The definition of appropriate calibration criteria for liquefaction-simulating constitutive models in sands is essential to properly simulate a liquefied state under seismic ground motions, enabling an adequate estimation of the liquefaction hazard. Therefore, a thorough quantitative characterisation of the behaviour of liquefaction is necessary to define liquefaction-triggering criteria that can describe a liquefied state in terms of stress and deformation. This paper presents a benchmark characterisation study of the behaviour of liquefaction, where liquefaction-triggering criteria, in terms of pore pressure ratio (r_u) and shear strain (γ), were determined using two cyclic undrained direct simple shear test databases of Ottawa F-65 sand. The behaviour of liquefaction was analysed considering variations of initial state, confinement pressure (σ’v0) and cyclic shearing (CSR) conditions. The onset of liquefaction-triggering markers was evaluated in terms of moment of occurrence. The research concluded that liquefaction-triggering markers r_u = 0.95 and γ = 3% could be used simultaneously to indicate the initiation of liquefaction in loose and dense Ottawa F-65 sand under various initial and cyclic shearing conditions.

Liquefaction hazards can cause damage to structures and loss of life and property. The simplified prediction equation, numerical simulation and model test are three commonly used approaches to evaluate the damage of the liquefaction hazards or the effectiveness of the mitigation plan. Because the numerical simulation can include the site-specific conditions into the evaluation and perform a parametric study under a reasonable time and affordable budget, many research and engineering projects choose this approach as an evaluation tool. In order to obtain rational and comparable simulation results, appropriate constitutive models and model inputs are essential. Many liquefaction constitutive models (Finn model, UBCSAND model, SANISAND model, PM4Sand model etc.) have been introduced and coded for numerical programs (PLAXIS, FLAC, MIDAS etc.) to study liquefaction hazards and many related topics. Among these constitutive models, PM4Sand model has been frequently used in recent projects to model the soil liquefaction. PM4Sand model is modified from the bounding surface plasticity model for geotechnical earthquake engineering applications and coded as a user-written constitutive model in FLAC. In this study, inputs of PM4Sand (version 3.1) model are calibrated against the triggering curve of simplified liquefaction analysis procedures suggested by Seismic Design Specifications and Commentary of Buildings of Taiwan for future liquefaction evaluation projects. In addition, model responses of PM4Sand model are discussed and compared with laboratory tests

Lateral spreading due to earthquake induced soil liquefaction is frequently observed, but the resulting deformation is usually limited within several meters in near level ground. However, lateral spreading of several hundred meters was observed in very gentle slope ground within 0-3° in Balaroa during the 2018 Sulawesi Earthquake. In this study, numerical simulations using Smoothed Particle Hydrodynamics (SPH) method are conducted to investigate the influence of Rayleigh wave on lateral spreading in gentle sloping ground, based on the Balaroa landslide conditions. Ground soil is simulated using the Herschel Bulkley Papanastasiou (HBP) rheology constitutive model, seismic wave is input using Dynamic Boundary Particles (DBP) boundary condition. 3D spatial modeling is achieved using Geographic Information System (GIS). The deformation characteristics of the gentle slope ground under Rayleigh wave and shear wave are compared, revealing a possible cause of the observed large lateral spreading in the 2018 Sulawesi Earthquake.

In this paper, we present a simple pile loading test aimed at estimating pile-head springs using human power. The proposed method involves evaluating a pile-head spring by analyzing the ratio of pile-head displacement to hammer load on the pile within the frequency domain. To validate our approach, we conducted a comparative analysis between the proposed method, a conventional static loading test and numerical simulations employing the axisymmetric finite element method. Our findings affirm the consistency of the proposed method with established approaches. We conducted these validations across a variety of pile types at 6 distinct sites.

