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There have been attempts to improve the operational efficiency of construction projects and plan response countermeasures for estimated damage following disasters through the utilization of accumulated electronic data, which constructs a digital twin that can reproduce a physical space in cyberspace and feedback the cyberspace simulation results to physical space. However, the application of such simulations is limited, unless numerical models can be automatically constructed from the data. In this study, we develop a program that utilizes a data processing platform to read, transform, and integrate data to create mediated data with a common data structure. This mediated data can be used to construct analytical models for various numerical analyses. Using the program developed, a grid model of 3-D ground surface as the mediated data was constructed based on borehole data obtained through a ground survey. Each grid point has basic material parameters of soil, and these parameters are estimated from borehole data and other investigation reports. Each grid point has general geotechnical parameters and can be easily converted to a 3-D finite-element model. When the borehole data is added or changed, the analytical model can be updated with almost no cost, whereas it would be very costly to create the model manually.

Earthquake induced liquefaction is one of the main geo-disasters threating urban regions, which not only causes direct damages to buildings, but also delays both real-time disaster relief actions and reconstruction activities. It is thus important to assess liquefaction hazard of urban regions effectively and efficiently for disaster prevention and mitigation. Conventional assessment approaches rely on engineering indices such as the factor of safety (FS) against liquefaction, which cannot take into account directly the uncertainties of soils. In contrast, a physics simulation-based approach, by solving soil dynamics problems coupled with excess pore water pressure (EPWP) it is possible to model the uncertainties directly via Monte Carlo simulations. In this study, we demonstrate the capability of such an approach for assessing an urban region with over 10 000 sites. The permeability parameters are assumed to follow a base-10-lognormal distribution among 100 model analyses for each site. A dynamic simulation is conducted for each model analysis to obtain the EPWP results. Based on over 1 million EPWP analysis models, we obtained a probabilistic liquefaction assessment. Empowered by high performance computing, we present for the first time a probabilistic liquefaction hazard assessment for urban regions based on dynamics analysis, which consider soil uncertainties.

In the wide area of the eastern part of Tokyo, the ground level is less than mean sea level. This area is more vulnerable to disasters than other areas. If large flood damage such as storm surge should occur in this area, the disaster would be a long-term catastrophe. On the coast of Tokyo Bay, countermeasures have been taken by tide embankments and floodgates. However, considering the damage scale when it occurs, an analysis in this area is very important. In this area, ground settlement occurred and groundwater head dropped because groundwater excessively withdrew by the industrial purpose during the period of economic growth. Currently, the groundwater head recovers and the ground settlement has been subsided. However, due to the groundwater head fluctuation, pore water pressure distribution had been different from hydrostatic pressure distribution. Therefore, in the analysis in this area, it is necessary to consider past groundwater head fluctuation. In this research, the ground settlement and the distribution of pore water pressure are simulated from groundwater level fluctuation over the past 100 years. Then, we conducted the seismic analysis by input the distribution of effective stress calculating from the simulated ground water pressure. The sites analyzed in this research are Tokyo Sea Life Park at the mouth of Arakawa River.

Recently, the occurrence of large earthquakes has become a concern in Japan, prompting the need for a numerical method that can accurately predict real phenomena, such as the elastoplastic soil-water coupled finite element method. Because the elastoplastic constitutive model requires many material parameters, various soil tests and specialized knowledge are needed to determine these material parameters. In this study, a new method was proposed to determine the material parameters from the limited ground information obtained by borehole inspections and the method was validated by comparing the numerical results with monitored seismic behavior. One-dimensional seismic analyses were conducted using the material parameters estimated from borehole data near the target sites. It was confirmed that the amplitude and predominant period obtained by numerical simulation were consistent with the monitored data. As a result, it was found that the dynamic numerical result was more consistent with the monitored data when the compression index was set to be larger than that in the static analysis.

The pagoda of Wat Krasai, built in the 17th century on the outskirts of the Ayutthaya district in the Kingdom of Thailand, tilts approximately 2° to the north and may continue to tilt further. The cause of this tilt is thought to be the uneven settlement of the foundation ground, but no supporting evidence has been presented. Three cohesive soil layers that may cause uneven settlement have been confirmed in the foundation ground around the pagoda, but soil tests are inadequate, leading to uncertainty in proving the cause of inclination. Hence, the cause of inclination was investigated in this study by calculating the inclination that can occur within the realistic ranges of the soil properties through numerical analysis using the finite element method. A method of correcting plane strain analysis, which has a low computational cost, with a three-dimensional effect coefficient, was utilized to assess over 500 cases considering ground material uncertainties, and the probability distribution of the possible inclinations was calculated. This method is useful as it considers fluctuations in the ground material parameters to address land settlement, which is largely influenced by the three-dimensional effects. This approach will also be applicable to future predictions aimed at pagoda preservation.

