Enhanced Integration of Shear Wave Velocity Profiling in Direct-Push Site Characterization Systems Alexander V. McGillivray 370 Pages Directed by Dr. Paul W. Mayne Shear wave velocity (VS) is a fundamental property of soils directly related to the shear stiffness at small-strains. Therefore, VS should be a routine measurement made during everyday site characterization. There are several lab and field methods for measuring VS, but the seismic piezocone penetration test (SCPTu) and the seismic dilatometer test (SDMT) are the most efficient means for profiling the small-strain stiffness in addition to evaluating large-strain strength, as well as providing evaluations of the geostratigraphy, stress state, and permeability, all within a single sounding. Although the CPT and DMT have been in use for over three decades in the USA, they are only recently becoming commonplace on small-, medium-, and large-size projects as more organizations begin to realize their benefits. Regrettably, the SCPTu and the SDMT are lagging slightly behind their non-seismic counterparts in popularity, in part because the geophysics component of the tests has not been updated during the 25 years since the tests were envisioned. The VS measurement component is inefficient and not cost effective for routine use. The purpose of this research is to remove the barriers to seismic testing during direct-push site characterization with SCPTu and SDMT. A continuous-push seismic system has been developed to improve the integration of VS measurements with SCPTu and SDMT, allowing VS to be measured during penetration without stopping the progress of the probe. A new type of portable automated seismic source, given the name RotoSeis, was created to generate repeated hammer strikes at regularly spaced time intervals. A true-interval biaxial seismic probe and an automated data acquisition system were also developed to capture the shear waves. By not limiting VS measurement to pauses in penetration during rod breaks, it is possible to make overlapping VS interval measurements. This new method, termed frequent-interval, increases the depth resolution of the VS profile to be more compatible with the depth intervals of the near-continuous non-seismic measurements of the SCPTu and the SDMT.

Although there exist some consensus regarding seismic soil liquefaction assessment of free field soil sites, estimating the liquefaction triggering potential beneath building foundations still stays as a controversial and difficult issue. Assessing liquefaction triggering potential under building foundations requires the estimation of cyclic and static stress state of the soil medium. For the purpose of assessing the effects of the presence of a structure three-dimensional, finite difference-based total stress analyses were performed for generic soil, structure and earthquake combinations. A simplified procedure was proposed which would produce unbiased estimates of the representative and maximum soil-structure-earthquake-induced iv cyclic stress ratio (CSRSSEI) values, eliminating the need to perform 3-D dynamic response assessment of soil and structure systems for conventional projects. Consistent with the available literature, the descriptive (input) parameters of the proposed model were selected as soil-to-structure stiffness ratio, spectral acceleration ratio (SA/PGA) and aspect ratio of the building. The model coefficients were estimated through maximum likelihood methodology which was used to produce an unbiased match with the predictions of 3-D analyses and proposed simplified procedure. Although a satisfactory fit was achieved among the CSR estimations by numerical seismic response analysis results and the proposed simplified procedure, validation of the proposed simplified procedure further with available laboratory shaking table and centrifuge tests and well-documented field case histories was preferred. The proposed simplified procedure was shown to capture almost all of the behavioral trends and most of the amplitudes. As the concluding remark, contrary to general conclusions of Rollins and Seed (1990), and partially consistent with the observations of Finn and Yodengrakumar (1987), Liu and Dobry (1997) and Mylonakis and Gazetas, (2000), it is proven that soil-structure interaction does not always beneficially affect the liquefaction triggering potential of foundation soils and the proposed simplified model conveniently captures when it is critical.

A macroelement is developed for soil-structure interaction analyses of piles in liquefiable soils, which captures efficiently the fundamental mechanisms of saturated granular soil behavior. The mechanical model comprises a nonlinear Winkler-type model that accounts for soil resistance acting along the circumference of the pile, and a coupled viscous damper that simulates changes in radiation damping with increasing material non-linearity. Three-dimensional (3D) finite element (FE) simulations are conducted for a pile in radially homogeneous soil to identify the critical parameters governing the response. The identified parameters, i.e., hydraulic conductivity, loading rate of dynamic loading, dilation angle and liquefaction potential are then expressed in dimensionless form. Next, the macroelement parameters are calibrated as a function of the soil properties and the effective stress. A semi-empirical approach that accounts for the effects of soil-structure interaction on pore pressure generation in the vicinity of pile is used to detect the onset of liquefaction. The predictions are compared with field data obtained using blast induced liquefaction and centrifuge tests and found to be in good agreement. Finally, the macroelement formulation is extended to account for coupling in both lateral directions. FEM simulations indicate that response assuming no coupling between the two horizontal directions for biaxial loading tends to overestimate the soil resistance and fails to capture features like 'apparent negative stiffness', 'strain hardening' and 'rounded corners'.

