Yes / Laboratory experiments have been carried out to investigate wave damping over the seabed, in which the excess pore pressure and free surface elevations are synchronously measured for examining the wave-induced soil dynamics and wave kinematics. Two types of soil, namely fine sand and silt, are tested to examine the role of soil in the wave damping. Observation of experiments shows that (i) soil liquefaction takes place for some tests with silty bed and soil particles suspend into the water layer when the bed is made of silt; (ii) sand ripples can be generated for experiments with sand bed. Measurements reveal that the wave damping greatly depends on the soil dynamic responses to wave loading and the wave damping mechanism over the silty seabed differs from that over the sand bed. On the one hand, the wave damping rate is greatly increased, when soil liquefaction occurs in the silty bed. On the other hand, the presence of sand ripples generated by oscillatory flow in the sand bed experiments also increases the wave damping to some extent. Furthermore, experimental results show that soil particle suspension in the silt bed test contributes to the wave damping. Theoretical analysis is presented to enhance discussions on the wave damping. The theoretical calculations demonstrate that the wave damping is mainly induced by the shear stress in the boundary layer for the cases when no liquefaction occurs. While for the cases when soil liquefaction takes place, the viscous flow in the liquefied layer contributes most towards to the wave damping. / the National Science Fund for Distinguished Young Scholars (Grant No. 51425901), the National Key Research and Development Program of China (2017YFC1404200), the Marine Renewable Energy Research Project of State Oceanic Administration (GHME2015GC01), and the 111 Project (Grant No. B12032)

Earthquake-induced soil liquefaction is a phenomenon in which saturated, sandy soil loses its strength and stiffness during earthquake shaking. Liquefaction can be extremely costly and damaging to infrastructure. The commonly used "simplified" stress-based liquefaction triggering framework is correlated with metrics computed from in-situ tests like the Cone Penetration Test (CPT). While CPT-based procedures have been shown to accurately predict liquefaction occurrence in homogenous, sandy soil profiles, they tend to over-predict the occurrence of liquefaction in challenging, highly interlayered soil profiles. One contributing factor to the over-prediction is multiple thin-layer effects in CPT data, a phenomenon in which data in interlayered zones is blurred or averaged, making it difficult to identify specific layer boundaries and associated CPT parameters like tip resistance. Multiple thin-layer correction procedures have been proposed to convert the measured tip resistance in an interlayered profile (qm) to the "true" or characteristic tip resistance (qt) that would be measured without the influence of multiple thin-layer effects. In this dissertation, the efficacy of existing multiple thin-layer correction procedures is assessed. It is shown that existing procedures are not effective for layer thicknesses equal to or less than about 1.6 times the diameter of the cone. Two new multiple thin-layer correction procedures are proposed. Furthermore, a framework for numerically simulating CPTs in interlayered soil profiles using the Material Point Method (MPM) is developed. A framework for linking uncertainties associated with the numerical analyses and the laboratory CPT calibration chamber tests used to calibrate the numerical analyses is also proposed. Finally, a database of laboratory and numerically-generated CPT data is presented. It is shown how this database can be used to improve existing, and develop new, multiple thin-layer correction procedures. Ultimately, the work detailed in this dissertation will improve the characterization of highly interlayered soil profiles using CPTs to support more accurate liquefaction hazard assessment at challenging soil sites. / Doctor of Philosophy / Earthquake-induced soil liquefaction is a phenomenon in which saturated, sandy soil loses its strength and stiffness during earthquake shaking. Liquefaction can be extremely costly and damaging to infrastructure. Existing procedures used to assess liquefaction hazard were developed specifically for homogenous, sandy soil profiles. These procedures do not perform well in challenging, highly interlayered soil profiles. One reason for this is the inadequate characterization of the soil profile by the chosen in-situ test method. For example, the cone penetration test (CPT) consists of hydraulically advancing a steel probe with a conical shaped tip ("cone") into the ground. Typically, the penetrometer is about 3.6 to 4.4 cm in diameter, and data are recorded at 1 to 5 cm depth intervals. However, data recorded at a specific depth are representative of soil that falls within a zone several times the diameter of the penetrometer ahead of and behind the tip of the cone. In a highly interlayered soil profile, this means the CPT records blurred or averaged data within interlayered zones. Typical liquefaction analyses compute a factor of safety against liquefaction at every depth in the soil profile where CPT data are recorded. Hence, having data that are blurred can result in an inaccurate factor of safety against liquefaction. To account for this blurring (called multiple thin-layer effects), correction procedures have been proposed. This dissertation evaluates the effectiveness of those procedures and develops new procedures. Additionally, a numerical simulation tool is shown to be capable of simulating CPTs in layered soil profiles. This reduces the need for costly laboratory testing to further evaluate multiple thin-layer effects. Finally, a combined laboratory and numerically-generated CPT database is developed to support the improvement of, and development of new, multiple thin-layer correction procedures. The broader impacts of this work support more accurate liquefaction evaluations in challenging soil profiles worldwide, like those in Christchurch, New Zealand, and the Groningen region of the Netherlands.

