This thesis presents a unique finite element investigation of the seismic behaviour of 2 retaining wall types – a rigid retaining wall and a cantilever retaining wall. The commercial finite element program PLAXIS2D was used to develop the numerical simulation models. The research includes: (1) validating the finite element model with the results of 3 previously existing centrifuge tests taken from literature; (2) investigating the seismic response of rigid and cantilever retaining walls including studying the effects of contribution of wall displacement, wall and backfill seismic inertia and stiffness of the foundation soil; (3) developing analytical methods to concrete the findings of the numerical models. Based on the results of the seismic response of a rigid retaining wall, a unique relationship between the seismic earth pressure and wall displacement has been developed for the active and passive modes of failure. The seismic active earth pressure has been found to be not dependent on the wall displacement while the seismic passive earth pressure has been found to be highly affected by the wall displacement. The maximum seismic passive earth pressure force and relative horizontal displacement are predicted when the ground earthquake acceleration is applied with maximum amplitude and minimum frequency content. The seismic response of the wall was not affected by the ratio of the frequency content of the earthquake to the natural frequency of the wall-soil system. For the cantilever retaining wall detailed structural integrity and global analyses have been carried out. It has been observed that the seismic earth pressure, computed at the stem and along a vertical virtual plane are found to be out of phase with each other during the entire duration of the earthquake, and hence, the structural integrity and global stability should be evaluated and assessed individually. A critical case for the structural integrity is observed when the earthquake acceleration is applied towards the backfill soil and has frequency content close to the natural frequency of the retaining wall, while, for the global stability, the critical case is observed when the earthquake acceleration has maximum amplitude and is applied towards the backfill soil with minimum frequency content. The structural integrity is also found to be highly dependent on the ratio between the frequency content of earthquake acceleration to the natural frequency of the cantilever retaining wall. The relative horizontal displacement of a rigid and cantilever retaining wall is found to be highly affected by the duration of the earthquake in contrast to what has been observed for the seismic earth pressure force. The structural integrity of a rigid and cantilever retaining wall reduces when the backfill soil has a higher relative density, while the global stability increases when the backfill soil has a high relative density during an earthquake. The results obtained from the analytical methods reveal that the wall seismic inertia force has a significant effect on the structural integrity only for the top of the stem while the base of the stem does not get affected significantly. The modified Newmark sliding block method provided a more reasonable estimation of the relative horizontal displacement of a rigid retaining wall and a cantilever retaining wall compared with the classic Newmark sliding block method.

Earthquakes have been historically perceived as one of the most damaging natural hazards. Seismic soil liquefaction is often one of the major sources of damage and disruptions, and has been observed to severely affect key lifelines. Settlement and tilting of shallow foundations resting on saturated sandy/silty soils has been repeatedly observed throughout the world as a consequence of liquefaction or softening of the foundation soil. Such settlements and tilts can render structures unusable, and homes uninhabitable, causing significant economic losses. Despite the undoubted relevance of this phenomenon, field data on the liquefaction induced settlement of shallow foundations are scarce. New data from 24 buildings that suffered settlement and tilting as a consequences of soil liquefaction during the February 27th 2010 Maule earthquake in Chile, are presented in this work to supplement the existing field cases database. Due to the complexity of this phenomenon, field data are not suffcient to fully understand the mechanisms controlling the settlement of structures resting on liquefied or softened ground.In this framework, centrifuge modelling provides a valuable tool for research by reproducing field conditions in a controlled environment. A series of 10 dynamic centrifuge tests were performed as part of this work. Thanks to the University of Dundee newly installed centrifuge-mounted servohydraulic earthquake simulator, scaled version of field earthquake motions were reproduced in the models tested, enhancing the reliability of experimental results. Particular attention was given to the effect of key parameters on the observed foundation settlement. These parameters are the bearing pressure of the foundation, the thickness of the liquefied soil layer and the soil's relative density. The effect of the soil layering pattern was also investigated, with particular attention to the effect of a low permeability soil crust overlying the liquefied soil. Results suggest that the excess pore pressure generation in the foundation soil is significantly influenced by the stress distribution due to the presence of the foundation itself. In particular, lower excess pore pressure where measured in soil subjected to high static shear stresses (i.e. below the edge of a footing). The soil stratification pattern, and the relative thicknesses of the liquefied and un-liquefied portions of the soil profile, were also found to play a crucial role in determining the seismic demand at foundation level and the type of failure mechanism leading to foundation settlement. Observed differences between centrifuge (i.e. field) and element testing soil response are also discussed. Experimental results are compared to field observations, with the aim of improving the current understanding of the behaviour of structures built on shallow foundations in the eventuality of seismic induced liquefaction of their foundation soil.

