scholarly journals Numerical and Experimental Analysis of Horizontal Stress Changes and Soil Collapse During Chemical Dissolution in a Modified Oedometer Cell

2016 ◽  
pp. 19-27
Author(s):  
Cecilia Lins ◽  
Nayra Silva ◽  
Leonardo Guimarães ◽  
Analice Lima ◽  
Igor Gomes
Keyword(s):  
Unsaturated Soils ◽  
Horizontal Stress ◽  
Sample Volume ◽  
General Purpose ◽  
Dissolution Process ◽  
Solid Matrix ◽  
Soil Behavior ◽  
Mineral Concentration ◽  
Basic Model ◽  
Stress Changes

The purpose of this paper is to investigate the horizontal stress evolution and soil collapse during the cement dissolution process using a combination of experimental and numerical methods. The experimental procedure was carried out using a modified oedometer cell with horizontal stress measurements and synthetic samples in order to simulate simultaneous cement dissolution, stress changes and sample deformation. The samples were loaded at a constant vertical stress and exposed to a reactive fluid which dissolved the cementation of the artificial soil. During the dissolution process, sample volume decreased and horizontal stress changes were observed. Initially the horizontal stress decreased due to grain mass loss and then increased due to solid matrix rearrangement. Numerical simulation of these coupled chemical and mechanical processes was performed using a general purpose finite element code capable of performing numerical analysis of engineering problems. The constitutive model adopted to reproduce the soil behavior is an extension of the Barcelona Basic Model for unsaturated soils including the cement mineral concentration as state variable. Some new features were incorporated to the original elasto-plastic model in order to represent the results observed in the experiments. In this paper a good agreement between experimental and numerical results was achieved.

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.

A Semianalytical Model for Evaluating the Performance of a Refractured Vertical Well With an Orthogonal Refracture

SPE Journal ◽  
2019 ◽  
Vol 24 (02) ◽  
pp. 891-911 ◽  
Author(s):  
Bailu Teng ◽  
Huazhou Andy Li
Keyword(s):  
Production Rate ◽  
Horizontal Stress ◽  
Fracture Flow ◽  
Vertical Well ◽  
Flow Equations ◽  
Stress Reversal ◽  
Reservoir Flow ◽  
Proposed Model ◽  
Stress Changes ◽  
Initial Fracture

Summary Production from a fractured vertical well will lead to a redistribution of the stress field in formations. If the induced stress changes are sufficiently large to overcome the effect of the initial horizontal-stress deviator, the direction of the minimum horizontal stress can be turned into the direction of the maximum horizontal stress within an elliptical region around the initial fracture, resulting in a stress-reversal region near the wellbore. In such cases, a refracturing treatment can create a refracture that propagates orthogonally to the initial fracture because of the stress reversal. As such, the high-pressure area of the formation can be stimulated by the refracture, and the productivity of the refractured well can be improved. In this work, we develop a semianalytical model to evaluate the performance of a refractured vertical well with an orthogonal refracture. To simulate the well performance throughout the entire production period, we divide the well production into three stages: the first stage, when the well is producing oil with the initial fracture; the second stage, when the well is shut down for the refracturing treatment; and the third stage, when the well is producing oil with both the initial fracture and the refracture. In addition, by discretizing the initial fracture and the refracture into small segments, the conductivity of the fractures can be taken into account, and the geometry of the fracture system can be captured. We use the Green-function method to analytically simulate the reservoir flow and use the finite-difference method to numerically simulate the fracture flow; therefore, a semianalytical model can be constructed by coupling the reservoir-flow equations with the fracture-flow equations. This proposed model is applied to different wellbore and reservoir conditions. The calculated results show that this proposed model is versatile because it can simulate various wellbore constraints, including the conditions of constant bottomhole pressure (BHP), varying BHP, constant production rate, and varying production rate. The permeability anisotropy of the reservoir system, as well as the nonuniform conductivity distribution along the fracture, can also be incorporated into this proposed model. In addition, we demonstrate that this proposed model can be used to simulate other types of refractured vertical wells with minor modifications.

