Advisor Feed
https://feeds.library.caltech.edu/people/Scott-R-F/advisor.rss
A Caltech Library Repository Feedhttp://www.rssboard.org/rss-specificationpython-feedgenenTue, 16 Apr 2024 01:55:11 +0000Design of a Granular Pressure Cell to be Used in Soils
https://resolver.caltech.edu/CaltechETD:etd-05052006-102954
Authors: {'items': [{'id': 'Meuris-Jean-Maurice', 'name': {'family': 'Meuris', 'given': 'Jean Maurice'}, 'show_email': 'NO'}]}
Year: 1961
DOI: 10.7907/BZGX-R355
In preliminary experimentation, a granular pressure cell was built and tested. From the results obtained, an improved method for the production of granular pressure cells was developed and a second pressure cell was built in order to determine the behavior of granular pressure cells, as designed, under variable external temperature conditions.
A third pressure cell was built for laboratory testing. A calibration curve was established and the pressure cell was used satisfactorily in simple laboratory testing.
Attempts were made to improve the constitution of granular pressure cells as used in the aforementioned tests. These attempts lead to suggestions intended to help in eventual further improvement of the granular pressure cells built and described in the following pages.https://thesis.library.caltech.edu/id/eprint/1629Mechanics of Consolidation with Reference to Experimentally Sedimented Clays
https://resolver.caltech.edu/CaltechETD:etd-05042006-130711
Authors: {'items': [{'id': 'Long-Dennis-Vernon', 'name': {'family': 'Long', 'given': 'Dennis Vernon'}, 'show_email': 'NO'}]}
Year: 1961
DOI: 10.7907/1KZR-E375
The problem of large strain consolidation in soils is investigated by analysis and experiment. A mathematical model is formulated to include the effects of large strains. Analytic and numerical solutions are discussed.
The design, fabrication and operation of apparatus to study consolidation and other phenomena in sedimented clays is described. Results of experiments on two types of clay are presented. Finally, the consolidation characteristics of one of these clays are shown to be in close agreement with a particular solution of the large strain consolidation equation.https://thesis.library.caltech.edu/id/eprint/1606Stress-Strain Characteristics of Cohesionless Granular Materials Subjected to Statically Applied Homogeneous Loads in an Open System
https://resolver.caltech.edu/CaltechETD:etd-03242003-102726
Authors: {'items': [{'id': 'Bell-James-Melvin', 'name': {'family': 'Bell', 'given': 'James Melvin'}, 'show_email': 'NO'}]}
Year: 1965
DOI: 10.7907/066B-HV20
A general stress-strain relationship in incremental and invariant form is derived for sand on the basis of experimental evidence. The resulting expression does not include the yield condition but makes allowance for the direction of loading and the state of stress. Two new modified and dimensionless invariant functions are introduced and a detailed description and classification of stress paths presented. A new first yield criterion for sand stressed to yield along one stress path is developed from experimental evidence. The friction angle in triaxial compression was minimum and 14[degrees] less than that in triaxial extension. The Mohr-Coulomb yield criterion extended to three dimensions is rejected.
Emphasis is placed on the importance of obtaining homogeneous stress in physical experiments. A new spherical compression apparatus was developed to study the behavior of sand under spherical compression. Disadvantages of former apparatuses were largely overcome by elimination of frictional loading, and a homogeneous state of stress was obtained. A new stress controlled three-dimensional compression apparatus capable of applying principal stresses to a rectangular, plate sample was developed to study the behavior of sand under a general stress state, particularly under deviatoric stress. This apparatus provided for the independent measurement of volumetric strain and allowed for the development of considerable deformation in obtaining yield.https://thesis.library.caltech.edu/id/eprint/1084Static Stress-Deformation Characteristics of Sand
https://resolver.caltech.edu/CaltechETD:etd-09252002-133202
Authors: {'items': [{'id': 'Ko-Hon-Yim', 'name': {'family': 'Ko', 'given': 'Hon-Yim'}, 'show_email': 'NO'}]}
Year: 1966
DOI: 10.7907/WWZB-SM07
NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in.pdf document.