Predicting sediment transport at sandy beaches is a significant challenge in civil engineering owing to the variability in hydrodynamic, morphological, and geotechnical properties within a site and across multiple sites. Additionally, there are difficulties in measuring in-situ properties, and challenges in identifying and quantifying the different relevant driving and resisting forces. These challenges are further exacerbated in the intertidal zone where the addition of infiltration-exfiltration, wave run-up and run-down, bore collapse, cyclic emergence and submergence of sediments, interactions between standing waves and incident bores, and other processes must be considered. Among these many processes, pore pressure gradients within sandy beach sediments affect sediment transport by reducing the sediment's effective stress to zero (this process is called liquefaction). Despite the known importance of these pressure gradients with respect to sediment transport, there has been little field evidence of the role that these pore pressure gradients have on sediment transport, how they relate to the hydrodynamic properties, and their inclusion into predictive sediment transport equations. This study is based on field measurements of hydrodynamic and geotechnical properties, as well as pore pressure gradients during storm and non-storm conditions at sandy beaches in the intertidal zone. From the analysis of these field measurements, it was found that (1) liquefying pressure gradients are likely to develop in sediments that are rapidly inundated during storm conditions; (2) the magnitude of pore pressure gradients is related to the asymmetry of the pressure gradient and can occur with shoreward-directed near bed velocities; and (3) during non-storm conditions, pressure gradients that often do not exceed liquefaction criteria occurred more (less) frequently during a time period where erosion occurred in large (small) quantities, indicating that small non-liquefying pore pressure gradients may facilitate sediment transport. The results of this study demonstrate that current methods of scour calculations must include effects of pore pressure gradients to reduce error. Additionally, from this work it was found that sediment transport can be directed shoreward under momentary liquefaction. Finally, the results of this study show that sediment pore pressure gradients are related to wave skewness, spatial group steepness, and temporal group steepness which may aid modelling of pore pressure gradients. / Doctor of Philosophy / The transport of sediment particles (in this case, sand grains at beaches) is difficult to predict because of the many different governing processes that can be hard to measure, may be hard to relate to erosion or sediment accumulation specifically, and the variability in sediment and flow properties (grain size, fluid velocity, and others) at a specific location and across different locations. Storms, like hurricanes, tropical storms, and tsunamis, can drastically change the expected water properties (like water depth, wave height, and wave period), and the effects of water pressure within the sand bed. When a wave moves across the sand it causes a change in the water pressure that is within the sand. This water pressure is not the same throughout the sand with depth. When the gradient, or the difference between the water pressure at two different vertical locations, is large enough, the sand behaves like a fluid (like quicksand) and becomes easier to move, this process is called liquefaction. Even though previous work has shown that these pressure gradients (and the resulting liquefaction) is important for sediment transport, there have been few field measurements demonstrating their impact on sediment transport and how these gradients (and the resulting liquefaction) relate to wave and sand properties. This study presents field measurements of pressure gradients, wave and sediment properties, and sediment transport events during both storm and non-storm conditions. From these field measurements, it was shown that (1) during an extreme storm event, pressure gradients that liquefy the sediment are likely to occur on sediments that are not normally subjected to waves; (2) liquefying pressure gradients can occur when waves arrive at the beach, which may cause sediment to be moved shoreward; and (3) during non-storm conditions, pressure gradients that do not liquefy the sand occurred frequently during a sediment transport event, suggesting that these smaller pressure gradients may contribute to sediment transport by reducing the effective weight of the sediment. This work can be used to further understand the behavior of sediment pore pressure gradients, their relation to hydrodynamic properties, and how they influence sediment transport allowing for better predictions of sediment transport, beach nourishment calculations, and the design of coastal structures.

