Experimental behaviour and modelling of an unsaturated compacted soil

2000 ◽  
Vol 37 (4) ◽  
pp. 748-763 ◽  
Author(s):  
Celestino Rampino ◽  
Claudio Mancuso ◽  
Filippo Vinale
Keyword(s):  
Unsaturated Soils ◽  
Mechanical Response ◽  
Stress Path ◽  
Silty Sand ◽  
Triaxial Tests ◽  
Experimental Program ◽  
State Variables ◽  
Soil Response ◽  
Optimum Water Content ◽  
Triaxial Cell

This paper reports the experimental study and modelling of the mechanical response of a silty sand used in the core of the Metramo dam, Italy. Specimens were prepared by compacting the soil at optimum water content conditions using the modified Proctor technique. Tests were performed under suction-controlled conditions by a stress path triaxial cell and an oedometer. The experimental program consists of 23 tests carried out in the suction range of 0-400 kPa. The findings indicate the strong influence of suction on compressibility, stiffness, and shear strength. The mechanical properties of the soil improve with suction following an exponential law with decreasing gradient. Furthermore, the soil exhibited collapsible behaviour upon wetting even at low stress levels. Interesting results were also achieved in elastoplastic modelling as well. The results led to characterization of soil behaviour with reference to widely accepted modelling criteria for unsaturated soils, providing noteworthy suggestions about their applicability for granular materials with a non-negligible fine component. Finally, some remarks are made for the extension under unsaturated conditions of the "Nor sand" model for saturated granular soils. The proposed approach yields improved predictions of deviator soil response of the tested soil when Cambridge-type frameworks prove invalid.Key words: unsaturated soils, stress state variables, triaxial tests, oedometer tests, constitutive model.

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.

Photogrammetry-Based Method to Determine the Absolute Volume of Soil Specimen during Triaxial Testing

2020 ◽  
Vol 2674 (8) ◽  
pp. 206-218
Author(s):  
Sara Fayek ◽  
Xiaolong Xia ◽  
Lin Li ◽  
Xiong Zhang
Keyword(s):  
Unsaturated Soils ◽  
Optimization Techniques ◽  
Triaxial Tests ◽  
Triaxial Testing ◽  
Soil Specimen ◽  
Compression Tests ◽  
Unconfined Compression ◽  
Absolute Volume ◽  
Triaxial Cell ◽  
The Absolute

Triaxial tests are used extensively to evaluate stress-strain behavior for both saturated and unsaturated soils. A literature review indicates that all conventional triaxial test methods measure the relative volume of soil; however, between the initial measurements and the start of the triaxial tests, there are unavoidably disturbances during installation that cause deviation of soil volume from that at the initial condition. Recently image-based methods have been developed to measure the absolute volume of soil specimens. However, these methods still have a major limitation in their inability to determine top and bottom boundaries between the soil specimen, and the top and bottom caps. This paper proposes a photogrammetry-based method to overcome this limitation by developing a mathematically rigorous technique to determine the upper and lower boundaries of soil specimens during triaxial testing. The photogrammetry technique was used to determine the orientations of the camera, and the shape and location of the acrylic cell. Multiple ray-tracings and least-square optimization techniques were also applied to obtain the coordinates of any point inside the triaxial cell, and thus back-calculate the upper and lower boundaries. With these boundaries and the side surface, a triangular surface mesh was constructed and the specimen volume was then calculated in both unconfined compression tests and triaxial tests. The calculation procedures are presented in detail with validation tests performed on a cylindrical specimen to evaluate the accuracy of the method. Results indicate that the accuracy of the proposed method is up to 0.023% in unconfined compression tests and 0.061% in triaxial tests.