A soil test box, capable of applying any combination of principal stresses to a cubical soil sample, was developed for the experimental investigation of the behavior of granular soils under static loading. A stress control device was also developed, enabling a continuous and proportionate change to be made in the stresses along a stress path and considerably simplifying the calculation of the stress state in the sample. The apparatus was used to investigate (a) the hydrostatic compression of an Ottawa sand, and (b) the behavior of the same soil under various deviatoric stress paths in both loading and unloading conditions.
A theoretical "holey" model was postulated for sand under hydrostatic stress and the results of the analysis of this model were found to correlate closely with the experimental data.
The qualitative behavior of sand under shear stresses was examined from a particulate point of view. Specially designed tests were performed on the Ottawa sand with loading and unloading along stress paths which involved different combinations of hydrostatic and deviatoric stresses, with the purpose of examining the proportions of recoverable and irrecoverable deformations. A failure envelope was obtained for a medium dense and a medium loose sand by monotonically increasing [...] while keeping [...] constant under various conditions of stress distribution, and it was found that the value of equivalent Coulomb [...] increased from 42? in triaxial compression to 48? in triaxial extension for the medium dense sand and from 36? in triaxial compression to 44? in triaxial extension for the medium loose sand.https://thesis.library.caltech.edu/id/eprint/3757Applications of plasticity theory to selected problems in soil mechanics
https://resolver.caltech.edu/CaltechTHESIS:04042016-082008001
Authors: {'items': [{'id': 'Baligh-Mohsen-Mohamed', 'name': {'family': 'Baligh', 'given': 'Mohsen Mohamed'}}]}
Year: 1972
DOI: 10.7907/EAM0-H226
<p>Two topics in plane strain perfect plasticity are studied using the method of characteristics. The first is the steady-state indentation of an infinite medium by either a rigid wedge having a triangular cross section or a smooth plate inclined to the direction of motion. Solutions are exact and results include deformation patterns and forces of resistance; the latter are also applicable for the case of incipient failure. Experiments on sharp wedges in clay, where forces and deformations are recorded, showed a good agreement with the mechanism of cutting assumed by the theory; on the other hand the indentation process for blunt wedges transforms into that of compression with a rigid part of clay moving with the wedge. Finite element solutions, for a bilinear material model, were obtained to establish a correspondence between the response of the plane strain wedge and its axi-symmetric counterpart, the cone. Results of the study afford a better understanding of the process of indentation of soils by penetrometers and piles as well as the mechanism of failure of deep foundations (piles and anchor
plates).</p>
<p>The second topic concerns the plane strain steady-state free rolling of a rigid roller on clays. The problem is solved approximately for small loads by getting the exact solution of two problems that encompass the one of interest; the first is a steady-state with a geometry that approximates the one of the roller and the second is an instantaneous solution of the rolling process but is not a steady-state. Deformations and rolling resistance are derived. When compared with existing empirical formulae the latter was found to agree closely.</p>
https://thesis.library.caltech.edu/id/eprint/9643I. Constitutive Relations for a Granular Material. II. The Distribution of Stresses and Development of Failure at the Toe of a Slope and Around the Tip of a Crack
https://resolver.caltech.edu/CaltechTHESIS:12132017-144159939
Authors: {'items': [{'id': 'Lu-Tyzz-Dwo', 'name': {'family': 'Lu', 'given': 'Tyzz-Dwo'}}]}
Year: 1973
DOI: 10.7907/P0H6-TA75
<p>In the first part of this thesis, a three-dimensional rheological
model was constructed to represent the deformation behavior of a
granular material. The constitutive relations for a granular material
were subsequently derived. The rheological model was conceived
from the observed behavior of granular material from laboratory
experiments and from theoretical considerations. The constitutive
relations were expressed in incremental forms to account for the
stress history and loading path dependency of a granular material's
behavior, such as non-linearity, initial or induced anisotropy, history
and path dependency, and shear dilatance.</p>
<p>The qualitative and quantitative behavior of a granular material