Liquefiable soils are common at ports due to the use of hydraulic fills for construction of waterfront facilities. Liquefaction-induced ground failure can result in permanent ground deformations that can cause loss of foundation support and structural damage. This can lead to substantial repair and/or replacement costs and business interruption losses that can have an adverse effect on the port and the surrounding community. Although numerous soil improvement methods exist for remediating a liquefaction-prone site, many of these methods are poorly suited for developed sites because they could damage existing infrastructure and disrupt port operations. An alternative is to use a passive remediation technique. Treating liquefiable soils with colloidal silica gel via permeation grouting has been shown to resist cyclic deformations and is a candidate to be used as a soil stabilizer in passive mitigation. The small-strain dynamic properties are essential to determine the response to seismic loading. The small-to-intermediate strain shear modulus and damping ratio of loose sand treated with colloidal silica gel was investigated and the influence of colloidal silica concentration was determined. The effect of introducing colloidal silica gel into the pore space in the initial phase of treatment results in a 10% to 12% increase in the small-strain shear modulus, depending on colloidal silica concentration. The modulus reduction curve indicates that treatment does not affect the linear threshold shear strain, however the treated samples reduce at a greater rate than the untreated samples in the intermediate-strain range above 0.01% cyclic shear strain. It was observed that the treated sand has slightly higher damping ratio in the small-strain range; however, at cyclic shear strains around 0.003% the trend reverses and the untreated sand begins to have higher damping ratio. Due to the nature of the colloidal silica gelation process, chemical bonds continue to form with time, thus the effect of aging on the dynamic properties is important. A parametric study was performed to investigate the influence of gel time on the increase in small-strain shear modulus. The effect of aging increases the small-strain shear modulus after gelling by 200 to 300% for the 40-minute-gel time samples with a distance from gelation (time after gelation normalized by gel time) of 1000 to 2000; 700% for the 2-hour-gel time sample with a distance from gelation of 1000; and 200 to 400% for the 20-hour-gel time samples with a distance from gelation of 40 to 100. The treatment of all potentially liquefiable soil at port facilities with colloidal silica would be cost prohibitive. Identifying treatment zones that would reduce the lateral pressure and resulting pile bending moments and displacements caused by liquefaction-induced lateral spreading to prevent foundation damage is an economic alternative. Colloidal silica gel treatment zones of varying size and location were evaluated by subjecting a 3-by-3 pile group in gently sloping liquefiable ground to 1-g shaking table tests. The results are compared to an untreated sample. The use of a colloidal silica treatment zone upslope of the pile group results in reduced maximum bending moments and pile displacements in the downslope row of piles when compared to an untreated sample; the presence of the treatment zone had minimal effect on the other rows of piles within the group.

No description available.

A thesis submitted to the Faculty of Engineering, Cape Peninsula University of Technology, Cape Town, in partial fulfilment of the requirements for the M-Tech Degree in Civil Engineering” Cape Town 16 MAY 2011 / Dwellings in impoverished and upper class urban areas of the Western Cape have undergone serious structural failure due to problematic underlying sand deposits, generally known as Cape Flats windblown found in areas such as Delft, Blue Downs and the Atlantic Beach Golf Estate. The problem is compounded further when moisture penetrates below the footings and reaches saturation in the winter months. When poorly graded sand with a high fines content is coupled with vibration (through earth tremors), liquefaction may occur and without proper precautions, this can lead to inadequate foundation design, more than expected settlement and eventual structural failure. Some sand deposits are highly contaminated with organic debris, leading to compressible and collapsible conditions. Little knowledge is locally available of liquefiable conditions in windblown dune sand and what long-term settlement can be expected. The Western Cape is not known as an area exposed to serious seismic activity, but an updated (and more locally applicable set of data) is needed to eliminate possible erroneous foundation design. Samples have been extracted from typical sandy sites in the Western Cape where windblown dune sand is evident. Laboratory tests have been carried out on representative samples for closer examination and have been placed inside a purpose built calibration chamber that facilitates easy densification and probe testing. A DMT (flat blade dilatometer) was used to hydraulically penetrate the chamber sand sample to varying depths (up to 800 mm). The device can measure (with reduction formula) horizontal stress, angle of friction, bearing capacity and settlement. An accelerometer was attached to the chamber wall and vibration measured with the sand in varying states of moisture. The DMT is an unexplored in-situ soil testing device in South Africa and so far the outcome indicates favourably compared to other devices such as the Dynamic Cone Penetrometer (DCP. The DMT has the ability to measure the in-situ stiffness, strength and stress history parameters of soil for better site characterisation. Settlement within the chamber is easily measured. The DMT has, for example, indicated that sand from the Philippi area are a problematic founding soil and should be treated with special care at shallow founding levels. The horizontal stress index is low and according to the available knowledge on soil stress history, these sand, coupled with low densities, can liquefy easily and result in structural damage. The West Coast dune sand, being coarser and easily consolidated, poses less of a problem under liquefiable conditions. A suitable terrain device for easy on-site manoeuvrability is required to assist the DMT in further testing.