scholarly journals Systematic Generation of a 3D DSM by Extracting Social Robot Behaviors from Literature

2019 ◽  
Vol 1 (1) ◽  
pp. 3731-3740
Author(s):  
Ilayda Ozer ◽  
Zuhal Erden
Keyword(s):  
Conceptual Design ◽  
Small Groups ◽  
General Purpose ◽  
Social Robots ◽  
Design Methods ◽  
Social Robot ◽  
Direct Communication ◽  
Basic Model ◽  
Physical Elements ◽  
People Today

AbstractSocial robots are in direct communication and interaction with people, thus it is important to design these robots for different needs of individuals or small groups. This has revealed the need to develop design methods for personalized or mass-individualized social robots, which are expected to respond to many different needs of people today and in the future. In this paper, a previously developed 3D DSM model is implemented in the systematic conceptual design of social robot families. The model is independent of any physical elements and based on behavioural elements as perception, cognition and motoric action. The data regarding 45 different social robots from 80 articles in the literature is used to identify these three behaviours of the existing social robots and the mutual relationships among these different behaviours are defined in order to develop a 3D DSM structure to be used as a basis for designing social robot families. The resulting novel 3D DSM is a general-purpose, basic model that can be used to identify behavioural modules to design social robot families.

On the Hypothesis of Effective Stress in Consolidation and Strength for Unsaturated Soils

2012 ◽  
Vol 256-259 ◽  
pp. 108-111
Author(s):  
Seboong Oh ◽  
Ki Hun Park ◽  
Oh Kyun Kwon ◽  
Woo Jung Chung ◽  
Kyung Joon Shin
Keyword(s):  
Shear Strength ◽  
Soil Water ◽  
Effective Stress ◽  
Unsaturated Soils ◽  
Water Retention Curve ◽  
Triaxial Tests ◽  
Residual Soil ◽  
Soil Behavior ◽  
Soil Water Retention Curve ◽  
Soil Water Retention

The hypothesis on effective stress of unsaturated soils is validated by consolidation strength results of triaxial tests for the compacted residual soil. The effective stress can describe the unsaturated soil behavior, which was defined from shear strength or from soil water characteristic curves. Since the effective stress from consolidation agrees with that from the shear strength, the effective stress from soil water retention curve could describe the unsaturated behavior consistently on both consolidation path and stress at failure. The effective stress can describe the entire unsaturated behavior from consolidation to failure.

An explicit analytical solution for calculating horizontal stress changes and displacements around an excavated diaphragm wall panel

2003 ◽  
Vol 40 (4) ◽  
pp. 780-792 ◽  
Author(s):  
C WW Ng ◽  
G H Lei
Keyword(s):  
Analytical Solution ◽  
Uniaxial Stress ◽  
Horizontal Stress ◽  
Ease Of Use ◽  
Elastic Solution ◽  
Diaphragm Wall ◽  
Wall Panel ◽  
Principle Of Superposition ◽  
Explicit Analytical Solution ◽  
Stress Changes

A new, simple, and explicit analytical solution has been derived for calculating horizontal stress changes and displacements caused by the excavation for a diaphragm wall panel. The theoretical solution is obtained by applying the principle of superposition appropriately to model diaphragm wall construction using a basic elastic solution to the problem of an infinite horizontal plate with a rectangular opening subjected to a uniaxial stress at infinity. The basic elastic solution can be obtained by using the method of complex variables with a simplified conformal transformation function. Key parameters governing the magnitude of horizontal stress changes and displacements are identified. Computed results are given in a normalized form in terms of aspect ratio (length to width) of a diaphragm wall panel. Two extreme cases for diaphragm wall panels with dimensions 1 m × 1 m and 10 m × 1 m have been analysed to investigate the distributions of stress changes and deformations around the panels during the bentonite stage. By performing a parametric study, calculation charts have been developed for computing horizontal stress changes and displacements for practising engineers and researchers to carry out preliminary designs and for numerical modellers to verify their sophisticated predictions. The ease of use of the charts is illustrated by two examples, and the limitations of the derived solutions are discussed.Key words: diaphragm wall, elasticity, stress change, displacement, stress analysis, earth pressure.