Liquefaction is one of the major causes of ground failures during an earthquake. Recent evidence shows that the existing variants of the "simplified" liquefaction evaluation procedure lead to inaccurate results for megathrust earthquakes in subduction interfaces. To overcome this drawback and to achieve better prediction of liquefaction cases in subduction zones, this research intends to develop new empirical models that could be used for the prediction of liquefaction triggering in subduction zones. Towards this goal, new models for number of equivalent cycles (n_eq) and stress-reduction factor (r_d) have been proposed. The models are developed by regressing site response data obtained from 254 pairs of subduction ground motions and 77 representative soil profiles. To account for tectonic differences and magnitude scaling, separate models are developed for interface and intraslab earthquakes. The uncertainties involved in the proposed models are quantified through standard deviations of regression coefficients, event, site, and residual terms. The resulting models differ from other published models, especially the model for number of equivalent cycles. It was found that n_eq is greatly influenced by the fundamental site period. The model for r_d predicts higher values at shallow depths and lower values at deeper layers than other published models. Comparing the factors of safety against liquefaction with those from other existing models revealed that the use of models proposed in this research is more likely to reduce the "false positives" in liquefaction predictions, especially when design ground motion acceleration is high. / Master of Science / During earthquake shaking, loose saturated sands may lose strength and behave more like a liquid than a solid. This phenomenon is referred to liquefaction. Liquefaction has been responsible for infrastructure failure during past earthquakes, thus leading to major economic losses. This prompts the prediction and mitigation of potential liquefaction effects in a building site. However, the current state-of-the-practice for predicting liquefaction is inaccurate for large magnitude earthquakes in subduction zones. This provided the impetus for this research which focusses on developing new liquefaction evaluation models for large magnitude earthquakes. New models for number of equivalent cycles and stress reduction factor are developed by analyzing the representative ground motions and soil strata. These empirical parameters are central to the prediction of liquefaction triggering. Comparing the new models with the existing models revealed that the factor of safety against liquefaction estimated using new models are greater than those obtained using existing models for large magnitude earthquake scenario when the ground acceleration is high. This implies that using the existing models for predicting liquefaction in a site subjected to high values of ground acceleration from a subduction earthquake will lead to "false positives." Developed using a comprehensive dataset and robust regression techniques, the models developed in this research will lead to better predictions of liquefaction due to large subduction events.

Small amounts of cementation in a sand increase its ability to sustain static and dynamic loads, even in a liquefaction type environment. This has been shown in previous research examining the behavior of both naturally cemented and artificially prepared samples. Cemented sands are present in many parts of the world and can be caused by either a variety of cementing agents or by cold welding at points of grain contact. They are generally quite difficult to sample, but artificially cemented sands have been shown to aptly model the behavior of natural materials, and allow for better test controls. Consequently, artificial samples were used exclusively for the present investigation which has three major objectives: to investigate the effects of a weakly cemented lens within a stronger mass; to determine how cementation affects the volume change characteristics of statically loaded samples; and, to describe the pore pressure generation of sands subjected to cyclic loading. Prior to commencing the test program, a number of index tests were performed on the uncemented and cemented sand used during the laboratory investigation. It was revealed that cementation leads to increased void ratios which distort relative density calculations used to compare cemented and uncemented samples of similar dry unit weight. The practice of identifying samples by dry unit weight was adopted for this report. Static triaxial compression tests were performed on 17 samples. Test results indicate that although the magnitude of volumetric strain at failure does not seem to be dictated by the level of cementation, there is a relationship with cementation and the rate of volume change at failure. A weak lens was seen to lower the static strength of the stronger mass. 26 stress controlled cyclic triaxial tests revealed that a weak lens lowers the liquefaction resistance of the stronger mass. The cyclic strength of the nonhomogeneous material, however, is higher than the independent strength of the weak lens. A weak lens has greater influence at relatively higher levels of cyclic stress. Pore pressure generation in cemented sands are seen to be controlled by strain. At shear strain levels below about 1%, cemented sands behave similarly to uncemented sands with pore pressures increasing more rapidly beyond that amount of strain. Consequently, pore pressure development during cyclic loading is described by a broken-back curve which is defined in the early stages by existing empirical relationships for uncemented sand. Pore pressure prediction may then be achieved using an equation for cemented sand, such as that developed in the present work. / Master of Science