The static cone penetrometer is an in-situ testing tool which was originally developed to derive information on soil type and soil strength. More recently, it has found application in liquefaction assessment. Typical cone penetrometers are heavy duty devices which are operated with the assistance of a drill rig. However, this capacity is not necessary in the case of field studies of liquefaction, since liquefaction usually occurs at relatively shallow depths. This thesis is directed to the goal of the development of a miniature, lightweight cone penetrometer which can be used in earthquake reconnaissance studies related to liquefaction problems. The research for this thesis involved four principal objectives: 1. Development of procedures to automatically acquire and process measurements from a miniature electrical cone; 2. Develop and perform tests in a model soil-filled bin to calibrate the cone; 3. Evaluate the utility and accuracy of the cone results as a means to assess conventional soil properties; and, 4. Conduct a preliminary evaluation of the cone results in the context of recently developed methods to predict liquefaction potential. The work in regard to the first objective involved assembling and writing software for a microcomputer based data acquisition system. Successful implementation of this system allowed data from the tests to be rapidly processed and displayed. Calibration tests with the cone were carried out in a four foot high model bin which was filled ten times with sand formed to variety of densities. The sand used is Monterey No. 0/30, a standard material with well known behavioral characteristics under static and dynamic loading. The test results showed the cone to produce consistent data, and to be able to readily distinguish the varying density configurations of the sand. Using the results in conventional methods for converting cone data into soil parameters yielded values which were consistent with those expected. Liquefaction potential predictions were less satisfying, although not unreasonable. Further research is needed in this area both to check the reliability of the prediction procedures and the ability to achieve the desired objectives. / M.S.

