Modified state-surface approach to the study of unsaturated soil behavior. Part II: General formulation

2009 ◽  
Vol 46 (5) ◽  
pp. 553-570 ◽  
Author(s):  
Xiong Zhang ◽  
Robert L. Lytton
Keyword(s):  
Unsaturated Soil ◽  
Material Properties ◽  
Stress Path ◽  
Companion Paper ◽  
Soil Behavior ◽  
Unified Framework ◽  
Collapsible Soil ◽  
Surface Approach ◽  
As Stress ◽  
A Minor

In the previous companion paper, a modified state-surface approach was proposed to algebraically represent unsaturated soil behavior under isotropic stress conditions. The present paper proposes a general theoretic formulation for the modified state-surface approach based on the theory proposed by Fredlund and co-workers. The signs and physical meanings of the material properties, the shapes of the loading–collapse (LC) and suction increase (SI) yield curves, and the mechanisms used in the Barcelona basic model (BBM) to model unsaturated soil behavior are discussed. Some other problems, such as stress-path independency and its implication on material properties, as well as coupling effects between the LC and SI curves, are also discussed. Based on analysis, it was found that with a minor modification, the modified state-surface approach can be used to study both unsaturated expansive and collapsible soil behavior in a unified framework.

Modified state-surface approach to the study of unsaturated soil behavior. Part I: Basic concept

2009 ◽  
Vol 46 (5) ◽  
pp. 536-552 ◽  
Author(s):  
Xiong Zhang ◽  
Robert L. Lytton
Keyword(s):  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Stress Path ◽  
Complex Stress ◽  
Soil Behavior ◽  
Elastic Surface ◽  
Surface Approach ◽  
Basic Model ◽  
Plastic Hardening ◽  
Complex Stress Path

The traditional state-surface approach to the study of unsaturated soil behavior is becoming much less popular these days, as it uses unique constitutive surfaces to represent unsaturated soil behavior. This approach is essentially a nonlinear elastic formation and cannot be used to explain complex stress-path dependency for unsaturated soils. In this paper, a modified state-surface approach (MSSA) is proposed to represent unsaturated soil behavior under isotropic stress conditions in which a conventional void-ratio state surface is considered to be made up of an elastic surface and a plastic hardening surface. The plastic hardening surface remains stationary at all times, whereas the elastic surface remains unchanged when the soil experiences elastic deformation and moves downward when there is plastic hardening occurrence. Using the MSSA, the loading–collapse (LC) and the suction increase (SI) yield curves in the Barcelona basic model (BBM) are derived. The prediction of three typical cases of soils under isotropic conditions and experimental results using the proposed approach confirmed its feasibility, simplicity, and potential for the study of unsaturated soil behavior.

scholarly journals The softness distribution index: towards the creation of guidelines for the modeling of soft-bodied robots

2019 ◽  
pp. 027836491989345
Author(s):  
Giovanna A Naselli ◽  
Barbara Mazzolai
Keyword(s):  
Material Properties ◽  
Soft Robotics ◽  
Dimensionless Quantity ◽  
Unified Framework ◽  
Soft Body ◽  
Computational Burden ◽  
Highly Nonlinear ◽  
Nonlinear Mechanical ◽  
Distribution Index ◽  
The Moment

Modeling soft robots is not an easy task owing to their highly nonlinear mechanical behavior. So far, several researchers have tackled the problem using different approaches, each having advantages and drawbacks in terms of accuracy, ease of implementation, and computational burden. The soft robotics community is currently working to develop a unified framework for modeling. Our contribution in this direction consists of a novel dimensionless quantity that we call the softness distribution index (SDI). The SDI for a given soft body is computed based on the distribution of its structural properties. We show that the index can serve as a tool in the choice of a modeling technique among multiple approaches suggested in literature. At the moment, the investigation is limited to bodies performing planar bending. The aim of this work is twofold: (i) to highlight the importance of the distribution of the geometrical and material properties of a soft robotic link/body throughout its structure; and (ii) to demonstrate that a classification based on this distribution provides guidelines for the modeling.

scholarly journals Improvement of Collapsible Soil Behavior of a Lateritic Soil Using Rice Husk Ash

2015 ◽  
Vol 668 ◽  
pp. 290-296 ◽  
Author(s):  
Luiza P. Fagundes ◽  
Jhaber D. Yacoub ◽  
Andrey C. Lima ◽  
Flávia R. Nakatsuchi ◽  
José A. Lollo ◽  
...  
Keyword(s):  
Rice Husk ◽  
Rice Husk Ash ◽  
Combined Effect ◽  
Building Construction ◽  
Lateritic Soil ◽  
Soil Behavior ◽  
Collapsible Soil ◽  
Lateritic Soils ◽  
Environmental Friendly

Great areas of Brazil present lateritic soils, such as the northeast and the south. Some of these soils have, as main characteristic, instable structures that can present considerable volumetric deformation in the presence of water. This behavior, also named collapse, is responsible for several problems on the building construction such as cracks and fractures that can damage the safety of structures. The aim of this paper is to assess the possibility of improvement of collapsible behavior of a lateritic soil using rice husk ash (RHA). A previous characterization of soil and RHA was performed in order to assess the combined effect of soil/RHA. The results are so promising, showing a new alternative to reduce the collapsible behavior of soils using an environmental friendly technology.

