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Author: Amr F. Elhakim
Publisher:
ISBN:
Category : Concrete footings
Languages : en
Pages :
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Book Description
Foundation performance is controlled significantly by the stress-strain behavior of the underlying soils. For geomaterials, the small-strain shear modulus Gmax is a fundamental stiffness applicable to both monotonic static and dynamic loading conditions, as well to both drained and undrained loading. Yet, Gmax is too stiff for direct use in computing foundation displacements. The main objectives of this research are to: (1) explore the scaled parallelism between the stress-strain-strength behavior of the single soil element response and the load-displacement-capacity of a shallow foundation system supported on soil; (2) develop a methodology for evaluating the performance of vertically-loaded footings using a rational framework based on the small-strain modulus Gmax, large-strain strength ([tau]max or su) and strain at failure [gamma]); and (3) calibrate the proposed method using a foundation database of full-scale load tests under both undrained and drained conditions. In geotechnical practice, foundation bearing capacity is handled as a limit plasticity calculation, while footing displacements are evaluated separately via elastic continuum solutions. Herein, a hybrid approach is derived that combines these two facets into a closed-form analytical solution for vertical load-deflection-capacity based on numerical studies. Here, a non-linear elastic-plastic soil model was developed to simulate the stress-strain-strength curves for simple shearing mode (LOGNEP) for each soil element. The model was encoded into a subroutine within the finite difference program FLAC. A large mesh was used to generate load-displacement curves under circular and strip footings for undrained and drained loading conditions. With proper normalization, parametric foundation response curves were generated for a variety of initial stiffnesses, shear strengths, and degrees of non-linearity in the soil stress-strain-strength response. Soil stress-strain non-linearity is described by a logarithmic function (Puzrin & Burland, 1996, 1998) that utilizes a normalized strain xL that relates strain at failure [gamma]f, shear strength ([tau]max or su), and small-strain stiffness Gmax, all having physical meaning. A closed-form algorithm is proposed for generating non-linear load-displacement curves for footings and mats within an equivalent elastic framework. The proposed method was calibrated using a database of well-documented footing load tests where soil input parameters were available from laboratory and/or in-situ field test results.
Author: Amr F. Elhakim
Publisher:
ISBN:
Category : Concrete footings
Languages : en
Pages :
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Book Description
Foundation performance is controlled significantly by the stress-strain behavior of the underlying soils. For geomaterials, the small-strain shear modulus Gmax is a fundamental stiffness applicable to both monotonic static and dynamic loading conditions, as well to both drained and undrained loading. Yet, Gmax is too stiff for direct use in computing foundation displacements. The main objectives of this research are to: (1) explore the scaled parallelism between the stress-strain-strength behavior of the single soil element response and the load-displacement-capacity of a shallow foundation system supported on soil; (2) develop a methodology for evaluating the performance of vertically-loaded footings using a rational framework based on the small-strain modulus Gmax, large-strain strength ([tau]max or su) and strain at failure [gamma]); and (3) calibrate the proposed method using a foundation database of full-scale load tests under both undrained and drained conditions. In geotechnical practice, foundation bearing capacity is handled as a limit plasticity calculation, while footing displacements are evaluated separately via elastic continuum solutions. Herein, a hybrid approach is derived that combines these two facets into a closed-form analytical solution for vertical load-deflection-capacity based on numerical studies. Here, a non-linear elastic-plastic soil model was developed to simulate the stress-strain-strength curves for simple shearing mode (LOGNEP) for each soil element. The model was encoded into a subroutine within the finite difference program FLAC. A large mesh was used to generate load-displacement curves under circular and strip footings for undrained and drained loading conditions. With proper normalization, parametric foundation response curves were generated for a variety of initial stiffnesses, shear strengths, and degrees of non-linearity in the soil stress-strain-strength response. Soil stress-strain non-linearity is described by a logarithmic function (Puzrin & Burland, 1996, 1998) that utilizes a normalized strain xL that relates strain at failure [gamma]f, shear strength ([tau]max or su), and small-strain stiffness Gmax, all having physical meaning. A closed-form algorithm is proposed for generating non-linear load-displacement curves for footings and mats within an equivalent elastic framework. The proposed method was calibrated using a database of well-documented footing load tests where soil input parameters were available from laboratory and/or in-situ field test results.