The material point method (MPM) has recently been used to perform soil–water interaction analysis for fully saturated soil in geotechnical engineering. In MPM, to treat fully saturated soil, two types of discretization methods have been mainly used: the single point formulation and the double point formulation. The former discretizes the soil–water mixture with a single set of particles, whereas the latter discretizes the soil phase and the water phase separately by using different sets of particles. In both the discretization methods, the flux boundary condition is imposed on the background mesh nodes, and the prescribed pore water pressure boundary condition is directly applied to the particles. This is the reason behind the complexity involved in the setting of boundary conditions for the coupled MPM. To reduce this complexity, this paper presents a discretization technique that combines MPM with smoothed particle hydrodynamics (SPH). SPH is used for the discretization of the generalized Darcy’s law to impose the flux boundary condition directly on the particles. The proposed formulation is validated through the soil–water interaction benchmark problems: the consolidation problems of Terzaghi and Mandel–Cryer. The numerical results are in good agreement with the analytical solutions, which validates the proposed method.

The engineering needs which have to consider the multi-physics are increasing. When the multi-phase problem is treated by monolithic coupling approach, there are some difficulties such as the increase in the number of degree of freedom, the complication of the program code and so on. In order to overcome these shortcomings in considering the new additional phase, we applied the partitioned iterative coupling approach to the Hydro-Mechanical coupled problem in this research. In the partitioned iterative coupling approach, the behavior of single phases can be individually calculated and the interaction between the phases has been considered at an appropriate timing by the middleware. The middleware plays a role to regulate the single-phase analysis. In this research, we carried out the numerical simulation of one-dimensional consolidation by both the partitioned iterative coupling scheme and the monolithic coupling scheme, and then we confirmed that the numerical results are the same. Through the research, it figured out the efficient iterative scheme.

Through quantitative measurement of the accuracy and the convergence of error, code verification can objectively assess the quality of a simulation code. A lack of analytical benchmark solution for nonlinear problems makes it difficult to verify soil dynamics simulations in geotechnical engineering. To overcome such difficulty, this study makes use of a novel code verification technique, the method of numerically manufactured solutions (MNMS). By utilizing MNMS, the accuracy of a simulation code for nonlinear soil dynamics problems was measured. The orders of the convergence rate of the errors, with respect to the spatial and to the temporal discretization, were found to be in good agreement with the theoretical orders of the numerical methods. By demonstrating the applicability of MNMS for verifying nonlinear soil dynamics simulations, it is hoped that the concept and the necessity of code verifications can be appreciated for simulations of geotechnical engineering problems.

Elaso-plastic constitutive models such as the (original) Cam Clay (Roscoe, Schofield and Thurairajah, 1963) and the model proposed by Sekiguchi and Ohta (1977) have a sharp corner (vertex) of the yield surface appearing at the effective stress point representing virgin consolidation state in the principal stress space. The corner causes the discontinuity of the gradient of the yield surface; therefore, the stress-strain relationship at this singular point cannot be evaluated by the simple associated flow rule. Special treatment is needed to describe stress-strain relationships at the singular point on the yield surface.

Effective and efficient liquefaction hazard assessment is critical in making disaster mitigation plans for urban regions. In this paper, we present a numerical-simulation (NS)-based method for assessing urban-wide liquefaction hazard. The method includes an automatic modelling for individual sites and an application of high-performance computing (HPC) for efficient assessment. The feasibility of the method is demonstrated by conducting simulations for more than 10,000 individual sites in an urban region. The urban-wide assessment results depend on a pressure threshold of liquefaction occurrence and the dependence increases as the ground motion increases. A comparison with a conventional method using engineering indices (EI) shows a tendency of the EI-based method to predict a considerably greater number of liquefied sites than the proposed method. With the continuing improvement on numerical simulations and on computer efficiency, NS-based assessments can be regarded as promising alternatives to conventional EI-based methods for urban-wide liquefaction assessment.

