airway preceded the onset and peak of inspiratory tidal volume by 84 +/- 8 and 638 +/- 47 ms, respectively. The volume cycle of the upper airway was nearly complete by the end of inspiratory airflow into the thorax. With progressive hypercapnia there was an increase in the change in both upper airway volume and tidal volume but the temporal sequence was preserved. End-expiratory tracheal occlusion increased the volume change in the isolated upper airway at any level of CO2; however, the effect was disproportionately greater at low rather than at high levels of CO2. Following hyperventilation-induced apnea, a change in volume in the upper airway and thorax occurred on the first inspiratory effort. In most animals at lower levels of CO2, the percent change in upper airway volume with inspiration was relatively less than tidal volume, but the reverse was true at higher levels of CO2. These differences represent dissimilarities in the mechanical forces occurring as the result of upper airway and chest wall muscle contraction during inspiration.

scholarly journals Yield stress, volume change, and shear strength behaviour of unsaturated soils: validation of the SFG model

2009 ◽  
Vol 46 (9) ◽  
pp. 1034-1045 ◽  
Author(s):  
Annan Zhou ◽  
Daichao Sheng
Keyword(s):  
Experimental Data ◽  
Shear Strength ◽  
Yield Stress ◽  
Volume Change ◽  
Unsaturated Soils ◽  
Strength Criterion ◽  
Single Equation ◽  
Compacted Soils ◽  
Shear Strength Criterion ◽  
Stress Changes

The model recently presented by Sheng, Fredlund, and Gens, known as the SFG model, provides a consistent explanation of yield stress, shear strength, and volume change behaviour of unsaturated soils as functions of suction. All these functions are based on one single equation that defines the volume change with suction and stress changes. This paper provides a systematic validation of the equation and the derived shear strength criterion against experimental data. The experimental data used include those for samples prepared from slurry soils and compacted soils. It is shown that (i) the method currently used to determine yield stresses of unsaturated soils is incorrect, (ii) volume change behaviour of unsaturated soils can be well predicted by the SFG model, and (iii) shear strength behaviour of unsaturated soils can be represented very well by the criterion in the SFG model.

An equation of state for unsaturated soils

2002 ◽  
Vol 39 (1) ◽  
pp. 125-140 ◽  
Author(s):  
Edward J Murray
Keyword(s):  
Equation Of State ◽  
Effective Stress ◽  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Deformation Behaviour ◽  
Water Volume ◽  
State Variables ◽  
Stress Equation ◽  
Stress Regime ◽  
Soil System

The enthalpy within a soil system under equilibrium conditions is investigated theoretically. Terzaghi's effective stress equation for a saturated soil is first examined and the approach extended to determine the enthalpy associated with the air, water, and solid phases, and the interactions between the phases, in an unsaturated soil. An equation of state is developed which links the stress state variables (p – ua) and (ua – uw) to the specific volume (v) and specific water volume (vw) and thus to the volumes of the phases. The equation is shown to provide a logical interpretation of the average volumetric "coupling" stress p'c within unsaturated soils which highlights the significance of the dual stress regime and bimodal structure. The new equation is compared with previously reported experimental data on kaolin and a lateritic gravel. The agreement is good and it provides insight into unsaturated soil strength and deformation behaviour and clarifies various previously identified anomalies.Key words: partial saturation, unsaturated soils, thermodynamics, effective stress, equation of state, critical state.

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.

Systemic soil modelling and the evaluation of functions

2021 ◽  
Author(s):  
Ulrich Weller ◽  
Sara König ◽  
Bibiana Betancur-Corredor ◽  
Birgit Lang ◽  
Mareike Ließ ◽  
...  
Keyword(s):  
Travel Time ◽  
Soil Structure ◽  
Field Experiments ◽  
Current Knowledge ◽  
Agricultural Management ◽  
Water Dynamics ◽  
Plant Production ◽  
Soil Processes ◽  
State Variables ◽  
Soil Functions

<p><span>We developed an integrated model of soil processes – the Bodium – that enables us to predict possible changes in soil functions under varying agricultural management and climatic change.</span></p><p><span>The model combines current knowledge on soil processes by integrating state-of-the-art modules on plant growth, root development, soil carbon and matter turnover with new concepts with respect to soil hydrology and soil structure dynamics. The model domain is at profile scale, with 1D nodes of variable thickness and weight. It is tested with long-term field experiments to ensure a consistent output of the combined modules. The model is site-specific and works with different soil types and climates (weather scenarios).</span></p><p><span>The output can be interpreted towards a broad spectrum of soil functions. Plant production and nutrient balances can be determined directly. The same is possible for water dynamics, with potential surface runoff (as infiltration surplus), storage and percolation together with travel time and groundwater recharge. In addition, nitrate losses are calculated, and the travel time distribution can help with the evaluation of pesticide percolation risk. To evaluate the habitat for biological activity, the activity is calculated in terms of carbon turnover, and the state variables carbon availability, water, air and temperature for the are accessible. Also, for macrofauna the earthworm activity is included. The comparison of scenario runs can be evaluated quantitatively in terms of potential developments of soil functions.</span></p><p><span>The model is work in progress. Further modules that will be implemented are pH dynamics, more explicit microbial activity, and a more complete set of effects of agricultural management on soil structure are integrated.</span></p>

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