For assessing seismic liquefaction triggering and its consequence of lateral spreading and permanent ground displacement estimation, there are various methods of evaluation, with varying degrees of sophistication and complexity. At one end of the spectrum, simplified, empirical or semi-empirical based approaches are available in the literature to assess the seismic liquefaction triggering and estimation of lateral spreading, primarily used as screening level tools. At the other end of the spectrum, advanced seismic numerical modelling using sophisticated soil constitutive models can be utilized to evaluate the seismic performance of liquefiable soils and an estimation of the permanent ground displacements due to liquefaction. This paper focuses on the seismic liquefaction and lateral spreading displacement assessment for a proposed pipeline river crossing using both simplified and advanced numerical methods.

The proposed pipeline crosses a major river using horizontal directional drilling (HDD) method, which will go through potentially liquefiable fluvial sand deposits and soft clays. The estimation of lateral spreading and permanent ground deformation along the proposed HDD path was required to ultimately assess the integrity of the pipeline under the design seismic load. At the initial phase of the study, simplified liquefaction triggering assessment using Idriss and Boulanger (2008) method was performed and then estimation of lateral spreading was made using semi-empirical correlations in the literature such as Youd et al (2002). Then refinements to the simplified liquefaction triggering assessments were made by performing one dimensional site response analysis to have a better estimate of seismic shear stresses. In the last phase of the study, detailed seismic numerical model of the crossing was analyzed using FLAC software. The seismic performance of the potentially liquefiable unit was assessed using the advanced soil constitutive model of UBCSAND and for non-liquefiable units UBCHYST constitutive model was used. Furthermore, in the FLAC model of the pipeline crossing, the spatial variability in the liquefiable sand unit was also accounted for, by having a distribution of Standard Penetration Test (SPT) measurements, using regression analyses, honoring field measurement values. The initial phase of the study indicated widespread liquefaction and large permanent ground deformation which required both ground improvement and thickening the pipe wall thickness as mitigation measures. However, through the more rigorous advanced FLAC analysis, it was illustrated that the spatial extent of the liquefaction was more constraint, and the predicted permanent ground deformation was also smaller, leading to only requiring thickening the pipe wall thickness.

Underground structures might experience a sequence of multiple shakings in a real seismic event, since earthquakes could contain more than one strong shaking during a short period of time. The soil-structure interaction (SSI) is very much dependent on the characteristics of the shakings, because typically the behavior of the surrounding soil is stress-path dependent. In this paper, the special case of a shallow tunnel in liquefiable ground subject to multiple shakings is considered via numerical method. The OpenSees platform and the PM4Sand constitutive model are employed for the numerical modelling, where a rectangular tunnel is buried in saturated Hostun sand. The validity of the numerical model is verified by the data of a centrifuge test of four consecutive shakings. Then, the numerical soil-structure system is configured for further investigation on the subject matter, and the signature seismic response of shallow tunnel in liquefied ground, namely, the uplift, is most intensely discussed.

Offshore wind is an ever-growing industry that is key to the future of green energy generation. As new windfarms are built in both seismic and scour prone regions, such as East Asia and North America, there is a need to understand the behaviour of rock-scour protection under seismic liquefaction. Rock dump is a common method to both combat and remediate scour, a phenomenon whereby the redirected water currents from a foundation create vortices which wash away the seabed sediment surrounding the foundation. Rock-scour protection usually consist of a filter layer, smaller rocks to reduce rock-sediment penetration, and armour rocks, larger boulders that resist the force of water. Under seismic loading, loose seabed sand will liquefy and lead to the settlement of rock. However, there is very limited research in this area. This paper presents the results of two dynamic, saturated centrifuge tests. A comparison is made between the behaviour of a scour protection rock berm and a shallow foundation model that exerts a similar overburden stress on the seabed as the rock berm. The main aim is to compare the differences in behaviour between the continuum based shallow foundation model (in the form of an aluminium plate) and a particulate rock berm model. The results show that for small magnitude input motions, the settlement of a plate is greater than that of rock, however, for larger earthquakes, their settlements are comparable, with the plate foundation model settlement being a fraction smaller. This result suggests that some amount of seabed material ingress into the rock berm following liquefaction, leading to slightly larger settlements. These observations from the centrifuge tests can have implications in using continuum based finite element models to estimate liquefaction induced scour settlements. The results presented in this paper form part of a larger research project that investigates the behaviour of rock-scour protection under seismic liquefaction to better aid future design.