In this study, the influence of the trajectory characteristics of horizontal bi-directional seismic motions on nonlinear seismic response and liquefaction was quantitatively evaluated using 1G shaking table tests. In order to evaluate the nonlinear response of liquefiable soils subject to bi-directional horizontal excitation, three types of bi-directional response spectrum-compatible ground motions with acceleration trajectories were used as inputs in the 1G shaking table test. The excitation acceleration in the shaking table test was based on the amplitude-adjusted wave of the NS component of the observed wave on the ground at the JMA Kobe in the 1995 Southern Hyogo Prefecture Earthquake, i.e., Level 2 earthquake ground motion for Type I ground (denoted by II-I-1) as shown in the specifications for highway bridges and its response spectrum. The accelerations are a kind of uni-directional input used in the current seismic design and seismic performance assessment, and two kinds of bi-directional accelerograms. The Uni-directional seismic wave is the linear trajectory with II-I-1. One of the two types of bi-directional seismic accelerograms is a circular trajectory, spectrum-compatible bi-directional accelerogram, which consists of a spectrum-matched unidirectional accelerogram and its Hilbert transform. The other type of bi-directional seismic acceleration is a bi-axial response spectrum-compatible with amplitude adjustment of the seismic ground motions observed at JMA Kobe in the 1995 Southern Hyogo Prefecture Earthquake. The bi-axial response spectra of these three acceleration trajectories are approximately identical. The 1G shaking table tests on liquefied soils were conducted at the Disaster Prevention Research Institute, Kyoto University, JAPAN. Liquefiable soils as a specimen were made of silica sand number 5, and the sand was prepared in a circular rigid steel container; response seismic acceleration and pore water pressure were measured in the saturated sand. By comparing the results of 1G shaking table tests of uni-directional and bi-directional excitations, the effect of bidirectional excitation on the nonlinear seismic response of liquefied soils was evaluated. As a result of the shaking table test, it is shown that the maximum response acceleration in the shallow part of the saturated sand is greater for bi-directional excitations than for uni-directional excitation. The maximum value of excess pore water pressure ratio was greater for bidirectional excitation than for uni-directional excitation. These results indicate that liquefaction is affected by bi-directional horizontal excitation. These results suggest the need to consider the influence of bi-directional horizontal excitation in seismic design and evaluation of seismic performance.

During recent decades, MSE walls have become an established solution for soil retention as they are cost-effective, simple, and fast to build with more than satisfactory resiliency during past earthquake events. In this study, a series of finite element (FE) dynamic analyses of OpenSees with the Manzari-Dafalias constitutive model and pseudo-static analyses of Plaxis 2D using the Hardening Soil model have been utilised to study the behaviour of MSE walls under seismic loads. With the assumption of soil medium laying and surrounded by outcrop, three seismic time-history records on outcrops (V_s > 700 m/s) have been selected for nonlinear time-history FE analyses of OpenSees. The height of MSE walls in this study is considered to be 8m with reinforcement lengths of 4 and 6m. To compare the findings of dynamic analyses of OpenSees, the pseudo-static method of Plaxis 2D with a different constitutive modelis employed. Both methodologies converge to a compelling observation: the reinforced soil within MSE walls displays a distinct pseudo-rigid response when subjected to seismic loading. This revelation carries the potential to inspire the engineering community, advocating for a simplified approach to MSE wall modeling in their analytical pursuits.

Failure of slopes, both natural and man-made, include slope instability as well as failures and in the seismic active zones, these slopes can become a real danger to the mankind. The failure consequences can range from the direct cost of failed rock mass to possibly indirect cost which includes the damage to vehicles and livelihood injury on the highways. The slope stability is dependent on various factors such as structural geological characteristics of the region, the local sub-soil conditions of the location, the groundwater conditions, structural loads, surcharge, the discontinuities, active faults in the region and most importantly the seismic zone of the region. These parameters have a critical role in governing the stability of the slope. From the type of soils such as clayey soil to cohesionless soil such as sandy soils to some of the stable rock mass. This paper deals with the parametric study of these cases which involves the assessment of slope stability through Strength Reduction Factor (SRF) analysis for different soil types with different slopes angles and in different seismic zones. The overall stability of the slopes in terms of the Factor of Safety (FoS), displacements as well as shear strain has been discussed and sheds light on the instrumentation of these slopes so that in case of the movements, the corrective measures can be taken at the initial stage so that it doesn’t evolve to become fatal and endanger several lives.