Plastic Collapse of Thin Internally Pressurized Torispherical Shells

1979 ◽  
Vol 101 (4) ◽  
pp. 311-320 ◽  
Author(s):  
S. K. Radhamohan ◽  
G. D. Galletly
Keyword(s):  
Strain Hardening ◽  
Yield Stress ◽  
Material Properties ◽  
Parametric Study ◽  
Companion Paper ◽  
Experimental Results ◽  
Plastic Collapse ◽  
Approximate Design ◽  
Mode Of Failure ◽  
Hardening Coefficient

The plastic collapse pressures of internally pressurized thin torispherical shells are given in the present paper. The influence of both the geometric parameters (i.e., r/D, RS/D and D/t) and the material properties (yield stress σyp and the strain-hardening coefficient) on the plastic collapse pressures were investigated. Both steel and aluminium shells were analyzed and, based on the present parametric study, approximate design equations for calculating the plastic collapse pressures are suggested. The asymmetric buckling pressures, pcr, for torispherical shells (obtained from a companion paper) are also compared with the plastic collapse pressures, pc, to determine which are the lower and, thus, control the mode of failure. In addition, the approximate design equations for pcr and pc are compared with some experimental results on small machined models; the agreement between theory and test was quite good.

The Design Tradeoffs of Linear Functionally Graded Piezoceramic Actuators

Aerospace ◽  
2003 ◽  
Author(s):  
Paul W. Alexander ◽  
Diann Brei
Keyword(s):  
Material Properties ◽  
High Stress ◽  
Functionally Graded ◽  
Homogeneous Material ◽  
Stress Concentrations ◽  
Practical Applications ◽  
Complex Electric Field ◽  
Design Tradeoffs ◽  
A Minor ◽  
The Cost

It is common practice to reduce the voltage level within piezoelectric actuators by utilizing multiple layers, typically bonded together. Unfortunately, this has a tendency to result in device failure due to delamination. For example, with benders the typical lifetime is 105 to 106 cycles, limiting its use in practical applications. This poses an interesting design tradeoff: the stroke is increased due to sharper gradients between material layers; however, the higher gradients lead to high stress concentrations at those interfaces. One approach to reducing these stresses is to grade the material properties through a monolithic piece of piezoceramic so that no interfaces or bonding elements exist, but this comes at the cost of stroke. This paper explores the design tradeoff inherent to monolithic functionally graded piezoelectrics. An analytical free-displacement model for a monolithic piezoceramic beam with a generic gradient is derived. Key to this is the inclusion of the complex electric field distribution which rises from the non-homogeneous material properties. This model is used along with finite element models to examine the effect of continuous linear and stepwise material gradients on the displacement performance as well as the stress levels. The study shows that using monolithic functionally graded piezocermics can significantly reduce the stresses with only a minor impact on the device stroke.

Influence of Initial Anisotropy, Stress Path and Principal Stress Rotation on Monotonic Behavior of Clean and Mixed Sands

2020 ◽  
Vol 857 ◽  
pp. 417-430
Author(s):  
Kazem Fakharian ◽  
Farzad Kaviani Hamedani
Keyword(s):  
Principal Stress ◽  
Stress Path ◽  
Silica Sand ◽  
Large Strains ◽  
Principal Stress Rotation ◽  
Soil Behavior ◽  
Stress Rotation ◽  
Fabric Evolution ◽  
Initial Anisotropy

It is widely accepted that soil behavior is complicated taking into account soil anisotropy owing to the fact that this phenomenon arises from oriented soil fabric or structure forged in the deposition stage. In this study, a review of major findings of authors’ previous studies are presented with the main focus on soil anisotropy using extensive experimental results incuding Triaxial (TXT), Simple Shear (SSA), and Hollow Cylinder (HCA) apparatus. Effects of initial anisotropy, fabric evolution, stress path, principal stress rotation and intermediate stress state are evaluated for a crushed silica sand. In addition, the effects of Portland cement content and granulated rubber contents on anisotropic behavior of the sand are investigated. Bender elments are mounted on triaxial specimens both in vertical and horizontal directions to measure the shear wave velocity and hence maximum shear modulus at the end of consolidation as well as during shearing up to large strains at critical state condition, as an index of evaluating the fabric evolution. The effects of principal stress rotation and stress paths reveals the crucial role of soil anisotropy on the behavior of clean sand. However, adding either cement or granulated rubber to the sand has considerably decreased anisotropy.