Failure, instability, and the second work increment in loose silty sand

2011 ◽  
Vol 48 (6) ◽  
pp. 943-955 ◽  
Author(s):  
Mehmet Murat Monkul ◽  
Jerry A. Yamamuro ◽  
Poul V. Lade
Keyword(s):  
Triaxial Compression ◽  
Failure Surface ◽  
Stress Path ◽  
Silty Sand ◽  
Triaxial Tests ◽  
Stability Conditions ◽  
Stability And Instability ◽  
Constant Shear Stress ◽  
The Mean ◽  
Undrained Conditions

Triaxial tests have been performed to demonstrate the conditions for stability and instability in loose silty sand. Drucker (1951) and Hill (1958) stability conditions in terms of the sign of the second work increment were employed in the design of the stress paths used in the triaxial compression and extension tests performed with quasi-constant shear stress while the mean normal stress was reduced until failure occurred. It is shown that the sand is completely stable under drained conditions for any stress path and irrespective of the sign of the second work increment. This is demonstrated by completely stopping the change in stresses and observing the stable behavior in the range of stresses where the sand contracts and where it dilates. Once the effective stress failure surface is passed, the sand becomes unstable, and the sign of the second work increment is always negative. Run-away instability can occur inside the failure surface for loose silty sand under undrained conditions for which the sand tends to contract, pore pressures continue to develop, and the second work increment is negative. Liquefaction may follow if the loose silty sand is sufficiently loose.

Laboratory investigation on the mechanical behaviour of Tournemire argillite

2015 ◽  
Vol 52 (3) ◽  
pp. 268-282 ◽  
Author(s):  
H. Abdi ◽  
D. Labrie ◽  
T.S. Nguyen ◽  
J.D. Barnichon ◽  
G. Su ◽  
...  
Keyword(s):  
Mechanical Behaviour ◽  
Mechanical Response ◽  
Damage Model ◽  
Orientation Angle ◽  
Triaxial Tests ◽  
Experimental Program ◽  
Emission Data ◽  
Testing Program ◽  
Bedding Planes ◽  
Rock Specimens

This paper presents the results of a laboratory testing program that was designed to investigate the mechanical behaviour of the Tournemire argillite. Eighty rock samples were obtained from boreholes drilled at different angles in the walls and floor of an existing gallery at the Tournemire Underground Research Laboratory (URL), France. The experimental program consists of the measurement of the physical properties of the argillite and its mechanical response to loading during uniaxial tests, triaxial tests with various confining pressures, unconfined and confined cyclic tests, and Brazilian tests. Since the Tournemire argillite is characterized by the presence of closely spaced bedding planes, the rock specimens were loaded in different directions to bedding planes (i.e., loading orientation angle, θ = 0°, 30°, 45°, 60°, and 90°). Acoustic emission data were also recorded to detect the initiation and propagation of micro-cracks during the uniaxial tests. Most of the tests were performed at the natural moisture content of the rock specimens as delivered to CANMET Laboratories in Ottawa, Canada, where the experiments were conducted. The main objective of the testing program is to identify the mechanical properties of the Tournemire argillite. This paper mainly focuses on the description and interpretation of the test results. The development of an elastoplastic-damage model to describe the mechanical behaviour of the Tournemire argillite is the subject of another paper.

Exploring the mechanical response of low-carbon soil improvement mixtures

2021 ◽  
Author(s):  
Alessandro Fraccica ◽  
Giovanni Spagnoli ◽  
Enrique E. Romero Morales ◽  
Marcos Arroyo ◽  
Rodrigo Gómez
Keyword(s):  
Colloidal Silica ◽  
Mechanical Response ◽  
Ground Improvement ◽  
Soil Improvement ◽  
Silty Sand ◽  
Triaxial Tests ◽  
Granular Soils ◽  
Low Carbon ◽  
Cyclic Triaxial Tests ◽  
Curing Conditions

As society moves towards decarbonisation it is important to assess the hydro-mechanical behaviour of binders that could offer a low-carbon alternative to Portland cement in ground improvement technologies. This work considers two such alterna-tives: one still largely unexplored (metakaolin-based geopolymers) and a better known one (colloidal silica). Results from unconfined compressive strength, permeability tests, undrained monotonic and cyclic triaxial tests on granular soils (sand and silty sand) treated with those two binders are presented and discussed, emphasizing simili-tudes and differences with the response of similar soils treated with other conventional and unconventional binders. Effects of silt content, curing conditions and soil/binder ratios are examined. Both colloidal silica and metakaolin-based geopolymer signifi-cantly improve the mechanical properties of the treated soils, although the geopolymer results in a stronger and stiffer material. Both treatments reduce much the permeabil-ity of the treated soil, but the reduction achieved with CS is larger.