such as sand under shear stress from experimental results and from
the proposed constitutive relations was examined and compared. It
was found that the experimental data and the proposed constitutive
relations were in close agreement.</p>
<p>Due to the number of parameters involved, and the non-symmetrical
resulting stiffness matrix in a general stress-strain formulation,
it is difficult to apply the proposed constitutive in a finite element
computer formulation at the present state of the art. Consequently
the application of finite element methods to non-linear problems was
examined in more detail as a preliminary step. The effect, or the
results of the material properties, the finite element mesh size and
the computational procedure was examined in detail in Part II of this thesis.</p>
https://thesis.library.caltech.edu/id/eprint/10608A Study of High-Frequency Strong Ground Motion from the San Fernando Earthquake
https://resolver.caltech.edu/CaltechTHESIS:01312018-100922603
Authors: {'items': [{'id': 'Berrill-John-Beauchamp', 'name': {'family': 'Berrill', 'given': 'John Beauchamp'}}]}
Year: 1975
DOI: 10.7907/B04E-Q851
<p>This thesis describes an investigation of the attentuation of
strong earthquake ground motion in the 0.4 to 16 Hz frequency band
during the M = 6.4, February 9, 1971, San Fernando, California
earthquake. It is found that Fourier amplitudes of ground acceleration decay
according to a simple expression incorporating a geometric spreading
term, and a material attenuation term with constant specific
attentuation Q. The scatter in the amplitude data about an expected
level given by the simple decay expression is nearly constant with
respect to both frequency and focal distance. Fourier amplitudes of
acceleration corrected to a reference hypocentral distance agree
well with those determined by a two-parameter source model of the
San Fernando earthquake. Focusing of energy to the south by the
southward propagating rupture is observed at frequencies below 8 Hz.
The propagation of rupture was incoherent with respect to higher-
frequency components.</p>
<p>The relationship between intensity of ground motion and site
geology is examined. It is found that while, in general, sedimentary
sites were accelerated more strongly than basement rock sites, no
clear difference could be found between sedimentary sites classified
as "soft" by Trifunac and Brady (1975) (generally recent alluvium) and
those classified as having "medium" soil stiffness, generally consisting
of older alluvium and sedimentary rock. The difference between amplitudes
recorded on basement rock and sediments is more complex. In
general, smoothed amplitude spectra from accelerograms recorded
on basement rock are lower than smoothed amplitudes at corresponding
sedimentary sites. However, basement site spectra show marked isolated
peaks, as high as those from sedimentary sites at similar distances.
This is attributed to the focusing effects of the irregular topography
normally accompanying basement rock outcrops. In the
frequency band considered, it is concluded that for the purposes
of a seismic design of structures no discrimination should be made
between the intensity of ground motion expected on basement rock,
sedimentary rock, and coarse-grained alluvium typical of Southern California.</p>
<p>The agreement between the recorded strong motion amplitudes
and those predicted by a simple two-parameter source model suggests
that the model can be used for the assessment of strong ground motion
to be used in design procedures. A procedure for estimating design
earthquakes using the source model and the amplitude decay expression
is presented.</p>https://thesis.library.caltech.edu/id/eprint/10660Edge function method applied to thin plates resting on Winkler foundation
https://resolver.caltech.edu/CaltechTHESIS:05072014-145934552
Authors: {'items': [{'id': 'Lam-I-P-C', 'name': {'family': 'Lam', 'given': 'Ignatius Po-cheung'}, 'show_email': 'NO'}]}
Year: 1976
DOI: 10.7907/RCTX-T347
The Edge Function method formerly developed by Quinlan<sup>(25)</sup> is
applied to solve the problem of thin elastic plates resting on spring
supported foundations subjected to lateral loads the method can be
applied to plates of any convex polygonal shapes, however, since most
plates are rectangular in shape, this specific class is investigated in
this thesis. The method discussed can also be applied easily to other
kinds of foundation models (e.g. springs connected to each other by a
membrane) as long as the resulting differential equation is linear.
In chapter VII, solution of a specific problem is compared with a known
solution from literature. In chapter VIII, further comparisons are given.