We study the applicability of a grid-form ground improvement method, whereby the ground around the pile foundation is enclosed by a ground improvement wall that is not in contact with the existing structure, as an aseismic reinforcement technique applicable to cases where the stability of pile foundations is only impaired due to liquefaction in volcanic ash ground, based on centrifugal model tests. As a result, it was considered that a grid spacing of 7.0 m or less and a separation distance of 2.0 m or more from the center of the outermost pile would be adequate to maintain the coefficient of horizontal subgrade reaction of the pile due to liquefaction without affecting the bridge upper and lower works or the entire bridge system. The optimum combination with improvement strength and layout should be set according to the required performance.

Pile foundations are the most widely used form of deep foundations to support both vertical and horizontal loads in geotechnical projects. Regarding the earthquake, pile foundation may lose their lateral resistance in the liquefied ground, which could cause critical economic losses and lead to severe consequences. Although research has been done on the buckling of pile foundations, there are still many observations on the structural failure of pile foundations in past earthquakes. It is essential to understand the behavior of the foundations under such conditions. In this paper, a series of centrifuge tests under different vertical loading conditions and ground conditions were performed to investigate the mechanism of buckling failure of piles. It was observed that the end-bearing single piles resting on a rigid layer can buckle under the effect of axial load and horizontal inertial load during earthquake-induced liquefaction. The failure type observed in the tests probably is the P-Δ failure, which is highly related to geometric nonlinearity. Under large axial loads, the relatively small lateral load will have a great influence on the capacity of the foundation. The pile foundations in the tests collapsed from 25 s to 265 s after the end of the shaking process (the duration of the shaking is 20 s). Besides, the soil layers offered considerable support to the piles even when the excess pore water pressure didn’t dissipate completely.

The reinforced soil retaining wall has been widely constructed since 1990’s because of the highly seismic performance, which was recognized in survey on earthquake disaster of Hyogoken-Nanbu Earthquake. However, the damages of such structure were reported in survey on earthquake disaster of Great East Japan. According to the detail investigation, although the appropriate drainage facilities had been designed and constructed, the reinforced structures which suffered from earthquake had high ground water level. The past study of test results, a series of dynamic centrifuge model tests on the multi-anchor reinforced soil wall (MAW) due to seepage flow showed that the reinforced area which constructed between facing panel and anchor plate behaved as one body under 2 m/s2 of earthquake acceleration. In this paper, the behaviors of reinforcement soil structure of multi-anchor during earthquake are discussed. The dynamic centrifuge model tests on multi-anchor wall were also conducted to clarify the deformation mode of reinforced area. In this test series, the grease was applied to neglect the friction between model ground and model container, and the acrylic plate was placed on the Teflon plate whose coefficient friction was investigated. To verify whether the displacement of reinforced area can be calculated or not, the Energy-Based Method for sliding during seismic wave was adopted. The calculated values of displacement of reinforced area which constructed with smaller relative density than usual construction, were smaller than those of centrifuge model tests. However, the displacement of the model case with high relative density was close to the calculated value. It shows that the deformation mode with small relative density was included the overturning mode and compaction by seismic wave. To establish the performance-based design on reinforced soil retaining wall, it is necessary to consider the deformation mode that could happen adequately.

Seismic loading can cause soil liquefaction, which results in weakened soil strength and stiffness, leading to significant horizontal displacement of soil and damage to structures. The liquefaction-induced lateral spread has been extensively studied through various approaches, including field case analyses and both physical and numerical modeling. However, the studies have typically been conducted on gentle slopes or backfill of quay walls. Nonetheless, foundations of waterfront structures are often located in finite slopes with relatively high inclination angles. Therefore, this study conducted a numerical analysis simulating centrifuge model tests on the liquefaction of relatively steep slopes using the FLAC 2D program. The centrifuge models of liquefiable sand with slopes of 15° and 27° were subjected to ramped sinusoidal base motion with peak amplitudes of 0.2 g. The liquefiable slope, soil container, and interface between the soil and container were modeled in the numerical simulation, and the simulation results were validated with experimental results such as excess pore pressure, acceleration, and settlement behind the crest. Based on the numerical analysis results, the mechanism of slope liquefaction and corresponding horizontal soil displacement due to liquefaction were discussed.