Shallow embankment slopes are commonly used to support elements of transport infrastructure in seismic regions. In this thesis, the seismic performance of such slopes in non-liquefiable granular soils has been investigated and an extensive programme of centrifuge testing was conducted to quantify the improvements to seismic slope performance which can be achieved by installing a row of discretely spaced vertical precast concrete piles. This study focussed on permanent movement and dynamic response at different positions within the slope, especially at the crest, which would form key inputs into the aseismic design of supported infrastructure. In contrast to previous studies, the evolution of this behaviour under multiple sequential strong ground motions is studied through dynamic centrifuge modelling, analytical (sliding-block) and numerical (Finite Element) models. This thesis makes three major contributions. Firstly, an improved sliding-block (‘Newmark’) approach is developed for estimating permanent deformations of unreinforced slopes during preliminary design phases, in which the formulation of the yield acceleration is fully strain-dependent, incorporating the effects of both material hardening/softening and geometric hardening (re-grading). This is supported by the development of numerical (Finite Element) models which can additionally predict the settlement profile at the crest of the slope and also the dynamic ground motions at this point, for detailed seismic design were also developed. It is shown that these new models considerably outperform existing state-of-the art models which do not incorporate the geometric changes for the case of an earthquake on a virgin slope. It is further shown that only the improved models can correctly capture the behaviour under further earthquakes (e.g. strong aftershocks) and therefore can be used to determine the whole-life performance of a slope under a suite of representative ground motions that the slope may see during its design life, and allow improved estimates of the seismic performance of slopes beyond their design life. The finite element models can accurately replicate the settlement profile at the crest (important for highway or rail infrastructure) and quantify the dynamic motions which would be input to supported structures, though these were generally over-predicted. Secondly, the principles of physical modelling have been used to produce realistically damageable model piles using a new model reinforced concrete (both a designed section specifically detailed to carry the bending moments induced by the slipping soil mass and a nominally reinforced section with low moment capacity). This was used to investigate how piles can stabilise slopes under earthquake events and how the permanent deformation and the dynamic response of stabilised slope are strongly influenced by the pile spacing (S/B) especially at the minimum pile spacing (i.e. S/B=3.5). This is consistent with previous suggestions made for the optimal S/B ratio for encouraging soil arching between piles at maximum spacing both under monotonic conditions, and for numerical investigations of the seismic problem. These were supported by further centrifuge tests on conventional ‘elastic’ piles which were instrumented to measure seismic soil-pile interaction. The importance of reinforcement detailing was also highlighted, with the nominally reinforced section yielding early in the earthquake; the damaged piles subsequently only offer a small (though measureable) reduction in seismic slope performance compared to the unreinforced case. It was demonstrated that both permanent deformations at the slope crest (e.g. settlement) and dynamic ground motions at the crest can be significantly reduced as pile spacing reduced. Finally, a coupled P-y and elastic continuum approach for modelling soil-pile interaction has been used to develop a Newmark procedure applicable for pile-reinforced slopes. It was observed that the single pile resistance is mobilising at beginning of the earthquake’s time and it is strongly influenced by pile stiffness properties, pile spacing and the depth of the slip surface. It was observed also that the depth of the slip surface and pile spacing (S/B) play an important role in the determination of the permanent deformation of the slope. The results show great agreement to centrifuge test data in term of the permanent deformation (settlement at the crest of the slope) with slight differences between the measured (centrifuge) and calculated (this procedure) maximum bending moments.

No description available.

