Evaluation for Earthquake Liquefaction of Loess Sites

Through the sinusoid loading dynamic triaxial test, the liquefaction property of saturated loess and sand selected from a civil airport of Lanzhou, Gansu is examined. Based on the laboratory results, a comprehensive assessment on the earthquake liquefaction potential of the loess and sand is given, using the liquefaction resistance shear stress method and the results of seismic hazard assessment. It is found that under the effect of ground motion with exceedance probability of 10% within 50 years, the loess in the study is more susceptible to liquefaction than sand.

Earthquake-induced liquefaction hazard mapping at national-scale in Australia using deep learning techniques

Australia is a relatively stable continental region but not tectonically inert,having geological conditions that are susceptible to liquefaction when subjected to earthquake ground motion.Liquefaction hazard assessment for Australia was conducted because no Australian liquefaction maps that are based on modern Al techniques are currently available.In this study,several conditioning factors including Shear wave velocity(Vs30),clay content,soil water content,soil bulk density,soil thickness,soil pH,distance from river,slope and elevation were considered to estimate the liquefaction potential index(LPI).By considering the Probabilistic Seismic Hazard Assessment(PSHA)technique,peak ground acceleration(PGA)was derived for 50 yrs period(500 and 2500 yrs return period)in Australia.Firstly,liquefaction hazard index(LHI)(effects based on the size and depth of the liquefiable areas)was estimated by considering the LPI along with the 2%and 10%exceedance probability of earthquake hazard.Secondly,ground acceleration data from the Geoscience Australia projecting 2%and 10%exceedance rate of PGA for 50 yrs were used in this study to produce earthquake induced soil liquefaction hazard maps.Thirdly,deep neural net-works(DNNs)were also exerted to estimate liquefaction hazard that can be reported as liquefaction hazard base maps for Australia with an accuracy of 94%and 93%,respectively.As per the results,very-high liquefaction hazard can be observed in Western and Southern Australia including some parts of Victoria.This research is the first ever country-scale study to be considered for soil liquefaction hazard in Australia using geospatial information in association with PSHA and deep learning techniques.This study used an earthquake design magnitude threshold of Mw 6 using the source model characterization.The resulting maps present the earthquake-triggered liquefaction hazard and are intending to establish a conceptual structure to guide more detailed investigations as may be required in the future.The limitations of deep learning models are complex and require huge data,knowledge on topology,parameters,and training method whereas PSHA follows few assumptions.The advantages deal with the reusability of model codes and its transferability to other similar study areas.This research aims to support stakeholders'on decision making for infrastructure investment,emergency planning and prioritisation of post-earthquake reconstruction projects.

A case study of seismic response of earth embankment foundation on liquefiable soils

A case study of seismic response of an earth embankment foundation on liquefiable soils in Kansai area,western Japan was presented. Based on a calibrated cyclic elasto-plastic constitutive model for liquefiable sand and Biot dynamic coupled theory,the seismic analysis was carried out by using a dynamic effective stress finite element method under plane strain condition. A recent design study was illustrated in detail for a river earth embankment subjected to seismic excitation on the saturated deposits with liquefiable sands. Simulated results of the embankment foundation during liquefaction were obtained for acceleration,displacement,and excess pore water pressures,which were considered to yield useful results for earthquake geotechnical design. The results show that the foundation soil reaches a fully liquefied state with high excess pore pressure ratios approaching to 1.0 due to the earthquake shaking. At the end of the earthquake,the extensive liquefaction causes about 1.0 m lateral spreading at the toe and 60 cm settlement at the crest of the earth embankment.

Numerical Analysis on the Influence of Thickness of Liquefiable Soil on Seismic Response of Underground Structure

Seismic response of underground structure in liquefiable soils was analyzed by means of fully coupled dynamic finite element method.The soils were simulated by a cyclic mobility constitutive model,which is developed at the base of modified Cam-Clay model with some concepts such as stress induced anisotropy,overconsolidation and structure.It is verified that the constitutive model can perfectly described the dynamic character of both liquefiable sand and non-liquefiable clay.Special emphasis was given for the influence of thickness of liquefiable soil on the seismic response.Results showed that soils at both sides of the structure flowed toward the bottom of the underground structure with the occurrence of liquefaction,which led to the uplift of structure.The uplift of underground structure increased with the increasing of thickness of liquefiable soils.