On September 28, 2018, an earthquake in Indonesia generated large-scale landslides. These landslides may be caused by not only ground liquefaction, but also the groundwater inflow from the base layer. As a result of numerical analysis considering groundwater inflow, although the amount of deformation was smaller than the observation, it was succeeded to simulate large-scale deformation of the ground. However, there may be mesh size effects in the results of the analysis. Therefore, in this research, we tried to evaluate the mesh size effects in numerical analysis considering water inflow. As a result, the deformation of soil layers did not change even when the mesh size was finer. Also, by making the mesh finer in the depth direction, the displacement distribution was determined with higher resolution.

Subsurface cavities under road pavement often occur widely after a large-scale earthquake, and those lead to secondary damages as sinkhole accidents. For this reason, in order to prevent prolonging post-disaster measures on roads damaged by earthquakes, the removal of cavities and loose parts that occur under the road pavement that lead to sinkhole formation is an important issue. This paper reviews past survey results on subsurface cavities under road pavement after major earthquakes in Japan and summarizes their characteristics. In addition, we investigate a non-destructive method for measuring the size of cavities and the state of loosening soils from the viewpoint of temperature change characteristics.

Foundation systems based on rigid inclusions have become an economic and efficient means to control total and differential settlements and improve bearing capacity in soft ground. However, even though rigid inclusions are being used in areas of high seismicity, there is a significant lack of knowledge regarding their behavior under earthquake loading. Within this context, this paper presents the results of a number of two-dimensional numerical dynamic soil-structure interaction analyses, using the finite element method, to assess the performance of a structure founded on rigid inclusions. For comparison, a typical piled foundation was also analyzed, where the piles are structurally connected to the building. The obtained results provide significant insights into the seismic performance of the system, including the response of the surface structure and the magnitude and distribution of internal forces in the inclusions.

The use of nonlinear dynamic analyses in effective stress conditions has been recognized as an essential tool for demonstrating the system response of soil columns, i.e., the interaction among soil layers and the dissipation/redistribution of the seismically induced excess pore water pressure during and after the shaking. These analyses contributed to a better understanding of the mechanisms beyond the occurrence or not of liquefaction manifestations at the surface, by overcoming the limitations of the existing methods based on empirical charts. In the framework of the effective-stress nonlinear dynamic analysis, two distinct approaches can be adopted to predict earthquake-induced pore pressures: a ‘loosely coupled’ approach in which pore water pressure generation is calculated using semi-empirical models and the effects of generation and cyclic degradation are included by degradation of soil strength and stiffness; a ‘fully coupled’ approach in which the formulation of the constitutive law is developed in the effective-stress space. In this paper, a simplified stress-based pore water pressure model, already implemented in a non-linear computer code according to a ‘loosely coupled’ approach, has been updated by improving the pore water pressure generation and considering the dependency from the applied seismic load. Application to two different types of soils as investigated in cyclic laboratory tests are performed with the scope to assess the efficiency of the updated model and also limitations and future perspective discussed under the light of possible applications in loosely coupled effective stress analysis.

We have detected an event of pore pressure changes (hereafter, we refer it to “pore pressure event”) from borehole stations in real time in March 2020 and March 2023, owing to the network developed by connecting three borehole stations to the Dense Oceanfloor Network System for Earthquakes and Tsunamis (DONET) observatories near the Nankai Trough. Slow earthquake is thought to have longer duration time with smaller stress drop than regular earthquake under the same magnitude. This means that the slow earthquake is more sensitive to external stress perturbation and useful to monitor the processes of stress accumulation and release. However, the pore pressure is also affected by tidal and oceanic fluctuations. To overcome this problem, we use the seafloor pressure gauges of DONET stations nearby boreholes instead of the reference by introducing time lag between them. The obtained results

demonstrate the detectability of volumetric strain change for nano-scale. The volumetric strain changes are reasonably explained by the slow slip events (SSEs) in the shallow extension of seismogenic segments, which is validated by the activation of very low-frequency events (sVLFEs) from the broadband seismometers of DONET. We also investigate the impact of seafloor pressure due to ocean fluctuation on the basis of ocean modelling, which suggests that the decrease of effective normal stress from the onset to the termination of the SSE is explained by Kuroshio meander and may promote updip slip migration, and that the increase of effective normal stress for the short-term ocean fluctuation may terminate the SSE as observed in the Hikurangi subduction zone.