Author: Andre Archer
Publisher:
ISBN:
Category : Geotechnical engineering
Languages : en
Pages :
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Book Description
Settlement prediction of shallow foundations is an essential part for the design of a structure. Accuracy is important, and to increase the accuracy, reliable input parameters are required. However, reliable input parameters do not necessarily render accurate results since the parameters used in design are only as good as the prediction method. Foundation design on sands consists of two aspects: bearing capacity and settlement, with settlement being the governing factor in almost all cases. Settlement prediction is not always an easy task. The main reason being that engineers are unable to measure stiffness accurately as well as how to use the stiffness value measured in certain settlement methods. An important soil stiffness value is the initial small-strain shear modulus (G0) which can be obtained relatively easy with in-situ test methods and the values obtained are generally reliable. With in-situ testing becoming increasingly popular, settlement prediction methods utilising the initial small-strain shear stiffness are also becoming more common. The main objective of this project is to determine whether the load-settlement behaviour of a shallow foundation can be estimated accurately using only the small-strain shear modulus of the granular soil below the foundation. Centrifuge tests were conducted on an equivalent 5m circular shallow foundation at three different density sands to establish if the stress-settlement behaviour can be predicted and to what level of accuracy. The different density sands were loose, medium dense and dense sands. Bender- and extender elements were used to determine the small-strain stiffness data which were used for the analysis. The main conclusion drawn from the study is divided into two parts; Full-range load-settlement behaviour and Practical-range load-settlement behaviour. The full-range results relate to full stress-settlement curve with the practical-scale results up to settlements of 0.1D. The method proposed for the load-settlement prediction is a non-linear stepwise method. The proposed method requires utilising a stiffness degradation curve and it was found that curves presented by Oztoprak & Bolton (2013) and Bolton & Whittle (1999) produced the best results. For the full-range load-settlement results, accurate predictions were found between the predicted and measured load-settlement curves for low density sand. However accuracy decreases with increase in density. For settlements up to 0.1D the load-settlement behaviour was predicted with reasonably good accuracy. The study showed that the settlement of a shallow foundation can be predicted with reasonable accuracy up to 0.1D settlement using only the small-strain shear stiffness value of the soil below the foundation and that there is merit in the proposed method for future use.
Author: D. Milovic
Publisher: Elsevier
ISBN: 0444597263
Category : Technology & Engineering
Languages : en
Pages : 637
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Book Description
This monograph presents the results of the theoretical analyses of stresses and displacements for shallow foundations subjected to various types of loads. In these analyses not only the classical models but more complex models of soils have been used, such as two-layer half-space, homogenous compressible layer of finite thickness, two-layer compressible layer of finite thickness, anisotropic compressible layer. Contact stresses, settlements, vertical stress distribution, bending moments and shear forces have been determined for foundations of any rigidity. Numerous values of the dimensionless coefficients "I" are tabulated, which can be of use in the solution of practical engineering problems.
Author: Thomas Benz
Publisher:
ISBN: 9783921837559
Category :
Languages : en
Pages : 187
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Book Description
Author: Andrew W. Strahler
Publisher:
ISBN:
Category : Bearing capacity
Languages : en
Pages : 214
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Book Description
Shallow foundations are extensively used to support structures of all sizes and derive their support from near surface soils. Thus, they are typically embedded up to a few meters into the soil profile. Designers of shallow foundations are required to meet two limit states: overall failure of the soil beneath the foundation (bearing capacity) and excessive settlement. Existing bearing capacity design methods use an assumed shearing plane within the soil and perfectly plastic soil behavior to estimate the ultimate resistance available. The immediate settlement of a shallow foundation is typically approximated using an elasticity-based method that does not account for actual, nonlinear soil behavior. A load test database was developed from footing load tests reported in the literature to assess the accuracy and uncertainty in existing design methodologies for calculating bearing capacity and immediate settlement. The assessment of uncertainty in bearing capacity and immediate settlement was accomplished through the application of a hyperbolic bearing pressure-displacement model, and the adaptation of the Duncan-Chang soil constitutive model to footing displacements. The prediction of bearing capacity using the general bearing capacity formula was compared to the bearing capacity extrapolated from the load test database using a hyperbolic bearing pressure-displacement model. On average the general bearing capacity formula under-predicts the bearing capacity and exhibits a significant amount of variability. The comparison was used to develop resistance statistics that were implemented to produce resistance factors for an LRFD based design approach using AASHTO load statistics. The Duncan-Chang model was adapted to predict bearing pressure displacement curves for footings in the load test database and used to estimate governing soil parameters. Bearing pressure-displacement curves fitted to the observed curves were used to back calculate soil stiffness. The soil stiffness was used with an elasticity-based displacement prediction method to evaluate the accuracy of the method. Finally, the back-calculated modulus from the fitted Duncan-Chang model was used to assess the accuracy and uncertainty associated with the elasticity-based K-factor, a correlation based stiffness parameter. In general the comparisons indicate that the current design procedures over-predict the bearing pressure associated with a given displacement and exhibit a significant amount of uncertainty.
Author: Delwyn G. Fredlund
Publisher: John Wiley & Sons
ISBN: 047185008X
Category : Technology & Engineering
Languages : en
Pages : 542
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Book Description
The principles and concepts for unsaturated soils are developed as extensions of saturated soils. Addresses problems where soils have a matric suction or where pore-water pressure is negative. Covers theory, measurement and use of the fundamental properties of unsaturated soils--permeability, shear strength and volume change. Includes a significant amount of case studies.