The problems of concentrated load on an edge and later on a corner of a
plate as long as they are far away from other boundaries are also given
in the chapter and generalized to other loading intensities and/or plates
springs constants for Poisson's ratio equal to 0.2https://thesis.library.caltech.edu/id/eprint/8223Wave propagation in saturated porous media
https://resolver.caltech.edu/CaltechTHESIS:03052010-152258919
Authors: {'items': [{'id': 'van-der-Kogel-H', 'name': {'family': 'van der Kogel', 'given': 'Hans'}, 'show_email': 'NO'}]}
Year: 1977
DOI: 10.7907/5REP-HK49
Wave propagation in saturated porous media is investigated in the framework of two models, a theoretical and an experimental one.
The theoretical model has two phases, a fluid phase and a solid phase, both modeled as a continuum. The solid phase consists of incompressible grains forming a compressible skeleton. The fluid phase represents a compressible fluid located between the grains. Interactive forces, due to relative motion between the skeleton and the fluid are taken into account. Non-linear balance laws and equations of state are formulated for plane waves. Linearization of the non-linear balance laws yields a set of equations which in limiting cases reduce to well-known results (e.g. consolidation equation, condition for fluidization). The harmonic solution of the linearized field equations contains two modes: one in which the phases move almost together (which is slightly damped) and one in which the phases move in opposite directions (which is highly damped). Solutions are presented in system form.
Applying a step loading in the variables at the boundary generates, in general, two propagating discontinuities in the variables and these discontinuities decay as they propagate. If we assume that the parameters take "practical" values of wet sand then the jump in pore-pressure is always large with respect to the jump in effective pressure along the faster discontinuity propagating into a medium at rest, while velocity differences between the phases are generated if the densities of the phases are different. Non-linear effects due to a non-linear constitutive equation for the fluid oppose the decay of gradients in the variables along the faster propagating discontinuity. The influence of non-linear convective terms can be neglected if the phase velocities are small with respect to the velocities of the discontinuities.
The solution to the problem of reflection and refraction of a discontinuity propagating in a fluid and impinging on a two-phase medium is presented. The theory is extended in multi-dimensions, in order to allow shear waves to propagate. The existence of non- propagating discontinuities in dilatant shear is demonstrated.
The experimental model consists of a disc configuration, dry and saturated. The interparticle stresses due to impact are visualized by a photo-elastic technique and recorded by a high-speed camera. Changing stress patterns in the discs behind the wavefront are observed. In the dry case a wavefront emerges, behind which the particles are relatively well stressed, while no such definite stress front can be identified in the saturated case. Phase velocity differences occur and separation of particles was observed to take place due to indirect loading of the discs via the fluid.https://thesis.library.caltech.edu/id/eprint/5580Centrifugal model testing of foundation piles in axial loading
https://resolver.caltech.edu/CaltechETD:etd-09142006-140129
Authors: {'items': [{'id': 'Christenson-J-E', 'name': {'family': 'Christenson', 'given': 'John Eric'}, 'show_email': 'NO'}]}
Year: 1982
DOI: 10.7907/FDZ3-F478
The recent growth in oil production from offshore flelds has stimulated demand for improvements in the analysis and prediction of foundation pile behavior. The traditional, empirical means of determining pile behavior under load, on-site load testing, is prohibitively expensive offshore. Moreover, extrapolation from experience with pile performance on land is liable to significant error, both because of the relatively diverse load-bearing requirements placed on piles by ocean structures, and the great size of these piles. Several classes of modeling and analytical techniques which have received extensive attention in the geotechnical literature of the past decade are described and evaluated.
Pile load tests in the fleld have been simulated using centrifugal modeling. Procedures and results are reported of six load tests on cylindrical steel piles embedded to depths ranging from 54 to 183 feet in dry and saturated sand and saturated silt soils. The strain gauge-instrumented piles were subjected to extensive sequences of axial loading, including loading to bearing capacity failure and cyclic loading. Graphs showing the distribution of axial force in the pile were produced for all tests, and soil-pile interaction was interpreted by means of "t-z diagrams", i.e., graphs of soil-pile shear stress versus pile axial displacement at particular depths along the pile. The accuracy of the model test results is assessed by comparing them with the published results of a matching full-scale test.