In recent years, Taiwan has been actively constructing the offshore wind farms off the west coast of Taiwan. For deeper water region, only the floating offshore wind turbines (OWT) can be used. One way to support the floating OWT would be to use the drag anchors. As Taiwan is a seismically active region, the performance of the drag anchors during earthquakes would be a concern. In this study, we simulate the behavior of the drag anchors subjected to seismic loading through a series of finite element modeling. The first phase of the numerical modeling would be to simulate the installation of the drag anchors. The capacity in this phase would be evaluated and served as reference. Then, in the second phase, seismic loading would be specified and the variation in the anchor capacity would be tracked.

This paper presents a dynamic p-y analysis method based on the cone penetration test (CPT) for piles embedded in sand. Focus was given on the full utilization of the cone resistance (q_c) for the dynamic p-y analysis. A pseudo-static approach was adopted to establish the dynamic p-y curve function. Static and dynamic stiffness and damping in the dynamic p-y function were all formulated as a function of the cone resistance, which enabled the direction application of CPT results into the seismic pile design. The continuous depth profile of the cone resistance was utilized in the CPT-based dynamic p-y analysis, which was programmed with an algorithm that involved steps for calculating the equivalent static load and solving the dynamic stiffness matrix. The advantageous aspect of fully utilizing in-situ test results for the seismic pile design was emphasized, which was effective to reduce uncertainties involved in soil characterization process based on sampling and lab testing of conventional approach. A case example of centrifuge load test was selected from the literature and adopted to compare measured and estimated pile displacements using the CPT-based dynamic p-y analysis method. From the comparison, it was shown that the calculated depth profile of lateral pile displacement was in reasonably close agreement with the measured displacement profile.

Reinforced soil walls situated at waterfront are susceptible to various modes of failure under dynamic conditions. The internal stability of a waterfront reinforced soil wall is a critical aspect of its design and construction. In the present study, internal stability analysis of waterfront reinforced soil wall which is subjected to combined action of earthquake and wave loads has been carried out by considering a log-spiral failure surface. A closed form solution is obtained for the stability of wall using limit equilibrium method (LEM). Internal stability analysis has been performed for soil strata comprising of c-φ partially submerged soil taking horizontal and vertical seismic acceleration (αh and αv) into account following pseudo-static approach. Stability analysis was carried out in terms of a non-dimensional parameter K_Teq which represents total geosynthetic reinforcement force required to sustain the stability. This study considers the effect of different parameters like cohesion (c), pore water pressure ratio (r_u), internal soil friction angle (φ) hydrostatic and hydrodynamic water pressure (P_st and P_dyn) due to wave loading on stability of wall. It is observed that, due to the increment in the horizontal seismic acceleration coefficient (k_h), vertical seismic acceleration coefficient (k_v,) and hydrodynamic pressure, the requirement of geosynthetic reinforcement also increases and the presence of water significantly affects the strength of the reinforcement and an increase in the ratio of wave height to the depth of water at the seaward side increases the requirement of reinforcement. Also, it is found that the present study has good agreement with the previous studies conducted.

With the development of urban construction, limited by geological and engineering conditions, newly constructed underground structures are inevitable constructed nearby the pre-existing underground structures. The seismic responses of the nearby underground structures are complex as it highly depends on the dynamic interaction between these underground structures. In this paper, a three-dimensional nonlinear numerical dynamic analysis is conducted to investigate underground structures’ seismic response in saturated sand with and without a nearby underground structure. In the numerical analysis, saturated sand is simulated using a plasticity constitutive model for large post-liquefaction deformation of sand. Numerical models are validated by the dynamic centrifuge test for a single precast underground structure in liquefiable sand. The influence of the underground structure on the nearby underground structure seismic response, including the uplifts and internal forces, is investigated by comparing the responses of the single underground structure. Results show that the influence of newly constructed underground structures on pre-existing underground structures in liquefiable ground merits more attention in seismic design.