Hawke's Bay is situated on the east coast of the North Island of New Zealand and has experienced several earthquakes in the past during which liquefaction occurred. The 1931 Hawke's Bay earthquake is particularly interesting because it was the deadliest and one of the most damaging earthquakes in New Zealand's history. The study presented herein provides insights into the liquefaction hazards in Napier and Hastings based on the assessment of data from the 1931 Hawke's Bay event. Previous studies on the liquefaction hazard of the region have been performed, but the present work differs from those in that the liquefaction triggering and severity procedures are used to see if they can accurately predict observations from the 1931 event. Towards this end, the Cone Penetration Test (CPT)-based liquefaction triggering evaluations are used in liquefaction vulnerability assessment frameworks. It was found that liquefaction hazard in Napier is greater than Hastings. Additionally, Liquefaction Potential Index and Liquefaction Severity Number distributions across Napier and Hastings suggest that the analysis frameworks used are over-predicting the liquefaction hazard. This observation was reached through the comparison of predictions and 1931 post-earthquake observations. Possible causes for this over-prediction include the shortcomings in the analysis frameworks to account for the influence of non-liquefied layers in the profile on the severity of surficial liquefaction manifestations, shortcomings of the simplified liquefaction evaluation procedures to fully account for the depositional and compositional characteristics of the soil on liquefaction resistance, and the use of the assumption that the soils below the ground water table are fully saturated, which has been shown not to be the case at sites in Christchurch, New Zealand. The research community is still learning about earthquakes and liquefaction and this study demonstrates how historical earthquake accounts in a region can be used to assess the risk of the region from future earthquakes. / Master of Science

Liquefaction of granular soil deposits can have extremely detrimental effects on the stability of embankment dams, natural soil slopes, and mine tailings. The residual or liquefied shear strength of the liquefiable soils is a very important parameter when evaluating stability and deformation of level and sloping ground. Current procedures for estimating the liquefied shear strength are based on extensive laboratory testing programs or from the back-analysis of failures where liquefaction was involved and in-situ testing data was available. All available procedures utilize deterministic methods for estimation and selection of the liquefied shear strength. Over the past decade, there has been an increasing trend towards analyzing geotechnical problems using probability and reliability. This study presents procedures for assessing the liquefied shear strength of cohesionless soil deposits within a risk-based framework. Probabilistic slope stability procedures using reliability methods and Monte Carlo Simulations are developed to incorporate uncertainties associated with geometrical and material parameters. The probabilistic methods are applied to flow liquefaction case histories from the 1999 Kocaeli/Duzce, Turkey Earthquake, where extensive liquefaction was observed. The methods presented in this paper should aid in making better decisions about the design and rehabilitation of structures constructed of or atop liquefiable soil deposits. / Master of Science