Conventional methods for liquefaction assessment using engineering indices such as Factor of safety against Liquefaction (FL) tend to overestimate liquefaction hazards. The soil dynamics analysis-based assessment with automatic modeling is more rational and robust. Soil properties are known for large uncertainties. Rather than deterministic soil models, statistical models for soil parameters should be considered. With automatic modeling, a large number of statistic models can be generated without difficulty. The problem becomes how to assess liquefaction hazard with statistic models in an efficient way. Using high performance computing, we develop an efficient liquefaction assessment method for statistical modeling of soils. A high parallel efficiency can be achieved and a large number of statical models of the order of 104 can be simulated within a reasonable time span. The method developed in this paper can be used as an efficient tool for unravelling critical parameters of soil liquefaction.

The isolated deep mixing columns, particularly the columns near the slope of the embankment, were reported to experience a minor horizontal resistance while supporting an embankment. In order to reinforce these columns and increase the stability of the improved area, which includes the group of columns, a shallow layer produced by shallow mixing method was proposed as a countermeasure. While many studies reported that the isolated columns may fail either by the external failure or the internal failure, the failure of this combined structure including the deep mixing columns and the shallow layer has not well studied yet. In the previous study, overturning and sliding failures were observed as the leading patterns in terms of the external stability, when the combined structure to supports embankment slope. In addition to the study of the external stability, the internal failure pattern of the columns reinforced by the shallow layer was concentrated in this study. It is worth to note that the low-strength columns are used here. Four centrifuge model tests were performed by varying the column strengths in models with and without the shallow layer of reinforcement. The results showed a significant influence of the shallow layer on the failure pattern of the deep mixing columns. The study further discusses the effect of the shallow layer and the column strength on the stability of the supported embankment.

The deep mixing method was developed in Japan in the 1970s and has been frequently applied to on land and marine constructions. The group column type improved ground is often applied to stability of embankment and soft ground. The current design procedure of the improved ground assumes the external and internal failures. The authors start a research project to investigate the applicability and the design procedure of the group column type deep mixing improvement on the stability of soft clay slope. As a primary research of the project, a series of centrifuge model tests and numerical analyses were carried out to investigate the influence of slope height on stability and deformation of soft clay slope. The study reveals that the height of embankment at failure increases with decrease of height of slope and can be evaluated by the Fellenius slip circle analysis precisely.

In this chapter, the stress–strain relationship on the singular point of the yield surface of the original Cam clay model and the Sekiguchi-Ohta’s model is derived in order to compute the volume change correctly. Metastable space, the range of increment of strain in which effective stress does not get away from the singular point of yield surface, was theoretically derived. In metastable space, the increment of volumetric strain is larger than the increment of deviatoric strain.

In the present soil–water coupled finite element method (FEM) analysis, a program known as deformation analysis considering stress anisotropy and reorientation (DACSAR; Iizuka and Ohta, Soil Found 27(3): 71–87, 1987), the spatial discretization procedure for representing the water head at the center of each finite element was adopted. However, it is known that the outflow of pore water from the element boundary happens to be incorrectly calculated depending on the mesh arrangement and the inclination of the boundary. To address this problem, this chapter proposes a more rigorous spatial discretization procedure for pore water flow. Namely, the hybrid-type penalty method (HPM) is introduced to spatially discretize the pore water flow in soil–water coupled finite element formulation, and the DACSAR program is modified using the proposed technique.

Soil liquefaction induced by earthquakes poses a great threat to urban areas, not only by causing direct damages to infrastructures but also by delaying rescue and relief actions. Established engineering assessment methods using indices such as factor of safety against liquefaction (FL) tend to overestimate liquefaction hazards. While the standard usage of soil dynamic analysis for liquefaction assessment is limited to a single site with detailed site information. In this paper, we propose a framework based on soil dynamics for assessing liquefaction hazard for urban areas which contain numerous sites with borehole logs only. The framework is featured by generating analysis models and by estimating material parameters automatically from available borehole information. The governing equations for soil dynamics are solved by a finite element code. Liquefaction hazard is assessed according to the solutions of excess pore water pressure for given seismic waves. As demonstrations, we show simulation results of simple shear tests and of seismic response for a target site under loadings of artificial and of actual seismic waves. The automatic model construction and parameter estimation enable this framework being applied effectively for urban-area-wide liquefaction assessment, as an alternative for the current practices based on engineering indices.