Comments on use of the Barcelona Basic Model for unsaturated soils

2002 ◽  
Vol 26 (15) ◽  
pp. 1561-1571 ◽  
Author(s):  
S. J. Wheeler ◽  
D. Gallipoli ◽  
M. Karstunen
Keyword(s):  
Unsaturated Soils ◽  
Basic Model

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 Investigating the Effect of Geocell Changes on Slope Stability in Unsaturated Soil

2020 ◽  
Vol 14 (1) ◽  
pp. 66-75
Author(s):  
Behnam Mehdipour ◽  
Hamid Hashemolhosseini ◽  
Bahram Nadi ◽  
Masoud Mirmohamadsadeghi
Keyword(s):  
Slope Stability ◽  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Bending Strength ◽  
Load Capacity ◽  
Three Dimensional ◽  
Bending Moment ◽  
Soil Conditions ◽  
Vertical Side ◽  
Basic Model

The purpose of this research is to investigate the performance and efficiency of reinforced slope in the stability of geocell layers in unsaturated soil conditions. Slope reinforced with geocell acts like a beam in the soil due to the geocell having a height (three-dimensional). Due to its flexural properties, it has moment of inertia as well as bending strength, which reduces the displacement and increases the safety factor of the slope. Taking into consideration unsaturated conditions of soil contributes a lot to making results close to reality. One of the well-known models among elastoplastic models for modeling unsaturated soils is Barcelona Basic Model, which has been added to the FLAC2D software by codification. Changes in thickness, length and number of geocell layers are remarkably effective on slope stability. The results show that the geocell's reinforcing efficiency depends on the number of layers and depth of its placement. As the depth of the geocell's first layer increases, the lateral and vertical side elevation of the upper part of the slope increases with respect to the elevation. Load capacity increases with increasing geocell length. By increasing the length of the geocell layer, the joint strength, the mobilized tensile strength, and the bending moment are increased. At u/H = 0.2, an increase in the bending momentum of about 20% occurs with increasing geocell thickness. In u/H = 1, the increase in bending momentum is 10.4%. In addition, by increasing the thickness of the geocell, the Value of moment of the inertia increases and, as a result, the amount of geocell reinforcement bending moment increases.

Modified state-surface approach to the study of unsaturated soil behavior. Part III: Modeling of coupled hydromechanical effect

2012 ◽  
Vol 49 (1) ◽  
pp. 98-120 ◽  
Author(s):  
Xiong Zhang ◽  
Robert L. Lytton
Keyword(s):  
Unsaturated Soils ◽  
Coupling Effect ◽  
Degree Of Saturation ◽  
Compression Tests ◽  
Soil Behavior ◽  
Volume Changes ◽  
Surface Approach ◽  
Soil Skeleton ◽  
Hydromechanical Behavior ◽  
Undrained Conditions

A modified state-surface approach (MSSA) was proposed in the authors’ previous study to investigate volume change of the soil skeleton for unsaturated soils. This paper discussed the coupling effect between volume changes of soil skeleton, water phase, and air phase for unsaturated soils based on the proposed MSSA and experimental results presented by other researchers. The MSSA was further extended to study the coupled hydromechanical behavior for unsaturated soils. Besides void ratio constitutive surface, conventional unique water content and degree of saturation constitutive surfaces were also divided into elastic and plastic regions by loading–collapse (LC) yield curves and simultaneously used to describe the coupled hydromechanical behavior for unsaturated soils. A general theoretic formulation was derived for the simultaneous use of the MSSA under isotropic conditions. Based on the derived formulation, existing elastoplastic models were reviewed, and compatibility and consistency in modeling the mechanical and hydraulic behavior of unsaturated soils were discussed. Afterwards, the results of a number of suction-controlled laboratory isotropic compression tests at different suctions were used to demonstrate the ability of the proposed approach to reproduce the observed soil behavior quantitatively and soil behavior under undrained conditions qualitatively.

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.

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