L'importance croissante de l'évaluation de la performance des structures soumis au chargement sismique souligne la nécessité d'estimer le risque de liquéfaction. Dans ce scénario extrême de la liquéfaction du sol, des conséquences dévastatrices sont observées, par exemple des tassements excessifs et des instabilités de pentes. Dans le cadre de cette thèse, la réponse dynamique et l'interaction d'un système ouvrage en terre-fondation sont étudiées, afin de déterminer quantitativement le mécanisme de ruine dû à la liquéfaction du sol de la fondation. Par ailleurs, les chargements sismiques peuvent induire dans les ouvrages en terre un mode de rupture générant des bandes de cisaillement. Une étude de sensibilité aux maillages a donc été engagée pour quantifier la dépendance des résultats de l'analyse dynamique. Par conséquent, l'utilisation d'une méthode de régularisation est évaluée au cours des analyses dynamiques. Le logiciel open-source Code_Aster, basé sur la méthode des Eléments Finis et développé par EDF R&D, est utilisé pour les simulations numériques, tandis que le comportement du sol est représenté par le modèle de comportement de l'ECP, développé à CentraleSupélec. En premier lieu, un modèle simplifié de propagation 1D des ondes SH dans une colonne de sol avec comportement hydromécanique couplé non linéaire a été simulé. L'effet des caractéristiques du signal sismique et de la perméabilité du sol sur la liquéfaction est évalué. Le signal sismique d'entrée est un élément important pour l'apparition de la liquéfaction, puisque la durée du choc principal peut conduire à de fortes non linéarités et à un état de liquéfaction étendu. En outre, quand une variation de perméabilité en fonction de l'état de liquéfaction est considérée, des changements significatifs sont observés pendant la phase de dissipation de la surpression interstitielle de l'eau et au comportement du matériau. En revanche, ces changements ne suivent pas une tendance unique. Puis, l'effet d'une méthode de régularisation avec cinématique enrichie, appelée premier gradient de dilatation, sur la propagation des ondes SH est étudié au travers d'une solution analytique. Des problèmes à la réponse dynamique du sol sont observés et discutés quand cette méthode de régularisation est appliquée. Ensuite, un modèle 2D d'un déblai est simulé et sa réponse dynamique est évaluée en conditions sèches, complètement drainées et hydromécanique couplées. Deux critères sont utilisés pour définir le début de la rupture de la structure. Le travail du second ordre est utilisé pour décrire l'instabilité locale à des instants spécifiques du mouvement sismique, tandis que l'estimation d'un facteur de sécurité locale est proposée prenant en compte la résistance résiduelle du sol. En ce qui concerne le mode de ruine, l'effet de la surpression interstitielle de l'eau est de grande importance, puisqu'un déblai stable en conditions sèches et complètement drainées, devient instable lors de l'analyse couplée à cause de la liquéfaction de la fondation. Enfin, un système digue-fondation est simulé et l'influence de la perméabilité du sol, la profondeur de la couche liquéfiable, ainsi que, les caractéristiques du séisme sur la ruine induite par la liquéfaction du sol est évaluée. Pour ce modèle de digue, le niveau de dommages est fortement lié à la fois à l'apparition de la liquéfaction dans la fondation et la dissipation de la surpression d'eau. Une surface d'effondrement circulaire est générée à l'intérieur de la couche du sol liquéfié et se propage vers la crête dans les deux côtés de la digue. Pourtant, lorsque la couche liquéfiée est située en profondeur, la digue n'est pas affectée par la liquéfaction de la fondation pour ce cas particulier de chargement. Ce travail de recherche se concentre sur une étude de cas de référence pour l'évaluation sismique des ouvrages en terre soumis à un séisme et fournit des méthodes et outils de calculs numériques performants accessibles aux ingénieurs. / The increasing importance of performance-based earthquake engineering analysis points out the necessity to assess quantitatively the risk of liquefaction. In this extreme scenario of soil liquefaction, devastating consequences are observed, e.g. excessive settlements, lateral spreading and slope instability. The present PhD thesis discusses the global dynamic response and interaction of an earth structure-foundation system, so as to determine quantitatively the collapse mechanism due to foundation’s soil liquefaction. As shear band generation is a potential earthquake-induced failure mode in such structures, the FE mesh dependency of results of dynamic analyses is thoroughly investigated and an existing regularization method is evaluated. The open-source FE software developed by EDF R&D, called Code_Aster is used for the numerical simulations, while soil behavior is represented by the ECP constitutive model, developed at CentraleSupélec. Starting from a simplified model of 1D SH wave propagation in a soil column with coupled hydromechanical nonlinear behavior, the effect of seismic hazard and soil’s permeability on liquefaction is assessed. Input ground motion is a key component for soil liquefaction apparition, as long duration of mainshock can lead to important nonlinearity and extended soil liquefaction. Moreover, when a variation of permeability as function of liquefaction state is considered, changes in the dissipation phase of excess pore water pressure and material behavior are observed, which do not follow a single trend. The effect of a regularization method with enhanced kinematics approach, called first gradient of dilation model, on 1D SH wave propagation is studied through an analytical solution. Deficiencies of the use of this regularization method are observed and discussed, e.g. spurious waves apparition in the soil’s seismic response. Next, a 2D embankment-type model is simulated and its dynamic response is evaluated in dry, fully drained and coupled hydromechanical conditions. Two criteria are used to define the onset of the structure’s collapse. The second order work is used to describe the local instability at specific instants of the ground motion, while the estimation of a local safety factor is proposed by calculating soil’s residual strength. Concerning the failure mode, the effect of excess pore water pressure is of great importance, as an otherwise stable structure-foundation system in dry and fully drained conditions becomes unstable during coupled analysis. Finally, a levee- foundation system is simulated and the influence of soil’s permeability, depth of the liquefiable layer, as well as, characteristics of input ground motion on the liquefaction-induced failure is evaluated. For the current levee model, its induced damage level (i.e. settlements and deformations) is strongly related to both liquefaction apparition and dissipation of excess pore water pressure on the foundation. A circular collapse surface is generated inside the liquefied region and extends towards the crest in both sides of the levee. Even so, when the liquefied layer is situated in depth, no effect on the levee response is found. This research work can be considered as a reference case study for seismic assessment of embankment-type structures subjected to earthquake and provides a high-performance computational framework accessible to engineers.

This thesis analyses the governing equation of elastic wave propagation by the finite difference method , and considered absorbing boundary condition and the material damping to simulate behavior of wave propagation. Otherwise, we combined with the mechanics of the soil pore water pressure raised by shear stress effected repeatedly and the soil property is changed by water pressure effected to simulate physical phenomenon in half-space, and probe into the soil liquefaction process during different force types. Using the developed numerical wave propagation model probe into reducing vibration by dug trench and filler trench, and analyzed data by 1/3 octave band method. This thesis discuss with reducing vibration effect by different trench disposed¡Bdifferent filler material property, complex filler, and extending the force source pile length.

A new reliability-based probabilistic model is developed for the estimation of liquefaction-induced lateral ground spreading, taking into consideration the uncertainties within the model functional form and the descriptive variables as well. The new model is also introduced as performance-based probabilistic engineering tool.