Over the past several decades, empirical formulas have been developed and improved to predict liquefaction and lateral spread based on a database of case histories from observed earthquakes, such as Youd et al. (2002) and Rauch and Martin (2000). The 2010 Maule Chile earthquake is unique first of all because it is recent and was not used to develop recent liquefaction and lateral spread evaluation methods, and therefore can be reasonably used to evaluate the effectiveness of such equations. Additionally, the 8.8 magnitude megathrust event fills a significant gap in the databases used to develop these empirical formulas, which tends to under represent large magnitude earthquakes and events which occur along subduction zones. Use of case histories from this event will therefore effectively test the robustness and accuracy of these methods.As a part of this comparison, data will be collected from two piers in Port Coronel, Chile: Lo Rojas or Fisherman's Pier, and el Carbonero. Lo Rojas is a municipally owned pier which failed in the 2010 earthquake. Dr. Kyle Rollins gathered detailed engineering survey data defining lateral spread displacements along this pier in a reconnaissance visit with other GEER investigators after the earthquake. El Carbonero was under construction during the earthquake, but no known lateral displacements were observed. Collaboration with local universities and personnel contributed a great deal of knowledge about the soil profile. In early April 2014, collection of SPT and CPT data began in strategic locations to fill gaps of understanding about the stratigraphy near the two piers. Additional testing will provide necessary information to carry out predictions of displacements using current empirical models, which can then be compared with observed displacements collected after the earthquake. Collected data will also be complied, and this alone will provide useful information as it represents a unique case history for future evaluation.The goals of this study are therefore: (1) Collect data for two piers (Lo Rojas and el Carbonero) in Port Coronel, Chile to provide a useful case history of lateral displacements observed; (2) Conduct a liquefaction and lateral spread analysis to predict displacement of the two piers in question, considering lateral spread and slope stability; (3) Compare predicted values with observed displacements and draw conclusions on the predictive capabilities of analyzed empirical equations for similar earthquakes (4) Make recommendations to improve when possible.

Improving seismic hazard analysis is an important part of building safer structures and protecting lives. Since large magnitude earthquakes are rarer than other earthquakes, it is harder to model seismic hazards such as lateral spread displacements for these events. Engineers are often required to extrapolate current lateral spreading models when designing utilities, bridges, and piers to withstand the ground displacements caused by earthquakes with magnitudes larger than 8.0. This study uses three case histories from the Maule Chile 2010 earthquake (Mw =8.8) to develop recommendations on which models are most accurate for large earthquake events and how to improve the accuracy of the models. Six empirical models commonly used in engineering practice are compared. The model that best matches the Maule Chile case histories uses local attenuation relationships to make it easier to apply the model to any seismic region. Models that use lab data from cyclic shear tests over predict displacements but using a strain-reduction factor with depth significantly improved the accuracy of the results. Site-to-source distances can vary greatly between geographic seismic and faulting mechanisms. For this reason, models that depend on an internal source-to-site distance show less promise with large subduction zone earthquakes throughout the world. Models with site-to-source distances are most accurate in the western United States and Japan because the case histories for these models came from those countries.

Temporally and spatially clustered earthquake sequences along plate boundary zones indicate that patterns of seismicity may be influenced by earthquake-induced stress changes. Many studies invoke Coulomb stress change (CSC) as one possible geo-mechanical mechanism to explain stress interactions between earthquakes, their aftershocks, or large subsequent earthquakes; however, few address the statistical robustness of CSC triggering beyond spatial correlations. To address this, I evaluate the accuracy of CSC predictions in subduction zones where Earth’s largest earthquakes occur and generate voluminous and diverse aftershock sequences. A series of synthetic tests are implemented to investigate the accuracy of inferred stress changes predicted by slip distributions inverted from suites of geodetic observations (InSAR, GPS, seafloor geodetic observations) that are increasingly available for subduction zone earthquakes. Through these tests, I determine that inferred stress changes are accurately predicted at distances greater than a critical distance from modeled slip that is most dependent on earthquake magnitude and the proximity of observations to the earthquake itself. This methodology is then applied to the 2010 Mw 8.8 Maule, Chile earthquake sequence to identify aftershocks that may be used to perform statistically robust tests of CSC triggering; however, only 13 aftershocks from a population of 475 events occurred where confidence in CSC predictions is deemed to be high. The inferred CSC for these events exhibit large uncertainties owing to nodal plane uncertainties assigned to the aftershock mechanisms. Additionally, tests of multiple published slip distributions result in inconsistent stress change predictions resolved for the 13 candidate aftershocks. While these results suggest that CSC imparted by subduction megathrust earthquakes largely cannot be resolved with slip distributions inverted from terrestrial geodetic observations alone, the synthetic tests suggest that dramatic improvements can be made through the inclusion of near-source geodetic observations from seafloor geodetic networks. Furthermore, CSC uncertainties will likely improve with detailed earthquake moment tensor catalogs generated from dense regional seismic networks.