The work demonstrates the feasibility of using centrifugal modeling to investigate the behavior of large piles under a broad range of axial loadings.https://thesis.library.caltech.edu/id/eprint/3539Dynamic Centrifuge Testing of Cantilever Retaining Walls
https://resolver.caltech.edu/CaltechETD:etd-12132006-104119
Authors: {'items': [{'id': 'Ortiz-Louis-Alexander', 'name': {'family': 'Ortiz', 'given': 'Louis Alexander'}, 'show_email': 'NO'}]}
Year: 1982
DOI: 10.7907/vep9-1127
<p>An investigation was made into the behavior of flexible cantilever walls retaining a cohesionless soil backfill and subjected to earthquake-type dynamic excitations using the centrifuge modelling technique. The study was motivated by the abundant observations of earth retaining structure damage and failures documented in earthquake damage reports.</p>
<p>The "prototype" typical walls were designed using the traditional Mononobe-Okabe dynamic lateral earth pressure theory, were properly scaled for use in the centrifuge at 50 g's and were subjected to lateral earthquake-like motions which were considered to be of realistic levels. The walls were amply instrumented with pressure and displacement transducers, accelerometers, and strain gages. Moment, pressure, shear, and displacement distributions (static, dynamic, and residual) were obtained.</p>
<p>From the test data, some empirical curves for relating the upper bound responses of the retaining walls to the strong motion characteristics of the applied earthquakes were obtained.</p>https://thesis.library.caltech.edu/id/eprint/4982Application of Plasticity Theory to Soil Behavior: A New Sand Model
https://resolver.caltech.edu/CaltechETD:etd-12212005-143343
Authors: {'items': [{'id': 'Bardet-Jean-Pierre', 'name': {'family': 'Bardet', 'given': 'Jean-Pierre'}, 'show_email': 'NO'}]}
Year: 1984
DOI: 10.7907/Z23J-9E80
<p>The representation of rheological soil behavior by constitutive equations is a new branch of soil mechanics which has been expanding for 30 years. Based on continuum mechanics, numerical methods (finite elements) and experimental techniques, this new discipline allows practicing engineers to solve complex geotechnical problems. Although all soils are constituted of discrete mineral particles, forces and displacements within them are represented by continuous stresses and strains. Most stress-strain relationships, which describe the soil behavior, are derived from plasticity theory. Originated for metals, the conventional plasticity is presented and illustrated simultaneously with a metal and a soil model. Each plasticity concept may be criticized when applied to soil. A recent theory, called "bounding surface plasticity," generalizes the conventional plasticity and describes more accurately the cyclic responses of metals and clays. This new theory is first presented and linked with the conventional plasticity, then applied to a new material, sand. Step by step a new sand model is constructed, mainly from data analysis with an interactive computer code. In its present development, only monotonic loadings are investigated. In order to verify the model ability to describe sand responses, isotropic, drained and undrained tests on the dense Sacramento River sand are simulated numerically and compared with real test results and predictions with another model. Finally the new constitutive equation, which was formulated in the p-q space for axisymmetric loadings, is generalized in the six-dimensional stress state with the assumption of isotropy and a particular Lode's angle contribution. This new model is ready to be used in finite element codes to represent a sand behavior.</p>https://thesis.library.caltech.edu/id/eprint/5102Experimental Studies of Dynamic Response of Foundations
https://resolver.caltech.edu/CaltechETD:etd-08152006-091708
Authors: {'items': [{'email': 'ben@hushmand-associates.com', 'id': 'Hushmand-Behnam', 'name': {'family': 'Hushmand', 'given': 'Behnam'}, 'show_email': 'YES'}]}
Year: 1984
DOI: 10.7907/6TJK-6088