Earthquake-induced liquefaction is considered as one of the most destructive natural phenomena for civil engineering structures causing high economic losses. In the last three decades, numerical methods, such as the Finite Element Method (FEM) and the Finite Difference Method (FDM), have increasingly been used to model the soil behaviour under cyclic loading. In this framework, the paper presents the procedure used for the calibration of advanced soil constitutive models for liquefaction studies based on in-situ investigation performed in an intensely urbanized area located on the eastern tip of Sicily (Italy). Eastern Sicily is considered as one of the Mediterranean areas most exposed to earthquakes due to the large seismic events that hit the area in the past, such as the 1169, 1693, 1793 and 1908 earthquakes. As reported by historical sources, these seismic events induced liquefaction phenomena along the coastal area. Liquefaction evidence were found in the Holocene deposit located in the eastern tip of Sicily where an intense geotechnical investigation, including in situ and laboratory tests, have been carried out in order to define the subsoil model. In this study, numerical aspects of liquefaction have been captured using two different constitutive models that are the UBC3D-PLM model and the PM4Sand model implemented in the finite element code PLAXIS and in the finite difference code FLAC, respectively. The parameters of both constitutive models were calibrated to the relationship proposed by Boulanger and Idriss (2014) for the cyclic resistance ratio based on SPT data, CRRMw=7.5, σv0΄=1atm, by the simulation of cyclic direct simple shear tests (CDSS). The results showed a satisfactory fit between the calibrated models and the Boulanger and Idriss liquefaction triggering curve.

In view of this convergence, this parametrical fitting provides a useful information for modelling profiles where liquefiable layers condition the behaviour of critical infrastructures in the area under consideration characterized by high seismic risk.

Earthfill dams are critical infrastructure and perform as a system by integrating various components such as foundation, core, shell, filter, outlet and spillway. To analyze the entire response, it is important to properly identify the dynamic characteristics of the system based on observations. This paper investigates analytical solutions of the shear beam approach to identify the dynamic characteristics of existing dams considering variable shear modulus with height. To this end, the governing differential equation is first solved in terms of Bessel functions. The corresponding response parameters are then derived for different modes. Results are presented for a range of expected shear wave propagation velocity profiles with depth. Transfer functions are derived from the bedrock to the crest for different shear modulus variations and levels of material damping. Fundamental periods are obtained from the analytical solutions and compared to the empirical observations from 2 dams in Japan to estimate the shear wave velocity profiles of the dams.

Currently available liquefaction triggering assessment method uses charts correlating the cyclic stress ratio and soil resistance to liquefaction initially developed by Seed and Idriss (1971). The shear stresses imposed on the soil during an earthquake are irregular in nature and transformed into an equivalent uniform shear stress, t_eq, based on its maximum shear stress, t_max, and coefficient of equivalent shear stress, c_t (e.g., t_eq = c_t×t_max, JRA, 1995). The coefficient was derived mostly from experimental data conducted on clean sand. It is needed to study further on other soil types; however, it is rather difficult to experimentally investigate response of many types of soils for many earthquake waves. An excess pore pressure prediction method has been proposed by Okamura (2022), which is simple and based only on the fundamental law of soil mechanics. This paper presents the capability of the model to predict the liquefaction triggering for irregular cyclic loading. A series of undrained cyclic triaxial tests with irregular loading were conducted, and the results are compared with those predicted by the model. It was confirmed that the model predicted the pore pressure generation and liquefaction triggering reasonably well.

Magnitude of damage to structures in liquified soil is affected by various parameters such as input motion, soil density, water table level and contact pressure of structures. This study conducted centrifugal shaking table tests, in which foundations with or without a superstructure were placed on liquefiable soil layer, and investigated the effects of superstructure response on foundation settlement in liquefied soil. The test results show that the overturning moment of structure due to the superstructure response induces an increase in the relative settlement of the foundation. The relative displacement of the foundation is larger with a superstructure than without a superstructure. However, in a case under an input motion with long-time duration, the relative settlement of the foundation without a superstructure becomes almost the same as that with a superstructure. The lengthy input motion causes extensive liquefaction and keeps soil liquefied in a long time. As a result, the soil strength might drop down significantly and the soil could not support the weight of the structure.