scholarly journals Modelling Unsaturated Soil Response Beyond Residual Suction State via Vapor-Pressure Controlled Triaxial Testing

2020 ◽  
Vol 195 ◽  
pp. 03029
Author(s):  
Mathilde Morvan ◽  
Ujwalkumar D. Patil ◽  
Laureano R. Hoyos ◽  
Surya S. C. Congress ◽  
Anand J. Puppala
Keyword(s):  
Unsaturated Soils ◽  
Silty Sand ◽  
Flow Rule ◽  
Model Parameters ◽  
Peak Strain ◽  
Reasonable Accuracy ◽  
Soil Response ◽  
Proposed Model ◽  
High Suction ◽  
Volumetric Response

Most of the previous research has been focused on developing and validating constitutive models to predict response of unsaturated soils in low-medium suction range. However, there is a scarcity of efforts in developing soil models to simulate its mechanical response in high suction range, particularly above the residual suction. This article presents a new constitutive model introducing net stress and suction as two independent variables. Furthermore, non-associative flow rule incorporating modified stress-dilatancy relationship to take unsaturated state into account is introduced to improve the model results in low-medium to high suction range. The essential soil model parameters are calibrated using suction-controlled triaxial test results for predictions of compacted silty sand response at high values of total suction above residual suction. Preliminary simulations show that proposed model can reasonably simulate the post-peak strain softening response obtained from suction-controlled CTC tests above residual suction value with reasonable accuracy. Although, the proposed model captures initial compression followed by dilation volumetric response with reasonable accuracy, it needs some improvements to be able to capture volumetric response accurately over entire suction range.

Unified hardening (UH) model for overconsolidated unsaturated soils

2014 ◽  
Vol 51 (7) ◽  
pp. 810-821 ◽  
Author(s):  
Y.P. Yao ◽  
L. Niu ◽  
W.J. Cui
Keyword(s):  
Unsaturated Soils ◽  
Path Dependence ◽  
Three Dimensional ◽  
Constitutive Models ◽  
Stress Path ◽  
Triaxial Tests ◽  
Additional Material ◽  
Basic Model ◽  
Proposed Model ◽  
Unsaturated Clays

Naturally deposited clays are often unsaturated and overconsolidated. Within the frameworks of the Barcelona Basic model (BBM) for normally consolidated unsaturated clays and the unified hardening (UH) model for overconsolidated saturated clays, a three-dimensional constitutive model for overconsolidated unsaturated clays is proposed in this paper. This model can be reduced to the original UH model for overconsolidated saturated clays when suction becomes zero and the BBM when the overconsolidated behaviour disappears. Compared with existing constitutive models for unsaturated clays, the influence of a high overconsolidation ratio (OCR) on wetting deformation can be adequately described. Also, many other characteristics of overconsolidated unsaturated clays can be modelled, including strain-hardening, softening, shear dilatancy, and stress path–dependence behaviour. Compared with the BBM, the proposed model requires no additional material parameter. The validity of the UH model for overconsolidated unsaturated clays has been confirmed by data from two groups of wetting tests performed by the authors and previous triaxial tests in the literature.

scholarly journals A Unified Elastoplastic Model of Unsaturated Soils Considering Capillary Hysteresis

2013 ◽  
Vol 2013 ◽  
pp. 1-15
Author(s):  
Tiantian Ma ◽  
Changfu Wei ◽  
Pan Chen ◽  
Huihui Tian ◽  
De'an Sun
Keyword(s):  
Soil Water ◽  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Mechanical Response ◽  
Internal State ◽  
Degree Of Saturation ◽  
State Variables ◽  
Soil Behavior ◽  
Capillary Hysteresis ◽  
Modified Cam Clay