Author: Swami Saran
Publisher: CRC Press
ISBN: 1351241281
Category : Science
Languages : en
Pages : 296
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Book Description
The book offers a systematic analysis of footings (i.e. shallow foundations) in a realistic way, using constitutive relationships of the soil. The aim of the book is to deal with the theme holistically, involving the determination of the constitutive law of the soil, and then proportioning the footing occurring in different situations in actual practice. The book has eleven chapters. After giving an introduction and scope of the book in the first chapter, second and third chapters are respectively devoted to constitutive laws of soil and basic stress equations. In the third chapter analysis of strip footings subjected to central vertical load has been dealt. This analysis has been extended for eccentric –inclined load in the fifth chapter. Since problems of shallow foundations resting adjacent to a slope are of prime importance, this aspect has been dealt in sixth chapter. In the seventh chapter, analysis pertaining to square and rectangular footings have been presented. Effect of interference between adjacent footing is covered in chapter eight. Since ring footings are usually provided for tanks, silos, towers etc., ninth chapter is devoted to this. Added attraction of the book is its chapter ten in which footings located in seismic regions have been covered. Effect of embedment below the ground surface on the behavior of footings located both in non-seismic and seismic regions has been dealt in the chapter eleven. The book is intended for senior undergraduate, postgraduate and Ph.D. students of civil engineering, research scholars, practicing engineers, teachers and academicians. The analyses are based on the latest information available. A number of illustrated examples have been included in the text. SI units have been used in the book.
Author: Braja M. Das
Publisher: CRC Press
ISBN: 9781420049565
Category : Technology & Engineering
Languages : en
Pages : 394
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Book Description
The First Comprehensive Guide to Shallow Foundations Over the last few decades, the bearing capacity of shallow foundations has been studied more thoroughly than any other subject in geotechnical engineering. Until now, however, most references on foundation engineering devoted only a single chapter to the subject. Shallow Foundations: Bearing Capacity and Settlement provides what many engineers have been waiting for-a concise, comprehensive reference containing all the relevant material on shallow foundation behavior under static and dynamic loads related to their ultimate bearing capacity, allowable bearing capacity, and settlement. Estimation Techniques, Earthquake Loading, and Experimental Results The author-a renowned expert-presents the various theories developed during the past fifty years for estimating the ultimate bearing capacity of shallow foundations under various types of loading and subsoil conditions. He discusses the principles of estimating foundation settlement and for estimating the stress increase in a soil mass supporting a foundation. Earthquake loading and its effects on ultimate bearing capacity have received considerable attention in recent years, and the author provides an overview of these developments. He also offers details regarding permanent foundation settlement caused by cyclic and transient loading-details derived from laboratory and field experimental observations. Progress in Soil Reinforcement Researchers have made steady progress in evaluating the potential of soil reinforcement to reduce settlement and increase ultimate and allowable bearing capacities of shallow foundations. This book provides an entire chapter on the subject, including discussions of the materials used: galvanized steel strips, geotextile, and geogrid. The presentation of Shallow Foundations is clear, concise, and filled with examples and exercises that illustrate the theory. This book stands alone as an in-depth, authoritative guide to shallow foundation bearing capacities and the effects of different soil types, slopes, settlement, reinforcement, and seismic activity. Researchers, students, and practicing engineers will all welcome its addition to their reference shelves.
Author: Lymon C. Reese
Publisher: John Wiley & Sons
ISBN: 0471431591
Category : Technology & Engineering
Languages : en
Pages : 608
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Book Description
One-of-a-kind coverage on the fundamentals of foundation analysis and design Analysis and Design of Shallow and Deep Foundations is a significant new resource to the engineering principles used in the analysis and design of both shallow and deep, load-bearing foundations for a variety of building and structural types. Its unique presentation focuses on new developments in computer-aided analysis and soil-structure interaction, including foundations as deformable bodies. Written by the world's leading foundation engineers, Analysis and Design of Shallow and Deep Foundations covers everything from soil investigations and loading analysis to major types of foundations and construction methods. It also features: * Coverage on computer-assisted analytical methods, balanced with standard methods such as site visits and the role of engineering geology * Methods for computing the capacity and settlement of both shallow and deep foundations * Field-testing methods and sample case studies, including projects where foundations have failed, supported with analyses of the failure * CD-ROM containing demonstration versions of analytical geotechnical software from Ensoft, Inc. tailored for use by students in the classroom
Author: Masaki Kitazume
Publisher: CRC Press
ISBN: 0203589637
Category : Technology & Engineering
Languages : en
Pages : 436
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Book Description
The Deep Mixing Method (DMM), a deep in-situ soil stabilization technique using cement and/or lime as a stabilizing agent, was developed in Japan and in the Nordic countries independently in the 1970s. Numerous research efforts have been made in these areas investigating properties of treated soil, behavior of DMM improved ground under static and d