Shake table tests were performed on a 5 MW offshore wind turbine supported by a monopile to assess its response during significant seismic events. The study aimed to analyze the vibration characteristics of the pile, a critical consideration in practical design assessment. To accomplish this, we investigated the correlation between the bending moment distribution of the pile and the waveform attributes of the input seismic motion. Our analysis, with a specific emphasis on eigenmodes, revealed variations in the wind turbine's vibration mode and timing concerning the peak bending moment of the pile. These variations were found to be influenced by the specific vibration attributes of the input seismic motion.

To prevent liquefaction, various preventive measures using cement such as consolidation process and grouting have been proposed. However, since liquefaction prevention measures using cement cause environmental problems such as groundwater pollution and increased carbon dioxide emissions, it is necessary to develop eco-friendly ground reinforcement materials. Biopolymer, an eco-friendly ground reinforcing material, is a material made through the biological activities of microorganisms, and when reinforced in the ground without damaging the vegetation environment, it has the effect of improving shear strength, water-repellent properties, vegetation, and erosion resistance increase. Accordingly, it is expected to increase the resistance to prevent liquefaction, but research on this is insufficient so far. Therefore, in this study, the effect of enhancing the liquefaction resistance strength of the biopolymer-treated samples was evaluated through the cyclic triaxial test. For the experimental conditions, the liquefaction resistance strength according to the type of biopolymer was evaluated, and the liquefaction resistance strength was compared with the untreated sample. Through the experiment, the liquefaction resistance strength enhancement ratio was evaluated according to the untreated sample, and the biopolymer effective in enhancing the liquefaction resistance strength was identified. Through this, the biopolymer is expected to be used to improve the liquefaction resistance strength in areas where liquefaction can occur.

In the case of the 2011 off the Pacific Coast of Tohoku Earthquake, long-period seismic wave causes large displacement in wide area of the Japan Islands. We have little knowledge about the effects of such long period strong motion on fluid saturated layers at depth. We introduced Drucker-Prager's elastic-plastic yield criterion and developed a hydraulic-mechanical coupling analysis using numerical manifold method (NMM) as a method to evaluate pore pressure increase due to earthquake-induced deformation and fluid movement and the health of CO₂ storage sites. This paper describes the fundamental formulations of the hydraulic-mechanical coupling analysis and compared the pore pressure response and local safety factor response of the caprock and CO₂ storage reservoirs during great earthquake due to differences in geological structures using Chuetsu Earthquake (2004) NIG019 recorded at Ojiya site seismic acceleration (maximum 150 gal). The safety factor response was evaluated using the effective stress. The pore pressure response in the caprock increased from the initial pore pressure by up to 1.3% in the flat model and 2.5% in the anticline model. The pore pressure response in the CO₂ storage reservoir increased from the initial pore pressure by up to 2.0% in the flat model and 3.6% in the anticline model. The local safety factor response was independent of geologic structure and was 2.7 for the caprock. This result suggests that the caprock is stable even during a great earthquake. These results suggest that the CO₂ storage site is stable during earthquakes of about 600gal.

It is observed from past experiences of earthquakes that local site conditions can significantly affect the strong ground motion characteristics. One-dimensional seismic site response analysis (SH1D) is the most common approach for investigating site response. This approach assumes that soil is homogeneous and infinitely extended in the horizontal direction. Therefore tying side boundaries together is one way to model this behavior, as the wave passage is assumed to be only vertical. However, SH1D cannot capture the 2D nature of wave propagation, soil heterogeneity, and 2D soil profile with inclined bedrock. In contrast, 2D seismic site response modeling can consider all of the mentioned factors to better understand local site effects on strong ground motions. The 2D wave propagation and considering that soil on two sides of the model is not identical in a soil profile clarifies the importance of a boundary condition on each side that can minimize the unwanted reflections from the edges of the model. Regarding site response, for the avoidance of wave reflections in the boundaries, the model size should be sufficiently large to minimize the wave reflection. However, due to computational limitations, increasing the model size is impractical in some cases. Another approach is to employ free-field boundary conditions (absorbing boundaries) to have a non-reflecting behavior in the boundaries while absorbing the wave energy by a factor. These boundary conditions must take into account free-field motion in the absence of the structure at the sides of the model. This research focuses on implementing free-field boundary conditions in OpenSees for 2D site response analysis with considering free-field 1D model results as input for 2D model.