On December 22nd, 2003, the Mw=6.5 San Simeon earthquake occurred 12 kilometers east of San Simeon, California, causing damage to buildings, roads, and other infrastructure throughout the central coast. The community of Oceano, 80 kilometers southeast of the epicenter, experienced damage to foundations, roads, and utilities due to liquefaction and lateral spreading. The unique geologic environment in Oceano caused a local amplification of ground motions, liquefaction, and lateral spreading. This study entailed developing ten liquefaction case histories from Oceano during the 2003 San Simeon earthquake. Four of the ten case histories are liquefaction cases and six are non-liquefaction cases, with Cyclic Stress Ratio (CSR) ranging from 0.17 to 0.43 and average corrected cone tip resistance (qc1) ranging from 2.67 to 23.53 kN/m^2. Subsurface data used to represent the geologic conditions in each case history included CPT soundings provided by the United States Geological Survey (Holzer et al., 2004). Ground motion data used to represent the earthquake conditions in each case history included the nearest relatively free field ground motion recordings from the SLO Rec Center Seismic Monitoring Station provided by the PEER strong motion center (PEER Ground Motions Database, 2003). CPT soundings were grouped together to develop representative case histories, allowing for averaging of parameters. The stratum with the single highest potential for liquefaction was selected and used as the ‘critical layer’ in each case history. To accurately represent the ground motion felt by each critical layer, a site response model was used to calculate average shear stress, which was used to calculate Cyclic Stress Ratio. The site response model was built using DEEPSOIL V6.1 with measured seismic shear wave velocities. Velocities were measured using passive geophysical methods in conjunction with Spatial Autocorrelation (SPAC) methods to process the data into shear wave velocity profiles. Measured velocities ranged from approximately 117 to 469 meters per second at depths ranging from 0 to 50 meters below the ground and were normally dispersive.

京都大学 / 新制・課程博士 / 博士(理学) / 甲第25123号 / 理博第5030号 / 京都大学大学院理学研究科地球惑星科学専攻 / (主査)教授 王 功輝, 教授 松四 雄騎, 教授 大見 士朗 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

The northern part of Algeria is located in the border zone between the African and Eurasian plates. The collision between the two plates is expressed by a moderate to high seismicity, generally localized at the margins of the Neogene basins. The Middle-Chelif Basin is located in the northwestern part of Algeria, between the northern and southern Tellian Atlas mountain belts. The seismic activity is mainly generated by the El-Asnam fault, a 40 km long reverse fault located on the western edge of the basin. The 1980 El-Asnam earthquake caused significant damage in the cities of the basin. In particular, the cities of Oued-Fodda, El-Attaf and El-Abadia were heavily affected. In the western part of the alluvial plain of the Middle-Chelif, phenomena of cracks, settlements, landslides and liquefaction, have also occurred following the earthquake. This research aims to quantify dynamic properties of the soils of the Middle-Chelif Basin in terms of shear-wave velocity (Vs), fundamental frequency or vulnerability index (Kg) for the estimation of liquefaction potential. The calculation of dynamic soil properties allows a better assessment of the seismic hazard in the region. We have focused more on the characterization of the Vs structure of the superficial sedimentary layers in the entire Middle-Chelif Plain because of the role it plays in the amplification of the seismic waves during an earthquake. Secondly, these same soil parameters allow the creation of microzonation maps classifying the surface soil according to the criteria of NEHRP (National Earthquake Hazard Reduction Program). For this purpose, techniques based on single-station and array ambient vibration measurements are applied. Ambient vibrations were recorded at 323 sites using single-station, and at 18 sites using array measurements. The measurements were densified within urban areas. This thesis is divided into three main parts; the first one consists in a seismic microzonation of the city of Oued-Fodda, located at 1-2 km from the El-Asnam fault. The Horizontal-to-Vertical Spectral Ratio (HVSR) method was applied on ambient vibration records measured at 103 sites in the city and its surroundings. Maps of the variation of soil resonance frequencies, as well as their amplitudes, were provided. Inversion of the HVSR curves allowed obtaining 1D Vs models at each site. The 2D velocity profiles were used to image the shape of the sedimentary layers and the bedrock outcrop in the central part of the city. The second part aims to characterize the sedimentary deposits in the basin. The HVSR method was applied on ambient noise records measured at 164 sites and aligned on 20 NW-SE profiles. The Frequency-Wavenumber (F-K) technique was applied on array measurements at 7 sites. The 2D velocity profiles imaged the synclinal shape of the sedimentary deposits. A bedrock model was also provided. The third and last part consists of a more complete seismic microzonation in the three other main cities of the basin; Ain-Defla, El-Attaf and El-Abadia. Ambient vibrations were measured using a single-station at 56 sites and using arrays at 11 sites. As a result, maps of resonance frequency variation, Vs variation over the first 30 meters of the soil (Vs30) and soil classification were proposed in addition to a prediction equation for Vs30 in the region.