Unlike its saturated counterparts, the mechanical behavior of an unsaturated soil depends not only upon its stress history but also upon its hydraulic history. In this paper, a soil-water characteristic relationship which is capable of describing the effect of capillary hysteresis is introduced to characterize the influence of hydraulic history on the skeletal deformation. The capillary hysteresis is viewed as a phenomenon associated with the internal structural rearrangements in unsaturated soils, which can be characterized by using a set of internal state variables. It is shown that both capillary hysteresis and plastic deformation can be consistently addressed in a unified theoretical framework. Within this context, a constitutive model of unsaturated soils is developed by generalizing the modified Cam-Clay model. A hardening function is introduced, in which both the matric suction and the degree of saturation are explicitly included as hardening variables, so that the effect of hydraulic history on the mechanical response can be properly addressed. The proposed model is capable of capturing the main features of the unsaturated soil behavior. The new model has a hierarchical structure, and, depending upon application, it can describe the stress-strain relation and the soil-water characteristics in a coupled or uncoupled manner.

Critical state for overconsolidated unsaturated silty soil

2008 ◽  
Vol 45 (3) ◽  
pp. 408-420 ◽  
Author(s):  
A. R. Estabragh ◽  
A. A. Javadi
Keyword(s):  
Critical State ◽  
Specific Volume ◽  
Laboratory Experiments ◽  
Experimental Tests ◽  
Triaxial Tests ◽  
State Variables ◽  
Shear Tests ◽  
Silty Soil ◽  
Deviator Stress ◽  
Triaxial Cell

The critical state concepts have been investigated for an overconsolidated unsaturated silty soil through a comprehensive set of controlled suction triaxial laboratory experiments. The experimental tests were conducted in a specially designed double-walled Bishop and Wesley triaxial cell on samples of unsaturated silty soil. Isotropic loading, unloading, and triaxial drained shear tests were performed on samples of unsaturated silty soil with different overconsolidation ratios at various suctions. The data from the triaxial tests were used in the development of a critical state framework for overconsolidated unsaturated silty soil. The framework is defined in terms of four state variables: mean net stress (p'), deviator stress (q), suction (s), and specific volume (v). The results show that the critical state lines in q:p' space for different soil suctions are not parallel and merge with each other. The slopes and intercepts of these lines are functions of suction. However, the critical state lines are nearly parallel in the v – ln p' plane except under saturation conditions, and the slope and intercept of these lines are also functions of suction.

scholarly journals A Laboratory Study on the Shear Strength Behavior of Two Till Deposits from Northern Germany

Energies ◽  
2021 ◽  
Vol 14 (6) ◽  
pp. 1692
Author(s):  
Henok Hailemariam ◽  
Frank Wuttke
Keyword(s):  
Shear Strength ◽  
Laboratory Study ◽  
Elevated Temperatures ◽  
Constitutive Models ◽  
Friction Angle ◽  
Triaxial Tests ◽  
Experimental Program ◽  
Soil Behavior ◽  
Northern Germany ◽  
Triaxial Cell

This paper presents the findings of a laboratory study of the shear strength and yielding behavior of two glacial till soil deposits from the area of Heiligenhafen, northern Germany. The tests were conducted on reconstituted forms of the soils using a triaxial cell capable of controlling the temperature of the specimens. The experimental program included a series of multi-stage consolidated drained (CD) compression triaxial tests at temperature ranges between 20 and 60 °C. For the temperature range considered in this study, a mild reduction in the effective friction angle of the two till soils of less than 1° was observed due to an increase in temperature from 20 to 60 °C. All the results were carefully assessed in view of the intrinsic soil behavior and fabric, and existing trends are highlighted. The findings of this study provide valuable insights into the shearing properties of till deposits, and can contribute to the enhancement of existing soil constitutive models as well as the development of new models that are particularly suited to the behavior of glacial tills under elevated temperatures.

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