<p>An investigation was made into the behavior of rigid foundations and structures resting on the surface or embedded in a cohesionless soil and subjected to transient active or passive excitations and forced vibrations using the centrifuge modeling technique. The investigation was aimed at studying both low and high amplitude vibrations of foundations under machine type loadings, earthquake or wave induced vibrations, and other sources of dynamic loads. Rigid "prototype" foundations of mass and size comparable to foundations of a low rise building were simulated in the centrifuge at a centrifugal acceleration of 50g. Rigid model structures (aluminum towers) attached to foundations of different shapes, sizes, masses, and moments of inertia were tested. The effect of soil depth, boundary conditions, and depth of foundation embedment were investigated. Mainly rocking and horizontal modes of vibration were studied. The impulse rocking-horizontal excitation of the models was provided by actively perturbing the model structures using explosive energy or by passively exciting them by shaking the whole soil bucket using a hydraulic shaking system. The forced vibration was produced by a miniature air-driven counterrotating eccentric mass shaker mounted on the model structures. During the tests detailed measurements of the static and dynamic contact pressure distributions, displacement components of the model, and acceleration amplitudes at different elevations of the model structure were obtained. The acceleration ratios were used to determine the modes of vibration of the foundation systems. Natural frequencies and damping coefficients of the modes were calculated by fitting the amplitude-frequency response of a single degree of freedom mass-spring-dashpot oscillator to the experimental response curves derived from the test data. Experimental results provided information regarding the influence of different geometrical, inertial, and loading conditions on the vibrational characteristics of the soil-structure system. In particular the effect of foundation embedment was to increase the model resonant frequencies and to cause an appreciable change in contact pressure distribution underneath the footing. However, the resonant frequencies predicted by the lumped parameter analysis for a simple two-degree-of-freedom (rocking and translation) model were about 20 to 55 per cent higher than those measured experimentally. These results were consistent with the comparisons made in similar theoretical and experimental studies such as those performed by Morris in the Cambridge centrifuge and those performed on full-scale footings by Stokoe and Richart. Damping ratios of the rocking-sliding vibration did not change considerably when footing size or depth of embedment changed. The existence of rigid boundaries around the soil mass in the bucket, and an inefficient contact between soil and the foundation side walls and lower surface could account for these observations. Uplift and nonlinear large amplitude vibrations were consistently observed during the steady-state vibration tests. Uplift led to a softer vibrating system which behaved non-linearly. As a result the frequency of vibration decreased with the amount of lift-off. In transient vibration uplift reduced the intensity of higher frequency vibration. Soil around the foundation edge yielded and plastic deformations and subsequent softening of the contact soil increased the material damping while it decreased the resonant frequency of the system. It was concluded that elastic half-space theory does not satisfy the needs for analysis of foundation behavior under high amplitude vibrations and more sophisticated methods of analysis are required.</p>https://thesis.library.caltech.edu/id/eprint/3131Two-Phase Soil Study: A. Finite Strain Consolidation. B. Centrifuge Scaling Considerations
https://resolver.caltech.edu/CaltechETD:etd-03082008-084249
Authors: {'items': [{'id': 'Tan-Thiam-Soon', 'name': {'family': 'Tan', 'given': 'Thiam-Soon'}, 'show_email': 'NO'}]}
Year: 1986
DOI: 10.7907/agt3-mf84
<p>Two different aspects of the behavior of soil as a two-phase medium are studied, namely, the consolidation of soil and scaling relations for soils in centrifuge testing.</p>
<p>PART A</p>