Analysis of Nonlinear Stress and Strain in Clay under the Undrained Condition

2011 ◽  
Vol 27 (2) ◽  
pp. 201-213 ◽  
Author(s):  
P.-G. Hsieh ◽  
C.-Y. Ou
Keyword(s):  
Soft Clay ◽  
Stress Path ◽  
Small Strain ◽  
Model Parameters ◽  
Soil Behavior ◽  
Total Stress ◽  
Soil Stiffness ◽  
Nonlinear Stress ◽  
Strength Tests ◽  
Laboratory Stress

ABSTRACTThough the total stress undrained analysis approach in geotechnical engineering is widely utilized by practicing engineers, it has some intrinsic imperfections that cause the obtained parameters to have unavoidable empirical correlations. In this study, an undrained soft clay model is developed, which overcomes the imperfections of the conventional total stress undrained approach. In addition, the high soil stiffness at small strain and the concept of yield surface are employed to realistically simulate actual soil behavior. The model parameters can be obtainable directly from conventional laboratory tests. The model is validated through different laboratory stress path tests and strength tests in this paper.

Capacity of shallow foundations on saturated cohesionless soils under combined loading

2009 ◽  
Vol 46 (6) ◽  
pp. 639-649 ◽  
Author(s):  
M. Tolga Yilmaz ◽  
B. Sadik Bakir
Keyword(s):  
Stress Path ◽  
Reduction Factor ◽  
Shallow Foundations ◽  
Combined Loading ◽  
Saturated Soils ◽  
Soil Behavior ◽  
Seismic Capacity ◽  
Moment Capacity ◽  
Overturning Moment ◽  
The Impact

Under seismically induced loading, shallow foundations commonly fail by overturning on saturated soils. While the excess pore pressures may have fully dissipated following construction, undrained conditions are typically presumed in the assessment of seismic capacity in conventional applications due to the high rates of loading induced during an earthquake. Undrained strength, however, can be critically dependent on the history of loading and significantly heterogeneous and anisotropic around a foundation. The finite element method is utilized in this study for a proper assessment of the impact of these factors on the overturning moment capacity of surficial foundations on saturated soils, with specific emphasis on failure under seismic loading. Uplift capability has been incorporated into the models and analyses have been conducted for different drainage conditions. Based on the analyses results and comparisons with analytical formulae, it is concluded that the assumption of homogeneous soil strength as well as the disregard of stress path followed can lead to significant overestimation of the overturning moment capacity. The proposed improved approach comprises calculation of the overturning moment capacity based on drained soil behavior and subsequent application of an undrained behavior reduction factor (URF) compatible with the representative pore-pressure parameter A.

scholarly journals Unsaturated soils in the context of tropical soils

2021 ◽  
Vol 44 (3) ◽  
pp. 1-25
Author(s):  
José Camapum de Carvalho ◽  
Gilson Gitirana
Keyword(s):  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Structural Characteristics ◽  
Soil Formation ◽  
Soil Classification ◽  
Tropical Soils ◽  
Engineering Practice ◽  
Soil Behavior ◽  
Specific Behavior ◽  
Engineering Problems

The practice of geotechnical engineering in tropical climate regions must consider the use of unsaturated soil concepts. However, these concepts must also take into account the specific behavior traits of tropical soils, particularly those related to soil aggregation, pore structure, and mineralogy. This paper will initially present considerations on the typical properties of unsaturated tropical soils as well as fundamental concepts. Throughout the article, several engineering problems will be presented alongside reflections on the complex interaction between the numerous variables involved in the modeling and engineering practice of tropical unsaturated soil behavior. The paper addresses issues related to soil formation, chemical and mineral composition, physical properties, tropical soil classification, and structural characteristics of soils. Issues related to compaction and the influence of weathering, geomorphology and bioengineering are also addressed.

scholarly journals State Variables in Saturated-Unsaturated Soil Mechanics

2016 ◽  
pp. 3-17
Author(s):  
Delwyn G. Fredlund
Keyword(s):  
Stress State ◽  
Continuum Mechanics ◽  
Unsaturated Soil ◽  
Material Properties ◽  
Soil Mechanics ◽  
Constitutive Relations ◽  
Saturated Soil ◽  
Clear Distinction ◽  
State Variables ◽  
Unsaturated Soil Mechanics

The description of the stress state in soils is the foundational point around which an applied science should be built for engineering practice. The stress state description has proven to be pivotal for saturated soil mechanics and the same should be true for unsaturated soil mechanics. Continuum mechanics sets forth a series of principles upon which a common science base can be developed for a wide range of materials. The principles require that there be a clear distinction between state variables and constitutive relations. Constitutive relations relate state variables and incorporate material properties. State variables, on the other hand, are independent of the material properties. It has been possible to maintain a clear distinction between variables of state and constitutive relations in the development of saturated soil mechanics and the same should be true for unsaturated soil mechanics. This paper presents a description of the source and character of stress state variables for saturated and unsaturated soils. The descriptions are consistent with the principles of multiphase continuum mechanics and provide an understanding of the source and importance of stress state variables.

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