Seismic considerations greatly influence the lateral and vertical design of a structure, often necessitating larger elements than would otherwise be required. Seismic isolation greatly reduces the demands on a structure due to earthquake loading, allowing the use of smaller, more efficient members and foundations. This case study illustrates the theory and procedure of evaluating the response of a recently built multi-span highway bridge using the most recent (2009) AASHTO code. Based on this response, an equivalent structure was designed to incorporate a seismic isolation system, and the substructure of the isolated bridge redesigned to meet the reduced demands more economically. The reduction in demands was quantified, and the member demands and overall responses of the two designs were compared. An overview of isolator design for the common isolator types available in the United States, with examples specific to the isolated structure that was designed, is also included as an addendum.

Reinforced concrete structures are usually vulnerable to collapse in areas where the earthquakes are frequent. Although plenty of research has been carried out in that regard the problem is still in place. Furthermore, there are buildings that did not collapse with the first and second earthquake but with the third one. That happens because many buildings are generally declared safe after being thoroughly inspected in the visible areas only, ignoring the extent of the damage in the column-to-foundation connections. The criterion of identifying the failure at the base of the columns of the ground floor is that after the earthquake there are no traces of failure. In other words, the cracks at the base of the columns have been healed and concealed the damage in the core of the columns. / thesis (PhDCivilEngineering)--University of South Australia, 2005.

The cyclic resistance of predominantly fine-grained soils has received considerable attention following ground and foundation failures at sites underlain by silt-rich soils during recent earthquakes. In several cases substantial ground deformation and reduced bearing capacity of silt soils has been attributed to excess pore pressure generation during cyclic loading. These field case studies are significant due to the occurrence of liquefaction related phenomena in soils that would be characterized as not susceptible to liquefaction using current geotechnical screening criteria. The most widely used of these criteria, the "Chinese Criteria" and its derivatives, are based solely on soil composition and they are essentially diagnostic tools that categorize the soil in a binary fashion as either liquefiable or non-liquefiable. The most significant limitations of these screening tools are that they fail to account for the characteristics of the cyclic loading. This investigation was undertaken to elucidate the potential for strain development in silts during cyclic loading, and to develop a practice-oriented procedure for evaluating the seismic performance of silts as a function of material properties, in situ stresses, and the characteristics of the cyclic loading. This dissertation presents the results of a multi-faceted investigation of the potential for seismically induced pore pressures and large strain development in silt soils. The primary focus of the research was on the synthesis of laboratory testing results on fine grained soils. Laboratory data from cyclic tests performed at Oregon State University and other universities formed the basis for enhanced screening criteria for potentially liquefiable silts. This data was supplemented with field data from sites at which excess pore pressure generation, liquefaction, and/or ground failures were observed during recent earthquakes. This investigation specifically addressed the behavior of silts during loading in cyclic triaxial tests due to the relative abundance of data obtained for this test. The data was used in conjunction with standard geotechnical index tests to enhance an existing energy based procedure for estimating excess pore pressure generation in silts. This pore pressure model can be used with the uncoupled, stress-based methods for estimating the post-cyclic loading volumetric strain developed in this investigation. The energy-based excess pore pressure model and empirical volumetric strain relationship were used to calibrate for applications involving silt soils a nonlinear, effective stress model for dynamic soil response (SUMDES). The SUMDES model was employed, along with the equivalent linear total stress model SHAKE, to estimate excess pore pressures generated at un-instrumented field sites that have exhibited evidence of liquefaction during recent earthquakes. A comparison of the SUMDES and SHAKE results highlighted the limitations of the latter model for simulating dynamic soil response at various levels of shaking and pore pressure response. The results of the SUMDES modeling at several well documented case study sites are presented in this dissertation. These comparisons are valuable for demonstrating the uncertainties associated with modeling of the effective stress behavior of silt during seismic loading. / Graduation date: 2005