In previous research works, soil-pile dynamic interaction has mostly been investigated considering an isolated pile supported structure with soil’s cyclic response being considered as truly undrained. However, previous earthquakes such as the 1995 Kobe earthquake highlighted that spatially located piles installed in a sloping ground may behave differently during the application of earthquake loading particularly owing to the differences in the mechanism responsible for the mobilization of kinematic effects (i.e., soil-fluid-pile interaction). This stems from the fact that during the course of shaking (particularly for long-duration earthquakes), pore-pressure redistribution phenomenon is very likely not only in upwards direction but also along the spatial zone of lateral spreading and therefore may govern the magnitude of co-seismic kinematic moment mobilized by the spatially located piles. The above-mentioned mechanisms contributing to the mobilization of kinematic effects for the spatially located piles have not been studied till date which is very critical as the densely populated cities with multiple adjacent pile supported buildings are expected to experience strong shakings in the near future. To this end, this paper shed novel insights on the mobilization of kinematic effects for spatially located piles based on the dynamic centrifuge testing. From the centrifuge experiments conducted on a uniformly liquefiable model and a stratified soil model inclined with 5-degrees comprising of spatially located piles, we found that lateral seepage played a significant role in the mobilization of kinematic moments towards the bottom of pile. To this end, it is important to correlate the internal stresses mobilized along the pile with the generated excess pore pressure. It is also recommended to design pile foundation as a spatially located structure along the zone of lateral spreading in order to achieve safer design loads.

In recent years, there have been research cases where information on liquefaction points during earthquakes has been developed and the occurrence rate and area rate of liquefaction can be evaluated. On the other hand, when predicting damage to structures due to liquefaction, it is necessary to evaluate not only the probability of occurrence and area rate, but also the amount of settlement due to liquefaction as a measure of the severity of liquefaction. The probability of occurrence is also important in considering structural countermeasures, and it is necessary to construct a probabilistic settlement hazard assessment. In this study, we used the amount of settlement as an index to evaluate the severity of liquefaction and developed a model to predict the amount of settlement due to liquefaction. Specifically, an estimation model that predicts the amount of settlement due to liquefaction based on geographical information such as seismic intensity and microtopography classification was developed using borehole data from liquefaction sites that occurred in Japan in recent years. Furthermore, using this model, we constructed a liquefaction hazard model for all of Japan with a mesh size of 250 m based on probabilistic seismic motion prediction maps and geographic information such as microtopography classification. Using the modeled hazard and building fragility corresponding to the amount of settlement, we evaluated liquefaction damage for an arbitrary earthquake scenario as a deterministic risk assessment. In addition, liquefaction damage with arbitrary probability was evaluated as a probabilistic risk assessment. The developed method makes it possible to assess liquefaction risk in a wide area throughout Japan based on the amount of settlement.

In this study, the impact of the building settlement due to the loss of foundation bearing capacity during soil liquefaction on buried pipelines was experimentally investigated. The forced displacement tests simulating the building settlement were conducted on full-scale physical models of buried service lines that connect distribution mains and buildings, including those for potable water and natural gas. Both complete liquefied and non-liquefied conditions of the soil surrounding the pipelines were simulated. During these tests, the longitudinal strains, deflection, and possible leakage of pipelines were monitored. The results showed that different conditions of surrounding soil led to different strain distribution and deflection along the pipeline. Yielding of the pipe material and the pulling out of the pipeline from the joint were caused if the settlement was large enough. Local buckling of the pipe near the loaded end was induced in non-liquefied cases due to the combination of forced displacement and soil reaction. Besides, the flexibility of pipes and the strength of joints were found influential on the resilience to the aforementioned damage modes. These findings provide better understanding of the resistance performance of buried pipelines against liquefaction-induced displacement and are beneficial to the seismic mitigation of lifelines.