<p>First a consistent approach is presented that unifies all current theories of consolidation of soil. For one-dimensional finite strain consolidation, a Lagrangian finite element scheme is then given and tested against three different experiments and found to give consistent results. For a quick solution to a particular problem, the regular perturbation method applied to the formulation in which the dependent variable is the natural strain is shown to give the most consistent results. For the Eulerian formulation, the material derivative contains a convective term. This convective effect is then analytically studied and found not to be negligible for a final natural strain greater than 10%. A method is then introduced that can account for both the moving boundary and the convective effect. This method is tested in a finite difference scheme and found to give identical results with the Lagrangian finite element scheme for the one-dimensional case. Finally the method is used for the axisymmetric problem of consolidation by vertical drain. The solution to this case suggests that arching and subsequent load redistribution should be considered.</p>
<p>PART B</p>
<p>Conceptually, when a centrifuge is used to test models, the centrifuge is assumed to produce an equivalent ng gravitational field (as on another planet) and the behavior of the model in the ng field is then assumed to be similar to that of the prototype. For most static problems, the centrifuge does model the prototype well but for some dynamic problems, these assumptions can break down. To investigate this, the similarity requirements are examined for the case of a single particle moving in a fluid. It is found that for the post-liquefaction process and for seepage flow, unless the Reynolds number is much less than one in both model and prototype, the centrifuge is not a good simulation of the prototype situation. But, perhaps contrary to expectations, the breakdown is due to the fact that the behavior in the ng planet is not similar to the prototype ig planet, whereas the centrifuge does simulate the ng planet well. Further, it is shown that the concept of "modeling of models" can lead to misleading results. Lastly, for cratering experiments, it is concluded that the centrifuge will only model the crater shape just after an explosion and not the final crater shape.</p>https://thesis.library.caltech.edu/id/eprint/902Failure of Slopes
https://resolver.caltech.edu/CaltechETD:etd-03012008-132659
Authors: {'items': [{'id': 'Burridge-Paul-Brian', 'name': {'family': 'Burridge', 'given': 'Paul Brian'}, 'show_email': 'NO'}]}
Year: 1987
DOI: 10.7907/2C4G-6R71
<p>The dynamic mechanism of slope failure is studied both experimentally and analytically to establish the spatial and temporal process of failure initiation and propagation during collapse of a natural or man-made slope.</p>
<p>Model slopes, constructed of a brittle cemented sand material, are tested to collapse in a geotechnical centrifuge and the dynamics of failure recorded by motion picture film and mechanical detectors within the slope specimen. Shear failure is observed to initiate at the toe and propagate rapidly to the crest in the presence of crest tension cracking.</p>
<p>A finite difference approach is taken to numerically solve the plane strain slope stability problem under gravity, based on unstable material behavior. Using a Lagrangian differencing scheme in space and explicit integration in time with dynamic relaxation, the numerical method finds the equilibrium state of the slope as the large-time limit of a dynamic problem with artificial parameters. The solution predicts localized shear failure zones which initiate at the slope toe and propagate to the slope crest in the manner and geometry observed in the centrifuge tests. In so doing, the finite difference algorithm also demonstrates an apparent ability to predict shear failure mechanisms in solid continua in general.</p>
https://thesis.library.caltech.edu/id/eprint/825Numerical simulations of two-dimensional saturated granular media
https://resolver.caltech.edu/CaltechETD:etd-06232005-154613
Authors: {'items': [{'id': 'Tan-P', 'name': {'family': 'Tan', 'given': 'Phalkun'}, 'show_email': 'NO'}]}
Year: 1990
DOI: 10.7907/e02e-mz83
The liquefaction phenomenon in soil has been studied in great detail during the past 20 years. The need to understand this phenomenon has been emphasized by the extent of the damages resulting from soil liquefaction during earthquakes. Although an overall explanation exists for this phenomenon through the concept of effective stress, the basic mechanism of loss of strength of the soil skeleton has not been thoroughly examined and remains unclear.
The present study proposes a numerical model for simulations of the behavior of saturated granular media. The model was developed with two main objectives:
1. To represent the mechanical response of an assemblage of discrete particles having the shape of discs.
2. To model and represent the interaction of interstitial pore fluid present with the idealized granular media.
The representation of the solid skeleton is based on Cundall and Strack's distinct element model, in which discrete particles are modelled as discs in two dimensions, each obeying Newton's laws. Interparticle contacts consisting of springs and frictional element dashpots are included. Assuming a Newtonian incompressible fluid with constant viscosity and density, and quasi-steady flow, the fluid phase is described by Stokes' equations. The solution to Stokes' equations is obtained through the boundary integral element formulation. Several validation test cases are presented along with four simple shear tests on dry and saturated granular assemblages. For these last four tests, the numerical results indicate that the model is able to represent qualitatively the behavior of real soil, while at the same time clarifying the processes occurring at the microscale that influence soil response.https://thesis.library.caltech.edu/id/eprint/2704Soil Stress Field Around Driven Piles
https://resolver.caltech.edu/CaltechETD:etd-02212007-130942
Authors: {'items': [{'id': 'Allard-Marie-Agnès', 'name': {'family': 'Allard', 'given': 'Marie-Agnès'}, 'show_email': 'NO'}]}
Year: 1990
DOI: 10.7907/GGE1-GC92
<p>The description, equipment, and results of a series of pile-driving experiments conducted in a centrifuge using a model pile driven in dry sand are presented.</p>
<p>The work was conceived on the basis of the modelling of a soil-structure system under an artificially generated gravitational field, and motivated by the need for experimental data for a better understanding of the complex phenomena involved in the pile-soil interaction during driving. The behavior of the pile itself has been the focus of more attention in the past, but few full-scale or model experimental results have been obtained to the present concerning the soil stress field during pile driving. These are necessary for comparison with analytical and theoretical work. The work presented here appears to be the first attempt to obtain dynamic response of the soil during driving. The objective was to obtain a good understanding of the physical phenomena occurring in the soil and pile during driving.</p>
<p>In order to achieve these objectives both dynamic (transient) and static responses of the soil and pile were measured by means of transducers: accelerometers and strain gages for the pile, pressure transducers for the soil. In particular, the relations between static and dynamic data were explored, which resulted in the modelling of the soil-transducer interaction with a non-linear, history-dependent, model.</p>
<p>Results were obtained regarding pile dynamics, soil dynamics, and soil stress field (radial and vertical distribution, stress contours). Both linear and soil-cell model assumptions were used, which enabled a comparison between the two, leading to an estimate that each constitutes a bound of the real stress field, with the linear giving the higher, and the non-linear the lower bound, and the true stress being closer to the lower bound.</p>
<p>The soil response during driving is obtained, filling the gap in the study of the pile-soil system, where only the pile response was known. Recommendations for further work and better experimental procedures are given.</p>https://thesis.library.caltech.edu/id/eprint/696Physical scale modeling of geotechnical structures at one-G
https://resolver.caltech.edu/CaltechETD:etd-01102008-140908
Authors: {'items': [{'id': 'Gibson-A-D', 'name': {'family': 'Gibson', 'given': 'Andrew Douglas'}, 'show_email': 'NO'}]}
Year: 1997
DOI: 10.7907/97V4-YE48
The use of physical scale modeling techniques for geotechnical applications is investigated. The scaling laws to relate a prototype structure to a model are developed for the centrifuge modeling technique and for the laboratory (or one-g) environment. A theory based on critical or steady state concepts for the constitutive scaling of the behavior of the soil in a one-g model is investigated. A series of one-g models of varying configurations was constructed in a laminar box and subjected to earthquake like motions on a shake table. A total of 73 tests was performed. Most tests were constructed of saturated Nevada sand placed in a loose and dense state in adjacent halves of a laminar box, and the results of these tests were compared with a similar centrifuge test (Model 3) which was performed as part of the VELACS study. Some of the one-g models were constructed with an alternate model sand and an alternate pore fluid to investigate these modeling variations. One-g models were also constructed with the sand at a uniform density throughout the laminar box.
The research indicates that there is a significant conflict between the time scaling for dynamic processes and dissipation processes in both the centrifuge and one-g techniques, which means that excess pore pressures generated in the model saturated sand by a simulated earthquake will be less than what would occur in the same sand in the real prototype. This effect is generally more severe in the centrifuge. This implies that model tests performed to investigate liquefaction, flow failure problems, and/or deformation problems in saturated sands may significantly underestimate the potential behavior of the prototype. In addition to the above, the research provides insight into the behavior of adjacent loose and dense sands and indicates the potential for high excess pore pressures to develop in the dense sand. Current practice ignores the potential for liquefaction in dense sands or the development of cyclic mobility in the assessment of the seismic performance of geotechnical structures.
https://thesis.library.caltech.edu/id/eprint/114